Human vaccinia virus immune globulin

Intravenous human vaccinia virus immune globulin (VIGIV) provides passive immunity for individuals with complications to vaccinia virus vaccination. The exact mechanism of action, however, is not yet formally known.

Nevertheless, VIGIV is ultimately an isotonic sterile solution obtained by plasmaphoresis of individuals who were vaccinated prior with vaccinia virus and possess high anti-VACV antibody titers. The potency and effect of VIGIV is described by its ability to neutralize mature virus (MV, or intracellular mature virus, IMV). Regardless, during an infection, various forms of infectious virions are generated. In particular, the MV is a more stable form of the virus and is considered to be the form that is transmitted from host-to-host. The other important form of the infectious virus is called the extracellular virus (EV, or extracellular enveloped virus, EEV), which is critical for the spread of the virus from cell-to-cell and to distant sites within a host. EV is subsequently an important element in pathogenesis. The major target of EV neutralizing antibody in VIGIV is against the EV-specific B5 protein. VIGIV also contains antibodies that react with viral encoded immune evasion molecules, which could also participate in VIGIV's anti-poxvirus activity. Researchers have begun to try to identify all of the VACV targets in VIGIV. Due to the highly homologous proteins encoded by orthopoxviruses, there is a high degree of shared serologic cross-reactivity. Thus VIGIV could react with proteins from other orthopoxviruses and have similar therapeutic effects against other poxvirus infections.

Ultimately, however, the most commonly held consideration regarding how VIGIV is capable of eliciting its therapeutic effect is the notion that such 'pre-generated' antibodies from individuals who have already been previously vaccinated with vaccinia virus, when administered to other people, may protect against VACV infections in these newly administered individuals in a method that is perhaps similar to the natural passive transfer of maternal antibodies from a mother to her baby.