Suppressor cells: Permitters and promoters of malignancy?

This chapter discusses the relationships between suppressor cells and tumors. It describes the data that demonstrate the augmentation of antitumor responses in experimental immunocrippled animals (adult thyniectomized, splenectomized, X-irradiated, or antithymocyte serum (ATS)-injected animals). Most of these experiments were performed before the recognition of the function of suppressor cells. The chapter presents the more direct experimental evidence showing the effect of specific and nonspecific suppressor cells on the relationships between the tumor and the host immune system. For the most part, the effects of suppressor cells on syngeneic tumors, and occasionally on the so-called nonspecific tumor cells, are discussed. Nonspecific neoplastic cells cannot stimulate a detectable allogeneic immune response after inoculation into an allogeneic host and they can grow progressively in such an environment. The suppressor cells are classified arbitrarily into permitter suppressor cells—which populate the host before its confrontation with the tumor and promoter suppressor cells—which are induced by the tumor. The chapter also describes the chemical, physical, and biological properties of some of these suppressor cells and offers various means for their selective elimination.