Lassa vaccine

Abstract

The invention relates to recombinant measles virus expressing Lassa virus polypeptides, and concerns in particular immunogenic LASV particles expressed by a measles virus and / or virus like particles (VLPs) that contain proteins of a Lassa virus. These particles are recombinant infectious particles able to replicate in a host after an administration. The invention provides means, in particular nucleic acid constructs, vectors, cells and rescue systems to produce these recombinant infectious particles. The invention also relates to the use of these recombinant infectious particles, in particular under the form of a composition, more particularly in a vaccine formulation, for the treatment or prevention of an infection by Lassa virus.

Description

FIELD OF THE INVENTIONThe application generally relates to recombinant genetic constructs comprising the recombinant measles virus and expressing at least one Lassa virus polypeptide, protein, antigen, or antigenic fragment thereof. The application also relates to the uses of genetic constructs or viruses, and more particularly their applications for inducing protection against the Lassa virus (LASV), and / or the measles virus (MV or MeV).The means of the invention are more particularly dedicated to a recombinant nucleic acid construct allowing the expression of at least one of the following polypeptides of the LASV, or a truncated version thereof or an antigenic fragment thereof: the Nucleoprotein (NP), the Glycoprotein precursor (GPC), the zinc-binding protein (Z), or a mutated version of the native NP protein (mutated NP or mNP) wherein the exonuclease activity of the NP protein has been knocked down.The invention also relates to a recombinant MeV-LASV virus expressing at least one of the previously mentioned LASV polypeptide, antigenic fragment thereof or antigen thereof or a truncated version thereof, namely NP, mNP, GPC and / or Z. The invention also concerns immunogenic particles expressed by the measles virus and comprising a LASV polypeptide, in particular at least the GPC polypeptide, or protein, or antigenic fragment thereof and / or infectious Virus-like particles (VLPs) that contains at least the Z polypeptide, or protein, or antigenic fragment thereof, said immunogenic particles and / or VLPs being able to elicit a cellular and / or humoral response against LASV, in particular a T cell response, in particular a CD4+ and / or CD8+ T cell response.In particular, the invention is related to the use of these genetic constructs, recombinant nucleic acid constructs, expression vectors like plasmid vectors and the like, recombinant virus infectious particles, VLPs, for inducing an immunogenic or antigenic response within a host.BACKGROUND OF THE INVENTIONLassa Virus (LASV) is an old world arenavirus of the Arenaviridae family. LASV are enveloped, single-stranded, bisegmented ambisense RNA viruses. Their genome contains two RNA segments each coding for two proteins, one in each sense, for a total of four viral proteins. The larger segment (approximatively 7 kb) encodes the zinc-binding protein Z. Z protein regulates replication and transcription. The larger segment also encodes the RNA polymerase L. The small segment (approximatively 3.4kb) encodes the nucleoprotein (NP) and the glycoprotein precursor (GPC), which is posttranslationnaly cleaved into the envelope glycoproteins GP1 and GP2 and the stable signal peptide SSP. These two glycoproteins mediate host cell entry. The synthesis capacity of an arenavirus is contained within the L polymerase protein. This protein uses viral RNA templates consisting in the genomic RNA encapsidated by the NP protein and viral ribonucleoproteins. Upon infection, the virus is delivered into the cytoplasm of the host cell, the L polymerase protein initiates transcription from the genome promoter located at the 3’ end of each genomic RNA segment. The primary transcription results in the synthesis of mRNA of the viral genes encoded in the antigenomic orientation, i.e. of NP and L genes. Transcription terminates at the distal end of the stem-loop structure within the intergenomic region. Then, the L polymerase moves across the intergenomic region to generate a complementary antigenomic RNA. This RNA serves as a template for the synthesis of the mRNA of viral genes GPC and Z and for the synthesis of a full length genomic RNA.LASV is the agent of the Lassa fever, a severe hemorrhagic fever, in humans. The natural reservoir of the virus is the African rodent Mastomys natalensis. Lassa virus is transmitted from rodents to humans, but the virus may also be transmitted from human to human, giving rise to local outbreaks.Between 100.000 and 300.000 patients, and sometimes up to 500.000 patients, are reported with the Lassa fever each year in the endemic regions of west Africa, especially in Guinea, Liberia, Nigeria and Sierra Leone. Therefore, Lassa fever is a major public health concern in these regions. The severity of the disease varies from asymptomatic infection to severe complications leading to fatal hemorrhagic fever. Clinical signs and symptoms include fever, cough, chest pain, dysuria, headache, vomiting, diarrhea, pharyngitis, conjunctivitis, bleeding and facial edema. The mortality rates of patients infected with the LASV is high, with a rate around 10% in some areas where the LASV is distributed. The fatality rate is as high as 50% in young children. Moreover, approximatively 20% of the survivors present long-term complications including hearing deficit. Therefore, the Lassa fever has a serious impact on the population of these regions and is a major health problem. Lately, the distribution of the Lassa fever infections seems to spread in other west African countries, since cases have been reported in Mali, Ghana, Ivory Coast and Burkina Faso during the last decade.Despite its discovery in 1969 in Nigeria, there is currently no preventive or prophylactic treatment against Lassa fever. Most of the patients are treated with Ribavirin, an antiviral drug. Unfortunately, treatment with the drug seems to be the most effective only when administrated early in the course of the illness and it is not fully efficient. The treatment should also be completed with supportive care, like maintenance of blood pressure and oxygenation, fluid and electrolyte balance, and the treatment of any other infections. Therefore, it may be difficult to effectively treat the patients in the endemic regions of west Africa where the Lassa fever spreads.Whether infection leads to severe illness or death seems to depend on host immune response. Most of the severe cases include a defective cellular response, wherein the dendritic cells and macrophages massively release LASV but are not activated and therefore do not produce cytokines, or not enough. The disease severity, as much as the evolution and spread of the virus into new geographic areas, are a serious health public matter that needs to be fixed.In this context, the development of a preventive treatment, like a preventive vaccine, is a major priority to meet the needs of these populations. There is therefore a need for a fully efficient treatment able to treat or prevent LASV infections, including to prevent outcomes of LASV primary infection, in particular to prevent the Lassa fever.One of the most promising therapy for preventing LASV infections is prophylactic vaccination but no such vaccine is currently available. Prophylaxis would be the easiest and safest way to control the LASV infections, and protect the local populations. Despite this urgent need, no vaccine candidate has successfully advanced to clinical trials yet.Therefore, there is a need for a vaccine and products such as active ingredients for preparing a vaccine, and method for producing these products and vaccine. The vaccine candidate should be safe and efficient when immunizing people in need thereof, without significant side effects, and induces the production of antibodies neutralizing the LASV, and possibly T cells like T helper cells and / or Cytotoxic T cells. In other words, the vaccine should elicit a strong cellular and / or humoral response. Advantageously, the vaccine should confer sterilizing immunity after a single immunization. To this end, there is a need for a vaccine that would enable the LASV proteins and / or LASV VLPs to generate in vivo in infected cells, in particular in infected cells of a host, and thus provide an efficient, long-lasting immunity, especially which induces life-long immunity after only a single, or two, administration steps.Another need is to facilitate the vaccination of the populations that hardly have access to medical centers or the like. A vaccine candidate that would elicit immunization against two disease agents could enhance global health of these populations. A single vaccination could therefore allow the immunization against several disease agents present in the regions mentioned above. In particular, with the aim to totally eradicate the measles virus (MeV), a vaccine immunizingagainst both the MeV and the LASV could clearly protect these populations against these two major threats, especially in west Africa.Measles virus has been isolated in 1954 (Enders, J. F., and T. C. Peebles. 1954. Propagation in tissue cultures of cytopathogenic agents from patients with measles. Proc. Soc. Exp. Biol. Med.86:277-286.). Measles virus is a member of the order mononegavirales, i.e. viruses with a non-segmented negative-strand RNA genome. The non-segmented genome of MeV has an antimessage polarity which results in a genomic RNA which is neither translated in vivo or in vitro nor infectious when purified. Transcription and replication of non-segmented (-) strand RNA viruses and their assembly into virus particles have been studied and reported especially in Fields virology (3rd edition, vol. 1 , 1996, Lippincott - Raven publishers - Fields BN et ai). Transcription and replication of the measles virus do not involve the nucleus of the infected cells but rather take place in the cytoplasm of host cell, just like the LASV. The genome of the MeV comprises genes encoding six major structural proteins designated N, P, M, F, H and L, and an additional two non-structural proteins from the P gene, C and V. The gene order is the following: from the 3’ end of the genomic RNA; N, P (including C and V), M, F, H and L large polymerase at the 5’ end. The genome furthermore comprises non coding regions in the intergenic region M / F. This non coding region contains approximatively 100 nucleotides of untranslated RNA. The cited genes respectively encode the proteins of the nucleocapsid of the virus or nucleoprotein (N), the phosphoprotein (P), the large protein (L) which together assemble around the genome RNA to provide the nucleocapsid, the hemagglutinin (H), the fusion protein (F) and the matrix protein (M).Attenuated viruses have been derived from MeV virus to provide vaccine strains and in particular from the Schwarz strain. The Schwarz measles vaccine is a safe and efficient vaccine currently available for preventing measles. Besides providing vaccine, strains attenuated measles virus such as the Schwarz strain have shown to be stable and suitable for the design of efficient delivery vector for immunization against other viruses, like Zika virus or Chikungunya virus. Measles vaccines have been administered to hundreds of millions of children over the last 30 years and have proved its efficiency and safety. It is produced on a large scale in many countries and is distributed at low cost.SUMMARY OF THE INVENTIONTo address, at least partially, the drawbacks of the state of the art, the inventors achieved the production of active components (or ingredients) for vaccines based on recombinant genetic constructs, and especially based on recombinant nucleic acid constructs comprising, within an infectious replicative measles virus, cloned polynucleotide(s) encoding Lassa virus polypeptides, proteins or antigens, or antigenic fragments thereof. Vaccines may be recovered when the recombinant measles virus replicates in the host after administration. The invention thus relates to a LASV vaccine, especially a pediatric vaccine, and relates to active ingredient based on an attenuated measles virus strain such as a known vaccine strain commercially available, especially the widely used Schwarz measles vaccine. For all these reasons, the inventors used attenuated measles viruses to generate recombinant measles virus particles stably expressing structural antigens of LASV, in particular immunogenic particles thereof and / or VLPs. The measles approach of the invention meets all of the relevant criteria of a future LASV vaccine.One aim of the invention is to provide a genetic construct, in particular recombinant genetic constructs, in particular nucleic acid constructs, for recovering infectious virus from the nucleic acid construct, and in particular a measles virus expressing LASV particles, and optionally also LASV Virus Like Particles (VLPs).The invention therefor relates to a nucleic acid construct which comprises a cDNA molecule encoding the full-length antigenomic (+) RNA strand of the measles virus, and a first heterologous polynucleotide encoding at least one polypeptide, or at least one protein, or at least one antigen, or at least one antigenic fragment thereof, of the Lassa virus, said at least one polypeptide, or at least one protein, or at least one antigen, or at least one antigenic fragment thereof, being selected from the group consisting of the nucleoprotein (NP), a mutated nucleoprotein (mNP), the Zinc-binding protein (Z) and the glycoprotein precursor (GPC). The first heterologous polynucleotide is operatively cloned within an additional transcription unit (ATU) inserted within the cDNA of the antigenomic (+) RNA strand of the MeV. Particular nucleic acid constructs according to this embodiment are illustrated in Fig.1 and in Fig. 31 to Fig. 36 and in the examples.The expression“encodes” in the above definition encompasses the ability of the cDNA to allow transcription of a full length antigenomic (+) RNA, said cDNA serving especially as a template for transcription and where appropriate translation for product expression into cells or cell lines. Flence, when the cDNA is a double stranded molecule, one of the strands has the same nucleotide sequence as the antigenomic (+) RNA of the measles virus with the first heterologous polynucleotide cloned within, except “U” nucleotides that are substituted by“T” nucleotides in the cDNA. The nucleic acid construct of the invention may comprise regulatory elements controlling the transcription of the coding sequences, in particular promoters and termination sequences for the transcription, and possibly enhancer and other cis-acting elements. These regulatory elements may be heterologous with respect to the heterologous polynucleotide issued or derived from LASV gene(s), in particular may be the regulatory elements of the measles virus strain.The expression“operatively cloned”, which can be substituted by the expression “operatively linked”, refers to the functional cloning, or insertion, of a heterologous polynucleotide within the nucleic acid construct of the invention such that said polynucleotide and nucleic acid construct are effectively, or efficiently, transcribed and if appropriate translated, in particular in cells, cell line, host cell used as a part of a rescue system for the production of recombinant infectious MeV particles or MeV expressing at least one polypeptide, or at least one protein, or at least one antigen, or at least an antigenic fragment thereof, of LASV. In other words, the nucleic acid construct of the invention allows the production, when placed in appropriate conditions, of an infectious antigenomic (+) RNA capable ofproducing at least one polypeptide, or at least one protein, or at least one antigen, or at least an antigenic fragment thereof, of LASV.In a particular embodiment of the invention, the nucleic acid construct comprising the cDNA encoding the nucleotides of the full-length infectious antigenomic (+) RNA strand of MeV but without the operatively cloned heterologous polynucleotide complies with the rule of six (6) of the measles virus genome. In other words, the cDNA encoding the nucleotides of the full-length, infectious antigenomic (+) RNA strand of MeV is a polyhexameric cDNA.The organization of the genome of measles viruses and their replication and transcription process have been fully identified in the prior art and are especially disclosed in Horikami S.M. and Moyer S.A. (Curr. Top. Microbiol. Immunol. (1995) 191 , 35-50 or in Combredet C. et al (Journal of Virology, Nov 2003, p1 1546-1 1554) for the Schwarz vaccination strain of the virus or for broadly considered negative-sense RNA viruses, in Neumann G. et al (Journal of General Virology (2002) 83, 2635-2662).The“rule of six” is expressed in the fact that the total number of nucleotides present in a nucleic acid representing the MeV (+) strand RNA genome or in the nucleic acid constructs comprising the same is a multiple of six. The“rule of six” has been acknowledged in the state of the art as a requirement regarding the total number of nucleotides in the genome of the measles virus, which enables efficient or optimized replication of the MeV genomic RNA. In the embodiments of the present invention defining a nucleic acid construct that meets the rule of six, said rule applies to the nucleic acid construct specifying the cDNA encoding the full-length MV (+) strand RNA genome. In this regard the rule of six applies individually to the cDNA encoding the nucleotide sequence of the full-length infectious antigenomic (+) RNA strand of the measles virus, possibly but not necessarily to the polynucleotide cloned into said cDNA and encoding at least one polypeptide of the LASV.The nucleic acid construct of the invention is in particular a purified DNA molecule, obtained or obtainable by recombination of at least one polynucleotide of MeV and at least one, or several, polynucleotide of the LASV, operably cloned or linked together.According to the invention, the nucleic acid construct is prepared by cloning a polynucleotide, or several polynucleotides, encoding at least one polypeptide, or a protein, or an antigen, or an antigenic fragment thereof, selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV in the cDNA encoding the full-length antigenomic (+) RNA of the measles virus. The MeV genome is illustrated on Fig .1 A, while several nucleic acid constructs according to the invention are illustrated on Fig.1 B and on Fig. 31 to Fig. 36. Alternatively, a nucleic acid construct of the invention may be prepared using steps of synthesis of nucleic acid fragments or polymerization from a template, including by PCR. The polynucleotide(s) and nucleic acid construct of the invention may rather be prepared in accordance with any known method in the art and in particular may be cloned, obtained by polymerization especially using PCR methods or may be synthesized.The heterologous polynucleotide may be issued from the fusion of several other polynucleotides, each encoding a particular polypeptide, or a particular protein, antigen or an antigenic fragment thereof, of LASV. For example, the heterologous polynucleotide may be issued from the fusion of polynucleotides each encoding a single protein, the GPC protein and the NP protein or the mNP protein for example, these two polynucleotides being linked within the nucleic acid construct by a linker sequence. A linker sequence is well known in the art and can be a short nucleotide sequence comprising or consisting in a regulatory sequence of the measles virus.Accordingly, the heterologous polynucleotide may encode a single polypeptide, two different polypeptides, two identical polypeptides, three different polypeptides, two identical polypeptides and another polypeptide, four different polypeptides, two identical polypeptides and two others identical polypeptides, two identical polypeptides and two others different polypeptides, three identical polypeptides and another different polypeptide. Any one of these polynucleotides encoding at least two (identical or different) polypeptides may be issued from the fusion of several polynucleotides, or prepared using steps of synthesis of nucleic acid fragments or polymerization from a template, including by PCR. Alternatively, any one of these polynucleotides may be a cDNA issued from the genomic RNA of the Lassa virus, after retrotranscription, said cDNA being either the full genomic cDNA or a fragment thereof, and encoding a polypeptide of the LASV.The heterologous polynucleotide, in particular LASV gene(s), is / are cloned within an additional transcription unit (ATU) inserted in the cDNA of the MeV. ATU sequences are known from the skilled person and comprise, for use in steps of cloning into cDNA of MeV, cis-acting sequences necessary for MeV-dependent expression of a transgene, such as a promoter of the gene preceding, in MeV cDNA, the insert represented by the polynucleotide encoding the LASV polypeptide(s) inserted into a multiple cloning sites cassette. The ATU may be further defined as disclosed by Billeter et al. in WO 97 / 06270. Three ATUs are represented on Fig. 1A. An ATU may also be defined as multiple cloning cassette inserted within the cDNA of the MeV, in particular between the N-P intergenic region of the MeV genome, and / or between the intergenic H-L region of the MeV genome. An ATU may contain cis-acting sequences necessary for the transcription of the P gene of MeV. The different ATUs in particular ATU1 and ATU2 may be identical regarding their nucleic acid sequence. ATUs are generally localized between two CTT codons corresponding respectively to the start and stop codons of the polymerase. ATUs may further comprise a ATG and a TAG codons corresponding respectively to the start and stop codons for translation of the heterologous polynucleotide cloned within the ATU. Alternatively, ATUs are localized between a ATG and a TAG codons corresponding respectively to the start and stop codons for translation of the heterologous polynucleotide cloned within the ATU. ATUs may further comprise a ATG and a TAG codons corresponding respectively to the start and stop codons for translation of the heterologous polynucleotide cloned within the ATU. In a preferred embodiment of the invention, an ATU is a polynucleotide comprising or consisting of SEQ ID No: 16.SEQ ID No: 16SEQ ID No: 16 is an ATU sequence localized within the cDNA molecule encoding a full-length antigenomic (+) RNA strand of a measles virus. CTT codons corresponding respectively to the start and stop codons of the polymerase are in bold. ATG and TAG codons corresponding to the start and stop codons for translation of the heterologous polynucleotide cloned within the ATU are underlined.CTTAGGAACCAGGTCCACACAGCCGCCAGCCCATCAacgcgtacgATG*TAGg eg eg cagcg ettag aeg teteg eg aTCGAT ACT AGTACAACCT AAAT CCATT AT AAAAA ACTT wherein the * corresponds to the heterologous codon-optimized sequence polynucleotide encoding at least one LASV polypeptide.An ATU with a heterologous polynucleotide encoding the GPC polypeptide is for example localized between amino acid residues 3487 and 5071 on SEQ ID No: 9. SEQ ID No: 17 corresponds to an ATU comprising as a cloned insert a codon-optimized heterologous polynucleotide encoding the GPC protein.An ATU (known under reference ATU2) is localized between the P and M genes of the MeV. Another ATU (known under reference ATU1 ) is located upstream the gene N of the MeV. Another ATU (known under reference ATU3) is located between the genes H and L of MeV. It has been observed that the transcription of the viral RNA of MeV follows a gradient from the 5’ to the 3’ end. This explains that, depending on where the heterologous polynucleotide is inserted, its level of expression will vary and be more or less efficient if inserted within ATU1 , ATU2 or ATU3.The term “polypeptide” is used interchangeably with the terms “antigen” or “protein” or “antigenic fragment” and defines a molecule resulting from a concatenation of amino acid residues. In particular, the polypeptides disclosed in the application originate from the LASV and are antigens, proteins, structural proteins, or antigenic fragments thereof, that may be identical to native proteins or alternatively that may be derived thereof by mutation, including by substitution (in particular by conservative amino acid residues) or by addition of amino acid residues or by secondary modification after translation or by deletion of portions of the native proteins(s) resulting in fragments having a shortened size with respect to the native protein of reference. Fragments are encompassed within the present invention to the extent that they bear epitopes of the native protein suitable for the elicitation of an immune response in a host in particular in a human host, including a child host, preferably a response that enables the protection against a LASV infection or against a LASV associated disease. Epitopes are in particular of the type of T epitopes involved in elicitation of Cell Mediated Immune response (CMI response). T epitopes are involved in the stimulation of T cells through presentation of some parts of the T-cell epitope which can bind on MHC class II molecules, leading to the activation of T cells. Epitopes may alternatively be of type B, involved in the activation of the production of antibodies in a host to whom the protein has been administered or in whom it is expressed following administration of the infectious replicative particles of the invention. Fragments may have a size representing more than 50% of the amino-acid sequence size of the native protein of LASV strain Josiah, preferably at least 90% or 95%. Polypeptide may have at least 50% identity with the native protein of LASV strain Josiah, preferably at least 60%, preferably at least 70%, preferably at least 85% or at least 95%.In a particular embodiment of the invention, each polynucleotide operatively cloned within the cDNA of the antigenomic (+) RNA encodes polypeptides comprising epitopes localized within any one of the LASV polypeptide(s). According to this embodiment, the epitope sequence(s) share(s) 100% identity with the epitope sequence(s) of the native LASV proteins. Such epitopes are listed in the Immune Epitope database and analysis resource (www.iedb.orq). Within the polypeptide(s) of the LASV encoded by the polynucleotide and having an epitope sequence(s) as defined herein, amino acid residue that does not belong to any epitope may be different from the sequence of the native LASV protein(s).By“polypeptide of LASV” is meant a“polypeptide” as defined herein (either a polypeptide, an antigen, a protein, or an antigenic fragment thereof), the amino acid sequence of which is identical to a counterpart in a strain of LASV, especially LASV strain Josiah, including a polypeptide which is a native mature or precursor of protein of LASV or is an antigenic fragment thereof or a mutant thereof as defined herein in particular an antigenic fragment or a mutant having at least 50%, at least 80%, in particular advantageously at least 90% or preferably at least 95% amino acid sequence identity to a naturally occurring LASV GPC, NP or Z protein. Amino acid sequence identity can be determined by alignment by one of skill in the art using manual alignments or using the numerous alignment programs available (for example, BLASTP - http: / / blast.ncbi.nlm.nih.gov / ). Fragments or mutants of LASV polypeptides of the invention may be defined with respect to the particular amino acid sequences illustrated herein, especially the amino acid sequences from the group consisting of SEQ ID No: 1 , SEQ ID No: 3, SEQ ID No: 5 and SEQ ID No: 7. In a particular embodiment of the invention, the polypeptides share at least 50%, at least 80%, in particular advantageously at least 90% or preferably at least 95% amino acid sequence identity with their native proteins of the LASV strain Josiah, or with the polypeptides of SEQ ID No.: 1 ; SEQ ID No.: 3; SEQ ID No.: 5; or SEQ ID No.: 7.According to one aspect of the invention, a polynucleotide encoding at least one polypeptide of LASV is issued or derived from the genome of isolated and purified wild strain(s) of LASV, including any Lassa strain whose genome has been fully or partially sequenced. At least some of these sequences may be found in the NCBI nucleotide database. In particular, the polynucleotide encoding at least one LASV polypeptide may be derived or issued from any Lassa strain sequenced and referenced in Clinical Sequencing Uncovers Origins and Evolution of Lassa Virus (Andersen Kristian G et al 2015; Cell. 2015 August 13; 162(4): 738-750. doi:10.1016 / j. cell.2015.07.020), especially in the supplementary data of the publication wherein the name of the strains and corresponding accession reference of the sequences are listed. Preferentially, the polynucleotide is issued or derived from the strain Josiah whose genomic sequences of the two RNAsegments may be found under GenBank accession no. J04324.1 for the short genomic RNA encoding NP protein and GPC protein, and under European Nucleotide Archive accession no. U73034.2 for the long genomic RNA encoding the Z protein and the L protein. Native protein of LASV strain Josiah may be defined as having the sequences issued from RNA segments found under GenBank accession no. J04324.1 for the short genomic RNA encoding NP protein and GPC protein, and under European Nucleotide Archive accession no. U73034.2 for the long genomic RNA. The term“derive” appearing in the definition of the polynucleotides merely specifies that the sequence of said polynucleotide may be identical to the corresponding sequence in a LASV strain or may vary to the extent that it encodes polypeptides, antigens, proteins, or fragments thereof, of LASV that meet(s) the definition of the“polypeptide” according to the present invention. In particular, a polynucleotide derives from the nucleic acid of a LASV strain when it is codon-optimized with respect to such sequence. Accordingly, the term does not restrict the production mode of the polynucleotide.Alternatively, fragments may be short polypeptides with at least 10 amino acid residues, which harbor epitope(s) of the native protein listed in the Immune Epitope database and analysis resource (www.iedb.orq). Fragments in this respect also include polyepitopes.According to another embodiment of the invention, the nucleic acid construct further comprises a second heterologous polynucleotide encoding at least one polypeptide, or an antigenic fragment thereof, of the LASV, said at least one polypeptide or antigenic fragment thereof being selected from the group consisting of the GPC protein, the NP protein, the mNP protein and Z protein, the second heterologous nucleotide being operatively cloned within another ATU at a location distinct from the location of the first cloned heterologous polynucleotide, preferentially upstream the N gene of the MeV, said another ATU being in particular the ATU1 inserted upstream the N gene of the MeV. The second heterologous polynucleotide or antigenic fragment thereof encodes in particular at least one polypeptide or antigenic fragment thereof different from the polypeptide(s) encoded by the first heterologous polynucleotide.According to this embodiment, another ATU (known under reference ATU1 ) is advantageously located in the N-terminal sequence of the cDNA molecule encoding the full-length (+) RNA strand of the antigenome of the MeV upstream the N gene of MeV, while the other ATU (ATU2) is preferentially located between the P and M genes of the virus. Since the transcription of the viral RNA of MeV follows a gradient from the 5’ to the 3’ end, the inventors found that cloning two polynucleotides at different locations within the cDNA encoding the full-length antigenomic (+) RNA of the measles virus may lead to the production of higher yield of antigenic particles and / or LASV virus like particles (VLPs) when the Z protein is encoded by at least one heterologous polynucleotide, while this production may be less important when the polynucleotides are all cloned within a single and same location. Furthermore, cloning the heterologous polynucleotides at different locations may reduce the attenuation of the expression of the encoded polypeptides. Indeed, when several genes are cloned within a single ATU, it may lead to reduction of the expression of the encoded polypeptides. Particular nucleic acid constructs according to this embodiment are illustrated in Fig.1 b and in the examples.Within the other ATU, the second polynucleotide may encode any one of the previously listed polypeptide, or antigenic fragment thereof, of the LASV. Accordingly, the second polynucleotide localized within the other ATU may encode the same polypeptide(s) than the first polynucleotide inserted within the first ATU, or the second polynucleotide may encode at least one common polypeptide with the polypeptide(s) encoded by the first polynucleotide. In a preferred embodiment of the invention, the first polynucleotide and the second polynucleotide encodes at least one different polypeptide, or an antigenic fragment thereof.The cDNA molecule encoding the full-length antigenomic (+) RNA strand of the MeV may be characteristic of or may be obtained from an attenuated strain of MeV. An“attenuated strain” of MeV is defined as a strain that is avirulent or less virulent than the parent strain in the same host, while maintaining immunogenicity and possibly adjuvanticity when administered in a host for preserving immunodominant T and B cell epitopes and possibly the adjuvanticity such as the induction of T cell costimulatory proteins or cytokine IL-12.An attenuated strain of a measles virus accordingly refers to a strain which has been serially passaged on selected cells and, possibly, adapted to other cells to produce seed strains suitable for the preparation of human vaccine strains, harboring a stable genome which would not allow reversion to pathogenicity nor integration in host chromosomes. As a particular“attenuated strain”, an approved strain for a vaccine is an attenuated strain suitable for the invention when it meets the criteria defined by the FDA (US Food and Drug Administration); i.e. it meets safety, efficacy, quality and reproducibility criteria, after rigorous reviews of laboratory and clinical data (www.fda.gov / cber / vaccine / vacappr.htm).In particular, the cDNA molecule encoding the full-length antigenomic (+) RNA strand of the MeV is obtained from an attenuated virus strain selected from the group comprising of consisting of the Schwarz strain, the Zagreb strain, the AIK-C strain, the Moraten strain, the Philips strain, the Beckenham 4A strain, the Beckenham 16 strain, the Edmonston seed A strain, the Edmonston seed B strain, the CAM-70 strain, the TD 97 strain, the Leningrad-16 strain, the Shanghai 191 strain and the Belgrade strain. All these strains have been described in the prior art. The invention uses in particular strains that have been allowed for use as commercial vaccines. In particular, the cDNA molecule encoding the full length antigenomic (+) RNA strand of the MeV is obtained from the Schwarz strain.According to a particular embodiment of the invention, the cDNA molecule is placed under the control of heterologous expression control sequences.The insertion of such a control for the expression of the cDNA, is favorable when the expression of this cDNA is sought in cell types which do not enable full transcription of the cDNA with its native control sequences.According to a particular embodiment of the invention, the heterologous expression control sequence comprises the T 7 promoter and T 7 terminator sequences. These sequences are respectively located 5’ and 3’ of the coding sequence for the full length antigenomic (+) RNA strand of MeV and from the adjacent sequences around this coding sequence.In a particular embodiment of the invention, the cDNA molecule, which is defined here above is modified, i.e. comprises additional nucleotide sequences or motifs.In a preferred embodiment, the cDNA molecule used according to the invention further comprises, at its 5’-end, adjacent to the first nucleotide of the nucleotide sequence encoding the full-length antigenomic (+) RNA strand of the MeV approved vaccine strain, a GGG motif followed by a hammerhead ribozyme sequence and comprises, at its 3’-end, adjacent to the last nucleotide of said nucleotide sequence encoding the full-length anti-genomic (+) RNA strand, the sequence of a ribozyme. The Hepatitis delta virus ribozyme (d) is appropriate to carry out this preferred embodiment.The GGG motif placed at the 5’ end, adjacent to the first nucleotide of the above coding sequence improves the efficiency of the transcription of said cDNA coding sequence. As a requirement for the proper assembly of measles virus particles is the fact that the cDNA encoding the antigenomic (+) RNA complies with the rule of six, when the GGG motif is added, a ribozyme is also added at the 5’ end of the coding sequence of the cDNA, 3’ from the GGG motif, in order to enable cleavage of the transcript at the first coding nucleotide of the full-length antigenomic (+) RNA strand of MeV.In order to prepare the nucleic acid construct of the invention, the preparation of a cDNA molecule encoding the full-length antigenomic (+) RNA of a measles virus disclosed in the prior art is achieved by known methods. The obtained cDNA provides especially the basis for the genome vector involved in the rescue of recombinant measles virus particles when it is inserted in a vector such as a plasmid.A particular cDNA molecule suitable for the preparation of the nucleic acid construct of the invention is the one obtained using the Schwarz strain of measles virus. Plasmid pTM-MVSchw, which contains an infectious MeV cDNA corresponding to the anti-genome of the Schwarz MV vaccine strain and is used for preparation of recombinant vectors encompassing the heterologous polynucleotides of the invention, has been described elsewhere (Combredet, C., et ai, A molecularly cloned Schwarz strain of measles virus vaccine induces strong immune responses in macaques and transgenic mice. J Virol, 2003. 77(21 ): p. 1 1546-54). Accordingly, the cDNA used within the present invention may be obtained as disclosed in W02004 / 000876 or may be obtained from plasmid pTM-MVSchw deposited by Institut Pasteur at the CNCM under No I-2889 on June 12, 2002, the sequence of which is disclosed in W02004 / 000876 incorporated herein by reference. The plasmid pTM-MVSchw has been obtained from a Bluescript plasmid and comprises the polynucleotide coding for the full-length measles virus (+) RNA strand of the Schwarz strain placed under the control of the promoter of the T7 RNA polymerase. It has 18967 nucleotides and a sequence represented as SEQ ID NO: 15. cDNA molecules (also designated cDNA of the measles virus or MeV cDNA for convenience) from other MeV strains may be similarly obtained starting from the nucleic acid purified from viral particles of attenuated MeV such as those described herein. An additional transcription unit may be a multiple-cloning site cassette previously inserted in the vector, as explained in Combredet et ai, 2003. An ATU may comprise cis- acting sequences necessary for the transcription of the inserted LASV genes. The heterologous polynucleotide(s) are cloned or inserted within additional transcription units (ATU) as defined here above.The heterologous polynucleotide may also be cloned or inserted within another ATU. As an example, a third ATU may be inserted between the H gene and the L gene of the MeV, and the first or second heterologous polynucleotide may be cloned or inserted within this third ATU. In a particular embodiment of the invention, the nucleic acid construct may comprise a first heterologous polynucleotide inserted within a first ATU, a second heterologous polynucleotidesequence inserted into a second ATU at a distinct location from the first ATU, and a third heterologous polynucleotide inserted within a third ATU at a distinct location from the first and second ATUs.In a preferred embodiment, the nucleic acid construct comprises heterologous polynucleotide(s) encoding a particular mutated NP protein, or an antigenic fragment thereof. The native NP protein may be mutated to knock down the exonuclease activity of the NP protein. A NP protein knocked down for its exonuclease activity may be determined by luciferase assay using a reporter luciferase gene placed under the control of an IRF3 dependent promoter as described in PMID: 210851 17 and illustrated on Fig. 29. NP is involved in the virus-induced inhibition of type I IFN signaling (Martinez-Sobrido, 2006). This activity is linked to the C-terminal domain of the native NP protein. Functional analysis confirmed the exonuclease activity of LASV NP, which has been proven to be a critical step for its type I IFN counteracting function (Qi, 2010). Flence, the inventors introduced two mutations within the exonuclease domain of the NP protein. The exonuclease domain of the NP protein is localized within the C-terminal domain of the NP protein, especially between amino acid residues 341 and 569 of SEQ ID no: 3. Accordingly, a mutated NP protein is in particular issued from a native NP protein mutated (by deletion(s) and / or addition(s) and / or substitution(s) of any amino acid residue) within the exonuclease domain as defined here above, and having its exonuclease activity knocked down according to the luciferase assay described here above. In particular, substitution(s) of at least one amino acid residue D389, E391 , D466, D533 and H528 of SEQ ID No: 3 may lead to a mutated NP protein without exonuclease activity. In particular, the amino acid residue at position 389 of SEQ ID No: 3 may be mutated, for example by substituting the Aspartic acid by an Alanine. Alternatively, amino acid residue at position 392 of SEQ ID No: 3 may be mutated, for example by substitution of the Glycine by an Alanine. In a preferred embodiment, both amino acids residues at position 389 and 392 of SEQ ID No.3 are mutated by substitution. In a more preferred embodiment, the mNP protein has the sequence of SEQ ID No: 5.According to this embodiment, the mNP polypeptide encoded by the polynucleotide(s) allows the induction of type I IFN. In other words, the immune suppressive function of the native NP is shut down in mNP. Therefore, it is provided nucleic acid constructs comprising polynucleotide(s) which increase the efficiency of chimeric recombinant MeV-LASV infectious particles immunogenicity.According to a preferred embodiment, the invention also concerns modification and in particular optimization of the polynucleotides to allow an efficient expression of the LASV polypeptides, proteins, antigens, or fragments thereof, in a host cell.Accordingly, optimization of the polynucleotide sequence can be operated avoiding cis-active domains of nucleic acid molecules: internal TATA-boxes, chi-sites and ribosomal entry sites; AT-rich or GC-rich sequence stretches; ARE, INS, CRS sequence elements; repeat sequences and RNA secondary structures; cryptic splice donor and acceptor sites, branch points.The optimized polynucleotides may also be codon optimized for expression in a specific cell type, in particular may be modified for the Maccaca codon usage or for the human codon usage. This optimization allows increasing the efficiency of chimeric infectious particles production in cells without impacting the amino acid composition of the expressed protein(s).In particular, the optimization of the polynucleotide encoding the LASV polypeptide(s) may be performed by modification of the wobble position in codons without impacting the identity of the amino acid residue translated from said codon with respect to the original one.Optimization is also performed to avoid editing-like sequences from Measles virus. The editing of transcript of measles virus is a process which occurs in particular in the transcript encoded by the P gene of measles virus. This editing, by the insertion of extra G residues at a specific site within the P transcript, gives rise to a new protein truncated compared to the P protein. Addition of only a single G residue results in the expression of the V protein, which contains a unique carboxyl terminus (Cattaneo R et al., Cell. 1989 Mar 10;56(5):759-64).In the polynucleotides according to this particular embodiment of the invention, the following editing-like sequences from measles virus can be mutated: AAAGGG, AAAAGG, GGGAAA, GGGGAA, as well as their complementary sequence: TTTCCC, TTTTCC, CCCTTT, CCCCTT. For example, AAAGGG can be mutated in AAAGGC, AAAAGG can be mutated in AGAAGG or in TAAAGG or in GAAAGG, and GGGAAA in GCGAAA.Hence, the heterologous polynucleotide(s) may comprise any one of the following sequences, or a plurality of the following sequences, or at least two of the following sequences, or at least three of the following sequences, or the four following sequences:- SEQ ID No: 2 which encodes the GPC protein; and / or- SEQ ID No: 4 which encodes the NP protein; and / or- SEQ ID No: 6 which encodes the mNP protein; and / or- SEQ ID No: 8 which encodes the Z protein.Within the heterologous polynucleotide(s), each sequence defined here above may be present a single time, or a plurality of times. In a preferred embodiment of the invention, each sequence is present a single time within a single heterologous polynucleotide, or is present a single time within the heterologous polynucleotides taken together.According to any one of the particular embodiments of the invention, it is provided nucleic acid constructs comprising polynucleotide(s) which increase the efficiency of chimeric recombinant MeV-LASV infectious particles production.Alternatively, or complementarily, the heterologous polynucleotide(s) may encode any one of the following polypeptides, or an antigenic fragment thereof, or at least two of the following polypeptides, or at least three of the following polypeptides, or the four following polypeptides:- the GPC protein of SEQ ID No: 1 or an antigenic fragment thereof; and / or- the NP protein of SEQ ID No: 3 or an antigenic fragment thereof; and / or- the mNP protein of SEQ ID No: 5 or an antigenic fragment thereof; and / or- the Z protein of SEQ ID No: 7 or an antigenic fragment thereof.It should be noted that the polynucleotide(s) may encode a polypeptide as defined here above a single time or a several times. In a preferred embodiment, each polypeptide is encoded a single time within a single heterologous polynucleotide, and more preferentially, each polypeptide is encoded a single time within the plurality of polypeptides. According to a particular embodiment of the invention, several polynucleotides wherein each polynucleotide encodes at least one LASV protein are combined or fused to form a polynucleotide encoding several proteins of the LASV. These polynucleotides may distinguish from each other by the fact that they code for proteins of various strains of the LASV, or for different proteins of a LASV strain.In a particular embodiment, the nucleic acid construct of the invention comprises from the 5’ to 3’ end the following polynucleotides:(a) a polynucleotide encoding the N protein of the MeV;(b) a polynucleotide encoding the P protein of the MeV;(c) the first heterologous polynucleotide encoding at least one polypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof, in particular encoding a single polypeptide which is the GPC protein or an antigenic fragment thereof, or encoding at least two polypeptides, which are the GPC protein or an antigenic fragment thereof and either the NP protein or the mNP protein, or an antigenic fragment thereof, in particular encoding the GPC protein and the mNP protein, wherein the first polynucleotide is in particular operatively cloned within an ATU, in particular ATU2;(d) a polynucleotide encoding the M protein of the MeV;(e) a polynucleotide encoding the F protein of the MeV;(f) a polynucleotide encoding the H protein of the MeV;(g) a polynucleotide encoding the L protein of the MeV;and wherein said polynucleotides are operatively linked within the nucleic acid construct and under the control of a viral replication and transcriptional regulatory elements such as MeV leader and trailer sequence(s).Several examples of this embodiment obtained according to the invention are schematically illustrated on fig. 1 B: the constructs named MeV-GPCi_Asv; MeV-NP+GPCLASV; MeV-NPExoN+GPCi_Asv belong to this particular embodiment, but other construct not illustrated on Fig.1 B are also included, like for example MeV-GPCi_Asv+NP; MeV-GPCi_Asv+NPExoN; MeV-Z+GPCu\sv; MeV-GPCi_Asv+Z; MeV-Z+NP; MeV-Z+NPExoN; MeV-NP+Z; MeV-NPExoN+Z; MeV-Z+GPCLAsv+NP; MeV-Z+GPCLAsv+NPExoN; MeV-Z-NP-GPCi_Asv; MeV-Z-NPExoN-GPCi_Asv;MeV-GPCi_Asv+NP+Z; MeV-GPCi_Asv+NPExoN+Z; MeV-GPCi_Asv+Z+NP;MeV-GPCLAsv+Z+NPExoN; MeV-NP+GPCLAsv+Z; MeV-NP-Z+GPCLAsv;MeV- N PEXON+G PCLASV+Z; MeV- N P EXON-Z+ G PCLASV;whereinMeV corresponds to the cDNA molecule encoding the full-length antigenomic (+) RNA strand of the measles virus (MeV);GPCLASV corresponds to a polynucleotide encoding a polypeptide of the GPC protein, or an antigenic fragment thereof;NP corresponds to a polynucleotide encoding a polypeptide of the NP protein, or an antigenic fragment thereof;NPEXON corresponds to a polynucleotide encoding a polypeptide of the mNP protein, or an antigenic fragment thereof;Z corresponds to a polynucleotide encoding a polypeptide of the Z protein, or an antigenic fragment thereof;The expressions "N protein", "P protein", "M protein", "F protein", "FI protein" and "L protein" refer respectively to the nucleoprotein (N), the phosphoprotein (P), the matrix protein (M), the fusion protein (F), the hemagglutinin protein (FI) and the RNA polymerase large protein (L) of a measles virus and encompass referenceto the respective polypeptides or antigenic fragments thereof. These components have been identified in the prior art and are especially disclosed in Fields, Virology (Knipe & Howley, 2001 ).In another particular embodiment of the invention, the nucleic acid construct comprises from the 5’ to 3’ end the following polynucleotides:(a) the second heterologous polynucleotide encoding at least one polypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof, in particular encoding the Z protein, or an antigenic fragment thereof, wherein the second polynucleotide is operatively cloned within an ATU localized upstream the N gene of the MeV, in particular within the ATU1 ;(b) a polynucleotide encoding the N protein of the MeV;(c) a polynucleotide encoding the P protein of the MeV;(d) the first heterologous polynucleotide encoding at least one polypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof, in particular encoding a single polypeptide which is the GPC protein or an antigenic fragment thereof, or encoding at least two polypeptides, which are the GPC protein or an antigenic fragment thereof and either the NP protein or the mNP protein, or an antigenic fragment thereof, in particular encoding the GPC protein and the mNP protein, wherein the first polynucleotide is in particular operatively cloned within an ATU, in particular ATU2;(e) a polynucleotide encoding the M protein of the MeV;(f) a polynucleotide encoding the F protein of the MeV;(g) a polynucleotide encoding the H protein of the MeV;(h) a polynucleotide encoding the L protein of the MeV,and wherein said polynucleotides are operatively linked within the nucleic acid construct and under the control of a viral replication and transcriptional regulatory elements such as MeV leader and trailer sequence(s).Several examples of this embodiment are schematically illustrated on fig. 1 B: the constructs named Z-MeV-GPCi_Asv; Z-MeV-NP+GPCi_Asv; Z-MeV-NPEXON+GPCLASV are encompassed within this particular embodiment. When the protein of LASV is named before MeV, said protein is cloned within the additional transcription unit localized upstream the N gene of the MeV. It should be noted that several non-represented constructs are also encompassed by this embodiment. As an example, a heterologous polynucleotide may be cloned within the third ATU. Nucleic acid constructs corresponding to Z-MeV-GPCLASV(ATU2)+NP(ATU3), or Z-MeV- NP(ATU2)- GPCLASV(ATU3), or Z-MeV-GPCLAsv(ATU2)+mNP(ATU3), or Z-MeV- mNP(ATU2)- GPCLASV(ATU3) are also encompassed by the present invention. It should be noted that a heterologous polynucleotide encoding at least one or any one of the Z polypeptide, the GPC polypeptide and / or the NP or mNP polypeptide could be inserted within ATU3. The various terms used therein have the same meaning as the one used in the previous particular embodiments.In a particular embodiment of the invention, the nucleic acid construct comprises within the first heterologous polynucleotide a nucleic acid encoding the NP protein, preferentially the NP protein of SEQ ID No: 3, or an antigenic fragment thereof; and a nucleic acid encoding the GPC protein, preferentially the GPC protein of SEQ ID No: 1 . In a preferred embodiment, this first heterologous polynucleotide is cloned between the P and M genes of the MeV, preferentially within ATU2 as defined here above.In a particular embodiment of the invention, the nucleic acid construct comprises within the first heterologous polynucleotide a nucleic acid of SEQ ID No: 4 encoding the NP protein, and a nucleic acid of SEQ ID No: 2 encoding the GPC protein, preferentially these two nucleic acids are separated by a linker sequence. In a preferred embodiment, the nucleic acid of SEQ ID No: 4 is localized upstream the nucleic acid of SEQ ID No: 2. This is for example illustrated on Fig.l B with the construct named MeV-NP+GPCi_Asv.In a particular embodiment of the invention, the nucleic acid construct comprises within the first heterologous polynucleotide a nucleic acid encoding the mNP protein, preferentially the mNP protein of SEQ ID No: 5, or an antigenic fragment thereof; and a nucleic acid encoding the GPC protein, preferentially the GPC protein of SEQ ID No: 1 .In a particular embodiment of the invention, the nucleic acid construct comprises within the first heterologous polynucleotide a nucleic acid of SEQ ID No: 6 encoding the mNP protein, and a nucleic acid of SEQ ID No: 2 encoding the GPC protein, preferentially these two nucleic acids are separated by a linker sequence. In a preferred embodiment, the nucleic acid of SEQ ID No: 6 is located upstream (towards the 5’ end of the construct) the nucleic acid of SEQ ID No: 2, as illustrated in Fig .1 B with the construct named MeV-NPExoN+GPCLAsv. In a preferred embodiment, this first heterologous polynucleotide is cloned between the P and M genes of the MeV, preferentially within ATU2 as defined here above.In a particular embodiment of the invention, the nucleic acid construct comprises the first heterologous polynucleotide and the second heterologous polynucleotide, and:- the second heterologous polynucleotide comprises a nucleic acid encoding the Z protein, or an antigenic fragment thereof, preferentially the Z protein of SEQ ID No: 7; the second heterologous polynucleotide being preferentially cloned within ATU1 as defined here above, and- the first heterologous polynucleotide comprises a nucleic acid encoding the GPC protein, or an antigenic fragment thereof, preferentially the GPC protein of SEQ ID No: 1 , the first heterologous polynucleotide being preferentially cloned within ATU2 as defined here above.In a particular embodiment of the invention, the nucleic acid construct comprises the first heterologous polynucleotide and the second heterologous polynucleotide, and:- the second heterologous polynucleotide comprises a nucleic acid of SEQ ID No: 8 encoding the Z protein, the second heterologouspolynucleotide being preferentially cloned within ATU1 as defined here above, and- the first heterologous polynucleotide comprises a nucleic acid of SEQ ID No: 2 encoding the GPC protein, the first heterologous polynucleotide being preferentially cloned within ATU2 as defined here above.In a particular embodiment of the invention, the nucleic acid construct comprises a recombinant cDNA whose sequence is selected from the group consisting of:SEQ ID No: 9 (MeV-GPC);SEQ ID No: 10 (MeV-NP-GPC);SEQ ID No: 1 1 (MeV-mNP-GPC);SED ID No: 12 (Z-MeV-GPC);SEQ ID No: 13 (Z-MeV-NP-GPC); andSEQ ID No: 14 (Z-MeV-mNP-GPC),wherein said sequences are described as follows:SEQ ID NO: 9SEQ ID No: 9 is the sequence of a nucleic acid construct according to a particular embodiment of the invention wherein said construct contains the pTM1 -MVSchwarz vector wherein the sequence encoding the GPC protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2.SEQ ID NO: 10SEQ ID No: 10 is the sequence of a nucleic acid construct according to another particular embodiment of the invention wherein said construct contains the pTM1 -MVSchwarz vector wherein the sequence encoding the GPC protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the NP protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2.SEQ ID NO: 11SEQ ID No: 1 1 is the sequence of a nucleic acid construct according to another particular embodiment of the invention wherein said construct contains the pTM1 -MVSchwarz vector wherein the sequence encoding the GPC protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the mutated NP protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2.SEQ ID NO: 12SEQ ID No: 12 is the sequence of a nucleic acid construct according to another particular embodiment of the invention wherein said construct contains the pTM1 -MVSchwarz vector wherein the sequence encoding the GPC protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the Z protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 1 .SEQ ID NO: 13SEQ ID No: 13 is the sequence of a nucleic acid construct according to another particular embodiment of the invention wherein said construct contains the pTM1 -MVSchwarz vector wherein the sequence encoding the GPC protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the NP protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the Z protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 1 .SEQ ID NO: 14SEQ ID No: 14 is the sequence of a nucleic acid construct according to another particular embodiment of the invention wherein said construct contains the pTM1 -MVSchwarz vector wherein the sequence encoding the GPC protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the mutated NP protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 2, and wherein the sequence encoding the Z protein of LASV strain Josiah has been cloned within the Additional Transcription Unit 1 .The invention also relates to a transfer vector, which may be used for the preparation of recombinant MeV-LASV particles when rescued from helper cells or production cells. Several transfer vectors are illustrated on Fig. 31 to 36. In a preferred embodiment of the invention, the transfer vector is a transfer vector plasmid suitable for the transfection of helper cells or of production cells, and comprising the nucleic acid construct according to the invention. The transfer vector plasmid may be obtained from a Bluescript plasmid and may be obtained by cloning the heterologous polynucleotide(s) of the invention in the pTM-MVSchw plasmid described here above. In particular embodiments of the invention, the transfer plasmid vector has the sequence of SEQ ID No: 9, SEQ ID No: 10, SEQ ID No: 1 1 , SEQ ID No: 12, SEQ ID No: 13 or SEQ ID No: 14.The invention also concerns the use of a transfer plasmid vector or the use of the nucleic acid construct according to the invention to transform cells suitable for the rescue of recombinant viral MeV-LASV particles, in particular to transfect or to transduce such cells respectively with plasmids or with viral vectors harboring the nucleic acid construct of the invention, said cells being selected for their capacity to express required measles virus proteins for appropriate replication, transcription and encapsidation of the recombinant genome of the virus corresponding to the nucleic acid construct of the invention in recombinant, infectious, replicative recombinant MeV-LASV particles.The nucleic acid construct of the invention and the transfer plasmid vector are suitable and intended for the preparation of recombinant infectious replicative recombinant measles - Lassa virus (MeV-LASV) and accordingly said nucleic acid construct and transfer plasmid vector are intended for insertion in a transfer genome vector that as a result comprises the cDNA molecule of the measles virus, especially of the Schwarz strain, for the production of said recombinant MeV-LASV virus and expression of LASV polypeptide(s), possibly as LASV VLPs when the Z protein is encoded by at least one heterologous polynucleotide. The pTM-MVSchw plasmid is suitable to prepare the transfer vector, by insertion of the heterologous polynucleotide(s) as described herein necessary for the expression of LASV polypeptide(s), protein(s), antigen(s), or antigenic fragment(s) thereof. As used herein, the term "virus-like particle" (VLP) refers to a structure that in at least one attribute resembles a virus but which has not been demonstrated to be infectious as such. Virus Like Particles in accordance with the invention do not carry genetic information encoding the proteins of the Virus Like Particles, in general, virus-like particles lack a viral genome and, therefore, are noninfectious and non- replicative. In accordance with the present invention, Virus Like Particles can be produced in large quantities and are expressed together with MeV-LASV recombinant particles.The invention also relates to the cells or cell lines thus transformed by the transfer vector of the invention and by further polynucleotides providing helper functions and proteins. Polynucleotides are thus present in said cells, which encode proteins that include in particular the N, P and L proteins of a measles virus (i.e., native MeV proteins or functional variants thereof capable of forming ribonucleoprotein (RNP) complexes), preferably as stably expressed proteins at least for the N and P proteins functional in the transcription and replication of the recombinant viral MeV-LASV particles. The N and P proteins may be expressed in the cells from a plasmid comprising their coding sequences or may be expressed from a DNA molecule inserted in the genome of the cell. The L protein may be expressed from a different plasmid. It may be expressed transitory. The helper cell is also capable of expressing a RNA polymerase suitable to enable the synthesis of the recombinant RNA derived from the nucleic acid construct of the invention, possibly as a stably expressed RNA polymerase. The RNA polymerase may be the T7 phage polymerase or its nuclear form (nlsT7).In an embodiment, the cDNA clone of a measles virus is from the same measles virus strain as the N protein and / or the P protein and / or the L protein. In another embodiment, the cDNA clone of a measles virus is from a different strain of virus than the N protein and / or the P protein and / or the L protein.The cells transformed or transfected with a nucleic acid construct according to the invention are able to produce recombinant measles viruses and and / or LASV VLPs when the Z protein is encoded by at least one heterologous polynucleotide. Accordingly, the recombinant measles virus comprises in its genome the nucleic acid construct of the invention and is able to express at least one polypeptide, protein or antigenic fragment thereof, of the LASV. Hence, the measles virus of the invention is able to express the GPC protein, or the GPC polypeptide, or an antigenic fragment thereof; and / or the NP protein, or the NP polypeptide, or anantigenic fragment thereof; and / or the mNP protein, or the mNP polypeptide, or an antigenic fragment thereof; and / or the Z protein, or the Z polypeptide, or an antigenic fragment thereof. LASV VLPs comprise at least the Z protein, or an antigenic fragment thereof, and may further comprise one other polypeptide of LASV; the GPC protein, a fragment of the GPC protein like GP1 or GP2, the NP protein and / or the mNP protein. In a preferred embodiment, the LASV VLPs comprise the Z protein, or an antigenic fragment thereof, and the GPC protein, or an antigenic fragment thereof, or a fragment of the GPC protein like GP1 and / or GP2. In another preferred embodiment, the LASV VLPs comprise the Z protein, or an antigenic fragment thereof, the GPC protein, or an antigenic fragment thereof, and the mNP protein or the NP protein, or an antigenic fragment thereof.In a preferred embodiment of the invention, the recombinant measles virus expresses the GPC protein and the mNP protein of the LASV. In another preferred embodiment of the invention, the recombinant measles virus expresses the GPC protein and the Z protein of LASV.Furthermore, according to some embodiments of the invention, the recombinant measles virus also expresses at least one polypeptide or protein, or an antigenic fragment thereof, of the measles virus. In other words, the recombinant measles virus expresses at least one of the following polypeptides: the N protein, the P protein, the M protein, the F protein, the H protein and the L protein of the MeV.According to this embodiment, the recombinant virus expresses recombinant antigenic particles of the measles virus and the Lassa virus, allowing the elicitation of cellular response, or a humoral response, or a cellular and humoral response against polypeptides of the LASV and against polypeptides of the MeV. In particular embodiments of the invention, the elicitation of the cellular response comprises elicitation of a T cell response, in particular CD4+ and / or CD8+ T cells response.The invention thus relates to a process for the preparation of recombinant infectious measles virus particles comprising:(a) transfecting cells, in particular helper cells, in particular HEK293 helper cells, stably expressing T 7 RNA polymerase and measles N and P proteins with the nucleic acid construct according to the invention or with the transfer plasmid vector according to the invention;(b) maintaining the transfected cells in conditions suitable for the production of recombinant measles virus and / or LASV VLPs;(c) infecting cells enabling propagation of the recombinant measles virus and / or the LASV VLPs by co-cultivating them with the transfected cells of step (b);(d) harvesting the recombinant measles virus expressing at least one LASV protein, preferentially at least the GPC protein and optionally the NP protein, the mNP protein and / or the Z protein, preferentially expressing the GPC protein and the mNP protein, and / or the LASV VLPs expressing at least the Z protein and possibly another LASV protein selected from the group consisting of the GPC protein, the NP protein and / or the mNP protein.According to a particular embodiment, the invention relates to a process for the preparation of recombinant infectious measles virus particles comprising:a) transferring, in particular transfecting, the nucleic acid construct of the invention or the transfer vector containing such nucleic acid construct in a helper cell line which also expresses proteins necessary for transcription, replication and encapsidation of the antigenomic (+) RNA sequence of MeV from its cDNA and under conditions enabling viral particles assembly andb) recovering the recombinant infectious MeV-LASV virus expressing at least one polypeptide or protein of LASV, or an antigenic fragment thereof.According to a particular embodiment of the invention, the process comprises: a) transfecting helper cells with a nucleic acid construct according to the invention with a transfer plasmid vector, wherein said helper cells are capable of expressing helper functions to express an RNA polymerase, and to express the N, P and L proteins of a MeV virus;b) co-cultivating said transfected helper cells of step 1 ) with passaged cells suitable for the passage of the MeV attenuated strain from which the cDNA originates;c) recovering the recombinant infectious MeV-LASV virus expressing at least one polypeptide of the LASV.According to another particular embodiment of the invention the method for the production of recombinant infectious MeV-LASV comprises:a) recombining a cell or a culture of cells stably producing a RNA polymerase, the nucleoprotein (N) of a measles virus and the polymerase cofactor phosphoprotein (P) of a measles virus, with a nucleic acid construct of the invention and with a vector comprising a nucleic acid encoding a RNA polymerase large protein (L) of a measles virus, andb) recovering the infectious, MeV-LASV virus from said recombinant cell or culture of recombinant cells.According to a particular embodiment of the process, recombinant MeV are produced, which express LASV protein(s) comprising at least the GPC protein and / or LASV VLPs comprising at least the Z protein, and wherein the recombinant MeV and / or VLPs may express at least one other LASV proteins, or antigen, or an antigenic fragment thereof, e.g. GPC or a fragment thereof, especially GP1 and / or GP2, and optionally mNP of LASV. In other embodiment, the LASV VLPs comprise the Z protein or a fragment thereof, and optionally the GPC protein, and possibly GP1 and / or GP2. In a preferred embodiment of the invention, the LASV VLPs comprise the Z protein, or antigenic fragment thereof, and the GPC protein, or an antigenic fragment thereof. As an illustration, a process to rescue recombinant MeV expressing LASV proteins, in particular LASV VLPs comprises the steps of:1 ) cotransfecting helper cells, in particular HEK293 helper cells, that stably express T 7 RNA polymerase, and measles N and P proteins with (i) a transfer vector, in particular a plasmid, comprising cDNA encoding the full-length antigenomic (+) RNA of a measles virus recombined with at least onepolynucleotide encoding at least one LASV protein, for example encoding the GPC protein, the NP protein, the mNP protein and / or the Z protein, and with (ii) a vector, especially a plasmid, encoding the MeV L polymerase cDNA;2) cultivating said cotransfected helper cells in conditions enabling the production of MV-LASV recombinant virus;3) propagating the thus produced recombinant virus by co-cultivating said helper cells of step 2) with cells enabling said propagation such as Vero cells;4) recovering replicating MeV-LASV recombinant virus and LASV protein(s), in particular LASV Virus Like Particles.As used herein,“recombining” means introducing at least one polynucleotide into a cell, for example under the form of a vector, said polynucleotide integrating (entirely or partially) or not integrating into the cell. According to a particular embodiment, recombination can be obtained with a first polynucleotide, which is the nucleic acid construct of the invention. Recombination can, also or alternatively, encompasses introducing a polynucleotide, which is a vector encoding a RNA polymerase large protein (L) of a measles virus, whose definition, nature and stability of expression has been described herein.In accordance with the invention, the cell or cell lines or a culture of cells stably producing a RNA polymerase, a nucleoprotein (N) of a measles virus and a polymerase cofactor phosphoprotein (P) of a measles virus is a cell or cell line as defined in the present specification or a culture of cells as defined in the present specification, i.e., are also recombinant cells to the extent that they have been transformed by the introduction of one or more polynucleotides as defined above. In a particular embodiment of the invention, the cell or cell line or culture of cells, stably producing the RNA polymerase, the N and P proteins, does not produce the L protein of a measles virus or does not stably produce the L protein of a measles virus, e.g., enabling its transitory expression or production. The production of recombinant MeV-LASV virus of the invention may involve a transfer of cells transformed as described herein.“Transfer” as used herein refers to the plating of the recombinant cells onto a different type of cells, and particularly onto monolayers of a different type of cells. These latter cells are competent tosustain both the replication and the production of infectious recombinant MeV-LASV virus i.e., respectively the formation of infectious viruses inside the cell and possibly the release of these infectious viruses outside of the cells possibly with release of LASV immunogenic particles and / or LASV VLPs. This transfer results in the co-culture of the recombinant cells of the invention with competent cells as defined in the previous sentence. The above transfer may be an additional, i.e., optional, step when the recombinant cells are not efficient virus-producing culture i.e., when infectious recombinant MeV-LASV virus cannot be efficiently recovered from these recombinant cells. This step is introduced after further recombination of the recombinant cells of the invention with any nucleic acid construct of the invention, and optionally a vector comprising a nucleic acid encoding a RNA polymerase large protein (L) of a measles virus.In a particular embodiment of the invention, a transfer step is required since the recombinant cells, usually chosen for their capacity to be easily recombined are not efficient enough in the sustaining and production of recombinant infectious MeV-LASV virus. In said embodiment, the cell or cell line or culture of cells of step 1 ) of the above-defined methods is a recombinant cell or cell line or culture of recombinant cells according to the invention.Cells suitable for the preparation of the recombinant cells of the invention are prokaryotic or eukaryotic cells, particularly animal or plant cells, and more particularly mammalian cells such as human cells or non-human mammalian cells or avian cells or yeast cells. In a particular embodiment, cells, before recombination of its genome, are isolated from either a primary culture or a cell line. Cells of the invention may be dividing or non-dividing cells.According to a preferred embodiment, helper cells are derived from human embryonic kidney cell line 293, which cell line 293 is deposited with the ATCC under No. CRL-1573. Particular cell line 293 is the cell line disclosed in W02008 / 078198 and referred to in the following examples as 293T7 / N / P. Thus, the invention also relates to a host cell, in particular an avian cell or a mammalian cell, transfected or transformed with the nucleic acid construct according to any embodiment of the invention, or transfected with a transfer plasmid vector. Suitable cells are the VERO NK cells (African green monkey kidney cells), and MRC5 cells (Medical Research Council cell strain 5). According to another aspect of this process, the cells suitable for passage are CEF cells (chick embryo fibroblasts). CEF cells can be prepared from fertilized chicken eggs as obtained from EARL Morizeau (8 rue Moulin, 28190 Dangers, France) or from any other producer of fertilized chicken eggs.The process which is disclosed according to the present invention is used advantageously for the production of infectious replicative recombinant MeV-LASV virus appropriate for use as immunization compositions. The invention thus relates to a composition, in particular an antigenic composition, whose active principle comprises infection replicative recombinant MeV-LASV virus rescued from the nucleic acid construct of the invention and in particular obtained by the process disclosed. The composition may be a vaccine composition for administration to a human in need thereof, especially children. Said composition may be used for the treatment against LASV infection. Said composition may be used for the protection against LASV. Thus, the composition may be an immunogenic or antigenic composition for the protective or prophylactic treatment against a LASV infection. In particular, the active ingredients or active principles within the composition comprise recombinant MeV-LASV particles, said recombinant MeV-LASV particles being rescued from a transfer plasmid vector according to the invention and being optionally associated with VLPs comprising the Z protein and optionally other protein(s) of LASV, or antigenic fragment(s) thereof. In the context of the invention, the terms“associated” or“in association” refer to the presence, in a single composition, of both MeV-LASV recombinant viral particles and LASV polypeptides or proteins, in particular as VLPs, usually as physically separate entities. In a particular embodiment of the invention, the composition is a vaccine.The invention also concerns the recombinant MeV-LASV infectious replicating virus particles in association with LASV polypeptide(s) or protein(s), or antigenic fragment(s) thereof, possibly associated LASV VLPs, or any compositionaccording to the invention, for the use in the treatment or the prevention of an infection by Lassa virus in a subject, in particular a human subject, in particular a child.The invention also concerns recombinant MeV-LASV infectious, replicative virus and associated LASV polypeptide(s) or protein(s), or antigenic fragment(s) thereof, and potentially associated LASV VLPs for use in an administration scheme and according to a dosage regime that elicits an immune response, advantageously a protective immune response, against LASV virus infection or induced disease, in particular in a human subject, in particular a child.In a particular embodiment of the invention, the composition or the use of the composition is able to elicit immunization of a subject, in particular a human subject, in particular a child, after a single injection. In other words, the composition or the use of the composition may require a single administration of a selected dose of the recombinant MeV-LASV infectious replicative virus. Alternatively, it may require multiple doses administration in a prime-boost regimen. Priming and boosting may be achieved with identical active ingredients consisting of recombinant MeV-LASV infectious, replicative virus and associated LASV polypeptide(s) and protein(s), or antigenic fragment(s) thereof, and / or LASV VLPs.The invention also concerns an assembly of different active ingredients including as one of these ingredients recombinant MeV-LASV infectious, replicative virus and associated LASV polypeptide(s) or protein(s), and / or LASV VLPs. The assembly of active ingredients is advantageously for use in immunization of a host, in particular a human host.The inventors have shown that administration of recombinant MeV-LASV infectious, replicative virus elicits an immune response and especially elicits production of neutralizing antibodies against LASV-related polypeptides. Accordingly, it has been shown that administration of the active ingredients according to the invention elicits immunization of the host. The vaccine according to the invention is safe, leads to immune answer within the host, which encompasses especially CD4+ and CD8+ T cell responses. As shown in the examples, the vaccine according to the invention induces antigen-specific T cell responses. It has also been shown that immunized monkey hosts survive lethal dose challenge of LASV.After immunization of a host, and LASV challenge, the level of liver enzymes (ALT and AST), lactate deshydrogenase (LDH), C-reactive protein (CRP) and albumin remained normal or slightly increases in immunized monkey hosts, while these levels increase several folds in non-immunized hosts.The composition according to the invention is able to elicit production of recombinant LASV-specific immunoglobulins, especially IgM and IgG, and neutralizing antibodies. The composition according to the invention is a safe vaccine, immunogenic and efficacious in a host. The compositions and their use confer at least T cell response and confer immunity against a Lassa virus infection in a vaccinated host.The composition according to the invention may also be able to elicit production of MeV-specific immunoglobulins, especially IgM and IgG, and neutralizing antibodies. The composition according to the invention is a safe vaccine, immunogenic and efficacious in a host. The compositions and their use confer at least T cell response and may confer immunity against a Measles virus infection in a vaccinated host.The composition according to the invention also concerns recombinant MeV-LASV infectious, replicative virus and associated LASV polypeptide(s) or protein(s), or antigenic fragment(s) thereof, and potentially associated LASV VLPs for use in an administration scheme and according to a dosage regime that elicits an immune response, advantageously a protective immune response, against measles virus infection or induced disease, in particular in a human subject, in particular a child.The invention also concerns the recombinant MeV-LASV infectious replicating virus particles in association with LASV polypeptide(s) or protein(s), or antigenic fragment(s) thereof, and / or LASV VLPs, or any composition according to the invention, for the use in the treatment or the prevention of an infection by measles virus in a subject, in particular a human subject, in particular a child.The invention also concerns a heterologous polynucleotide comprising any one of the codon-optimized sequence encoding the GPC protein, the Z protein, the NP protein and / or the mNP protein. Thus, the invention also concerns the codon-optimized polynucleotide comprising or consisting of SEQ ID No: 2; SEQ ID No: 4, SEQ ID No: 6 and / or SEQ ID No: 8.DESCRIPTION OF THE FIGURESSome of the figures, to which the present application refers, are in color. The application as filed contains the color print-out of the figures, which can therefore be accessed by inspection of the file of the application at the patent office.Figure 1. Schematic representation of nucleic acid constructs. A: MeV vector. B: nucleic acid constructs according to the invention. MeV genes are indicated in grey and LASV genes are indicated in green, blue and red. For the MV genes: N (nucleoprotein); P / V / C (phosphoprotein and V / C proteins); M (matrix); F (Fusion protein); H (hemagglutinin): L (polymerase). For the LASV genes: NP (nucleoprotein); N PEXON (also referenced N PKO on some figures; mutated sequence encoding a mutated NP with its exonuclease activity knocked down); GPC (glycoprotein precursor); Z (zinc-binding protein). ATUs are indicated by the black arrows. ATU1 is localized on the left, upstream the N gene of MeV while ATU2 is localized centrally, between P and M MeV genes.Figure 2. Growth kinetics of viruses on Vero E6 cells. MeV-GFP corresponds to a construct wherein a polynucleotide encoding a Green Fluorescent Protein has been inserted within ATU2. MeV-GPCu\sv corresponds to a construct wherein a polynucleotide encoding the GPC protein of LASV has been insertedwithin ATU2. MeV-NP+GPCi_Asv corresponds to a construct wherein genes encoding the GPC protein and the NP protein of LASV has been inserted within ATU2. MeV-NPExoN+GPCi_Asv corresponds to a construct wherein polynucleotide encoding the GPC protein and a mutated NP protein (exonuclease activity knocked down) of LASV has been inserted within ATU2. MeV-Z+GPCi_Asv corresponds to a construct wherein a polynucleotide encoding the GPC protein has been inserted within ATU2, and wherein a polynucleotide encoding the Z protein has been inserted within ATU1. Titers obtained in typical experiments, measured by TCID50 from 3 independent experiments. Means and standard errors are represented.Figure 3. Expression of LASV proteins (GPC, NP and Z) and MeV protein (F) in infected Vero E6 cells and in the supernatants of infected Vero E6 cells. The effect of each construct was assessed by Western blot as detailed in the material and method. Nl: non-infected cells ns: non specific.Figure 4. MeV-GFP entry and replication in immune antigen presenting cells derived from human peripheral blood mononuclear cells.Figure 5. Expression of type I IFN in human primary macrophages infected with different MeV-LASV vectors. Quantitative RNA analysis by qPCR analyses of type I IFN response (quantitative expression of IFNal , IFNa2 and IFNb). Expression 24h post-infection. All results are normalized to GAPDH gene and expressed as fold induction relative to GAPDH.Figure 6. Cell surface expression of cluster of differentiation markers CD80, CD86 and CD83 CD40 in macrophages infected with different MeV-LASV vectors. Flow cytometry for the cell surface expression of co-activation molecules 48h post-infection.Figure 7. Expression of type I IFN in human primary dendritic cells infected with different MeV-LASV vectors. Quantitative RNA analysis by qPCR analyses of type I IFN responses (quantitative expression of IFNal , IFNa2 and IFNb). Expression 24h post-infection. All results are normalized to GAPDH gene and expressed as fold induction relative to GAPDH.Figure 8. Cell surface expression of cluster of differentiation markers CD80, CD86, CD83 and CD40 in human primary dendritic cells infected withdifferent MeV-LASV vectors. Flow cytometry for the cell surface expression of co-activation molecules 48h post-infection.Figure 9. Body temperature in cynomolgus monkeys (Macaca fascicularis) during a 30-day period post immunization. 3, 4 and 4 monkeys were subcutaneously immunized with 2.106 Tissue culture Infective Dose 50 (TCID50) of respectively a recombinant MeV strain Schwarz vaccine, a recombinant MeV-NPEXON-GPC vaccine and a recombinant Z-MeV-GPC vaccine.Figure 10. LASV antigens-specific CD4 and CD8 T cells responses in vaccinated cynomolgus monkeys (Macaca fascicularis). Flow cytometry after stimulation of whole blood by overlapping peptides specific to GPC, NP and Z. Figure 11. Clinical scores in cynomolgus monkeys (Macaca fascicularis) after challenge with a lethal dose of LASV strain Josiah. Clinical score is based on body temperature, body weight, capacity to feed and hydrate normally, behavior, clinical signs. A score of 15 is the endpoint for killing. Lethal dose of LASV strain consists in 1 .500 FFU of LASV strain Josiah subcutaneously injected to the animals.Figure 12. Body temperature in cynomolgus monkeys (Macaca fascicularis) challenged with a lethal dose of LASV strain Josiah.Figure 13. Liver enzymes (AST and ALT) levels in plasma of immunized cynomolgus monkeys.Figure 14. Plasma level of LDH (A), CRP (B) and albumin (C) in cynomolgus monkeys (Macaca fascicularis) challenged with a lethal dose of LASV strain Josiah.Figure 15. Viremia (RNA(A) and Titer (B)) in cynomolgus monkeys challenged with a lethal dose of LASV strain Josiah. RNA quantification by qPCR. Titration according to known method in the art.Figure 16. Viral RNA quantification in the nasal (A) and oral secretions (B) and in the urine (C) of cynomolgus monkeys challenged with a lethal dose of LASV strain Josiah. RNA quantification by qPCR.Figure 17. LASV RNA levels detected in organs of challenged cynomolgus monkeys previously immunized with different MeV-LASV.Figure 18. LASV infectious titers detected in organs of challenged cynomolgus monkeys previously immunized with different MeV-LASV.Figure 19. IgM and IgG responses against LASV in cynomolgus monkeys challenged with a lethal dose of LASV strain Josiah. A. IgM LASV specific. B: IgG LASV specific. Immunoglobulin levels measured by ELISA. Optical density calculated according to the absorbance at 450 nM.Figure 20. LASV GP- and NP- specific CD8+ and CD4+ T cell responses after immunization. The percentage of CD8+ and CD4+ T cells that produced IFNg, TNFa and / or IL-2 after stimulation with overlapping peptides covering the whole LASV GP and NP have been determined using flow cytometry.Figure 21. LASV antigens-specific CD4 and CD8 T cell responses of immunized cynomolgus monkeys challenged with a lethal dose of LASV strain Josiah. Flow cytometry after stimulation of whole blood by overlapping peptides specific to GPC and NP.Figure 22. Proliferation and activation of CD4 and CD8 T cells in of cynomolgus monkeys challenged with a lethal dose of LASV strain Josiah.CD8 proliferation assessed by Ki67 staining (A). CD4 (B) and CD8 (C) Activation assessed by quantification of granzyme B expression.Figure 23. LASV GP- and NP-specific CD8+ T cell responses after LASV challenge. The percentage of CD8+ T cells that produced IFNg, TNFa and / or IL-2 after LASV challenge with overlapping peptides covering the whole LASV GP (23A) and NP (23B) have been determined with flow cytometry. The proportion of different sub-populations of responding T cells is presented using pie chart. Figure 24. LASV GP- and NP-specific CD4+ T cell responses after LASV challenge. The percentage of CD4+ T cells that produced IFNg, TNFa and / or IL-2 after LASV challenge with overlapping peptides covering the whole LASV GP (23A) and NP (23B) have been determined with flow cytometry. The proportion of different sub-populations of responding T cells is presented using pie chart. Figure 25. KEGG pathway analysis performed on the transcriptomic data obtained from cynomolgus monkeys PBMC collected at different time points post-immunization with MeV-NPExoN-GPCLAsv·Figure 26. KEGG pathway analysis performed on the transcriptomic data obtained from cynomolgus monkeys PBMC collected at different time points post-immunization with MeV-Z+GPCLAsv-Figure 27. Quantification of cytokines in the plasma of immunized monkeys after LASV challenge. Different cytokines have been quantified in the plasma of MeV-, MeV-NPExoN-GPCi_Asv, and MeV-Z+GPCi_Asv immunized cynomolgus monkeys after LASV challenge. Significant differences (p<0.05) between different conditions are indicated: n-c (MeV-NPExoN-GPCi_Asv and MeV), n-z (MeV-NPExoN-GPCLASV and MeV-Z+GPCu\sv) and n-cz (MeV-NPExoN-GPCi_Asv and MeV; MeV-N PEXON-GPCLASV and MeV-Z+GPCi_Asv).Figure 28. IgM and IgG responses against MeV in cynomolgus monkeys challenged with a lethal dose of LASV strain Josiah. A: IgM MeV specific. B: IgG MeV specific. IgG and IgM MeV-specific were not measures at days 7 and 14 for the monkeys immunized with the MeV construct.Figure 29. Determination of the Exonuclease activity of native and mutated NP protein. Fold induction of Luciferase activity virus-induced and immunostimulatory RNAs-induced interferon-beta activation. CT: control. N PLASV: native NP protein. N PEXONLASV: mutated NP protein of SEQ ID No: 5. SeV : Sendai virus at moi=1 .Figure 30. Analysis of MeV-NPExoN-GPCLAsv tropism. CHO cell lines were infected with either a Mopeia virus pseudotyped with LASV GPC or with MeV-N PEXON-GPCLASV. Expression of GPC was analyzed by staining with an anti-GP1 antibody. The nuclei are in blue, while the anti-GP1 stained is in green.Figure 31. Schematic representation of transfer vector plasmid according to a first embodiment of the invention. The transfer vector has the sequence of SEQ ID No: 9. The measles gene encoding the N protein is localized between nucleotides 189 and 1767. The measles gene encoding the P protein is localized between nucleotides 1889 and 3412. The codon-optimized heterologous polynucleotide of SEQ ID No: 2 encoding the GPC is localized between nucleotides 3532 and 5007. ATU2 is localized between nucleotides 3487 and 5071 minus the heterologous polynucleotide insert. The measles gene encoding the M protein is localized between nucleotides 5104 and 61 1 1 .Figure 32. Schematic representation of transfer vector plasmid according to a second embodiment of the invention. The transfer vector has the sequence of SEQ ID No: 10. The measles gene encoding the N protein is localized between nucleotides 190 and 1767. The measles gene encoding the P protein is localized between nucleotides 1889 and 3412. The codon-optimized heterologous polynucleotide of SEQ ID No: 4 encoding the NP protein is localized between nucleotides 3532 and 5241 . The codon-optimized heterologous polynucleotide of SEQ ID No:2 encoding the GPC is localized between nucleotides 5386 and 6861 . A linker sequence comprising regulatory sequence of the measles virus is localized between nucleotides 5242 and 5385. ATU2 is localized between nucleotides 3487 and 6925 minus the heterologous polynucleotide insert and the linker sequence. The measles gene encoding the M protein is localized between nucleotides 6958 and 7965.Figure 33. Schematic representation of transfer vector plasmid according to a third embodiment of the invention. The transfer vector has the sequence of SEQ ID No: 1 1 . The measles gene encoding the N protein is localized between nucleotides between 190 and 1767. The measles gene encoding the P protein is localized between nucleotides 1889 and 3412. The codon-optimized heterologous polynucleotide of SEQ ID No: 6 encoding the mutated NP protein is localized between nucleotides 3532 and 5241 . The codon-optimized heterologous polynucleotide of SEQ ID No:2 encoding the GPC is localized between nucleotides 5386 and 6861 . A linker sequence comprising regulatory sequence of the measles virus is localized between nucleotides 5242 and 5385. ATU2 is localized between nucleotides 3487 and 6925 minus the heterologous polynucleotide insert and the linker sequence. The measles gene encoding the M protein is localized between nucleotides 6958 and 7965.

Claims

CLAIMS1. A nucleic acid construct which comprises:(1 ) a cDNA molecule encoding a full length antigenomic (+) RNA strand of a measles virus (MeV);(2) a first heterologous polynucleotide encoding at least one polypeptide, or an antigenic fragment thereof, of a Lassa virus (LASV), said at least one polypeptide being selected from the group consisting of the nucleoprotein (NP), a mutated nucleoprotein (mNP), the glycoprotein precursor (GPC) and the zinc-binding protein (Z);and wherein the first heterologous polynucleotide is operatively cloned within an additional transcription unit (ATU) inserted within the cDNA of the antigenomic (+) RNA, in particular an ATU localized between the P gene and the M gene of the MeV, in particular the ATU2 inserted between the P gene and the M gene of the MeV.

2. A nucleic acid construct according to claim 1 further comprising a second heterologous polynucleotide encoding at least one polypeptide, or an antigenic fragment thereof, of the LASV, said at least one polypeptide being selected from the group consisting of the GPC protein, the NP protein, the mNP protein and Z protein, the second heterologous polynucleotide being operatively cloned within another ATU at a location distinct from the location of the first cloned heterologous polynucleotide, preferentially upstream the N gene of the MeV, said another ATU being in particular the ATU1 inserted upstream the N gene of the MeV, the second heterologous polynucleotide encoding in particular at least one polypeptide or antigenic fragment thereof different from at least one polypeptide encoded by the first heterologous polynucleotide.

3. The nucleic acid construct according to claim 1 or 2, wherein theheterologous polynucleotide(s) encoding the GPC protein, the NP protein, the mNP and / or the Z protein, or an antigenic fragment thereof, is(are) from the LASV strain Josiah, or is(are) derived from the LASV strain Josiah, in particular the heterologous polynucleotide(s) is(are) issued or derived from the sequence of Genbank J04324.1 and / or U73034.2.

4. The nucleic acid construct according to any one of claims 1 to 3, wherein the first and / or second heterologous polynucleotide(s) encode(s) the mNP protein, or an antigenic fragment thereof , wherein the mNP protein has a mutated exonuclease domain, in particular wherein the amino acid sequence of the encoded mNP protein is mutated on amino acid residue 389 and / or 392, preferentially by substitution on amino acid residues 389 and 392, of SEQ ID No: 3, in particular the encoded mNP protein is the sequence of SEQ ID No: 5, in particular the heterologous polynucleotide encoding the mNP protein comprises SEQ ID No: 6.

5. The nucleic acid construct according to any one of claims 1 to 4, wherein the heterologous polynucleotide(s) encoding the GPC protein, the NP protein, the mNP protein and / or the Z protein, or an antigenic fragment thereof, has (have) codon-optimized open reading frame(s) (ORF), in particular, the heterologous polynucleotide(s) comprise(s) at least one of the following sequence:- SEQ ID No: 2 which encodes the GPC protein; and / or- SEQ ID No: 4 which encodes the NP protein; and / or- SEQ ID No: 6 which encodes the mNP protein; and / or- SEQ ID No: 8 which encodes the Z protein.

6. The nucleic acid construct according to any one of claims 1 to 5, wherein the heterologous polynucleotide(s) encode(s):- the GPC protein of SEQ ID No: 1 or an antigenic fragment thereof; and / or- the NP protein of SEQ ID No: 3 or an antigenic fragment thereof; and / or- the mNP protein of SEQ ID No: 5 or an antigenic fragment thereof; and / or- the Z protein of SEQ ID No: 7 or an antigenic fragment thereof.

7. The nucleic acid construct according to any one of claims 1 to 6comprising from 5’ to 3’ end the following polynucleotides:(a) a polynucleotide encoding the N protein of the MeV;(b) a polynucleotide encoding the P protein of the MeV;(c) the first heterologous polynucleotide encoding at least onepolypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof, in particular encoding a single polypeptide which is the GPC protein or an antigenic fragment thereof, or encoding at least two polypeptides, which are the GPC protein or an antigenic fragment thereof and either the NP protein or the mNP protein, or an antigenic fragment thereof, in particular encoding the GPC protein and the mNP protein, wherein the first polynucleotide is in particular operatively cloned within an ATU, in particular ATU2;(d) a polynucleotide encoding the M protein of the MeV;(e) a polynucleotide encoding the F protein of the MeV;(f) a polynucleotide encoding the H protein of the MeV;(g) a polynucleotide encoding the L protein of the MeV;and wherein said polynucleotides are operatively linked within the nucleic acid construct and under the control of a viral replication and transcriptional regulatory elements such as MeV leader and trailer sequence(s).

8. The nucleic acid construct according to any one of claims 2 to 6(a) the second heterologous polynucleotide encoding at least onepolypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof, in particular encoding the Z protein, or an antigenic fragment thereof, wherein the second polynucleotide isoperatively cloned within an ATU localized upstream the N gene of the MeV, in particular within the ATU1 ;(b) a polynucleotide encoding the N protein of the MeV;(c) a polynucleotide encoding the P protein of the MeV;(d) the first heterologous polynucleotide encoding at least one(e) a polynucleotide encoding the M protein of the MeV;(f) a polynucleotide encoding the F protein of the MeV;(g) a polynucleotide encoding the H protein of the MeV;(h) a polynucleotide encoding the L protein of the MeV,9. The nucleic acid construct according to any one of claims 1 to 8, wherein the first heterologous polynucleotide comprises from 5’ to 3’ end:(a) a nucleic acid encoding the NP protein or the mNP protein of the LASV, or an antigenic fragment thereof, in particular whose nucleic acid is SEQ ID No: 4 for the NP protein or SEQ ID No: 6 for the mNP protein; and(b) a nucleic acid encoding the GPC protein of the LASV, or an antigenic fragment thereof, in particular whose nucleic acid is SEQ ID No: 2; and wherein the first heterologous polynucleotide is operatively cloned between the P gene and the M gene of the MeV, in particular within an ATU, in particular ATU2.

10. The nucleic acid construct according to any one of claims 1 to 9, wherein the first heterologous polynucleotide comprises from 5’ to 3’ end:(a) the nucleic acid of SEQ ID No: 6 encoding the mNP protein; and(b) the nucleic acid of SEQ ID No: 2 encoding the GPC protein;and wherein the first heterologous polynucleotide sequence is operatively cloned between the gene P and the gene M of the MeV, in particular within an ATU, in particular ATU2.

11. The nucleic acid construct according to any one of claims 2 to 10,wherein the second heterologous polynucleotide encodes the Z protein of the LASV, or an antigenic fragment thereof, and wherein the first heterologous polynucleotide encodes the GPC protein of the LASV, or an antigenic fragment thereof, in particular wherein the sequence of the second heterologous polynucleotide comprises the sequence of SEQ ID No: 8 and the sequence of the first heterologous polynucleotide comprises the sequence of SEQ ID No: 2.

12. The nucleic acid construct according to claim 11 , wherein the firstheterologous polynucleotide and the second heterologous polynucleotide are operatively cloned within ATUs located at different position in the cDNA molecule of the MeV, in particular the first heterologouspolynucleotide is operatively cloned with the ATU2 and the second heterologous polynucleotide is operatively cloned within the ATU1.

13. The nucleic acid construct according to any one of claims 1 to 12,wherein the measles virus is an attenuated virus strain selected from the group consisting of the Schwarz strain, the Zagreb strain, the AIK-C strain, the Moraten strain, the Philips strain, the Beckenham 4A strain, the Beckenham 16 strain, the Edmonston seed A strain, the Edmonstonseed B strain, the CAM-70 strain, the TD 97 strain, the Leningrad-16 strain, the Shanghai 191 strain and the Belgrade strain, in particular the Schwarz strain.

14. The nucleic acid construct according to any one of claims 1 to 13,wherein the sequence of the first heterologous polynucleotide comprises at least one of SEQ ID No: 2, SEQ ID No: 4, SEQ ID No: 6, and / or SEQ ID No: 8, and preferentially at least SEQ ID No: 2, in particular SEQ ID No: 2 and SEQ ID No: 6.

15. The nucleic acid construct according to any one of claims 1 to 14 whose recombinant cDNA sequence is selected from the group consisting of:- SEQ ID No: 9 (construct MeV-GPC);- SEQ ID No: 10 (construct MeV-NP-GPC);- SEQ ID No: 1 1 (construct MeV-mNP-GPC);- SED ID No: 12 (construct Z-MeV-GPC);- SEQ ID No: 13 (construct Z-MeV-NP-GPC); and- SEQ ID No: 14 (construct Z-MeV-mNP-GPC).

16. A transfer plasmid vector comprising the nucleic acid construct according to any one of claims 1 to 15, in particular comprising or consisting of a sequence selected from the group consisting of:- SEQ ID No: 9 (Plasm MeV-GPC);- SEQ ID No: 10 (Plasm MeV-NP-GPC);- SEQ ID No: 1 1 (Plasm MeV-mNP-GPC);- SED ID No: 12 (Plasm Z-MeV-GPC);- SEQ ID No: 13 (Plasm Z-MeV-NP-GPC); and- SEQ ID No: 14 (Plasm Z-MeV-mNP-GPC).

17. A recombinant measles virus, said virus comprising in its genome anucleic acid construct according to any one of claims 1 to 15, or a transfer plasmid vector according to claim 16, or whose genome consists of the transfer plasmid vector of claim 16.

18. The recombinant measles virus according to claim 17 expressing at least one polypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof, in particular expressing at least two polypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of the LASV, or an antigenic fragment thereof.

19. The recombinant measles virus according to claim 17 or 18 expressing the GPC protein and the mNP protein of the LASV, or antigenic fragments thereof.

20. The recombinant measles virus according to claim 17 or 18 expressing the GPC protein and the Z protein of the LASV, or antigenic fragments thereof.21.The recombinant measles virus according to any one of claims 17 to 20 furthermore expressing at least one of the N protein, the P protein, the M protein, the F protein, the H protein and the L protein of the MeV.

22. The recombinant measles virus according to any one of claims 17 to 21 , which elicits a cellular and / or humoral and cellular response, in particular after a single immunization, against the antigenic fragment(s) of the GPC protein, the NP protein, the mNP protein and / or the Z protein of LASV, in particular against the antigenic fragments of the N protein, the P protein, the M protein, the F protein, the FI protein and / or the L protein of MeV, in particular a T cell response, in particular a CD4+ and CD8+ T cell response.

23. A host cell transfected with the nucleic acid construct according to any one of claims 1 to 15 or with the transfer plasmid vector according to claim 16, or infected with the recombinant measles virus according to any one of claims 17 to 22, in particular a mammalian cell, a VERO NK cells, CEF cells, human embryonic kidney cell line 293 or MRC5 cells.

24. Recombinant virus like particles (VLPs) comprising a Z protein and optionally a GPC protein and / or a NP protein and / or a mNP protein, or an antigenic fragment thereof, of the LASV, in particular expressing at least the Z protein and the GPC protein, or an antigenic fragment thereof, wherein the protein(s) or antigenic fragments thereof is(are) encoded by the first and / or second heterologous polynucleotide(s) of the nucleic acid construct according to claims 1 to 15, or of the transfer plasmid vector of claim 16, or the recombinant measles virus according to any one of claims 17 to 22, or produced within the host cell of claim 23.

25. An immunogenic composition, especially a virus vaccine composition, comprising the recombinant VLPs according to claim 24, or the recombinant measles virus according to any one of claims 17 to 22, or the recombinant VLPs according to claim 24 and the recombinant measles virus according to any one of claims 17 to 22, and apharmaceutically acceptable vehicle.

26. The composition according to claim 25 for use in the elicitation of aprotective, and preferentially prophylactic, immune response against the Lassa virus by the elicitation of antibodies directed against LASV protein(s) or antigenic fragment(s) thereof, and / or a cellular and / or humoral and cellular response against the Lassa virus, in a host in need thereof, in particular a human host, in particular a child.

27. The composition of claim 26 for use in the elicitation of a protective, and preferentially prophylactic, immune response against measles virus by the elicitation of antibodies directed against measles virus protein(s), and / or a cellular and / or humoral and cellular response against the measles virus, in a host in need thereof, in particular a human host, in particular a child.

28. A process for rescuing recombinant Lassa virus like particles (VLPs) and / or recombinant measles virus expressing at least one of polypeptide selected from the group consisting of the GPC protein, the NP protein, the mNP protein and the Z protein of LASV, or an antigenic fragment thereof, comprising:(a) transfecting cells, in particular helper cells, in particular HEK293helper cells, stably expressing T 7 RNA polymerase and measles virus N and P proteins with the nucleic acid construct according to any one of claims 1 to 15 or with the transfer plasmid vector according to claim 16;(b) maintaining the transfected cells in conditions suitable for theproduction of recombinant measles virus and / or LASV VLPs;(c) infecting cells enabling propagation of the recombinant measles virus and / or the LASV VLPs by co-cultivating them with the transfected cells of step (b);(d) harvesting the recombinant measles virus expressing at least one of the GPC protein, the NP protein, the mNP protein and / or the Z protein of LASV, in particular expressing at least the GPC protein and another LASV protein, in particular expressing the GPC protein and the mNP protein, and / or the LASV VLPs expressing at least the Z protein and optionally at least one of the GPC protein, the NP protein and / or the mNP protein of LASV, in particular expressing the Z protein and the GPC protein.

29. A method for preventing a Lassa virus related disease, said methodcomprising the immunization of a mammalian, especially a human, in particular a child, by the injection, in particular by subcutaneous injection, of recombinant Lassa virus VLPs according to claim 24, and / or a measles virus according to any one of claims 17 to 22.

30. A method for treating a Lassa virus related disease, said methodcomprising the immunization of a mammalian, especially a human, in particular a child, by the injection, in particular subcutaneous injection, of recombinant Lassa virus VLPs according to claim 24, and / or a measles virus according to any one of claims 17 to 22.