TUMOR-IMMUNOTHERAPY USING AN ADENOVIRAL VECTOR EXPRESSING A MEMBRANE-BOUND MUTANT OF MURINE TNF-ALPHA

The most limiting factor regarding the use of TNF alpha in tumour ther apy is systemic toxicity. The expression of membrane-bound (nonsecrete d) TNF alpha within a tumour may serve to reduce systemic toxicity whi le retaining anti-tumour activity. Two adenovirus (Ad) vectors were co nstructed: (1) Ad-m TNF-wt expressing wild-type murine TNF alpha; and (2) Ad-mTNF-MEM expressing a mutant nonsecreted (membrane-bound) form. Only the Ad-mTNF-wt vector induced high levels of TNF alpha secretion in transduced cells approximately 400 ng/10(6) cells), however, both vec- induced efficient cell surface expression as detected by FACS. Th ese vectors were used in tumour immunotherapy trials in a murine trans genic breast cancer model. High serum concentrations of mTNF alpha (ap proximately 1 ng/ml) were detected only in Ad-mTNF-wt-treated mice, wh ile both vectors induced substantial disruption of tumour pathology. T he wt TNF vector was highly toxic, killing 12 of 16 mice at a dose of 5 x 10(8) p.f.u., whereas the Ad-mTNF-MEM vector showed low toxicity k illing three of 27 at the same dose. Both vectors induced partial, and in some cases, permanent tumour regressions, with cured mice displayi ng protective immunity and specific CTL activity against the tumour. T hese results indicate that the use of a nonsecreted form of TNF alpha can result in a relatively large reduction in systemic toxicity with l ittle or no reduction in antitumour activity.