Interferon-alpha can alter the lytic susceptibility of murine bladder transitional cell carcinoma (MBT-2) by their original poor specific cytotoxic tumor infiltrating lymphocytes.

Fresh isolated or short term in vitro cultured tumor infiltrating lymphocytes derived from MBT-2 tumor possess little specific cytotoxicity on MBT-2 cells despite the presence of low (10 units/ml.), moderate (500 units/ml.), or high (1000 units/ml.) dose interleukin-2 and irradiated tumor cells; however the lytic susceptibility of the MBT-2 cells and their expression of MHC class I antigen can be significantly enhanced if the tumor cells are preincubated with interferon-alpha for 24 hours. But the specific antitumor activity of tumor infiltrating lymphocytes cannot be further augmented by coculturing them with irradiated interferon-alpha pretreated MBT-2 tumor cells. In vivo experiments by subcutaneous peritumor injection of interferon-alpha (500 units/ml.) combined with interleukin-2 (500 units/ml.) can suppress the tumor growth of those three-day inoculated MBT-2 cells significantly but not on those already established tiny tumors. We therefore concluded that interferon-alpha can alter the specific antitumor activity of tumor infiltrating lymphocytes chiefly through its modulating effect on the target tumor cells instead of the tumor infiltrating lymphocytes.