T-CELL GROWTH-PROMOTING ACTIVITY OF INTERFERON-GAMMA - MITOGENIC EFFECT OF THE RECOMBINANT CYTOKINE ON CELLS FROM A HUMAN T-CHRONIC LYMPHOCYTIC-LEUKEMIA

Interferon-gamma (IFN-gamma) has previously been described as exerting a growth factor activity for murine and human stimulated normal T lym phocytes, in addition to its established role in regulating the cytoto xic activity of T and NK cells. We analyzed the effect of human recomb inant IFN-gamma on the proliferation of leukemic lymphocytes isolated from the peripheral blood of a patient affected by a T-cell chronic ly mphocytic leukemia (T-CLL). Incubation with IFN-gamma induced the prol iferation of unstimulated leukemic cells. Cell proliferation was maxim al after 6 days of culture with the cytokine; the half-maximal effect of IFN-gamma was observed at a concentration of approximately 800 U/ml . We also measured the production of IFN-gamma by leukemic cells. Cell s incubated in control medium released small quantities of IFN-gamma a ctivity, while the addition of low doses of the exogenous cytokine to the cell cultures induced high levels of IFN-gamma mRNA and protein pr oduction. Furthermore, anti-HLA class I monoclonal antibodies, that ex ert a mitogenic effect on these neoplastic lymphocytes, also induced t he IFN-gamma gene expression in the same cells. These results indicate that IFN-gamma may stimulate the proliferation of human neoplastic T cells and suggest that this cytokine might have a role in the expansio n of T-leukemic cell clones in vivo.