Prolonged survival of rats with intracranial C6 gliomas by treatment with TGF-beta antisense gene

Using an intracranial rat C6 glioma model, we tested the hypothesis that ge ne modification of glioma cells to block the expression of the immunosuppre ssive cytokine TGF-beta (transforming growth factor beta) may enhance anti- tumor immune responses and thereby prolong survival of rumor-bearing animal s. The cDNA for simian TGF-beta(2) was ligated in antisense orientation int o the episomal plasmid mammalian expression vector pCEP-4. This TGF-beta-an tisense vector was transfected into C6 glioma cells by standard electropora tion techniques. PCR was used to determine that the rat C6 clones were succ essfully transfected with the antisense-TGF beta construct Twenty-nine adul t female Wistar rats harboring 7-day-old intracranial C6 tumors were then s ubcutaneously injected with either saline (n = 9), unmodified C6 glioma cel ls (n = 10), or TGF-beta-antisense-modified C6 cells (n = 10). Animals were followed for survival, and Fisher's exact method was used to interpret the significance of differences between experimental groups. The survival of t umor-bearing rats injected with TGF-beta-antisense-modified C6 cells was si gnificantly prolonged relative to the survival of rats receiving injections of saline or unmodified C6 cells alone. Six of the ten (60%) TGF-beta-anti sense treated animals survived for 12 weeks, whereas none of the nine (0%) animals treated with saline and none of ten (0%) of those treated with C6 c ells alone survived past 5 weeks. These results indicate that the genetic i nhibition of immunosuppressive cytokines (such as TGF-beta) may reverse the phenotypic immunosuppression caused by such factors, and thereby prolong t he survival of C6 tumor-bearing animals. Future investigations using cytoki ne gene modifications in other brain tumor models are warranted.