Enhancing anti-EGFRvIII CAR T cell therapy against glioblastoma with a paracrine SIRPγ-derived CD47 blocker

Abstract

A significant challenge for chimeric antigen receptor (CAR) T cell therapy against glioblastoma (GBM) is its immunosuppressive microenvironment, which is densely populated by protumoral glioma-associated microglia and macrophages (GAMs). Myeloid immune checkpoint therapy targeting the CD47-signal regulatory protein alpha (SIRP alpha) axis induces GAM phagocytic function, but CD47 blockade monotherapy is associated with toxicity and low bioavailability in solid tumors. In this work, we engineer a CAR T cell against epidermal growth factor receptor variant III (EGFRvIII), constitutively secreting a signal regulatory protein gamma-related protein (SGRP) with high affinity to CD47. Anti-EGFRvIII-SGRP CAR T cells eradicate orthotopic EGFRvIII-mosaic GBM in vivo, promoting GAM-mediated tumor cell phagocytosis. In a subcutaneous CD19+ lymphoma mouse model, anti-CD19-SGRP CAR T cell therapy is superior to conventional anti-CD19 CAR T. Thus, combination of CAR and SGRP eliminates bystander tumor cells in a manner that could overcome main mechanisms of CAR T cell therapy resistance, including immune suppression and antigen escape.

EGFRvIII-targeted CAR T cells have been proposed as a therapeutic option for patients with glioblastoma (GBM), however, clinical responses remain suboptimal. Here the authors engineer anti-EGFRvIII CAR T cells to secrete an optimized SIRP gamma-derived CD47 blocker, showing that combining CAR T cell effector functions with enhanced macrophage-mediated tumor cell phagocytosis improves anti-tumor efficacy in preclinical models.