Immunosuppressive factor derived from renal cancer cells.

An immunosuppressive factor derived from conditioned medium of a human renal cancer cell line, KU2, was analyzed, using mitogen-activated normal peripheral blood lymphocytes. Addition of conditioned medium to lymphocyte cultures resulted in suppression of [3H]-thymidine incorporation to DNA of lymphocytes in a dose-dependent manner. This effect was cytostatic and reversible. This factor inhibited lymphocyte activation stimulated by mitogen at an early stage, and it also suppressed Interleukin-2 production by activated lymphocytes. This factor was non-dialyzable and heat sensitive at 56 degrees C. DNA replication of the cells was necessary for the production of this factor.