Abstract 2111: In vivo expansion of autologous GD2-CAR-T cells in patients with aggressive primary tumors may be impaired by previous alkylator therapy

Abstract GD2 is a validated cancer immunotherapy target and has a highly restricted normal tissue expression. Clinically activity of GD2-CAR-T cell therapy has been observed in the high GD2-expressing tumor types of diffuse midline glioma and neuroblastoma. Recently, we initiated two phase 1 clinical trials of escalating doses of intravenously administered autologous GD2-CAR-T cells either in pediatric patients with diffuse midline glioma at Sydney Children’s Hospital (LEVI’S-CATCH; www.anzctr.org.au - ACTRN12622000675729) or adult patients with recurrent glioblastoma at Royal Adelaide Hospital (KARPOS; ACTRN12622001514796). Our ex vivo CAR-T cell manufacturing protocol was changed from the original method to a modified method, which permitted CAR-T cells of memory phenotype to dominate in vitro. Our published 12-patient GD2-CAR-T cell trial in solid tumor patients showed that in vivo expansion of GD2-CAR-T cells was significantly greater among patients whose cells were prepared using the modified over the original method. Hence, we adopted the modified method for our current brain tumors trials. In the KARPOS study, six patients have been enrolled without experiencing DLTs. In the first dose cohort of three patients, none received lymphodepletion chemotherapy whereas in the second dose cohort of three patients, all received lymphodepletion chemotherapy. Clinical histories, which recorded the extent of previous alkylator therapy used for the treatment of primary and recurrent glioblastoma in adult patients, led us to hypothesize that cumulative exposure to alkylator drugs limited CAR-T cell expansion in vivo.The presence of CAR-T cells in serial peripheral blood samples was measured using quantitative DNA-PCR. The extent of CAR-T cell expansion in peripheral blood samples was described using two measures: (i) area under the curve (AUC), and (ii) peak expansion or Cmax. From the concentration of the CAR transgene in total genomic DNA (ng/μg gDNA) in blood plasma as a function of time, AUC values were calculated using GraphPad Prism according to the trapezoid rule. We found correlation coefficients of -0.90 and -0.83 for the relationship between cumulative dose of prior alkylator therapy and AUC and Cmax, respectively. These data are consistent with previous clinical data that indicate temozolomide has deleterious effects on human lymphocyte number and function. Our data suggest that patient selection may be an important parameter to consider when enrolling glioblastoma patients to clinical trials of CAR-T cell therapy. For example, randomized controlled trial evidence indicates that patients who are considering such trials and whose tumors lack MGMT promoter methylation may reasonably be spared exposure to six months of consolidation temozolomide chemotherapy as part of the conventional treatment protocol. Citation Format: Michael P. Brown, Sidra Khan, Jesikah Logan, Nga T. Truong, David S. Ziegler, Tessa Gargett, Abbey LeBlanc. In vivo expansion of autologous GD2-CAR-T cells in patients with aggressive primary tumors may be impaired by previous alkylator therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2111.