T cell subpopulations defined by monoclonal antibodies after HLA-identical sibling marrow transplantation. II. Activated and functional subsets of helper-inducer and cytotoxic-suppressor subpopulations defined by two-colour fluorescence flow cytometry.

Two-colour fluorescence flow cytometry was utilized to define subsets within the Leu-3+ (T4+) helper-inducer and the Leu-2+ (T8+) cytotoxic-suppressor T cell subpopulations in recipients of unmanipulated HLA-identical sibling bone marrow transplants. The absolute number of activated cytotoxic-suppressor T cells expressing the HLA-DR and OKT10 activation antigens was increased. The proportion (or relative number) of cells bearing each of these activation antigens was also elevated in both the Leu-2+ and the Leu-3+ subpopulations, with up to 60% of Leu-2+ cells and up to 40% of Leu-3+ cells expressing them. Interestingly, absolute numbers of cells expressing two other activation-associated antigens, the interleukin-2 (IL-2) and transferrin receptors, were not increased in either major T cell subpopulation, although the relative number of Leu-3+ cells expressing both these surface structures was increased early post-transplant. Three putative functional subsets were also enumerated: the Leu-3+, Leu-8+ suppressor-inducer subset was depressed in absolute and relative numbers at most time points post-transplant. The Leu-4+, Leu-15+ suppressor-effector subset subpopulation was normal at all time points posttransplant, while the Leu-2+, 9.3+ cytotoxic precursor subset showed low relative and absolute numbers both early and late post-transplant. None of the abnormalities demonstrated in the present study was correlated with presence or absence of graft-versus-host disease. The study further demonstrates the heterogeneity of the abnormalities in the immune system after human marrow transplantation and lays the basis for functional studies involving these cell populations.