Antigenic Entities of the Tumor That Induce Suppressor Cells May Prevent the Potentiation of Coexpressed Immunogenic Entities

The apparent inactivity of the immune system in the face of antigenic stimuli delivered by tumor cells appearing spontaneously in man and animal, has been used as a major argument against the immune surveillance hypothesis (219), claiming that malignant transformation is continuously regulated by immunocompetent cells (220). The lack of an immune response against a spontaneous tumor does not, however, negate the possibility that the tumor antigens can, under the right circumstances, induce an immune response. As an example, tumors may express both moieties that induce suppressor cells (suppressogenic entities) and those that induce immune cells (immunogenic entities). The resultant dominant function of the suppressor cells may result in a restraint of the immune response against the tumor. If this conception is correct, we may consider the possibility of blocking or altering the suppressogenic moieties, thus preventing their function and allowing the other entities to express their immunogenicity. This concept has been considered in a previous review written by one of us (7); as a result, we shall discuss this issue briefly, referring only to new findings.