We have shown before that mutant Kit combined with immunodeficiency mediated by null mutations in the recombination activating gene 2 (Rag2) and interleukin 2 receptor gamma chain gene (Il2rgc) facilitates near-complete engraftment of murine syngeneic but also histoincompatible allogeneic donor mouse HSCs in the absence of any further conditioning therapy (Waskow et al., 2009). This evidence concerns the gene RAG2 and Immunodeficiency.