The role of serum factors in the acceleration by Freund's complete adjuvant of the growth of transplanted murine leukemic cells

Attempted nonspecific immunotherapy led to acceleration rather than retardation of tumor growth. Mice given injections of Freund's adjuvant were more susceptible to transplanted syngeneic Gross virus-induced leukemic cells when Freund's complete adjuvant was administered i.p. 0 to 7 days before or 1 day after tumor; thereafter, the adjuvant had no effect. Two serum-mediated phenomeana were demonstrated in vitro: (a) sera from mice immunized with Freund's complete adjuvant and tumor facilitated killing of tumor cells by peritoneal exudate cells from nonimmune mice; (b) sera from all mice with progressive tumor blocked the cytotoxicity of a xenogeneic tumor-specific serum. Certain sera produced both effects. However, sera that either blocked or facilitated tumor killing in vitro had no effect on the growth in vivo of transplanted tumor cells.