IL7R and T-B+ severe combined immunodeficiency due to gamma chain deficiency: HSCT required for survival. Conditioning is not required to attain T cell reconstitution. However, in the absence of conditioning, functional B and NK cell reconstitution is typically not achieved in X-linked SCID and JAK3 deficiency. In IL7R deficiency B and NK cells are functional, thus no or low-dose conditioning is indicated