Immune response of mice in immunotherapy of tumors with syngeneic antitumor serum plus lipopolysaccharide.

Humoral and cellular immune responses were investigated after combination therapy with syngeneic antitumor serum and bacterial lipopolysaccharide (LPS). The titer of antitumor antibody determined by using a macrophage-mediated system was very high in mice cured by the combination therapy, and this high titer lasted for a long time. In contrast, no significant titer was detected using an antibody-dependent lymphocyte-mediated system. Thus, antibody-dependent macrophage-mediated cytolysis was a more sensitive method for detecting antitumor antibody. The cellular immune response was measured as the delayed hypersensitivity reaction to tumor cells. In mice that had been cured by combination therapy, this reaction appeared at an early stage, before any antitumor antibody was detectable, but it soon decreased. On the other hand, tumor-bearing mice showed a low level of antibody and no significant delayed hypersensitivity reaction.