Unum Therapeutics Reports First Quarter Financial Results and Provides Corporate Updates CAMBRIDGE, MA

Unum Therapeutics Reports First Quarter Financial Results and Provides Corporate Updates

CAMBRIDGE, MA, May 11, 2020 Unum Therapeutics Inc. (NASDAQ: UMRX), a biopharmaceutical company focused on developing curative cell therapies for

solid tumors, today announced financial results for the first quarter ended March 31, 2020, and provided corporate updates.

Corporate Highlights

First Quarter 2020 Financial Results

About Unum s BOXR1030 and BOXR Platform

BOXR1030 was discovered from its Bolt-on Chimeric (BOXR) platform that is designed to discover novel bolt-on transgenes to be

co-expressed with CARs, a T-cell receptor, or ACTR, to help T cells survive longer and perform better in the solid tumor microenvironment. BOXR candidates consist of two

main components: 1) a targeting receptor that directs the T cell to attack tumor cells, which may be a traditional CAR receptor, a T-cell receptor, or Unum s ACTR receptor, and 2) a novel bolt-on transgene that improves the intrinsic function of the T cell. Once discovered, BOXR transgenes are designed to be incorporated into

several different types of therapeutic T cells, including both ACTR T cells and CAR-T cells, to impart new functionality to T cells.

Unum s first product candidate selected from the BOXR platform, BOXR1030, expresses GPC3+ targeted CAR and incorporates the bolt-on GOT2 transgene to improve T cell function in the solid tumor microenvironment (TME) by enhancing T cell metabolism. Preclinical data with BOXR1030 was presented at the Society for Immunotherapy of Cancer

(SITC) Annual Meeting in November 2019. In preclinical studies, BOXR1030 T cells were resistant to suppressive TME-like conditions, showing improved T cell proliferation under both hypoxic and low glucose

conditions compared with control GPC3+ CAR-T cells. In vivo, BOXR1030 demonstrated superior activity compared to the parental CAR-T with treated animals achieving

complete tumor regressions. Tumor infiltrating lymphocytes isolated from the tumors of treated animals revealed that BOXR1030 cells were more resistant to dysfunction and had fewer markers of exhaustion as compared to the control CAR-T cells.

About Unum Therapeutics

Unum Therapeutics is a biopharmaceutical company focused on developing curative cell therapies to treat patients with solid tumor cancers. Unum s novel

proprietary technology includes BOXR, which is designed to improve the functionality of engineered T cells by incorporating a bolt-on transgene to overcome resistance of the solid tumor

microenvironment to T cell attack. Unum s preclinical program BOXR1030 expresses the GOT2 transgene and targets GPC3+ solid tumor cancers. The Company is headquartered in Cambridge, MA.

Follow Unum Therapeutics on social media: @UnumRx, and LinkedIn.

Forward looking Statements

This press release contains

forward-looking statements including, without limitation, statements regarding our future expectations, plans and prospects, including the Company s strategic alternatives review process and the potential transactions that may be identified and

explored as a result of that process, projections regarding our long-term growth, enrollment and results for our preclinical and clinical activities, the development of our product candidate, BOXR1030, and the anticipated timing and success of

any of our preclinical studies, clinical trials and regulatory filings, and our strategies, business plans, and focus, as well as other statements containing the words anticipate, believe, continue,

could, estimate, expect, intend, may, might, plan, potential, predict, project, should, target,

will, or would and similar expressions, constitute forward-looking statements within the meaning of the safe harbor provisions of The Private Securities Litigation Reform Act of 1995, as amended. We may not actually achieve

the forecasts disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results could differ materially from the projections disclosed in the

forward-looking statements we make as a result of a variety of risks and uncertainties, including risks related to the ability of the Company to identify and consummate strategic alternatives

that yield additional value for shareholders; the timing, benefits and outcome of the Company s strategic alternatives review process, including the determination of whether or not to pursue or consummate any strategic alternative; the

structure, terms and specific risks and uncertainties associated with any potential strategic transaction; potential disruptions in our business and the stock price as a result of our exploration, review and pursuit of strategic alternatives or the

public announcement thereof and any decision or transaction resulting from such review; the accuracy of our estimates regarding expenses, future revenues, capital requirements, and the need for additional financing, the success, cost and timing

of our product development activities and clinical trials, our ability to obtain and maintain regulatory approval for our product candidates, the impact of COVID-19 on our business, preclinical and clinical

activities and strategic alternatives review, and the other risks and uncertainties described in the Risk Factors sections of our public filings with the Securities and Exchange Commission. In addition, the forward-looking statements

included in this press release represent our views as of the date hereof. We anticipate that subsequent events and developments may cause our views to change. However, while we may elect to update these forward-looking statements at some point in

the future, we specifically disclaim any obligation to do so. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date hereof.

UNUM THERAPEUTICS INC.

CONSOLIDATED STATEMENTS OF OPERATIONS

(unaudited, $ in thousands, except share and per share amounts)

UNUM THERAPEUTICS INC.

CONSOLIDATED SELECTED BALANCE SHEET DATA

(unaudited, in thousands)