Incomplete T-cell immune reconstitution in two major histocompatibility complex class II-deficiency/bare lymphocyte syndrome patients after HLA-identical sibling bone marrow transplantation

To study the effects of major histocompatibility complex (MHC) class II exp ression on T-cell development, we have investigated T-cell immune reconstit ution in two MHC class II-deficiency patients after allogeneic bone marrow transplantation (allo-BMT). Our study showed that the induction of MHC clas s II antigen expression on BM graft-derived T cells in these allo-BMT recip ients was hampered upon T-cell activation. This reduction was most striking in the CD8(+) T-cell subset. Furthermore, the peripheral T-cell receptor ( TCR) repertoire in these graft-derived MHC class II-expressing CD4(+) and i n the CD8(+) T-cell fractions was found to be restricted on the basis of TC R complementarity determining region 3 (CDR3) size profiles. Interestingly, the T-cell immune response to tetanus toroid (TT) was found to be comparab le to that of the donor. However, when comparing recipient-derived TT-speci fic T cells with donor-derived T cells, differences were observed in TCR ge ne segment usage and in the hydropathicity index of the CDR3 regions. Toget her, these results reveal the impact of an environment lacking endogenous M HC class II on the development of the T-cell immune repertoire after allo-B MT. (C) 1999 by The American Society of Hematology.