Therapeutic Targeting of the TGFβ Pathway Augments CAR T cell Efficacy in Glioblastoma

Chimeric Antigen Receptor (CAR) T therapy represents a promising approach to improve outcomes for patients with high-grade gliomas (HGG). Recently, we reported on a phase I trial assessing the local delivery of CAR T cells for HGG. Despite notable clinical benefits to CAR T treatment, clinical responses were highly variable between patients. Here we report that TGFβ levels in the tumor cavity fluid (TCF) decreased following CAR T treatment and that lower TGFβ levels positively correlated with improved patient responses to CAR T therapy. Patients were stratified based on baseline TGFβ levels in the TCF before CAR T therapy. Single-cell RNA sequencing of patient tumor tissues identified significant upregulation of genes associated with angiogenesis and epithelial-to-mesenchymal transition, and IL6 and SLRP pathways in TGFβ high patients, while IL2, chemokine signaling and NK-mediated cytotoxicity pathways were significantly upregulated in TGFβ low patients. Preclinically, we demonstrated that systemic treatment with a TGFβR1 inhibitor markedly improved CAR T efficacy in syngeneic murine glioma models, correlating with changes in the tumor microenvironment (TME) that benefited both endogenous and CAR T cell phenotype and trafficking. Further studies demonstrated that inhibition of the TGFβ pathway in CAR T cells, through either TGFβR1 inhibitor or CRISPR/Cas9 knockout of TGFβR2 (TGFβR2-KO), significantly enhanced CAR T cell expansion and antitumor activity. Collectively, our clinical and preclinical findings strongly indicate that targeting the TGFβ pathway could significantly enhance CAR T therapy for patients with high-grade gliomas.