Abrogation of tumor rejection by trypan blue.

Trypan blue treatment prevented tumor-specific rejection in three animal model systems. These included the spontaneous rejection of tumors of mice (UVT-2051) and guinea pig (line 1 hepatoma) as well as vaccine-induced rejection of a guinea pig tumor (line 10 hepatoma). Secondary immune reactions to line 10 cell challenges were not abolished by trypan blue treatment. Although trypan blue is a potent inhibitor of macrophage cytotoxicity in vitro, the mechanism by which it inhibited tumor-specific rejection has not been established.