Abstract 5244: SIRPα knockout iPSC-derived macrophages (iMACs) are resistant to CD47-dependent inhibition of phagocytosis and efficiently kill tumor cells in pre-clinical models

Abstract The CD47-SIRPα axis is a critical checkpoint that prevents SIRPα-positive macrophages from phagocytosing CD47-expressing solid tumors. Several agents aiming to block this axis have recently entered early clinical trials including anti-CD47 and anti-SIRPα monoclonal antibodies (mAb). These checkpoint inhibitors (CPI) aim to modulate the phagocytotic activity of endogenous tumor associated macrophages (TAMs). However, the adoptive transfer of macrophages resistant to CD47-based inhibition in the tumor microenvironment (TME) could also increase clinical efficacy while avoiding side effects linked to the use of anti-CD47 mAb. Cell therapy based on autologous macrophages have gained increasing attention for cancer treatment due to their ability to infiltrate into the immunosuppressive TME and their unique immunomodulatory characteristics. However, due to required intricate genetic manipulation of autologous macrophage cell product for each patient, optimization and consistency of the cell product remains challenging. In contrast, the use of induced pluripotent stem cell (iPSC) -derived macrophages (iMACs) facilitates the introduction of genetic modifications to further optimize the iMAC cell product and limits the need for combination therapies. The knockout (KO) of the SIRPα gene in iMACs is a promising genetic modification that results in a potent iMAC cell therapy product resistant to phagocytosis inhibition by CD47-expressing tumor cells. A SIRPα KO was introduced in a fully characterized GMP iPSC line that was then differentiated to iMACs using Evotec’s 3D differentiation protocol. The SIRPα KO iMACs were then evaluated for their antibody-dependent cellular phagocytosis (ADCP) capacity in comparison to antibody-loaded wildtype (WT) iMACs when co-cultured with CD47-expressing tumor cells. SIRPα KO iPSCs showed differentiation potential comparable to WT iPSC and resulted in iMACs expressing typical markers of fully differentiated macrophages. SIRPα KO iMACs exhibited increased phagocytic potency and killing capacity compared to WT iMACs when both cell types were exposed to CD47-positive tumor cells and loaded with the same tumor-targeting mAb. This increased phagocytosis of tumor cells by antibody-loaded SIRPα KO iMACs was also comparable to ADCP observed for WT iMACs in the presence of an anti-CD47 blocking antibody. Using Evotec’s gene editing platform we were able to efficiently generate SIRPα-deficient iPSCs that serve as the starting material to manufacture highly pure, genetically modified iMACs that lack SIRPα expression rendering them resistant to CD47-dependent inhibition of phagocytosis. This novel allogeneic off-the-shelf iMAC cell product overcomes the need to combine this cell therapeutic with CD47-SIRPα axis CPIs and provides the basis to develop innovative treatments for solid tumors. Citation Format: Kathrin Haake, Michela Mirenda, Quentin Bernard, Philip Hublitz, Lucie Gouxette, Martin Briscadieu, Philine Scheinpflug, Garima Singh, Alica Hinkelmann, Tanja Schneider, Michael Esquerré, Audrey Holtzinger, Michael Epstein, Daniel Sommermeyer, Michael Paillasse, Andreas Scheel, Markus Dangl, Monika Braun, Nadja Wagner. SIRPα knockout iPSC-derived macrophages (iMACs) are resistant to CD47-dependent inhibition of phagocytosis and efficiently kill tumor cells in pre-clinical models abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5244.