Structural Basis for a Convergent Immune Response against Ebola Virus.

Ebola virus disease is a severe health problem in Africa. Vaccines that display the Zaire ebolavirus glycoprotein spike complex are a prime component for the effort to combat it. The VH3-15/Vλ1-40-based class of antibodies was recently discovered to be a common response in individuals who received the Ebola virus vaccines. These antibodies display attractive properties, and thus likely contribute to the efficacy of the vaccines. Here, we use cryo-EM to elucidate how three VH3-15/Vλ1-40 antibodies from different individuals target the virus and found a convergent mechanism against a partially conserved site on the spike complex. Our study rationalizes the selection of the VH3-15/Vλ1-40 germline genes for specifically targeting this site and highlights Ebolavirus species-specific sequence divergences that may restrict breadth of VH3-15/Vλ1-40-based humoral response. The results from this study could help develop improved immunization schemes and further enable the design of immunogens that would be efficacious against a broader set of Ebolavirus species.

Polyclonal and convergent antibody response to Ebola virus vaccine rVSV-ZEBOV.

Recombinant vesicular stomatitis virus-Zaire Ebola virus (rVSV-ZEBOV) is the most advanced Ebola virus vaccine candidate and is currently being used to combat the outbreak of Ebola virus disease (EVD) in the Democratic Republic of the Congo (DRC). Here we examine the humoral immune response in a subset of human volunteers enrolled in a phase 1 rVSV-ZEBOV vaccination trial by performing comprehensive single B cell and electron microscopy structure analyses. Four studied vaccinees show polyclonal, yet reproducible and convergent B cell responses with shared sequence characteristics. EBOV-targeting antibodies cross-react with other Ebolavirus species, and detailed epitope mapping revealed overlapping target epitopes with antibodies isolated from EVD survivors. Moreover, in all vaccinees, we detected highly potent EBOV-neutralizing antibodies with activities comparable or superior to the monoclonal antibodies currently used in clinical trials. These include antibodies combining the IGHV3-15/IGLV1-40 immunoglobulin gene segments that were identified in all investigated individuals. Our findings will help to evaluate and direct current and future vaccination strategies and offer opportunities for novel EVD therapies.

Interaction and Mutual Activation of Different Innate Immune Cells Is Necessary to Kill and Clear Hepatitis C Virus-Infected Cells.

Innate immune cells can sense hepatitis C virus (HCV)-infected cells and respond with anti-viral actions including secretion of interferons (IFNs). In previous studies, the response of individual innate immune cells against HCV was analyzed in detail. We hypothesized that interaction of multiple innate immune cells increases the magnitude of the immune response and eventually leads to clearance of HCV-infected cells. To investigate this, we co-cultured Huh-7 HCV subgenomic replicon (SGR) cells with peripheral blood mononuclear cells (PBMCs). We confirm secretion of IFNα by plasmacytoid dendritic cells (pDCs) and IFNγ by natural killer (NK) cells in the co-culture setup. Moreover, we observed that also monocytes contribute to the anti-viral response. Flow cytometry and ImageStream analysis demonstrated that monocytes take up material from HCV SGR cells in co-culture with PBMCs. Preceding the uptake, PBMCs caused apoptosis of HCV SGR cells by tumor necrosis factor-related apoptosis inducing ligand (TRAIL) expression on NK cells. We observed that only the interplay of monocytes, pDCs, and NK cells resulted in efficient clearance of HCV SGR cells, while these cell populations alone did not kill HCV SGR cells. Despite similar TRAIL receptor expression on Huh-7 control cells and HCV SGR cells, HCV activated PBMCs specifically killed HCV SGR cells and did not target Huh-7 control cells. Finally, we showed that HCV replicating cells per se are sensitive toward TRAIL-induced apoptosis. Our results highlight the importance of the interplay of different innate immune cells to initiate an efficient, rapid, and specific response against HCV-infected cells.

Erythropoietin acts as an anti-inflammatory signal on murine mast cells.

Recently it was found that the erythropoietin receptor (EpoR) is expressed on innate immune cells, such as dendritic cells and macrophages. We found that murine bone marrow-derived mast cells express the EpoR and that its expression is increased under hypoxic conditions. Interestingly, Epo stimulation of the cells did not activate signal transducer and activator of transcription molecules, nor did we find differences in the expression of typical STAT-dependent genes, the proliferation rate, and the ability to differentiate or to protect the cells from apoptosis. Instead, we demonstrate that stimulation of mast cells with Epo leads to phosphorylation of the receptor tyrosine kinase c-kit. We hypothesize that this is due to the formation of a receptor complex between the EpoR and c-kit. The common beta chain of the IL-3 receptor family, which was described as part of the tissue protective receptor (TPR) on other non-erythroid cells, however is not activated. To investigate whether the EpoR/c-kit complex has tissue protective properties, cells were treated with the Toll-like receptor ligand LPS. Combined Epo and LPS treatment downregulated the inflammatory response of the cells as detected by a decrease in IL-6 and TNF-α secretion.