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Summary The nucleoside analogue decitabine can deplete the epigenetic regulator DNA methyltransferase 1 (DNMT1), an effect that occurs, and is saturated at, low concentrations/doses. A reason to pursue this molecular‐targeted effect instead of the DNA damage/cytotoxicity produced with high concentrations/doses, is that non‐cytotoxic DNMT1‐depletion can cytoreduce even p53‐null myeloid malignancies while sparing normal haematopoiesis. We thus identified minimum doses of decitabine (0·1–0·2 mg/kg) that deplete DNMT1 without off‐target anti‐metabolite effects/cytotoxicity, and then administered these well‐tolerated doses frequently 1–2X/week to increase S‐phase dependent DNMT1‐depletion, and used a Myeloid Malignancy Registry to evaluate long‐term outcomes in 69 patients treated this way. Consistent with the scientific rationale, treatment was well‐tolerated and durable responses were produced (~40%) in genetically heterogeneous disease and the very elderly.

T-cell large granular lymphocyte leukaemia (T-LGLL) is a chronic clonal lymphoproliferative disorder of cytotoxic T lymphocytes (CTL), which commonly occurs in older patients and is often associated with autoimmune diseases. Among 246 patients with T-LGLL seen at our institution over the last 10 years, we encountered 15 cases following solid organ or haematopoietic stem cell transplantation. Here, we studied the clinical characterization of these cases and compared them to de novo T-LGLL. This experience, represented a clear picture of the intricate nature of the disease manifestation and the complexities of several immune mechanisms triggering the clonal expansion.