✓ Monoclonal antibodies were produced by immunization of the human glioma cell line SK-MG-4. One of the antibodies, designated G-22, reacted with 18 of 20 glioma cell lines, two melanoma cell lines, and three lung cancer cell lines, but not with 39 cell lines derived from sarcoma, carcinoma, or hematopoietic tumors. The antigen was expressed in the brain of human fetuses in early gestation (9 weeks) but not in late gestation (8 months) or in normal adult brain, suggesting that the antibody recognizes neural differentiation antigens expressed by neuroectodermal origin. A high incidence of positive antigens has been observed in gliomas but not in the other neural tumors, such as ependymomas, meningiomas, and neuroblastomas. Thus, the antigen defined by the G-22 monoclonal antibody could be defined as glioma-associated antigen. Pulse-labeling with tritiated leucine and subsequent immunoprecipitation of the solubilized cell membrane revealed that the antigen recognized by this antibody had a molecular weight of 67 kD on sodium dodecyl sulfate-poly-acrylamide gel electrophoresis (SDS-PAGE).
It was shown by dot-blot enzyme-linked immunospecific assay (ELISA) that the antigen could be detected in the cerebrospinal fluid (CSF) from patients with gliomas. From analysis of affinity chromatography and SDS-PAGE, the antigen present in the CSF had a molecular weight similar to that of a 1% Nonidet P-40 (NP-40) extract from a glioma cell line. When the antigen in CSF was quantitatively assayed by ELISA, the mean antigen level (expressed as optical density at 450 nm) in the CSF of seven patients was 0.8 ± 0.28 (mean ± standard deviation), which was significantly higher than the 0.38 ± 0.14 level observed in the CSF of 15 patients with nonglioma brain tumors and the 0.23 ± 0.09 level in the CSF of four patients without brain tumors. These results indicate that the monoclonal antibody G-22 is useful for the diagnosis of glioma.