Cooperative role of TET2 and IDH2 mutations in angioimmunoblastic T-cell lymphomagenesis

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Abstract Angioimmunoblastic T-cell lymphoma (AITL) is the most common subtype of peripheral T-cell lymphoma (PTCL) with distinct pathological and clinical characteristics. It is a difficult-to-diagnose and lacks effective therapies due to poor understanding of the molecular pathogenesis. Using genome-wide gene expression profiling (GEP), we have defined a robust molecular classifier for accurate diagnosis, identified oncogenic pathways, discovered its cell-of-origin, and deciphered the role of the tumor milieu in disease prognosis. Using high-throughput genomic analysis, we also identified frequent mutations in epigenetic regulators (TET2, IDH2 and DNMT3A) and regulators of T-cell activation (RHOA and CD28) in AITL. Co-occurrence of TET2 mutations with IDH2 mutation (hotspot: arginine-172; IDH2R172) is unique in AITL compared to other hematological malignancies where they are mutually exclusive, suggesting their cooperative role in T-cell lymphomagenesis. We have generated unique murine models with conditional loss of Tet2 (Tet2-/-) and double mutant (Tet2-/- /IDH2R172K) in CD4+ T-cells, and murine lymphomas with follicular helper T-cell (TFH) phenotype were observed. In addition, we generated several patient-derived xenografts (PDX) of AITL with IDH2R172 and/or TET2 mutations. We hypothesize that TET2 deficiency in T cells alters the DNA methylation profile leading to an altered genetic program favoring TFH cell differentiation and clonal expansion, facilitating transformation with subsequent hits, including IDH2R172 mutation, which will further alter the epigenome and oncogenic pathways in TFH -cell transformation. We will define the precise role of these genetic lesions in T-cell differentiation and in AITL pathogenesis. We also edited normal human CD4+ T-cells using CRISPR/CAS9 to generate TET2-/- T-cells for functional analysis and cross-validation of murine models. SinceTET2 mutations are in hematopoietic stem/progenitor cells (HSPC) in some AITLs, interactions between TET2 deficient T- and stromal cells during lymphomagenesis will be explored. We will test the efficacy of therapeutic interventions, including demethylating agents for TET2 deficiency and IDH2 inhibitors and/or glutamine depletion for TET2/IDH2 double mutant tumors in murine models and PDX of AITL. To accomplish the objective, three aims are planned: Specific Aim 1: To determine the mechanisms by which Tet2 deficiency mediates T-cell transformation and the role of Tet2 mutation in stromal cells in lymphomagenesis. Specific Aim 2: To delineate the mechanisms of combined Tet2 and IDH2R172K mutations in AITL pathogenesis. Specific Aim 3: To evaluate therapies targeting oncogenic mechanisms mediated by Tet2 and IDH2R172 mutations. Our long-term research goal is to define the pathobiology of AITL, through integrated functional epigenomic approaches using in vitro modified human T-cells, patient samples and relevant murine models, thus identifying promising novel targets for treatment that may be tested pre-clinically in PDX models.