Hypomethylating agents for treatment and prevention of relapse after allogeneic blood stem cell transplantation

Despite the curative potential of allogeneic stem cell transplantation (allo-SCT) in patients with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), many patients will relapse. Until recently therapeutic options mainly consisted of palliative care, chemotherapy, donor lymphocyte infusions and second transplantation in selected cases. Still many patients either do not tolerate intensive therapies or do not achieve durable remissions and will finally succumb. Given this unmet medical need the hypomethylating agents (HMA), Azacitidine (Aza) and Decitabine (DAC) have been tested as salvage therapy in patients with myeloid malignancies relapsing after allo-SCT. Furthermore, they have also been incorporated into prophylactic and pre-emptive approaches to avoid haematological relapse. In this review, we summarize the evidence from retrospective studies but also from a few prospective trials regarding the use of HMA after transplant. To aid clinicians in their daily clinical practice, we also comment on some practical aspects such as dosing and schedule, the choice of HMA and the use of complementary cellular therapies. Finally, this review also gives an overview on potential mechanisms mediating the efficacy of HMA after transplant as well as ongoing preclinical research and clinical activities aiming to further improve this treatment approach.