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The Impact of TCR Affinity on T-Cell Dysfunction and Immunotherapeutic Reprogramming in Solid Tumors


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Although tumor-specific CD8 T cells are found in human tumors, cancers progress, indicating that these T cells are dysfunctional; yet the regulatory mechanisms underlying tumor-specific T cell dysfunction remain poorly defined. T cell-mediated immune responses are triggered by T cell receptor (TCR) binding to peptide-major histocompatibility complex (pMHC). In acute infections, affinity of TCR:pMHC interaction is a critical determinant of T cell expansion and effector function. However, little is known about how tumor antigen affinity impacts T cell differentiation and dysfunction in progressing tumors. To investigate the functional and molecular programs determined by affinity, we generated an in vivo tumor model expressing altered peptide ligands (APL) derived from SV40 large T antigen epitopeI (TAG) and recognized by TAG-specific transgenic CD8 T cells (TCRTAG) with varying functional avidity. While affinity did not impact T cell activation and differentiation in tumor draining lymph nodes, it drove distinct functional and molecular programs at the tumor site. Interestingly, key transcription factors and effector molecules were regulated by signal strength, preserving a cell-intrinsic functional program in T cells with low-affinity interactions. In contrast, certain hallmarks of T cell dysfunction, including the expression of inhibitory receptors (e.g. PD1 and LAG3), were affinity-independent, revealing that even very weak TCR ligations can induce a typical exhaustion phenotype. Ongoing studies will define the transcriptional and epigenetic programs underlying the distinct dysfunctional T cell states in tumors driven by TCR signal strength.



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