The cytokine receptor common gamma chain mutation in X-linked SCID results
in a failure of T and NK cell development and an as yet undefined defect of
B cells. Using immunoglobulin isotype-specific reverse transcription-PCR w
e show that although hematopoietic stem cell transplantation restores a div
erse repertoire of class-switched B cell clones, on further analysis these
are almost all of donor origin. This suggests that host B cells, which pred
ominate after unconditioned transplantation, are still defective even in th
e presence of normal T cells. These studies imply that effective humoral re
constitution can only be achieved by the engraftment of normal donor B cell
s.