000148500312/312020Q3FALSE129,339,617us-gaap:AccountingStandardsUpdate201602MemberP4M00014850032020-01-012020-09-30xbrli:shares00014850032020-11-02iso4217:USD00014850032020-09-3000014850032019-12-31iso4217:USDxbrli:shares00014850032020-07-012020-09-3000014850032019-07-012019-09-3000014850032019-01-012019-09-300001485003us-gaap:CommonStockMember2019-12-310001485003us-gaap:AdditionalPaidInCapitalMember2019-12-310001485003us-gaap:RetainedEarningsMember2019-12-310001485003us-gaap:RetainedEarningsMember2020-01-012020-03-3100014850032020-01-012020-03-310001485003us-gaap:AdditionalPaidInCapitalMember2020-01-012020-03-310001485003us-gaap:CommonStockMember2020-01-012020-03-310001485003us-gaap:CommonStockMember2020-03-310001485003us-gaap:AdditionalPaidInCapitalMember2020-03-310001485003us-gaap:RetainedEarningsMember2020-03-3100014850032020-03-310001485003us-gaap:RetainedEarningsMember2020-04-012020-06-3000014850032020-04-012020-06-300001485003us-gaap:AdditionalPaidInCapitalMember2020-04-012020-06-300001485003us-gaap:CommonStockMember2020-04-012020-06-300001485003us-gaap:CommonStockMember2020-06-300001485003us-gaap:AdditionalPaidInCapitalMember2020-06-300001485003us-gaap:RetainedEarningsMember2020-06-3000014850032020-06-300001485003us-gaap:RetainedEarningsMember2020-07-012020-09-300001485003us-gaap:AdditionalPaidInCapitalMember2020-07-012020-09-300001485003us-gaap:CommonStockMember2020-07-012020-09-300001485003us-gaap:CommonStockMember2020-09-300001485003us-gaap:AdditionalPaidInCapitalMember2020-09-300001485003us-gaap:RetainedEarningsMember2020-09-300001485003us-gaap:CommonStockMember2018-12-310001485003us-gaap:AdditionalPaidInCapitalMember2018-12-310001485003us-gaap:RetainedEarningsMember2018-12-3100014850032018-12-310001485003us-gaap:RetainedEarningsMember2019-01-012019-03-3100014850032019-01-012019-03-310001485003us-gaap:AdditionalPaidInCapitalMember2019-01-012019-03-310001485003us-gaap:CommonStockMember2019-01-012019-03-310001485003us-gaap:CommonStockMember2019-03-310001485003us-gaap:AdditionalPaidInCapitalMember2019-03-310001485003us-gaap:RetainedEarningsMember2019-03-3100014850032019-03-310001485003us-gaap:RetainedEarningsMember2019-04-012019-06-3000014850032019-04-012019-06-300001485003us-gaap:AdditionalPaidInCapitalMember2019-04-012019-06-300001485003us-gaap:CommonStockMember2019-04-012019-06-3000014850032019-06-300001485003us-gaap:CommonStockMember2019-06-300001485003us-gaap:AdditionalPaidInCapitalMember2019-06-300001485003us-gaap:RetainedEarningsMember2019-06-300001485003us-gaap:RetainedEarningsMember2019-07-012019-09-300001485003us-gaap:AdditionalPaidInCapitalMember2019-07-012019-09-300001485003us-gaap:CommonStockMember2019-07-012019-09-300001485003us-gaap:CommonStockMember2019-09-300001485003us-gaap:AdditionalPaidInCapitalMember2019-09-300001485003us-gaap:RetainedEarningsMember2019-09-3000014850032019-09-30sesn:patient00014850032018-04-012018-04-30sesn:segment0001485003sesn:ViventiaBioIncMember2016-09-012016-09-30xbrli:pure0001485003sesn:ViventiaBioIncMember2016-09-300001485003sesn:ViventiaBioIncMembersrt:EuropeMembersesn:ViciniumMembersesn:CollaborativeArrangementRevenueBasedOnSpecifiedMilestoneMember2016-09-012016-09-300001485003sesn:ViventiaBioIncMembercountry:JPsesn:ViciniumMembersesn:CollaborativeArrangementRevenueBasedOnSpecifiedMilestoneMember2016-09-012016-09-300001485003sesn:ViventiaBioIncMembersesn:ViciniumMembersesn:CollaborativeArrangementRevenueBasedOnSpecifiedMilestoneMember2016-09-012016-09-300001485003us-gaap:CarryingReportedAmountFairValueDisclosureMember2020-09-300001485003us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EstimateOfFairValueFairValueDisclosureMember2020-09-300001485003us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:EstimateOfFairValueFairValueDisclosureMember2020-09-300001485003us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:EstimateOfFairValueFairValueDisclosureMember2020-09-300001485003us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EstimateOfFairValueFairValueDisclosureMember2020-09-300001485003us-gaap:CarryingReportedAmountFairValueDisclosureMember2019-12-310001485003us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EstimateOfFairValueFairValueDisclosureMember2019-12-310001485003us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:EstimateOfFairValueFairValueDisclosureMember2019-12-310001485003us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:EstimateOfFairValueFairValueDisclosureMember2019-12-310001485003us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EstimateOfFairValueFairValueDisclosureMember2019-12-310001485003us-gaap:FairValueInputsLevel3Member2019-12-310001485003us-gaap:FairValueInputsLevel3Member2020-01-012020-09-300001485003us-gaap:FairValueInputsLevel3Member2020-09-300001485003us-gaap:MeasurementInputDiscountRateMember2019-12-310001485003us-gaap:MeasurementInputDiscountRateMember2020-03-310001485003us-gaap:MeasurementInputDiscountRateMember2020-06-300001485003us-gaap:MeasurementInputDiscountRateMember2020-09-300001485003country:USsesn:ViciniumMemberus-gaap:InProcessResearchAndDevelopmentMember2020-09-300001485003country:USsesn:ViciniumMemberus-gaap:InProcessResearchAndDevelopmentMember2019-12-310001485003srt:EuropeMembersesn:ViciniumMemberus-gaap:InProcessResearchAndDevelopmentMember2020-09-300001485003srt:EuropeMembersesn:ViciniumMemberus-gaap:InProcessResearchAndDevelopmentMember2019-12-310001485003sesn:ViciniumMemberus-gaap:InProcessResearchAndDevelopmentMember2020-09-300001485003sesn:ViciniumMemberus-gaap:InProcessResearchAndDevelopmentMember2019-12-31utr:sqft0001485003country:CA2020-01-012020-09-300001485003country:CA2020-09-30sesn:term0001485003country:CA2020-07-012020-09-300001485003country:CA2019-07-012019-09-300001485003country:CA2019-01-012019-09-300001485003srt:MinimumMember2020-09-300001485003srt:MaximumMember2020-09-300001485003sesn:FormerChiefFinancialOfficerMember2019-09-092019-09-090001485003sesn:FormerChiefFinancialOfficerMember2019-09-090001485003sesn:FormerChiefMedicalOfficerMember2019-08-022019-08-020001485003sesn:FormerChiefMedicalOfficerMember2019-08-020001485003sesn:FormerChiefMedicalOfficerMember2019-11-020001485003sesn:FormerChiefMedicalOfficerMember2019-08-030001485003sesn:ATMFacilityMember2019-11-012019-11-300001485003sesn:ATMFacilityMember2019-11-012020-03-310001485003sesn:ATMFacilityMember2020-01-012020-09-300001485003sesn:ATMFacilityMember2020-07-012020-09-3000014850032019-06-012019-06-3000014850032020-06-210001485003us-gaap:WarrantMember2020-09-300001485003us-gaap:WarrantMember2019-12-310001485003us-gaap:EmployeeStockOptionMember2020-09-300001485003us-gaap:EmployeeStockOptionMember2019-12-310001485003us-gaap:StockCompensationPlanMember2020-09-300001485003us-gaap:StockCompensationPlanMember2019-12-310001485003us-gaap:EmployeeStockMember2020-09-300001485003us-gaap:EmployeeStockMember2019-12-310001485003sesn:WarrantsExpiringJune2020Member2020-09-300001485003sesn:WarrantsExpiringJune2020Member2019-12-310001485003sesn:WarrantsExpiringJune2020Member2020-01-012020-09-300001485003sesn:WarrantsExpiringJune2020Member2019-01-012019-09-300001485003sesn:WarrantsExpiringMarch2023Member2020-09-300001485003sesn:WarrantsExpiringMarch2023Member2019-12-310001485003sesn:WarrantsExpiringMarch2023Member2020-01-012020-09-300001485003sesn:WarrantsExpiringMarch2023Member2019-01-012019-09-300001485003sesn:WarrantsExpiringNovember2022Member2020-09-300001485003sesn:WarrantsExpiringNovember2022Member2019-12-310001485003sesn:WarrantsExpiringNovember2022Member2020-01-012020-09-300001485003sesn:WarrantsExpiringNovember2022Member2019-01-012019-09-300001485003sesn:WarrantsExpiringNovember2024IssuedMay2015Member2020-09-300001485003sesn:WarrantsExpiringNovember2024IssuedMay2015Member2019-12-310001485003sesn:WarrantsExpiringNovember2024IssuedMay2015Member2020-01-012020-09-300001485003sesn:WarrantsExpiringNovember2024IssuedMay2015Member2019-01-012019-09-300001485003sesn:WarrantsExpiringNovember2024IssuedNovember2014Member2020-09-300001485003sesn:WarrantsExpiringNovember2024IssuedNovember2014Member2019-12-310001485003sesn:WarrantsExpiringNovember2024IssuedNovember2014Member2020-01-012020-09-300001485003sesn:WarrantsExpiringNovember2024IssuedNovember2014Member2019-01-012019-09-300001485003us-gaap:CommonStockMember2018-03-012018-03-310001485003sesn:A2018WarrantAmendmentAmendmenttoSecuritiesPurchaseAgreementMember2018-03-310001485003sesn:A2018WarrantAmendmentAmendmenttoSecuritiesPurchaseAgreementMember2018-03-012018-03-310001485003us-gaap:WarrantMember2020-07-012020-09-300001485003us-gaap:WarrantMember2019-07-012019-09-300001485003us-gaap:WarrantMember2020-01-012020-09-300001485003us-gaap:WarrantMember2019-01-012019-09-300001485003us-gaap:EmployeeStockOptionMember2020-07-012020-09-300001485003us-gaap:EmployeeStockOptionMember2019-07-012019-09-300001485003us-gaap:EmployeeStockOptionMember2020-01-012020-09-300001485003us-gaap:EmployeeStockOptionMember2019-01-012019-09-300001485003us-gaap:ResearchAndDevelopmentExpenseMember2020-07-012020-09-300001485003us-gaap:ResearchAndDevelopmentExpenseMember2019-07-012019-09-300001485003us-gaap:ResearchAndDevelopmentExpenseMember2020-01-012020-09-300001485003us-gaap:ResearchAndDevelopmentExpenseMember2019-01-012019-09-300001485003us-gaap:GeneralAndAdministrativeExpenseMember2020-07-012020-09-300001485003us-gaap:GeneralAndAdministrativeExpenseMember2019-07-012019-09-300001485003us-gaap:GeneralAndAdministrativeExpenseMember2020-01-012020-09-300001485003us-gaap:GeneralAndAdministrativeExpenseMember2019-01-012019-09-300001485003us-gaap:EmployeeStockOptionMembersesn:StockIncentivePlanTwoThousandFourteenMember2020-01-012020-09-300001485003us-gaap:ShareBasedCompensationAwardTrancheOneMemberus-gaap:EmployeeStockOptionMembersesn:StockIncentivePlanTwoThousandFourteenMember2020-01-012020-09-300001485003us-gaap:ShareBasedCompensationAwardTrancheTwoMemberus-gaap:EmployeeStockOptionMembersesn:StockIncentivePlanTwoThousandFourteenMember2020-01-012020-09-300001485003us-gaap:EmployeeStockOptionMembersesn:StockIncentivePlanTwoThousandFourteenMember2020-09-300001485003sesn:StockIncentivePlan2009Memberus-gaap:EmployeeStockOptionMember2020-01-012020-09-300001485003us-gaap:ShareBasedPaymentArrangementEmployeeMember2020-09-3000014850032020-01-012020-06-300001485003sesn:A2014EmployeeStockPurchasePlanMember2014-02-280001485003sesn:A2014EmployeeStockPurchasePlanMember2020-01-012020-09-300001485003sesn:A2014EmployeeStockPurchasePlanMember2020-09-300001485003sesn:UniversityOfZurichMembersesn:CollaborativeArrangementRevenueBasedOnClinicalDevelopmentMilestoneMember2020-01-012020-09-300001485003sesn:UniversityOfZurichMember2020-01-012020-09-30iso4217:EUR0001485003sesn:MicrometAGMember2020-01-012020-09-300001485003sesn:XOMAIrelandLimitedMember2020-01-012020-09-300001485003sesn:RocheMember2016-08-012016-08-310001485003sesn:RocheMembersesn:FirstIndicationMember2016-08-012016-08-310001485003sesn:CollaborativeArrangementRevenueBasedonDevelopmentMilestoneMembersesn:RocheMember2016-08-012016-08-310001485003sesn:CollaborativeArrangementRevenueBasedonRegulatoryMilestoneMembersesn:RocheMember2016-08-012016-08-310001485003sesn:CollaborativeArrangementRevenueBasedonCommercializationMilestoneMembersesn:RocheMember2016-08-012016-08-310001485003sesn:CollaborativeArrangementRevenueBasedonDevelopmentMilestoneMembersesn:EBI031Membersesn:RocheMember2016-09-012016-09-300001485003sesn:SecondIndicationMembersesn:RocheMember2020-01-012020-09-300001485003srt:MinimumMembersesn:EBI031Membersesn:RocheMember2020-09-300001485003srt:MaximumMembersesn:EBI031Membersesn:RocheMember2020-09-300001485003sesn:IL6Membersesn:RocheMember2020-09-30sesn:option0001485003sesn:RocheMember2016-06-012016-06-300001485003us-gaap:LicensingAgreementsMembersesn:QiluPharmaceuticalCoLtdMember2020-07-302020-07-300001485003sesn:QiluPharmaceuticalCoLtdMember2020-09-012020-09-300001485003us-gaap:LicensingAgreementsMembersesn:QiluPharmaceuticalCoLtdMember2020-09-012020-09-300001485003us-gaap:LicensingAgreementsMembersesn:QiluPharmaceuticalCoLtdMember2020-07-012020-09-300001485003us-gaap:LicensingAgreementsMembersesn:QiluPharmaceuticalCoLtdMember2020-01-012020-09-300001485003us-gaap:MajorityShareholderMembersesn:RentExpenseAssociatedWithLeaseFacilityInWinnipegManitobaMember2020-07-012020-09-300001485003us-gaap:MajorityShareholderMembersesn:RentExpenseAssociatedWithLeaseFacilityInWinnipegManitobaMember2020-01-012020-09-300001485003us-gaap:MajorityShareholderMembersesn:RentExpenseAssociatedWithLeaseFacilityInWinnipegManitobaMember2019-07-012019-09-300001485003us-gaap:MajorityShareholderMembersesn:RentExpenseAssociatedWithLeaseFacilityInWinnipegManitobaMember2019-01-012019-09-300001485003us-gaap:IntellectualPropertyMembersrt:DirectorMember2020-01-012020-09-300001485003us-gaap:IntellectualPropertyMembersrt:DirectorMember2019-01-012019-09-300001485003sesn:ATMFacilityMemberus-gaap:SubsequentEventMember2020-10-302020-10-30

☒			QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended September 30, 2020

☐			TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from         to        

Delaware			26-2025616
(State or other jurisdiction of incorporation or organization)			(I.R.S. Employer Identification No.)

245 First Street, Suite 1800 Cambridge, MA			02142
(Address of principal executive offices)			(Zip Code)

Title of each class			Trading Symbol(s)			Name of each exchange on which registered
Common Stock, $0.001 par value			SESN			The Nasdaq Stock Market

Large accelerated filer			☐			Smaller reporting company			☒
Accelerated Filer			☒			Emerging growth company			☐
Non-accelerated filer			☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

						Page
			PART I - FINANCIAL INFORMATION
Item 1.			Financial Statements.			1
			Condensed Consolidated Balance Sheets as of September 30, 2020 and December 31, 2019			1
			Condensed Consolidated Statements of Operations and Comprehensive Loss for the Three and Nine Months ended September 30, 2020 and 2019			2
			Condensed Consolidated Statements of Changes in Stockholders' Equity (Deficit) for the Three and Nine Months ended September 30, 2020 and 2019			3
			Condensed Consolidated Statements of Cash Flows for the Nine Months ended     September 30, 2020 and 2019			5
			Notes to Condensed Consolidated Financial Statements			6
Item 2.			Management’s Discussion and Analysis of Financial Condition and Results of Operations.			21
Item 3.			Quantitative and Qualitative Disclosures About Market Risk.			40
Item 4.			Controls and Procedures.			40
			PART II - OTHER INFORMATION
Item 1.			Legal Proceedings.			41
Item 1A.			Risk Factors.			41
Item 2.			Unregistered Sales of Equity Securities and Use of Proceeds.			41
Item 3.			Defaults Upon Senior Securities.			41
Item 4.			Mine Safety Disclosures.			41
Item 5.			Other Information.			41
Item 6.			Exhibits.			43
			SIGNATURES

			September 30, 2020						December 31, 2019
Assets
Current assets:
Cash and cash equivalents			$	41,969					$	48,121
Prepaid expenses and other current assets			7,072						6,326
Total current assets			49,041						54,447
Restricted cash			20						20
Property and equipment, net of accumulated depreciation     of $850 and $758, respectively			154						238
Intangible assets			46,400						46,400
Goodwill			13,064						13,064
Other assets			349						196
Total Assets			$	109,028					$	114,365
Liabilities and Stockholders’ Deficit
Current liabilities:
Accounts payable			$	1,524					$	1,902
Accrued expenses			7,703						6,169
Other current liabilities			481						446
Total current liabilities			9,708						8,517
Contingent consideration			103,200						120,020
Deferred tax liability			12,528						12,528
Other liabilities			145						—
Total Liabilities			$	125,581					$	141,065
Commitments and contingencies
Stockholders’ Deficit:
Preferred stock, $0.001 par value per share; 5,000,000 shares authorized at September 30, 2020 and December 31, 2019; no shares issued and outstanding at September 30, 2020 and December 31, 2019			—						—
Common stock, $0.001 par value per share; 200,000,000 shares authorized at September 30, 2020 and December 31, 2019; 123,645,007 and 106,801,409 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively			123						107
Additional paid-in capital			284,236						266,717
Accumulated deficit			(300,912)						(293,524)
Total Stockholders’ Deficit			(16,553)						(26,700)
Total Liabilities and Stockholders’ Deficit			$	109,028					$	114,365

			Three Months ended September 30,												Nine Months ended September 30,
			2020						2019						2020						2019
License revenue			$	11,236					$	—					$	11,236					$	—
Operating expenses:
Research and development			10,196						6,613						23,625						19,243
General and administrative			4,115						3,238						10,882						8,910
Change in fair value of contingent consideration			18,400						3,600						(16,820)						46,600
Total operating expenses			32,711						13,451						17,687						74,753
Loss from operations			(21,475)						(13,451)						(6,451)						(74,753)
Other income (expense), net:
Other income (expense), net			(1)						319						195						806
Net Loss and Comprehensive Loss Before Taxes			(21,476)						(13,132)						(6,256)						(73,947)
Provision for income taxes			(1,132)						—						(1,132)						—
Net Loss and Comprehensive Loss After Taxes			$	(22,608)					$	(13,132)					$	(7,388)					$	(73,947)
Deemed dividend on adjustment of exercise price on certain warrants			$	—					$	—					(147)						$	—
Net Loss and Comprehensive Loss Attributable to Common Shareholders			$	(22,608)					$	(13,132)					$	(7,535)					$	(73,947)
Net loss per common share - basic and diluted			$	(0.19)					$	(0.13)					$	(0.07)					$	(0.85)
Weighted-average common shares outstanding - basic and diluted			117,886						101,266						113,437						86,575

			Common Stock												Additional Paid-in Capital						Accumulated Deficit						Stockholders’ Equity (Deficit)
			Shares						Amount
Balance at December 31, 2019			106,801,409						$	107					$	266,717					$	(293,524)					$	(26,700)
Net income (loss)			—						—						—						41,564						41,564
Share-based compensation			—						—						407						—						407
Sales of common stock under 2014 ESPP			2,785						—						1						—						1
Issuance of common stock under ATM Offering, net of issuance costs of $0.1 million			3,187,359						3						3,176						—						3,179
Balance at March 31, 2020			109,991,553						$	110					$	270,301					$	(251,960)					$	18,451
Net income (loss)			—						—						—						(26,344)						(26,344)
Share-based compensation			—						—						491						—						491
Issuance of common stock under ATM Offering, net of issuance costs of $0.1 million			6,636,100						6						4,768						—						4,774
Balance at June 30, 2020			116,627,653						$	116					$	275,560					$	(278,304)					$	(2,628)
Net income (loss)			—						—						—						(22,608)						(22,608)
Share-based compensation			—						—						453						—						453
Sales of common stock under 2014 ESPP			25,401						—						9												9
Issuance of common stock under ATM Offering, net of issuance costs of $0.3 million			6,991,953						7						8,214						—						8,221
Balance at September 30, 2020			123,645,007						$	123					$	284,236					$	(300,912)					$	(16,553)

			Common Stock												Additional Paid-in Capital						Accumulated Deficit						Stockholders’ Equity
			Shares						Amount
Balance at December 31, 2018			77,456,180						$	77					$	230,154					$	(186,024)					$	44,207
Net income (loss)			—						—						—						(6,480)						(6,480)
Share-based compensation			—						—						326						—						326
Sales of common stock under 2014 ESPP			8,601						—						7						—						7
Balance at March 31, 2019			77,464,781						$	77					$	230,487					$	(192,504)					$	38,060
Net income (loss)			—						—						—						(54,335)						(54,335)
Share-based compensation			—						—						356						—						356
Exercise of stock options			30,000						—						45						—						45
Exercise of common stock warrants			3,361,115						4						3,430						—						3,434
Issuance of common stock and common stock warrants, net of issuance costs of $2.2 million			20,410,000						20						27,789						—						27,809
Balance as of June 30, 2019			101,265,896						$	101					$	262,107					$	(246,839)					$	15,369
Net income (loss)			—						—						—						(13,132)						(13,132)
Share-based compensation			—						—						229						—						229
Sales of common stock under the 2014 ESPP			1,682						—						1						—						1
Balance at September 30, 2019			101,267,578						$	101					$	262,337					$	(259,971)					$	2,467

			Nine Months ended September 30,
			2020						2019
Cash Flows from Operating Activities:
Net loss			$	(7,388)					$	(73,947)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation			92						164
Share-based compensation			1,351						911
Change in fair value of contingent consideration			(16,820)						46,600
Changes in operating assets and liabilities:
Prepaid expenses and other assets			(899)						(421)
Accounts payable			(378)						1,216
Accrued expenses and other liabilities			1,714						1,761
Net Cash Used in Operating Activities			(22,328)						(23,716)
Cash Flows from Investing Activities:
Net Cash Used in Investing Activities			(8)						(137)
Cash Flows from Financing Activities:
Proceeds from issuance of common stock under ATM Offering, net of issuance costs			16,174						—
Proceeds from sales of common stock under 2014 ESPP			10						8
Proceeds from exercises of stock options			—						45
Proceeds from the issuance of common stock and common stock warrants, net of issuance costs			—						27,809
Proceeds from the exercise of common stock warrants			—						3,434
Net Cash Provided by Financing Activities			16,184						31,296
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash			(6,152)						7,443
Cash, Cash Equivalents and Restricted Cash - Beginning of Period			48,141						50,442
Cash, Cash Equivalents and Restricted Cash - End of Period			$	41,989					$	57,885
Supplemental disclosure of non-cash operating activities:
Right-of-use assets related to the adoption of ASC 842			$	—					$	236
Right-of-use assets obtained in exchange for lease obligations			290						$	—
Cash paid for amounts included in the measurement of lease liabilities			$	113					$	115
Supplemental disclosure of non-cash financing activities:
Deemed dividend on adjustment of exercise price on certain warrants			$	147					$	—

Sesen Bio, Inc. ("Sesen" or the “Company”), a Delaware corporation formed in February 2008, is a late-stage clinical company developing targeted fusion protein therapeutics ("TFPTs") for the treatment of patients with cancer. The Company’s most advanced product candidate, VicineumTM, also known as VB4-845, is a locally-administered targeted fusion protein composed of an anti-epithelial cell adhesion molecule ("EpCAM") antibody fragment tethered to a truncated form of Pseudomonas exotoxin A. The Company has an ongoing single-arm, multi-center, open-label Phase 3 clinical trial of Vicineum as a monotherapy in patients with high-risk, bacillus Calmette-Guérin ("BCG")-unresponsive non-muscle invasive bladder cancer ("NMIBC") (the "VISTA Trial"). The VISTA Trial completed enrollment in April 2018 with a total of 133 patients, and in December 2019, the Company initiated submission of the Biologics License Application ("BLA") for Vicineum to the United States Food and Drug Administration ("FDA") under Rolling Review, which enables individual modules to be submitted and reviewed on an ongoing basis, rather than waiting for all sections to be completed before submission. The Company operates in one segment under the direction of its Chief Executive Officer (chief operating decision maker).

Under Accounting Standards Codification ("ASC") Topic 205-40, Presentation of Financial Statements - Going Concern, management is required at each reporting period to evaluate whether there are conditions and events, considered in the aggregate, that raise substantial doubt about an entity's ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management's plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists, management evaluates whether the mitigating effect of its plans sufficiently alleviates the substantial doubt about the Company's ability to continue as a going concern. The mitigating effect of management's plans, however, is only considered if both (i) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued and (ii) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity's ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved by the Company's board of directors before the date that the financial statements are issued.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets held. The amendments in ASU 2016-13 eliminate the probable threshold for initial recognition of a credit loss in GAAP and reflect an entity’s current estimate of all expected credit losses. ASU 2016-13 is effective for annual and interim periods beginning January 1, 2020 and is to be applied using a modified retrospective transition method. The Company adopted this guidance effective January 1, 2020, and it did not have a material impact on the Company’s financial position, results of operations or cash flows.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurements ("ASU 2018-13"). ASU 2018-13 modifies fair value measurement disclosure requirements. ASU 2018-13 is effective for annual and interim periods beginning after December 15, 2019. The Company adopted this guidance effective January 1, 2020, and although it resulted in some additional footnote disclosures, it did not have a material impact on the Company’s disclosures. For the new disclosures regarding our Level 3 instruments, please read Note 5, Fair Value Measurements and Financial Instruments, to these condensed consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service

Contract ("ASU 2018-15"). ASU 2018-15 requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance to determine which implementation costs to defer and recognize as an asset. The effective date for ASU 2018-15 is for annual and interim periods beginning after December 15, 2019. The amendments in this ASU should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company adopted this guidance effective January 1, 2020, and it did not have a material impact on the Company’s financial position, results of operations or cash flows.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments in ASU 2019-12 also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. ASU 2019-12 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted. The method with which the amendments in this ASU are to be applied varies depending on the nature of the tax item impacted by amendment. Because the Company generates losses and pays no income taxes, it does not expect the adoption of ASU 2019-12 to have a material impact on the Company's financial position, results of operations or cash flows.

Level 1:    Inputs are quoted prices for identical instruments in active markets.

Level 2:    Inputs are quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; or model-derived valuations whose inputs are observable or whose significant value drivers are observable.

Level 3:    Inputs are unobservable and reflect the Company’s own assumptions, based on the best information available, including the Company’s own data.

			September 30, 2020
															Fair Value Measurement Based on
			Carrying Amount						Fair Value						Quoted Prices in Active Markets (Level 1)						Significant other Observable Inputs (Level 2)						Significant Unobservable Inputs (Level 3)
Assets:
Money market funds (cash equivalents)			$	16,370					$	16,370					$	16,370					$	—					$	—
Liabilities:
Contingent consideration			$	103,200					$	103,200					$	—					$	—					$	103,200

			December 31, 2019
															Fair Value Measurement Based on
			Carrying Amount						Fair Value						Quoted Prices in Active Markets (Level 1)						Significant other Observable Inputs (Level 2)						Significant Unobservable Inputs (Level 3)
Assets:
Money market funds (cash equivalents)			$	31,146					$	31,146					$	31,146					$	—					$	—
Liabilities:
Contingent consideration			$	120,020					$	120,020					$	—					$	—					$	120,020

Balance at December 31, 2019			$	120,020
Change in fair value of contingent consideration			(16,820)
Balance at September 30, 2020			$	103,200

			September 30, 2020						December 31, 2019
IPR&D intangible assets:
Vicineum United States rights			$	31,700					$	31,700
Vicineum European Union rights			14,700						14,700
Total Intangibles			$	46,400					$	46,400

On January 1, 2019, the Company adopted ASC Topic 842, Leases using the optional transition method. The Company’s lease portfolio includes:

1.An operating lease for its 31,100 square foot facility in Winnipeg, Manitoba which consists of manufacturing, laboratory, warehouse and office space. In September 2020, the Company entered into an extension of this lease for an additional two years, through September 2022, with a right to extend the lease for one subsequent three-year term. The minimum monthly rent under this lease is $13,500 per month. In addition to rent expense, the Company expects to incur $12,300 per month in related operating expenses. Operating lease cost under this lease, including the related operating costs, was $75,000 and $223,000 for the three and nine months ended September 30, 2020 and $76,000 and $222,000 for the three and nine months ended September 30, 2019, respectively;

2.Short-term property leases for modular office space for 1) its corporate headquarters in Cambridge, MA and 2) office space in Philadelphia, PA. The short-term leases renew every four to nine months and currently extend through May 2021. The minimum monthly rent for these office spaces is $21,400 per month, which is subject to change if and as the Company adds or deducts space to or from the leases. The Company recorded $64,000 and $195,000 in rent expense for the three and nine months ended September 30, 2020, respectively, and $59,000 and $188,000 in rent expense for the three and nine months ended September 30, 2019, respectively, for these leases.

			September 30, 2020						December 31, 2019
Research and development			$	5,145					$	3,688
Payroll-related expenses			1,474						1,638
Severance to former Executives and other employees			—						378
Professional fees			1,060						378
Other			24						87
Total Accrued Expenses			$	7,703					$	6,169

In November 2019, the Company entered into an Open Market Sale Agreement SM (the "Sale Agreement") with Jefferies LLC ("Jefferies"), under which the Company may issue and sell shares of its common stock from time to time for an aggregate sales price of up to $35.0 million through Jefferies (the "ATM Offering"). Sales of common stock under the Sale Agreement are made by any method that is deemed to be an ATM offering as defined in Rule 415(a)(4) of the Securities Act of 1933, as amended, including but not limited to sales made directly on or through the Nasdaq Global Market or any other existing trading market for the common stock. The Company has no obligation to sell any of its common stock and may at any time suspend offers under the Sale Agreement or terminate the Sale Agreement. Subject to the terms and conditions of the Sale Agreement, Jefferies will use its commercially reasonable efforts to sell common stock from time to time, as the sales agent, based upon the Company’s instructions, which include a prohibition on sales below a minimum price set by the Company from time to time. The Company has provided Jefferies with customary indemnification rights, and Jefferies is entitled to a commission at a fixed rate equal to 3.0% of the gross proceeds for each sale of common stock under the Sale Agreement. The Company incurred $0.2 million in legal, accounting and printing costs related to the commencement of the ATM Offering. For the nine months ended September 30, 2020, the Company raised $16.2 million of net proceeds from the sale of 16.8 million shares of common stock at a weighted-average price of $0.99 per share under the ATM Offering, including $8.2 million of net proceeds from the sale of 7.0 million shares of common stock at a weighted-average price of $1.21 per share during the three months ended September 30, 2020. Share issue costs, including sales agent commissions, related to the ATM Offering totaled $0.3 million and $0.5 million during the three and nine months ended September 30, 2020, respectively.

Pursuant to its Amended and Restated Certificate of Incorporation (the "Certificate of Incorporation"), the Company is authorized to issue 5.0 million shares of "blank check" preferred stock, $0.001 par value per share, which enables its board of directors, from time to time, to create one or more series of preferred stock. Each series of preferred stock issued shall have the rights, preferences, privileges and restrictions as designated by the board of directors. The issuance of any series of preferred stock could affect, among other things, the dividend, voting and liquidation rights of the common stock. The Company had no preferred stock issued and outstanding as of September 30, 2020 and December 31, 2019.

Pursuant to its Certificate of Incorporation, the Company is authorized to issue 200.0 million shares of common stock, $0.001 par value per share, of which 123.6 million and 106.8 million shares were issued and outstanding as of September 30, 2020 and December 31, 2019, respectively. In addition, the Company had reserved for issuance the following amounts of shares of its common stock for the purposes described below as of September 30, 2020 and December 31, 2019 (in thousands):

			September 30, 2020						December 31, 2019
Shares of common stock issued			123,645						106,801
Shares of common stock reserved for issuance for:
Warrants			2,485						22,895
Stock options			10,227						6,236
Shares available for grant under 2014 Stock Incentive Plan			4,795						8,753
Shares available for sale under 2014 Employee Stock Purchase Plan			—						28
Total shares of common stock issued and reserved for issuance			141,152						144,713

All of the Company’s outstanding warrants are non-tradeable and permanently classified as equity because they meet the derivative scope exception under ASC Topic 815-40, Derivatives and Hedging - Contracts in Entity’s Own Equity ("ASC 815-40"). The following table sets forth the Company's warrant activity for the nine months ended September 30, 2020 (in thousands):

																		Year-to-Date Warrant Activity
Issued						Exercise Price (1)						Expiration						December 31, 2019						Issued						(Exercised)						(Expired)						September 30, 2020
Jun-2019						$1.47						Jun-2020						20,410						—						—						(20,410)						—
Mar-2018						$0.55*						Mar-2023						1,943						—						—						—						1,943
Nov-2017						$0.55*						Nov-2022						487						—						—						—						487
May-2015						$11.83						Nov-2024						28						—						—						—						28
Nov-2014						$11.04						Nov-2024						27						—						—						—						27
																		22,895						—						—						(20,410)						2,485

(1) As of September 30, 2020.

* Exercise price shown subject to further adjustment based on down round provision added by amendment.

			Three Months Ended September 30,									Nine Months Ended September 30,
			2020						2019			2020						2019
Warrants			2,485						6,450			2,485						6,450
Stock options			10,227						26,307			10,227						26,307
			12,712						32,757			12,712						32,757

			Three Months ended September 30,									Nine Months ended September 30,
			2020						2019			2020						2019
Research and development			$	95					$	(20)		$	266					$	119
General and administrative			358						249			1,085						792
			$	453					$	229		$	1,351					$	911

			Number of Shares under Option (in thousands)						Weighted-average Exercise Price per Option						Weighted-average Remaining Contractual Life (in years)						Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2019			6,236						$1.52						8.8						$	358
Granted			4,044						$0.87
Exercised			—						$0.00
Canceled or forfeited			(53)						$0.84
Outstanding at September 30, 2020			10,227						$1.26						8.6						$	3,541
Exercisable at September 30, 2020			3,637						$1.73						8.0						$	786

			September 30, 2020			September 30, 2019
Fair value of common stock			$0.56			$0.69
Exercise price			$0.87			$1.02
Expected term (in years)			6.10			5.98
Risk-free interest rate			1.3			2.1
Expected volatility			71.5			78.1
Dividend yield			—%			—%

On July 30, 2020, the Company and its a wholly-owned subsidiary, Viventia Bio, Inc., entered into the License Agreement with Qilu pursuant to which the Company granted Qilu an exclusive, sublicensable, royalty-bearing license, under certain intellectual property owned or exclusively licensed by the Company, to develop, manufacture and commercialize Vicineum™ (the “Licensed Product”) for the treatment of NMIBC and other types of cancer (the “Field”) in China, Hong Kong, Macau and Taiwan (the “Territory”). The Company also granted Qilu a non-exclusive, sublicensable, royalty-bearing sublicense, under certain other intellectual property licensed by the Company to develop, manufacture and commercialize the Licensed Product in the Territory. The Company retains development, manufacturing and commercialization rights with respect to Vicineum in the rest of the world.

Qilu also agreed to pay the Company a 12% royalty based upon annual net sales of Licensed Products in the Territory. The royalties are payable on a Licensed Product-by-Licensed Product and region-by-region basis commencing on the first commercial sale of a Licensed Product in a region and continuing until the latest of (i) twelve years after the first commercial sale of such Licensed Product in such region, (ii) the expiration of the last valid patent claim covering or claiming the composition of matter, method of treatment, or method of manufacture of such Licensed Product in such region, and (iii) the expiration of regulatory or data exclusivity for such Licensed Product in such region (collectively, the “Royalty Term”). The royalty rate is subject to reduction under certain circumstances, including when there is no valid claim of a licensed patent that covers a Licensed Product in a particular region or no data or regulatory exclusivity of a Licensed Product in a particular region.

Overview

Our most advanced product candidate, Vicineum, also known as VB4-845, is a locally-administered targeted fusion protein composed of an anti-epithelial cell adhesion molecule ("EpCAM") antibody fragment tethered to a truncated form of Pseudomonas exotoxin A for the treatment of high-risk non-muscle invasive bladder cancer ("NMIBC"). On December 6, 2019, we initiated our Biologics License Application ("BLA") submission for Vicineum to the United States Food and Drug Administration ("FDA") under Rolling Review. "Rolling Review" of the BLA enables individual modules to be submitted and reviewed on an ongoing basis, rather than waiting for all sections to be completed before submission. The submission consisted of Modules 1, 2, 4 and 5, with information amendments to be submitted to these modules throughout 2020. We anticipate completing Module 3 (Chemistry, Manufacturing and Controls ("CMC")) to finalize the BLA submission by the end of 2020. We may experience disruptions as a result of the COVID-19 pandemic that may impact our expected timeline to finalize the BLA submission, including manufacturing activities of our contract manufacturers due to limitations on work and travel imposed or recommended by federal or state governments, employers and others.

In August 2019, we reported updated preliminary efficacy data from our ongoing single-arm, multi-center, open-label Phase 3 clinical trial of Vicineum as a monotherapy in patients with high-risk, bacillus Calmette-Guérin ("BCG")-unresponsive NMIBC (the "VISTA Trial"). As of the May 29, 2019 data cutoff date, we reported the preliminary complete response rates ("CRRs") in evaluable carcinoma in situ ("CIS") patients following three, six, nine and 12 months of treatment in the clinical trial. The results were consistent with the results observed in the previously completed Phase 1 and Phase 2 clinical trials of Vicineum for the treatment of high-risk NMIBC. The VISTA Trial completed enrollment in April 2018 with a total of 133 patients across three cohorts based on histology and time to disease recurrence after adequate BCG treatment (under 2018 FDA guidance on treatment of NMIBC, adequate BCG is defined as at least two courses of BCG with at least five doses in an initial induction course of treatment, plus at least two doses in a second course of treatment):

•Cohort 1 (n=86): Patients with CIS with or without papillary disease that were determined to be refractory or recurred within six months of their last course of adequate BCG;

•Cohort 2 (n=7): Patients with CIS with or without papillary disease that recurred after six months, but less than 11 months, after their last course of adequate BCG; and

•Cohort 3 (n=40): Patients with high-risk (Ta or T1) papillary disease without CIS that was determined to be refractory or recurred within six months of their last course of adequate BCG.

Time Point			Evaluable Patients*			Complete Response Rate (95% Confidence Interval)
3-months			n=82			39% (28%-50%)
6-months			n=82			26% (17%-36%)
9-months			n=82			20% (12%-30%)
12-months			n=82			17% (10%-27%)

Time Point			Evaluable Patients*			Complete Response Rate (95% Confidence Interval)
3-months			n=7			57% (18%-90%)
6-months			n=7			57% (18%-90%)
9-months			n=7			43% (10%-82%)
12-months			n=7			14% (0%-58%)

Time Point			Evaluable Patients*			Complete Response Rate (95% Confidence Interval)
3-months			n=89			40% (30%-51%)
6-months			n=89			28% (19%-39%)
9-months			n=89			21% (13%-31%)
12-months			n=89			17% (10%-26%)

Time Point			Preliminary Phase 3 Pooled CRR (95% Confidence Interval)			Phase 2 Pooled CRR (95% Confidence Interval)
3-months			40% (30%-51%)			40% (26%-56%)
6-months			28% (19%-39%)			27% (15%-42%)
9-months			21% (13%-31%)			18% (8%-32%)
12-months			17% (10%-26%)			16% (7%-30%)

Time Point			Evaluable Patients*			Recurrence-Free Rate (95% Confidence Interval)
3-months			n=38			71% (54%-85%)
6-months			n=38			58% (41%-74%)
9-months			n=38			45% (29%-62%)
12-months			n=38			42% (26%-59%)

Duration of Response: The median DoR for patients in Cohort 1 and Cohort 2 combined (n=93) is 287 days (lower 95% confidence interval ("CI") = 154 days, upper 95% confidence interval is not estimable ("NE") due to the limited number of events occurring beyond the median), using the Kaplan-Meier method. The Kaplan-Meier method is a non-parametric statistical analysis used to estimate survival times and times to event when incomplete observations in data exist. Additional ad hoc analysis of pooled data for all patients with CIS (Cohorts 1 and 2, n=93) shows that among patients who achieved a complete response at 3 months, 52% remained disease-free for a total of 12 months or longer after starting treatment, using the Kaplan-Meier method. DoR is defined as the time from first occurrence of complete response to documentation of treatment failure or death.

•Time to Cystectomy: Across all 133 patients treated with Vicineum in the VISTA Trial, greater than 75% of all patients are estimated to remain cystectomy-free at 3 years, using the Kaplan-Meier method. Additional ad hoc analysis shows that approximately 88% of responders are estimated to remain cystectomy-free at 3 years. Time to cystectomy is defined as the time from the date of first dose of study treatment to surgical bladder removal. The first 2018 FDA guidance on treatment of BCG-unresponsive NMIBC patients states that the goal of therapy in such patients is to avoid cystectomy. Therefore, time to cystectomy is a key secondary endpoint in the VISTA Trial.

•Time to Disease Recurrence: High-grade papillary (Ta or T1) NMIBC is associated with higher rates of progression and recurrence. The median time to disease recurrence for patients in Cohort 3 (n=40) is 402 days (95% CI, 170-NE), using the Kaplan-Meier method. Time to disease recurrence is defined as the time from the date of the first dose of study treatment to the first occurrence of treatment failure or death on or prior to treatment discontinuation.

•Progression-Free Survival ("PFS"): 90% of all 133 patients treated with Vicineum in the VISTA Trial are estimated to remain progression-free for 2 years or greater, using the Kaplan-Meier method. PFS is defined as the time from the date of first dose of study treatment to the first occurrence of disease progression (e.g. T2 or more advanced disease) or death on or prior to treatment discontinuation.

•Event-Free Survival: 29% of all 133 patients treated with Vicineum in the VISTA Trial are estimated to remain event-free at 12 months, using the Kaplan-Meier method. Event-free survival is defined as the time from the date of first dose of study treatment to the first occurrence of disease recurrence, progression or death on or prior to treatment discontinuation.

◦Overall Survival ("OS"): 96% of all 133 patients treated with Vicineum in the VISTA Trial are estimated to have an overall survival of 2 years or greater, using the Kaplan-Meier method. OS is defined as the time from the date of first dose of study treatment to death from any cause.

On May 29, 2020, we received CMC Scientific Advice from the CHMP of the EMA, stating that the committee agreed that our comparability plan provides a strong analytical package, and no additional clinical trials to establish comparability are deemed necessary at this time. Furthermore, the CHMP agreed to accept the Good

Vicineum has also been evaluated for the treatment of squamous cell carcinoma of the head and neck ("SCCHN"). Vicineum for the treatment of SCCHN had previously been designated as ProxiniumTM to indicate its different fill volume and vial size as well as its different route for local administration via intratumoral injection. In addition to our locally-administered TFPTs, our pipeline also includes systemically-administered TFPTs that are built around our proprietary de-immunized variant of the plant-derived cytotoxin bouganin ("deBouganin"). One of these product candidates, VB6-845d, is a TFPT consisting of an EpCAM-targeting fragment antigen binding domain ("Fab") genetically linked to deBouganin, a novel plant derived cytotoxic payload that we have optimized for minimal immunogenic potential and is administered by intravenous infusion. We have deferred further development of Vicineum for the treatment of SCCHN and of VB6-845d in order to focus our efforts and our

resources on our ongoing development of Vicineum for the treatment of high-risk NMIBC. We are also exploring collaborations for Vicineum for the treatment of SCCHN and for VB6-845d.

On July 30, 2020, we and our wholly-owned subsidiary, Viventia Bio, Inc., entered into an exclusive license agreement with Qilu Pharmaceuticals, Ltd. ("Qilu") ("License Agreement with Qilu") pursuant to which we granted Qilu an exclusive, sublicensable, royalty-bearing license, under certain intellectual property owned or exclusively licensed by us, to develop, manufacture and commercialize Vicineum for the treatment of NMIBC and other types of cancer in China, Hong Kong, Macau and Taiwan ("the Territory"). We also granted Qilu a non-exclusive, sublicensable, royalty-bearing sublicense, under certain other intellectual property licensed by us to develop, manufacture and commercialize Vicineum™ in the Territory. We retained development, manufacturing and commercialization rights with respect to Vicineum in the rest of the world.

Through September 30, 2020, we have received a total of $10 million in net proceeds associated with the $12 upfront payment due pursuant to the License Agreement with Qilu. We are also entitled to receive up to an additional $23 million upon the achievement of certain technology transfer, development and regulatory milestones, as well as a 12% royalty based upon annual net sales of Vicineum in the Territory. The royalties are payable upon the first commercial sale of Vicineum in a region and continuing until the latest of (i) twelve years after the first commercial sale of Vicineum in such region, (ii) the expiration of the last valid patent claim covering or claiming the composition of matter, method of treatment, or method of manufacture of such Vicineum in such region, and (iii) the expiration of regulatory or data exclusivity for such Vicineum in such region. The royalty rate is subject to reduction under certain circumstances, including when there is no valid claim of a licensed patent that covers Vicineum in a particular region or no data or regulatory exclusivity of Vicineum in a particular region.

Under Accounting Standards Codification Topic 205-40, Presentation of Financial Statements - Going Concern, we are required at each reporting period to evaluate whether there are conditions and events, considered in the aggregate, that raise substantial doubt about our ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of our plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists, we evaluate whether the mitigating effect of our plans sufficiently alleviates the substantial doubt about our ability to continue as a going concern. The mitigating effect of our plans, however, is only considered if both (i) it is probable that our plans will be effectively implemented within one year after the date that our financial statements are issued and (ii) it is probable that our plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about our ability to continue as a going concern within one year after the date that our financial statements are issued. Generally, to be considered probable of being effectively implemented, our plans must have been approved by our board of directors before the date that our financial statements are issued.

•employee-related expenses, including salaries, benefits, travel and share-based compensation expense;

•expenses incurred under agreements with contract research organizations ("CROs") and investigative sites that conduct our clinical trials;

•expenses associated with developing manufacturing capabilities;

•expenses associated with transferring manufacturing capabilities to contract manufacturing organizations ("CMOs") for commercial-scale production;

•facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, insurance and other supplies; and

•expenses associated with regulatory activities.

•the scope, progress, outcome and costs of our clinical trials and other research and development activities;

•the efficacy and potential advantages of Vicineum for the treatment of high-risk NMIBC compared to alternative treatments, including any standard of care;

•the market acceptance of Vicineum for the treatment of high-risk NMIBC;

•the cost and timing of the implementation of commercial-scale manufacturing of Vicineum;

•obtaining, maintaining, defending and enforcing patent claims and other intellectual property rights;

•significant and changing government regulation;

•the impact of the COVID-19 pandemic; and

•the timing, receipt and terms of any marketing approvals.

			Three Months ended September 30,									Nine Months ended September 30,
			2020						2019			2020						2019
Programs:
Vicineum for the treatment of high-risk NMIBC			$	8,506					$	4,248		$	19,005					$	12,620
Total direct program expenses			8,506						4,248			19,005						12,620
Personnel and other expenses:
Employee and contractor-related expenses			1,314						1,916			3,688						4,973
Platform-related lab expenses			184						51			264						464
Facility expenses			109						94			322						319
Other expenses			83						304			346						867
Total personnel and other expenses			1,690						2,365			4,620						6,623
Total Research and Development			$	10,196					$	6,613		$	23,625					$	19,243

			Three Months ended September 30,												Increase/(Decrease)
			2020						2019						Dollars						Percentage
			(in thousands, except percentages)
License revenue			$	11,236					$	—					$	11,236					—
Operating expenses:
Research and development			$	10,196					$	6,613					$	3,583					54		%
General and administrative			4,115						3,238						877						27		%
Change in fair value of contingent consideration			18,400						3,600						14,800						411		%
Total operating expenses			32,711						13,451						19,260						143		%
Loss from operations			(21,475)						(13,451)						(8,024)						60		%
Other income (expense), net:
Other income (expense), net			(1)						319						(320)						(100)		%
Net Loss and Comprehensive Loss Before Taxes			$	(21,476)					$	(13,132)					$	(8,344)					64		%
Provision for income taxes			$	(1,132)					$	—					$	(1,132)					—
Net Loss and Comprehensive Loss After Taxes			$	(22,608)					$	(13,132)					$	(9,476)					72		%

			Nine Months ended September 30,												Increase/(Decrease)
			2020						2019						Dollars						Percentage
			(in thousands, except percentages)
License revenue			$	11,236					$	—					$	11,236					—		%
Operating expenses:
Research and development			$	23,625					$	19,243					$	4,382					23		%
General and administrative			10,882						8,910						1,972						22		%
Change in fair value of contingent consideration			(16,820)						46,600						(63,420)						(136)		%
Total operating expenses			17,687						74,753						(57,066)						(76)		%
Loss from operations			(6,451)						(74,753)						68,302						(91)		%
Other income (expense), net:
Other income (expense), net			195						806						(611)						(76)		%
Net Loss and Comprehensive Loss			$	(6,256)					$	(73,947)					$	67,691					(92)		%
Provision for income taxes			$	(1,132)					$	—					(1,132)						—		%
Net Loss and Comprehensive Loss			$	(7,388)					$	(73,947)					$	66,559					(90)		%

In November 2019, we entered into an Open Market Sale Agreement SM (the "Sale Agreement") with Jefferies LLC ("Jefferies"), under which we may issue and sell shares of our common stock from time to time for an aggregate sales price of up to $35.0 million through Jefferies (the "ATM Offering"). Sales of common stock under the Sale Agreement are made by any method that is deemed to be an ATM offering as defined in Rule 415(a)(4) of the Securities Act of 1933, as amended, including but not limited to sales made directly on or through the Nasdaq Global Market or any other existing trading market for our

•continue our Phase 3 VISTA Trial for Vicineum for the treatment of high-risk NMIBC;

•seek marketing approvals for Vicineum for the treatment of high-risk NMIBC;

•establish sales, marketing and distribution capabilities and scale up and validate external manufacturing capabilities (including completing the manufacturing process and technology transfer to any third-party manufacturers) to commercialize Vicineum for the treatment of high-risk NMIBC, if approved;

•maintain, expand and protect our intellectual property portfolio;

•add equipment and physical infrastructure to support our research and development;

•hire additional clinical, regulatory, quality control, scientific and management personnel;

•expand our operational, financial and management systems and personnel;

•conduct research and pre-clinical and clinical development of Vicineum for the treatment of high-risk NMIBC and our other product candidates;

•seek to discover and develop additional product candidates; and

•in-license or acquire the rights to other products, product candidates or technologies.

•the scope, initiation, progress, timing, costs and results of pre-clinical development and laboratory testing and clinical trials for Vicineum for the treatment of high-risk NMIBC and our other product candidates;

•the cost and timing of any new clinical trials or studies of Vicineum for the treatment of high-risk NMIBC;

•the ongoing COVID-19 pandemic and its impact on our business;

•our ability to establish collaborations or licensing arrangements on favorable terms, if at all, particularly manufacturing, marketing and distribution arrangements for our product candidates;

•the costs and timing of the implementation of commercial-scale manufacturing activities, including those associated with the manufacturing process and technology transfer to third-party manufacturers to facilitate such commercial-scale manufacturing of Vicineum;

•the costs and timing of establishing sales, marketing and distribution capabilities for Vicineum for the treatment of high-risk NMIBC, if approved;

•the costs and timing of preparing, filing and prosecuting patent applications, maintaining and enforcing our intellectual property rights and defending any intellectual property-related claims;

•our obligation to make milestone, royalty and other payments to third-party licensors under our licensing agreements;

•the extent to which we in-license or acquire rights to other products, product candidates or technologies;

•the outcome, timing and cost of regulatory review by the FDA, EMA and comparable foreign regulatory authorities for Vicineum for the treatment of high-risk NMIBC, including the potential for the FDA, EMA or comparable foreign regulatory authorities to require that we perform more studies than those that we currently expect to perform;

•our ability to achieve certain future regulatory, development and commercialization milestones under the License Agreement with Roche and our License Agreement with Qilu;

•the effect of competing technological and market developments; and

•the revenue, if any, received from commercial sales of Vicineum for the treatment of high-risk NMIBC, if approved.

			Nine Months ended September 30,
			2020						2019
Net Cash Used in Operating Activities			$	(22,328)					$	(23,716)
Net Cash Used in Investing Activities			(8)						(137)
Net Cash Provided by Financing Activities			16,184						31,296
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash			$	(6,152)					$	7,443

Net cash provided by financing activities was $16.2 million for the nine months ended September 30, 2020 and consisted of net proceeds from the sale of common stock under the ATM Offering and sales of common stock under our 2014 ESPP. Net cash provided by financing activities for the nine months ended September 30, 2019 consisted of (i) $27.8 million in net proceeds on the sale of 20.4 million shares of common stock and accompanying warrants to purchase an additional 20.4 million shares of common stock in an underwritten public offering in June 2019 and (ii) $3.4 million in proceeds from the exercise of 3.4 million of warrants to purchase our common stock.

Indefinite-Lived Intangible Assets

We maintain disclosure controls and procedures, as defined in Exchange Act Rules 13a-15(e) and 15d-15(e), that are designed to ensure information required to be disclosed by us in reports we file or submit under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the SEC's rules and forms and that such information is accumulated and communicated to our management, including our principal executive officer and principle financial officer, to allow timely decisions regarding required disclosure.

•difficulties in raising additional capital needed to commercialize Vicineum for the treatment of high-risk NMIBC due to the slowing of our economy and near term and/or long term negative effects of the pandemic on the financial, banking and capital markets;

•delays in necessary interactions with regulators and other important agencies and contractors due to limitations in employee resources, travel restrictions or forced furlough of government employees;

•interruption of key business activities due to illness and/or quarantine of key individuals and delays associated with recruiting, hiring and training new temporary or permanent replacements for such key individuals, both internally and at our third party service providers;

•changes in local regulations as part of a response to the COVID-19 coronavirus outbreak that may require us to change the ways in which operate, which may result in unexpected costs;

•interruption of key commercialization, manufacturing, and related activities due to limitations on work and travel imposed or recommended by federal or state governments, employers and others; and

•delays or difficulties related to any future clinical trials that may be required, including delays in clinical trial sites receiving the supplies and materials needed to conduct clinical trials, difficulties in recruiting clinical site investigators and clinical site staff and difficulties in enrolling patients or treating patients in active trials.

Exhibit Index

Exhibit No.			Description
3.1			Restated Certificate of Incorporation of Eleven Biotherapeutics, Inc. Incorporated by reference to Exhibit 3.1 to our Current Report on Form 8-K filed on February 18, 2014 (File No. 001-36296).
3.2			Amended and Restated By-laws of Eleven Biotherapeutics, Inc. Incorporated by reference to Exhibit 3.1 to our Current Report on Form 8-K filed on April 16, 2015 (File No. 001-36296).
3.3			Certificate of Amendment of Certificate of Incorporation. Incorporated by reference to Exhibit 3.1 to our Current Report on Form 8-K filed on May 17, 2018 (File No. 001-36296).
3.4			Amendment to Amended and Restated By-laws. Incorporated by reference to Exhibit 3.2 to our Current Report on Form 8-K filed on May 17, 2018 (File No. 001-36296).
4.1			Specimen Stock Certificate evidencing the shares of common stock. Incorporated by reference to Exhibit 4.1 to our Registration Statement on Form S-1/A filed on January 23, 2014 (Reg. No. 333-193131).
4.2			Registration Rights Agreement, dated as of September 20, 2016 by and among Eleven Biotherapeutics, Inc. and the shareholders named therein. Incorporated herein by reference to Exhibit 4.1 to our Current Report on Form 8-K filed on September 21, 2016 (File No. 001-36296).
4.3			Form of Warrant issued to Silicon Valley Bank and Life Science Loans, LLC dated November 25, 2014. Incorporated by reference to Exhibit 10.23 to our Registration Statement on Form S-1 filed with the SEC on December 19, 2014 (Reg. No. 333-201176).
4.4			Form of Common Warrant. Incorporated by reference to Exhibit 4.1 to our Current Report on Form 8-K filed with the SEC on November 3, 2017 (File. No. 001-36296).
4.5			Form of Warrant. Incorporated by reference to Exhibit 4.1 to our Current Report on Form 8-K filed with the SEC on March 23, 2018 (File. No. 001-36296).
10.1* #			Exclusive License Agreement, dated July 30, 2020, by and among Sesen Bio, Inc., Viventia Bio, Inc. and Qilu Pharmaceutical Co., Ltd.
31.1*			Certification of the Chief Executive Officer Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
31.2*			Certification of the Chief Financial Officer Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
32.1**			Certification of the Chief Executive Officer Pursuant to 18 U.S.C. Section 1350, as Adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
32.2**			Certification of the Chief Financial Officer Pursuant to 18 U.S.C. Section 1350, as Adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
101			Interactive Data File (Form 10-Q for the Quarterly Period ended September 30, 2020 filed in XBRL). The financial information contained in the XBRL-related documents is "unaudited" and "unreviewed." The instance document does not appear in the interactive file because its XBRL tags are embedded within the Inline XBRL document.
104			Cover Page Interactive File (embedded within the Inline XBRL document and included in Exhibit 101).

*			Filed herewith.
**			This certification is being furnished solely to accompany this Quarterly Report on Form 10-Q pursuant to 18 U.S.C. Section 1350 and is not being filed for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liability of that section, nor shall it be deemed incorporated by reference into any filing of the registrant under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended, whether made before or after the date hereof, regardless of any general incorporation language in such filing.
#			Portions of this exhibit have been omitted in compliance with Item 601 of Regulation S-K.

						SESEN BIO, INC.
						(Registrant)
Date:			November 9, 2020			By:			/s/ Thomas R. Cannell, D.V.M.
						Name:			Thomas R. Cannell, D.V.M.
						Title:			President and Chief Executive Officer
									(Principal Executive Officer and Duly Authorized Officer)