A monoclonal antibody detecting a novel antigen expressed in the HTLV-I-infected cells.

A monoclonal antibody, FTF 148, was prepared by hybridizing murine myelomal cells (NS-1) and spleen cells of BALB/c mice immunized with cultured cells derived from an adult T cell leukemia (ATL) patient (KUT-2 cells). This monoclonal antibody reacted with all of the human T cell leukemia virus I (HTLV-I)-infected cell lines tested but did not react with other T cell lines derived from acute lymphocytic leukemia, Epstein-Barr virus-transformed B cell lines, or an erythroleukemic cell line. This monoclonal antibody was not directed to viral antigens because it reacted equally well with almost all KUT-2 and MT-1 cells, only 1% to 3% of which were ATL-associated antigen-positive. In contrast to interleukin 2 receptors expressed on both ATL cells and normal phytohemagglutinin-stimulated blasts, this antigen was not expressed on the latter cells. The antigen, mainly expressed on the cell membrane, was analyzed by metabolic labeling with 3H-leucine and surface labeling with 125I followed by cell lysis and immunoprecipitation with the FTF 148 antibody. The findings obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that p50 and p74 proteins were specifically precipitated and the antigen was also different from the product of the Xs gene of HTLV-I.