[Immunosuppressive phenomena in experimental tumor systems (author's transl)].

During the growth of spontaneous or chemically-induced tumors in animals, it has been reported that T lymphocytes are present in the spleen and/or the thymus which are able (i) to specifically block tumor rejection by syngeneic immunized animals in in vivo transfer experiments, and (ii) to specifically inhibit the in vitro cell-mediated immune reactions. The relationship between both types of suppressor cells is unclear. On the other hand, mitogen insensitive cells, acting in vitro in a non specific way on normal cell mitosis and cell-mediated cytotoxicity induction, and having macrophage characteristics, are described in viral and non viral tumor bearing hosts as well as in non tumoral animals after hematopoietic hypoplasia. The various suppressor cells types and their possible mechanisms of action are discussed along with soluble factors when present in experimental tumor systems, but the role of these cells in tumor pathogenesis is not yet clear.