Engineered CD47 protects T cells for enhanced antitumor immunity

Adoptively transferred T cells and agents designed to block the CD47/SIRPalpha axis are promising cancer therapeutics that activate distinct arms of the immune system. We administered anti-CD47 with adoptively transferred T cells with the goal of enhancing antitumor efficacy but observed rapid macrophage-mediated clearance of T cells expressing chimeric antigen receptors (CARs) or engineered T cell receptors, which abrogated therapeutic benefit. anti-CD47 mediated CAR T clearance was potent and rapid enough to serve as an effective safety switch. To overcome this challenge, we engineered a CD47 variant (47E) that engaged SIRPalpha and provided a “don’t-eat-me” signal that was not blocked by anti-CD47 antibodies. TCR or CAR T cells expressing 47E were resistant to clearance by macrophages following anti-CD47, and mediated significant, sustained macrophage recruitment into the TME. Although many of the recruited macrophages manifested an M2-like profile, the combined therapy synergistically enhanced antitumor efficacy. This work identifies macrophages as major regulators of T cell persistence and illustrates the fundamental challenge of combining T cell directed therapeutics with those designed to activate macrophages. It further delivers a therapeutic approach capable of simultaneously harnessing the antitumor effects of T cells and macrophages that manifests enhanced potency against solid tumors.