Humoral immunodeficiency in patients after bone marrow transplantation.

Ex vivo IgG production was determined in 17 children and adolescents and in 14 adult patients between 10 months and 6 years after BMT. Twenty-four patients received allogeneic transplants. Seven patients were transplanted with autografts. Seven patients received immunosuppressive therapy. B cells were purified by positive selection with a CD20 antibody. After IL-2 or IL-10 stimulation, IgG production of SAC-preactivated B cells in patients with immunosuppression (median/range: 11/4-15 ng/ml or 14210-29 ng/ml) was significantly reduced compared with patients receiving allogenic (30/3-860 ng/ml or 33/2-3431 ng/ml; P < 0.01) or autologous transplants (75/7-1431 ng/ml or 269-/7-13600 ng/ml, P < 0.01). In 14/31 patients ex vivo IgG production was defective. Investigations of B cell function in patients with defective IgG production was performed significantly earlier after BMT compared with patients with normal IgG production ex vivo (2 +/- 1 years vs 3.3 +/- 1.5 years; P < 0.05). In addition, only patients with a B cell deficiency received immunosuppression. However, patients ex vivo IgG produced by B cells was decreased, but IgG production/sIgG+ B cells was within range of healthy volunteers. The number of IgG-committed B cells in these patients was significantly reduced compared to patients without deficiency (23/19-45/microliter vs 100/14-336/microliter; P < 0.05), indicating an in vivo switching defect. Although IL-10 is known to induce IgG-isotype switching in vitro, production of IL-10 by anti-CD3 activated MNCs obtained from patients with a switching defect did not differ from patients without B cell defects (1699/400-2662 pg/ml vs 724-112-1826 pg/ml). In nine patients IgG production and IgG production/sIgG+ B cells were impaired. The number of sIgG+ B cells was not decreased compared with patients without B cell deficiency (115/18-288/microliter), indicating a defective terminal differentiation of IgG-committed B cells to plasma cells. Although autocrine IL-6 is essential for plasma cell formation of isotype-determined B cells, it was comparable in patients with a terminal deficiency and without deficiency (3838/583-5967 pg/ml vs 2423/1643-6184 pg/ml). However, IL-10 production by anti-CD3 activated MNCs in patients with a terminal B cell defect (426/54-2262 pg/ml, P < 0.05) was significantly lower than in patients without deficiency, indicating a deviant cytokine production by T cells which might in part account for the B cell defect. Defective isotype switching as well as impaired terminal differentiation of B cells were found. Further analysis of factors regulating isotype-switching in vivo as well as cytokine receptor expression or signalling processes of differentiation factors in activated B cells might help to characterize the nature of these B cell deficiencies after BMT.