Immunostimulation-inhibition of tumor cell growth in vitro utilizing tumor target cells labeled with ¹²⁵i-iodo-deoxyuridine

Immune stimulation-inhibition of normal and sensitized syngeneic, allogeneic and xenogeneic lymphocytes with the B16 melanoma was tested by an in vitro assay. Various numbers of lymphocytes were mixed with non-labeled or with ¹²⁵IUDR-labeled B₁₆ cells incubated for 2 hours on a rotating platform and plated into culture dishes. One, 2 or 3 days later the dishes were fixed and viable tumor cells counted either by microscopy or by radioactive monitoring. Sensitized but not normal lymphocytes at ratios up to 1:1000 repeatedly and significantly enhanced the plating efficiency and growth of the target cells. At higher lymphocyte doses, colony inhibition was evident. Numbers of viable target cells calculated from radioactive monitoring agreed closely with visual counts of the cultures. It appears that the technique utilizing ¹²⁵IUDR-labeled cells affords a relatively easy, fast and accurate assay for in vitro studies of immune stimulation-inhibition of target growth.