Long-term persistence of oligoclonal serum IgM repertoires in patients treated with allogeneic bone marrow transplantation (BMT).

Immunoglobulin gene rearrangements in patients treated with BMT have restricted repertoire diversity. Clonal variability remains low for 3 months and reconstitution of the humoral immune system appears to follow a wave-like pattern. In the present study we analysed serum IgM and IgG repertoires in 44 patients from 1 week to 3 years after transplantation. We applied a quantitative immunoblot technique in combination with a newly developed method for estimation of repertoire diversity in complex mixtures of antibodies. Our results demonstrate that 60% of BMT patients have severely reduced diversity in the IgM repertoire during and after the first year post-BMT, compared with healthy controls. In contrast, the majority of patients have a polyclonal IgG repertoire, similar to that of healthy controls. Serum IgM repertoires remain oligoclonal even though the serum concentration of total IgM is within normal range around 6 months post-BMT. During the first years after transplantation IgM as well as IgG repertoires are less diverse in patients receiving a BM graft from a sibling donor compared with those receiving a graft from an HLA-matched unrelated donor. Patients in the latter group show a higher incidence of infections and minor antigen mismatches which may promote the development of a diverse immunoglobulin repertoire post-BMT.