Dissecting mechanisms by which PD1 deletions drive aggressive cutaneous T cell lymphoma

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Project Summary/Abstract Cutaneous T-cell lymphoma (CTCL) is a non-Hodgkin lymphoma of skin homing T cells. Although late stage disease has a median survival of less than five years, outcomes are highly heterogenous with some patients surviving <6 months and others >10 years. The molecular mechanisms which drive heterogeneity of disease outcomes in CTCL remain poorly understood. By employing genome sequencing, RNA sequencing, and functional assays in a large cohort of samples, we identified deletion in the gene PDCD1, which encodes the co- inhibitory receptor PD1, as a major driver of differences in CTCL patient phenotypes. We found that PD1- deletions led to increased ex vivo proliferation and cytokine production, decreased expression of exhaustion markers, and reduced signatures of T cell exhaustion, a dysfunctional state of T cells that limits effector functions. Furthermore, in a multi-institution cohort, we found that PD1 deletions predict a significantly worse overall survival. Therefore, in this proposal, we aim to mechanistically dissect the pathways that govern aggressive phenotypes in PD1-deleted CTCL samples. Our preliminary RNAseq data indicates that two key pathways, mTOR-related metabolic pathways and activity of a transcription factor FOXM1, are upregulated in PD1-deleted CTCLs. In Aim 1, we will utilize CTCL cells and primary patient samples to determine whether mTOR drives PD1-dependent metabolism, T cell exhaustion, and growth. We will determine whether PD1 signaling is sufficient to suppress mTOR, the PD1 dependent changes in CTCL metabolism, and whether mTOR signaling is necessary for the growth and un-exhausted phenotype of PD1-deleted CTCLs. In Aim 2, we will utilize CTCL cells and primary patient samples to test first whether FOXM1 is activated downstream of PD1 signaling, then systematically identify FOXM1 target genes in CTCL, and finally test whether FOXM1 is necessary and sufficient for the growth of PD1-deleted CTCLs. Because there are pharmacological inhibitors of both mTOR and FOXM1, our work will address whether PD1 deletions may predict responses to novel classes of CTCL therapeutics, and thus new therapeutic avenues for patients with the most aggressive disease. My overall career goal is to become a successful, independent physician-scientist. The rigorous training plan proposed in this fellowship will allow me to achieve that goal by gaining research skills and knowledge in cellular immunology, cancer signaling pathways, and metabolism. I will be mentored by Dr. Jaehyuk Choi, an expert physician-scientist in CTCL, and Dr. Stephen Miller, a world-renowned T cell biologist, who have devised a joint training plan to develop all necessary research skills, communication skills and promote my professional development. This fellowship will broaden our understanding of CTCL pathogenesis and identify potential novel therapeutic strategies, as well as provide the necessary foundation for my future career as a physician-scientist.