Human T cell antigens defined by monoclonal antibodies: the 65,000-dalton antigen of T cells (T65) is also found on chronic lymphocytic leukemia cells bearing surface immunoglobulin.

Peripheral blood lymphocytes from 15 patients with chronic lymphocytic leukemia (CLL), four patients with lymphosarcoma cell leukemia (LCL), four patients with hairy cell leukemia, and three patients with a monoclonal gammopathy (two with IgM, one with IgA) were tested for reactivity with the anti-T cell monoclonal antibody, T101. By immunofluorescent staining, all of the patients had circulating monoclonal surface Ig+ (sIg+) lymphocytes except for three CLL patients whose leukemia cells were sIg-. The leukemia cells of all of the sIg+ CLL cases were reactive with T101 antibody by indirect immunofluorescence; however, the abnormal cells in all of the remaining cases were unreactive. Reactivity of sIg+ CLL cells with T101 was confirmed by a radioactive binding assay, absorption analysis, and complement-dependent cytotoxicity. Moreover, a 65,000-dalton protein (T65), similar to that found on T cells, was precipitated by T101 antibody from the surface of sIg+ CLL cells. The fluorescent staining of sIg+ CLL cells by T101 antibody was weak as was the staining of the sIg. This was in contrast to the LCL cells, which had intense staining sIg and absence of staining with T101 antibody. These data demonstrate the existence of two major subtypes of CLL that have phenotypes sIg+ and T101+ and sIg-T101-. The implication of the finding of dual T and B markers on the major type of CLL, but not other B cell malignancies is discussed.