THERAPEUTIC EFFECT OF GAG-NUCLEASE FUSION PROTEIN ON RETROVIRUS-INFECTED CELL-CULTURES

Capsid-targeted viral inactivation is a novel protein-based strategy f or the treatment of viral infections. Virus particles are inactivated by targeting toxic fusion proteins to virions, where they destroy vira l components from within. We have fused Staphylococcus nuclease (SN) t o the C-terminal end of Moloney murine leukemia virus Gag and demonstr ated that expression of this fusion protein in chronically infected ch icken embryo fibroblasts resulted in its incorporation into virions an d subsequent inactivation of the virus particles by degradation of vir al RNA. Release of particles incorporating Gag-SN fusion proteins into the extracellular milieu activates the nuclease and results in destru ction of the virion from within. By comparing the effects of incorpora ted SN and SN, an enzymatically inactive missense mutant form of SN, on the infectivity of virus particles, we have clearly demonstrated th at nucleolytic activity is the antiviral mechanism. Expression of Gag- SN fusion proteins as a therapeutic agent causes a stable reduction of infectious titers by 20- to 60-fold. The antiviral effect of capsid-t argeted viral inactivation in our model system, using both prophylacti c and therapeutic approaches, suggests that a similar anti-human immun odeficiency virus strategy might be successful.