Haploidentical Donors

There are different kinds of donors for stem cell transplantation. The best matched donors are siblings but not everyone has siblings. The ultimate such donor is an identical twin, which is called syngeneic transplantation. On the other end of the spectrum is unrelated donor. Inevitably, an unrelated donor is less of a match than a properly screened sibling.

Related haploidentical BMT is an alternative method for expanding the potential pool of stem cell donors; any patient shares one HLA haplotype with each biologic parent or child and siblings or half-siblings have a 50% chance of being haploidentical and 50% chance of not being haploidentical. Despite as an optimal matching as possible, such donors have more subtle genetic differences from the transplanted patient than a properly matched sibling. The more differences between the patient and the donor, they higher is the incidence of graft rejection and severe graft vs. host disease. Thus, the disadvantage of the haploidentical approach has been the high incidence of graft rejection and severe GVHD.

Continued research is needed to better define preferred conditioning regimens, methods and degree of T-cell depletion, and optimal CD34+ cell dose in the allograft, all of which modify the risk and severity of graft versus host disease. Although haploidentical transplantation is a potentially curative option for AML patients lacking a suitable sibling or unrelated donor, experts believe that at this time it should be performed only in experienced centers, within the context of clinical trials, especially in patients with poor-risk AML in CR1.

Alternatives include umbilical cell and related donor transplantation.

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