Transactions Table

Explanation of Responses:

Id	Content
F1	Includes 1,994 restricted stock units (each, an "RSU") of IGM Biosciences, Inc. (the "Issuer") issued to Felix J. Baker, a managing member of Baker Bros. Advisors (GP) LLC (the "Adviser GP") pursuant to the Issuer's Outside Director Compensation Policy (the "Stock Incentive Plan") in lieu of director retainer fees of $11,500. The RSUs are fully vested. Felix J. Baker serves on the Issuer's board of directors (the "Board") as a representative of 667, L.P. ("667") and Baker Brothers Life Sciences, L.P. ("Life Sciences", and together with 667, the "Funds") and their affiliates and control persons.
F2	After giving effect to the transaction reported herein and as a result of their ownership interest in (i) Baker Biotech Capital, L.P. and (ii) 667, Julian C. Baker and Felix J. Baker each may be deemed to have an indirect pecuniary interest in Common Stock reported in column 5 of Table I held directly by or held for the benefit of 667, a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to their interest in 667 and Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667.
F3	Baker Bros. Advisors LP (the "Adviser") serves as the investment adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held directly by the Funds or for the benefit of the Funds. The Adviser GP is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are managing members of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held directly by the Funds or for the benefit of the Funds. The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held directly by the Funds or for the benefit of the Funds.
F4	Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds or for the benefit of the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.
F5	Includes beneficial ownership of 4,210 shares of Common Stock previously issued to Felix J. Baker pursuant to the Stock Incentive Plan in lieu of director retainer fees in his capacity as a director and 892 shares of Common Stock previously issued to Dr. Kelvin Neu, a former employee of the Adviser, pursuant to the Stock Incentive Plan in lieu of director retainer fees and 11,210 shares of Common Stock received previously from the exercise of 11,210 non-qualified options exercisable soley into Common Stock ("Stock Options") that were issued to Dr. Neu in his previous capacity as a director of the Issuer, of which the Funds are deemed to own a portion.
F6	The acquisitions of RSUs reported on this form represent a single grant of 1,994 RSUs on Table I. The 1,994 RSUs are reported for each of the Funds as each has an indirect pecuniary interest in such securities.
F7	Pursuant to the policies of the Adviser, Felix J. Baker does not have any right to any of the Issuer's securities issued as compensation for his service on the Board and Dr. Neu, a former employee of the Adviser, does not have any right to any of the Issuer's securities issued as compensation for his previous service on the Board and the Funds are entitled to an indirect proportionate pecuniary interest in the Stock Options and RSUs. Solely as a result of their ownership interest in (i) the general partners of the Funds and (ii) the Funds, Felix J. Baker and Julian C. Baker may be deemed to have an indirect pecuniary interest in the Stock Options, RSUs and any Common Stock acquired upon the exercise of Stock Options or vesting of RSUs (i.e. no direct pecuniary interest).
F8	Pursuant to the policies of the Adviser, the Adviser has voting and dispositive power over the Common Stock received in lieu of director retainer fees, Stock Options, RSUs and any Common Stock received as a result of the exercise of Stock Options.
F9	After giving effect to the transaction reported herein and as a result of their ownership interest in (i) Baker Brothers Life Sciences Capital, L.P. and (ii) Life Sciences, Julian C. Baker and Felix J. Baker each may be deemed to have an indirect pecuniary interest in Common Stock reported in column 5 of Table I held directly by or held for the benefit of Life Sciences, a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to their interest in Life Sciences and Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences.

Remarks:

Felix J. Baker, a managing member of Baker Bros. Advisors (GP) LLC, the sole general partner of Baker Bros. Advisors LP, is a director of IGM Biosciences, Inc. (the "Issuer"). By virtue of their representation on the board of directors of the Issuer, for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, the reporting persons other than Felix J. Baker are deemed directors by deputization of the Issuer.