Tumour immunotherapy using an adenoviral vector expressing a membrane-bound mutant of murine TNFα

The most limiting factor regarding the use of TNFα in tumour therapy is systemic toxicity. The expression of membrane-bound (nonsecreted) TNFα within a tumour may serve to reduce systemic toxicity while retaining antitumour activity. Two adenovirus (Ad) vectors were constructed: (1) Ad-mTNF-wt expressing wild-type murine TNFα; and (2) Ad-mTNF-MEM expressing a mutant nonsecreted (membrane-bound) form. Only the Ad-mTNF-wt vector induced high levels of TNFα secretion in transduced cells (approximately 400 ng/10 6 cells), however, both vectors induced efficient cell surface expression as detected by FACS. These vectors were used in tumour immunotherapy trials in a murine transgenic breast cancer model. High serum concentrations of mTNFα (approximately 1 ng/ml) were detected only in Ad-mTNF-wt-treated mice, while both vectors induced substantial disruption of tumour pathology. The wt TNF vector was highly toxic, killing 12 of 16 mice at a dose of 5 × 108 p.f.u., whereas the Ad-mTNF-MEM vector showed low toxicity killing three of 27 at the same dose. Both vectors induced partial, and in some cases, permanent tumour regressions, with cured mice displaying protective immunity and specific CTL activity against the tumour. These results indicate that the use of a nonsecreted form of TNFα can result in a relatively large reduction in systemic toxicity with little or no reduction in antitumour activity.