Project 1 Melnick

PROJECT 1: ABSTRACT One of the critical unmet needs from both the scientific and therapeutic standpoints in the B-cell lymphoma field is understanding how these tumors evade the normal checks and balances of the immune system they arise from. A majority of B-cell lymphomas arise from the germinal center (GC) reaction, during which B-cells undergo extensive and rapid shifts in epigenetic programming, including transient suppression of immune signaling receptors involved in forming synapse-like interactions with GC T-cell subpopulations. Notably, the genetic hallmark of these tumors are somatic mutations in epigenetic regulatory genes, among which those affecting the histone acetyl-transferase CREBBP and the histone methyltransferase KMT2D are the most common, and moreover are highly co-occurrent. Prior work from our group showed that KMT2D and CREBBP mutations have a tumor suppressor effect and function by disrupting gene enhancer activity. In both cases this led to aberrant and persistent repression of different sets of immune synapse genes. More recently, we have explored the manner in which CREBBP and KMT2D mutations might cooperate to drive lymphomagenesis and have made a series of surprising preliminary observations, such as finding that these proteins engage in biochemical synergy at gene enhancers, and that their disruption seems to reprogram the immune microenvironment in ways not previously known to occur. Such data lead us to hypothesize that KMT2D and CREBBP mutations result in profound and cooperative suppression of a broad range of immune synapse genes, distinct from those affected by either mutation alone. We postulate that KMT2D and CREBBP form a complex at key regulatory enhancer and superenhancers with their combined loss disrupting the epigenetic and architectural state of the target genes in such a way as to prevent their response to immune synapse signaling leading in turn to reprogramming of GC immune microenvironment. Specifically, we propose that this is due to induced differentiation of specialized T follicular helper cells into T follicular regulatory (TFR) cells, which support expansion of GC B-cells, prevent their differentiation, and suppress T-cell mediated immune surveillance. Ultimately this leads to an immune suppressive environment that prevents entry and activation of cytotoxic CD8 T-cells. Finally, we we predict that therapeutic approaches specifically inhibiting the aberrant TFR axis in KMT2D/CREBBP lymphoma will enable more effective and rationally designed combinatorial immunotherapy approaches for the successful treatment of these tumors especially when coupled with epigenetic therapies that restore the aberrant chromatin programming induced by CREBBP and KM2D mutations. Hence the outcome of this proposal aside from the novel mechanistic findings, will be the implementation of rational multi-layer regimens that will restore immune eradication of these tumors.