With the widespread availability of HSCT for leukemia, long-term survival can still be achieved with transplantation from partially HLA-matched donors when an exact match for the human leukocyte antigen allele cannot be found; HLA mismatch is not a contraindication to donor selection. There are more than 30 HLA motifs within the HLA genetic region, and only those encoding HLA-class I antigens and HLA-class II antigens are associated with bone marrow transplantation outcomes. HLA-DQ and HLA-DP motif mismatches have no significant effect on HSCT outcomes. hla-dr mismatches are in between. The current odds of finding an HLA-exactly matched unrelated donor range from 10-70%, and it is easier to find HLA-hemimatched donors among family members. In the case of HLA hemimatch, the number of mismatched HLA antigens between the donor and recipient is 1-3. With current mature transplantation techniques, bone marrow transplantation using HLA hemimatched family members donors has similar survival rates as using HLA-matched unrelated donors. Along with the continuous updating and maturation of HLA matching technology and transplantation methods, the expansion of allogeneic HSCT from genetic allogeneic and sibling donors to unrelated donor transplantation, cord blood transplantation and HLA haploidentical transplantation has greatly expanded the source of donors, allowing all patients who were otherwise hopeless to benefit and regain a chance of regeneration.