Reconstitution of the B cell repertoire after bone marrow transplantation does not recapitulate human fetal development.

Immune reconstitution during bone marrow transplantation has been proposed to produce a fetal-type immune system. This characteristic may contribute to the relative immunodeficiency that occurs in the early post-transplant period. This review reappraises recent studies of immunoglobulin heavy chain genes produced by the recovering immune system. Comparison of these genes to those that are generated by fetal and adult B cells, demonstrates that there is no evidence to support the conclusion that adult lymphocytes in the graft reverse to a fetal stage of differentiation. In terms of lymphocyte diversity, the inadequacy of the recovering immune system is more likely to be explained by a combination of other factors - such as the delayed occurrence of somatic hypermutation and class switching, and clonal dominance.