Exhibit 99.1

IGM Biosciences Announces Fourth Quarter and Full Year 2021 Financial Results and Provides Corporate Update

– Announced Global Collaboration Agreement with Sanofi for Oncology, Autoimmune and Inflammation Targets;

IGM to Receive $150 Million Upfront Payment and potentially more than $6 Billion in Aggregate Development,

Regulatory and Commercial Milestones –

– Ongoing Progress in Clinical Programs with Two Phase 2 Studies of Two Doses of IGM-2323, 100 mg and

300 mg, in Patients with DLBCL and FL Initiated –

– Company to Host Conference Call and Webcast Today at 8:00 a.m. EST –

MOUNTAIN VIEW, Calif., March 29, 2022 – IGM Biosciences, Inc. (Nasdaq: IGMS), a clinical-stage biotechnology company focused on creating and developing IgM antibodies, today announced its financial results for the fourth quarter and full year ended December 31, 2021 and provided an update on recent developments.

“IGM continues to make progress in creating a new class of antibody medicines, which strengthens our commitment to use our expertise to develop and improve upon the inherent qualities of IgM antibodies,” said Fred Schwarzer, Chief Executive Officer of IGM Biosciences. “Notably, our exclusive collaboration agreement with Sanofi, announced today, will accelerate the development of our IgM antibody platform across multiple areas of high unmet need beyond our current pipeline efforts. This partnership is a significant step towards exploring and validating our platform in multiple therapeutic areas, and we look forward to working with Sanofi’s impressive team. Simultaneously, our pipeline continues to progress with considerable speed. Namely, the initiation of two Phase 2 studies for our T cell bispecific antibody IGM-2323 and the continued progress in our DR5 agonist IGM-8444 Phase 1 combination treatment regimens. We look forward to sharing information on these efforts later this year.”

Global R&D Collaboration with Sanofi

Pipeline Updates

IGM-2323 (CD20 x CD3)

IGM-8444 (DR5)

IGM-7354 (IL-15 x PD-L1)

IGM-2644 (CD38 x CD3)

Corporate Updates

Fourth Quarter and Full Year 2021 Financial Results

2022 Financial Guidance:

IGM expects full year GAAP operating expenses of $250 million to $260 million including estimated non-cash stock-based compensation expense of approximately $50 million. Concurrent with the Company’s first quarter 2022 financial results expected in May, IGM anticipates providing full year collaboration and license revenue guidance as well as ending 2022 cash and investments guidance.

Conference Call and Webcast

IGM will host a conference call and webcast to discuss the Sanofi R&D collaboration announcement today, March 29, at 8:00 a.m. ET. The conference call may be accessed by dialing (866) 649-1996 (domestic) or (409) 217-8769 (international) and referring to conference ID 4983742. A live webcast of the presentation will be available on the “Events and Presentations” page in the “Investors” section of the Company’s website at https://investor.igmbio.com/news-and-events/events-and-presentations. A replay of the webcast will be archived on the Company’s website for 90 days following the presentation.

About IGM Biosciences, Inc.

Headquartered in Mountain View, California, IGM Biosciences is a clinical-stage biotechnology company focused on creating and developing engineered IgM antibodies. Since 2010, IGM Biosciences has worked to overcome the manufacturing and protein engineering hurdles that have limited the therapeutic use of IgM antibodies. Through its efforts, IGM Biosciences has created a proprietary IgM technology platform for the development of IgM antibodies for those clinical indications where their inherent properties may provide advantages as compared to IgG antibodies.

Cautionary Note Regarding Forward-Looking Statements

This press release contains forward-looking statements, including statements relating to IGM’s plans, expectations and forecasts and to future events. Such forward-looking statements include, but are not limited to: the potential of, and expectations regarding, IGM’s technology platform and its IgM and IgA antibodies and product candidates, including IGM-2323, IGM-8444, IGM-7354 and IGM-2644; expectations regarding the transaction with Sanofi, including all financial aspects of the collaboration and an equity investment; the potential benefits and results of the transaction with Sanofi, including goals of the collaboration and the potential for accelerated development of IGM’s platform; IGM’s plans and expectations regarding its clinical development efforts and activities; statements regarding the clinical development of IGM-2323, including the potential for the Phase 2 studies to potentially serve as the basis for a regulatory filing and accelerated review and approval of IGM-2323; statements regarding the clinical development of IGM-8444, including timing for data and the safety profile of IGM-8444; the expected timing of filing INDs with for IGM-7354 and IGM-2644; IGM’s expectations regarding a grant agreement with the Bill & Melinda Gates Foundation; IGM’s expectations regarding its financial position and guidance, including operating expenses and stock-based compensation expense, and the timing of providing guidance for full year collaboration and license revenue and ending 2022 cash and investments; and statements by IGM’s Chief Executive Officer. Such statements are subject to numerous important factors, risks and uncertainties that may cause actual events or results to differ materially, including but not limited to: potential delays and disruption resulting from the COVID-19 pandemic and governmental responses to the pandemic, including any future impacts to IGM’s operations, the manufacturing of its product candidates, the progression of its clinical trials, enrollment in its current and future clinical trials and progression of its collaborations and related efforts; the risks that the transaction with Sanofi may not be completed in a timely manner or at all; the possibility that certain closing conditions to the transaction with Sanofi will not be satisfied, including the risks related to obtaining the requisite regulatory approvals, such as those required under antitrust laws; the risk of the occurrence of any event, change or other circumstance that could give rise to the termination of collaborations with third parties, including the agreement with Sanofi (including without limitation the failure to timely obtain requisite regulatory approvals); the possibility that Sanofi may not invest in IGM; risks related to the effect of the announcement of the Sanofi transaction on IGM’s business relationships, operating results, stock price and business generally; IGM’s early stages of clinical drug development; risks related to the use of engineered IgM antibodies, which is a novel and unproven therapeutic approach; IGM’s ability to demonstrate the safety and efficacy of its product candidates; IGM’s ability to successfully and timely advance its product candidates through preclinical studies and clinical trials; IGM’s ability to enroll patients in its clinical trials; the potential for the results of clinical trials to differ from preclinical, preliminary, initial or expected results; the risk of significant adverse events, toxicities or other undesirable side effects; IGM’s ability to successfully manufacture and supply its product candidates for clinical trials; the potential impact of continuing or worsening supply chain constraints; the risk that all necessary regulatory

approvals cannot be obtained; the potential market for IGM’s product candidates, the potential diminishing need for therapeutics to address COVID-19, particularly in the United States and other major markets, and the progress and success of alternative therapeutics currently available or in development; IGM’s ability to obtain additional capital to finance its operations, if needed; uncertainties related to the projections of the size of patient populations suffering from the diseases IGM is targeting; IGM’s ability to obtain, maintain and protect its intellectual property rights; developments relating to IGM’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties, including those more fully described in IGM’s filings with the Securities and Exchange Commission (SEC), including IGM’s Annual Report on Form 10-K filed with the SEC on March 29, 2022 and in IGM’s future reports to be filed with the SEC. Any forward-looking statements contained in this press release speak only as of the date hereof, and IGM specifically disclaims any obligation to update any forward-looking statement, except as required by law.

Contact:

Argot Partners

David Pitts

212-600-1902

igmbio@argotpartners.com

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IGM Biosciences, Inc.

Selected Statement of Operations Data

(unaudited)

(in thousands, except share and per share data)

IGM Biosciences, Inc.

Selected Balance Sheet Data

(unaudited)

(in thousands)