sqz-defa14a_20210426.htm

Proxy Statement Pursuant to Section 14(a) of the
Securities Exchange Act of 1934
(Amendment No. )

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SQZBIOTECH ® P.O. BOX 8016, CARY, NC 27512-9903 SQZ Biotechnologies Company Important Notice Regarding the Availability of Proxy Material Stockholders Meeting to be held on June 15, 2021 For Stockholders of record on April 22, 2021 This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. This is not a ballot. You cannot use this notice to vote your shares. We encourage you to access and review all of the important information contained in the proxy materials before voting. To view the proxy materials, and to obtain directions to attend the meeting, go to: www.proxydocs.com/SQZ To vote your proxy while visiting this site, you will need the 12 digit control number in the box below. Under United States Securities and Exchange Commission rules, proxy materials do not have to be delivered in paper. Proxy materials can be distributed by making them available on the Internet. For a convenient way to view proxy materials and VOTE online go to www.proxydocs.com/SQZ Have the 12 digit control number located in the shaded box above available when you access the website and follow the instructions. You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the stockholder meeting to be held on June 15, 2021. If you want to receive a paper or e-mail copy of the proxy material, you must request one. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year's meeting, you must make this request on or before June 04, 2021. To order paper materials, use one of the following methods: INTERNET www.investorelections.com/SQZ TELEPHONE (866) 648-8133 * E-MAIL paper@investorelections.com When requesting via the Internet or telephone you will need the 12 digit control number located in the shaded box above. * If requesting material by e-mail, please send a blank e-mail with the 12 digit control number (located above) in the subject line. No other requests, instructions OR other inquiries should be included with your e-mail requesting material. SQZ Biotechnologies Company Meeting Type: Annual Meeting of Stockholders Date: Tuesday, June 15, 2021 Time: 09:30 AM, Eastern Time Place: Annual Meeting to be held live via the Internet Please visit www.proxydocs.com/SQZ for more details. You must register to attend the meeting online and/or participate at www.proxydocs.com/SQZ SEE REVERSE FOR FULL AGENDA

SQZ Biotechnologies Company Annual Meeting of Stockholders THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. Please follow the instructions on the reverse side to vote on these important matters. MANAGEMENT RECOMMENDS A VOTE "FOR" ON PROPOSALS 1 AND 2 PROPOSAL 1. To elect two Class I Directors to serve until the 2024 Annual Meeting of Stockholders 1.01 Marc Elia 1.02 Pushkal Garg, M.D. 2 To ratify the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2021