Abstract 3636: Myeloid cell rebound associated with GD2-CAR-T cell therapy in solid tumor patients

Abstract GD2 is a validated cancer immunotherapy target with highly restricted normal tissue expression. Promising activity of GD2-CAR-T cell therapy in diffuse midline glioma and neuroblastoma has promoted interest in this therapy. We initiated three phase 1 clinical trials of escalating doses of intravenously administered autologous GD2-CAR-T cells in patients with advanced GD2-positive solid tumors. Emerging evidence suggests that CAR-T cells may increase circulating myeloid derived suppressor cells (MDSCs) and that this event may be mediated and/or triggered by CAR-T cell-derived cytokines and chemokines. These findings may help to explain the limited persistence of CAR-T cell therapy in solid tumor patients. Hence, we sought evidence of MDSC generation and secretion of relevant cytokines and chemokines in our clinical trial patients. The CARPETS trial (www. anzctr. org. au: ACTRN12620000622909) recently closed to recruitment after enrolling 12 patients (7 melanoma, 4 colorectal cancer, and 1 sarcoma). No significant adverse events were attributable to CAR-T cell therapy. We opened two other GD2-CAR-T cell therapy trials in 2023: LEVI’S-CATCH (ACTRN12622000675729) in patients with diffuse midline glioma at Sydney Children’s Hospital and KARPOS (ACTRN12622001514796) in adult patients with recurrent glioblastoma at Royal Adelaide Hospital. To date, 3 patients have enrolled to LEVI’S-CATCH with the first patient clearing the dose limiting (DLT) evaluation period. Three patients completed enrolment to the first dose cohort of KARPOS without DLTs. In all CARPETS patients, CAR-T cell expansion, which was measured by by DNA quantitative PCR and flow cytometry, peaked during the 6-week post-CAR-T infusion DLT evaluation period. In 6 CARPETS patients for whom peripheral blood samples were available, we found by flow cytometry, newly formed or increased size of pre-existing subpopulations of non-classical monocytes and/or MDSCs of mononuclear and/or polymorphonuclear class, which peaked at or after the time of peak CAR-T cell expansion. Typically, serum levels of inflammatory cytokines and chemokines such as TNF, IL-6, IL-8, CCL2, GM-CSF, and CXCL10, were detected only after the CAR-T cell infusion with variable patterns of the timing and concentration of analyte observed among the 12 patients. At the time of writing, blood samples from the first KARPOS patient showed CAR-T cell expansion and the subsequent increases in circulating myeloid derived suppressor cells and inflammatory cytokines. We expect that full data sets for these parameters will be presented for current and future enrolled patients to both studies. To improve CAR-T cell persistence in solid tumor patients, these data indicate the need for new therapeutic strategies to mitigate effects of CAR-T cell induced myeloid cells with antitumor activity. Citation Format: Michael P. Brown, Tessa Gargett, Nga T. Truong, Orazio Vittorio, David S. Ziegler. Myeloid cell rebound associated with GD2-CAR-T cell therapy in solid tumor patients abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3636.