Abstract
BALB/c mice were rendered immune to a syngeneic SV40‐induced sarcoma by subcutaneous injection of mKSA‐TU5 tissue‐culture adapted cells. Spleen cells from immune mice were examined for tumor‐cell neutralization in the Winn assay as well as in in vitro lymphocyte stimulation assays. A microculture (200 μl) lymphocyte stimulation (LS) assay utilizing immune spleen cells was employed with mixed lymphocyte/tumor‐cell cultures (MLTC) and with papain crude soluble (CS) extracts from mKSA‐TU5 cells. Specificity in the LS assay was determined using spleen cells from mice immune to other syngeneic tumors and by soluble antigenic preparation of normal BALB/c spleen cells. The Winn assay studies demonstrated that spleen cells from mKSA‐sensitized mice neutralized mKSA tumor cells and this was corroborated by their resistance to direct tumor challenge. Positive lymphocyte transformation responses in MLTC were observed when mKSA‐TU5‐sensitized spleen cells were mixed with mitomycin‐C‐treated intact tumor cells or when papain‐solubilized antigens of mKSA cells were employed, but not with non‐immune spleen cells or with a soluble antigen from normal cells. Papain‐solubilized antigen preparations employed in in vitro assays also immunized against challenge with mKSA tumor cells. Specificity of these lymphocyte transformation reactions was demonstrated with non‐sensitized lymphoid cells or lymphoid cells from mice sensitized with a syngeneic Kirsten virus‐induced sarcoma (KA‐31) or a mineral‐oil‐induced plasmacytoma (Adj‐PC5), which failed to respond. Thus, mKSA tumor surface antigens were recognized on intact tumor cells or with microgram quantities of papain‐solubilized extracts from these tumor cells. We believe the lymphocyte stimulation assay affords a method for demonstrating the presence of tumor‐specific antigen and for monitoring further purification procedures.