BACKGROUND: Patients with severe combined immunodeficiency disease who have matched sibling donors (MSDs) can proceed to hematopoietic cell transplantation (HCT) without conditioning chemotherapy. OBJECTIVE: We sought to determine whether the results of HCT without chemotherapy-based conditioning from matched unrelated donors (URDs), either from volunteer adults or umbilical cord blood, are comparable with those from MSDs. METHODS: We performed a multicenter survey of severe combined immunodeficiency transplantation centers in North America, Europe, and Australia to compile retrospective data on patients who have undergone unconditioned HCT from either URDs (n = 37) or MSDs (n = 66). RESULTS: Most patients undergoing URD HCT (92%) achieved donor T-cell engraftment compared with 97% for those with MSDs; however, estimated 5-year overall and event-free survival were worse for URD recipients (71% and 60%, respectively) compared with MSD recipients (92% and 89%, respectively; P < .01 for both). URD recipients who received pre-HCT serotherapy had similar 5-year overall survival (100%) to MSD recipients. The incidences of grade II to IV acute and chronic graft-versus-host disease were higher in URD (50% and 39%, respectively) compared with MSD (22% and 5%, respectively) recipients (P < .01 for both). In the surviving patients there was no difference in T-cell reconstitution at the last follow-up between the URD and MSD recipients; however, MSD recipients were more likely to achieve B-cell reconstitution (72% vs 17%, P < .001). CONCLUSION: Unconditioned URD HCT achieves excellent rates of donor T-cell engraftment similar to that seen in MSD recipients, and reconstitution rates are adequate. However, only a minority will have myeloid and B-cell reconstitution, and attention must be paid to graft-versus-host disease prophylaxis. This approach might be safer in children ineligible for intense regimens to spare the potential complications of chemotherapy.

• Keywords
• Severe combined immunodeficiency, conditioning, hematopoietic cell transplantation, serotherapy, sibling donors, umbilical cord blood, unrelated donors,
• MeSH
• Survival Analysis MeSH
• B-Lymphocytes immunology   MeSH
• Chimerism MeSH
• Child MeSH
• Volunteers MeSH
• Adult MeSH
• Histocompatibility MeSH
• Infant MeSH
• Humans MeSH
• Graft vs Host Disease etiology   prevention & control   MeSH
• Unrelated Donors * MeSH
• Infant, Newborn MeSH
• Transplantation Conditioning MeSH
• Retrospective Studies MeSH
• Siblings * MeSH
• T-Lymphocytes immunology   MeSH
• Histocompatibility Testing MeSH
• Severe Combined Immunodeficiency diagnosis   mortality   therapy   MeSH
• Hematopoietic Stem Cell Transplantation * MeSH
• Treatment Outcome MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Infant MeSH
• Humans MeSH
• Male MeSH
• Infant, Newborn MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Multicenter Study MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Comparative Study MeSH
• Geographicals
• Australia MeSH
• Europe MeSH
• North America MeSH