Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (allo-CSH). Recently, in the context of semi-identical (=haploidentical) HLA donors, but also of compatible HLA donors, the use of cyclophosphamide (CY) administered in high doses at early post-transplant (PT) (=PTCY) (Days +3 and +4 or +5) has shown excellent control of acute and chronic GVH, even enabling the discontinuation of other immunosuppressive drugs administered after allo-CSH (ciclosporin, mycophenolate mofetyl (MMF) or Cellcept). This step has already been taken in the context of allo-CSH with myeloablative conditioning (MAC), which is a minoritary conditioning in adults. However, in the context of allo-CSH with reduced-intensity conditioning (RIC), which predominates in adults, this strategy seems insufficient to prevent the risk of GVHD. The idea of reducing the use of immunosuppressants in the context of RIC/HLA-compatible transplants seems, however, still relevant, in order to reduce their adverse effects, improve patients' quality of life and enhance the reconstitution of the post-transplant immune system.