B7.1 expression by the weakly immunogenic F98 rat glioma does not enhance immunogenicity

Enhanced immunogenicity has been reported following transfection of a varie ty of immunogenic tumors with the B7.1 co-stimulatory molecule. The purpose of the present study was to determine ii transfection of a weakly immunoge nic rat brain tumor, the F98 glioma, with the gene encoding B7.1 could enha nce its immunogenicity. F98 cells were transfected with a plasmid containin g the B7.1 gene, and stable transfectants (F98/B7.1) were obtained Flow cyt ometric analysis confirmed the expression of B7.1 and MHC class I antigens on the cell surface. To investigate the effects of B7.1 expression on the t umorigenicity of the F98 glioma, Fischer rats were implanted intracerebrall y with either F98 (wild-type) or F98/B7. 1 transfected cells. No significan t differences in survival times were noted Mean survival times of 21.8 and 24.0 days were observed for the respective groups at a challenge dose of 10 (3) cells. These differences in survival time were not significant. To dete rmine if expression of B7.1 enhanced the immunogenicity of the F98 glioma, rats were vaccinated weekly for 3 weeks with 10(7) mitomycin C-treated F98 or F98/B7. I cells injected subcutaneously and then challenged intracerebra lly with F98 cells 1 week later. Unvaccinated animals or those that receive d wild-type F98 cells as a vaccine had a survival time (mean +/- s.d.) of 2 2.3 +/- 1.5 days following tumor challenge versus 20.0 +/- 1.7 days for rat s that had been vaccinated with F98/B7. I. Although we recognize that it mi ght be possible to design more effective vaccination regimes, nevertheless, our data indicate that transfection of the B7.1 gene into the F98 rat glio ma did not enhance its immunogenicity, and that other approaches will be re quired.