SIRPa ablation overcomes exhaustion and enhances the antibody- and CAR-mediated antitumor activities of iPSC-derived CAR Macrophages

SIRPa-CD47 “don’t eat me” checkpoint axis plays a critical role in defining anti-tumor activities of macrophages within the tumor microenvironment. However, targeting this axis with anti-CD47 antibodies to improve anti-tumor responses in clinical trials has proven challenging. Here, we demonstrated that iPSC-derived macrophages (iMacs) with ablated SIRPa yield a superior antitumor effect in conjunction with cancer-targeted antibodies (Ab) or chimeric antigen receptor (CAR) against a variety of CD47-expressing tumors in vitro. Moreover, SIRPA-KO protected macrophages from Ab- or CAR-driven exhaustion, allowing for efficient phagocytosis of tumors after multiple rounds of cancer re-challenges. Ablation of SIRPa in iMacs improved survival of mice grafted ovarian carcinoma and treated with anti-HER2 Abs, while anti-GD2 CAR iMacs with KO SIRPA demonstrated reduction of initial tumor burden in mice with metastatic neuroblastoma xenograft. Overall, our studies support the feasibility of using the iPSC platform to generate SIRPα-ablated iMacs that are resistant to CD47-mediated inhibition for therapeutic applications.