Comparative density of the human T-cell antigen T65 on normal peripheral blood T cells and chronic lymphocytic leukemia cells

A 65,000 dalton T-cell specific antigen previously demonstrated to be present on the surface of normal and malignant T cells, but not normal B cells, has been detected on the surface of leukemic cells from patients wih nonsecretory, surface immunoglobulin-positive chronic lymphocytic leukemia (CLL). By means of immunofluorescence and flow cytometry, the relative surface density of the T65 antigen on CLL cells was compared to that on normal peripheral blood T cells and human thymocytes, as well as cell lines of T-cell lineage. In all cases, the CLL cells had a more homogeneous and a lower median fluorescence intensity than that of normal circulating T cells. Thymocytes were composed of three populations, two with low surface density of T65 resembling the CLL cells and the other with higher density similar to normal T cells. The staining of cell lines varied from bright, heterogeneous staining (8402) to uniform, low-density staining (Molt- 4). The implications of these findings with regard to lymphocyte differentiation are discussed.