RESUMEN
A neonate was diagnosed as having SCID from his umbilical cord blood cells immediately after birth because his older brother had died of SCID eight months earlier. One locus-mismatched unrelated umbilical cord blood cell transplantation without conditioning was performed at the age of 30 days. The CD3-positive cells were detected on day 14 post-transplantation. There were no peri-transplantation complications. Four yr after transplantation, the boy is in excellent condition and T and NK cell engraftments are complete. His peripheral B cells with a common gamma chain were not detected by flow cytometry, and he still needs IgG replacement; however, his IgM and IgA levels have gradually increased, and the dosage of IVIG per body weight has gradually decreased. We speculate that the very few B cells that proliferate from transplanted cord blood cells produce gamma globulin. Unrelated cord blood cell transplantation, even though mismatched, without conditioning would be a treatment option for neonates with severe combined immunodeficiency.