Induction of Human T Colony Formation by Phorbol Myristate Acetate

Phorbol myristate acetate (PMA) is a potent inducer of T colony formation by peripheral blood lymphocytes. A mean cloning efficiency of 0.3% (0.05‐0.5%) is obtained with PMA concentrations of 100‐1000 ng/ml. PMA‐induced T colony formation does not require the presence of monocytes and therefore differs from other mitogens in this respect. Purified T‐colony‐promoting activity (TCPA) (devoid of phytohaemagglutinin (PHA)) increases PMA‐induced T colony numbers and induces T colony formation at low PMA doses (0.01 to 1 ng), concentrations at which no T colonies are detected in the absence of added TCPA. PMA‐induced colonies are mainly composed of cells bearing Fc receptors for IgM (54%), which is not the case for colonies obtained with PHA (11 %). PMA‐induced colony cells do not bind OKT3 and OKT4 monoclonal antibodies, whereas 23% are able to bind OK‐T8 antibody. These results demonstrate that PMA is a potent inducer of T colony formation and may therefore serve as a useful tool for the study of T‐cell differentiation.