BALB/c mice were rendered immune to 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 mul) lymphocyte stimulation (LS) assay utilizing immune spleen cells was employed with mixed lymphocyte/
tumor-cell cultures (MLTC) and the
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 mitocycin-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 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.