Engrafted maternal T cells in human severe combined immunodeficiency: evidence for a TH2 phenotype and a potential role of apoptosis on the restriction of T-cell receptor variable beta repertoire.

Engraftment of transplacentally derived maternal T lymphocytes in infants with severe combined immuno- deficiency (SCID) is caused by lack of rejection of the HLA-mismatched maternal T cells by the recipient’s immune system. Although the engrafted T cells express surface activation markers, they are anergic.1 Restriction of T-cell receptor variable (TCRV-) segment use has been demonstrated in engrafted maternal T cells,2, 3 but it remains to be explained how it occurs. The high IgE levels and eosinophilia typical of Omenn’s syndrome, a SCID characterized by the emergence of a limited number of autoreactive endog- enous T-cell clones, has been attributed to the TH2 phenotype of these cells.4 However, little is known about the TH phenotype of engrafted maternal T cells in other patients with SCID with elevated serum IgE levels and eosinophilia. In one such patient described here, the engrafted maternal T cells had a predomi- nantly TH2 phenotype and a restricted pattern of TCRV-beta gene use. In addition, evidence was obtained suggesting that the latter phenomenon might result from apoptosis.