Together, in the long-term, in unconditioned transplants, superior thymopoiesis is observed in IL-2Rγ-, JAK3-, IL-7 receptor alpha- (IL-7Rα), or ADA- deficient SCID compared with recombination activating genes 1 and 2- (RAG1/2) and DCLRE1C (Artemis) -deficient SCID. Here, ADA is linked to severe combined immunodeficiency.