In vitro cellular tropism and immunomodulatory response to rVSVΔG-ZEBOV-GP in human cells derived from tissues associated with adverse events

The recombinant vesicular stomatitis virus-vectored Zaire Ebola virus glycoprotein (rVSV Delta G-ZEBOV-GP) vaccine, while effective and well-tolerated, exhibits notable reactogenicity, manifesting in expected adverse events (AEs), such as fever, headache, and pain, along with rare, unexpected AEs, including skin lesions, cutaneous vasculitis, and transient arthritis. The presence or absence of AEs following rVSV Delta G-ZEBOV-GP vaccination is associated with a specific innate plasma signature. This study aims to elucidate in vitro the tropism of the vaccine for different cell types derived from tissues previously reported to be involved in the unexpected AEs. Upon in vitro infection with rVSV Delta G-ZEBOV-GP, various cell types, such as synoviocytes, fibroblasts, keratinocytes, and endothelial cells (except chondrocytes), demonstrate productive infection, which in dermal fibroblasts triggered the release of many innate plasma signature markers, including keratinocytes' pro-inflammatory and proapoptotic cytokines such as OSM and TRAIL. Infected monocytes from buffy coats, activated by infection, produce most innate plasma signature markers. In co-culture, rVSV Delta G-ZEBOV-GP-infected monocytes serve as a source to synoviocyte infection, resulting in distinct kinetics modulation in innate biomarkers (transcription and secretion) and upregulation of specific genes, such as NEDD8 and SIGLEC-1, which have been associated with inflammatory arthritis in animal models. Altogether, our work, based on in vitro studies, provides insights into the possible mechanisms of rVSV Delta G-ZEBOV-GP underlying the observed reactogenicity by showing tropism of the vaccine for off-target cells derived from AE-affected compartments (skin, joints, vessels). Furthermore, in vitro interaction with infected monocytes modulates the innate response of synoviocytes.IMPORTANCEOur study expanded knowledge about the cellular tropism of rVSV Delta G-ZEBOV-GP vaccine toward peripheral blood mononuclear cells and cell lines derived from tissues (skin, vessels, and joints) associated with unexpected AEs, as well as their possible contribution to the vaccine-induced innate response. Using in vitro infection and co-culture techniques, we showed that rVSV Delta G-ZEBOV-GP-infected monocytes can transmit the virus to synoviocytes, and how infection affects human monocytes and synoviocytes at the protein and transcriptomic levels. Our findings provide insights into the in vitro off-target infection dynamics and innate immune response triggered by rVSV Delta G-ZEBOV-GP vaccine. While these results may enhance understanding of rVSV-based vectors, in vivo relevance remains unclear, as does whether the effects come from the VSV backbone or Ebola GP. These findings support the evaluation of off-target effects of rVSV-based vaccine candidates, including those under development for hemorrhagic fever viruses, such as Marburg virus, Sudan virus, and Lassa virus, especially if similar AEs are observed.