Abstract 4076: 4-1bb selection augments DC/AML fusion vaccine-educated T cells for adoptive cell therapy
Authors: Rallis* Kathrine S. , Liegel* Jessica , Cheloni Giulia , Stroopinsky Dina , Bindal Poorva , Dufort Kenel , Torres Daniela , Saldarriaga Isabella , Herzlinger Samuel , Morin Abigael , Kesselman Raphael , Rosenbaum Jeremy , Chedid Georges , Adamia Sophia , Kufe Donald , Rosenblatt Jacalyn , Avigan David 
Published: April 2023

Introduction: Our group has pioneered a novel vaccine by fusion of patient-derived tumor with autologous dendritic cells (DCs) that presents an array of tumor antigens generating a polyclonal immune response. DC/AML vaccination led to expansion of leukemia-specific T cells with survival benefit in a phase II clinical trial. We postulated that ex vivo generation of vaccine-educated T cells would provide a powerful platform for adoptive immunotherapy with opportunity to augment T-cell functional potency prior to infusion. We report on an ex vivo system in which vaccine-educated T cells are further enriched for activated antigen-specific effector cells via an agonistic 4-1bb antibody. We report phenotypic and functional characteristics of 4-1bb-enriched vaccine-educated T cells.

Methods: DC/AML fusion vaccines were generated from C57BL/6J mice DCs and syngeneic C1498 mCh/luc+ AML cells. Splenic T cells were co-cultured with autologous irradiated DC/AML fusions in presence of IL-2/7/15. Selection with biotinylated agonistic 4-1bb (3H3) was performed on vaccine-educated T cells followed by expansion with anti-CD3/CD28 activation beads. T cells were phenotyped for activation (CD25/CD69), immune checkpoints (PD1/LAG3/TIM3), memory (CD44+CD62L-) and enrichment (anti-rat H&L). Cytotoxicity was evaluated by luminescence. Mice were inoculated with C1498 and injected with T cells 7 days later. BLI imaging was performed and 100-day survival measured.

Results: Vaccine-educated T cells demonstrated evidence of immune activation and memory phenotype compared to unstimulated naïve T-cell controls (TN) (7.24-fold, CD4+CD25+CD69+; 1.7-fold, CD3+CD44+CD62L-). Vaccine-educated T cells selected based on 4-1bb expression showed enhanced markers of activation (15.3-fold, CD4+CD25+CD69+) and memory phenotype (5-fold, CD3+CD44+CD62L-) compared to TN. Selection enriched for 4-1bb+ vaccine-educated T cells resulting in enhanced antigen-specific recognition as measured by tumor lysate induction of IFNg expression. Tumor specificity and activation was maintained following CD3/CD28-mediated expansion. The 4-1bb+ vaccine-educated T cells showed enhanced cytotoxicity (1.9-fold increase/TN at 10:1 E/T, P&lt;0.0001). Phenotypic and functional analysis support 3-5 days as the optimal duration of time for T-cell vaccine education. In vivo, 60% of mice treated with 4-1bb+ vaccine-educated cells were alive at 60 days vs. 20% treated with unselected vaccine-educated cells.

Conclusion: We demonstrate that vaccine-educated T cells subject to selection via an agonist 4-1bb antibody confer enhanced tumor selectivity and potency. Optimal duration for T-cell education was 3-5 days. T-cell stimulation and enrichment by agonistic 4-1bb selection enhanced cytotoxicity and memory phenotype. Thus, 4-1bb selection is a novel approach for antigen-specific T-cell enrichment for superior adoptive immunotherapy in AML.

Citation Format: Kathrine S. Rallis*, Jessica Liegel*, Giulia Cheloni, Dina Stroopinsky, Poorva Bindal, Kenel Dufort, Daniela Torres, Isabella Saldarriaga, Samuel Herzlinger, Abigael Morin, Raphael Kesselman, Jeremy Rosenbaum, Georges Chedid, Sophia Adamia, Donald Kufe, Jacalyn Rosenblatt, David Avigan. 4-1bb selection augments DC/AML fusion vaccine-educated T cells for adoptive 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 4076.