PROJECT SUMMARY Outcomes for patients with relapsed/refractory diffuse large B cell lymphoma (DLBCL) remain poor despite recent therapeutic advances, particularly in the area of immunotherapy. Classification of solid tumor microenvironments as immune “inflamed” or “non-inflamed” through bulk transcriptional profiling enriches for a subset that is checkpoint blockade therapy (CBT) responsive. Conversely, the DLBCL immune landscape has not been as well-characterized, and the extent to which immune environmental features can predict for immunotherapy response in DLBCL patients is unknown. Given that a growing number of immunotherapies are being explored in the relapsed/refractory DLBCL space, a deeper understanding of the DLBCL immune landscape might uncover clues that aid in identifying patients likely to benefit from checkpoint blockade and/or CAR T cell therapies. Additionally, growing evidence indicates that cancer cell-intrinsic alterations can profoundly affect the tumor immune environment, which directly impacts immunotherapy sensitivity. How recurring genetic alterations and related pathways in malignant B cells contribute to shaping the DLBCL immune environment is unclear. Additional research is clearly needed in order to address these gaps in knowledge. Toward that end, we incorporated curated immune- and cell-of-origin (COO)-related gene sets into a gene set variation analysis (GSVA) on transcriptomes of 874 DLBCL specimens. Among the four clusters that emerged (germinal center B cell (GCB) hot, GCB cold, activated B cell (ABC) hot, and ABC cold), analysis of whole exome sequencing data revealed significantly enriched genetic alterations in each. For instance, loss- of-function (LOF) mutations in SOCS1, a negative regulator of JAK/STAT signaling, were enriched in GCB hot DLBCLs, suggesting these lymphomas may be particularly sensitive to IFNγ signaling and vulnerable to anti- PD-1 therapy. Conversely, LOF alterations in TMEM30A, which regulates phosphatidylserine (PS) orientation in the plasma membrane, were common among ABC cold DLBCLs, which may render these lymphomas sensitive to immunotherapies that enhance macrophage phagocytosis. These observations support the central hypothesis that lymphoma cell-intrinsic mechanisms contribute significantly to shaping unique DLBCL immune environments, the characterization of which will identify patients who will or will not benefit from CBT or CAR T cell therapy. The main objectives of the proposal are: 1) to determine mechanisms by which select genetic alterations in lymphoma cells shape the DLBCL immune environment, and 2) to develop a DLBCL “immune score” and determine its utility in identifying patients for whom PD-1 blockade or CAR T cell therapy will be effective. The principal investigator, a physician-scientist with clinical expertise in lymphoma and a research background in cancer immunology, is well-suited to oversee the experiments proposed in this application. In order to execute compu...