ACET Adicet Bio Inc

Item 8.01 Other Events.

On June 6, 2022, the Company issued a press release and presented on interim data from the Company’s Phase 1 study of ADI-001 for the potential treatment of relapsed or refractory B-cell Non-Hodgkin’s Lymphoma (NHL). Data highlights as of the May 31, 2022 data-cut date are as follows:

Table 1: Summary of ADI-001 interim data from three dosing cohorts: *

*Efficacy-evaluable patients as of the May 31, 2022 data-cut date. Data are subject to further review and verification.

BOR= best overall response. PD=progressive disease.

Table 2: ADI-001 Preliminary Efficacy Data:

(Per protocol analysis, independent radiographic assessment using Lugano 2014)

*Efficacy-evaluable patients as of the May 31, 2022, data-cut date. Data are subject to further review and verification.

As of the May 31, 2022, data-cut date, of the six patients who achieved CR:

Dose level 1:

As previously disclosed, one patient administered ADI-001 in dose level 1, a 66-year-old female who had achieved a CR, developed COVID-19 related pneumonia approximately two and a half months after ADI-001 administration and later died of complications from it, unrelated to ADI-001. This patient was previously reported as a partial response (PR) by local radiological assessment and has been assessed as a CR by independent central reading.

One patient with triple-hit high grade B-cell lymphoma in dose level 1 who had relapsed following two prior treatments with autologous anti-CD19 CAR T therapy, had a CR after treatment with ADI-001. The patient developed a local skin relapse at four months, and was administered local radiotherapy. The skin lesion resolved with no systemic therapy provided to the patient. The patient continues to be cancer free seven and a half months following administration of ADI-001, as measured by a negative PET/CT scan.

Dose level 2:

Both patients administered ADI-001 in dose level 2 have ongoing CR. One patient has a CR beyond seven months and one patient has a CR beyond four and a half months.

Dose level 3:

Both patients administered ADI-001 in dose level 3 have ongoing CR with follow-up beyond three and one month, respectively.

In summary, 50% of evaluable patients with at least six months follow up (2 of 4) remain cancer free.

Table 3: ADI-001 Preliminary Safety Data in Efficacy-Evaluable Patients+

+Safety assessment was performed using the Common Terminology Criteria for Adverse Events (v5) and the American Society for Transplantation and Cellular Therapy criteria. The two ADI-001-related adverse events of special interest (AESI) were a Grade 1 CRS at DL1 and a Grade 1 ICANS at DL2, which resolved within 24 hours without medical intervention​; No DLTs or GvHD; No treatment discontinuations due to AEs​; two patients administered standard lymphodepletion (sLD) and six patients eLD​; There were no eLD-associated clinical infection.

*One patient in DL 1 who received sLD developed COVID-19 pneumonia later died of complications of it, unrelated to ADI-001.

Given the safety profile to date, the protocol was amended to include a new DL 4 (1E9 CAR+ cells) and a potential ADI-001 consolidation dosing at DL3 to finalize the recommended Phase 2 dose in the second half of 2022. The Company expects to backfill enrollment to DL3 with additional potential patients in the second half of 2022. The Company expects to provide at least one additional clinical update for the ADI-001 Phase 1 study in the second half of 2022. The Company will discuss with the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) the design of two pivotal intent studies and a potential path to support a Biologics License Application (BLA) and Marketing Authorization Application (MAA) for ADI-001 and initiate at least one potentially pivotal study in the first half of 2023.

Adicet has six additional internal gamma delta T cell therapy programs in preclinical development and plans one new investigational new drug application (IND) every 12-18 months, including one new IND in 2023.

The disclosure under this Item 8.01 contains "forward-looking statements" of Adicet within the meaning of the Private Securities Litigation Reform Act of 1995 relating to business and operations of Adicet. These forward-looking statements include, but are not limited to, express or implied statements regarding: the potential safety, durability, tolerability and therapeutic effects of ADI-001, including the expected design, implementation, timing of success of ADI-0001; plans and timing for the release of additional clinical data from Adicet’s Phase 1 trial of ADI-001 in relapsed/refractory NHL patients; future progress of the GLEAN study, including ongoing patient enrollment; expectations regarding future regulatory filings for product candidates in the Company’s pipeline; the outcome of discussions with the FDA and EMA regarding the design of two pivotal studies and a BLA and MAA submission for ADI-001; and timing of a dose selection for the Phase 2 trial in the second half of 2022 and initiation of a potentially pivotal program in the first half of 2023.

Any forward-looking statements in this press release are based on management's current expectations and beliefs of future events, and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in or implied by such forward-looking statements, including without limitation, the effect of COVID-19 on Adicet’s business and financial results, including with respect to disruptions to Adicet’s clinical trials, business operations and ability to raise additional capital; Adicet's ability to execute on its strategy, including obtaining the requisite regulatory approvals on the expected timeline, if at all; that positive results, including interim results, from a clinical study may not necessarily be predictive of the results of future or ongoing clinical studies; clinical studies may fail to demonstrate adequate safety and efficacy of Adicet’s product candidates, which would prevent, delay, or limit the scope of regulatory approval and commercialization; and regulatory approval processes of the FDA and comparable foreign regulatory authorities are lengthy, time-consuming, and inherently unpredictable. For a discussion of these and other risks and uncertainties, and other important factors, any of which could cause Adicet's actual results to differ from those

contained in the forward-looking statements, see the section entitled "Risk Factors" in Adicet's most recent Annual Report on Form 10-K for the year ended December 31, 2021 and subsequent filings with the Securities and Exchange Commission. All disclosure under this Item 8.01 is as of the date of this Form 8-K, and Adicet undertakes no duty to update this information unless required by law.