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

Tomoyuki Abe,Takao Hinoi,Jinlian Piao,Takashi Matozaki,Yuka Tanaka,Naohide Oue,Naoki Tanimine,Hideki Ohdan,Noel Verjan Garcia,Masayuki Miyasaka,Wataru Yasui

doi:10.1002/ags3.12205

Abstract

AimImmunotherapies 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.MethodsWe 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.ResultsSystemic 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.

Highlights

The integrin‐associated protein CD47 is a ubiquitously expressed cell surface glycoprotein that serves as a ligand for signal regulatory protein (SIRP) α, an immune inhibitory receptor on macrophages
We have demonstrated that interspecies CD47 incompatibility in xenotransplantation leads to SIRPα‐mediated “don't eat me” signal absence, resulting in the rejection of xenogeneic cells by human macrophages.[14,20]
We have demonstrated that a CD47‐SIRPα inhibitory signal induced by genomic manipulation overrides such an activating signal delivered to macrophages by xeno‐antigens

Summary

| INTRODUCTION

The integrin‐associated protein CD47 is a ubiquitously expressed cell surface glycoprotein that serves as a ligand for signal regulatory protein (SIRP) α ( known as CD172a, SHPS‐1), an immune inhibitory receptor on macrophages. Porcine CD47 does not induce SIRPα tyrosine phosphorylation in human macrophages, and porcine cell manipulation for expression of human CD47 markedly reduces their susceptibility to human macrophage‐mediated phagocytosis.[14] Beyond such interspecies incompatibility, the non‐obese diabetic (NOD) mouse strain provides a better background for human leukocyte and cancer cell engraftment than those of other strains with equivalent immunodeficiency‐related mutations owing to the stronger engagement of the SIRPα inhibitory receptor with human CD47, preventing engulfment of human grafts.[15] By using NOD mice with multiple immunodeficient phenotypes, anti‐human CD47 monoclonal antibodies (mAbs), as inhibitors of the CD47‐SIRPα interaction, have been shown to display anti‐tumor activity against various human cancers including leukemia and solid tumors.[9,13] In these xenograft models, anti‐human CD47 mAb targets human CD47 on inoculated human cancer cells but does not recognize mouse CD47 ubiquitously expressed on the host mouse cells This has raised concerns that effects caused by CD47 binding to multiple other ligands, such as integrins and thrombospondin, which govern a number of processes in normal tissues, might be overlooked. We investigated the anti‐tumor effects of mAbs targeting CD47 or SIRPα, which exhibits relatively restricted tissue expression, by use of a mouse model in which syngeneic gastrointestinal cancer cells are intraperitoneally inoculated and a gene‐targeting mouse model in which colon cancers grow sporadically

| MATERIALS AND METHODS

| RESULTS

| DISCUSSION

Findings

DISCLOSURES