Measurements of Vaccinia Virus Dissemination Using Whole Body Imaging: Approaches for Predicting of Lethality in Challenge Models and Testing of Vaccines and Antiviral Treatments

Abstract

Preclinical evaluation of novel anti-smallpox vaccines and antiviral treatments often rely on mouse ­challenge models using pathogenic vaccinia virus, such as Western Reserve (WR) strain or other orthopoxviruses. Traditionally, efficacy of treatment is evaluated using various readouts, such as lethality (rare), measurements of body weight loss, pox lesion scoring, and determination of viral loads in internal organs by enumerating plaques in sensitive cell lines. These methodologies provide valuable information about the contribution of the treatment to protection from infection, yet all have similar limitations: they do not evaluate dissemination of the virus within the same animal and require large numbers of animals. These two problems prompted us to turn to a recently developed whole body imaging technology, where replication of recombinant vaccinia virus expressing luciferase enzyme (WRvFire) is sensed by detecting light emitted by the enzyme in the presence of d-luciferin substrate administered to infected animal. Bioluminescence signals from infected organs in live animals are registered by the charge-coupled device camera in IVIS instrument developed by Caliper, and are converted into numerical values. This chapter describes whole body bioimaging methodology used to determine viral loads in normal live BALB/c mice infected with recombinant WRvFire vaccinia virus. Using Dryvax vaccination as a model, we show how bioluminescence data can be used to determine efficacy of treatment. In addition, we illustrate how bioluminescence and survival outcome can be combined in Receiver Operating Characteristic curve ­analysis to develop predictive models of lethality that can be applied for testing of new therapeutics and second-generation vaccines.