Ubiquitinated Hepatitis D Antigen-Loaded Microvesicles Induce a Potent Specific Cellular Immune Response to Inhibit HDV Replication in Vivo

Hepatitis D is the most severe form of human viral hepatitis and currently lacks an efficient therapy. Dendritic cell-derived exosomes (Dexs) have been found to induce immune responses capable of eliminating viruses. However, the therapeutic potential of antigen-loaded exosomes in hepatitis D is still unknown. Recently, we designed exosomes loaded with ubiquitinated hepatitis delta virus (HDV) small delta antigen (Ub-S-HDAg) and then treated mice bearing replicating HDV with these exosomes to explore their antiviral effect and mechanism. Mature dendritic cell-derived exosomes (mDexs) were loaded with Ub-S-HDAg and their antivirus function was evaluated in mice with HDV viremia. Furthermore, the proportion of CD8⁺ cells, the ratio of Th1/Th2 cells, the postimmunization levels of cytokines were explored, and the Janus kinases (JAK)/signal transducer and activator of transcription (STAT) pathway was evaluated with a JAK2 inhibitor AG490. In Ub-S-HDAg-Dexs group, the HDV RNA viral load was significantly decreased compared with other groups by CD8⁺ cell enrichment and an increase Th1/Th2 cell ratio. Furthermore, lymphocyte infiltration was increased, while the HDAg level was decreased in mouse liver tissue. However, there were no significant differences in HBV surface antigen (HBsAg), alanine aminotransferase (ALT), or aspartate aminotransferase (AST) levels among the groups. Moreover, p-JAK2, p-STAT1, p-STAT4, STAT1, and STAT4 expression was increased in Ub-S-HDAg-Dexs group. In conclusion, Ub-S-HDAg-Dexs might be a potential immunotherapeutic agent for eradicating HDV by inducing specific cellular immune response via the JAK/STAT pathway. IMPORTANCE Hepatitis D is the most severe viral hepatitis with accelerating the process of liver cirrhosis and increasing the risk of hepatocellular carcinoma. However, there are no effective antiviral drugs. Exosomes derived from mature dendritic cells are used not only as immunomodulators, but also as biological carriers to deliver antigens to induce robust immune response. Based on these properties, exosomes could be used as a biological immunotherapy by enhancing adaptive immune response to inhibit hepatitis D virus replication. Our research may provide a new therapeutic strategy to eradicate HDV in the future.

HTNV infection of CD8+ T cells is associated with disease progression in HFRS patients

Hantaan viruses (HTNVs) are zoonotic pathogens transmitted mainly by rodents and capable of infecting humans. Increasing knowledge of the human response to HTNV infection can guide the development of new preventative vaccines and therapeutic strategies. Here, we show that HTNV can infect CD8+ T cells in vivo in patients diagnosed with hemorrhagic fever with renal syndrome (HFRS). Electron microscopy-mediated tracking of the life cycle and ultrastructure of HTNV-infected CD8+ T cells in vitro showed an association between notable increases in cytoplasmic multivesicular bodies and virus production. Notably, based on a clinical cohort of 280 patients, we found that circulating HTNV-infected CD8+ T cell numbers in blood were proportional to disease severity. These results demonstrate that viral infected CD8+ T cells may be used as an adjunct marker for monitoring HFRS disease progression and that modulating T cell functions may be explored for new treatment strategies.

Novel Mechanism of Microvesicle Regulation by the Antiviral Protein Tetherin During HIV Infection

Background Microvesicles are cell membrane-derived vesicles that have been shown to augment inflammation. Specifically, monocyte-derived microvesicles (MDMVs), which can express the coagulation protein tissue factor, contribute to thrombus formation and cardiovascular disease. People living with HIV experience higher prevalence of cardiovascular disease and also exhibit increased levels of plasma microvesicles. The process of microvesicle release has striking similarity to budding of enveloped viruses. The surface protein tetherin inhibits viral budding by physically tethering budding virus particles to cells. Hence, we investigated the role of tetherin in regulating the release of MDMVs during HIV infection. Methods and Results The plasma of aviremic HIV-infected individuals had increased levels of tissue factor + MDMVs, as measured by flow cytometry, and correlated to reduced tetherin expression on monocytes. Superresolution confocal and electron microscopy showed that tetherin localized at the site of budding MDMVs. Mechanistic studies revealed that the exposure of monocytes to HIV-encoded Tat triggered tetherin loss and subsequent rise in MDMV production. Overexpression of tetherin in monocytes led to morphologic changes in the pseudopodia directly underneath the MDMVs. Further, tetherin knockout mice demonstrated a higher number of circulating MDMVs and less time to bleeding cessation. Conclusions Our studies define a novel regulatory mechanism of MDMV release through tetherin and explore its contribution to the procoagulatory state that is frequently observed in people with HIV. Such insights could lead to improved therapies for individuals infected with HIV and also for those with cardiovascular disease.

Capsid-deficient alphaviruses generate propagative infectious microvesicles at the plasma membrane

Alphavirus budding is driven by interactions between nucleocapsids assembled in the cytoplasm and envelope proteins present at the plasma membrane. So far, the expression of capsid and envelope proteins in infected cells has been considered an absolute requirement for alphavirus budding and propagation. In the present study, we show that Semliki Forest virus and Sindbis virus lacking the capsid gene can propagate in mammalian and insect cells. This propagation is mediated by the release of infectious microvesicles (iMVs), which are pleomorphic and have a larger size and density than wild-type virus. iMVs, which contain viral RNA inside and viral envelope proteins on their surface, are released at the plasma membrane and infect cells using the endocytic pathway in a similar way to wild-type virus. iMVs are not pathogenic in immunocompetent mice when injected intravenously, but can infect different organs like lungs and heart. Finally, we also show that alphavirus genomes without capsid can mediate the propagation of heterologous genes, making these vectors potentially interesting for gene therapy or vaccination studies. The minimalist infectious system described in this study shows that a self-replicating RNA able to express membrane proteins with binding and fusion properties is able to propagate, providing some insights into virus evolution.