[B-cell content after bone marrow transplantation--molecular basis of the limited antibody diversity]

Despite B-cell counts and serum immunoglobulin levels usually normalized by one year, humoral immunity and the incidence of bacterial infections continue to be abnormal even after years following bone marrow transplantation. This immunodeficiency could be partially caused by B-cell repertoire restriction similar to that observed early in ontogeny. Immune reconstitution after haematopoietic stem cell transplantation really follows many established ontogenetic patterns relating to the appearance of particular membrane markers, immunoglobulin classes and subclasses, and onset of antigen receptor rearrangements. The sequence of events that occur during successful bone marrow transplantation can be regarded as a blueprint for immune reconstitution in other clinical settings as well. However, the repertoire does not resemble a fetal one, because it displays adult-size IgH CDR3s, adult-type immunoglobulin gene utilization and no evidence of bias towards any particular VH-gen family. Therefore, in the description and interpretation of these events, it is important to realize that immune reconstitution does not appear to recapitulate human fetal ontogeny. In terms of B lymphocyte diversity, the inadequacy of the recovering immune system is more likely to be explained by a combination of other factors--such as clonal dominance and the delayed occurrence of somatic hypermutation.