Summary Cytotoxicity was observed in murine tumor cell monolayers overlaid with syngeneic, bacillus Calmette-Guérin (BCG)-immune, spleen cell suspensions in the presence of purified protein derivative (PPD). Spleen cell suspensions from normal donors with and without PPD or suspensions from BCG-immune donors without PPD had no effect on the tumor monolayers. This cytotoxicity depends on both number of spleen cells and concentration of PPD. Under optimal conditions, cytotoxicity was apparent in two anti-genically unrelated tumor lines, whereas monolayers of syngeneic normal cells (mass embryo and adult fibroblast cells) were unaffected. Supernatants from PPD-stimulated, BCG-immune spleen cell suspensions were cytotoxic to tumor cell monolayers, while the same supernatants had no effect on normal cell monolayers.
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Meltzer et al. (1972) studied this question.