Imbalance of T-cell subpopulations and defective pokeweed mitogen-induced B-cell differentiation after bone marrow transplantation in man

Peripheral blood T-cell subpopulations were studied in eight patients undergoing bone marrow transplantation (BMT) for severe aplastic anemia (SAA) or acute leukemia (AL). Seven received an allogeneic graft and one a syngeneic graft: seven showed clinical and pathological signs of graft versus host disease (GvHD) and a marked imbalance in T-cell subpopulations. In spite of normal numbers of circulating unfractionated T cells, T lymphocytes with receptors for IgG (T_G cells) were increased 2- to 5-fold, whereas T cells with receptors for IgM (T_M cells) showed a 2- to 20-fold decrease. The T_M-T_G imbalance paralleled the development of GvHD. The patient who received the syngeneic graft showed no T_M-T_G imbalance and no signs of GvHD. In addition pokeweed mitogen (PWM)-induced B-cell differentiation in vitro was severely impaired in these patients in the presence of either autologous or normal allogeneic T cells. Patients' T cells did not provide adequate help for autologous or normal B cells either in the presence or absence of T_G cells. The patients' purified T_G cells were capable of suppressing normal B-cell responses to PWM but to a lesser degree than normal T_G cells. The imbalance of T-cell subpopulations with defective helper activity and the impaired B-cell function may play an important role in the development of immunodeficiency after bone marrow transplantation and particularly during GvHD.