Production of a mouse monoclonal antibody reactive with a human nuclear antigen associated with cell proliferation

The production of a mouse monoclonal antibody, Ki‐67, is described. The Ki‐67 antibody recognized a nuclear antigen present in proliferating cells, but absent in resting cells. Immunostainings with Ki‐67 revealed nuclear reactivity in cells of germinal centres of cortical follicles, cortical thymocytes, neck cells of gastrointestinal mucosa, un‐differentiated spermatogonia and cells of a number of human cell lines. The Ki‐67 antibody did not react with cells known to be in a resting stage, such as lymphocytes, monocytes, parietal cells and Paneth's cells of gastrointestinal mucosa, hepatocytes, renal cells, mature sperm cells, brain cells, etc. Expression of the antigen recognized by Ki‐67 could be induced in peripheral blood lymphocytes after stimulation with phytohaemagglutinin, whereas it disappeared from HL‐60 cells stimulated with phorbol esters to differentiate into mature macrophages in a resting stage. These findings suggest that Ki‐67 is directed against a nuclear antigen associated with cell proliferation. A first series of immunostainings of tumour biopsies indicated that Ki‐67 may be a potent tool for easy and quick evaluation of the proportion of proliferating cells in a tumour.