 2.3. In addition to aforementioned approaches, use of RIC in the setting of HLA-mismatched familial donor HCT has been explored. Various RIC regimens, utilizing total body irradiation TBI,14, 15 busulfan,16, 17 or melphalan,18 along with fludarabine, have been shown to be effective in achieving successful engraftment with less transplantation-related mortality TRM, especially in elderly patients and in patients with organ dysfunctions, in the setting of HLA-matched donor HCT. These findings showed that under adequate immunosuppression, but not necessarily myeloablation, of the patients, donor hematopoietic cells can engraft and complete donor hematopoietic chimerism can be achieved. There are data that suggest the same principle may be extended to HLA-mismatched HCT settings as well. Successful engraftment of allogeneic hematopoietic cells across HLA-haplotype difference has been well-documented after RIC in animal models,19-21 and in infants with severe combined immunodeficiency syndrome.22, 23 In adult patient with hematologic malignancies, several studies involving small number of patients showed feasibility of successful engraftment of hematopoietic cell graft from HLA-haploidentical familial donor after RIC.24-27 