Characterization of human lymphocyte subpopulations: Alloreactive cytotoxic T-lymphocyte precursor and effector cells are phenotypically distinct from Leu 2⁺ suppressor cells

The OKT8/Leu 2⁺ human T-cell subset contains cells which perform suppressor and cytotoxic functions. We have recently produced two monoclonal antibodies (termed 2D2 and D12) which define four subpopulations of human E⁺ cells. Previous studies have shown that the Leu 2⁺ cells that suppress T-cell proliferative responses have the 2D2⁺D12⁺ phenotype. In the present studies, we have used these antibodies and fluorescence-activated cell sorter techniques to characterize the phenotype of cytotoxic T lymphocytes generated in allogeneic mixed lymphocyte cultures. These studies indicate that the cytolytic effector cells which recognize class I major histocompatibility antigens express the 2D2⁺D12^- phenotype. The phenotype of the precursor cells for these cytotoxic T cells was similarly demonstrated to be 2D2⁺D12^-. The subset of E⁺ cells with NK cytolytic activity expressed the 2D2^-D12⁺ phenotype. These data demonstrate that the Leu 2⁺ precursor and effector cytotoxic T cells reactive against class I alloantigens are phenotypically distinct from the Leu 2⁺ cells previously shown to suppress T-cell proliferative responses.