Abstract
Human Nude/SCID (severe combined immunodeficiency) is the first severe combined immunodeficiency caused by mutation of the winged–helix–nude (WHN) gene, which is expressed in the thymus but not in the hematopoietic lineage. The disease is characterized by a T-cell defect, congenital alopecia, and nail dystrophy. A Nude/SCID patient who underwent bone marrow transplantation from the human leukocyte antigen–identical heterozygote brother was studied to investigate, in this unique model, the role of the thymus in immunologic reconstitution. Despite an increase in CD3+, CD4+, and CD8+cells, CD4+ CD45 RA naive lymphocytes were not regenerated. Conversely, naive CD8+ cells were normal. After an initial recovery, lymphocyte proliferation to mitogens progressively declined compared with controls and genotypically identical donor cells grown in the WHN+/−environment. Analysis of the T-cell receptor (TCR) repertoire of CD4+ cells revealed that only 3 of 18 Vβ families had an altered CDR3 heterogeneity length profile. Conversely, CD8+lymphocytes showed an abnormal distribution in most Vβ families. These data indicate that the thymus is differentially required in the reconstitution of CD4+ and CD8+ naive subsets and in the maintenance of their TCR repertoire complexity. Taken together, these findings suggest that bone marrow transplantation is ineffective in the long-term cure of this form of SCID.
