PTPRZ1-targeting RNA CAR T cells exert antigen-specific and bystander antitumor activity in glioblastoma

The great success of chimeric antigen receptor (CAR) T-cell therapy in the treatment of patients with B-cell malignancies has prompted its translation to solid tumors. In the case of glioblastoma (GBM), clinical trials have shown modest efficacy, but efforts to develop more effective anti-GBM CAR T cells are ongoing. In this study, we selected PTPRZ1 as a target for GBM treatment. We isolated six anti-human PTPRZ1 scFv from a human phage display library and produced 2nd generation CAR T cells in an RNA format. Patient-derived GBM PTPRZ1-knock-in cell lines were used to select the CAR construct that showed high cytotoxicity while consistently displaying high CAR expression (471_28z). CAR T cells incorporating 471_28z were able to release IFN-γ, IL-2, TNF-α, Granzyme B, IL-17A, IL-6, and soluble FasL, and displayed low tonic signaling. Additionally, they maintained an effector memory phenotype after in vitro killing. In addition, 471_28z CAR T cells displayed strong bystander killing against PTPRZ1-negative cell lines after pre-activation by PTPRZ1-positive tumor cells but did not kill antigen-negative non-tumor cells. In an orthotopic xenograft tumor model using NSG mice, a single dose of anti-PTPRZ1 CAR T cells significantly delayed tumor growth. Taken together, these results validate PTPRZ1 as a GBM target and prompt the clinical translation of anti-PTPRZ1 CAR T cells.