Increased immunogenicity of two lymphoma lines after drug treatment of athymic (nude) mice

Highly immunogenic sublines of L1210 and LSTRA lymphomas were obtained from athymic (nude) mice treated with 4(5)-(3,3-dimethyl-1-triazeno)imidazole-5(4)carboxamide (DIC) in vivo. Conventional mice, compatible with the parent tumor, rejected the DIC-treated sublines and were relatively resistant to a subsequent challenge with the parent lines. The DIC-treated sublines were not rejected by athymic mice, which indicated that the transplantation resistance to these tumors in conventional mice was thymus-cell dependent. In addition, there was marginal or no increase of tumor-cell immunogenicity when the parent lines were passaged in nude mice without DIC treatment. This indicated that the DIC-dependent immunogenic changes in DIC-treated leukemic conventional mice could not be ascribed merely to protection by naturally occurring antigenic clones that resulted from DIC-induced immunodepression.

Relationship of tumor immunogenicity to concentration of the oncogen

Tumors were induced sc in (BALB/c x DBA/2)F1 female mice by various concentrations of 3-methylcholanthrene (MCA) in paraffin pellets. There was an inverse relationship between MCA concentration and tumor latency (interval between MCA implantation and detection of gross tumor). The tumors were transplanted into syngeneic recipients, and material from this first transplant generation was used to immunize a series of syngeneic mice; any resulting growth was excised. Nonimmunized mice were controls. Immunized and control mice were irradiated and given an sc inoculation of a near-threshold number of tumor cells. Tumor growth from that inoculation was measured weekly in both groups and the antigenicity ratio (mean tumor size in controls/mean tumor size in immunized mice) was calculated. In a series of tumors with similar latencies, the only ones with high antigenicity ratios were those resulting from the high MCA concentration. The results suggested that tumors induced by low levels of oncogen may be good models of spontaneous neoplasia, strengthened the hypothesis that "spontaneous' tumors may actually result from low levels of oncogen, and indicated that neoplastic transformation and the development of immunogenicity are, at least in chemically induced tumors, independent changes that may be produced in the same cell when the concentration of oncogen is sufficient.

Inhibition of murine plasmocytoma tumours with antibody activity by their respective specific antigens

Three murine plasmocytoma tumour which secrete specific antibodies have been studied for the effect of specific antigens (pneumococcal C polysaccharide and dinitrophenylated bovine gamma globulin) on the growth of these tumours in vivo. In each case, the effect of the specific antigen was to inhibit the growth of that tumour which synthesized the specific antibody. Low molecular weight haptens had no effect on tumour growth. We suggest that this antigen specific growth inhibitory effect is a function of the antigen's binding to membrane bound antibody resulting in defective membrane function.

Histocompatibility antigens acting as helper determinants for tumor-associated antigens of murine lymphosarcoma

The mechanism of effectiveness of allogeneic versus syngeneic immunization in mounting a humoral specific immune response against tumor-associated antigens of murine urethan-induced thymic lymphosarcomas was studied. C57BL mice immunized with untreated or blocked C3Hf lymphoma cells yielded sera with complement-dependent cytotoxicity for C57BL lymphosarcomas, whereas they did not respond to repeated injections of blocked syngeneic lymphoma cells, indicating a helper activity of alien alloantigens in the reflex of tumor antigens. Thymectomized, lethally-irradiated and T, but not B-reconstituted mice produced active sera, suggesting a T-dependent response. The anti-tumor activity of the serum ran parallel with the anti-histocompatibility one. The tumor-associated and the alien histocompatibility determinants had to be present on the same cell membrane. In addition, active sera were obtained when immunizing syngeneic lymphoma cell inocula were followed by allogeneic normal immunocompetent cells. It is suggested that either a helper mechanism with B and T cells cooperating in recognizing haptenic tumor-associated and carrier histocompatibility antigens or a graft-versus-host reaction determining an abnormal induction of the immune system is needed in order to detect the weak tumor-associated antigens of urethan-induced lymphomas.

Effect of the rhythm of cyclophosphamide administration on its antitumor action and the immune response of mice with methylcholanthrene sarcoma

The therapeutic effect of cyclophosphamide (CP) in relation to the dose and rhythum of its administration was studied in C57BL/6 mice with a methycholanthrene-induced sarcoma. The optimal scheme giving a complete cure of the experimental animals was 5 injections, each of 199 mg/kg CP at intervals of 10 days. The effect of the total dose of CP on humoral antitumor immunity was demonstrated: after injection of 100 mg/kg CP the animals' serum lost its ability to stimulate tumor growth and acquired cytotoxic properties. The serum of animals receiving the total doses of CP above 400 mg/kg lost its effect on tumor growth. The doses of CP used did not affect cellular antitumor immunity (the cytotoxicity of the lymphocytes and resistance of the tumor to retransplantation.).

Development of specific cell-dependent antibody during growth of a syngeneic rat sarcoma

A micro-cytotoxicity assay was adapted for the detection of cell-dependent antibodies (CDA). Using normal rat spleens as the source of effector cells such CDA activity was readily demonstrable in allo-immune sera tested on cultured sarcoma cells. The same technique was then used to examine for tumour specific antibodies in the sera of Hooded rats bearing a "non-immunogenic" syngeneic metastasizing sarcoma. During the early stages of tumour growth, at Days 7 and 14, tumour specific CDA cytotoxicity was detectable at high titres. By Day 21, however, this activity had completely disappeared from the serum. This cell-dependent cytotoxicity was tumour specific in that it did not kill cells from an unrelated syngeneic sarcoma, and the activity was probably confined to immunoglobulin G as detected by molecular weight separation techniques. Following tumour amputation at Day 21, this type of specific antibody activity rapidly re-appeared in the serum. The presence of tumour specific CDA showed an inverse correlation with the presence of specific inhibitors of cell-mediated immunity in the same sera. At no stage in tumour growth could complement-dependent cytotoxicity be detected in tumour bearing rat sera.It is concluded that cell-dependent cytotoxic activity is not associated with conventional complement dependence, that this CDA type of assay is exquisitely sensitive and is suitable for the detection of anti-TSTA antibodies in tumour bearing rats.The possible significance of CDA activity in syngeneic tumour immunity is discussed briefly. The results suggest that the role of humoral immune mechanisms in host resistance to tumour growth needs re-appraisal.