A soluble factor distinct from interleukin 2 is involved in the generation and differentiation of cytotoxic T cells.

The involvement of cytotoxic cell-generating factor (CGF) in the generation of cytotoxic cells against syngeneic tumor (T-9) cells and in the rejection of the tumor cells has been investigated. It was found that Con A-sup (culture supernatant of concanavalin A-stimulated rat spleen cells) contained CGF, which was distinct from interleukin (IL) 2 and interferon. It should be noted that spleen cells produced CGF upon inoculation of syngeneic tumor cells into tumor-sensitized rats. Production of CGF preceded the appearance of cytotoxic cells against inoculated tumor cells. In these rats, the inoculated tumor was rejected. In contrast, spleen cells failed to produce CGF upon inoculation of tumor cells into normal rats; in these rats, cytotoxic cells were not detected and the inoculated tumor grew. These data suggested that CGF was produced as an in vivo response of the host immune system and was involved in the generation of cytotoxic T cells. CGF obtained from sensitized spleen cells was chromatographically separated from IL 1, IL 2, and colony-stimulating factor, and the chromatographically separated CGF did not contain IL 3 activity.