PROJECT SUMMARY/ABSTRACT This project focus in the biology of diffuse large B-cell lymphoma (DLBCL) that are common aggressive malignancies with a curability rate of 65% despite intensive chemoimmunotherapy. DLBCLs display an array of genetic alterations, that define molecular subtypes, and strong dependence on the microenvironment for survival. We hypothesize that reprogramming of the stromal microenvironment is critical for the oncogenicity of hallmark mutations that mediate lymphoma progression and immune evasion. We propose to elucidate the roles of the cancer-associated fibroblasts (CAF) and extracellular matrix (ECM) components of the lymphoma microenvironment to identify therapeutic vulnerabilities. CAFs are derived from healthy fibroblasts that have been reprogrammed by cancer cells into a novel biological entity. Our long-term goal is to therapeutically exploit reprogrammed CAFs with consideration of genetically-defined DLBCLs. For this reason, it is critical to elucidate the mechanisms involved in CAF reprogramming. Not all CAFs are reprogrammed in the same way. Moreover, rather than a terminal effect, CAF reprogramming as a transcriptionally dynamic process that allows the establishment of a variety of adaptive phenotypes. Our preliminary data suggest the activation of “shared” and “private” pathways in the reprogramming of CAFs. We specifically identify and studied the role of HSF1, one of the “shared” transcription factors in CAFs. CAFs without HSF1 failed to produce an ECM with the biochemical composition and mechanical properties required for lymphoma progression. Concomitantly, lack of HSF1 in the TME allowed the establishment of an effective lymphoma immune response leading to tumor eradication. We plan to test our central hypothesis and accomplish the objective of this application by pursuing these specific aims: Aim 1. Elucidate mechanisms of CAFs reprogramming that sustain genetically diverse DLBCLs: We will identify CAFs sub-populations and ECM composition in genetic DLBCL subtypes; and identify molecular pathways and reprogramming factors across and within CAFs sub-populations using HSF1 as lead effector. Aim 2. Elucidate the role of CAFs in functionalizing the ECM for immune evasion. We will characterize biomechanical and biochemical constraints imposed by CAFs to an effective lymphoma immunity. Aim 3. Determine the therapeutic impact of targeting CAFs in genetic DLBCL subtypes. We will determine the anti-lymphoma effect of co-targeting CAFs and lymphoma cells in molecularly-defined pre-clinical DLBCL murine models. The studies that we propose will provide significant insights on the mechanisms of stromal TME reprogramming for the establishment of genetically defined DLBCLs and will contribute towards development of novel therapeutic strategies focused on targeting the stromal TME in these entities to increase curability.