Selection of allogeneic stem donor

The choice of donor for an allogeneic HSCT takes into account several factors, including the patient's disease, disease state, and urgency in obtaining a donor. When allogeneic HSCT is being considered for a patient, a fully HLA-matched sibling is the preferred donor, as the risk of graft rejection and GVHD are the least with this source of allogeneic stem cells.3 For patients who lack a fully HLA-matched sibling donor, the preferred alternative sources for allogeneic stem cells include an unrelated fully HLA-matched donor, a partially HLA-matched cord blood unit, or a partially HLA-matched family member.54-56 A major disadvantage of an unrelated donor is that the average time required to identify and procure an HLA-matched unrelated donor is approximately 2-4 months, which may be inadequate for patients with rapidly progressive malignancies.57 The alternative stem cell source to an unrelated bone marrow donor for allogeneic HSCT is umbilical cord blood.55 57 58 The major advantages of umbilical cord stem cells is that they can be obtained in fewer than 4 weeks and cord blood units mismatched for up to 3 of 6 HLA may be used for allogeneic HSCT. This degree of HLA mismatching is acceptable, as the overwhelming percentage of T cells within the cord blood unit are naive, and the incidence of GVHD is comparable or less than that associated with an HLA-matched unrelated bone marrow donor. The major disadvantage of umbilical cord blood units is that they are associated with a high degree of graft rejection, especially in adults. Engraftment- and treatment-related mortality appears to be directly related to umbilical cord cell dose.55'57 58 The other significant disadvantage is that once the cord blood unit is used, there is no way to go back and get additional cells for a DLI or in the event of graft failure.

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