Signal regulatory protein alpha blockade potentiates tumoricidal effects of macrophages on gastroenterological neoplastic cells in syngeneic immunocompetent mice

AIM: Immunotherapies blocking the CD47‐SIRPα pathway by targeting CD47 enhance macrophage phagocytosis of neoplastic cells in mouse models. As SIRPα exhibits relatively restricted tissue expression, SIRPα antagonists may be better tolerated than agents targeting CD47, which is ubiquitously expressed in many tissues. Here, we investigated the therapeutic impact of monoclonal antibodies (mAbs) against CD47 and/or SIRPα on gastroenterological tumors in syngeneic immunocompetent mouse models. METHODS: We used in vitro and in vivo phagocytosis assays in C57BL/6J (B6) mice to investigate anti‐CD47/SIRPα mAb effects on Hepa1‐6 and CMT93 originating from B6 mice. The influence of these mAbs on macrophage transmigration was also assessed. To investigate anti‐SIRPα mAb therapy‐induced inhibitory effects on sporadic colon cancer growth, we used a CDX2P9.5‐NLS Cre;APC (+) /FLOX (CPC‐APC) mouse model. RESULTS: Systemic anti‐SIRPα mAb administration significantly increased Hepa1‐6 and CMT93 cell susceptibility to macrophage phagocytosis, both in vitro and in vivo. Conversely, similarly administered anti‐CD47 mAb did not promote macrophage phagocytosis of target cells, whereas cells incubated with anti‐CD47 mAb prior to inoculation were more susceptible to macrophage phagocytosis. In vitro cell migration assays revealed that binding with anti‐CD47 mAb inhibited macrophage transmigration. Anti‐SIRPα mAb treatment inhibited tumor progression in CPC‐APC mice and significantly improved overall survival. Anti‐CD47 mAb administration in vivo eliminated the phagocytosis‐promoting CD47 blockade effect, probably by inhibiting macrophage transmigration/chemotaxis. In contrast, anti‐SIRPα mAb exhibited enhanced macrophage phagocytic activity and marked anti‐tumor effects against gastroenterological malignancies. CONCLUSION: SIRPα mAb augmentation of macrophage phagocytic activity may represent an effective treatment strategy for human gastrointestinal tumors.