Regeneration of T cell subpopulations after bone marrow transplantation: cytomegalovirus infection and lymphoid subset imbalance.

Immune reconstitution was studied serially by using T lymphocyte cell surface differentiation antigens in 37 individuals receiving bone marrow transplants. Antigen expression was assessed by immunofluorescence analysis using monoclonal antibodies to T lymphocytes including Leu-3, which defines a T lymphocyte subpopulation in healthy individuals with T helper or inducer activity (L3+), and Leu-2, which defines a T lymphocyte subpopulation in healthy individuals with T helper or inducer activity (L3+), and Leu-2, which defines a T lymphocyte subpopulation with suppressor or cytotoxic activity (L2+). These studies demonstrated that the L2+ subpopulation regenerated more rapidly after transplant than did the L3+ subpopulation. Imbalances between these two T lymphocyte subpopulations, indicated by a decreased L3/L2 ratio, persisted for periods up to 12 mo post-transplant. Expression of a cell surface antigen associated with immature lymphocytes (OKT-10), and of HLA-DR (Ia-like) antigens was markedly increased during the post-transplant period. HLA-DR antigen expression did not appear related to immune activation in that increased reactivity was not detected with a monoclonal antibody (anti-TAC) specific for activated T cells. These observations in bone marrow transplant recipients and other disorders characterized by lymphoid restoration or immaturity indicate that inversion of the normal L3/L2 ratio and increased expression of OKT-10 and HLA-DR antigens may be features of a regenerating immune system. Furthermore, serial observation of individual patients indicated that infection with cytomegalovirus was associated with a progressive decrease in the L3/L2 ratio.