Pathways of Immune Evasion in Acute Myeloid Leukemia

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Project Summary/Abstract Acute Myeloid Leukemia (AML) is the most common adult leukemia and has a very poor prognosis; most patients diagnosed with AML will die from this disease. AML results from uncontrolled proliferation of poorly differentiated myeloid precursor cells. Immune therapies, including checkpoint blockade, are currently being studied in the context of AML. Our previous work has established that the percentage of T cells present in the bone marrow of patients with AML at the time of diagnosis correlates with overall survival, providing evidence that the adaptive immune system, and specifically T cells, are able to recognize malignant cells. Our lab and others have shown that AML evades attack by the immune system by suppressing T cell function. Significantly, this functional suppression can be reversed in vitro in most cases by immune checkpoint molecule blockade. Previous literature has demonstrated that the exhausted state of the immune system can result from an epigenetic program imparted on T cells after chronic stimulation. We have previously shown a role for the map kinase pathway (MAPK) in maintaining this exhausted state in T cells present in AML. Transformation of cells to AML results from a combination of mutations affecting proliferation, differentiation and epigenetic state. For this reason, drugs targeting signaling and epigenetic state are approved or are being actively studied for the treatment of AML. For this project, our long-term goals are to provide a better understanding of functional T cell exhaustion and its relevance in AML. Our immediate goal is to study the role of the MAPK pathway, DNA methyltransferases and the epigenetic reader BET proteins in T cell exhaustion in the context of AML. We will conduct these studies with the central hypothesis that immune evasion via T cell exhaustion in AML is imparted by signaling pathways such as MEK and epigenetic states in T cells and that targeting these pathways in AML will reverse immune suppression. To accomplish this goal, we propose the following three aims: 1) Understand the role of the MAPK pathway on T cell function in AML. This will consist of mechanistic studies in T cells, but also study tumor and other lymphoid and myeloid populations in the immune microenvironment of AML. 2) Assess the impact of epigenetic pathways on the immunological function of T cells in mouse models of AML. Based on our preliminary data we will focus on DNA methylation and BET protein function. 3) Define cells and pathways of immune suppression in the tumor microenvironment of human AML. We will study a cell type associated with T cell suppression in patient samples. We will also study effects of MEK, BET and DNMT inhibitors on patient samples. Together these experiments will give us a better understanding of the biology of T cell exhaustion in AML disease. Importantly, results from these studies will have impact on treatment of this lethal disease by allowing rational design of combined small molecule and immune targeted therapies.