Concomitant loss of TET2 and TET3 results in T cell expansion and genomic instability [WGS]

TET proteins are tumor suppressors that through their catalytic activity oxidize 5-methylcytosine to 5-hydroxymethylcytosine, to promote DNA demethylation and to regulate gene expression. Notably, TET2 is one of the most frequently mutated genes in hematological malignancies, including T cell lymphomas. However, murine models with deletion of TET2 do not exhibit T cell expansion, presumably due to redundancy with other members of the TET family of proteins. In order to gain insight on the TET mediated molecular events that safeguard T cells from aberrant proliferation we performed serial adoptive transfers of murine CD4 T cells that lack concomitantly TET2 and TET3 to fully immunocompetent congenic mice. Our data reveal a progressive acquisition of malignant traits upon loss of TET2 and TET3 that is characterized by loss of genomic integrity, acquisition of aneuploidy and upregulation of the protooncogene Myc. To test whether loss of TET2 and TET3 could endow Tet2/3 DKO CD4 cells with hyperproliferative capacity, we performed serial transplantations of sorted, highly pure Tet2/3 DKO CD4 cells in congenic CD45.1+ recipients, that have not received any irradiation. After 16 weeks, we witnessed that the transferred CD45.2+ Tet2/3 DKO cells have evaded the immune surveillance of the recipients and have expanded. At this point, we isolated CD45.2+ cells by FACS sorting and re-transplanted them in new CD45.1+ immunocompetent recipients. The second transplantation resulted in significant acceleration of the expansion of the transplanted cells which became apparent within 2-4 weeks. To assess chromosomal copy number we performed whole genome sequencing. Genomic DNA was isolated from sorted wild type CD4 cells, or sorted expanded CD45.2+ Tet2/3 DKO cells after one or two serial transplantations in congenic CD45.1+ recipient mice.