Patent Publication Number: US-11638751-B2

Title: Immunogenic composition comprising a recombinant attenuated mopeia virus with a modified nucleoprotein displaying reduced exonuclease activity

Description:
SEQUENCE LISTING 
     The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 22, 2018, is named 373946_D36598_CMB_SL.txt and is 84,079 bytes in size. 
     INTRODUCTION 
     Mopeia virus (MOPV) is an old-world arenavirus, phylogenetically closely related to Lassa (LASV). MOPV was first isolated in Mastomys rodent in Mozambique, whereas LASV is endemic in West Africa. On the contrary to LASV, MOPV infection was never observed in human and experimental infection of monkeys with MOPV is asymptomatic. LASV, the etiological agent of Lassa Fever (LF), infects 100,000 to 300,000 persons each year, killing about 5,000 of them 1 . The virus is naturally present in Mastomys rodents and human contamination occurs through direct contact with rodents or their dejections. After a relatively short incubation period, the onset of the disease starts with flu-like symptoms, such as fever, myalgia, headaches. In the severe forms, haemorrhages and oedema are then observed 2 . In the late stages, death of patients occurs in a hypovolemic, hypotensive and hypoxic shock context. For those who survive, severe complications have been reported, such as persistent myalgia and deafness 3 . To date, no licensed vaccine or efficient treatment is available for use on the field. Moreover, the virus is also sometimes exported to industrial countries 4    
     Other arenaviruses are also responsible for severe hemorrhagic fevers, with a similar clinical picture: Lujo virus 5  (belonging to the old world arenavirus Clade), Junin 6 , Chapare 7 , Machupo 8 , Sabia 9 , Guanarito 10  and Whitewater Arroyo 11  (all belonging to the New World Clade). New arenaviruses are frequently isolated, either in humans or in rodents, and the area affected by these viruses are expanding, demonstrating the dynamism of this viral family and the threat they represent for public health. 
     To date, no treatment is available to fight against those deadly agents. The only FDA-approved vaccine available is the Candid #1 vaccine 12 , a natural attenuated strain of Junin virus, which is able to protect humans against this virus. Thus, the development of a vaccine strategy directed against arenavirus-induced diseases is an important challenge and probably represents the most valuable approach to cope with this threat. 
     Experimental vaccination of non-human primates (NHP) with MOPV protected them against an experimental challenge with LASV, shedding light on the protective potential of MOPV against LASV. However, the administration of such a natural virus in humans is not feasible, due to the lack of full knowledge regarding its safety in human and more particularly in immunocompromised people, elderly people and pregnant women. Moreover, administration of a live, natural virus as a vaccine raises ethical concerns and for a variety of reasons is not feasible. 
     Accordingly, there is a need in the art for a vaccine platform and vaccines against pathogenic arenaviruses, including against LASV, for use as a vaccine and/or therapeutic against arenaviruses responsible for hemorrhagic fevers and other conditions in humans. The inventions disclosed and provided herein meet these and other needs. 
     SUMMARY 
     The inventors have made the discovery that the nucleoprotein (NP) of MOPV has an exonuclease function similar to that of LASV. In LASV, the exonuclease function plays a role in pathogenicity because it digests double-stranded RNA (dsRNA), which is an important Pathogen Associated Molecular Pattern (PAMPs) which is expected to be recognized by the innate immune system to fight against infection. Because LASV NP is able to digest these dsRNA, their recognition by the immune system and subsequent IFN activation is thus avoided 14 , leading to relentless virus replication and dissemination. It is surprising that the NP of MOPV also exhibits this exonuclease function because the MOPV is non pathogenic. As described in the examples, the inventors have generated a recombinant MOPV, in which the exonuclease function has been abrogated (MOPV-ExoN). The examples characterize this virus for its replicative properties and immunogenicity, and identified that this virus is poorly replicative in immune cells, able to strongly activate dendritic cells (DC) and macrophages (MP), and is much more immunogenic than its wild type counterpart. Based in part on this data, this invention provides a new vaccine platform against pathogenic arenaviruses. 
     The examples describe making of exemplary recombinant attenuated MOPV comprising an NP having attenuated exonuclease activity and optionally a heterologous glycoprotein (GP), notably a heterologous glycoprotein precursor (GPC) from a pathogenic arenavirus (e.g., Lasso). As demonstrated in the examples, the recombinant attenuated MOPV exhibit several desirable properties demonstrating that recombinant attenuated MOPVs of the invention are particularly useful as agents for inducing immunogenic responses in a subject against an arenavirus, such as for immunizing against or treating an arenavirus infection. 
     Accordingly, this invention provides recombinant attenuated Mopeia virus (MOPV). In some embodiments, the recombinant attenuated MOPV comprises a heterologous nucleic acid and a nucleic acid encoding a nucleoprotein having attenuated exonuclease activity. The recombinant attenuated MOPV are useful, for example, to induce an immunogenic response against an arenavirus in a subject. 
     In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises an amino acid substitution at amino acid position D390 or G393. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393. 
     In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitution at amino acid position D390 or G393, and further comprises at least one amino acid substitution at a position selected from E392, H430, D467, H529, and D534. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 or G393, and further comprises amino acid substitution at position E392. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 or G393, and further comprises amino acid substitutions at positions E392 and H430. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 or G393, and further comprises amino acid substitutions at positions E392, H430 and D467. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions 0390 or G393, and further comprises amino acid substitutions at positions E392, H430, D467 and H529. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 or G393, and further comprises amino acid substitutions at positions E392, H430, D467 and D534. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 or G393, and further comprises amino acid substitutions at positions E392, H430, D467, H529 and D534. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises at least one amino acid substitution at a position selected from E392, H430, 0467, H529, and D534. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises amino acid substitutions at position E392. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises amino acid substitutions at positions E392 and H430. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions 0390 and G393, and further comprises amino acid substitutions at positions E392, H430 and D467. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises amino acid substitutions at positions E392, H430, D467 and H529. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises amino acid substitutions at positions E392, H430, D467 and 0534 (designated MOPV-ExoNM6b). In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises amino acid substitutions at positions E392, H430, D467, H529 and 0534. 
     In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises a D390A or a G393A amino acid substitution. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises the D390A and G393A amino acid substitutions. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises at least one amino acid substitution selected from E392A, H430A, D467A, H529A, and D534A. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises amino acid substitutions at position E392A (designated MOPV-ExoNM3). In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises amino acid substitutions at positions E392A and H430A (designated MOPV-ExoNM4). In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises amino acid substitutions at positions E392A, H430A and D467A (designated MOPV-ExoNM5). In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises amino acid substitutions at positions E392A, H430A, D467A and H529A (designated MOPV-ExoNM6a). In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises amino acid substitutions at positions E392A, H430A, D467A and D534A (designated MOPV-ExoNM6b). In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises amino acid substitutions at positions E392A, H430A, D467A, H529A and D534A (designated MOPV-ExoNM7). 
     In some embodiments of the recombinant attenuated MOPV, the heterologous nucleic acid encodes a non-MOPV arenavirus glycoprotein (GP), notably a non-MOPV arenavirus glycoprotein precursor (GPC). In some embodiments of the recombinant attenuated MOPV, the non-MOPV arenavirus is a Lasso virus (LASV). 
     In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells, strongly activates at Least one of dendritic cells (DC) and macrophages (MP), and/or is more immunogenic than unmodified MOPV. In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells. In some embodiments, the recombinant attenuated MOPV is strongly activates at least one of dendritic cells (DC) and macrophages (MP). In some embodiments, the recombinant attenuated MOPV is more immunogenic than unmodified MOPV. 
     In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells and strongly activates at least one of dendritic cells (DC) and macrophages (MP). 
     In some embodiments, the recombinant attenuated MOPV strongly activates at least one of dendritic cells (DC) and macrophages (MP), and is more immunogenic than unmodified MOPV. 
     In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells and is more immunogenic than unmodified MOPV. 
     The invention also provides immunogenic compositions that comprise at least one of the recombinant attenuated MOPVs disclosed herein. 
     The invention also provides methods of inducing an immune response against an arenavirus in a subject. In some embodiments, the method is a method of inducing a protective immune response against an arenavirus in a subject at risk of infection with the arenavirus. Such methods may comprise administering an effective amount of an arenavirus of the invention, such as in the form of an immunogenic composition comprising an arenavirus of the invention, to the subject. 
     In some embodiments, the method is a method of inducing a therapeutic immune response against an arenavirus in a subject Infected with the arenavirus. Such methods may comprise administering an effective amount of an arenavirus of the invention, such as in the form of an immunogenic composition comprising an arenavirus of the invention, to a subject infected with the arenavirus. 
     The invention also provides a eukaryotic cell comprising a recombinant MOPV of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A  to IC show rational design used herein to make the disclosed anti-LASV vaccine prototype. (A) Identification of critical residues in NP protein which are important for abrogation of MOPV NP exonuclease function, localisation of the DEDDH domain. SEQ ID NO. 6: PNAKTWIDIEGRPED (B) Genetic manipulation of the MOPV Short segment. 1. Site-directed mutagenesis was used to introduce D390A/6393A (and others) toss of function mutations in NP open-reading frame. 2. Swapping of GPc gene in MOPV short genomic segment. 3. Combination of both approaches resulting in MOPV-ExoN-GP LASV . (C) Reverse genetics strategy for the obtention of the mutated recombinant viruses. The engineered pPOLI-MOPV-Sag was transfected together with PTM1-LPol, PTM1-NP, pPOL1-MOPV-Lag in T7 polymerase harboring cells, leading to production of rec-MOPV, MOPV-ExoN, MOPV-ExoN enhanced , MOPV-ExoNM6b, MOPV-GP LASV , MOPV-ExoN-GP LASV , MOPV-ExoN enhanced -GP LASV  and MOPV-ExoNM6b-GPC viruses expressing other GPCs. 
         FIGS.  2 A to  2 B  show replicative properties of MOPV-ExoN. (A) Vero E6 cells were infected at a MOI of 0.01. Celt supernatants were collected daily for up to 7 days, and virus concentration was determined by plaque assay. Results are expressed in tog of Focus-Forming Unit/ml (log FFU/ml). (B) Monocytes-derived Dendritic Cells (left panel) and Macrophages (right panel) were infected with rec-, nat-MOPV or MOPV-ExoN, at a MOI of 0.1. Supernatants were harvested daily for up to 4 days, and viral titers were determined. Data are representative of 3 different experiments, error bars mean Standard Error. 
         FIGS.  3 A to  3 B  show immunological properties of MOPV ExoN. Monocytes-derived Dendritic Cells (panel A) or Monocytes-derived Macrophages (panel B) were infected at a MOI of 1 with nat-, rec-MOPV or MOPV-ExoN, or MOCK-infected. 48 h post-infection, cells were harvested and analysed by Flow Cytometry for expression of CD80, CD83, CD40 and CD86 surface markers, and in the case of Macrophages, for intra-cellular presence of activated Caspase 3. Data are expressed in percentage of total cells. Data are expressed as the mean of 4 different experiments, and error bars mean Standard Errors. (*): P&lt;0.05; (**): P&lt;0.01; (***): P&lt;0.001. 
         FIGS.  4 A to  4 B  show activation of innate immunity by MOPV-ExoN. Monocytes-derived Dendritic Cells (panel A) or Monocytes-derived Macrophages (panel B) were infected at a MOI of 1 with nat-, rec-MOPV or MOPV-ExoN, or MOCK-infected. 24 h post-infection, cells were harvested and cellular RNA was extracted, reverse-transcribed using oligo-dT primers, and submitted to quantitative PCR for IFNalpha1, IFNalpha2, IFNbeta, TNFalpha and CXCL10. Data are represented as normalized expression to GAPDH housekeeping gene, and are the mean of 4 independent experiments, error bar mean Standard Errors. (*): P&lt;0.05. 
         FIG.  5    shows the impact of swapping of gp genes on viral replication. Vero E6 cells infected with rec-MOPV, rec-MOPV-GP LASV  or rec-MOPV-ExoN-GP LASV , at a MOI of 0.01. Cell supernatants were collected 24, 48, 72 and % hours post-infection, and viral titers, determined by plaque assays, are expressed in tog of Focus Forming Units/mi (log FFU/ml). Data represent means of two concomitant experiments, for which each titre was determined twice. Error bars mean Standard Error. 
         FIGS.  6 A to  6 B  show that Lassa GPC is not involved in the type I IFN response during infection. (A) Kinetics of LASV-wt, LASV-GPC MOPV , MOPV-wt and MOPV-GPC LASV  viruses in VeroE6 cells infected at MOI of 0.01. Viral titers were determined by titration of culture supernatants in VeroE6 and expressed as logs of Focus Forming Units/ml (FFU/mL). (B) 
       Human monocyte-derived macrophages were mock infected or infected at MOI of 1 with LASV-wt, LASV-GPC MOPV , MOPV-wt and MOPV-GPC LASV . Total cellular RNA was extracted using RLT reagent (Qiagen). The levels of IFN-alpha1 (left graph), IFN-alpha2 (middle graph), and IFN-beta (right graph) mRNAs in mock infected or infected cells were determined by quantitative RT-PCR 24 h after infection. The results reported are the numbers of copies of the mRNA considered/number of copies of GADPH mRNA and represent the mean±standard error from three independent experiments (different donors). *=P&lt;0.05; ns=not statistically relevant. 
         FIGS.  7 A to  7 E  show the consolidation of the ExoN KO activity. (A) Residues involved in the coordination of the divalent cation mandatory for the ExoN activity of the nucleoprotein NP and proposed mutants; SEQ ID NO. 8: D390, E392, G393, H430, 0467, H529, D534; SEQ ID NO. 9: ExoNM; SEQ ID NO. 10: ExoNM3; SEQ ID NO. 11: ExoNM4; SEQ ID NO. 12: ExoNM5; SEQ ID NO. 13: ExoNM6a; SEQ ID NO. 14: ExoNM6b; SEQ ID NO. 15: ExoNM7. (B) IFN-antagonist activity of the NP mutants in a reporter gene assay. In this assay, the induction of an IFN-derived promoter by Sendai virus (SeV) is assessed in transfected cells expressing different NP mutants. Kinetics of MOPV-wt, MOPV-ExoNM2 and MOPV-ExoNM6b mutant viruses (C) in VeroE6 cells infected at MOI of 0.01 and (D) in human monocyte-derived macrophages infected at MOI of 0. 5. Viral titers were determined by titration of culture supernatants in VeroE6 as mentioned above. (E) Total cellular RNAs were extracted from mock infected or infected macrophages and the levels of IFN-α1 (upper graph), IFN-α2 (middle graph), and IFN-β (lower graph) mRNAs were determined by quantitative RT-PCR 24 h after infection. The results are reported as shown in  FIG.  6 B . 
         FIGS.  8 A to  8 D  show that Mopeia M6b based viruses harbouring GPC of cognate arenaviruses activate immune cells and are strong Inducers of the type I IFN response. (A) Infectious foci induced in VeroE6 cells by the different recombinant MOPV-wt and -ExoNM6b based viruses expressing GPC Lassa (Josiah), Lujo, Machupo (Carvallo), Guanarito (INH95551), Chapare and Sabia viruses and revealed by immunostaining. (B) Kinetics of MOPV-wt, MOPV-ExoNM6b, MOPV-ExoNM6b-GPC LASV  and MOPV-ExoNM6b-GPC MACV  viruses in human monocyte-derived macrophages infected at MOI of 0.05. (C, D) Human monocyte-derived macrophages mock infected or infected at MOI of 0.5 with MOPV-wt, MOPV-ExoNM6b, 
       MOPV-ExoNM6b-GPC LASV  and MOPV-ExoNM6b-GPC MACV . Flow cytometry detection of cell surface activation markers CD40, CD80 and CD86 in mock or infected human macrophages 48 h post infection (C). Total cellular RNAs were extracted and the levels of IFN-α1 (left graph), IFN-α2 (middle graph), and IFN-β (right graph) mRNAs were determined by quantitative RT-PCR 24 h or 48 h after infection (D). The results are reported as shown in  FIG.  66   . 
         FIG.  9    shows a simplified schematic of the Mopeia reverse genetic system. 
     
    
    
     DETAILED DESCRIPTION 
     A. Arenaviruses 
     Arenavirus is a genus of virus that infects rodents and occasionally humans. At least eight arenaviruses are known to cause human disease. The diseases derived from arenaviruses range in severity. Aseptic meningitis, a severe human disease that causes inflammation covering the brain and spinal cord, can arise from the Lymphocytic choriomeningitis virus (LCMV) infection. Hemorrhagic fever syndromes may be derived from infections by guanarito virus (GTOV), junin virus (JUNV), lassa virus (LASV), lujo virus (LUJV), machupo virus (MACV), sabia virus (SABV), or whitewater arroyo virus (WWAV). Arenaviruses are divided into two groups: the Old World and the New World viruses. The differences between these groups are distinguished geographically and genetically. 
     Arenaviruses are round, pleomorphic, and enveloped with a diameter of 60 to 300 nm. Although they are often miscategorized as negative sense viruses, they are in fact ambisense. This confusion stems from the fact that while sections of their genome are considered negative sense, and encode genes in the reverse direction, other sections encode genes in the opposite (forward/positive sense) direction. This complex gene expression structure is theorized to be the viruses primitive regulatory system, allowing the virus to control what proteins are synthesized when. The life cycle of the arenavirus is restricted to the cell cytoplasm. Virus particles, or virions, are pleomorphic because they vary in appearances but in many cases they are spherical in shape and covered with surface glycoprotein spikes. 
     Arenaviruses have a segmented RNA genome that consists of two single-stranded ambisense RNAs. The genomic RNA alone is not infectious and the viral replication machinery is required to initiate infection within a host cell. Genomic sense RNA packaged into the arenavirus virion is designated negative-sense RNA, and must first be copied into a positive-sense mRNA in order to produce viral protein. The two RNA segments are denoted Small (S) and Large (L), and code for four viral proteins in a unique ambisense coding strategy. Each RNA segment codes for two viral proteins in opposite orientation such that the negative-sense RNA genome serves as the template for transcription of a single mRNA and the positive-sense copy of the RNA genome templates a second mRNA. Specifically, the S-segment RNA encodes the viral nucleocapsid protein (NP) and the glycoprotein (GP), notably the glycoprotein precursor (GPC); and the L-segment RNA encodes the viral RNA-dependent RNA-polymerase (L) and a small RING-domain containing protein (Z). The separate coding sequences of the two viral proteins are divided by an intergenic region RNA sequence that is predicted to fold into a stable hairpin structure. The skilled person will appreciate that genomic sequences of the various arenaviruses, as well as of the proteins encoded by these viruses, are publicly available. They can be found e.g., on the web site of the Virus Sequence Database(VSD) established and maintained by the Center for Immunology and Pathology, National Institute of Health, Korea Centers for Disease Control and Prevention. 
     In the application, when reference is made a (RNA) virus, reference is equally (and implicitly) made to a clone of said (RNA) virus, such as a RNA, DNA or cDNA clone. 
     The extreme termini of each RNA segment contains a highly conserved sequence for recruitment of the viral replication machinery and initiation of viral mRNA transcription and genomic replication. The conserved 5′ and 3′ RNA termini sequences are complementary and allow each RNA segment to adopt a double-stranded RNA panhandle structure that maintains the termini in close proximity and results in a circular appearance to purified arenavirus genomic templates visualized by electron microscopy. 
     The Z protein forms homo oligomers and a structural component of the virions. The formation of these oligomers is an essential step for particle assembly and budding. Binding between Z and the viral envelope glycoprotein complex is required for virion infectivity. Z also interacts with the L and NP proteins. Polymerase activity appears to be modulated by the association between the L and Z proteins. Interaction between the Z and NP proteins is critical for genome packaging. The glycoprotein (GP) is synthesised as a precursor molecule (glycoprotein precursor, GPC). It is post-translationally cleaved into three parts: the mature virion glycoproteins GP1 and GP2, and a stable signal peptide (5SP). These reactions are catalysed by cellular signal peptidases and the cellular enzyme Subtilisin Kexin Isozyme-1 (SKI-1)/Site-1 Protease (SIP). 
     Arenaviruses can be divided into two serogroups, which differ genetically and by geographical distribution. When the virus is classified “Old World”, this means it was found in the Eastern Hemisphere in places such as Europe, Asia, and Africa. When it is found in the Western Hemisphere, in places such as Argentina, Bolivia, Venezuela, Brazil, and the United States, it is classified “New World”. Lymphocytic choriomeningitis virus (LCMV) is the only Arenavirus to exist in both areas but is classified as an Old World virus. The Old World complex includes Gairo virus, Gbagroube virus, Ippy virus, Kodoko virus, Lassa virus, Lujo virus, Luna virus, Lunk virus, Lymphocytic choriomeningitis virus, Merino Walk virus, Menekre virus, Mobata virus, Morogoro virus, Mopeia virus, Wenzhou virus, and Tacaribe virus. The New World complex includes Amapari virus, Chapare virus, Flexal virus, Guanarito virus, Junin virus, Latino virus, Machupo virus, Oliveros virus, Paraná virus, Patawa virus, Pichinde virus, Pirital virus, Sabia virus, Tacaribe virus, Tamiami virus, and Whitewater Arroyo virus. 
     A “heterologous nucleic acid” is a nucleic acid sequence that is inserted into a genomic segment of an arenavirus where it does not naturally occur. The heterologous nuclei acid is generally at least 15 nucleotides in length. In some embodiments, it is at least 20, at least 25, at least 30, at least 35, at least 40, at least 45, at least 50, at least 75, or at least 100 nucleotides in length. In some embodiments, the heterologous nucleic acid is a nucleic acid sequence from the genome of a first arenavirus that is Inserted into the genome of a second arenavirus. For example, the first arenavirus may be a pathogenic arenavirus (such as LASV) and the second arenavirus may be a non-pathogenic arenavirus (such as MOPV). In some embodiments, the heterologous nucleic acid encodes an arenavirus protein, such as an arenavirus GP, preferably an arenavirus GPC. 
     A nucleoprotein is said to have “attenuated exonuclease activity” when the exonuclease activity of the nucleoprotein is reduced by at least 60%, at least 70%, at Least 80%, at least 90%, at least 95%, or at least 98% relative to the exonuclease activity of a reference nucleoprotein in an in vitro exonuclease assay. In some embodiments, the exonuclease activity is abrogated. In some embodiments, the reference nucleoprotein is a naturally occurring nucleoprotein of an arenavirus, such as the nucleoprotein of MOPV strain AN21366 (accession numbers JN561684 and JN561685). The techniques for measuring said exonuclease activity are well known in the art. Such techniques are explained fully in the literature. See, for example Qi, X. et at. Cap binding and immune evasion revealed by Lassa nucleoprotein structure. Nature 468, 779-83 (2010). See also, for example, Hastie K. M. et al. Structure of the Lassa virus nucleoprotein reveals a dsRNA-specific 3′ to 5′ exonuclease activity essential for immune suppression. Proc Natl Acad Sci USA 108, 2396-401 (2011). 
     B. Reverse Genetic System for MOPV 
     The Examples describe a reverse genetic system that may be used to make recombinant attenuated MOPV. Skilled artisans will appreciate that in view of the teachings of this disclosure alternative embodiments of systems may be provided and utilized to practice embodiments of this invention and to make the disclosed recombinant attenuated MOPV and compositions. 
     The systems typically comprise a recombinant eukaryotic cell that comprises a first nucleic acid sequence comprising a coding sequence for an L segment antigenomic transcript of an MOPV. In some embodiments, the MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2) L segment coding sequence is used. 
     In some embodiments, the coding sequence for an L segment antigenomic transcript of an MOPV is a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the nucleotide level to the coding sequence of the L segment antigenomic transcript of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, the coding sequence for an L segment antigenomic transcript of an MOPV is a sequence that encodes Z and L(pol) proteins that are each independently at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the amino acid level to the Z and L(pol) proteins of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). 
     The recombinant eukaryotic cell typically further comprises a second nucleic acid sequence comprising a coding sequence for an S segment antigenomic transcript of an MOPV. In some embodiments, the MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2) S segment coding sequence is used. In some embodiments, the coding sequence for an S segment antigenomic transcript of an MOPV is a sequence that is at least 80%, at least 85%, at Least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the nucleotide level to the coding sequence of the S segment antigenomic transcript of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, the coding sequence for an 5 segment antigenomic transcript of an MOPV is a sequence that encodes NP and GPC precursor proteins that are each independently at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the amino acid level to the GPC and NP precursor proteins (SEQ ID NOS. 3 &amp; 4, respectively) of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). 
     In some embodiments, the second nucleic acid sequence comprises a coding sequence for a chimeric S segment antigenomic transcript of an arenavirus. The second nucleic acid sequence may be a chimeric S segment coding sequence that comprises a coding sequence for an antigenomic transcript for an MOPV nucleoprotein or an attenuated MOPV nucleoprotein, and a coding sequence for an antigenomic transcript for glycoprotein precursor (GPC) of an arenavirus that is not MOPV. In some embodiments, the arenavirus that is not MOPV is LASV. The LASV may be strain Josiah (accession number J04324). 
     In some embodiments, the MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2) S segment nucleoprotein coding sequence is used. In some embodiments, the S segment nucleoprotein coding sequence is a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at Least 96%, at least 97%, at least 98%, at least 99Y, or 100% identical at the nucleotide level to the coding sequence of the nucleoprotein of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, the S segment nucleoprotein coding sequence is a sequence that encodes a nucleoprotein that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at Least 97%, at least 98%, at least 99%, or 100% identical at the amino acid level to the nucleoprotein of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). 
     In some embodiments, the encoded nucleoprotein differs from a reference (wild-type) arenavirus nucleoprotein sequence at position D390 or G393. In some embodiments, the encoded nucleoprotein differs from a reference (wild type) arenavirus nucleoprotein sequence at positions D390 and G393. In some embodiments, the encoded nucleoprotein further differs from a reference (wild type) arenavirus nucleoprotein sequence at one, two, three, four, or five positions selected from E392, H430, D467, H529, and D534. In some embodiments, the reference arenavirus nucleoprotein sequence is the MOPV strain AN21366 (accession numbers JN561684 and JN561685) nucleoprotein sequence (SEQ ID NO. 4). In some embodiments, the encoded nucleoprotein differs from a reference (wild-type) arenavirus nucleoprotein sequence by comprising D390A or G393A amino acid substitution. In some embodiments, the encoded nucleoprotein differs from a reference (wild type) arenavirus nucleoprotein sequence by comprising D390A and G393A amino acid substitutions. In some embodiments, the encoded nucleoprotein differs from a reference (wild type) arenavirus nucleoprotein sequence by further comprising one, two, three, four, or five of the amino acid substitutions E392A, H430A, D467A, H529A, and D534A. 
     The first and/or second nucleic acid sequences may be any suitable vector including a plasmid. The vectors may be the same except that they comprise different coding sequences for the L and the S segment or they may be different. The first and/or second nucleic acid sequences typically further comprise transcription regulatory sequences sufficient to drive expression of the coding sequences for the L and the S segments in a host cell of interest. In some embodiments, the host cell of interest is BHKT7/9 cells. In some embodiments, the first and/or second nucleic acid sequences are present in plasmids that comprise sequences necessary to drive expression by mouse RNA polymerase I. 
     The systems may further comprise a third nucleic acid sequence encoding an MOPV L(poi) protein. In some embodiments, the systems may further comprise a fourth nucleic acid sequence encoding an MOPV nucleoprotein. In some embodiments, the systems may further comprise a third nucleic acid sequence encoding an MOPV L(pol) protein and a fourth nucleic acid sequence encoding an MOPV nucleoprotein. The third and/or fourth nucleic acid sequences may be present on any suitable vector such as a plasmid. The vector will typically comprise sequences necessary to drive expression of the third nucleic acid sequence encoding an MOPV L(pol) protein and/or the fourth nucleic acid sequence encoding an MOPV nucleoprotein. Suitable sequences necessary to drive expression include a T7 promoter. 
     The reverse genetic system is useful, for example, to assemble recombinant MOPV. Typically, the recombinant MOPV comprises the NP encoded by the S segment antigenomic transcript present in the recombinant MOPV, however in certain embodiments the recombinant MOPV may be produced such that the NP sequence encoded by the S segment antigenomic transcript present in the recombinant MOPV is different than at least some of the NP protein present in the recombinant MOPV. Typically, the recombinant MOPV comprises GPs, preferably GPCs encoded by the 5 segment antigenomic transcript present in the recombinant MOPV, however in certain embodiments the recombinant MOPV may be produced such that the GP precursor sequence encoded by the S segment antigenomic transcript present in the recombinant MOPV is different than at least some of the GPCs present in the recombinant MOPV. 
     C. Attenuation of MOPV 
     LASV NP contains an exonuclease that circumvents the host IFN response by digesting double-strand RNA (dsRNA). dsRNA are not normally present in mammalian cells, and as such, when they appear during viral replication, they are recognized as PAMP (Pathogen-Associated-Molecular-Pattern). Digestion of these replication intermediates allows the virus to escape from the innate defense system. Alignment of MOPV-NP with LASV-NP showed that amino acids critical for this function were conserved between LASV and MOPV, suggesting that exonuclease activity (and subsequent escape to IFN response) was also present in MOPV virus. The inventors confirmed that MOPV NP is able to digest dsRNA using an in vitro approach. This result is surprising because MOPV is non-pathogenic while LASV is. 
     Mutations were introduced in the MOPV nucleoprotein and the modified nucleoprotein used to generate a recombinant attenuated MOPV. 
     Advantageously, the recombinant attenuated MOPV of the application still is a live virus. 
     In the context of the present application, the expression “recombinant MOPV” designates a virus obtained by reverse genetics, i.e. is one which has been manipulated in vitro, e.g. using recombinant DNA techniques to introduce changes to the viral genome. In the meaning of the present application, a recombinant wild-type MOPV (also termed “rec-MOPV”) is a Mopeia virus which is obtained by reverse genetics and which comprises a nucleic sequence coding for the reference (wild-type) nucleoprotein. In some embodiments, the recombinant MOPV of the invention is a Mopeia virus in which at least one mutation has been Introduced in the MOPV nucleoprotein and results in the partial or total lost of exonuclease activity of said nucleoprotein. 
     A “mutation,” as used herein, refers to a change in nucleic acid or polypeptide sequence relative to a reference sequence (which is preferably a naturally-occurring normal or «wild-type» or «reference» sequence), and includes translocations, deletions, insertions, and substitutions/point mutations. 
     A mutation by “substitution” as used with respect to amino acids, refers to the replacement of one amino acid residue by any other amino acid residue, excepted the substituted amino acid residue. Advantageously, small amino acid residues are used for substitution in order to limit any effect on the overall protein structure. For example, alanine residues are used to substitute charged and polar amino acid residues and serine residues are used to substitute apolar amino acids. In some embodiments, the said “any amino acid residue” is an alanine residue. In some embodiments, there may be at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7 substitutions. The term “amino acid substitution set” or “substitution set” refers to a group of amino acid substitutions. A substitution set can have 1, 2, 3, 4, 5, 6, 7 or more amino acid substitutions. 
     Attenuation is herein intended in accordance with its ordinary meaning in the field. More particularly, the term “attenuated” (by reference to the expression «recombinant attenuated MOPV») refers to a recombinant Mopeia virus (RNA) or (RNA, DNA or cDNA) clone, which comprises a heterologous glycoprotein (GP), more particularly a precursor (GPC), from a pathogenic arenavirus (i.e., from a non-MOPV arenavirus), and which has a reduced pathogenic phenotype compared to the wild-type pathogenic arenavirus (i.e., compared to the infectious and/or virulent arenavirus), more particularly compared to a wild-type virus of the same genus, species, type or subtype (i.e., compared to an infectious and/or virulent virus of the same genus, species, type or subtype). 
     A reduced pathogenic phenotype encompasses a reduced infection capacity and/or a reduced replication capacity, and/or a reduced and/or restricted tissue tropism, and/or a default or defect in the assembly of the viral particles, more particularly a reduced infection capacity. 
     A reduced pathogenic phenotype, more particularly a reduced infection capacity, encompasses a (viral) infection, which is impeded, obstructed or delayed, especially when the symptoms accompanying or following the infection are attenuated, delayed or alleviated or when the infecting virus is cleared from the host. 
     The application thus provides a recombinant attenuated MOPV or clone thereof which is able to replicate to an extent that is sufficient for inducing an immune response but that is not sufficient for inducing a disease. 
     Specifically, the data in the examples demonstrate that substitution of amino acid positions D390 and G393 of the MOPV nucleoprotein attenuates the function of the nucleoprotein and that recombinant MOPV comprising the nucleoprotein having attenuated exonuclease activity are also attenuated. In some embodiments, the amino acid substitutions are D390A and G393A and the recombinant attenuated MOPV is named MOPV-ExoN. In some embodiments, the recombinant attenuated MOPV replicates weaker in Vero cells and has a continuous lower titer over time in comparison to non-attenuated MOPV. In some embodiments, replication of the recombinant attenuated MOPV in DC and/or MP is reduced by at least about 10%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or more, compared to replication of recombinant wild type (rec-MOPV) or wild type MOPV (nat-MOPV) in the same cell type. The techniques for evaluating the replicative properties of a virus are well known for the man skilled in the art. Such techniques are explained fully in the literature. See, for example Baize, S. et al. Lassa virus infection of human dendritic cells and macrophages is productive but fails to activate cells. J Immunol. 172(5): 2861-9 (2004). See also, for example Pannetier, D. et at. Human macrophages, but not dendritic cells, are activated and produce alpha/beta interferons in response to Mopeia virus infection. J Virol. 78(19):10516-24 (2004). 
     The examples also demonstrate activation of DC and MP by a prototype recombinant attenuated MOPV. Specifically, the examples demonstrate that both recombinant and natural MOPV exhibit a strong activation profile in MP, illustrated by the induction of CD86, CD80, and, to a lesser extent, of CD40, but do not induce DC. However, in both MOPV-ExoN infected MP and DCs, a strong level of expression of CD80, CD83 and CD40 was observed, indicating that cells were activated by MOPV-ExoN, and probably prone to present antigens to lymphocytes. The Level of CD86 was also strongly increased in DC infected with MOPV-ExoN, as compared to MOCK or nat-/rec-MOPV infected cells. This marker is important for co-stimulation and maturation of T lymphocytes, thus indicating that priming of lymphocytes should be efficient in response to infection with MOPV-ExoN. Together, these results obtained with a prototype recombinant attenuated MOPV demonstrate the utility of the recombinant attenuated MOPVs of the invention. Accordingly, in some embodiments the recombinant attenuated MOPV of the invention induces an immune response in DC. In some embodiments, the recombinant attenuated MOPV of the invention Induces an immune response in MP. In some embodiments, the recombinant attenuated MOPV of the invention induces an immune response characterized by an increase in expression of at least one molecule selected from CD80, CD83, CD40, and CD86. 
     The examples also demonstrate that both MP and DC were controlling MOPV-ExoN replication, and that MOPV-ExoN infection induced apoptosis of infected MP, as reflected by a strong increase in the level of Caspase 3 in MOPV-ExoN-infected MP. Accordingly, in some embodiments, replication of the recombinant attenuated MOPV of the invention in DC and/or MP is controlled. In some embodiments, infection of MP by the recombinant attenuated MOPV of the invention induces expression of Caspase 3. In some embodiments, Infection of MP by the recombinant attenuated MOPV of the invention induces MP cell death. 
     The examples also demonstrate Induction of an innate immune response in DC and MP infected with a recombinant attenuated MOPV of the invention. Specifically, the examples show that expressions of mRNA in rec-MOPV- and nat-MOPV-infected cells is quite similar, but that the innate response is stronger when DC are infected with MOPV-ExoN, as compared with infection with MOPV (rec- or nat-). This result was also observed in MP, as type I IFNs, TNFalpha and CXCL10 levels were higher in response to MOPV-ExoN than to wild type MOPV. Accordingly, in some embodiments, administration of a recombinant attenuated MOPV of the invention induces an innate immune response in DC and/or MP. In some embodiments, the innate immune response comprises expression of at Least one of type I IFNs, TNFalpha and CXCL10. 
     The examples demonstrate that introduction of D390A and G393A amino acid substitutions in the nucleoprotein of MOPV produces a recombinant attenuated MOPV that is poorly replicative in immune cells, strongly activates at least one of dendritic cells (DC) and macrophages (MP), and/or is more immunogenic than unmodified MOPV. By adding at least one further amino acid substitution at a position selected from E392, H430, D467, H529, and 0534, a recombinant attenuated MOPV having attenuated ExoN function without reduction in replicative properties is provided. In some embodiments, the further substitution is selected from E392A, H430A, D467A, H529A, and D534A. 
     In some embodiments, the recombinant attenuated MOPV comprises a heterologous nucleic acid and a nucleic acid encoding a nucleoprotein having attenuated exonuclease activity. The recombinant attenuated MOPV are useful, for example, to induce an immunogenic response against an arenavirus in a subject. 
     In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises an amino acid substitution at amino acid position D390 or G393. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises an amino acid substitution at amino acid position D390 or G393, and further comprises at least one amino acid substitution at a position selected from E392, H430, 0467, H529, and D534. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393. 
     In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises amino acid substitutions at amino acid positions D390 and G393, and further comprises at least one amino acid substitution at a position selected from E392, H430, D467, H529, and D534. 
     In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises a D390A or G393A amino acid substitution. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein comprises D390A and G393A amino acid substitutions. In some embodiments of the recombinant attenuated MOPV, the nucleoprotein further comprises at least one amino acid substitution selected from E392A, H430A, D467A, H529A, and D534A. The recombinant attenuated MOPV comprising amino acid substitutions at amino acid positions D390A, G393A, E392A, H430A, D467A, H529A, and D534A is named MOP-ExoN enhanced. 
     In some embodiments of the recombinant attenuated MOPV, the heterologous nucleic acid encodes a non-MOPV arenavirus glycoprotein, more preferably a non-MOPV arenavirus glycoprotein precursor. In some embodiments of the recombinant attenuated MOPV, the non-MOPV arenavirus is a Lassa virus (LASV). 
     In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells, strongly activates at least one of dendritic cells (DC) and macrophages (MP), and/or is more immunogenic than unmodified MOPV. In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells. In some embodiments, the recombinant attenuated MOPV is strongly activates at least one of dendritic cells (DC) and macrophages (MP). In some embodiments, the recombinant attenuated MOPV is more immunogenic than unmodified MOPV. 
     In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells and strongly activates at least one of dendritic cells (DC) and macrophages (MP). 
     In some embodiments, the recombinant attenuated MOPV is strongly activates at least one of dendritic cells (DC) and macrophages (MP), and is more immunogenic than unmodified MOPV. 
     In some embodiments, the recombinant attenuated MOPV is poorly replicative in immune cells and is more immunogenic than unmodified MOPV. 
     In some embodiments, the recombinant attenuated MOPV comprises a coding sequence for an L segment antigenomic transcript of an MOPV. In some embodiments, the coding sequence for an L segment antigenomic transcript of an MOPV is a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the nucleotide level to the coding sequence of the L segment antigenomic transcript of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, the coding sequence for an L segment antigenomic transcript of an MOPV is a sequence that encodes Z and L(pol) proteins that are each Independently at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%. at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the amino acid level to the Z and L(pol) proteins of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, any Z and L(pol) proteins present in the recombinant attenuated MOPV are proteins encoded by the coding sequence for an L segment antigenomic transcript of an MOPV that is present in the recombinant attenuated MOPV. 
     In some embodiments, the recombinant attenuated MOPV comprises a coding sequence for an S segment antigenomic transcript of an MOPV. In some embodiments, the coding sequence for an S segment antigenomic transcript of an MOPV is a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the nucleotide level to the coding sequence of the S segment antigenomic transcript of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, the coding sequence for an S segment antigenomic transcript of an MOPV is a sequence that encodes NP and GP precursor proteins that are each independently at least 80%, at Least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical at the amino acid level to the NP and GP precursor proteins of MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2). In some embodiments, any NP and GP proteins present in the recombinant attenuated MOPV are proteins encoded by the coding sequence for an S segment antigenomic transcript of an MOPV that is present in the recombinant attenuated MOPV. 
     In some embodiments, the coding sequence for an S segment antigenomic transcript of an MOPV present in a recombinant attenuated MOPV of the invention encodes a nucleoprotein that differs from a reference (wild type) arenavirus nucleoprotein sequence at positions D390 and G393. In some embodiments, the encoded nucleoprotein further differs from a reference (wild type) arenavirus nucleoprotein sequence at one, two, three, four, or five positions selected from E392, H430, D467, H529, and 0534. In some embodiments, the reference arenavirus nucleoprotein sequence is from an MOPV strain. In some embodiments, the reference arenavirus nucleoprotein sequence is the MOPV strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2) nucleoprotein sequence. In some embodiments, the encoded nucleoprotein differs from a reference (wild type) arenavirus nucleoprotein sequence by comprising D390A and G393A amino acid substitutions. In some embodiments, the encoded nucleoprotein differs from a reference (wild type) arenavirus nucleoprotein sequence by further comprising one, two, three, four, or five of the amino acid substitutions E392A, H430A, D467A, H529A, and D534A. 
     The recombinant attenuated MOPV also comprises a heterologous nucleic acid. The heterologous nucleic acid may be inserted anywhere in the genome of the MOPV. in some embodiments, it is inserted into the S segment. In some embodiments, it is inserted into the L segment. In some embodiments, it is inserted into Z protein coding region. In some embodiments, it is inserted into the L(Pol) coding region. In some embodiments, it is inserted into the NP coding region, in some embodiments, it is inserted into the GP precursor coding sequence. In some embodiments, the heterologous nucleic acid is inserted without deleting bases present in the starting MOPV genome while in other embodiments bases present in the starting MOPV genome are deleted at the site of insertion. In some embodiments, the inserted heterologous nucleic acid is the same size as a corresponding region that is deleted at the site of insertion. 
     In some embodiments, the recombinant attenuated MOPV comprises a recombinant genomic S segment encoding a non-MOPV arenavirus glycoprotein. The examples demonstrate incorporation of an LASV glycoprotein into a recombinant attenuated MOPV. In such an embodiment, the recombinant attenuated MOPV may be used to induce an immune response against LASV glycoprotein, more preferably against LASV glycoprotein precursor which may be protective or therapeutic against infection by LASV In a host. Accordingly, in the exemplified embodiment, LASV is the targeted arenavirus. In other embodiments, the targeted arenavirus is any non-MOPV arenavirus. In some embodiments, the targeted arenavirus is selected from Gairo virus, Gbagroube virus, Ippy virus, Kodoko virus, Lassa virus, Lujo virus, Luna virus, Lunk virus, Lymphocytic choriomeningitis virus, Merino Walk virus, Menekre virus, Mobala virus, Morogoro virus, Wenzhou virus, Tacaribe virus, Amapari virus, Chapare virus, Flexal virus, Guanarito virus, Junin virus, Latino virus, Machupo virus, Oliveros virus, Parana virus, Patawa virus, Pichinde virus, Pirital virus, Sabiá virus, Tacaribe virus, Tamiami virus, and Whitewater Arroyo virus. 
     The examples provide strong evidence that introduction of mutations that abrogate exonuclease function of MOPV-NP results in strong attenuation of MOPV. In order to better enhance specific protection against a target arenavirus, the inventors engineered a vaccine candidate against LASV, and to produce a chimeric virus in which the surface GP, more preferably the surface GPC, of MOPV is replaced by the GP, more preferably the surface GPC, of LASV. The examples demonstrate that swapping of the GP, more preferably the surface GPC, coding sequence in the MOPV backbone did not significantly affect the replication properties of MOPV, as MOPV-GPC LASV  replicates similarly to rec-MOPV. However, the replication of MOPV-ExoN-GPC LASV  was to some extent attenuated compared to rec-MOPV, as also observed for MOPV-ExoN. This indicates that attenuation of the replication capacity of MOPV-ExoN-GPC LASV  is due to the defect in the NP exonuclease function and not to the swapping of gp genes between LASV and MOPV. Therefore, this result demonstrates that the recombinant attenuated MOPV platform provided herein is useful for vaccinating against a targeted arenavirus. 
     D. Compositions 
     The application also relates to a composition. The term “composition” encompasses pharmaceutical composition, antiviral composition, immunogenic composition and vaccine, more particularly antiviral composition, immunogenic composition and vaccine. The composition of the application comprises at least one recombinant attenuated virus of the application, such as at least one live and attenuated virus of the application. 
     The invention also includes immunogenic compositions comprising a recombinant attenuated MOPV as described herein. The immunogenic compositions can be formulated according to standard procedures in the art. In certain embodiments, the immunogenic compositions are administered in combination with an adjuvant. The adjuvant for administration in combination with a composition described herein may be administered before, concomitantly with, or after administration of said composition. In some embodiments, the term “adjuvant” refers to a compound that when administered in conjunction with or as part of a composition described herein augments, enhances and/or boosts the immune response to a recombinant attenuated MOPV present in the immunogenic composition, but when the compound is administered alone does not generate an immune response to the recombinant attenuated MOPV. Adjuvants can enhance an immune response by several mechanisms including, e.g., lymphocyte recruitment, stimulation of B and/or T cells, stimulation of macrophages, and stimulation of dendritic cells. When a vaccine or immunogenic composition of the invention comprises adjuvants or is administered together with one or more adjuvants, the adjuvants that can be used include, but are not limited to, mineral salt adjuvants or mineral salt get adjuvants, particulate adjuvants, microparticulate adjuvants, mucosal adjuvants, and immunostimulatory adjuvants. Examples of adjuvants include, but are not limited to, aluminum salts (alum) (such as aluminum hydroxide, aluminum phosphate, and aluminum sulfate), 3 De-O-acylated monophosphoryl lipid A (MPL) (see GB 222021 1), MF59 (Novartis), AS03 (GlaxoSmithKline). AS04 (GlaxosmithKline), polysorbate 80 (Tween 80; ICL Americas, Inc.), imidazopyridine compounds (see International Application No. PCT/US2007/064857, published as International Publication No. WO2007/109812), imidazoquinoxaline compounds (see International Application No. PCT/US2007/064858, published as International Publication No. WO2007/109813) and saponins, such as QS21 (see Kensil et ah, in Vaccine Design: The Subunit and Adjuvant Approach (eds. Powell &amp; Newman, Plenum Press, NY, 1995); U.S. Pat. No. 5,057,540). In some embodiments, the adjuvant is Freund&#39;s adjuvant (complete or incomplete). Other adjuvants are oil in water emulsions (such as squalene or peanut oil), optionally in combination with immune stimulants, such as monophosphoryl lipid A (see Stoute et ah, N. Engl. J. Med. 336, 86-91 (1997)). 
     In certain embodiments, the immunogenic compositions comprise the recombinant attenuated MOPV alone or, preferably, together with a pharmaceutically acceptable carrier. Suspensions or dispersions of the recombinant attenuated MOPV, especially isotonic aqueous suspensions or dispersions, can be used. The pharmaceutical compositions may be sterilized and/or may comprise excipients, e.g., preservatives, stabilizers, wetting agents and/or emulsifiers, solubilizers. salts for regulating osmotic pressure and/or buffers and are prepared in a manner known per se, for example by means of conventional dispersing and suspending processes. The dispersions or suspensions may comprise viscosity-regulating agents. The suspensions or dispersions may be kept at temperatures around 2-4° C., or for longer storage may be frozen and then thawed shortly before use. For injection, the vaccine or immunogenic preparations may be formulated in aqueous solutions, such as in physiologically compatible buffers such as Hanks&#39;s solution, Ringer&#39;s solution, or physiological saline buffer. The solution may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. 
     In certain embodiments, the compositions described herein additionally comprise a preservative, e.g., the mercury derivative thimerosal. In some embodiments, the pharmaceutical compositions described herein comprises 0.001% to 0.01% thimerosal. In other embodiments, the pharmaceutical compositions described herein do not comprise a preservative. 
     The immunogenic compositions may comprise from about 10 2  to about 10 12  focus forming units of the recombinant attenuated MOPV. Unit dose forms for parenteral administration are, for example, ampoules or vials. e.g., vials containing from about 10 2  to 10 12  focus forming units or 10 4  to 10 14  physical particles of recombinant attenuated MOPV. 
     In some embodiments, an immunogenic composition provided herein is administered to a subject by, including but not limited to, oral, intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, percutaneous, intranasal and inhalation routes, and via scarification (scratching through the top layers of skin, e.g., using a bifurcated needle). In some embodiments, a subcutaneous or intravenous route is used. 
     For administration intranasally or by inhalation, the preparation for use according to the present invention can be conveniently delivered in the form of an aerosol spray presentation from pressurized packs or a nebulizer, with the use of a suitable propellant, e.g., dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol the dosage unit may be determined by providing a valve to deliver a metered amount. Capsules and cartridges of, e.g., gelatin for use in an inhaler or insufflators may be formulated containing a powder mix of the compound and a suitable powder base such as lactose or starch. 
     As skilled artisans will appreciate, the dosage of the recombinant attenuated MOPV depends upon the type of vaccination and upon the subject, and their age, weight, individual condition, the individual pharmacokinetic data, and the mode of administration. 
     E. Use of Recombinant Attenuated MOPV 
     This invention also provides methods of inducing an immunogenic response in a subject. The methods comprise administering to the subject recombinant attenuated MOPV of the invention, typically in the form of an immunogenic composition of the invention. 
     In another aspect, the invention also relates to the subject recombinant attenuated MOPV of the invention for use in inducing an immunogenic response in a subject. in a preferred embodiment, said subject recombinant attenuated MOPV is in the form of an immunogenic composition of the invention. 
     In yet another aspect, the invention provides a use of the subject recombinant attenuated MOPV of the invention for making a vaccine for inducing an immunogenic response in a subject. in a preferred embodiment, said subject recombinant attenuated MOPV is in the form of an immunogenic composition of the invention. 
     The term “immunogenic response” is intended in accordance with its ordinary meaning in the field, and includes one or several from antibody production, induction of cell mediated immunity, complement activation, development of immunological tolerance, alteration of cytokine production and alteration of chemokine production, more particularly antibody production. Antibody production encompasses neutralizing antibody production, such as seroneutralization. 
     The subject is typically a mammal, such as a human, a primate, or a non-human primate. In some embodiments, the subject is a mouse, a rat, or a rabbit. In some embodiments, the subject is a domesticated animal, such as, but not limited to, a cow, a horse, a sheep, a pig, a goat, a cat, a dog, a hamster, and a donkey. in some embodiments, the immunogenic response comprises a response to the glycoprotein portion of a recombinant attenuated MOPV of the invention. 
     The subject recombinant attenuated MOPV or the composition of the application can be used in the prevention and/or treatment and/or palliation, of an arenavirus infection and/or of a disease or disorder induced by an arenavirus. Thus, the invention also relates to the subject recombinant attenuated MOPV or the composition for use in the prevention and/or treatment and/or palliation, of an arenavirus infection and/or of a disease or disorder induced by do arenavirus. The invention also relates to the use of the subject recombinant attenuated MOPV or the composition for making a vaccine for preventing and/or treating and/or palliating, an arenavirus infection and/or a disease or disorder induced by an arenavirus. In some embodiments, the recombinant attenuated MOPV or the composition is used to prevent an arenavirus infection and/or a disease or disorder induced by an arenavirus. In some embodiments the immunogenic response is protective. A protective response is a response that confers immunity to the subject. For example, in some embodiments, the subject is administered a recombinant attenuated MOPV, the recombinant attenuated MOPV comprising a glycoprotein of an arenavirus, preferably a precursor thereof, or an immunogenic composition comprising said recombinant attenuated MOPV and following the administration the subject mounts and immune response to the glycoprotein of the arenavirus. If the immune response confers to the subject an immunity to the arenavirus from which the glycoprotein is derived then the immunogenic response in the subject is protective. As a skilled artisan will appreciate a protective immune response is one that reduces the risk that a subject will become infected with an arenavirus and/or reduces the severity of an infection with an arenavirus. Accordingly, protective immune responses include responses of varying degrees of protection. 
     According to another embodiment, the invention also relates to the subject recombinant attenuated MOPV of the invention for use in inducing a protective immune response in a subject, in a preferred embodiment, said subject recombinant attenuated MOPV is in the form of an immunogenic composition of the invention. 
     In yet another embodiment, the invention provides a use of the subject recombinant attenuated MOPV of the invention for making a vaccine for inducing a protective immune response in a subject. In a preferred embodiment, said subject recombinant attenuated MOPV is in the form of an immunogenic composition of the invention. 
     In some embodiments, the subject is infected with an arenavirus prior to administration of the recombinant attenuated MOPV of the invention or of a composition comprising said recombinant attenuated MOPV, and administration of said recombinant attenuated MOPV or of said composition is therapeutic. In such embodiments, administration of said recombinant attenuated MOPV or of said composition to the subject infected with the arenavirus may have the effect of ameliorating at least one symptom of the arenavirus infection in the subject. In some embodiments, administration of said recombinant attenuated MOPV or said composition to the subject infected with the arenavirus may have the effect of reducing the risk of death of the subject. 
     In some embodiments, administering the recombinant attenuated MOPV or a composition thereof reduces the risk that a subject will develop an infection with a targeted arenavirus by at least about 10%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or more, compared to the risk of developing an infection with the targeted arenavirus in the absence of administering the recombinant attenuated MOPV or a composition thereof. 
     In some embodiments, recombinant attenuated MOPV or a composition thereof reduces the symptoms of an infection of the subject with a targeted arenavirus by at least about 10%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 50%, at least about 60%. at least about 70%, at least about 80%. at least about 90%, or more, compared to the manifestation of the symptoms of an infection with the targeted arenavirus in the absence of administering the recombinant attenuated MOPV or a composition thereof. 
     Other characteristics and advantages of the invention appear in the continuation of the description with the examples and the figures whose legends are represented below. 
     EXAMPLES 
     Materials and Methods 
     Viruses 
     The MOPV, strain AN21366 (accession numbers JN561684 and JN561685: SEQ ID Nos. 1 &amp; 2) and the LASV, strain Josiah (accession number J04324) were used 20,21  and passaged no more than 4 times on VeroE6 cells. Cell culture supernatants were collected 4 days post-infection and clarified by centrifugation 5 min at 5000 rpm. Viruses were tittered and used as viral stocks for further experiments. Hereafter, this virus is named nat-MOPV to distinguish it from recombinant wild-type MOPV obtained by reverse genetics (rec-MOPV). 
     Cells 
     Stably expressing the T7 polymerase. BHK T7/9 cells, were used to rescue recombinant viruses and were maintained as described elsewhere 14 . VeroE6 cells, grown in Glutamax Dulbecco Modified Eagle&#39;s Medium (DMEM—Life Technologies) supplemented with 5% FCS and 0.5% Penicillin-Streptomycin, were used for amplification and titration of viral stocks. 
     Plasmids 
     The pTM1 plasmid was used to drive the expression of the LPol and the NP proteins under the T7 promoter. pTM1 plasmids expressing MOPV LPol (pTM1-LPol) and MOPV NP (pTM1-NP) were obtained by cloning respectively the LPol and the NP ORFs between the NcoI and XhoI sites of the plasmid. To obtain a complete transcription of both viral segments, the L and 5 sequences in antigenomic orientation of the MOPV were reverse transcribed from viral RNA extracts and the cDNA finally cloned into a plasmid that drives the correct transcription under the control of the mouse RNA polymerase I. For both correct transcription and replication of the viral segments, an extra non templated-G base, was included at the beginning of the cloned sequences 14,22 . All plasmids were sequenced and corrected by site directed mutagenesis to match the consensus sequence of the AN21366 MOPV strain, except for purposely-introduced mutations to discriminate between rec- and nat-MOPV. 
     The swap of GPC ORFs in pPOLI-MOPV Sag plasmid was generated by the introduction of the BsmBI restriction sites downstream and upstream the Start and Stop codons of MOPV GPC ORF respectively. The GPC ORF of Lassa (Josiah, SEQ ID NO. 16), Lujo (NC_012776; SEQ ID NO. 17), Machupo (Carvallo, KM198592.1; SEQ ID NO. 18), Guanarito (INH95551, AF485258.1; SEQ ID NO. 19), Chapare (NC_010562.1; SEQ ID NO. 20) or Sabia (NC_006317.1; SEQ ID NO. 21) was then inserted into the aforementioned modified plasmid deleted of the MOPV GPC ORF. To generate a pPOLI MOPV Sag based minigenome, a similar strategy was used to generate a pPOLI MOPV Sag FF Luc, where the NP ORF is replaced by the Firefly Luciferase ORF. 
     Site-Directed Mutagenesis 
     All mutations were introduced using the site directed mutagenesis strategy accordingly to manufacturer instructions (Agilent). Plasmids were then sequenced to confirm the presence of the desired mutations. 
     Virus Titration 
     Supernatants of infected cells were collected and clarified by centrifugation at 5000 rpm for 5 min. Ten-fold serial dilutions of viral supernatants were added to subconfluent VeroE6 cells. One hour after incubation, the cells were covered with a 1:1 mixture of 5% 5VF-DMEM and Carboxy-Methyl Cellulose (CMC), and incubated for 7 days. Cells were then fixed with paraformaldehyde (PFA, SIGMA Aldrich, France), permeabilized with triton, and the presence of the virus revealed with a mix of mouse antibody against the GP (or GPC) and the NP proteins. Results were expressed in FFU/ml (Focus Forming Unit/ml). 
     Rescue Experiments 
     4×10 6  BHK-T7/9 cells were seeded in 75 cm 2  flasks. The following day, cells were transfected with pPOLI MOPV SAg and pPOLI MOPV LAg using Fugene 6 reagent (Promega, France). Transfection was performed for 6 h at 37° C. Cells were then washed and left for 5 days in DMEM 2.5% SVF. Supernatants of BHK-T7/9 cells constitute the seed stock. The virus of the seed stock was then amplified on VeroE6 cells. The first passage of seed stock on VeroE6 constitute the “passage 1” virus stock. After titration, the “passage 1” virus was used to infect VeroE6 cells at a multiplicity of infection (MOI) of 0.001 or 0.01. Infection was carried out for 3 or 4 days, before the supernatant collection. This tittered second passage on VeroE6 cells provides the viral stocks used for all other experiments. For all viral stocks, the absence of  mycoplasma  contamination was determined using  Mycoplasma  detection kit (Lonza, Switzerland). Viral RNAs were extracted from stocks using QIAmp (QJAGEN) and amplified by One step RT-PCR (Titan, Roche Applied Biosciences). PCR products were sequenced by Sanger sequencing (GATC, Konstanz, Germany). 
     Generation of Monocytes Derived Dendritic Cells and Macrophages 
     Blood samples were obtained from Etablissement Français du Sang (EFS). Mononuclear cells were purified by Ficoll density gradient centrifugation (GE Healthcare). Autologous plasma was collected and decomplemented for 30 min at 56° C. Monocytes were separated from peripheral Blood Leucocytes by centrifugation on a cushion of 50% Percoll (GE Healthcare) in PBS. Remaining PBL were removed from the monocytes fraction with anti-CD3, anti-CD19 and anti-CD56 dynabeads (Life Technologies) or with the Monocyte Isolation Kit Ii, human (Miltenyl Biotec). Macrophages (MP) were obtained by incubating monocytes for 4 to 6 days in RPMI, 10% SVF, 10% autologous plasma supplemented with 100 ng/ml of M-CSF (Macrophage-Colony Stimulating Factor, Miltenyi Biotec). Dendritic cells (DC) were differentiated for 6 days in RPMI 10% SVF supplemented with 1,000. U/mL of GM-CSF (Granulocytes Macrophages Colony Stimulating Factor) and 500 U/mL of IL-4 (both from Peprotech). For both cell types (DC and MP), cytokines were added every 2 days and one-third of the culture medium was replaced. 
     Flow Cytometry 
     Surface molecules were stained using fluorescent dye conjugated monoclonal antibodies against CD83, CD80, CD86, CD40, (BD Biosciences) for 30 min at 4° C. Intracellular staining for Caspase 3 was performed using Phycoerythrin conjugated anti-Caspase 3 monoclonal antibody (BD Biosciences) for 20 min, after Cytofix/Cytoperm permeabilization (Beckton Díckinson). Cells were finally washed and resuspended in PBS 1% PFA, before analyse by Flow Cytometry using a Gallios cytometer (Beckman Coulter). Data were analysed using Kaluza software (Beckman Coulter). 
     RT, cDNA Synthesis and gPCR 
     RNA was isolated from infected cells using RNeasy Mini Kit (Qiagen), according to manufacturer&#39;s instructions. Reverse Transcription (RT) was then performed on total RNAs, using oligo dT primers and Superscript III reverse transcriptase kit according to manufacturer instructions (Life Technologies). For cDNA amplification and cloning, the KOD DNA polymerase (EMD Millipore) and gene specific primers were used. 
     For RT-qPCR experiments, cDNAs were amplified using Gene Expression Master Mix kit and primer/probe mix developed and optimized for each gene (Applied Biosystems Thermo Scientific), except for type I IFNs developed in house 23 . qPCR assays were run in LightCycler 480 (Roche Applied Biosciences). For all genes, expression was standardized to GAPDH gene, and expressed as fold induction compared to GAPDH. 
     Statistical Analysis 
     Statistical analyses were performed using SigmaPlot software (Systat Software Inc, California) or GraphPad Prism 6. Differences among groups were assayed running one-way ANOVA followed by post hoc Holm-Sidak test. 
     Example 1: Set Up of a Reverse Genetic System for MOPV 
     The reverse genetic system for MOPV developed here was similar to that used previously for LASV 14 . The short and long segments of MOPV in antigenomic sense were cloned in a plasmid that drives the transcription through the mouse RNA polymerase I. These plasmids were transfected, along with pTM1-NP and pTM1-LPol, into BHKT7/9 cells. The expression of genomic length segments and viral proteins Lpol and NP allowed reconstituting the viral transcription and replication unit RNPs (ribonucleoproteins) from which expression of the four viral genes occurs, ultimately leading to the assembly and the budding of recombinant MOPV (rec-MOPV). 
     Example 2: Abrogation of Exonuclease Activity in MOPV NP 
     Previous work 14-16  has shown that LASV NP is able to circumvent IFN response thanks to its exonuclease function, which is able to digest double-strand RNA (dsRNA). Indeed, dsRNA are not normally present in mammalian cells, and as such, when they appear during viral replication, they are recognized as PAMP (Pathogen-Associated-Molecular-Pattern). Digestion of these replication intermediates allows the virus to escape from the innate defence system. Interestingly, this exonuclease function is borne by a DEDDH domain. Alignment of MOPV-NP with LASV-NP showed that amino acids critical for this function were conserved between LASV and MOPV, suggesting that exonuclease activity (and subsequent escape to IFN response) was also present in MOPV virus. We have confirmed that MOPV NP is able to digest dsRNA using an in vitro approach and block the IFN response to dsRNA in cells (data not shown). In addition, mutations of the DDEDH domain (D390, E392, 0530, D534 and H430) abrogate the IFN-antagonist activity of MOPV NP without reducing its ability to support viral transcription/replication. Thus, by analogy with LASV, we designed a MOPV-ExoN virus by introducing the mutations D390A and G393A to knock-down exonuclease function of MOPV in the live virus ( FIG.  1   ). Mutations were introduced in the pPOLI-MOPV-Sag, and this modified plasmid was used as described previously to generate a MOPV-ExoN virus. Both recombinants viruses were passaged twice in Vero E6 cells, and virus sequences were verified. The only mutations retrieved were those introduced purposely, either for abrogation of the Exonuclease function of MOPV, or for the discrimination between natural and recombinant MOPV (silent mutations). 
     Both rec-MOPV (wild-type virus obtained by reverse genetic system) and MOPV-ExoN (rec-MOPV in which NP 0390 and NP G393 were substituted to Alanine) were characterized for their replicative properties in Vero E6 cells, and compared to the naturally isolated nat-MOPV virus ( FIG.  2 A ). in both cases, viruses were replicating similarly, reaching a replicative peak at 12 hours post-infection, and slightly decreasing afterwards. Nat-MOPV and rec-MOPV have a similar replication pattern. In contrast, MOPV-ExoN is replicating weaker, as reflected by its continuous lower titre over time, even though this virus reaches also a peak 3 days post-infection. 
     Similarly, replication of those three viruses was measured in DC ( FIG.  28   , left panel) and MP ( FIG.  28   , right panel). As expected, recombinant and natural MOPV presented a similar behaviour, with a peak at 3 days after infection of DC, and to a lower extent, at 2 days after infection of MP. MOPV-ExoN replication was totally abrogated in both cells. These results indicate that Antigen-Presenting Cells (APC) strongly control replication of our vaccine prototype, thus excluding the possibility of massive and long-lasting replication of this agent after inoculation. 
     Example 3: Characterization of Dendritic Cells and Macrophages Following MOPV-ExoN Infection 
     In order to evaluate vaccine potential of the MOPV-ExoN prototype, we analyzed its capacity to activate DC and MP. To this end, monocytes-derived DC and MP were either MOCK infected, or infected with nat-MOPV, rec-MOPV or MOPV-ExoN, at a MOI of 1 for 48 hours. Expression profile of CD80, CD83, CD40, and CD86 was quite similar when cells were infected with rec-MOPV or nat-MOPV virus ( FIGS.  3 A  and B). Compared to MOCK-infected cells, both rec- and nat-MOPV showed a strong activation profile in MP, illustrated by the induction of CD86, CD80, and, to a lesser extent, of CD40. This activation was not observed in DC. However, in both MOPV-ExoN infected MP and DCs, a strong level of expression of CD80, CD83 and CD40 was observed, indicating that cells were activated by MOPV-ExoN, and probably prone to presents antigens to lymphocytes. interestingly, CD86 level was also strongly increased in DC infected with MOPV-ExoN, as compared to MOCK or nat-/rec-MOPV infected cells. This marker is important for co-stimulation and maturation of T lymphocytes, thus indicating that priming of lymphocytes should be efficient in response to infection with MOPV-ExoN. 
     An important feature for a live vaccine candidate is the capacity of cells to eliminate this agent. In our case, both MP and DC were controlling MOPV-ExoN replication, and even more, MOPV-ExoN infection induced apoptosis of infected MP, as reflected by the strong increase in Caspase 3 level in MOPV-ExoN-infected MP. This is an important feature as some arenaviruses, such as lymphochoriomeningitis virus (LCMV), are known to induce persistent infections in cells 24 . 
     We also looked for induction of an innate immune response in DC and MP infected with nat- or rec-MOPV or with MOPV-ExoN ( FIG.  4   ). The expressions of mRNA observed in rec-MOPV- and nat-MOPV-infected cells were quite similar. Interestingly, the innate response was stronger when DC were infected with MOPV-ExoN, as compared with infection with MOPV (rec- or nat-). Even if it was more moderated, this result was also observed in MP, as type I IFNs, TNFalpha and CXCL10 levels were higher in response to MOPV-ExoN than to wild type MOPV. 
     Altogether, these results concerning the activation of APC in response to MOPV-ExoN virus shed light on the properties of this attenuated virus to be a valuable vaccine prototype: Indeed, this virus is able to strongly induce both innate and probably adaptive immune response, and, on the other hand, its replication remains under control into these cells. Even more, induction of apoptosis of MOPV-ExoN Infected MP is consistent with an absence of persistence in infected cells. 
     Example 4: Production and preliminary characterization of MOPV-ExoN-GP LASV    
     Nat-MOPV was previously shown to be an efficient vaccine against LASV. However, its safety is difficult to prove and some minor lesions have been described after MOPV infection in mice and non-human primates 25 . Here, we provide strong evidences that introduction of mutations that abrogate Exonuclease function of MOPV-NP results in strong attenuation of MOPV. In order to better enhance specific protection against LASV, we thought to engineer our vaccine candidate, and to produce a chimeric virus in which the surface GP of MOPV has been replaced by the one of LASV. To do so, we manipulated the pPOLI_Sag_MOPV plasmid to replace MOPV gp ORF by LASV gp ORF, in both wild type pPOL_Sag_MOPV and pPOLI_Sag_MOPV_ExoN. Chimeric MOPV-GP LASV  and MOPV-ExoN-GP LASV  were rescued, titrated, and amplified. 
     Replication properties of these viruses were assayed by infecting VeroE6 cells at a MOI of 0.01, and collecting supernatants daily for 4 days. Virus titres were determined for each time point, and compared to those obtained for rec-MOPV ( FIG.  5   ). 
     Swapping of gp gene in MOPV backbone did not significantly affect replication properties of MOPV, as MOPV-GP LASV  replicates similarly to rec-MOPV. However, the replication of MOPV-ExoN-GP LASV  was to some extent attenuated compared to rec-MOPV, as it was also observed for MOPV-ExoN. Thus, attenuation of replication capacity of MOPV-ExoN-GP LASV  is rather due to the defect in NP exonuclease function than to the swapping of gp genes between LASV and MOPV. indeed, the exonuclease activity of NP of arenaviruses might have important role in the conservation of genome integrity, and shutting down this function could imply substantially replication capacity of arenaviruses, even in Vero E6 cells, which are deficient for type I IFN response. All the viruses we generated in this study are able to replicate and to be produced at good infectious titres in Vero E6 cells, which is an important parameter to the required specifications of a vaccine prototype. 
     Example 5: GPC Swapping does not Affect the Immunogenic Properties of Recombinant Viruses 
     In order to evaluate whether exchange of the GPC of MOPV by the GPC of LASV could affect the immune response of Antigen Presenting Cells (APC), we generated recombinant MOPV and LASV viruses respectively expressing the GPC of LASV or MOPV. 
     As shown on  FIG.  6 A , these viruses presented similar growth kinetics on VeroE6 cells, with LASV-GPC MOPV  replicating to lower titers at 24 hours post infection but to similar titers than all other viruses by 48 hours post infection and until the end of the replication kinetics. We then infected primary human macrophages with these viruses at a MOI of 1 and analysed their type I IFN responses at 24 hours by RT-qPCR. As shown on  FIG.  68   , exchanging the GPC protein had no effect on the ability of recombinant viruses to induce type I IFN expression in macrophages. In addition, MOPV-wt an MOPV-GPC LASV  were slightly more immunogenic than LASV-wt and LASV-GPC MOPV , confirming previously observed results and suggesting than the attenuation of MOPV is not dependent on the GPC protein. 
     Example 6: Consolidation of the ExoN KO Activity 
     To avoid any possible reversion of two mutations introduced in the np gene to abrogate the ExoN activity, we thought about mutating more residues in the ExoN site. At least 7 residues have been involved in the function of the ExoN domain: D390, E392, G393, H430, D467, H529 and D534. In addition to the two previously described mutations, D390A and G393A (ExoN), we proximally mutated all the residues of the ExoN domain, thus generating 6 additional mutants ( FIG.  7 A ). We first checked the effect of these mutations on the ExoN activity in a reporter gene assay. In this assay, cells transfected with a plasmid encoding an IRF-3-promoter driven luciferase and a plasmid encoding wild type (wt) or mutant forms of NP were infected with SeV, a strong inducer of IRF-3 and IFN responses.  FIG.  7 B  demonstrate that NP-wt can block the Induction of the luciferase expression in response to SeV. On the contrary, all the mutants of the ExoN domain were affected in their ability to reduce induction of the reporter gene expression. 
     We then introduced the corresponding mutations in reverse genetics plasmids in order to generate recombinant viruses harbouring these mutations. All viruses could be rescued except for MOPV-ExoNM6a and ExoNM7. To avoid the smallest chance to observe any reversion of the NP mutations, the MOPV-ExoNM6b was chosen, containing 6 mutations, as our vaccine platform. We demonstrated that MOPV-ExoNM6b replication in VeroE6 cells was similar to the replication of MOPV-ExoN ( FIG.  7 C ), confirming that additional mutations in the ExoN domain had no additional effect on the capacity of NP to support viral transcription/replication. On the contrary, replication of MOPV-ExoNM6b was abrogated in immune-competent macrophages compared to MOPV-wt, as observed with MOPV-ExoN ( FIG.  7 D ). In infected macrophages, mutant MOPV-ExoN and MOPV-ExoNM6b also induced slightly more type I IFN than MOPV-wt ( FIG.  7 E ). Altogether, these results support the choice of MOPV-ExoNM6b as a vaccine platform. 
     Example 7: Characterization and Immunogenic Properties of MOPV-Based Vaccine Candidates 
     Having chosen the MOPV-ExoNM6b as a vaccine platform, we replaced the GPC protein of MOPV by the GPC protein of other pathogenic arenaviruses: old-world Lassa and Lujo viruses; new-world Machupo, Guanarito, Chapare and Sabia. All recombinant viruses were rescued and replicated on VeroE6 cells ( FIG.  8 A ). 
     As a proof of principle, we characterized the replication and immunogenic properties of two vaccine candidates, namely MOPV-ExoNM6b-GPC LASV  and MOPV-ExoNM6b-GPC MACV . in immune-competent macrophages. As expected, while MOPV-wt could replicate in macrophages, MOPV-ExoNM6b-GPC LASV  and MOPV-ExoNM6b-GPC MACV  could not replicate efficiently in these cells like the parental MOPV-ExoNM6b ( FIG.  88   ), suggesting a control by the immune response. We analysed the expression of activation molecules on the surface of infected macrophages using flow cytometry and showed that all viruses were inducing an upregulation of CD40, CD80 and CD86 compared to non-infected macrophages, with higher CD40 and CD86 induction for ExoNM6b viruses compared to MOP-wt ( FIG.  8 C ). In accordance with these results, all viruses induced high levels of type I IFN genes expression ( FIG.  8 D ). 
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