Abstract 12: TCR-gated control of costimulatory switch protein (CSP) activation in rTCR-T cells expressing PD1-41BB
Authors: Buerdek Maja , Prinz Petra U. , Mutze Kathrin , Coluccio Andrea , Tippmer Stefanie , Bosch Miriam , Longinotti Giulia , Catarinella Mario , Davari Kathrin , Geiger Christiane , Loesch Barbara , Crame Kirsty , Schendel Dolores J. 
Published: March 2024

Abstract
Chimeric antigen receptor (CAR-)/T cell receptor (TCR-)T-based immunotherapies have shown promising results in the treatment of patients suffering from hematological malignancies. However, targeting solid cancer patients with CAR-T/TCR-T cells represents a more challenging approach, due to various factors present within the hostile tumor micro-environment (TME), inhibiting T cell functionality and leading to T cell exhaustion. Programmed cell death ligand-1 (PD-L1) is expressed on tumor cells as well as various cell types within the TME and binds to programmed cell death protein 1 (PD-1) expressed on the surface of activated T cells, thereby inducing T cell exhaustion and mediating tumor immune escape. To impair this inhibitory mechanism and improve TCR-T cell efficacy for the treatment of solid tumors, we use the chimeric costimulatory switch protein (CSP) PD1-41BB that turns the inhibitory signal mediated via the PD-1-PD-L1 axis into a costimulatory one. The CSP-mediated costimulatory signal is TCR-gated, whereby costimulation can only occur if a specific peptide-HLA complex present on a target cell interacts with a recombinant TCR expressed in T cells. In vitro co-cultures of rTCR-T cells expressing the CSP (CSP rTCR-T cells) and antigen-negative or -positive cell lines carrying or lacking PD-L1 demonstrated that CSP rTCR-T cells display functionality only if the respective target antigen is expressed in target cells, but not in the absence of target antigen. PD-L1-positive, antigen-negative tumor cells are not lysed by CSP rTCR-T cells, not even in the presence of antigen-positive tumor cells, showing gated functionality and a favorable safety profile of CSP-armored TCR-T cells. CSP rTCR-T cells displayed enhanced cytokine release and killing after encounter of PD-L1-positive tumor cell lines, compared to tumor cells lacking PD-L1, and showed the capacity to recognize and lyse a large panel of tumor cell lines expressing various levels of HLA-A*02, target antigen and PD-L1 in vitro. 3D spheroids derived from PD-L1-positive, target antigen-positive tumor cell lines mimicking cell-cell interactions within a solid tumor mass efficiently triggered CSP rTCR-T cells, leading to specific IFN-γ release and lysis of tumor spheroids. Furthermore, CSP rTCR-T cells showed enhanced proliferative capacity and expansion in co-cultures with PD-L1-positive tumor cells, compared to tumor cells lacking PD-L1 expression. Importantly, various target antigen-negative healthy cell types expressing or lacking PD-L1 and representing different vital organs were not cross-recognized by CSP rTCR-T cells in vitro. Our preclinical in vitro assessments of CSP rTCR-T cell functionality and safety proved their superior and gated functionality as well as favorable safety profile, showing the great potential for the treatment of cancer patients suffering from advanced solid tumor malignancies.
Citation Format: Maja Buerdek, Petra U. Prinz, Kathrin Mutze, Andrea Coluccio, Stefanie Tippmer, Miriam Bosch, Giulia Longinotti, Mario Catarinella, Kathrin Davari, Christiane Geiger, Barbara Loesch, Kirsty Crame, Dolores J. Schendel. TCR-gated control of costimulatory switch protein (CSP) activation in rTCR-T cells expressing PD1-41BB [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 12.