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Lassa mammarenavirus (LASV) is a rodent-borne arenavirus endemic to several West African countries. It is the causative agent of human Lassa fever, an acute viral hemorrhagic fever disease. To date, no therapeutics or vaccines against LASV have obtained regulatory approval. Polyclonal neutralizing antibodies derived from hyperimmunized animals may offer a useful strategy for prophylactic and therapeutic intervention to combat human LASV infections. The LASV envelope surface glycoprotein complex (GP) is the major target for neutralizing antibodies, and it is the main viral antigen used for the design of an LASV vaccine. Here, we assessed the immunogenic potential of mammalian cell-derived virus-like particles (VLPs) expressing GP from the prototypic LASV strain Josiah in a native-like conformation as the sole viral antigen. We demonstrate that an adjuvanted prime-boost immunization regimen with GP-derived VLPs elicited neutralizing antibody responses in rabbits, suggesting that effective antigenic epitopes of GP were displayed. Notably, these antibodies exhibited broad reactivity across five genetic lineages of LASV. VLP-based immunization strategies may represent a powerful approach for generating polyclonal sera containing cross-reactive neutralizing antibodies against LASV.

International audience; Paramyxoviruses and pneumoviruses have similar life cycles and share the respiratory tract as a point of entry. In comparative genome-scale siRNA screens with wild-type-derived measles, mumps, and respiratory syncytial viruses in A549 cells, a human lung adenocarcinoma cell line, we identified vesicular transport, RNA processing pathways, and translation as the top pathways required by all three viruses. As the top hit in the translation pathway, ABCE1, a member of the ATP-binding cassette transporters, was chosen for further study. We found that ABCE1 supports replication of all three viruses, confirming its importance for viruses of both families. More detailed characterization revealed that ABCE1 is specifically required for efficient viral but not general cellular protein synthesis, indicating that paramyxoviral and pneumoviral mRNAs exploit specific translation mechanisms. In addition to providing a novel overview of cellular proteins and pathways that impact these important pathogens, this study highlights the role of ABCE1 as a host factor required for efficient paramyxovirus and pneumovirus translation.IMPORTANCE The Paramyxoviridae and Pneumoviridae families include important human and animal pathogens. To identify common host factors, we performed genome-scale siRNA screens with wild-type-derived measles, mumps, and respiratory syncytial viruses in the same cell line. A comparative bioinformatics analysis yielded different members of the coatomer complex I, translation factors ABCE1 and eIF3A, and several RNA binding proteins as cellular proteins with proviral activity for all three viruses. A more detailed characterization of ABCE1 revealed its essential role for viral protein synthesis. Taken together, these data sets provide new insight into the interactions between paramyxoviruses and pneumoviruses and host cell proteins and constitute a starting point for the development of broadly effective antivirals.

Long-term hematopoietic stem cells (LT-HSC) persist in quiescence to maintain their hematopoietic potential throughout life. In the case of need LT-HSC can be activated to replenish the pool of blood cells. We investigated the impact of acute influenza A virus (IAV) infection on hematopoiesis in C57Bl/6N mice, focusing on the most immature HSC and progenitors. Mice were infected with a lethal dose of IAV PR/8/1934 H1N1 (humane endpoints reached within 6 days post infection (dpi)). In two further groups, mice were treated daily with oseltamivir (antiviral neuraminidase inhibitor, dpi 0-4) or were vaccinated with single-cycle vesicular stomatitis virus replicon particles expressing a miss-matched neuraminidase from influenza A virus Yamaguchi/7/2004 H5N1 four weeks prior to infection. Both treatments rescued mice from infection-induced mortality. Every day 6-9 mice were analyzed for differences in the bone marrow (BM) and blood by flow cytometry and multiplex cytokine assays as well as in the lung to determine viral tissue titers and histopathology. HSC functionality was analyzed in a competitive BM transplantation of infected and non-infected mice. Irrespective of the treatment, high IAV lung tissue titers (≥5x106 tissue culture infectious dose 50) in the first days post infection (dpi 1-5) were associated with activation of HSC into the cell cycle. LT-HSCs (LSK, CD150+, CD34- and CD48-) were 50% less quiescent and shifted into the G1/S-G2-M phase (dpi 2-6) and returned to quiescence state after virus clearance (dpi 10). Furthermore, we detected 1.5-fold increase in proliferation of phenotypic LT-HSC. Differentiation was increased towards lymphoid progenitors (≥3-fold more compared to non-infected mice) during the acute phase of infection in untreated and oseltamivir treated mice and myeloid progenitors were reduced ~50% in all groups (dpi 4-8). We found the inflammatory cytokines IFNγ, IL-1α, IL-6, and TNFα to be significantly upregulated in the BM of untreated and oseltamivir treated mice but less in vaccinated animals (dpi 2-4). IL-1α or IL-6 stimulation of LT-HSCs was sufficient to initiate proliferation in cell culture. In all groups the initial drop of the peripheral platelet count (~30% lower compared to non-infected mice, dpi 2) was replenished with an excessive production of platelets (~45% increased, dpi 8-15). Histopathology and electron microscopy revealed the sequestration and accumulation of platelets in pulmonary capillaries and vessels. Subsequently, we detected twice as many mature megakaryocytes in the BM (dpi 2-4) and elevated CD41 expression on HSCs (LSK, CD150+ and CD34-; 3-fold more compared to non-infected mice dpi 2-6) indicating a myeloid/platelet-biased HSC compartment in response to infection. Competitive whole BM transplantation with activated LT-HSCs from the acute phase of infection vs non-infected mice showed delayed reconstitution of T-cells but a preferential differentiation towards platelets in recipient mice. Taken together, local IAV infection in the lung substantially affected LT-HSC quiescence and differentiation by inflammatory cytokines with systemic consequences and a myeloid/platelet-biased lineage output. Disclosures No relevant conflicts of interest to declare.