Development of an animal model of progressive vaccinia in nu/nu mice and the use of bioluminescence imaging for assessment of the efficacy of monoclonal antibodies against vaccinial B5 and L1 proteins

Comparative pathogenicity of vaccinia virus and mpox virus infections in CAST/EiJ mice: Exploring splenomegaly and transcriptomic profiles

BACKGROUND

Vaccinia virus (VACV) and mpox virus (MPXV) belong to the orthopoxvirus genus and share high genetic similarity, making VACV widely used in the mpox pandemic. CAST/EiJ mice have been widely used for studying orthopoxvirus infection. However, the histopathological features of CAST/EiJ mice with mpox virus (MPXV) and vaccinia virus (VACV) infections have not been fully elucidated.

METHODS

Four group of CAST/EiJ mice were challenged with low-dose VACV (103 PFU, VACV-L), high-dose VACV (106 PFU, VACV-H), MPXV (106 PFU) or PBS via intraperitoneal route, and the disease signs and body weight were monitored daily. Subsequently, viral loads and titers in the blood and spleen of CAST/EiJ mice were analyzed via qPCR and TCID50 assay. Finally, the spleen samples were analyzed for histopathological, immunohistochemical and RNA-seq.

RESULTS

Herein, we found that VACV-L and MPXV caused splenomegaly via the intraperitoneal route, whereas VACV-H caused rapid lethality with limited splenomegaly. Transcriptome analysis from spleen revealed significant differences in gene expression between VACV-L and VACV-H groups, but the differentially expressed genes induced by splenomegaly between VACV-L and MPXV groups were highly similar. Furthermore, pathway enrichment analysis demonstrated that the VACV-L, VACV-H, and MPXV groups were all associated with the calcium, MAPK, and PI3K-Akt signaling pathway. Compared to the lethal infection observed in VACV-H group, the splenomegaly in the VACV-L and MPXV groups was characterized by extramedullary hematopoiesis and increased macrophages infiltration in the red pulp. Transcriptome analysis of the spleen demonstrated that the Wnt, tumor necrosis factor (TNF), and transforming growth factor β (TGF-β) signaling pathways may promote splenomegaly by modulating granulocyte infiltration and inflammatory responses. Compared to VACV-L group, the limited splenomegaly but lethality in VACV-H-infected mice might be associated with extensive splenic necrosis, diffuse congestion, and hemorrhage in the red pulp, as well as changes in the cGMP-PKG, Ras signaling, and Fc gamma R-mediated phagocytosis pathways.

CONCLUSIONS

Our findings systematically compared the pathogenicity of VACV and MPXV in CAST/EiJ mice, incorporating splenic transcriptome analysis to provide insights into the potential molecular mechanism behind orthopoxvirus-induced splenomegaly in CAST/EiJ mice.

Immunogenic proteins and potential delivery platforms for mpox virus vaccine development: A rapid review

Since May 2022, the mpox virus (MPXV) has spread worldwide and become a potential threat to global public health. Vaccines are important tools for preventing MPXV transmission and infection in the population. However, there are still no available potent and applicable vaccines specifically for MPXV. Herein, we highlight several potential vaccine targets for MPVX and emphasize potent immunogens, such as M1R, E8L, H3L, A29L, A35R, and B6R proteins. These proteins can be integrated into diverse vaccine platforms to elicit powerful B-cell and T-cell responses, thereby providing protective immunity against MPXV infection. Overall, research on the MPXV vaccine targets would provide valuable information for developing timely effective MPXV-specific vaccines.

Imaging viral infection in vivo to gain unique perspectives on cellular antiviral immunity

The past decade has seen near continual global public health crises caused by emerging viral infections. Extraordinary increases in our knowledge of the mechanisms underlying successful antiviral immune responses in animal models and during human infection have accompanied these viral outbreaks. Keeping pace with the rapidly advancing field of viral immunology, innovations in microscopy have afforded a previously unseen view of viral infection occurring in real-time in living animals. Here, we review the contribution of intravital imaging to our understanding of cell-mediated immune responses to viral infections, with a particular focus on studies that visualize the antiviral effector cells responding to infection as well as virus-infected cells. We discuss methods to visualize viral infection in vivo using intravital microscopy (IVM) and significant findings arising through the application of IVM to viral infection. Collectively, these works underscore the importance of developing a comprehensive spatial understanding of the relationships between immune effectors and virus-infected cells and how this has enabled unique discoveries about virus/host interactions and antiviral effector cell biology.

Bioluminescence Imaging as a Tool for Poxvirus Biology

Bioluminescence imaging, with luciferase as a reporter-encoding gene, has been successfully and widely used for studies to follow viral infection in an organism and to measure therapeutic efficacy of antiviral agents in small animal models. Bioluminescence is produced by the reaction of a luciferase enzyme stably inserted into the viral genome with a defined substrate systemically delivered into the animal. The light emitted is captured allowing the detection of viral infection sites and the quantification of viral replication in the context of tissues of a living animal. The goal of this chapter is to provide a technical background for the evaluation of poxvirus infection in cells and animals through bioluminescence imaging technology using luciferase-expressing recombinant poxviruses.