- HLA-haploidentical, first-degree relatives or half-siblings of the recipient participant at the allele or allele group. The donor and recipient must be HLA identical for at least one allele (using high resolution DNA based typing) at the following genetic loci: HLA-A, HLA-B, HLA-C, and HLA-DRB1. Fulfillment of this criterion shall be considered sufficient evidence that the donor and recipient share one HLA haplotype.