Induction of antitumor immunity by tumor cells treated with abrin

Abrin is known as a cytotoxic lectin. Immunization with Meth-A tumor cells which were treated in vitro with abrin induced a strong antitumor immunity in syngeneic BALB/c mice. The immunizing effect was stronger than that produced by an irradiated Meth-A tumor cell vaccine. Studies on the mechanisms of the immunizing effect with the abrin-treated tumor cells demonstrated that abrin acts as an immunoadjuvant. Furthermore, the regression of a growing Meth-A tumor was observed after abrin was injected into the tumor, while the induction of a strong antitumor immunity also occurred. It appears, therefore, that the antitumor effects of abrin are attributable to two kinds of activity: cytotoxicity and adjuvant activity.