Post Transplant High-Dose Cyclophosphamide as GvHD Prophylaxis in Patients Receiving 1-Antigen/Allele HLA Mismatched (7/8 Matched) Unrelated Hemopoietic Stem Cell Transplantation for Myeloid Malignancies

The experimental treatment consists in the application of a therapeutic strategy with post Transplant High-Dose Cyclophosphamide as GvHD Prophylaxis in Patients Receiving 1-Antigen/Allele HLA Mismatched (7/8 matched) Unrelated Hemopoietic Stem Cell Transplantation for Myeloid Malignancies Allogeneic hematopoietic stem cell transplantation is a potentially curative therapy for a variety of hematologic malignancies due to two separate components: chemo/radiotherapy administered before the transplant (conditioning regimen) and the presence of immunocompetent cells in the graft, capable of inducing a "graft-versus-malignancy effect" also known as "GvL" effect. However, this immune-reaction usually carries the risk of detrimental effects seen as a multi-organ syndrome known as graft-versus-host disease (GvHD), which remains the most feared complication of Allogeneic hematopoietic stem cell transplantation. GvHD may be given to disparities between donor and recipient in presence of gene mismatches in the Major Histocompatibility Complex, also known as Human Leucocyte Antigen (HLA) system, or in any minor histocompatibility antigen. Thus, GvHD is obviously more common (and possibly more severe) in patients transplanted from HLA-mismatched donors as compared with those receiving grafts from HLA-matched donors.

A major limitation of allo-HSCT is the availability of a donor given that only a small percentage of patients has a HLA identical family donor. For the majority of patients (approximately 70%) who lack a HLA-identical sibling, alternative donors include HLA-matched unrelated donors and cord blood units. The chance of identifying a suitable marrow unrelated donor (MUD) in the international voluntary donor registries is limited by the frequency of a certain HLA genotype in the general population.

One of the alternative options in such cases is the use of a HLA-mismatched unrelated donor (MMUD). HLA-mismatching is defined as the presence of unshared antigens/alleles in recipient-donor pairs for HLA-A, -B, -C or DRB1 loci.

Patients undergoing MUD or MMUD transplants usually receive an intensified three-drug immunosuppressive regimen: anti-thymocyte globulin in addition to the standard platform of a calcineurine-inhibitor and an anti-metabolite.

The effect of HLA mismatches on clinical outcomes has been investigated in several studies. Single HLA mismatches at HLA-A, -B, -C, or -DRB1 locus (7/8 HLA-matched) were associated with lower overall survival and disease free survival, higher non-relapse mortality, and higher incidence of acute GvHD as compared with 8/8 HLA-matched pairs.