Refractoriness of lymph-node cells from tumour-bearing animals

Mixed lymphocyte/tumor-cell interaction in a murine sarcoma virus (Moloney)-induced tumor system. Comparison between lymphoproliferation and lymphocyte cytotoxicity

Studies of the MLTI were performed in a primary MSV-induced tumor system. Reactivity against mitomycin-C-treated RBL-5 cells could be detected during a limited period at about 14 days after virus injection. The degree of reactivity of MSV 14 spleen cells was quite variable; stimulation indices ranged from 2.2 to 9.4. Activity in the MLTI appeared to a great extent to be dependent on T-lymphocytes. A relatively broad spectrum of specificity was demonstrated in experiments using additional stimulating cells besides RBL-5. The kinetics of the MLTI correlated well with the kinetics of the primary cytotoxic response in the CRA against RBL-5 cells. However, positive results in the in vivo and in vitro secondary cytotoxicity assays could be detected between 21 and 100 days after MSV injection when the MLTI was negative. Transplantation resistance against challenge with RBL-5 tumor cells also persists for a long time after MSV inoculation. Our data therefore indicate that the MLTI, in contrast to the secondary cytotoxicity assays, does not correlate well with the status of in vivo immunity.

In vitro assessment of cell-mediated immunity in patients with renal cell carcinoma

We evaluated 25 patients with renal cell carcinoma for cell-mediated immunity using the microtoxicity assay. Normal controls frequently exhibited significant cell inhibition. The mean percentage cell inhibition in patients after nephrectomy was significantly higher than in patients before nephrectomy and significantly higher than normal male subjects. No other correlation was found with respect to the stage of the disease. The incidence of significant autoblocking activity was noted more commonly in patients after nephrectomy than in patients before nephrectomy.

A long-term 51chromium assay for in vitro cell-mediated tumor immunity. Correlation with simultaneously performed microplate assays

In vitro assays of cell-mediated tumor immunity utilizing 51Chromium (51Cr) labelling of cultured adherent solid tumor cells were designed which allowed an effector cell/target cell incubation time of 48 h without overriding spontaneous 51Cr release. In a series of 16 consecutive experiments, blood lymphocytes from healthy human donors, from patients with tumors unrelated to the cultural tumor target cells, and from colon carcinoma and melanoma patients were tested for their cytotoxic effects on various target cell pairs, human colon carcinoma, melanoma, or skin fibroblasts. The same reagents were used in simultaneously performed microplate and 51Cr assays. Results obtained by visual counting of microplate tests and by 24-h assays of 51Cr release or 51Cr retention correlated in 20/25 effector-cell/target-cell combinations. In a series of six consecutive experiments, lymph-node cells from untreated Wistar/Furth rats, and rats bearing either chemically-induced colon carcinoma NG-W1 or polyoma virus-induced sarcoma P-W13 were tested for their cytotoxicity on syngeneic rat colon carcinoma and sarcoma target cells. Criss-cross type experiments were performed by microplate and 15Cr techniques done in parallel. Results obtained by visual counting of microplate tests and by 48 h assays of 51Cr release or 51Cr retention correlated in 15/18 effector-cell/target-cell combinations.

Studies of lymphocyte stimulation by intact tumor-cell and solubilized tumor antigen

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.

Inhibition of in vitro lymphoproliferative responses to tumor-associated antigens by suppressor cells from rats bearing progressively growing Gross leukemia virus-induced tumors

W/Fu rats were injected subcutaneously with low numbers of cells from the Gross leukemia virus-induced lymphoma, (C58NT)D, which induced transient tumor growth and regression (regressors), or with high numbers of tumor cells resulting in progressive tumor growth (progressors). Spleen cells from regressors had a significant reactivity in the mixed leukocyte tumor cell interation (MLTI), while spleen cells from progressors were unresponsive. Similarly, the responses to the non-specific mitogens, phytohemagglutinin and concanavalin A, were suppressed in spleen-cell cultures of progressors. Passage of spleen cells from progressors over rayon adherence columns or pretreatment with an iron/magnet technique resulted in almost complete restoration of MLTI and mitogen responses. Addition of spleen cells from progressors depressed the MLTI of spleen cells from regressors and the mitogen reactivity of normal spleen cells. Serum from progressors also suppressed MLTI and mitogen reactivity. These data indicate that, in spleens of rats bearing progressively growing tumors, suppressor cells can be demonstrated which inhibit specific reactivity to tumor-associated antigens and non-specific reactivity to mitogens. The presence of suppressor cells or of inhibitory factors in the serum may contribute to the immunosuppression frequently observed in tumor-bearing hosts.