Epigenetic blueprint identifies poor outcome and hypomethylating agent-responsive T-ALL subgroup

Adult T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy still associated with poor outcome calling for new therapeutic options. DNA methylation landscapes of adult T-ALL remain largely uncharacterized. Here, we systematically analyzed the DNA methylation profiles of normal thymic sorted T-cell subpopulations and 143 primary adult T-ALLs as part of French GRAALL 2003-2005 trial. Our results indicated that T-ALL is epigenetically distinct from normal T-cell subpopulations and consisted of five major subtypes (C1-C5) which were either associating with co-occurring DNMT3A/IDH2 mutations (C1), TAL1 deregulation (C2), TLX3 (C3), TLX1/in cis-HOXA9 (C4) or in trans-HOXA9 (C5) overexpression. Importantly, our data identified an unexpected subset of hypermethylated T-ALL associated with poor outcome and primary therapeutic response. Using mouse xenografts, we showed that hypermethylated T-ALL samples displayed therapeutic response to the DNA hypomethylating agent, 5-Azacitidine, which significantly delayed tumor progression suggesting epigenetic-based therapies as a novel treatment option in hypermethylated T-ALL. To assess the heterogenity among adult T-ALLs, DNA methylation landscape of 143 primary adult T-ALL samples along with 6 distinct sorted normal thymic cell types were analysed using Illumina Methylation EPIC arrays.