Nonspecific antigen reactions. 
Cell-mediated immune challenge reactions to a number of antigens at tumor sites resulted in regressions of various types of benign, premalignant, and malignant lesions in man.  Regressions varied from partial to complete and lasted from several months to more than 10 years.  Increased levels of cell-mediated immunocompetence were attained by several means, including reduction of tumor burden, immunopotentiation, or transfer of immunity.  Antitumor activities of immune challenge reactions are selective for tumor cells and appear to be independent of the nature of the antigens used or the type of neoplasm.  Combinations of immunotherapy with other treatment modalities resulted in augmentation of antitumor effects.  Preliminary studies indicate that cellular and noncellular mediators of delayed hypersensitivity induce antitumor activities that may be significant in the regressions of neoplasms induced by cell-mediated immune challenge reactions.  Since cell-mediated immune reactions are frequent occurrences, they may be a factor in apparently spontaneous regressions of neoplasms.