Enhancing anti-EGFRvIII CAR T cell therapy against glioblastoma with a paracrine SIRPγ-derived CD47 blocker
Martins TA. et al. (2024) Enhancing anti-EGFRvIII CAR T cell therapy against glioblastoma with a paracrine SIRPγ-derived CD47 blocker. Nat Commun. 15, 9718. DOI:10.1038/s41467-024-54129-w
Glioblastoma (GBM) is an aggressive brain tumor that frequently resists conventional therapies, underscoring the need for innovative treatment strategies. A key feature of GBM is the tumor-specific EGFRvIII mutation, which arises alongside increased EGFR gene copies as the tumor evolves. This results in a mosaic tumor composition, where some cells express the EGFRvIII mutation while others do not, contributing to antigen escape, one of the major challenges in chimeric antigen receptor (CAR) T cell therapy resistance. This study explores an enhanced CAR T cell therapy designed not only to target EGFRvIII-expressing cells but also to address antigen escape within these heterogeneous tumors. To achieve this, anti-EGFRvIII CAR T cells were further engineered to co-express and secrete signal regulatory protein gamma (SGRP), a SIRPγ-derived CD47 blocker. CD47 expression on tumor cells enables them to evade immune cell-mediated destruction. By blocking CD47, this approach disrupts tumor immune evasion and restores the phagocytic function of immune cells within the tumor microenvironment, effectively creating a dual-function therapy delivered by the aEGFRvIII-SGRP CAR T cells.
To assess the in vivo behavior and therapeutic efficacy of the aEGFRvIII-SGRP CAR T cells, researchers employed dual-reporter bioluminescence imaging of an orthotopic glioblastoma xenograft model. Given the heterogeneous nature of GBM, two distinct luciferase reporters, NanoLuc® (Nluc) and Firefly luciferase (Fluc), were used to track the effects of different treatments on separate tumor cell populations. Fluc was expressed in glioblastoma cells lacking the EGFRvIII mutation, enabling real-time monitoring of EGFRvIII-negative tumor burden using D-luciferin as the reporter substrate. Meanwhile, Nluc was used to label EGFRvIII-positive tumor cells, allowing researchers to track their response to CAR T cell therapy using fluorofurimazine as the substrate. Because these luciferase reporters have distinct substrate specificities, the study was able to independently monitor the dynamics of EGFRvIII-positive and EGFRvIII-negative tumor populations within this in vivo GBM model, offering a comprehensive view of tumor heterogeneity and therapeutic impact over time.
The findings demonstrated that aEGFRvIII-SGRP CAR T cells exhibited superior anti-tumor activity compared to conventional CAR T cells, including eradication of the majority of the EGFRvIII negative reporter cell population. By blocking CD47, these engineered cells lead to improved tumor clearance and extended survival in preclinical glioblastoma models. These results suggest that integrating a CD47-blocking strategy within the CAR T cell therapy could help overcome immune evasion in glioblastoma, providing valuable insights for future therapeutic applications.
Keywords: glioblastoma, CAR T cell therapy, EGFRvIII, CD47 blockade, SIRPγ, bioluminescence imaging, macrophage phagocytosis, immune evasion, NanoLuc luciferase, Firefly luciferase, Fluorofurimazine, D-luciferin, tumor heterogeneity
