Prospectus Filed Pursuant to Rule 424(b)(5) (424b5)

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-237810

PROSPECTUS SUPPLEMENT

(To prospectus dated May 4, 2020)

Up to US$50,000,000

Common Shares

We have entered into a sales agreement, or Sales Agreement, with Evercore Group L.L.C., or Evercore, dated May 5, 2020, relating to the sale of our common shares from time to time offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the Sales Agreement, we may offer and sell our common shares having an aggregate offering price of up to US$50,000,000 from time to time through Evercore, acting as our sales agent.

Our common shares are listed on the Toronto Stock Exchange, or the TSX, and on the Nasdaq Capital Market, or the Nasdaq, under the symbol "TRIL". On May 4, 2020, the last trading day before the date of this prospectus supplement, the closing price of the common shares on the TSX was C$7.50 per common share, and the closing price of the common shares on the Nasdaq was US$5.30 per common share.

Sales of our common shares, if any, under this prospectus supplement may be made by any method permitted that is deemed an "at the market offering" as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended, or the Securities Act. Evercore is not required to sell any specific number or amount of our common shares, but will act as our sales agent using commercially reasonable efforts, consistent with its normal trading and sales practices on mutually agreed terms between Evercore and us. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

No sales of our common shares under this prospectus supplement will be made in Canada, to anyone known by the sales agent to be a resident of Canada or over or through the facilities of the TSX or any other exchange or market in Canada.

Evercore will receive from us a commission equal to 3.0% of the gross sales price of all shares sold through it under the Sales Agreement. In connection with the sale of common shares on our behalf, Evercore may be deemed to be an "underwriter" within the meaning of the Securities Act and the compensation of Evercore may be deemed to be underwriting commissions or discounts.

An investment in our securities involves a high degree of risk. Please read "Risk Factors" on page S-7 of this prospectus supplement and in the documents incorporated by reference into this prospectus supplement before investing in our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Evercore ISI

The date of this prospectus supplement is May 5, 2020.

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT

	PAGE
ABOUT THIS PROSPECTUS SUPPLEMENT	S-1
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS	S-2
PROSPECTUS SUPPLEMENT SUMMARY	S-5
THE OFFERING	S-6
RISK FACTORS	S-7
USE OF PROCEEDS	S-10
DILUTION	S-11
PLAN OF DISTRIBUTION	S-12
CERTAIN U.S. FEDERAL INCOME TAX CONSIDERATIONS	S-14
CERTAIN CANADIAN FEDERAL INCOME TAX CONSIDERATIONS	S-22
LEGAL MATTERS	S-24
EXPERTS	S-24
ENFORCEABILITY OF CIVIL LIABILITIES	S-24
WHERE YOU CAN FIND MORE INFORMATION	S-24
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE	S-25

ACCOMPANYING PROSPECTUS

	PAGE
ABOUT THIS PROSPECTUS	2
WHERE YOU CAN FIND MORE INFORMATION	2
FORWARD-LOOKING STATEMENTS	3
TRILLIUM THERAPEUTICS INC.	6
CAPITALIZATION	7
USE OF PROCEEDS	7
PRICE RANGE	7
DESCRIPTION OF SHARE CAPITAL	7
DESCRIPTION OF SUBSCRIPTION RECEIPTS	11
DESCRIPTION OF WARRANTS	12
DESCRIPTION OF UNITS	12
RISK FACTORS	13
CERTAIN INCOME TAX CONSIDERATIONS	13
PLAN OF DISTRIBUTION	13
LEGAL MATTERS	14
EXPERTS	15
ENFORCEABILITY OF CIVIL LIABILITIES	15
EXPENSES	15

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering and the securities offered hereby, and also adds to and updates information contained in the accompanying prospectus and the documents incorporated into each by reference. The second part, the accompanying prospectus, gives more general information and disclosure. When we refer only to the "prospectus," we are referring to both parts combined.

If there is any inconsistency between information in or incorporated by reference into the accompanying prospectus and information in or incorporated by reference into this prospectus supplement, you should rely only on the information contained in or incorporated by reference into this prospectus supplement. This prospectus supplement, the accompanying prospectus and the documents incorporated into each by reference include important information about us, the common shares being offered and other information you should know before investing. You should read this prospectus supplement and the accompanying prospectus together with the additional information described under the heading "Where You Can Find More Information" before investing in our common shares.

Neither we nor Evercore have authorized anyone to provide any information or to make any representations other than those contained in this prospectus supplement and the accompanying prospectus, the documents incorporated by reference herein or therein or in any free writing prospectuses prepared by us or on our behalf or to which we have referred you. We are not, and Evercore is not, making an offer to sell these securities in any jurisdiction where the offer or sale thereof is not permitted. We are not offering to sell, or seeking offers to buy, common shares in Canada, to anyone known by the sales agent to be a resident of Canada or over or through the facilities of the TSX or any other exchange or market in Canada. The distribution of this prospectus and the offering of common shares in certain jurisdictions may be restricted by law. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus and the documents incorporated into each by reference is accurate only as of the respective dates of the applicable documents. Our business, financial condition, results of operations and prospects may have changed since those dates.

Market data and certain industry forecasts used in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein or therein were obtained from market research, publicly available information and industry publications. We believe that these sources are generally reliable, but the accuracy and completeness of this information is not guaranteed. We have not independently verified such information, and we do not make any representation as to the accuracy of such information.

Unless otherwise indicated in this prospectus supplement and the accompanying prospectus all dollar amounts and references to "$" or "US$" are to U.S. dollars and references to "C$" are to Canadian dollars. This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein contain translations of some Canadian dollar amounts into U.S. dollars solely for your convenience. On May 4, 2020, the Bank of Canada daily average rate of exchange was US$1.00 = C$1.4085.

In this prospectus supplement and the accompanying prospectus, unless the context otherwise requires, references to "we," "us," "our" or similar terms, as well as references to "Trillium" or the "Company," refer to Trillium Therapeutics Inc., either alone or together with our subsidiary.

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein include references to trade names and trade-marks of other companies, which trade names and trade-marks are the property of their respective owners.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, contain certain statements that are "forward-looking statements" within the meaning of the U.S. Private Securities Litigation Reform Act and applicable Canadian securities laws. All statements contained herein that are not clearly historical in nature are forward-looking, and the words "anticipate", "believe", "expect", "estimate", "may", "will", "could", "leading", "intend", "contemplate", "shall" and similar expressions are generally intended to identify forward-looking statements. Such forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause the Company's actual results, performance or achievements to be materially different from any future results, performance or achievements that may be expressed or implied by such forward-looking statements. Examples of such forward-looking statements include, but are not limited to:

• our expected future loss and accumulated deficit levels;

• our projected financial position and estimated cash burn rate;

• our requirements for, and the ability to obtain, future funding on favorable terms or at all;

• our projections for the SIRPαFc development plans and progress of each of our products and technologies, particularly with respect to the timely and successful completion of studies and trials and availability of results from such studies and trials;

• our plans to focus our intravenous TTI-621 and TTI-622 programs on large hematologic malignancy indications, specifically acute myeloid lymphoma & myelodysplastic syndromes (AML/MDS), peripheral T-cell lymphoma (PTCL), diffuse large B-cell lymphoma (DLBCL) and multiple myeloma;

• our expectations about our products' safety and efficacy;

• our expectations regarding our ability to arrange for and scale up the manufacturing of our products and technologies;

• our expectations regarding the progress, and the successful and timely completion, of the various stages of the regulatory approval process;

• our expectations about the timing of achieving milestones and the cost of our development programs;

• our observations and expectations regarding the relative low binding of SIRPαFc to red blood cells, compared to anti-CD47 monoclonal antibodies and proprietary CD47-blocking agents and the potential benefits to patients;

• our ability to intensify the dose of TTI-621 with the goal of achieving increased blockade of CD47;

• our expectation that we will achieve levels of TTI-622 in patients sufficient to obtain sustained CD47 blockade;

• our expectation that TTI-622 is likely to be more effective in combination with agents that provide additional "eat" signals to macrophages or other forms of immune activation;

• our plans to market, sell and distribute our products and technologies;

• our expectations regarding the acceptance of our products and technologies by the market;

• our ability to retain and access appropriate staff, management and expert advisers;

• our ability to secure strategic partnerships with larger pharmaceutical and biotechnology companies;

• our expectations with respect to existing and future corporate alliances and licensing transactions with third parties, and the receipt and timing of any payments to be made by us or to us in respect of such arrangements; and

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• our strategy with respect to the protection of our intellectual property.

All forward-looking statements reflect our beliefs and assumptions based on information available at the time the assumption was made. These forward-looking statements are not based on historical facts but rather on management's expectations regarding future activities, results of operations, performance, future capital and other expenditures (including the amount, nature and sources of funding thereof), competitive advantages, business prospects and opportunities.

By its nature, forward-looking statements involve numerous assumptions, inherent risks and uncertainties, both general and specific, known and unknown, that contribute to the possibility that the predictions, forecasts, projections or other forward-looking statements will not occur. In evaluating forward-looking statements, readers should specifically consider various factors, including the risks outlined under the heading "Risk Factors" in this prospectus supplement and in the documents incorporated by reference herein. Some of these risks and assumptions include, among others:

• substantial fluctuation of losses from quarter to quarter and year to year due to numerous external risk factors, and anticipation that we will continue to incur significant losses in the future;

• uncertainty as to our ability to raise additional funding to support operations;

• uncertainty as to the duration and impact of the current COVID-19 pandemic, including its impact on patient enrollment and participation in our clinical trials;

• our ability to generate product revenue to maintain our operations without additional funding;

• the risks associated with the development of our product candidates which are at early stages of development;

• positive results from preclinical and early clinical research are not necessarily predictive of the results of later-stage clinical trials;

• reliance on third parties to plan, conduct and monitor our preclinical studies and clinical trials;

• our product candidates may fail to demonstrate safety and efficacy to the satisfaction of regulatory authorities or may not otherwise produce positive results;

• risks related to filing Investigational New Drug applications, to commence clinical trials and to continue clinical trials if approved;

• the risks of delays and inability to complete clinical trials due to difficulties enrolling patients;

• the risk that we may not achieve our publicly announced milestones according to schedule, or at all;

• the risk of being required to repurchase the outstanding warrants in the event of a "Fundamental Transaction", and possibility of price protection reset of the exercise price of the warrants at prices below the exercise price;

• competition from other biotechnology and pharmaceutical companies;

• our reliance on the capabilities and experience of our key executives and scientists and the resulting loss of any of these individuals;

• our ability to fully realize the benefits of acquisitions;

• our ability to adequately protect our intellectual property and trade secrets;

• our ability to source and maintain licenses from third-party owners;

• the risk of patent-related litigation;

• the risk of loss of our status as a foreign private issuer; and

• our expectations regarding our status as a passive foreign investment company, or PFIC.

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Although the forward-looking statements contained in this prospectus supplement are based upon what our management believes to be reasonable assumptions, we cannot assure readers that actual results will be consistent with these forward-looking statements.

Any forward-looking statements represent our estimates only as of the date of this prospectus supplement and should not be relied upon as representing our estimates as of any subsequent date. We undertake no obligation to update any forward-looking statement or statements to reflect events or circumstances after the date on which such statement is made or to reflect the occurrence of unanticipated events, except as may be required by applicable securities laws.

You should read carefully the risk factors described in this prospectus supplement and the documents incorporated by reference in this prospectus supplement for a description of certain risks that could, among other things, cause actual results to differ from these forward-looking statements.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights key aspects of this offering and certain information contained elsewhere in this prospectus supplement and the documents incorporated by reference. This summary is not complete and does not contain all of the information that may be important to you or that you should consider before investing in our common shares. You should read carefully the other information included and incorporated by reference in this prospectus supplement and the accompanying prospectus before investing in our common shares. You should pay special attention to the risks and uncertainties identified under the captions "Risk Factors," "Cautionary Note Regarding Forward-Looking Statements" and elsewhere in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein or therein, including our most recent Annual Report on Form 40-F, when determining whether an investment in our common shares is appropriate for you.

Our Company

We are a clinical stage immuno-oncology company developing innovative therapies for the treatment of cancer. Our most advanced program, TTI-621, is a SIRPαFc fusion protein that consists of the extracellular CD47-binding domain of human signal regulatory protein alpha ("SIRPα"), linked to the Fc region of a human immunoglobulin G1, or IgG1. It is designed to act as a soluble decoy receptor, preventing CD47 from delivering its inhibitory ("do not eat") signal. Neutralization of the inhibitory CD47 signal enables the activation of macrophage anti-tumor effects by pro-phagocytic ("eat") signals. The IgG1 Fc region of TTI-621 may also assist in the activation of macrophages by engaging Fc receptors. TTI-621 has shown single agent activity by both local and/or systemic delivery in multiple B- and T-cell lymphoma indications and has been well tolerated in over 200 patients to date.

We are also developing a second SIRPαFc fusion protein, TTI-622, which is in a phase 1 clinical trial. TTI-622 consists of the extracellular CD47-binding domain of human SIRPα linked to a human immunoglobulin G4, or IgG4 Fc region, which has a decreased ability to engage Fc receptors than an IgG1 Fc. Both SIRPαFc fusion proteins enable CD47 blockade with different levels of Fc receptor engagement on macrophages and thus may find unique applications. TTI-622 has been well tolerated with no dose-limiting toxicities observed in the 19 patients dosed to date.

We are concentrating our development efforts for TTI-621 and TTI-622 on intravenous product candidate delivery for large hematologic malignancy indications, specifically acute myeloid lymphoma & myelodysplastic syndromes (AML/MDS), peripheral T-cell lymphoma (PTCL), diffuse large B-cell lymphoma (DLBCL) and multiple myeloma.

We were incorporated under the Business Corporations Act (Alberta) on March 31, 2004 as Neurogenesis Biotech Corp. On October 19, 2004, we amended our articles of incorporation to change our name to Stem Cell Therapeutics Corp. ("SCT"), and on November 7, 2013 SCT was continued under the Business Corporations Act (Ontario). Articles of amalgamation were filed on June 1, 2014 to amalgamate SCT with its wholly-owned subsidiary, Trillium Therapeutics Inc., and the amalgamated entity continued to operate under the name Trillium Therapeutics Inc. On December 18, 2019, we were continued under the laws of the Province of British Columbia. We are now governed under the Business Corporations Act (British Columba) (the "BCBCA"). Additionally, on December 18, 2019, we adopted new articles which are substantially similar to our previous by-laws but for changes that were required to be made in accordance with the BCBCA.

Company Information

We are a company domiciled in Ontario, Canada. Our head office is located at 2488 Dunwin Drive, Mississauga, Ontario, Canada, L5L 1J9. Our registered office is located at Suite 1750-1055 W. Georgia Street, P.O. Box 11125, Vancouver, British Columbia, V6E 3P3. We have one wholly-owned subsidiary, Trillium Therapeutics USA Inc., which was incorporated March 26, 2015 in the State of Delaware, with an office in Cambridge, Massachusetts. Our website address is www.trilliumtherapeutics.com. Information contained on, or that can be accessed through, our website does not constitute a part of this prospectus supplement. We have included our website address in this prospectus supplement solely as an inactive textual reference.

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THE OFFERING

The following summary contains basic information about the offering and is not intended to be complete. It does not contain all the information that is important to you. You should carefully read the entire prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein before making an investment decision.

Issuer Trillium Therapeutics Inc.

Common shares offered by us Shares having an aggregate offering price of up to US$50,000,000.

Common shares to be outstanding

following the offering Up to 92,117,387 shares, based on 82,683,425 common shares outstanding as of March 31, 2020 and assuming sales of 9,433,962 of our common shares in this offering at an offering price of US$5.30 per share, which was the last reported sale price of our common shares on the Nasdaq on May 4, 2020. The actual number of shares issued will vary depending on the sale price under this offering.

Plan of distribution At prevailing market prices in an "at the market offering" within the meaning of Rule 415(a)(4) under the Securities Act that may be made from time to time through our sales agent, Evercore. See "Plan of Distribution."

Use of proceeds We intend to use the net proceeds from the sale of our common shares pursuant to this offering, if any, together with our existing cash and cash equivalents, for working capital and general corporate purposes. See "Use of Proceeds" on page S-10.

Risk factors Investing in our common shares involves risks. See "Risk Factors" beginning on page S-7 of this prospectus supplement, as well as those risks and uncertainties identified in the documents incorporated by reference herein or therein, including our most recent Annual Report on Form 40-F.

Nasdaq symbol TRIL

TSX symbol TRIL

Income tax considerations The common shares will be subject to special and complex tax rules for U.S. taxpayers. Holders are urged to consult their own tax advisors with respect to the U.S. and Canadian federal, state, provincial, territorial, local and foreign tax consequences of purchasing, owning and disposing of the common shares. See "Certain U.S. Federal Income Tax Considerations" and "Certain Canadian Federal Income Tax Considerations" on pages S-14 and S-22 of this prospectus supplement.

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RISK FACTORS

Investing in our common shares is speculative and involves a high degree of risk. The following risk factors, as well as risks currently unknown to us, could materially adversely affect our future business, operations and financial condition and could cause them to differ materially from the estimates described in forward-looking information relating to us, or our business, property or financial results, each of which could cause purchasers of our common shares to lose part or all of their investment. In addition to the other information contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, prospective investors should carefully consider the factors set out under "Risk Factors" in the accompanying prospectus and our Annual Report on Form 40-F for the year ended December 31, 2019 and the factors set out below in evaluating Trillium and its business before making an investment in our common shares.

Risks Relating to the Offering

Trillium's management team will have broad discretion to use the net proceeds from this offering and its investment of these proceeds may not yield a favorable return. They may invest the proceeds of this offering in ways with which investors disagree.

Our management team will have broad discretion in the application of the net proceeds from this offering and could spend or invest the proceeds in ways with which our shareholders disagree. Accordingly, investors will need to rely on our management team's judgment with respect to the use of these proceeds. We intend to use the proceeds from this offering in the manner described under "Use of Proceeds." However, the failure by management to apply these funds effectively could negatively affect our ability to operate and grow our business.

We cannot specify with certainty all of the particular uses for the net proceeds to be received from this offering. Accordingly, we will have broad discretion in using these proceeds. Until the net proceeds are used, they may be placed in investments that do not produce significant income or that may lose value.

You may experience immediate dilution in the book value per share of the common shares you purchase.

Given that the price per share of our common shares being offered is expected to be higher than the book value per share of our common shares, you may suffer substantial dilution in the net tangible book value of the common shares you purchase in this offering. See the section entitled "Dilution" below for a more detailed discussion of the dilution you will incur if you purchase common shares in this offering.

While we currently qualify as an emerging growth company under the JOBS Act, we will cease to be an emerging growth company on or before the end of 2020, and, to the extent we do not qualify as a smaller reporting company, at such time our costs and the demands placed upon our management will increase.

As an emerging growth company under the JOBS Act, we are permitted to, and intend to, rely on exemptions from certain disclosure requirements. While we currently qualify as an emerging growth company under the JOBS Act, we will cease to be an emerging growth company on or before the end of 2020, and, to the extent we do not qualify as a smaller reporting company, at such time our costs and the demands placed upon our management will increase unless we subsequently qualify as a smaller reporting company. For as long as we continue to be an emerging growth company, we may take advantage of exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies, including not being required to comply with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act, reduced disclosure obligations regarding executive compensation in our periodic reports and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and shareholder approval of any golden parachute payments not previously approved. Once we cease to be an emerging growth company, we may qualify as a smaller reporting company, and if so qualified, we will remain a smaller reporting company for so long as (i) our voting and non-voting common stock held by nonaffiliates is less than US$250 million measured on the last business day of our second fiscal quarter or (ii) our annual revenue is less than US$100 million during the most recently completed fiscal year and our voting and non-voting common stock held by non-affiliates is less than US$700 million measured on the last business day of our second fiscal quarter. Similar to emerging growth companies, smaller reporting companies are able to provide simplified executive compensation disclosure, are exempt from the auditor attestation requirements of Section 404, and have certain other reduced disclosure obligations, including, among other things, being required to provide only two years of audited financial statements. We cannot predict if investors will find our common shares less attractive because we may rely on these exemptions. If some investors find our common shares less attractive as a result, there may be a less active trading market for our common shares and our share price may be more volatile.

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We expect to lose our foreign private issuer status which will require us to comply with the US domestic reporting regime under the Exchange Act and result in significant additional compliance activity and increased costs and expenses.

We are currently a "foreign private issuer," as such term is defined in Rule 405 under the Securities Act, and, therefore, we are not required to comply with all the periodic disclosure and current reporting requirements of the Exchange Act and related rules and regulations. As a result, there may currently be less publicly available information about us than if we were a United States domestic issuer. For example, currently we are not subject to the proxy rules in the United States and disclosure with respect to our annual meetings will be governed by Canadian requirements. Under Rule 405, the determination of foreign private issuer status is made annually on the last business day of an issuer's most recently completed second fiscal quarter and, accordingly, the next determination will be made with respect to us on June 30, 2020. We expect to lose our foreign private issuer status on the next determination date since (i) we believe at least 50% of our outstanding common shares were held by US residents and (ii) the majority of our directors are US citizens, which we do not expect to change before the next determination date. As a result, we expect to be required to comply with US domestic issuer requirements beginning January 1, 2021.

The regulatory and compliance costs to us under US securities laws as a US domestic issuer may be significantly more than costs we incur as a foreign private issuer. If we are not a foreign private issuer, we will be required to file periodic reports and registration statements on US domestic issuer forms with the SEC, which are more detailed and extensive in certain respects than the forms available to a foreign private issuer. We will be required under current SEC rules to prepare our consolidated financial statements in accordance with US generally accepted accounting principles ("US GAAP") and modify certain of our policies to comply with corporate governance practices associated with US domestic issuers. In addition, we may lose our ability to rely upon exemptions from certain corporate governance requirements on US stock exchanges that are available to foreign private issuers, and exemptions from requirements related to the preparation and solicitation of proxies (including compliance with full disclosure obligations regarding executive compensation in proxy statements and the requirements of holding a nonbinding advisory vote on certain executive compensation matters, such as "say on pay" and "say on frequency"). Moreover, we will no longer be exempt from certain of the provisions of US securities laws, such as Regulation FD (which restricts the selective disclosure of material information), exemptions for filing beneficial ownership reports under Section 16(a) for officers, directors and 10% shareholders and the Section 16(b) short swing profit rules. In light of our expectations, we have already started to prepare for the consequences of becoming a US domestic issuer, including those described above, and we expect that the loss of foreign private issuer status will increase our legal and financial compliance costs and will make some activities highly time-consuming and costly. The additional costs could have an adverse impact on our results of operations, financial position and cash flows.

In addition, the transition to being treated as a US domestic issuer may make it more difficult and expensive for us to obtain director and officer liability insurance, and we may be required to accept reduced coverage or incur substantially higher costs to obtain coverage.

We are likely a PFIC, which may have adverse US federal income tax consequences for US shareholders.

US investors should be aware that we believe we were classified as a PFIC during the tax years ended December 31, 2019 and 2018, and based on current business plans and financial expectations, we believe that we may be a PFIC for the current tax year and may be a PFIC in future tax years. If Trillium is a PFIC for any taxable year during which a U.S. Holder (as defined under "Certain U.S. Federal Income Tax Considerations") holds our common shares, it would likely result in adverse U.S. federal income tax consequences for such U.S. Holder. U.S. Holders should carefully read "Certain U.S. Federal Income Tax Considerations - Passive Foreign Investment Company Rules" for more information and consult their own tax advisors regarding the consequences of Trillium being treated as a PFIC for U.S. federal income tax purposes, including the advisability of making a qualified electing fund election (including a protective election), which may mitigate certain possible adverse U.S. federal income tax consequences but may result in an inclusion in gross income without receipt of such income.

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Other Risks Related to Trillium's Business

The duration and impact of the current COVID-19 pandemic is uncertain.

Our business relies, to a certain extent, on free movement of goods, services and capital from around the world, which has been significantly restricted as a result of COVID-19. We have implemented a response designed to maintain our operations despite the outbreak of the virus. However, we may experience direct or indirect impacts from the pandemic, including delays in the enrollment of new patients in our TTI-621 and TTI-622 clinical studies. For instance, on April 8, 2020, we announced that we are following the U.S. FDA and Health Canada COVID-19 guidance regarding the conduct and management of clinical trials during the pandemic, and that we are addressing COVID-19 derived challenges on a patient-by-patient basis. Currently, all active patients on the TTI-621 and TTI-622 clinical studies are continuing treatment, and the Company expects that these patients will continue treatment on study. Going forward, we expect that enrollment in the TTI-621 and TTI-622 clinical studies will slow down or potentially pause as many clinical sites are putting enrollment of new patients on hold. Given the rapidly evolving nature of the pandemic, the Company will update trial timelines after it has more visibility on the length and extent of the COVID-19 crisis.

In addition to a slow-down in enrollment, the COVID-19 pandemic may impact our studies in other ways in the future. For instance, although we currently have a sufficient supply of TTI-621 and TTI-622 to complete our ongoing dose escalation studies and have not experienced any supply chain disruptions to date, our future manufacturing campaigns may be delayed, which could delay our future clinical studies and development efforts. Other ways that the COVID-19 pandemic may impact our business include, but are not limited to:

• delays or difficulties in initiating new clinical trials;

• increased rates of patients withdrawing from our clinical trials;

• diversion of healthcare resources away from the conduct of clinical trials;

• the need to modify, suspend, or terminate clinical trials;

• interruption of key clinical trial activities, clinical trial noncompliance, and clinical trial deviations, which may impact the integrity of the resulting data;

• interruption or delays in FDA's or other regulatory authorities' review of submissions;

• delays or disruptions in preclinical experiments and investigational new drug application-enabling studies; and

• interruption of, or delays in receiving necessary study materials.

The COVID-19 pandemic and the government and public health response thereto continue to rapidly evolve. In light of the COVID-19 outbreak, the FDA has issued a number of new guidance documents. Specifically, as a result of the potential effect of the COVID-19 outbreak on many clinical trial programs in the US and globally, the FDA issued guidance concerning potential impacts on clinical trial programs, changes that may be necessary to such programs if they proceed, considerations regarding trial suspensions and discontinuations, the potential need to consult with or make submissions to relevant ethics committees, IRBs, and the FDA, the use of alternative drug delivery methods, and considerations with respect the outbreak's impacts on endpoints, data collection, study procedures, and analysis. Additionally, in March 2020, the US Congress passed the Coronavirus Aid, Relief, and Economic Security Act, which includes a number of provisions that are applicable to the pharmaceutical industry.

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We may also have some risk that our contracting counterparties could fail to meet their obligations due to restrictions on the movement of goods that may be required for the manufacturing of our cancer drugs. Given the ongoing and dynamic nature of the circumstances surrounding COVID-19, it is difficult to predict how significant the impact of COVID-19, including any responses to it, will be on the global economy and our business or for how long any disruptions are likely to continue. The extent of such impact will depend on future developments, which are highly uncertain, rapidly evolving and difficult to predict, including new information which may emerge concerning the severity of COVID-19 and additional actions which may be taken to contain COVID-19. Such developments could have an adverse effect on our business, financial condition, results of operations and cash flow.

USE OF PROCEEDS

The amount of net proceeds from this offering will depend upon the number of our common shares sold and the market prices at which they are sold. There can be no assurance that we will be able to sell any shares under or fully utilize the Sales Agreement as a source of financing.

We intend to use the net proceeds from the sale of our common shares pursuant to this offering, if any, together with our existing cash and cash equivalents, for working capital and general corporate purposes.

Our management will have broad discretion in the application of the net proceeds, if any, from this offering, and the amounts and timing of our actual expenditures will depend on numerous factors, including those listed under the heading "Risk Factors" in this prospectus supplement and the accompanying prospectus and the documents incorporated by reference herein and therein. We therefore cannot estimate with certainty the amount of net proceeds to be used for the purposes described above. While we intend to spend the net proceeds of the offering as stated above, there may be circumstances where, for sound business reasons, a re-allocation of funds may be necessary or advisable.

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DILUTION

If you invest in our common shares, your interest will be diluted to the extent the price per share you pay in this offering exceeds the net tangible book value per share of our common shares immediately after you purchase shares in this offering. As of December 31, 2019, our net tangible book value (deficit) was approximately (US$168,000), or approximately US$0.00 per share, based on 28,938,831 common shares outstanding as of December 31, 2019. Our net tangible book value per share represents the amount of our total tangible assets reduced by the amount of our total liabilities, divided by the total number of our common shares outstanding as of December 31, 2019.

After giving effect to the sale of our common shares in the assumed aggregate amount of US$50,000,000 at an assumed offering price of US$5.30 per common share, which is the last reported sale price of our common shares on the Nasdaq on May 4, 2020, and after deducting estimated offering expenses and commissions payable by us, our net tangible book value as of December 31, 2019 would have been US$48.2 million, or US$1.26 per share. This would represent an immediate increase in net tangible book value of US$1.26 per share to our existing shareholders and an immediate dilution in net tangible book value of US$4.04 per share to new investors in this offering.

The following table illustrates this calculation on a per common share basis:

	Assumed public offering price per share	US$ 5.30
	Net tangible book value per share at December 31, 2019	US$ 0.00
	Increase in net tangible book value per share attributable to the offering	US$ 1.26
	As adjusted net tangible book value per share after giving effect to the offering	US$ 1.26
	Dilution in net tangible book value per share to new investors in this offering	US$ 4.04

Notwithstanding the assumptions reflected in this table, the shares sold in this offering, if any, will be sold from time to time at various prices. The dilution per share to new investors purchasing our common shares in this offering will depend on the number and price of our common shares that are sold in this offering.

The number of common shares shown as outstanding in the table above is based on 28,938,831 common shares outstanding as of December 31, 2019 and excludes:

• 9,440,788 shares issuable upon conversion of outstanding first preferred shares;

• 18,750,000 shares issuable upon exercise of outstanding warrants; and

• 5,366,645 shares issuance upon exercise of outstanding options.

To the extent that outstanding first preferred shares, warrants or options are converted or exercised or other shares are issued, investors purchasing our common shares in this offering may experience further dilution. In addition, we may choose to issue additional common shares, or securities convertible into or exchangeable for common shares, in the future. The issuance of these securities could result in further dilution for investors purchasing our common shares in this offering.

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PLAN OF DISTRIBUTION

We have entered into the Sales Agreement with Evercore under which we may offer and sell our common shares from time to time for an aggregate sales price of up to US$50,000,000 through Evercore, acting as agent. Sales of our common shares, if any, under this prospectus supplement and the accompanying prospectus will be made by any method that is deemed to be an "at the market offering" as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended, or the Securities Act. No sales of our common shares under this prospectus supplement will be made in Canada, to anyone known by the sales agent to be a resident of Canada or over or through the facilities of the TSX or any other exchange or market in Canada.

Each time we wish to issue and sell common shares under the Sales Agreement, we will notify Evercore of the number of shares to be issued, the dates on which such sales are anticipated to be made, any limitation on the number of shares to be sold in any one day and any minimum price below which sales may not be made. Once we have so instructed Evercore, unless Evercore declines to accept the terms of such notice, Evercore has agreed to use its commercially reasonable efforts consistent with its normal trading and sales practices to sell such shares up to the amount specified on such terms. The obligations of Evercore under the Sales Agreement to sell our common shares are subject to a number of conditions that we must meet. The settlement of sales of shares between us and Evercore is generally anticipated to occur on the second trading day following the date on which the sale was made. Sales of our common shares as contemplated in this prospectus supplement will be settled through the facilities of The Depository Trust Company or by such other means as we and Evercore may agree upon. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

We will pay Evercore a commission of 3.0% of the gross proceeds we receive from each sale of our common shares. Because there is no minimum offering amount required as a condition to close this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. In addition, we have agreed to reimburse Evercore for the fees and disbursements of its counsel, payable upon execution of the sales agreement, in an amount not to exceed US$50,000, in addition to certain ongoing disbursements of its legal counsel. We estimate that the total expenses for the offering, excluding any commissions or expense reimbursement payable to Evercore under the terms of the Sales Agreement, will be approximately US$200,000, which includes legal, accounting and printing costs and various other fees associated with registering the common shares. The remaining sale proceeds, after deducting any other transaction fees, will equal our net proceeds from the sale of such shares.

Evercore will provide written confirmation to us before the open on the Nasdaq on the day following each day on which common shares are sold under the Sales Agreement. Each confirmation will include the number of shares sold on that day, the aggregate gross proceeds of such sales and the net proceeds to us.

In connection with the sale of our common shares on our behalf, Evercore will be deemed to be an "underwriter" within the meaning of the Securities Act and the compensation of Evercore will be deemed to be underwriting commissions or discounts. We have agreed to indemnify Evercore against certain liabilities, including liabilities under the Securities Act. We have also agreed to contribute to payments Evercore may be required to make in respect of such liabilities.

The offering of common shares pursuant to the Sales Agreement will terminate upon the earlier of (i) the sale of all common shares subject to the Sales Agreement and (ii) the termination of the Sales Agreement as permitted therein. We and Evercore may each terminate the Sales Agreement at any time upon two days' prior notice.

This summary of the material provisions of the Sales Agreement does not purport to be a complete statement of its terms and conditions. A copy of the Sales Agreement will be filed as an exhibit to a current report on Form 6-K filed under the Securities Exchange Act of 1934, or the Exchange Act, and incorporated by reference in this prospectus supplement.

Evercore and its affiliates may in the future provide various investment banking, commercial banking, financial advisory and other financial services for us and our affiliates, for which services they may in the future receive customary fees. In the course of its business, Evercore may actively trade our securities for its own account or for the accounts of customers, and, accordingly, Evercore may at any time hold long or short positions in such securities.

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A prospectus supplement and the accompanying prospectus in electronic format may be made available on a website maintained by Evercore, and Evercore may distribute the prospectus supplement and the accompanying prospectus electronically.

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CERTAIN U.S. FEDERAL INCOME TAX CONSIDERATIONS

The following is a general summary of certain material US federal income tax considerations applicable to a US Holder, as defined below, arising from and relating to the acquisition, ownership, and disposition of our common shares acquired in the offering.

This summary is for general information purposes only and does not purport to be a complete analysis or listing of all potential US federal income tax considerations that may apply to a US Holder arising from and relating to the acquisition, ownership, and disposition of our common shares. In addition, this summary does not take into account the individual facts and circumstances of any particular US Holder that may affect the US federal income tax consequences to such US Holder, including, without limitation, specific tax consequences to a US Holder under an applicable income tax treaty. Accordingly, this summary is not intended to be, and should not be construed as, legal or US federal income tax advice with respect to any US Holder. This summary does not address the US federal alternative minimum, US federal estate and gift, US state and local, and non-US tax consequences to US Holders of the acquisition, ownership, and disposition of our common shares. In addition, except as specifically set forth below, this summary does not discuss applicable tax reporting requirements. Each prospective US Holder should consult its own tax advisors regarding the US federal, US federal alternative minimum, US federal estate and gift, US state and local, and non-US tax consequences relating to the acquisition, ownership and disposition of our common shares.

No ruling from the Internal Revenue Service, or the "IRS", has been requested, or will be obtained, regarding the US federal income tax consequences of the acquisition, ownership, and disposition of our common shares. This summary is not binding on the IRS, and the IRS is not precluded from taking a position that is different from, and contrary to, the positions taken in this summary. In addition, because the authorities on which this summary is based are subject to various interpretations, the IRS and the US courts could disagree with one or more of the conclusions described in this summary.

Scope of this Summary

Authorities

This summary is based on the Internal Revenue Code of 1986, as amended, or the "Code", Treasury Regulations (whether final, temporary, or proposed), published rulings of the IRS, published administrative positions of the IRS, the Convention Between Canada and the United States of America with Respect to Taxes on Income and on Capital, signed September 26, 1980, as amended, or the "Treaty", and US court decisions that are applicable, and, in each case, as in effect and available, as of the date hereof. Any of the authorities on which this summary is based could be changed in a material and adverse manner at any time, and any such change could be applied retroactively. This summary does not discuss the potential effects, whether adverse or beneficial, of any proposed legislation.

US Holders

For purposes of this summary, the term "US Holder" means a beneficial owner of our common shares acquired in the offering that is for US federal income tax purposes:

• an individual who is a citizen or resident of the United States;

• a corporation (or other entity classified as a corporation for US federal income tax purposes) organized under the laws of the United States, any state thereof or the District of Columbia;

• an estate whose income is subject to US federal income taxation regardless of its source; or

• a trust that (a) is subject to the primary supervision of a court within the United States and the control of one or more US persons for all substantial decisions or (b) has a valid election in effect under applicable Treasury Regulations to be treated as a US person.

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US Holders Subject to Special US Federal Income Tax Rules Not Addressed

This summary does not address the US federal income tax considerations applicable to US Holders that are subject to special provisions under the Code, including, but not limited to, US Holders that: (a) are tax-exempt organizations, qualified retirement plans, individual retirement accounts, or other tax-deferred accounts; (b) are financial institutions, underwriters, insurance companies, real estate investment trusts, or regulated investment companies; (c) are broker-dealers, dealers, or traders in securities or currencies that elect to apply a mark-to-market accounting method; (d) have a "functional currency" other than the US dollar; (e) own our common shares as part of a straddle, hedging transaction, conversion transaction, constructive sale, or other arrangement involving more than one position; (f) acquire our common shares in connection with the exercise of employee stock options or otherwise as compensation for services; (g) hold our common shares other than as a capital asset within the meaning of Section 1221 of the Code (generally, property held for investment purposes); (h) own, have owned or will own (directly, indirectly, or by attribution) 10% or more of the total combined voting power or value of our outstanding shares or (i) US expatriates or former long-term residents of the United States. US Holders that are subject to special provisions under the Code, including, but not limited to, US Holders described immediately above, should consult their own tax advisors regarding the US federal, US federal alternative minimum, US federal estate and gift, US state and local, and non-US tax consequences relating to the acquisition, ownership and disposition of our common shares.

If an entity or arrangement that is classified as a partnership (or other "pass-through" entity) for US federal income tax purposes holds our common shares, the US federal income tax consequences to such entity or arrangement and the partners (or other owners or participants) of such entity or arrangement generally will depend on the activities of the entity or arrangement and the status of such partners (or owners or participants). This summary does not address the tax consequences to any such partner (or owner or participants). Partners (or other owners or participants) of entities or arrangements that are classified as partnerships or as "pass-through" entities for US federal income tax purposes should consult their own tax advisors regarding the US federal income tax consequences arising from and relating to the acquisition, ownership, and disposition of our common shares.

General Rules Applicable to the Ownership and Disposition of Common Shares

The following discussion describes the general rules applicable to the ownership and disposition of our common shares but is subject in its entirety to the special rules described below under the heading "PFIC Rules."

Distributions on Common Shares

Subject to the discussion under "PFIC Rules," a US Holder that receives a distribution, including a constructive distribution, as described below, with respect to common shares will be required to include the amount of such distribution in gross income as a dividend (without reduction for any Canadian income tax withheld from such distribution) to the extent of our current and accumulated "earnings and profits," as computed for US federal income tax purposes. To the extent that a distribution exceeds our current and accumulated "earnings and profits," such distribution will be treated first as a tax-free return of capital to the extent of a US Holder's tax basis in our common shares and thereafter as gain from the sale or exchange of such common shares. (See "Sale or Other Taxable Disposition of Common Shares", below.) However, we may not maintain the calculations of our earnings and profits in accordance with US federal income tax principles, and each US Holder should assume that any distribution by us with respect to our common shares will constitute dividend income. Any corporate US Holders should consult their tax advisor on the eligibility to receive the "dividends received deduction," including in connection with the rules applicable to PFICs, discussed below. Subject to applicable limitations and provided we are eligible for the benefits of the Treaty, dividends paid by us to non-corporate US Holders, including individuals, generally will be eligible for the preferential tax rates applicable to dividends, provided certain holding period and other conditions are satisfied, including that we not be classified as a PFIC in the tax year of distribution or in the preceding tax year with respect to such U.S. Holder. A dividend generally will be taxed to a US Holder at ordinary income tax rates if we are a PFIC for the tax year of such distribution or the preceding tax year. We believe that dividends received on our common shares by non-corporate US Holders are not expected to be eligible for the preferential "qualified dividend" income tax rate. The dividend rules are complex, and each US Holder should consult its own tax advisors regarding the application of such rules.

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Sale or Other Taxable Disposition of Common Shares

Subject to the discussion under "PFIC Rules," upon the sale or other taxable disposition of our common shares, a US Holder generally will recognize capital gain or loss in an amount equal to the difference between the US dollar value of cash received plus the fair market value of any property received and such US Holder's tax basis in such common shares sold or otherwise disposed of. A US Holder's tax basis in our common shares generally will be such holder's US dollar cost for such common shares (adjusted for gains or losses previously recognized in connection with the rules applicable to PFICs, to the extent applicable, discussed below). Gain or loss recognized on such sale or other disposition generally will be long-term capital gain or loss if, at the time of the sale or other disposition, our common shares have been held for more than one year.

Preferential tax rates currently apply to long-term capital gain of a US Holder that is an individual, estate, or trust. There are currently no preferential tax rates for long-term capital gain of a US Holder that is a corporation. Deductions for capital losses are subject to significant limitations under the Code.

PFIC Rules

PFIC Status

We believe we were classified as a PFIC during the tax years ended December 31, 2019 and 2018, and based on current business plans and financial expectations, we believe that we may be a PFIC for the current tax year and in future tax years. If we are a PFIC for any year during a US Holder's holding period, then certain potentially adverse rules may affect the US federal income tax consequences to a US Holder as a result of the acquisition, ownership and disposition of our common shares. The determination of whether any corporation is, was, or will be, a PFIC for a tax year depends, in part, on the application of complex US federal income tax rules, which are subject to differing interpretations. In addition, whether any corporation will be a PFIC for any tax year depends on the assets and income of such corporation over the course of each such tax year and, as a result, cannot be predicted with certainty as of the date hereof. Accordingly, there can be no assurance that the IRS will not challenge any determination made by us (or any subsidiary) concerning its PFIC status. Each US Holder should consult its own tax advisors regarding our PFIC status and the PFIC status of our subsidiaries.

In any year in which we are classified as a PFIC, a US Holder of our common shares will be required to file an annual report with the IRS containing such information as Treasury Regulations and/or other IRS guidance may require. In addition to penalties, a failure to satisfy such reporting requirements may result in an extension of the time period during which the IRS can assess a tax. US Holders should consult their own tax advisors regarding the requirements of filing such information returns under these rules, including the requirement to file an IRS Form 8621 annually.

We generally will be a PFIC if, for a tax year, (a) 75% or more of our gross income is passive income, or the "income test", or (b) 50% or more of the value of our assets either produce passive income or are held for the production of passive income, based on the quarterly average of the fair market value of such assets, or the "asset test". For purposes of the PFIC income test and asset test described above, if we own, directly or indirectly, 25% or more of the total value of the outstanding shares of another corporation, we will be treated as if we (a) held a proportionate share of the assets of such other corporation and (b) received directly a proportionate share of the income of such other corporation.

Under certain attribution rules, if we are a PFIC, US Holders will generally be deemed to own their proportionate share of our direct or indirect equity interest in any company that is also a PFIC, or a Subsidiary PFIC, and will generally be subject to US federal income tax on their proportionate share of (a) any "excess distributions," as described below, on the stock of a Subsidiary PFIC and (b) a disposition or deemed disposition of the stock of a Subsidiary PFIC by us or another Subsidiary PFIC, both as if such US Holders directly held the shares of such Subsidiary PFIC. In addition, US Holders may be subject to US federal income tax on any indirect gain realized on the stock of a Subsidiary PFIC on the sale or disposition of our common shares. Accordingly, US Holders should be aware that they could be subject to tax under the PFIC rules even if no distributions are received and no redemptions or other dispositions of our common shares are made.

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Default PFIC Rules Under Section 1291 of the Code

If we are a PFIC for any tax year during which a US Holder owns our common shares, the US federal income tax consequences to such US Holder of the acquisition, ownership, and disposition of such shares will depend on whether and when such US Holder makes an election to treat us and each Subsidiary PFIC, if any, as a QEF Election under Section 1295 of the Code, or makes a Mark-to-Market Election with respect to our common shares under Section 1296 of the Code. A US Holder that does not make either a QEF Election or a Mark-to-Market Election will be referred to in this summary as a "Non-Electing US Holder."

A Non-Electing US Holder will be subject to the rules of Section 1291 of the Code (described below) with respect to (a) any gain recognized on the sale or other taxable disposition of our common shares and (b) any "excess distribution" received on our common shares. A distribution generally will be an "excess distribution" to the extent that such distribution (together with all other distributions received in the current tax year) exceeds 125% of the average distributions received during the three preceding tax years (or during a US Holder's holding period for our common shares, if shorter).

Under Section 1291 of the Code, any gain recognized on the sale or other taxable disposition of our common shares (including an indirect disposition of the stock of any Subsidiary PFIC), and any "excess distribution" received on our common shares or with respect to the stock of a Subsidiary PFIC, must be ratably allocated to each day in a Non-Electing US Holder's holding period for the common shares. The amount of any such gain or excess distribution allocated to the tax year of disposition or distribution of the excess distribution and to years before the entity became a PFIC, if any, would be taxed as ordinary income (and not eligible for certain preferred rates). The amounts allocated to any other tax year would be subject to US federal income tax at the highest tax rate applicable to ordinary income in each such year, and an interest charge would be imposed on the tax liability for each such year, calculated as if such tax liability had been due in each such year. A Non-Electing US Holder that is not a corporation must generally treat any such interest paid as "personal interest," which is generally not deductible.

If we are a PFIC for any tax year during which a Non-Electing US Holder holds our common shares, we will continue to be treated as a PFIC with respect to such Non-Electing US Holder, regardless of whether we cease to be a PFIC in one or more subsequent tax years. A Non-Electing US Holder may be able to terminate this deemed PFIC status by electing to recognize gain (which will be taxed under the rules of Section 1291 of the Code discussed herein), but not loss, as if such common shares were sold on the last day of the last tax year for which we were a PFIC.

QEF Election

A US Holder that makes a timely and effective QEF Election for the first tax year in which the holding period of its common shares begins generally will not be subject to the rules of Section 1291 of the Code discussed above with respect to its common shares. A US Holder that makes a timely and effective QEF Election with respect to its common shares will be subject to US federal income tax on such US Holder's pro rata share of (a) our net capital gain, which will be taxed as long-term capital gain to such US Holder, and (b) our ordinary earnings, which will be taxed as ordinary income to such US Holder. Generally, "net capital gain" is the excess of (a) net long-term capital gain over (b) net short-term capital loss, and "ordinary earnings" are the excess of (a) "earnings and profits" over (b) net capital gain. The IRS has not issued rules regarding the allocation of net capital gain and ordinary earnings amounts to multiple classes of stock. Accordingly, the proper manner for allocating such items between our common shares is not certain. A US Holder that makes a QEF Election with respect to its common shares will be subject to US federal income tax on such amounts for each tax year in which we are a PFIC, regardless of whether such amounts are actually distributed to such US Holder by us. However, for any tax year in which we are a PFIC and have no net income or gain, US Holders that have made a QEF Election would not have any income inclusions as a result of the QEF Election. If a US Holder that made a QEF Election has an income inclusion, such a US Holder may, subject to certain limitations, elect to defer payment of current US federal income tax on such amounts, subject to an interest charge. If such US Holder is not a corporation, any such interest paid will generally be treated as "personal interest," which is generally not deductible.

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A US Holder that makes a timely and effective QEF Election with respect to us generally (a) would receive any distributions from us tax free to the extent that such distribution represents our "earnings and profits" that were previously included in income by the US Holder because of such QEF Election and (b) would adjust its tax basis in our common shares to reflect the amount included in income and/or received as a tax-free distribution because of such QEF Election. In addition, a US Holder that makes a QEF Election generally will recognize capital gain or loss on the sale or other taxable disposition of our common shares.

The procedure for making a QEF Election, and the US federal income tax consequences of making a QEF Election, will depend on whether such QEF Election is "timely". A QEF Election will be treated as timely if such QEF Election is made for the first year in the US Holder's holding period for our common shares in which we were a PFIC. A US Holder may make a timely QEF Election by filing the appropriate QEF Election documents at the time such US Holder files a US federal income tax return for such year. If a US Holder does not make a timely and effective QEF Election for the first year in the US Holder's holding period for our common shares the US Holder may still be able to make a timely and effective QEF Election in a subsequent year if such US Holder meets certain requirements and makes a "purging" election to recognize gain (which will be taxed under the rules of Section 1291 of the Code discussed above) as if such common shares were sold for their fair market value on the day the QEF Election is effective. If a US Holder makes a QEF Election but does not make a "purging" election to recognize gain, as discussed in the preceding sentence, then such US Holder shall continue to be subject to tax under the rules of Section 1291 discussed above. If a US Holder owns PFIC stock indirectly through another PFIC, separate QEF Elections must be made for the PFIC in which the US Holder is a direct shareholder and the Subsidiary PFIC for the QEF rules to apply to both PFICs.

A QEF Election will apply to the tax year for which such QEF Election is timely made and to all subsequent tax years, unless such QEF Election is invalidated or terminated or the IRS consents to revocation of such QEF Election. If a US Holder makes a QEF Election and, in a subsequent tax year, we cease to be a PFIC, the QEF Election will remain in effect (although it will not be applicable) during those tax years in which we are not a PFIC. Accordingly, if we become a PFIC in another subsequent tax year, the QEF Election will be effective and the US Holder will be subject to the QEF rules described above during any subsequent tax year in which we qualify as a PFIC.

We: (a) will use commercially reasonable efforts to make available to US Holders, upon their written request after the end of a tax year, information as to our status as a PFIC, and (b) for each year in which we are a PFIC, provide to a US Holder, upon written request, all information and documentation that a US Holder making a QEF Election with respect to us is required to obtain for US federal income tax purposes. We may elect to provide such information on our website. However, US Holders should be aware that we can provide no assurances that we will provide any such information relating to a Subsidiary PFIC. Because we may own shares in one or more Subsidiary PFICs at any time, US Holders will continue to be subject to the rules discussed above with respect to the taxation of gains and excess distributions with respect to any Subsidiary PFIC for which the US Holders do not obtain the required information. Each US Holder should consult its own tax advisors regarding the availability of, and procedure for making, a QEF Election with respect to us and any Subsidiary PFIC.

A US Holder makes a QEF Election by attaching a completed IRS Form 8621, including a PFIC Annual Information Statement, to a timely filed US federal income tax return. However, if we do not provide the required information with regard to us or any of our Subsidiary PFICs, US Holders will not be able to make a QEF Election for such entity and will continue to be subject to the rules of Section 1291 of the Code, discussed above, that apply to Non-Electing US Holders with respect to the taxation of gains and excess distributions.

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Mark-to-Market Election

A US Holder may make a Mark-to-Market Election with respect to our common shares only if our common shares are marketable stock. Our common shares generally will be "marketable stock" if our common shares are regularly traded on (a) a national securities exchange that is registered with the SEC, (b) the national market system established pursuant to section 11A of the Exchange Act, or (c) a foreign securities exchange that is regulated or supervised by a governmental authority of the country in which the market is located, provided that (i) such foreign exchange has trading volume, listing, financial disclosure, and surveillance requirements, and meets other requirements and the laws of the country in which such foreign exchange is located, together with the rules of such foreign exchange, ensure that such requirements are actually enforced and (ii) the rules of such foreign exchange effectively promote active trading of listed stocks. If such stock is traded on such a qualified exchange or other market, such stock generally will be "regularly traded" for any calendar year during which such stock is traded, other than in de minimis quantities, on at least 15 days during each calendar quarter. Our common shares are currently traded on Nasdaq, a national securities exchange in the United States which is registered with the SEC. We believe that our common shares were "regularly traded" in the third and fourth calendar quarters of 2019 and the first calendar quarter of 2020 and we expect that our common shares will be "regularly traded" in the second calendar quarter of 2020. However, there can be no assurance that our common shares will be "regularly traded" in subsequent calendar quarters. US Holders should consult their own tax advisors regarding the marketable stock rules.

A US Holder that makes a Mark-to-Market Election with respect to its common shares generally will not be subject to the rules of Section 1291 of the Code discussed above with respect to such common shares. However, if a US Holder does not make a Mark-to-Market Election beginning in the first tax year of such US Holder's holding period for our common shares for which we are a PFIC or such US Holder has not made a timely QEF Election, the rules of Section 1291 of the Code discussed above will apply to certain dispositions of, and distributions on, our common shares.

A US Holder that makes a Mark-to-Market Election will include in ordinary income, for each tax year in which we are a PFIC, an amount equal to the excess, if any, of (a) the fair market value of our common shares, as of the close of such tax year over (b) such US Holder's adjusted tax basis in such common shares. A US Holder that makes a Mark-to-Market Election will be allowed a deduction in an amount equal to the excess, if any, of (a) such US Holder's adjusted tax basis in our common shares, over (b) the fair market value of such common shares (but only to the extent of the net amount of previously included income as a result of the Mark-to-Market Election for prior tax years).

A US Holder that makes a Mark-to-Market Election generally also will adjust such US Holder's tax basis in our common shares to reflect the amount included in gross income or allowed as a deduction because of such Mark-to-Market Election. In addition, upon a sale or other taxable disposition of our common shares, a US Holder that makes a Mark-to-Market Election will recognize ordinary income or ordinary loss (not to exceed the excess, if any, of (a) the amount included in ordinary income because of such Mark-to-Market Election for prior tax years over (b) the amount allowed as a deduction because of such Mark-to-Market Election for prior tax years). Losses that exceed this limitation are subject to the rules generally applicable to losses provided in the Code and Treasury Regulations.

A US Holder makes a Mark-to-Market Election by attaching a completed IRS Form 8621 to a timely filed United States federal income tax return. A Mark-to-Market Election applies to the tax year in which such Mark-to-Market Election is made and to each subsequent tax year, unless our common shares cease to be "marketable stock" or the IRS consents to revocation of such election. Each US Holder should consult its own tax advisors regarding the availability of, and procedure for making, a Mark-to-Market Election.

Although a US Holder may be eligible to make a Mark-to-Market Election with respect to our common shares, no such election may be made with respect to the stock of any Subsidiary PFIC that a US Holder is treated as owning, because such stock is not marketable. Hence, the Mark-to-Market Election will not be effective to avoid the application of the default rules of Section 1291 of the Code described above with respect to deemed dispositions of Subsidiary PFIC stock or excess distributions from a Subsidiary PFIC.

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Other PFIC Rules

Certain additional adverse rules may apply with respect to a US Holder if we are a PFIC, regardless of whether such US Holder makes a QEF Election. For example, under Section 1298(b)(6) of the Code, a US Holder that uses our common shares as security for a loan will, except as may be provided in Treasury Regulations, be treated as having made a taxable disposition of such shares.

Special rules also apply to the amount of foreign tax credit that a US Holder may claim on a distribution from a PFIC. Subject to such special rules, foreign taxes paid with respect to any distribution in respect of stock in a PFIC are generally eligible for the foreign tax credit. The rules relating to distributions by a PFIC and their eligibility for the foreign tax credit are complicated, and a US Holder should consult with its own tax advisors regarding the availability of the foreign tax credit with respect to distributions by a PFIC.

The PFIC rules are complex, and each US Holder should consult its own tax advisors regarding the PFIC rules and how the PFIC rules may affect the US federal income tax consequences of the acquisition, ownership, and disposition of our common shares.

Additional Considerations

Additional Tax on Passive Income

Certain US Holders that are individuals, estates or trusts (other than trusts that are exempt from tax) will be subject to a 3.8% tax on all or a portion of their "net investment income," which may include dividend income and net gains from the disposition of our common shares. Further, excess distributions treated as dividends, gains treated as excess distributions, and Mark-to-Market inclusions and deductions may all be included in the calculation of net investment income. US Holders that are individuals, estates or trusts should consult their own tax advisors regarding the applicability of this tax to any of their income or gains in respect of our common shares.

Receipt of Foreign Currency

The amount of any distribution paid to a US Holder in foreign currency, or on the sale, exchange or other taxable disposition of our common shares generally will be equal to the US dollar value of such foreign currency based on the exchange rate applicable on the date of receipt (regardless of whether such foreign currency is converted into US dollars at that time). A US Holder will have a basis in the foreign currency equal to its US dollar value on the date of receipt. Any US Holder who converts or otherwise disposes of the foreign currency after the date of receipt may have a foreign currency exchange gain or loss that would be treated as ordinary income or loss, and generally will be US source income or loss for foreign tax credit purposes. Different rules apply to US Holders who use the accrual method. Each US Holder should consult its own US tax advisors regarding the US federal income tax consequences of receiving, owning, and disposing of foreign currency.

Foreign Tax Credit

Subject to the PFIC rules discussed above, a US Holder generally may claim the amount of Canadian withholding tax withheld either as a deduction from gross income or as a credit against US federal income tax liability. Generally, a credit will reduce a US Holder's US federal income tax liability on a dollar-for-dollar basis, whereas a deduction will reduce a US Holder's income that is subject to US federal income tax. This election is made on a year-by-year basis and applies to all foreign taxes paid (whether directly or through withholding) by a US Holder during a year.

Complex limitations apply to the foreign tax credit, including the general limitation that the credit cannot exceed the proportionate share of a US Holder's US federal income tax liability that such US Holder's "foreign source" taxable income bears to such US Holder's worldwide taxable income. In applying this limitation, a US Holder's various items of income and deduction must be classified, under complex rules, as either "foreign source" or "US source." Generally, dividends paid by a foreign corporation should be treated as foreign source for this purpose, and gains recognized on the sale of stock of a foreign corporation by a US Holder should be treated as US source for this purpose, except as otherwise provided in an applicable income tax treaty, and if an election is properly made under the Code. However, the amount of a distribution that is treated as a "dividend" may be lower for US federal income tax purposes than it is for Canadian federal income tax purposes, resulting in a reduced foreign tax credit allowance to a US Holder. In addition, this limitation is calculated separately with respect to specific categories of income. The foreign tax credit rules are complex, and each US Holder should consult its own US tax advisors regarding the foreign tax credit rules.

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Backup Withholding and Information Reporting

Under US federal income tax law, certain categories of US Holders must file information returns with respect to their investment in, or involvement in, a foreign corporation. For example, US return disclosure obligations (and related penalties) are imposed on individuals who are US Holders that hold certain specified foreign financial assets in excess of certain thresholds. The definition of specified foreign financial assets includes not only financial accounts maintained in foreign financial institutions, but also, unless held in accounts maintained by a financial institution, any stock or security issued by a non-US person, any financial instrument or contract held for investment that has an issuer or counterparty other than a US person and any interest in a foreign entity. US Holders may be subject to these reporting requirements unless their common shares are held in an account at certain financial institutions. Penalties for failure to file certain of these information returns are substantial. US Holders should consult with their own tax advisors regarding the requirements of filing information returns, including the requirement to file an IRS Form 8938.

Payments made within the US, or by a US payor or US middleman, of dividends on, and proceeds arising from the sale or other taxable disposition of, our common shares will generally be subject to information reporting and backup withholding tax, at the rate of 24%, if a US Holder (a) fails to furnish such US Holder's correct US taxpayer identification number (generally on Form W-9), (b) furnishes an incorrect US taxpayer identification number, (c) is notified by the IRS that such US Holder has previously failed to properly report items subject to backup withholding tax, or (d) fails to certify, under penalty of perjury, that such US Holder has furnished its correct US taxpayer identification number and that the IRS has not notified such US Holder that it is subject to backup withholding tax. However, certain exempt persons generally are excluded from these information reporting and backup withholding rules. Backup withholding is not an additional tax. Any amounts withheld under the US backup withholding tax rules will be allowed as a credit against a US Holder's US federal income tax liability, if any, or will be refunded, if such US Holder furnishes required information to the IRS in a timely manner.

The discussion of reporting requirements set forth above is not intended to constitute a complete description of all reporting requirements that may apply to a US Holder. A failure to satisfy certain reporting requirements may result in an extension of the time period during which the IRS can assess a tax, and, under certain circumstances, such an extension may apply to assessments of amounts unrelated to any unsatisfied reporting requirement. Each US Holder should consult its own tax advisors regarding the information reporting and backup withholding rules.

THE FOREGOING DISCUSSION DOES NOT COVER ALL US TAX MATTERS THAT MAY BE IMPORTANT TO US HOLDERS. PROSPECTIVE US HOLDERS ARE STRONGLY ENCOURAGED TO CONSULT THEIR TAX ADVISORS REGARDING THE FEDERAL, STATE, LOCAL, NON-US AND OTHER TAX CONSEQUENCES TO THEM OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF OUR COMMON SHARES IN LIGHT OF THEIR PARTICULAR CIRCUMSTANCE.

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CERTAIN CANADIAN FEDERAL INCOME TAX CONSIDERATIONS

The following is, as of the date hereof, a summary of the principal Canadian federal income tax considerations under the Income Tax Act (Canada) and the regulations thereunder (the "Tax Act") generally applicable to a holder, or "Holder", who acquires as beneficial owner common shares pursuant to the offering and who, for the purposes of the Tax Act and at all relevant times deals at arm's length with us, is not affiliated with us, is not exempt from tax under Part I of the Tax Act, and who acquires and holds the common shares as capital property. Generally, a common share will be considered to be capital property to a Holder thereof provided that the Holder does not use the common share in the course of carrying on a business of trading or dealing in securities and such Holder has not acquired or been deemed to have acquired the common share in one or more transactions considered to be an adventure or concern in the nature of trade.

This summary is generally applicable to a Holder, or a "Non-Resident Holder", who, at all relevant times, for purposes of the Tax Act: (i) is not, and is not deemed to be, resident in Canada for the purposes of the Tax Act or any applicable income tax treaty or convention; and (ii) does not and will not use or hold, and is not and will not be deemed to hold, the common shares in connection with carrying on a business in Canada. This summary does not apply to a Holder that has or will enter into a "synthetic disposition arrangement" or "derivative forward agreement" (as such terms are defined in the Tax Act). This summary is also not applicable to a Non-Resident Holder that carries on, or is deemed to carry on, an insurance business in Canada and elsewhere. Such Holders should consult their own tax advisors with respect to an investment in the common shares.

This summary is based upon the current provisions of the Tax Act and the Treaty in force as of the date hereof and an understanding of the current administrative policies and assessing practices of the Canada Revenue Agency, or the "CRA", published in writing by the CRA prior to the date hereof. This summary takes into account all specific proposals to amend the Tax Act publicly announced by or on behalf of the Minister of Finance (Canada) prior to the date hereof, or the "Tax Proposals", and assumes that the Tax Proposals will be enacted in the form proposed, although no assurance can be given that the Tax Proposals will be enacted in their current form or at all.

Other than the Tax Proposals, this summary does not otherwise take into account or anticipate any changes in law, whether by legislative, governmental, administrative or judicial decision or action, nor does it take into account or consider any provincial, territorial or foreign income tax considerations, which considerations may differ significantly from the Canadian federal income tax considerations discussed in this summary. This summary also does not take into account any change in the administrative policies or assessing practices of the CRA.

This summary is of a general nature only, is not exhaustive of all possible Canadian federal income tax considerations and is not intended to be, nor should it be construed to be, legal or tax advice to any particular Holder. Holders should consult their own tax advisors with respect to their particular circumstances.

Currency

For purposes of the Tax Act, all amounts relating to the acquisition, holding or disposition of common shares (including dividends, adjusted cost base and proceeds of disposition) must generally be expressed in Canadian Dollars. Amounts denominated in any other currency must be converted into Canadian Dollars generally based on the exchange rate quoted by the Bank of Canada for the applicable day or such other rate of exchange as is acceptable to the Minister of National Revenue (Canada).

Acquisition of Common Shares

When common shares are acquired by a Non-Resident Holder who already owns common shares, the cost of the newly acquired common shares will be averaged with the adjusted cost base of all common shares owned by the Non-Resident Holder as capital property before that time for the purpose of determining the Non-Resident Holder's adjusted cost base of all common shares held by such person.

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Dividends

Dividends paid or credited or deemed to be paid or credited to a Non-Resident Holder by us are subject to Canadian withholding tax at the rate of 25% on the gross amount of the dividend unless such rate is reduced by the terms of an applicable tax treaty. For example, under the Treaty, the rate of withholding tax on dividends paid or credited to a Non-Resident Holder beneficially owning the dividends that is a resident of the United States for purposes of the Treaty, and entitled to the benefits of the Treaty, is generally limited to 15% of the gross amount of the dividend (or 5%, in the case of a Non-Resident Holder that is a resident of the United States for purposes of the Treaty, entitled to the benefits of the Treaty, and that is a company beneficially owning at least 10% of our voting shares). Non-Resident Holders are urged to consult their own tax advisors to determine any entitlement to relief under an applicable income tax treaty.

Disposition of Common Shares

Upon a disposition (or a deemed disposition) of a common share (other than a disposition of common shares to us unless purchased by us in the open market in the manner in which shares are normally purchased by any member of the public in the open market), a Non-Resident Holder generally will realize a capital gain (or a capital loss) equal to the amount by which the proceeds of disposition of such share, net of any reasonable costs of disposition, are greater (or are less) than the adjusted cost base of such share to the Non-Resident Holder.

A Non-Resident Holder generally will not be subject to tax under the Tax Act in respect of a capital gain realized on the disposition or deemed disposition of a common share, unless the common share constitutes "taxable Canadian property" to the Non-Resident Holder thereof for purposes of the Tax Act, and the Non-Resident Holder is not entitled to relief under the terms of an applicable tax treaty. In addition, capital losses arising on the disposition or deemed disposition of a common share will not be recognized under the Tax Act unless the common share constitutes "taxable Canadian property" to the Non-Resident Holder thereof for purposes of the Tax Act.

Provided the common shares are listed on a "designated stock exchange", as defined in the Tax Act (which currently includes the Nasdaq and TSX), at the time of disposition, the common shares generally will not constitute taxable Canadian property of a Non-Resident Holder at that time, unless at any time during the 60 month period immediately preceding the disposition the following two conditions are met concurrently: (i) one or any combination of (a) the Non-Resident Holder, (b) persons with whom the Non-Resident Holder did not deal at arm's length, and (c) partnerships in which the Non-Resident Holder or a person with whom the Non-Resident Holder did not deal at arm's length held a membership interest, directly or indirectly through one or more partnerships, owned 25% or more of our issued shares of any class or series of shares; and (ii) more than 50% of the fair market value of our common shares was derived directly or indirectly from one or any combination of (a) real or immovable property situated in Canada, (b) "Canadian resource properties" (as defined in the Tax Act), (c) "timber resource properties" (as defined in the Tax Act) and (d) an option, an interest or right in any of the foregoing property, whether or not such property exists. Notwithstanding the foregoing, a common share may in certain circumstances otherwise be deemed to be taxable Canadian property to a Non-Resident Holder for purposes of the Tax Act.

Non-Resident Holders whose common shares may be taxable Canadian property should consult their own tax advisors.

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LEGAL MATTERS

Certain legal matters in connection with the securities offered hereby will be passed upon on behalf of the Company by Goodwin Procter LLP with respect to U.S. legal matters and by Baker & McKenzie LLP with respect to Canadian legal matters. Evercore is being represented in connection with this offering by Morgan, Lewis & Bockius LLP with respect to U.S. legal matters and Blake, Cassels & Graydon LLP with respect to Canadian legal matters.

EXPERTS

The consolidated financial statements of Trillium Therapeutics Inc. included in our Annual Report on Form 40-F for the year ended December 31, 2019, have been audited by Ernst & Young LLP, independent registered public accounting firm as set forth in their report, thereon, included therein, and incorporated herein by reference in this prospectus supplement and elsewhere in the registration statement of which this prospectus supplement forms a part. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

ENFORCEABILITY OF CIVIL LIABILITIES

We are a corporation existing under the BCBCA. Some of our officers, directors and experts named in this prospectus supplement are Canadian residents, and many of our assets or the assets of our officers and directors are located outside the United States. We have appointed an agent for service of process in the United States, but it may be difficult for holders of common shares who reside in the United States to effect service within the United States upon those directors, officers and experts who are not residents of the United States. It may also be difficult for holders of common shares who reside in the United States to realize in the United States upon judgments of courts of the United States predicated upon our civil liability and the civil liability of our officers and directors under the United States federal securities laws. We have been advised by our Canadian counsel, Baker & McKenzie LLP, that a judgment of a United States court predicated solely upon civil liability under U.S. federal securities laws would probably be enforceable in Canada if the United States court in which the judgment was obtained has a basis for jurisdiction in the matter that would be recognized by a Canadian court for the same purposes and if certain other conditions are met. We have also been advised by Baker & McKenzie LLP, however, that there is substantial doubt whether an action could be brought in Canada in the first instance on the basis of liability predicated solely upon U.S. federal securities laws. See "Risk Factors."

WHERE YOU CAN FIND MORE INFORMATION

We are required to file documents with securities commissions or similar authorities in the provinces of British Columbia, Alberta, Manitoba, Ontario and Nova Scotia in Canada. In addition, we are subject to the informational requirements of the Exchange Act, and, in accordance with the Exchange Act, we also file reports with, and furnish other information to, the SEC. As a foreign private issuer, certain of these reports and other information (including financial information) may be prepared in accordance with the disclosure requirements of Canada, which differ in certain respects from those in the United States. In addition, as a foreign private issuer, we are exempt from the rules under the Exchange Act prescribing the furnishing and content of proxy statements, and our officers, directors and principal shareholders are exempt from the reporting and short-swing profit recovery provisions contained in Section 16 of the Exchange Act. We are also not required to publish financial statements as promptly as U.S. companies.

You may read any document we file with or furnish to the securities commissions and authorities of the provinces of Canada through the Internet on the Canadian System for Electronic Document Analysis and Retrieval, or SEDAR. Please call the SEC at l-800-SEC-0330 for further information on the public reference rooms. Certain of our filings are also electronically available on EDGAR, and may be accessed at www.sec.gov.

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INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to incorporate by reference certain information that we file with them, which means that we can disclose important information to you by referring you to those documents. Information that is incorporated by reference is an important part of this prospectus supplement. We incorporate by reference the documents listed below, which were filed with the SEC:

(a) Our Annual Report on Form 40-F for the fiscal year ended December 31, 2019, filed with the SEC on March 10, 2020, containing our (i) Annual Information Form dated March 5, 2020; (ii) audited annual consolidated financial statements as of December 31, 2019 and 2018 and for each of the years in the two-year period ended December 31, 2019, including the notes thereto and the auditor's report thereon; and (iii) Management's Discussion and Analysis for the year ended December 31, 2019 and 2018; and

(b) Our Reports on Form 6-K filed with the SEC on January 7, 2020, January 16, 2020, January 22, 2020, January 23, 2020, January 29, 2020, February 7, 2020, April 8, 2020 and April 23, 2020.

We also incorporate by reference each of the following documents we file with the SEC after the date of this prospectus supplement and until the common shares offered hereby have been sold or until such time as the Sales Agreement is terminated: (i) all annual reports on Form 40-F, Form 20-F or Form 10-K; (ii) all quarterly reports on Form 10-Q; (iii) all current reports on Form 8-K; and (iv) those portions of any reports on Form 6-K that we indicate in such reports are to be deemed incorporated by reference into this prospectus supplement.

Any statement contained in this prospectus supplement or in a document (or part thereof) incorporated by reference, or deemed to be incorporated by reference, in this prospectus supplement shall be deemed to be modified or superseded, for purposes of this prospectus supplement, to the extent that a statement contained in the prospectus supplement or in any subsequently filed document (or part thereof) that also is, or is deemed to be, incorporated by reference in this prospectus supplement modifies or replaces such statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute part of this prospectus supplement. The modifying or superseding statement need not state that it has modified or superseded a prior statement or include any other information set forth in the document which it modifies or supersedes.

You may obtain a copy of any of any filings that are incorporated by reference into this prospectus, at no cost, by writing to or telephoning us at the following address:

Trillium Therapeutics Inc.
2488 Dunwin Drive
Mississauga, Ontario L5L 1J9
Canada
(416) 595-0627
Attention: Corporate Secretary

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US$250,000,000

Common Shares

First Preferred Shares

Subscription Receipts

Warrants

Units

We may from time to time offer and sell our common shares, first preferred shares, subscription receipts, warrants and units (collectively, the "Securities") having an aggregate offering amount of up to US$250,000,000. Securities may be offered separately or together, in amounts, at prices and on terms to be determined based on market conditions at the time of sale and set forth in one or more prospectus supplements. These Securities may be offered and sold in the United States and elsewhere where permitted by law. We will provide the specific terms of these Securities in supplements to this prospectus that will be delivered to purchasers together with this prospectus. You should read this prospectus and any prospectus supplement carefully before you invest in the Securities.

Investment in the Securities involves certain risks that should be considered by a prospective purchaser. See "Risk Factors" on page 13 of this prospectus along with the risk factors described in the applicable prospectus supplement pertaining to the Securities and the other information contained in and incorporated by reference in this prospectus and in the applicable prospectus supplement before purchasing the Securities offered hereby. See "Where You Can Find More Information".

We may sell the Securities to or through underwriters or dealers purchasing as principals and may also sell the Securities to one or more purchasers directly or through agents. See "Plan of Distribution". The prospectus supplement relating to a particular offering of Securities will identify each underwriter, dealer or agent, as the case may be, engaged by us in connection with the offering and sale of Securities, and will set forth the terms of the offering of such Securities, including the method of distribution of such Securities, the public offering price, the proceeds to us, any fees, discounts or other compensation payable to underwriters, dealers or agents, and any other material terms of the plan of distribution. Securities may be sold from time to time in one or more transactions at a fixed price or fixed prices, or at non-fixed prices.

Our common shares are listed on the Toronto Stock Exchange (the "TSX") and on the Nasdaq Capital Market (the "Nasdaq") under the symbol "TRIL". On April 22, 2020, the last trading day before the date of this prospectus, the closing price of the common shares on the TSX was C$7.05 per common share, and the closing price of the common shares on the Nasdaq was US$4.97 per common share.

Unless otherwise specified in the applicable prospectus supplement, the first preferred shares, subscription receipts, warrants and units will not be listed on any securities or stock exchange. There is no market through which the first preferred shares, subscription receipts, warrant and units may be sold and purchasers may not be able to resell such securities purchased under this prospectus and the applicable prospectus supplement. This may affect the pricing of the first preferred shares, subscription receipts, warrants and units in the secondary market, the transparency and availability of trading prices, the liquidity of the first preferred shares, subscription receipts, warrants and units and the extent of our regulation.

Our head office is located at 2488 Dunwin Drive, Mississauga, Ontario, Canada, L5L 1J9. Our registered office is located at Suite 1750-1055 W. Georgia Street, P.O. Box 11125, Vancouver, British Columbia, V6E 3P3.

Neither the United States Securities and Exchange Commission (the "SEC") nor any state securities commission has approved or disapproved these Securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offence.

The date of this prospectus is May 4, 2020.

TABLE OF CONTENTS

Page

ABOUT THIS PROSPECTUS	2

WHERE YOU CAN FIND MORE INFORMATION	2

FORWARD-LOOKING STATEMENTS	3

TRILLIUM THERAPEUTICS INC.	6

CAPITALIZATION	7

USE OF PROCEEDS	7

PRICE RANGE	7

DESCRIPTION OF SHARE CAPITAL	7

DESCRIPTION OF SUBSCRIPTION RECEIPTS	11

DESCRIPTION OF WARRANTS	12

DESCRIPTION OF UNITS	12

RISK FACTORS	13

CERTAIN INCOME TAX CONSIDERATIONS	13

PLAN OF DISTRIBUTION	13

LEGAL MATTERS	14

EXPERTS	15

ENFORCEABILITY OF CIVIL LIABILITIES	15

EXPENSES	15

ABOUT THIS PROSPECTUS

Unless the context otherwise requires, all references in this prospectus and any prospectus supplement to "Trillium", the "Company", "we", "us" and "our" mean Trillium Therapeutics Inc. and its consolidated subsidiaries.

In this prospectus and in any prospectus supplement, unless otherwise specified or the context otherwise requires, all dollar amounts are expressed in United States dollars, references to "dollars", "$" or "US$" are to United States dollars and all references to "C$" are to Canadian dollars.

Unless otherwise indicated, all financial information included and incorporated by reference in this prospectus or included in any prospectus supplement is prepared in accordance with International Financial Reporting Standards as issued by the International Accounting Standards Board, or "IFRS". Thus, it may not be comparable to financial information of United States companies.

This prospectus is part of a Registration Statement on Form F-3 relating to the Securities that has been filed with the SEC. Under the Registration Statement, we may, from time to time, sell any combination of the Securities described in this prospectus in one or more offerings up to an aggregate offering amount of US$250,000,000. This prospectus provides you with a general description of the Securities that we may offer. Each time we sell Securities under this prospectus, we will provide a prospectus supplement that will contain specific information about the terms of that offering of Securities. The prospectus supplement may also add, update or change information contained in this prospectus. Before you invest in the Securities, you should read both this prospectus and any applicable prospectus supplement together with additional information described under the heading "Where You Can Find More Information". This prospectus does not contain all of the information set forth in the Registration Statement we have filed with the SEC of which this prospectus forms a part, certain parts of which are omitted in accordance with the rules and regulations of the SEC. You may refer to the Registration Statement of which this prospectus forms a part and the exhibits to the Registration Statement for further information with respect to us and the Securities.

WHERE YOU CAN FIND MORE INFORMATION

We are subject to the informational requirements of the United States Securities Exchange Act of 1934, as amended (the "Exchange Act") and, in accordance with the Exchange Act, we also file reports with and furnish other information to the SEC. Under the multijurisdictional disclosure system adopted by Canada and the United States, these reports and other information (including financial information) may be prepared, in part, in accordance with the disclosure requirements of Canada, which differ from those in the United States. You may obtain any document we file with or furnish to the SEC at the SEC's public reference room at 100 F Street, N.E., Washington D.C. 20549 by paying a fee. Please call the SEC at 1-800-SEC-0330 or contact them at www.sec.gov for further information on the public reference room. Our filings are also electronically available from the SEC's Electronic Document Gathering, Analysis, and Retrieval system ("EDGAR"), which can be accessed at www.sec.gov, as well as from commercial document retrieval services.

Additionally, we file documents with securities commissions or similar authorities in the provinces of British Columbia, Alberta, Manitoba, Ontario, Nova Scotia in Canada. These documents are available through the internet on the Canadian System for Electronic Document Analysis and Retrieval ("SEDAR"), which can be accessed at www.sedar.com.

The SEC allows us to incorporate by reference certain information that we file with them, which means that we can disclose important information to you by referring you to those documents. Information that is incorporated by reference is an important part of this prospectus. We incorporate by reference the documents listed below, which were filed with the SEC:

(a)

Our Annual Report on Form 40-F for the fiscal year ended December 31, 2019, filed with the SEC on March 10, 2020, containing our (i) Annual Information Form dated March 5, 2020 (our "AIF"); (ii) audited annual consolidated financial statements as of December 31, 2019 and 2018 and for each of the years in the two-year period ended December 31, 2019, including the notes thereto and the auditor's report thereon; and (iii) Management's Discussion and Analysis for the year ended December 31, 2019 and 2018 (our "MD&A"); and

(b)

Our Reports on Form 6-K filed with the SEC on January 7, 2020, January 16, 2020, January 22, 2020, January 23, 2020, January 29, 2020, February 7, 2020, April 8, 2020 and April 23, 2020.

We also incorporate by reference each of the following documents we file with the SEC after the date of this prospectus and prior to the filing of a post-effective amendment that indicates that all Securities offered hereby have been sold or which deregisters all Securities then remaining unsold: (i) all annual reports on Form 40-F, Form 20-F or Form 10-K; (ii) all quarterly reports on Form 10-Q; (iii) all current reports on Form 8-K; and (iv) those portions of any reports on Form 6-K that we indicate in such reports are to be deemed incorporated by reference into this prospectus.

Any statement contained in this prospectus or in a document (or part thereof) incorporated by reference, or deemed to be incorporated by reference, in this prospectus shall be deemed to be modified or superseded, for purposes of this prospectus, to the extent that a statement contained in the prospectus or in any subsequently filed document (or part thereof) that also is, or is deemed to be, incorporated by reference in this prospectus modifies or replaces such statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute part of this prospectus. The modifying or superseding statement need not state that it has modified or superseded a prior statement or include any other information set forth in the document which it modifies or supersedes.

You may obtain a copy of any of any filings that are incorporated by reference into this prospectus, at no cost, by writing to or telephoning us at the following address:

Trillium Therapeutics Inc.

2488 Dunwin Drive

Mississauga, Ontario L5L 1J9

Canada

(416) 595-0627

Attention: Corporate Secretary

All shelf information permitted under applicable law to be omitted from this prospectus will be contained in one or more prospectus supplements that will be delivered to purchasers together with this prospectus. A prospectus supplement or prospectus supplements containing the specific terms for an issue of Securities will be delivered to purchasers of such Securities together with this prospectus and will be deemed to be incorporated by reference into this prospectus as of the date of such prospectus supplement but only for the purposes of the Securities issued thereunder.

FORWARD-LOOKING STATEMENTS

This prospectus and documents incorporated herein by reference contain certain forward-looking statements or information (collectively, "forward-looking statements") within the meaning of applicable securities legislation. In addition to the cautionary statement below, with respect to forward-looking statements contained in the documents incorporated by reference herein, prospective purchasers should refer to "Cautionary Statement Regarding Forward-Looking Statements" in our AIF and MD&A as well as to similar sections of any documents incorporated by reference in this prospectus that are filed after the date hereof.

All statements contained herein that are not clearly historical in nature are forward-looking, and the words "anticipate", "believe", "expect", "estimate", "may", "will", "could", "leading", "intend", "contemplate", "shall" and similar expressions are generally intended to identify forward-looking statements. Forward-looking statements in this prospectus and documents incorporated herein by reference include, but are not limited to, statements with respect to:

• our expected future loss and accumulated deficit levels;

• our projected financial position and estimated cash burn rate;

• our requirements for, and the ability to obtain, future funding on favorable terms or at all;

• our plans to focus development of TTI-621 on patients with hematological malignancies, such as peripheral T-cell lymphoma, cutaneous T-cell lymphoma, and acute myeloid leukemia, based on our early clinical results;