• T-cell-depleted HCT: expansion of effector memory cells, enhanced TCR diversity (8 pts. >15 years old, Phase I, published) • Non-HCT: treatment of HIV-1 pts. (Phase I; NCT00477321; NCT01190111, NCT01241643) • Idiopathic CD4 lymphocytopenia (21 pts.; Phase I/II, completed, NCT00839436, published). The gene discussed is CD4; the disease is lymphopenia.