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Abstract
The threat of Variola virus (VARV), the causative agent of smallpox, remains today although the disease was declared eradicated in 1980. The development of medical counter measures (MCMs) for smallpox are vital to biopreparedness should smallpox re-emerge. To determine the efficacy of MCMs, surrogate orthopoxviruses (OPXV), such as Monkeypox virus (MPXV), are required. VARV is a solely human pathogen and previous attempts to identify an animal model with a route of infection and disease progression that mimics human smallpox post VARV challenge have been unsuccessful. The goal of this work is to characterize new models for studying antivirals against VARV by utilizing the prairie dog MPXV surrogate model to determine if a potential MCM, a monoclonal antibody (mAb) cocktail called Mix4, is efficacious and to determine if humanized mice could serve as a VARV animal model. Our longevity study demonstrated that prairie dogs had no side effects to intraperitoneal administration of human mAbs (48 mg/kg). A plaque reduction neutralization assay (PRNT) determined 50% virus neutralization was seen beginning 1 day post injection until >7 days. In an efficacy study where animals were treated 1 day pre-challenge, challenged on day 0 and treated again 6 days post infection, Mix4 treatment resulted in 80% survival compared to 40% for Vaccinia Immune Globulin and 25% for a non-specific mAb. Mix4 did not provide protection from morbidity and PRNTs assessing the two main forms of OPXV progeny identified that Mix4 only strongly neutralized one form of viral progeny. PRNTs against the main forms of viral progeny have identified different mAbs combinations (Universal Pox Mix) that could serve as a MCM against MPXV and VARV. While surrogate models are useful, MCMs testing against VARV directly would be beneficial. Humanized (hu-) mice, hu-BLT, hu-CD34+ and hu-PBMC were all susceptible to intranasal VARV challenge. Hu-mice developed high pain scores, requiring euthanasia prior to study end. Molecular analysis, including viral titers as high as 1.66x1011 pfu/gram of tissue, and histopathology supported VARV as the cause death. Due to delayed mortality in the hu-PBMC mice, hu-BLT and hu-CD34+ are the best candidates for further characterization.