An extract of seeds from Aeginetia indica L., a parasitic plant, induces potent antigen-specific antitumor immunity in Meth A-bearing BALB/c mice.
The antitumor activity of an extract of seeds from Aeginetia indica L., a parasitic plant, was investigated. BALB/c mice, inoculated i.p. 1 x 10(5) syngeneic Meth A tumor cells, were administered 2.5 mg/kg A. indica extract i.p. every 2 days from day 0. The untreated mice died of an ascitic form of tumor growth within 21 days, whereas all the treated mice completely recovered from tumor challenge without any side-effects. The extract did not exert direct cytotoxic activity against Meth A in vitro. Mice that survived after the first challenge as a result of A. indica treatment overcame the rechallenge with homologous Meth A without additional administration of the extract. On the other hand, those mice could not survive after rechallenge with Meth 1 tumor cells, which were also established in BALB/c mice but were different in antigenicity from Meth A, suggesting the development of antigen-specific concomitant immunity in the A. indica-cured mice. In the induction phase of antitumor resistance in this system, CD4+ T cells appeared to be the main contributors, since in vivo administration of anti-CD4 mAb completely abolished such resistance. In contrast, anti-CD8 mAb administration did not influence the effect of A. indica. The importance of CD4+ T cells in antitumor immunity was again clarified by Winn assay; that is, spleen and lymph node cells depleted of CD4+ T cells in vitro prior to assay abolished antitumor activity on co-grafted Meth A tumor cells in vivo.