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Abstract Background Lassa fever (LF) is a devastating hemorrhagic viral disease that is endemic to West Africa and responsible for thousands of human deaths each year. Analysis of humoral immune responses (IgM and IgG) by antibody-capture ELISA (Ab-capture ELISA) and Lassa virus (LASV) viremia by antigen-capture ELISA (Ag-capture ELISA) in suspected patients admitted to the Kenema Government Hospital (KGH) Lassa Fever Ward (LFW) in Sierra Leone over the past five years is reshaping our understanding of acute LF. Results Analyses in LF survivors indicated that LASV-specific IgM persists for months to years after initial infection. Furthermore, exposure to LASV appeared to be more prevalent in historically non-endemic areas of West Africa with significant percentages of reportedly healthy donors IgM and IgG positive in LASV-specific Ab-capture ELISA. We found that LF patients who were Ag positive were more likely to die than suspected cases who were only IgM positive. Analysis of metabolic and immunological parameters in Ag positive LF patients revealed a strong correlation between survival and low levels of IL-6, -8, -10, CD40L, BUN, ALP, ALT, and AST. Despite presenting to the hospital with fever and in some instances other symptoms consistent with LF, the profiles of Ag negative IgM positive individuals were similar to those of normal donors and nonfatal (NF) LF cases, suggesting that IgM status cannot necessarily be considered a diagnostic marker of acute LF in suspected cases living in endemic areas of West Africa. Conclusion Only LASV viremia assessed by Ag-capture immunoassay, nucleic acid detection or virus isolation should be used to diagnose acute LASV infection in West Africans. LASV-specific IgM serostatus cannot be considered a diagnostic marker of acute LF in suspected cases living in endemic areas of West Africa. By applying these criteria, we identified a dysregulated metabolic and pro-inflammatory response profile conferring a poor prognosis in acute LF. In addition to suggesting that the current diagnostic paradigm for acute LF should be reconsidered, these studies present new opportunities for therapeutic interventions based on potential prognostic markers in LF.

Abstract Lassa fever (LF) is a devastating viral disease prevalent in West Africa. Efforts to take on this public health crisis have been hindered by lack of infrastructure and rapid field deployable diagnosis in areas where the disease is prevalent. Recent capacity building at the Kenema Government Hospital Lassa Fever Ward (KGH LFW) in Sierra Leone has lead to a major turning point in the diagnosis, treatment and study of LF. Herein we present the first comprehensive rapid diagnosis and real time characterization of an acute hemorrhagic LF case at KGH LFW. This case report focuses on a third trimester pregnant Sierra Leonean woman from the historically non-endemic Northern district of Tonkolili who survived the illness despite fetal demise. Employed in this study were newly developed recombinant LASV Antigen Rapid Test cassettes and dipstick lateral flow immunoassays (LFI) that enabled the diagnosis of LF within twenty minutes of sample collection. Deregulation of overall homeostasis, significant hepatic and renal system involvement, and immunity profiles were extensively characterized during the course of hospitalization. Rapid diagnosis, prompt treatment with a full course of intravenous (IV) ribavirin, IV fluids management, and real time monitoring of clinical parameters resulted in a positive maternal outcome despite admission to the LFW seven days post onset of symptoms, fetal demise, and a natural still birth delivery. These studies solidify the growing rapid diagnostic, treatment, and surveillance capabilities at the KGH LF Laboratory, and the potential to significantly improve the current high mortality rate caused by LF. As a result of the growing capacity, we were also able to isolate Lassa virus (LASV) RNA from the patient and perform Sanger sequencing where we found significant genetic divergence from commonly circulating Sierra Leonean strains, showing potential for the discovery of a newly emerged LASV strain with expanded geographic distribution. Furthermore, recent emergence of LF cases in Northern Sierra Leone highlights the need for superior diagnostics to aid in the monitoring of LASV strain divergence with potentially increased geographic expansion.

Abstract Lassa fever is a neglected tropical disease with a significant impact on the health care system of endemic West African nations. To date, case reports of Lassa fever have focused on laboratory characterisation of serological, biochemical and molecular aspects of the disease imported by infected individuals from Western Africa to the United States, Canada, Europe, Japan and Israel. Our report presents the first comprehensive real time diagnosis and characterization of a severe, hemorrhagic Lassa fever case in a Sierra Leonean individual admitted to the Kenema Government Hospital Lassa Fever Ward. Fever, malaise, unresponsiveness to anti-malarial and antibiotic drugs, followed by worsening symptoms and onset of haemorrhaging prompted medical officials to suspect Lassa fever. A recombinant Lassa virus protein based diagnostic was employed in diagnosing Lassa fever upon admission. This patient experienced a severe case of Lassa hemorrhagic fever with dysregulation of overall homeostasis, significant liver and renal system involvement, the interplay of pro- and anti-inflammatory cytokines during the course of hospitalization and an eventual successful outcome. These studies provide new insights into the pathophysiology and management of this viral illness and outline the improved infrastructure, research and real-time diagnostic capabilities within LASV endemic areas.

Abstract Background Lassa hemorrhagic fever (LHF) is a neglected tropical disease with significant impact on the health care system, society, and economy of Western and Central African nations where it is endemic. With a high rate of infection that may lead to morbidity and mortality, understanding how the virus interacts with the host's immune system is of great importance for generating vaccines and therapeutics. Previous work by our group identified a soluble isoform of the Lassa virus (LASV) GP1 (sGP1) in vitro resulting from the expression of the glycoprotein complex (GPC) gene 12. Though no work has directly been done to demonstrate the function of this soluble isoform in arenaviral infections, evidence points to immunomodulatory effects against the host's immune system mediated by a secreted glycoprotein component in filoviruses, another class of hemorrhagic fever-causing viruses. A significant fraction of shed glycoprotein isoforms during viral infection and biogenesis may attenuate the host's inflammatory response, thereby enhancing viral replication and tissue damage. Such shed glycoprotein mediated effects were previously reported for Ebola virus (EBOV), a filovirus that also causes hemorrhagic fever with nearly 90% fatality rates 345. The identification of an analogous phenomenon in vivo could establish a new correlate of LHF infection leading to the development of sensitive diagnostics targeting the earliest molecular events of the disease. Additionally, the reversal of potentially untoward immunomodulatory functions mediated by sGP1 could potentiate the development of novel therapeutic intervention. To this end, we investigated the presence of sGP1 in the serum of suspected LASV patients admitted to the Kenema Government Hospital (KGH) Lassa Fever Ward (LFW), in Kenema, Sierra Leone that tested positive for viral antigen or displayed classical signs of Lassa fever. Results It is reasonable to expect that a narrow window exists for detection of sGP1 as the sole protein shed during early arenaviral biogenesis. This phenomenon was clearly distinguishable from virion-associated GP1 only prior to the emergence of de novo viral particles. Despite this restricted time frame, in 2/46 suspected cases in two studies performed in late 2009 and early 2010, soluble glycoprotein component shedding was identified. Differential detection of viral antigens GP1, GP2, and NP by western blot yielded five different scenarios: whole LASV virions (GP1, GP2, NP; i.e. active viremia), different combinations of these three proteins, sGP1 only, NP only, and absence of all three proteins. Four additional samples showed inconclusive evidence for sGP1 shedding due to lack of detection of GP2 and NP by western blot; however, a sensitive LASV NP antigen capture ELISA generated marginally positive signals Conclusions During a narrow window following active infection with LASV, soluble GP1 can be detected in patient sera. This phenomenon parallels other VHF infection profiles, with the actual role of a soluble viral glycoprotein component in vivo remaining largely speculative. The expenditure of energy and cellular resources toward secretion of a critical protein during viral biogenesis without apparent specific function requires further investigation. Future studies will be aimed at systematically identifying the role of LASV sGP1 in the infection process and outcome in vitro and in vivo.

Abstract Background Lassa fever is a neglected tropical disease with significant impact on the health care system, society, and economy of Western and Central African nations where it is endemic. Treatment of acute Lassa fever infections has successfully utilized intravenous administration of ribavirin, a nucleotide analogue drug, but this is not an approved use; efficacy of oral administration has not been demonstrated. To date, several potential new vaccine platforms have been explored, but none have progressed toward clinical trials and commercialization. Therefore, the development of a robust vaccine platform that could be generated in sufficient quantities and at a low cost per dose could herald a subcontinent-wide vaccination program. This would move Lassa endemic areas toward the control and reduction of major outbreaks and endemic infections. To this end, we have employed efficient mammalian expression systems to generate a Lassa virus (LASV)-like particle (VLP)-based modular vaccine platform. Results A mammalian expression system that generated large quantities of LASV VLP in human cells at small scale settings was developed. These VLP contained the major immunological determinants of the virus: glycoprotein complex, nucleoprotein, and Z matrix protein, with known post-translational modifications. The viral proteins packaged into LASV VLP were characterized, including glycosylation profiles of glycoprotein subunits GP1 and GP2, and structural compartmentalization of each polypeptide. The host cell protein component of LASV VLP was also partially analyzed, namely glycoprotein incorporation, though the identity of these proteins remain unknown. All combinations of LASV Z, GPC, and NP proteins that generated VLP did not incorporate host cell ribosomes, a known component of native arenaviral particles, despite detection of small RNA species packaged into pseudoparticles. Although VLP did not contain the same host cell components as the native virion, electron microscopy analysis demonstrated that LASV VLP appeared structurally similar to native virions, with pleiomorphic distribution in size and shape. LASV VLP that displayed GPC or GPC+NP were immunogenic in mice, and generated a significant IgG response to individual viral proteins over the course of three immunizations, in the absence of adjuvants. Furthermore, sera from convalescent Lassa fever patients recognized VLP in ELISA format, thus affirming the presence of native epitopes displayed by the recombinant pseudoparticles. Conclusions These results established that modular LASV VLP can be generated displaying high levels of immunogenic viral proteins, and that small laboratory scale mammalian expression systems are capable of producing multi-milligram quantities of pseudoparticles. These VLP are structurally and morphologically similar to native LASV virions, but lack replicative functions, and thus can be safely generated in low biosafety level settings. LASV VLP were immunogenic in mice in the absence of adjuvants, with mature IgG responses developing within a few weeks after the first immunization. These studies highlight the relevance of a VLP platform for designing an optimal vaccine candidate against Lassa hemorrhagic fever, and warrant further investigation in lethal challenge animal models to establish their protective potential.

Abstract Background There is a significant requirement for the development and acquisition of reagents that will facilitate effective diagnosis, treatment, and prevention of Lassa fever. In this regard, detection of early markers of Lassa virus (LASV) infection may improve diagnosis and ultimately successful treatment with antivirals. Characterization of LASV GP1 ectodomain shedding is an important step toward developing sensitive diagnostics to detect circulating levels of this viral glycoprotein in infected patient sera. Results Secretion of GP1 from mammalian cells expressing a native LASV GPC gene was not mediated by proteolytic cleavage, as determined by treatment with a panel of matrix metalloprotease (MMP) inhibitors. The shedding of GP1 was also not the result of over-expression of GPC under the control of a strong intron-A containing CMV promoter, as the soluble component could be immunoprecipitated from supernatants of cells expressing low levels of GPC under the control of an intronless promoter. Cells transfected with GPC retained surface membrane-associated expression of GP1 as determined by immunofluorescence assay, in addition to secreting the glycoprotein. Secreted GP1 derived from GPC expression has a higher content of high mannose N-linked glycosylation than sGP1 expressed independently from the GP2 portion of the protein. Neither GP1 isoform contains sialylated N-glycans, O-linked carbohydrate chains, or galactose-β(1-4)-N-acetylglucosamine commonly present in complex and hybrid N-glycan structures. Conclusion These results demonstrate the non-proteolytic secretory nature of GP1 shedding during expression of the arenaviral glycoprotein complex. This phenomenon parallels shedding of a secretory glycoprotein component in filovirus replication. The glycosylation pattern of soluble GP1 resulting from expression of GPC was different from that of a soluble GP1 construct (sGP1-RRAA-FLAG), highlighting the intricately orchestrated post translational processing of the LASV glycoprotein complex.

Abstract Background Sera from convalescent Lassa fever patients often contains antibodies to Lassa virus (LASV) glycoprotein 1 (GP1), and glycoprotein 2 (GP2); Immunization of non-human primates with viral vectors expressing the arenaviral glycoprotein complex (GPC) confers full protective immunity against a lethal challenge with LASV. Thus, the development of native or quasi native recombinant LASV GP1 and GP2 as soluble, uncoupled proteins will improve current diagnostics, treatment, and prevention of Lassa fever. To this end, mammalian expression systems were engineered for production and purification of secreted forms of soluble LASV GP1 and GP2 proteins. Results Determinants for mammalian cell expression of secreted uncoupled Lassa virus (LASV) glycoprotein 1 (GP1) and glycoprotein 2 (GP2) were established. Soluble GP1 was generated using either the native glycoprotein precursor (GPC) signal peptide (SP) or human IgG signal sequences (s.s.). GP2 was secreted from cells only when (1) the transmembrane (TM) domain was deleted, the intracellular domain (IC) was fused to the ectodomain, and the gene was co-expressed with a complete GP1 gene in cis; (2) the TM and IC domains were deleted and GP1 was co-expressed in cis; (3) expression of GP1 was driven by the native GPC SP. These data implicate GP1 as a chaperone for processing and shuttling GP2 to the cell surface. The soluble forms of GP1 and GP2 generated through these studies were secreted as homogeneously glycosylated proteins that contained high mannose glycans. Furthermore, observation of GP1 ectodomain shedding from cells expressing wild type LASV GPC represents a novel aspect of arenaviral glycoprotein expression. Conclusion These results implicate GP1 as a chaperone for the correct processing and shuttling of GP2 to the cell surface, and suggest that native GPC SP plays a role in this process. In the absence of GP1 and GPC SP the GP2 protein may be processed by an alternate pathway that produces heterogeneously glycosylated protein, or the polypeptide may not fully mature in the secretory cascade in mammalian cells. The expression constructs developed in these studies resulted in the generation and purification of soluble, uncoupled GP1 and GP2 proteins from mammalian cells with quasi-native properties. The observation of GP1 ectodomain shedding from cells expressing wild type LASV GPC establishes new correlates of disease progression and highlights potential opportunities for development of diagnostics targeting the early stages of Lassa fever.

Abstract Background There is a significant requirement for the development and acquisition of reagents that will facilitate effective diagnosis, treatment, and prevention of Lassa fever. In this regard, recombinant Lassa virus (LASV) proteins may serve as valuable tools in diverse antiviral applications. Bacterial-based systems were engineered for expression and purification of recombinant LASV nucleoprotein (NP), glycoprotein 1 (GP1), and glycoprotein 2 (GP2). Results Full-length NP and the ectodomains of GP1 and GP2 were generated as maltose-binding protein (MBP) fusions in the Rosetta strains of Escherichia coli (E. coli) using pMAL-c2x vectors. Average fusion protein yields per liter of culture for MBP-NP, MBP-GP1, and MBP-GP2 were 10 mg, 9 mg, and 9 mg, respectively. Each protein was captured from cell lysates using amylose resin, cleaved with Factor Xa, and purified using size-exclusion chromatography (SEC). Fermentation cultures resulted in average yields per liter of 1.6 mg, 1.5 mg, and 0.7 mg of purified NP, GP1 and GP2, respectively. LASV-specific antibodies in human convalescent sera specifically detected each of the purified recombinant LASV proteins, highlighting their utility in diagnostic applications. In addition, mouse hyperimmune ascitic fluids (MHAF) against a panel of Old and New World arenaviruses demonstrated selective cross reactivity with LASV proteins in Western blot and enzyme-linked immunosorbent assay (ELISA). Conclusion These results demonstrate the potential for developing broadly reactive immunological assays that employ all three arenaviral proteins individually and in combination.