Immunosuppressive and immunizing activities in human tumor cell-free extract

Cell-free extracts (CFE) from cultured human tumor cells, when used to sensitize lymphocytes, were capable of inducing distinct lymphocyte-mediated cytotoxicity (LMC) at low dose and had relatively low or no activity at a high dose. The higher dose of CFE suppressed markedly the induction of LMC when added to the mixed lymphocyte tumor cell cultures. The ability to induce LMC was associated most with 10,000 g fractions. All fractions, 1,000, 20,000 and 100,000 g, were able to suppress the induction of LMC, but 100,000 g fractions had the most suppressive activity. The supernatants of 100,000 g fractions were only slightly suppressive. Lymphocytes activated with tumor cell fractions were also cytotoxic to K-562 cells.