Role of cellular density, in vitro, in anti-tumor activity of CFA-treated and immunized cells.

Incorporation of tritiated deoxythymidine (3HdT) into DNA was used to measure growth, in vitro, of P815 tumor cells admixed with spleen and peritoneal effector cells. At a high tumor cell density ((1x10(5) cells per dish), using anti-theta and anti-macrophage sera, T-cells and macrophages from the peritoneum of immunized mice could be identified as cells possessing anti-tumor activity. A nonspecific inhibition by normal effector cells, which occurred at the high tumor cell density, did not occur at a lower tumor cell density (1x10(4) cells per dish). Therefore, the effects of immunization and Freund's adjuvant treatment on the anti-tumor activity of effector cells were determined more accurately when normal cells were no longer inhibitory. Thus, experimental variables dealing with cellular density (cells/mm2 of the culture vessel surface) and effector:tumor cell ratios play an important role in the anti-proliferative capacity of effector cells.