Immune Stimulation-Inhibition of Experimental Cancer Metastasis1

The interaction of normal, tumor-bearing, nonspecifically sensitized, and immunized syngeneic lymphocytes and the B16 melanoma was tested in vivo by experimental pulmo nary métastases. Various numbers of lymphocytes were mixed and incu bated with the tumor cells for 90 min on a rotating platform, and then the mixtures were injected i.v. into C57BL/6 mice. Normal, tumor-bearing, and nonspecifically sensitized lym phocytes mixed with tumor cells significantly increased the incidence of experimental metastasis. On the other hand, a high number (5000:1) of immunized syngeneic lympho cytes mixed with the B16 melanoma cells brought about a dramatic decrease in the incidence of subsequent pulmonary métastases. Following the in vitro incubation of tumor cells with syngeneic lymphocytes, clumping of tumor cells was observed. The relative importance of this clumping phenom enon to the outcome of experimental metastasis is dis cussed. Mice that were either immunized against the B16 mela noma or thymectomized and X-irradiated demonstrated a significant decrease in incidence of experimental pulmonary metastasis following i.v. injection of tumor cells as com pared to normal, thymectomized. or X-irradiated mice. The decrease in pulmonary métastasesin thymectomized Xirradiated mice was completely reversible with i.v. injection of 1 x IO7syngeneic tumor-bearing lymphocytes adminis