Donor selection and conditioning for typical SCID. 1Excludes Omenn syndrome and leaky SCID, both classified as atypical SCID for transplant purposes and requiring at least some conditioning; also excludes radiation sensitive SCID (DCLREC1, LIG4, etc.), for which donor selection and conditioning are individualized to balance risks of rejection vs. chemotherapy toxicity. 2Gene therapy clinical trials should be considered for X-linked or ADA SCID when there is no HLA matched sibling. 3Based on availability, CMV status, donor age, and other variables. 4Non-radiation-sensitive T-B-NK+ SCID generally requires chemotherapy plus serotherapy for unrelated donor transplant. 5For X-linked and JAK3 SCID a maternal donor with serotherapy alone is preferred over a 9/10 unrelated or 6–7/8 cord donor. 6Consider chemotherapy conditioning for enhanced B and/or T cell reconstitution and to prevent rejection.