Reprogramming the neuroblastoma tumor immune microenvironment to enhance GPC2 CAR T cells

Poor tumor trafficking and the immunosuppressive tumor microenvironment (TME) limit chimeric antigen receptor (CAR) T cell efficacy in solid tumors, such as neuroblastoma. We previously optimized GPC2 CARs in human neuroblastoma xenografts leading to clinical translation, however, there have not been preclinical studies using immunocompetent models. Thus, here we generated murine GPC2 CAR T cells using the D3-GPC2-targeting single-chain variable fragment being utilized clinically (NCT05650749) and tested them in neuroblastoma syngeneic allografts. Immune profiling of GPC2 CAR T cell-treated tumors revealed significant reprogramming of the TME, most notably poor intra-tumor CAR T cell persistence being associated with increased recruitment of myeloid-derived suppressor cells (MDSCs), along with MDSC-recruiting CXCL1/2 chemokines. These tumor-infiltrating MDSCs directly inhibited GPC2 CAR T cell activation and proliferation ex vivo. To both capitalize on this chemokine gradient and mitigate MDSC-tumor trafficking, we engineered GPC2 CAR T cells to express the CXCL1/2 receptor, CXCR2. CXCR2-armored GPC2 CAR T cells migrated towards CXCL1/2 gradients, enhanced anti-neuroblastoma efficacy, and reduced the level of MDSCs in the TME. Together, these findings suggest CAR T cell studies in immunocompetent models are imperative to define mechanisms of solid tumor immune escape and rationally design armoring strategies that will lead to durable clinical efficacy.