UNRAVELING THE CROSSTALK BETWEEN T CELL IMMUNOTHERAPIES AND THE TUMOR MICROENVIRONMENT

T cell-based immunotherapies such as tumor infiltrating lymphocyte therapy (TILs), chimeric antigen receptor T cells (CAR T), and T cell receptor-engineered T cells (TCR-T) are revolutionizing cancer treatment. Yet, their broader use remains limited by safety and efficacy concerns. On one hand, most patients develop systemic toxicities from excessive immune activation. On the other hand, their translation beyond hematologic malignancies and a very limited number of solid tumors remains limited due to poor T cell infiltration and the onset of T cell exhaustion by immunosuppressive cues in the tumor niche. We realized that these limitations could be better understood by investigating how therapeutic T cells engage with, reshape, and are influenced by the tumor microenvironment (TME). To address this, we employed an immunocompetent model of adoptive T cell therapy (ACT) to which we integrated novel genetically engineered enzymatic labeling systems to directly assess intercellular contacts between therapeutic T cells and TME components. We observed a profound remodeling of the myeloid compartment following therapy, including the expansion of inflammatory Ly6Chigh macrophages and increased production of several myeloid recruiting chemokines such as CCL3, CCL4, and CCL5. In vivo interaction assessment revealed that 72 hours after therapy, therapeutic T cells engaged in direct contact with multiple macrophage and dendritic cell subsets. Antigen dependency interrogation in vivo pointed towards cross-presentation, and mixed bone marrow chimera experiments suggested a “two-hit” model in which an initial cognate interaction primes the TME for subsequent bystander interactions that support TME reshaping. Single-cell RNA sequencing revealed profound transcriptional reprogramming of myeloid cells following therapy, hallmarked by strong proinflammatory signatures in macrophages as well as generalized interferon stimulation across the myeloid compartment. Further efforts are needed for dissecting the temporal dynamics and functional consequences of the observed ACT – TME interactions. Ultimately, this work provides a mechanistic insight into how ACT reshapes and communicates with the TME and establishes a platform to uncover key TME targets and T cell pathways that could be leveraged for improving T cell-based immunotherapies.