Local production of tumor necrosis factor encoded by recombinant vaccinia virus is effective in controlling viral replication in vivo

Tumor necrosis factor (TNF) has pleiotropic effects on a wide variety of cell types. In vitro studies have demonstrated that TNF has antiviral properties and is induced in response to viral infections. However, a role for TNF in the antiviral immune response of the host has yet to be demonstrated. Here we describe the construction of and studies using a recombinant vaccinia virus that encodes the gene for murine TNF-α. By comparing the replication of and immune responses elicited by the TNF-encoding virus to a similarly constructed control virus, we hoped to observe immunobiological effects of TNF in the host. The in vivo experiments with this recombinant virus demonstrate that the localized production of TNF-α during a viral infection leads to the rapid and efficient clearance of the virus in normal mice and attenuates the otherwise lethal pathogenicity of the virus in immunodeficient animals. This attenuation occurs early in the infection (by postinfection hour 24) and is not due to the enhancement of cellular or antibody responses by the vaccinia virus-encoded TNF. This evidence suggests that attenuation of the recombinant virus is due to a direct antiviral effect of TNF on cells at the site of infection. Therefore, these results support the suggestion that TNF produced by immune cells may be an important effector mechanism of viral clearance in vivo.