A 7-month-old boy has had multiple bouts of otitis media, sinusitis, bronchitis, oral candidiasis, and multiple viral infections. Cessation of the recurrent infections follows successful engraftment of a bone marrow transplant. The basis of the clinical improvement is

Severe combined immunodeficiency disease(SCID) Characterized by failure to thrive and increased susceptibility to bacterial, fungal, and viral infections. Laboratory studies reveal decreased numbers of both B cells and T cells and deficiency of immunoglobulins. The treatment of choice is bone marrow (or other sources of hematopoietic stem cells) transplantation and is based on maturation of donor lymphoid progenitor cells