Antigenic inhibition of cell-mediated cytotoxicity against tumour cells

Guinea pig cell-mediated tumor immunity: the chromium release assay detects both cytolysis and serum blocking for syngeneic chemically-induced tumors

The chromium release test (CRT) was used to assess cell-mediated immunity to syngeneic, chemically-induced tumors in guinea pigs. The animal models were Sewall Wright strain 13 guinea pigs with 3-methyl-cholanthrene (MCA)-induced fibrosarcomas and strain 2 guinea pigs with diethylnitrosamine (DEN)-induced hepatocarcinomas. Regional lymph node cells were significantly cytolytic for the immunizing tumors, specifically so for three of the four tumors, and tumor-bearer sera could significantly block cytolysis. The two DEN-induced strain 2 hepatomas, line 1 and line 10, are antigenically distinct by the CRT but the two MCA-induced tumors have tumor specific antigens as well as a common, cross-reactive antigen.

Membrane-associated antigen from the SV40-induced hamster fibrosarcoma, para-7. I. Role in immune complex formation and effector cell blockade

PARA-7 membrane-associated antigen was prepared by treatment of the tumor cells with pH 9.4 glycine buffer, or by concentration of spent cell culture medium. When admixed with sensitized effector cells, both preparations could specifically block cellular cytotoxicity for PARA-7 target cells. Pretreatment of target cells with antigen did not result in blocking. Incubation of antigen extract with simian virus 40 (SV40) anti-serum caused neutralization of antibody-dependent cellular cytotoxicity (ADCC) with concomitant formation of a factor which blocked at the target cell level but not at the effector cell level. Serum from tumor-bearing hamsters exhibited blocking characteristics comparable to those of the antigen-SV40 teristics comparable to those of the antigen-SV40 antiserum preparation. Washing experiments indicated that PARA-7 antigen was more efficient than PARA-7 antigen-antibody complexes in blocking cell-mediated immunity in vitro. Material extracted from untransformed hamster embryo fibroblasts either by itself or when admixed with SV40 antiserum exhibited no significant blocking activity. These observations support the concept that loss of serum ADCC during progressive tumor growth is due to immune complex formation.

Fractionation of cytotoxic cells from tumour-immune rats on derivatized collagen gels

Incubation at 37 degrees C of spleen cells from rats, immunized with Gross virus-induced lymphoma, on collagen gels coated with membrane extracts of lymphoma cells yielded two different cell populations. The non-adherent cells showed greatly diminished cytotocicity for lymphoma cells compared with unfractionated spleen cell suspensions, whilst the specifically adherent cells which were recovered after collagenase digestion of the gels, showed enrichment of cytotoxic activity.

Studies on a gross-virus-induced lymphoma in the rat. III. Optimisation, specificity and applications of the in vitro immune response

Conditions are described for optimal stimulation in vitro of lymphocytes from rats primed in vivo with syngeneic MuLV-G leukaemia cells. Cultures generate effector cells which show high cytotoxic activity against leukaemic cells. Specific stimulation can be obtained with leukaemic cells and with disrupted MuLV. Leukaemic cells, normal spleen cells and the viron internal protein p30 competitively inhibit effector cells, but purified virus exerts non-specific inhibition. These findings are interpreted as supporting the hypothesis that virion antigens constitute a major target of anti-tumour cytotoxic immunity.

Inhibition of cell-mediated cytotoxicity to chemically induced rat tumours by soluble tumour and embryo cell extracts

When lymph-node and spleen cells from rats bearing or immunized against aminoazo dye-induced rat hepatomas or 3-methylcholanthrene-induced rat sarcomas were pretreated with 3 M KCl extracts of these tumors, their cytotoxicity for cultured cells from the corresponding tumour was specificially inhibited. In cross-test combinations of target tumour and tumour-bearer effector-cell donor, tumour extracts only inhibited cytotoxic responses when they were derived from the tumour homologous to the target-cell and not when the extract was from the tumour borne by the effector-cell donor. One component of the tumour-bearer cytotoxic response was shown to be directed against tumour-associated embryonic antigens since soluble extracts of embryos or tumour extracts containing embryonic antigens inhibited tumour-bearer cell-mediated cytotoxicity in both specific and cross-test combinations of target tumour and effector cells. These findings are discussed in relation to tumour antigen expression and the immune responses that these tumour-associated antigens may evoke in tumour-bearing rats.

Primary and secondary in vitro generation of cytolytic T lymphocytes in the murine sarcoma virus system

Cell-mediated cytotoxic responses in vitro to surface antigens associated with murine sarcoma virus (MSV)-induced tumors were investigated using mixed leukocyte-tumor cell cultures (MLTC). The source of responding cells was either spleens from normal C57BL/6 mice (primary MLTC) or spleens of C57BL/6 mice carrying or having rejected a MSV-induced tumor (secondary MLTC). Graffi virus-induced GiL-4 leukemia cells, Rauscher virus-induced RB1-5 leukemia cells, and MSV-induced MSV-B16 sarcoma cells were used as stimulating syngeneic tumor cells and/or target cells. Under appropriate culture conditions, cytolytic T lymphocytes (CTL) were generated in both primary and secondary MLTC. As assessed by a quantitative short-term 51Cr release assay system, CTL activity in secondary MLTC populations was at least 10-fold higher than that in primary MLTC populations, and 100-fold higher than that in spleen cells taken at the peak of the in vivo response of MSV-infected mice. The ability of spleen cells to mount a secondary CTL response in vitro could be observed as early as 5 days after virus injection, increased up to the time of maximum tumor size and persisted long after tumor regression. This suggests the development of increased numbers of CTL progenitors and/or the formation of "memory" CTL in spleens of MSV-injected mice.

Studies on a gross-virus-induced lymphoma in the rat. II. The role of cell-membrane-associated and serum P30 antigen in the antibody and cell-mediated response

The internal viral protein, p30-1, has been identified by cytotoxicity tests using xenogeneic sera, on MuLV-G-induced rat lymphoma cells. In this system internal virion antigens, and in particular p30, are cytotoxic target antigens for syngeneic antibody and cell-mediated cytotoxicity; p30 is also present in the serum of rats with progressively growing lymphomas, and is the principal antigen responsible for the inhibition of cell-mediated cytotoxicity produced by these sera.