A Monoclonal Antibody with Selective Reactivity with Functionally Mature Human Thymocytes and All Peripheral Human T Cells

Abstract A monoclonal antibody directed at a determinant on human peripheral blood T cells was produced and characterized. This hybridoma antibody, termed OKT1, was reactive by indirect immunofluorescence with the entire human peripheral blood T cell population and a subset of human thymocytes. In contrast, OKT1 was unreactive with normal B cells, Null cells, macrophages, and ≥90% of human thymocytes. These findings suggested that OKT1 defines a mature T cell differentiation antigen. In support of this notion was the observation that T cell acute lymphoblastic leukemia cells were nonreactive with OKT1, whereas T cell chronic lymphocytic leukemia cells were reactive. Concomitant functional studies on FACS-separated lymphocytes showed that the T cell proliferative responses to mitogens and soluble and cell surface antigens were contained in the OKT1+ population. Fractionation of peripheral blood T cells into strongly and weakly reactive OKT1+ subgroups uncovered no functional T cell heterogeneity. In addition, when the thymocyte population was separated into OKT1+ and OKT1- subsets, only the OKT1+ thymocytes were MLC responsive. However, unlike peripheral T cells, neither the OKT1+ or OKT1- thymocytes proliferated to the mitogens PHA and Con A. Thus, OKT1+ thymocytes are functionally distinct from OKT1+ peripheral blood T cells. These studies show that a hybridoma antibody can be produced that detects a human differentiation antigen that appears during late intrathymic T cell ontogeny and persists on peripheral T cells.