Abstract 1096: Enhancing effector function in T cell adoptive cell therapy in murine models of pediatric sarcomas
Authors: Sanchez Jessica P. , Davila Eduardo , Ladle Brian H. 
Published: March 2024

Abstract
New treatment approaches for high-risk pediatric sarcomas are desperately needed. Immunotherapy advances with adoptive cell therapy in hematologic malignancies have not yet translated to pediatric solid tumors including sarcomas. Hallmarks of the immune microenvironment in pediatric sarcomas include the presence of immunosuppressive cytokines and immune cells and a lack of potent T cell activation. We are seeking ways to overcome these barriers to effective adoptive cell therapy in pediatric sarcoma. We are exploring introduction of a novel synthetic co-receptor, CD8a:MyD88, that can augment tumor-specific T cell effector function and potentially improve outcomes in murine models of sarcoma. Tumor-antigen specific T cells or tumor-infiltrating T cell populations are transduced ex vivo to express the CD8a:MyD88 synthetic co-receptor resulting in MyD88 signaling when T cells encounter their cognate MHC I/epitope complex. We have studied the effects of CD8a:MyD88 expression on cytokine production and lytic activity against murine sarcoma cell lines in vitro. Initial experiments utilized the OT1 T cell model (specific to the model antigen chicken ovalbumin) which we introduced into our murine sarcoma cell lines (KPSarc pleomorphic sarcoma and M3-9M rhabdomyosarcoma). Using GFP as a marker of T cell transduction, the production of effector cytokine interferon gamma was measured following T cell activation compared with GFP-negative non-transduced T cells. CD8a:MyD88 expressing T cells expressed higher levels of interferon gamma at basal levels and following antigen-specific activation when co-cultured with Ova-expressing sarcoma cells. Improved tumor-specific lytic function in CD8a:MyD88 expressing T cells was also observed in co-culture experiments compared to untransduced or control vector- transduced T cells. We further hypothesized that skewing T cell differentiation toward an effector phenotype with the addition of interleukin-12 during T cell expansion would increase the anti-tumor effect of the CD8a:MyD88 expressing T cells. Co-culture with our murine sarcoma cell lines showed increased tumor-lytic function in T cells primed with IL-12. We have ongoing experiments studying the in vivo effects of the CD8a:MyD88 expressing T cells in model antigen-expressing murine sarcoma models. In addition, the ability of the CD8a:MyD88 co-receptor to augment the effector function of polyclonal sarcoma infiltrating T cells is being explored. These results will further define the obstacles and potential solutions to successful adoptive T cell therapy for pediatric sarcomas.
Citation Format: Jessica P. Sanchez, Eduardo Davila, Brian H. Ladle. Enhancing effector function in T cell adoptive cell therapy in murine models of pediatric sarcomas [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 1096.