Poxviridae have been successful pathogens throughout recorded history, infecting humans among a variety of other hosts. Although eradication of the notorious smallpox has been a globally successful healthcare phenomenon, the recent emergence of Monkeypox virus, also belonging to the Orthopoxvirus genus and causing human disease, albeit milder than smallpox, is a cause of significant public health concern. The ongoing outbreak of monkeypox, demonstrating human-human transmission, in previously non-endemic countries, calls for critical need into further research in the areas of viral biology, ecology and epidemiology to better understand, prevent and treat human infections. In the wake of these recent events, it becomes important to revisit poxviral infections, their pathogenesis and ability to cause infection across multiple non-human hosts and leap to a human host. The poxviruses that cause human diseases include Monkeypox virus, Molluscum contagiosum virus and Orf virus. In this review we summarize the current understanding of various poxviruses causing human diseases, provide insights into their replication and pathogenicity, disease progression and symptoms, preventive and treatment options and their importance in shaping modern medicine through application in gene therapy, oncolytic viral therapies for human cancers or as poxvirus vectors for vaccines.

Declaration of smallpox eradication by the WHO on 1980 led to discontinuation of the world-wide vaccination campaign. The increasing percentage of unvaccinated individuals, the existence of its causative infectious agent variola virus (VARV) and the recent synthetic achievements, increases the threat of intentional or accidental release and reemergence of smallpox. Control of smallpox would require an emergency vaccination campaign as no other protective measure has been approved to achieve eradication and ensure world-wide protection. Experimental data in surrogate animal models support the assumption, based on anecdotal, uncontrolled historical data, that vaccination up to 4 days postexposure, confers effective protection. The long incubation period and the uncertainty of the exposure status in the surrounding population calls for the development and evaluation of safe and effective methods that would allow to extend the therapeutic window and to reduce the disease manifestations and vaccine adverse reactions. To achieve these goals, we need to evaluate the efficacy of novel and already licensed vaccines as a sole treatment or in conjunction with immune modulators and antiviral drugs. In this review, we address the available data, recent achievements and open questions.

Mycobacterium tuberculosis was responsible for 1.3 million deaths worldwide in 2022. Bacillus Calmette-Guérin (BCG) is the only licensed vaccine against tuberculosis (TB); however, it has limited protective efficacy in adults. In this study, we constructed a recombinant vaccinia virus expressing Ag85B from M. tuberculosis using a novel attenuated vaccinia virus (KVAC103). We then analyzed the immunogenicity of prime-boost inoculation strategies using recombinant KVAC103 expressing Ag85B (rKVAC85B) compared to BCG. In both the rKVAC85B prime-boost and the BCG prime-rKVAC85B boost inoculation regimens, rKVAC85B induced the generation of specific IgG and the secretion of IFN-γ by immune cells. In vitro analysis of Mycobacterium growth inhibition revealed a comparable immune-mediated pattern of outcomes. Furthermore, bacterial loads in the lungs were significantly lower in mice inoculated with the BCG prime-rKVAC85B boost, than in the BCG-only group following a rechallenge infection with both H37Rv and HN878 strains of M. tuberculosis. These findings collectively suggest that KVAC103, incorporated into a viral vector, is a promising candidate for a novel TB vaccine platform that is effective against multiple TB strains, including H37Rv and HN878, and that rKVAC85B effectively stimulates immune responses against TB infection.

The COVID-19 pandemic has underscored the importance of swift responses and the necessity of dependable technologies for vaccine development. Our team previously developed a fast cloning system for the modified vaccinia virus Ankara (MVA) vaccine platform. In this study, we report the construction and preclinical testing of a recombinant MVA vaccine obtained using this system. We obtained recombinant MVA expressing the unmodified full-length SARS-CoV-2 spike (S) protein containing the D614G amino acid substitution (MVA-Sdg) and a version expressing a modified S protein containing amino acid substitutions designed to stabilize the protein a in a pre-fusion conformation (MVA-Spf). S protein expressed by MVA-Sdg was found to be expressed and correctly processed and transported to the cell surface, where it efficiently produced cell-cell fusion. Version Spf, however, was not proteolytically processed and despite being transported to the plasma membrane, it failed to induce cell-cell fusion. We assessed both vaccine candidates in prime-boost regimens in the susceptible transgenic K18-human angiotensin converting enzyme 2 (K18-hACE2) mice and in golden Syrian hamsters. Robust immunity and protection from disease was induced with either vaccine in both animal models. Remarkably, the MVA-Spf vaccine candidate produced higher levels of antibodies, a stronger T cell response, and a higher degree of protection from challenge. In addition, the levels of SARS-CoV-2 in the brain of MVA-Spf inoculated mice was decreased to undetectable levels. Those results add to our current experience and range of vaccine vectors and technologies for developing a safe and effective COVID-19 vaccine

Nucleocytoplasmic large DNA viruses (NCLDVs) have massive genomes and particle sizes compared to other known viruses. NCLDVs, including poxviruses, encode ATPases of the FtsK/HerA superfamily to facilitate genome encapsidation. However, their biochemical and structural characteristics are yet to be discerned. In this study, we demonstrate that the viral ATPases are significantly shorter than their bacterial homologs, representing the minimal ATPase core of the FtsK/HerA superfamily. We analyzed the sequence and structural features of the vaccinia virus A32 protein and determined their roles in the stability of the A32 protein and its ATPase activity. We sought to purify A32 by various techniques and noted that recombinant A32 expressed in E. coli is highly insoluble and unstable in solution, possibly because of the disordered C-terminus. N-terminal fusion with the thioredoxin solubility tag could alleviate this issue to some extent, but subsequent tag cleavage results in increased susceptibility to precipitation and degradation. We also predicted a conserved coiled-coil motif (CCM) towards the C-terminus of VV A32. ATPase activity of A32 is known to increase in the presence of DNA. Our comparative analysis of wildtype A32 versus CCM mutants suggests that this DNA dependence of A32’s ATPase activity is likely regulated by the CCM. Since CCM is also known to facilitate protein oligomerization, these findings provide new opportunities for further detailed characterization of A32.