Tumor-promoting phorbol esters selectively abrogate the expression of the T4 differentiation antigen expressed on normal and malignant (Sézary) T helper lymphocytes.

12-O-tetradecanoylphorbol-13-acetate (TPA) selectively abrogates, in nanomolar concentrations, the expression of the T4 differentiation antigen, as defined by the monoclonal anti-T4 antibody (1) on Il-2-producing T helper lymphocytes from normal donors and on T helper lymphocytes from a patient with malignant T cell lymphoma (Sézary's syndrome); this compound does not affect the expression of cell surface antigens as defined by the antibodies anti-OKT3, -T6, -T8, -T11, Ia, or anti-surface immunoglobulin. Abrogation of the T4 antigen expression is concentration dependent, completed within 8 h of incubation at 37 degrees C, does not occur at 4 degrees C, and is reversible. Only those phorbol-esters known to have tumor-promoting activity in vivo (2) affect the T4 antigen, whereas nonpromoting compounds are ineffective.