Biology-Driven Approaches to Prevent and Treat Relapse of Myeloid Neoplasia after Allogeneic Hematopoietic Stem Cell Transplantation

•Major mechanisms of relapse include HLA loss, HLA down-regulation, and expression of coinhibitory ligands.•Combination of donor lymphocyte infusion with immunomodulating agents and tyrosine kinase inhibitors may enhance the graft-versus-leukemia (GVL) effect.•Immune checkpoint inhibitors can induce a significant GVL effect, but toxicity is high. The curative potential of allogeneic hematopoietic cell transplantation (allo-HCT) in the treatment of acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS) relies mainly on the graft-versus-leukemia effect. Relapse after allo-HCT occurs in a considerable proportion of patients and has a dismal prognosis, with still very limited curative potential. This review provides an overview of the established and evolving approaches to preventing or treating relapse of AML and MDS after allo-HCT, in the context of novel insight into the biology of relapse. Established prophylactic measures to prevent relapse include optimized conditioning and graft-versus-host disease (GVHD) prophylaxis, as well as donor lymphocyte infusion (DLI) for high-risk patients; novel immunomodulatory interventions and maintenance approaches are still experimental. Improved diagnostics can detect persistent or recurring disease at a molecular level, enabling early preemptive interventions. Established options include hypomethylating agents and DLI. Standard treatments for hematologic relapse include chemotherapy, cessation of immunosuppressive treatment, and DLI. Experimental approaches include molecular targeted therapies, novel immunomodulatory treatments, and second allo-HCT. For all interventions, the potential risks, including occurrence of GVHD, must be weighed against the benefits individually in each patient. Concurrently, prevention and treatment of relapse after allo-HCT remain challenging and unmet medical needs.