Mesothelin-Directed CAR-T Cells With Dominant-Negative TGF-beta Receptor for Malignant Pleural Mesothelioma: Phase 1 Safety, Persistence, and Tumor Infiltration

This study investigates safety, CAR-T cell persistence, tumor infiltration, and preliminary anti-tumor activity of mesothelin-directed CAR-T cells co-expressing dominant-negative TGF-beta receptor II in patients with malignant pleural mesothelioma within the context of thoracic oncology and cellular immunotherapy, an area of growing scientific importance given its implications for Phase 2 dose selection for mesothelin CAR-T in MPM, TGF-beta armoring strategy validation, and intrapleural delivery as solid tumor CAR-T route. Using Phase 1 dose escalation (3+3 design) with intrapleural CAR-T infusion at 1e7, 3e7, and 1e8 cells/m2 with lymphodepletion, weekly tumor imaging, CAR-T persistence by ddPCR blood monitoring, and tumor biopsy at week 4 for infiltration histology, we examine mesothelin-directed scFv CAR providing tumor-specific recognition with 4-1BB costimulation for T cell persistence, and dnTGFbRII blocking TGF-beta-mediated CAR-T suppression in the immunosuppressive mesothelioma pleural microenvironment in 24 patients with unresectable MPM (18 epithelioid, 6 sarcomatoid, median 2 prior lines, median KPS 80) enrolled at Pacific and 2 affiliate centers drawn from intrapleural catheter infusion post-cyclophosphamide/fludarabine lymphodepletion at Pacific Cancer Center with 28-day inpatient safety monitoring and 12-month outpatient follow-up. Results indicate that no dose-limiting toxicity at any level; grade 1-2 CRS in 10/24 (41.7%); peak CAR-T expansion correlates with tumor mesothelin density (r=0.68, p<0.001); tumor CD8+ infiltration increases 3.84-fold at week 4 in dose level 3; disease control rate 62.5% (15/24) (p < 0.001), with no DLT; 62.5% disease control; 3.84-fold CD8+ infiltration increase; r=0.68 expansion-mesothelin as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to thoracic oncology and cellular immunotherapy and carry actionable implications for the design of programs and policies targeting Phase 2 dose selection for mesothelin CAR-T in MPM, TGF-beta armoring strategy validation, and intrapleural delivery as solid tumor CAR-T route.