Loss of 5-Hydroxymethylcytosine Is an Epigenetic Biomarker in Cutaneous T-Cell Lymphoma.

DNA hydroxymethylation at the 5 position of cytosine (5-hmC) is a product of the TET family of DNA hydroxylases. Accumulating evidence shows that loss of 5-hmC is critical for various biological and pathological processes. However, its level in cutaneous T-cell lymphoma (CTCL) remains largely unknown. Here, we report that the loss of 5-hmC is an epigenetic hallmark of CTCL, with diagnostic and prognostic implications. Immunohistochemistry staining on 90 mycosis fungoides (MF) samples showed a significant decrease of 5-hmC staining in CD4+ T cells in patch and tumor stages, especially in MF with large cell transformation, compared with benign inflammatory dermatoses. The 5-hmC staining level decreased with disease progression and showed remarkable loss in the large cells of large cell transformed MF samples, regardless of the CD30 positivity. Furthermore, 5-hmC decrease was correlated to poor overall survival in our patient cohort. Pharmacological augments of global 5-hmC with l-ascorbic acid in CTCL cell lines led to remarkable 5-hmC accumulation and promoted apoptosis in CTCL cell lines, as well as in patient-derived CTCL cells. In conclusion, 5-hmC is an epigenetic mark of predictive value in MF prognosis. Restoration of 5-hmC levels in MF may serve as a therapeutic regimen in CTCL.