Bone marrow transplantation in children with severe aplastic anemia: reconstitution of cellular immunity.

Cellular immune functions were evaluated longitudinally in seven children with severe aplastic anemia, who were successfully transplanted with bone marrow cells from an HLA-identical, mixed lymphocyte culture (MLC)-negative sibling. Several parameters were followed: the number of lymphocytes and E rosette-forming cells in the peripheral blood and the lymphocyte reactivity toward various mitogens, antigens, and allogeneic lymphocytes. Some patients already displayed decreased in vitro lymphocyte reactivity before transplantation, especially with regard to the response to pokeweed mitogen (PWM). After transplantation, a severe cellular immunodeficiency developed in all patients, with low numbers of T cells and markedly impaired responsiveness to mitogens, antigens, and allogeneic lymphocytes. Variations between patients were substantial, both with regard to the severity and duration of the immunodeficiency and to the pattern of the recovery of lymphocyte responses to mitogens and antigens. This variability might be attributable to an imbalanced proliferation of different lymphocyte subsets and/or the sequence of appearance of receptors for mitogens on the cell surface.