TUMOR IMMUNOLOGY

Malignant tumors express antigens that may stimulate and serve as targ ets for antitumor immunity. Virally induced tumors usually contain int egrated proviral genomes in their cellular genomes and often express v iral genome-encoded proteins that may stimulate specific host immune r esponses. Antigens unique to individual tumors that stimulate specific rejection of transplanted tumors have been demonstrated only in exper imental animals. Other tumor antigens that potentially can stimulate i mmune responses are shared by different tumors. These include products of mutated or rearranged oncogenes or tumor-suppressor genes. Tumors may also overexpress tissue differentiation antigens or embryonic anti gens, which also have the potential to be recognized by the immune sys tem. The recent identification of tumor antigens recognized by cytotox ic T cells opens up new possibilities for constructing chemically defi ned antigens for specific immunotherapy. Treatment of malignant tumors in humans by immunologic approaches, although theoretically attractiv e, has not yet succeeded on a large scale. Important progress in immun otherapy of cancer is emerging with several different treatment modali ties.