The effect of passage in vitro and in vivo on the properties of murine fibrosarcomas. II. Sensitivity to cell-mediated cytotoxicity in vitro.

The sensitivity of cultured and mouse-passaged cloned lines of chemically-induced murine fibrosarcomas to killing by NK and NC cells, and to cell-mediated immunity, has been studied in in vitro assays, using target cells labelled with 51Cr or 125IUDR. None of the lines tested proved sensitive to NK cells. Three cultured lines were, at most, only slightly sensitive to NC cells; a fourth cultured line was moderately sensitive and became less so, but not completely insensitive, after passage in susceptible hosts. The primary object of these experiments was to test the hypothesis that cultured cell lines which ordinarily fail to grow in normal mice are able to grow after being passaged in a susceptible immunodeficient host because, during this passage, they become resistant to NK or NC cells. This has been shown to occur with one clone, but will not serve as a general explanation because, with other clones, both cultured and mouse-passaged lines were NC-insensitive. The cell-mediated immunity assays confirm our previous conclusion that cultured and mouse-passaged lines of the same clone differ little, if it all, in immunogenicity.