Administration to mice of a monoclonal antibody that neutralizes the intracellular mature virus form of vaccinia virus limits virus replication efficiently under prophylactic and therapeutic conditions.

The WHO smallpox eradication program was concluded 21 years ago and the non-vaccinated population is now at risk of poxvirus infections, either by contact with monkeypox or through bioterrorism. Since drugs specific against poxvirus infections are limited, neutralizing monoclonal antibodies (mAbs) that are effective in vivo may be an important tool in controlling poxvirus infections. To this end, we studied the efficacy of the mAb C3, reactive against the trimeric 14-kDa protein of vaccinia virus (VV) localized in the membrane of the intracellular form of mature virus, for its ability to neutralize VV infection in mice. The results show that prophylactic as well as therapeutic administration of mAb C3 can be an effective means of control of VV replication within the host. The interval of antibody efficacy following a single administration, before and after VV inoculation, has been defined. This study reinforces the notion that neutralizing mAbs should be developed to control health-related human infections by poxviruses.