Chimeric antigen receptor T cells (CAR-Ts) have demonstrated remarkable efficacy in leukemia and lymphomas but limited responses in solid tumors. We conducted a phase I trial (NCT02107963) of GD2 CAR-Ts (GD2-CAR.OX40.28.z.ICD9), demonstrating feasibility and safety of administering GD2 CAR-Ts in children and young adults with neuroblastoma and, for the first time, osteosarcoma. 15 patients aged 8-28 years were enrolled on four dose levels, of which 13 patients were infused. No dose-limiting toxicities were observed, and administration of up to 1x107 GD2-CAR-T/kg was feasible and safe for children and young adults with neuroblastoma and osteosarcoma. At Day 28 following GD2 CAR-T infusion, 23.1% (3/13) of evaluable patients had progressive disease and 76.9% (10/13) had stable disease (SD). 3/10 SD patients remained stable at 60 days post-infusion of GD2 CAR-T, but all patients eventually progressed. Since a major barrier to CAR-T efficacy is inadequate CAR-T expansion, we evaluated CAR-T levels and found that patients stratified into good and poor expander groups, observed across dose levels and associated with pro-inflammatory cytokine signatures in patients. To understand the immune cell contributors to CAR-T expansion, patient pre-treatment apheresis, CAR-T product, and post-infusion samples were evaluated by high-dimensional proteomic (CyTOF), transcriptomic (RNAseq), and epigenetic (ATACseq) analyses. In patient apheresis, good CAR-T expansion associated with more open chromatin and with both proteomic and transcriptomic enrichment of naïve T cells, while poor CAR-T expansion associated with increased levels of T effector memory (TEMRA) cells and enrichment of myeloid derived suppressor cell (MDSC) transcriptomic signatures. CAR-T products across patients, regardless of CAR-T expansion, demonstrated increased T cell activation proteomic signatures, with enhanced exhaustion transcriptomic signatures in poor expanders compared to good. The most robust cellular correlate to good CAR-T expansion was a population of CXCR3-expressing monocytes in pre-treatment apheresis. Interestingly, this CXCR3+ monocyte population reduced in post-infusion timepoints of good expanders, resembling levels found in poor expanders. Our findings were validated in TARGET-OS patient data in The Cancer Genome Atlas, where high CXCR3 expression was found to be associated with survival benefit in osteosarcoma patients. CXCR3 has been extensively studied on T cells, but its function on myeloid populations is yet to be fully explored. These results are the first to demonstrate that the peripheral immune environment prior to CAR-T administration may effectively predict and modulate CAR-T expansion in patients.

Citation Format: Tara Murty, Sabina Kaczanowska, Ahmad Alimadadi, Cristina Contreras, Caroline Duault, Priyanka Balasubrahmanyan, Warren Reynolds, Norma Gutierrez, Reema Baskar, Catherine Wu, Franziska Michor, Jennifer Altreuter, Yang Liu, Aashna Jhaveri, Vandon Duong, Hima Anbunathan, Radim Moravec, Joyce Hong, Roshni Biswas, Stephen Van Nostrand, James Lindsay, Mina Pichavant, Elena Sotillo, Bita Sahaf, Sean Bendall, Holden Maecker, Steven Highfill, David Stroncek, Melinda Merchant, John Glod, Catherine Hedrick, Crystal Mackall, Sneha Ramakrishna, Rosandra Kaplan. Immune determinants of CAR-T expansion in solid tumor patients receiving GD2 CAR-T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2142.