Effect of immunomodulation on the fate of tumor cells in the central nervous system and systemic organs of mice. Distribution of [125I]5-Iodo-2'-deoxyuridine-labeled KHT tumor cells after left intracardial injection.

The effect of systemic immunomodulation on tumor cell arrest and retention in the central nervous system was studied by following radioactively labeled tumor cells. KHT mouse sarcoma tumor cells were labeled in vitro with [125I]IdUrd, and 1 X 10(5) tumor cells were injected into the left side of the hearts of syngeneic C3H mice. Experimental groups consisted of untreated normal mice, mice pretreated iv with Corynebacterium parvum, and mice chronically infected with Toxoplasma gondii; in this model both groups of immunomodulated mice are protected from developing systemic metastatic tumor, but only Toxoplasma-infected mice have protection against metastatic brain tumor. At time intervals from 1 to 96 hours, groups of mice from each experimental group were killed, and the brain and other organs were monitored for radioactivity to determine the number of viable tumor cells that had been present at the time of death. Normal mice demonstrated significant retention of tumor cells in the brain and kidneys plus adrenals at 96 hours. By contrast, in both groups of immunomodulated mice tumor cells were rapidly eliminated from systemic organs, but tumor cells were significantly retained in the central nervous system even at 96 hours after tumor cell injections. The results indicated that generalized immunomodulation had more effect in elimination of tumor cells from systemic organs than from the brain and that the elimination of tumor cells from the brain in Toxoplasma-infected mice was a delayed phenomenon.