Structural characterization of the human T cell surface antigen (p67) isolated from normal and neoplastic lymphocytes.

Abstract

Abstract A 67,000-dalton glycoprotein (p67) on normal and neoplastic T cells is defined by reactivity with a monoclonal antibody (antibody SC1 ) derived against human T chronic lymphocytic leukemia (T-CLL) cells. This antigen is present on greater than 90% of normal thymocytes, normal peripheral blood (PBL) T cells, T acute lymphoblastic leukemia (T-ALL), T-CLL, and B cell chronic lymphocytic leukemia (B-CLL). It is absent from normal B cells, B cell lines, myeloid cells, and stem cell precursors. By using immunoprecipitation of 125I-labeled glycoproteins and chymotrypsin digestion, the peptide maps of p67 from normal and leukemic lymphocytes revealed that the antigen is highly related among these cell sources, but at least two major forms of the molecule could be identified. One form was prevalent on the T-ALL-derived cell line 8402 and a second form on cell line HPB-T ALL. Peptide maps of PBL from a normal patient, from a T-ALL patient, and from a B-CLL patient were similar to HPB-T ALL cells. In addition to the two major forms of p67, subtle shifts in certain peptides were noted in lymphocytes from each source. The peptide fingerprints of p67 were similar to those obtained from murine Lyt-1 antigen, suggesting possible homology, and were distinctly different from those of murine gp70. Sequential immunoprecipitation experiments verified that the p67 antigen is carried on the same molecule recognized by other independently derived monoclonal antibodies including SC1, L1F12, T101, and OKT1. Cross-blocking experiments indicated that preincubation with antibody L17F12 or T101, but not OKT1, could block subsequent binding of biotin-conjugated antibody SC1. Thus, four of five monoclonal antibodies derived by separate immunizations recognize identical or closely located antigenic sites on p67.