Transplantation of haploidentically mismatched stem cells for the treatment of malignant diseases

Hematopoietic stem cell transplantation (HSCT) from HLA haploidentical mismatched donors has recently been developed for patients with high-risk acute leukemia who do not have a matched donor. After a high intensity conditioning regimen the HLA barrier is overcome by infusing a graft containing a megadose of T cell-depleted progenitor cells. Nowadays, for graft processing automated peripheral blood CD34(+) cell immunoselection is time and labor saving and ensures a high CD34(+) cell recovery rate. Besides providing 4.5 log T cell depletion of the graft, it guarantees a 3.5 log B cell depletion, which helps prevent EBV-related lymphoproliferative disorders. Excellent engraftment rates are associated with a very low incidence of graft-versus-host disease and regimen-related mortality even in patients who are over 40 years old. Overall, event-free survival and transplant-related mortality compare favorably with reports from unrelated matched transplants. Donor natural killer cell alloreactivity also plays a role in improving outcome in patients with acute myeloid leukemia. These results show the haploidentical transplant to be a viable, alternative source of stem cells for adults with acute leukemia at high-risk of relapse who do not have matched donors, and encourage extending it to patients with an indication to transplant.