In vitro immunoreactivity against ethynitrosourea-induced tumours of the nervous system in the rat

The humoral antibody response of rats immunized with chemically modified syngeneic brain cells and glioma cells

Six-month-old Fischer rats (F344) were given the carcinogen methylnitrosourea in their drinking water. Of the induced brain tumors, four were established in culture and propagated as 78FR-G-219 (pleomorphic glioma), 78FR-G-299 (astrocytoma), 78FR-G-284 and 78FR-G-344 (mixed glioma) permanent lines. All cell lines produced S-100 protein and grew as tumors when inoculated s.c. or i.c. in syngeneic hosts. A comparative study of the antigenicity of these lines at different passage levels was carried out using native and chemically modified cells. Syngeneic rats were immunized with cells conjugated with dimethylsulfate and trinitrobenzene sulfonic acid. The immune response was characterized and quantified by an indirect immunofluorescence method and by a complement-dependent microcytotoxicity test. Chemical modification of the tumor cells enhanced antigenicity of the treated cells. The best results were attained with trinitrobenzene sulfonic-acid-treated cells and constituted a two-fold increase in the cytotoxicity index. Cytotoxicity values varied in the different cell lines. Antisera raised with trinitrobenzene sulfonic-acid-modified cells of all lines cross-reacted with cells of all lines. Cytotoxicity values were insignificantly reduced by absorbing the antisera with a variety of syngeneic tissues. Antisera raised against native syngeneic brain cells showed virtually no cytotoxicity for glioma cells. Antisera raised against syngeneic brain cells treated with trinitrobenzene sulfonic acid, however, were slightly cytotoxic for normal brain cells and glioma cells as well. The results of the present studies show that antigenicity of glioma cells can be definitely raised with trinitrobenzene sulfonic acid treatment. Furthermore, it would seem that haptenization of glioma-associated antigens may be a promising approach ot the study of glioma-host interactions.

[Antigenicity of a chemically induced neurogenic rat sarcoma (author's transl)]

A neurogenic sarcoma was induced in the plexus brachialis of a male Long-Evans rat by administration of N-methyl-N-nitrosourea in the drinking water. The tumor was established in vitro and designated 76LE-NS-369. Cells from tissue culture grew as tumors when isografted in young rats. 76LE-NS-369 cells did not react with antiserum directed against gliaspecific S-100 protein. We used the cultured cells as target cells, and found specific antibodies in the sera of tumor-bearing and immunized rats by indirect fluorescent antibody stain and a complement-dependent antibody-mediated microcytotoxicity assay. In immunization experiments, incubation of tumor cells with Vibrio cholerae neuraminidase yielded higher antibody titers than an antigen preparation with untreated cells. Incubation with neuraminidase enhanced the sensitivity of tumor cells to antibody and complement in vitro, whereas trypsinized cells showed complete loss of reactivity with autologous antisera. The specificity of antisera was tested by absorption with tumor, lyophilized rat whole body and rat nerve tissues.

Immune surveillance and tumors of the nervous system

The theory of immune surveillance postulates that one function of the immune system is to eliminate small numbers of malignant cells that arise spontaneously within the organism. Although there has been a great deal of both clinical and experimental evidence in favor of thistheory as it applies to general oncology, the question of whether or not such a surveillance system would be effective for tumors arising within the nervous system has never been studied. The young of pregnant rats which had been exposed to the neurocarcinogen ethylnitrosourea (ENU) were divided into control, immunosuppressed, and immunoenhanced groups. These lifetime alterations of the immune system had no effect on the course of nervous system tumor fromation. We believe that the most likely explanation for our results is that the "immunological privilege" of the brain prevents the usual interaction of the neoplasm and the immune system from occurring.

Immunofluorescence study of lymphocytic infiltration in gliomas. Identification of T-lymphocytes

Five human brain tumours (3 glioblastomas and 2 astrocytomas) and 5 rat brain tumours induced in Sprague--Dawley animals by systemic administration of N-methyl-N-nitrosourea (3 pleomorphic gliomas and 2 mixed gliomas) were studied. The human brain tumours were surgical specimens excised from patients with no cranial surgery prior to their disease. The experimental brain tumour had been adapted to tissue culture, propagated in vitro and then transplanted to immunocompetent and immunodeficient rats of the same stock. The above-described material was selected in consideration of the mononuclear cell infiltrates occurring in these tumours. Frozen sections of human and rat gliomas, the latter both primary and transplanted, were prepared and investigated as to the presence of T-lymphocytes within the mononuclear round cell infiltrates. This was done with the indirect immunofluorescence method using rabbit antisera against man and rat T-lymphocytes. With this technique a variable percentage of T-lymphocytes was demonstrated in the cell infiltrates of human and rat gliomas alike. The tumour transplanted in thymectomized rats showed only isolated, scattered, positive-reacting cells, i.e., cells recognizable as T-lymphocytes by the above method. The results can be interpreted as circumstantial evidence for the occurrence of tumour-specific and/or tumour-associated antigens in the parenchymal cells of spontaneous and chemically-induced gliomas.