Abstract 4020: Donor-dependent anti-tumoral efficacy of human CD19 CAR T cells in a leukemic xenograft mouse model

Abstract The recent advances in cellular immunotherapies have revolutionized the treatment options for hematological malignancies. Among others, genetically engineered T cells to express chimeric antigen receptors targeting CD19 have shown clinical success in patients with B cell malignancies. However, depending on the study design only one to two thirds of the patients experience a complete response upon CD19 CAR T cells treatment. Antigen escape, immune suppressive microenvironment, CAR T cell dysfunction as well as lack of CAR T cell persistence have been discussed to be reasons for the lack of sustained therapy response. Well established models for the preclinical evaluation of cellular therapies are needed for the evaluation of next generation CAR T cells as well as novel combination therapies. Here, we describe a xenograft animal model of human acute lymphoblastic leukemia (NALM-6 cells) with a suboptimal treatment response to human CD19 CAR T cells from three different donors. First, the activation status and memory phenotype of the CAR T cells from the different donors was characterized by flow cytometry and the anti-tumoral efficacy of the CD19 CAR T cells was evaluated in an in vitro co-culture killing assay using luciferase expressing NALM-6 cells. Next, CD19 CAR T cells from three donors were injected in NALM-6_luc tumor bearing animals. The tumor growth was monitored by bioluminescence imaging and the phenotype of the transferred CAR T cells was checked by flow cytometry. The frequency of memory T cells differed between the donors whereas the T cells from all donors exhibited all low expression of activation markers. In vitro, all three donors showed high and comparable anti-tumoral killing efficacy independent of their memory status. In vivo, CD19 CAR T cells from all three donors delayed the tumor growth significantly although none of the animals had a complete remission. In line with the individual memory status of the CAR T cells prior to infusion, there were slight differences in the kinetics of the anti-tumoral response. The flow cytometric analysis revealed that the transferred CAR T cells were almost absent in the peripheral blood and spleen whereas for individual animals tumor cells and highly activated CAR T cells were detectable in the bone marrow of the animals. In summary, the NALM-6_luc xenograft model is a value tool for evaluating next generation cellular therapies and novel combination strategies to overcome the current limitations of cellular therapies. Citation Format: Philipp Metzger, Carla N. Castro, Jonas F. Hummel, Maria Silvia Roman Azcona, Dinu Antony, Claudio Mussolino, Daniel Zurr, Swetlana Adamsky, Holger Weber. Donor-dependent anti-tumoral efficacy of human CD19 CAR T cells in a leukemic xenograft mouse model [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(6_Suppl):Abstract nr 4020.