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 protein tyrosine phosphatase receptor type Z (PTPRZ1) as a target for GBM treatment. We isolated six anti-human PTPRZ1 single-chain variable fragments from a human phage display library and produced second-generation CAR T cells in an RNA format. Patient-derived GBM PTPRZ1-knockin 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 IFNγ, IL2, TNFα, granzyme B, IL17A, IL6, 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 preactivation by PTPRZ1-positive tumor cells but did not kill antigen-negative nontumor cells. In an orthotopic xenograft tumor model using NOD/SCIDγ 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.