Effect of unblocking therapy and levamisole on primary gastrointestinal tumors in rats: immunologic and histologic correlation.

The effect of multimodal immunotherapy was studied in WF rats bearing primary gastrointestinal (GI) tumors induced by 1,2-dimethylhydrazine dihydrochloride. The alterations induced in antitumor immune responses of the treated rats were studied in vitro and were correlated with tumor status in vivo. Multimodal immunotherapy consisted of unblocking serum, unblocked lymphoid cells, and levamisole. Such immunologic intervention resulted in significant inhibition of tumor growth, inhibition of metastases, and prolonged survival of the host. Serum blocking activity could be completely counteracted in 6 rats, all of which showed complete tumor regression. Of 20 rats, 8 showed inadequate counteraction of serum blocking activity and transient appearance of cytotoxic antibodies. All 8 rats showed marked tumor inhibition and prolonged survival. Six remaining rats succumbed from either GI or extra-GI tumors, although they survived significantly longer than untreated rats; these 6 rats had only transient counteraction of their serum blocking activity. All 20 tumors in 14 rats of the therapy group showed histologic evidence of tumor rejection. Our studies suggested that a complete counteraction of blocking activity in conjunction with methods capable of improving the specific and nonspecific immune competence of the host may be important to achieve optimal antitumor effects.