A survey of ethylnitrosourea-induced rat gliomas for the presence of tumour rejection antigens expressed in vivo.

Transplanted lines of seven F-344 (Fischer) rat malignant gliomas induced transplacentally with ethylnitrosourea (ENU) were surveyed by in vivo immunoprotection assays for the presence of tumour rejection antigens. These gliomas were representative of commonplace histological types of human primary brain tumours and were analyzed in early transplantation passages. The classical tumour ligation method of immunizing animals was attempted with five glioma lines, but was found unusable in four of these because of a high incidence of local tumour recurrences and distant metastases. In most experiments the animals were immunized by repeated inoculations of heavily-irradiated tumour cells. Two gliomas, a glioblastoma multiforms and a mixed astrocytoma-ependymoma, demonstrated weak but statistically significant tumour rejection responses. Immunization with three other tumours, a mixed oligodendroglioma-astrocytoma and two glioblastomas multiforme, led to enhanced outgrowth of the challenge cell inocula. Neither a rejection nor an enhancement response was observed in assays of the remaining two neoplasms, a glioblastoma multiforme and a mixed astrocytoma-oligodendroglioma. Immunization with a 3-methylcholanthrene-induced urinary bladder carcinoma line, used as a control in assays of six gliomas, had no effect on the outgrowth of transplanted glioma cells. These results suggest that ENU-induced malignant rat gliomas do not uniformly elicit strong tumour-rejection responses in vivo.