WO2018204080A1 - Compositions and methods related to arenavirus immunogens - Google Patents

Abstract

The present invention provides engineered arenavirus immunogens and vaccine compositions. Some of the immunogens contain a soluble arenavirus GPC ectodomain that harbors one or more mutations such as an engineered disulfide bond to covalently link GP1and GP2, a stabilizing mutation in the metastable region of HR1 of GP2, and replacement of the native SIP GP1-GP2 cleavage site with a furin cleavage site. The invention also provides methods of using the arenavirus immunogens or vaccine compositions for eliciting an immune response or treating arenavirus infections. The invention also describes tools for identification and characterization of antibodies against arenaviruses, as well as evaluation of immune responses elicited by vaccines or by natural infection.

Description

COMPOSITIONS AND METHODS RELATED TO ARENAVIRUS IMMUNOGENS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The subject patent application claims the benefit of priority to U.S.

Provisional Patent Application Numbers 62/500,095 (filed May 2, 2017). The full disclosure of the priority application is incorporated herein by reference in its entirety and for all purposes. STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under R21 All 16112 awarded by the National Institutes of Health. The government has certain rights in the invention. BACKGROUND OF THE INVENTION

[0003] The arenavirus family includes over 30 known pathogens that exist on all populated continents on Earth. The family is divided into Old World and New World groups of viruses. The Old World category of arenaviruses contains Lassa virus (LASV) which causes hemorrhagic fever and is endemic in West Africa; lymphocytic choriomeningitis virus (LCMV), which causes febrile illness, neurological disease and birth defects with a 2-5% seroprevalence in North American and Europe; and 80% Lujo virus (LUJV), which also causes hemorrhagic fever and emerged in Southern Africa in 2008. The New World category of arenaviruses includes Machupo virus (MACV) which causes Bolivian hemorrhagic fever, Junin virus (JUNV) which causes

Argentinian hemorrhagic fever, Sabia virus, Guanarito virus, and others.

[0004] Lassa virus (LASV), in particular, causes a major and annual disease burden. LASV is the etiologic agent of Lassa fever (LF), an often-fatal viral hemorrhagic fever endemic in West Africa, with estimated 20-70% lethality and hundreds of thousands of cases every year. The virus has extended its geographic spread, as outbreaks in 2016 were accompanied by demonstrated human-to-human transmission in Africa and Germany. There is no approved Lassa fever vaccine, and the nucleoside analog ribavirin and supportive therapy are the only treatment options currently in use for LASV infection.

[0005] A major challenge with candidate LASV vaccines is the instability of the surface glycoprotein to which antibodies would be directed. The natural form of the envelope glycoprotein (GP) precursor (GPC) is unstable and tends to separate into individual subunits and to change conformation into forms not recognized by the most effective types of antibodies. The majority of antibodies shown to confer lifesaving protection only recognize a properly assembled GPC trimer in its prefusion conformation. Their epitopes, or binding sites, on GPC are termed "quaternary" in nature. GPCs that have separated or spring into different conformation are not bound by these antibodies, and vaccines that present the natural GPC tend to not elicit these types of protective antibodies. Indeed, most candidate vaccines rely on T cell-mediated protection, and antibody -mediated protection is thought to be difficult to achieve. Similarly, attempts to use the antibodies contained in convalescent plasma against LASV have met with variable results. Elicitation of neutralizing antibodies is further limited by a thick cloak of carbohydrate on the arenavirus GPC, particularly that of the Old World arenaviruses. How the prefusion GPC of any arenavirus assembles and which sites on GPC do lead to effective protection remained unknown.

[0006] There is a need in the art for more effective means to prevent and treat various arenaviral infections (e.g., LASV infection). There is a need in the art for more effective means to display the right assembly and structure of the surface GPC antigen so that protective antibody responses can be achieved by vaccination. There is a need in the art for stable, prefusion GPC as a clinical and research tool to determine if such quaternary antibodies have been elicited by vaccination or in natural infection. The present invention is directed to these and other unmet needs in the art.

SUMMARY OF THE INVENTION

[0007] The invention relates to methods and compositions for presenting the surface glycoprotein antigen of LASV and other arenaviruses in their prefusion conformation, which is necessary and relevant for eliciting protective antibodies. The invention describes means for engineering the GPC of LASV and other arenaviruses into a stable, consistent and immunogenic representation capable of eliciting and being recognized by potently protective antibodies. In one aspect, the invention provides engineered arenavirus glycoprotein polypeptides that contain the soluble ectodomain of an arenaviral GPC except for at least one of the modifications including (1) an engineered disulfide bond to covalently link GP1 and GP2, (2) a stabilizing missense substitution in the metastable region of HR1 of GP2, and (3) substitution of the native SIP cleavage site between GP1 and GP2 with a furin cleavage site. In some embodiments, the soluble ectodomain of the arenaviral GPC contains all three of these modifications. In various embodiments, the stabilizing substitution in the metastable region of HR1 of GP2 is substitution with a Pro residue.

[0008] Some engineered arenavirus glycoprotein polypeptides of the invention are derived from LASV GPC. In some of these embodiments, the soluble ectodomain is derived from LASV GPC strain Josiah. Some of these engineered arenavirus glycoprotein polypeptides have a sequence that is at least 90% identical to SEQ ID NO:l. In some embodiments, the soluble GPC ectodomain has a sequence shown in SEQ ID NO: 1, except for one or more of the mutations (1) an engineered disulfide bond between modified residues R207C in GP1 and G360C in GP2, G243C in GP1 and

I350C in GP2, G98C in GP1 and A330C in GP2, or A132C in GP1 and Q331C in GP2, (2) a stabilizing substitution E329P, and (3) SIP to furin cleavage site substitution _rrll256-₂59_→rrrr256-₂59 _{Some of me} engineered LASV glycoprotein polypeptides have a sequence that contains all three of these mutations or conservative substitutions thereof. Some of the engineered LASV glycoprotein polypeptides contain all three of these mutations as exemplified in SEQ ID NOs:2-5. Some of the engineered LASV glycoprotein polypeptides have a sequence that, except for one or more of the three mutations, is identical to SEQ ID NO:l except for conservatively substituted residues. Some of the engineered LASV glycoprotein polypeptides have a sequence that is at least 99% identical to a sequence selected from SEQ ID NOs:2-5.

[0009] Some engineered arenavirus glycoprotein polypeptides of the invention are derived from LCMV GPC. In some of these embodiments, the stabilizing substitution is Gln→Pro, and the SIP cleavage site substitution is RRLA²⁶²-²⁶⁵→RRRR^262"265. Some of these engineered LCMV glycoprotein polypeptides have a sequence that contains (1) mutations R249C in GP1 and L356C in GP2, (2) mutation Q334P or a conservative substitution thereof, and (3) SIP cleavage site substitution RRLA^{262" 265}→RRRR^262"265. Some of the engineered LCMV glycoprotein polypeptides have a sequence that is at least 90% identical to SEQ ID NO: 8. [0010] Some engineered arenavirus glycoprotein polypeptides of the invention are derived from JUNV GPC. In some of these embodiments, the stabilizing substitution is Asn→Pro, and the SIP cleavage site substitution is RSLK^248"251→RRRR²⁴⁸-²⁵¹. Some of these engineered JUNV glycoprotein polypeptides have a sequence that contains (1) mutations H235C in GP1 and L342C in GP2, (2) mutation N319P or a conservative substitution thereof, and (3) SIP cleavage site substitution RSLK²⁴⁸-²⁵¹→RRRR^248"251. Some of these engineered JUNV glycoprotein polypeptides have a sequence that is at least 90% identical to SEQ ID NO:9.

[0011] Some engineered arenavirus glycoprotein polypeptides of the invention are derived from MACV GPC. In some of these embodiments, the stabilizing substitution is Asn→Pro, and the SIP cleavage site substitution is RSLK^259"262→RRRR²⁵⁹-²⁶². Some of these engineered MACV glycoprotein polypeptides have a sequence that contains (1) mutations H246C in GP1 and L353C in GP2, (2) N330P or a conservative substitution thereof, and (3) SIP cleavage site substitution RSLK²⁵⁹-²⁶²→RRRR^259"262. Some of the engineered MACV glycoprotein polypeptides have a sequence that is at least 90% identical to SEQ ID NO: 10.

[0012] Some engineered arenavirus glycoprotein polypeptides of the invention are derived from LUJV GPC. In some of these embodiments, the stabilizing substitution is Arg→Pro, and the SIP cleavage site substitution is RSLK²¹⁸-²²¹→RRRR^218"221. Some of these engineered LUJV glycoprotein polypeptides have a sequence that contains (1) mutations R205C in GP1 and L312C in GP2, (2) mutation R289P or a conservative substitution thereof, and (3) SIP cleavage site substitution RSLK²¹⁸-²²¹→RRRR^218"221. Some of the engineered LUJV glycoprotein polypeptides have a sequence that is at least 90% identical to SEQ ID NO: 11.

[0013] In a related aspect, the invention provides arenavirus vaccine compositions that contain an engineered arenavirus glycoprotein immunogen described herein. In another related aspect, the invention provides purified or isolated polynucleotides that encode the engineered arenavirus glycoprotein polypeptides described herein. In some related embodiments, the invention provides vectors or expression constructs that harbor one or more of these polynucleotide sequences.

[0014] In another aspect, the invention provides methods for preventing an arenavirus infection in a subject. These methods entail administering to the subject a therapeutically effective amount of an engineered arenavirus glycoprotein immunogen described herein. In some related embodiments, the invention provides methods of treating an arenavirus infection or eliciting an immune response against an arenavirus in a subject by administering to the subject a pharmaceutical composition that contains a therapeutically effective amount of an engineered arenavirus glycoprotein immunogen described herein. In various embodiments, the therapeutic methods of the invention are directed to treating or preventing infections of LAS V, LCMV, JUNV, MACV or LUJV.

[0015] A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and claims.

DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 shows expression and purification of LAS V GPCysR4. (A) Schematic of the LASV GPCysR4 construct (bottom) in comparison to full-length GPC (top). N-linked glycans are indicated with a "Y" and numbered on their respective Asn residues. Disulfide bridges are indicated with lines and "S". The cysteine, proline and cleavage site mutations are noted. SSP, stable signal peptide; TM, transmembrane domain; CTD, C-terminal, zinc-binding domain; EK, enterokinase cleavage site. (B) SEC-MALS analysis of GPCysR4 demonstrates the protein elutes as a monomer. When incubated with 37.7H Fab, both trimeric and monomeric complexes are formed. (C) Streptactin-purified GPCysR4 run on a Coomassie-stained gel with and without DTT demonstrates the disulfide linkage maintains association between the GP1 and GP2 subunits and that the GP is efficiently processed. N.B. GP1 and GP2 are the same size and thus are not separated by SDS-PAGE. (D) ELISA analysis of reactivity between GPCysR4 and a panel of antibodies. Subunit specificity for each antibody has been previously determined (Robinson et al., Nat. Commun. 7, 11544, 2016) and is as follows: 12. IF - neutralizing anti-GPl; 3.3B - non-neutralizing anti-GPl; 3.6H - non- neutralizing anti-GP2, specific for post-fusion GP2; 13.4E - non-neutralizing anti-GP2, recognizes a linear epitope in the T-loop of GP2; 25. IOC - neutralizing anti-GP; 37.7H - neutralizing anti-GP; 9.7A - non-neutralizing anti-GP. Positive reactivity for antibodies 25. IOC, 37.7H and 9.7A and negative reactivity to antibody 3.6H suggests the engineered GP is in a pre-fusion conformation. The competition group for each antibody is indicated to the left. DETAILED DESCRIPTION

I. Overview

[0017] Arenaviruses cause a global disease burden and for most there are no vaccines. Lassa virus in particular, presents the greatest annual threat with thousands to hundreds of thousands of infections each year. The Lassa fever zone stretches over an area of over 3 million square kilometers, from Guinea and perhaps Senegal in the western coast, crossing Sierra Leone, reaching Nigeria in the east and Mali in the north. The world's highest incidence of Lassa fever occurs in Kenema district in the Eastern Province of Sierra Leone. Nosocomial infection is common, with recent human-to- human transmission occurring in medical workers and an undertaker working in

Germany in 2016. There is a substantial unmet need to protect against endemic LASV infection, particularly with the continuing economic development of West African nations recently impacted by the largest recorded epidemic of EBOV. The susceptible population numbers over 300 million people. Persons traveling to endemic areas across West Africa would also benefit from a Lassa fever vaccine, as there have been dozens of cases of importation of LASV to Europe, Israel, North America and other industrialized nations, the most of any VHF agent. Provision of a vaccine will be essential for health care workers (HCWs) and first responders, and a vaccine can also serve as a deterrent from using this easily acquired pathogen as a bioweapon. LASV vaccine could also be employed in a ring-vaccination strategy for reactive/emergency (outbreak) control or as a post-exposure therapeutic. However, these uses require rapid induction of protective responses, which will be assisted by development of vaccine expressing a LASV GPC that is structurally stabilized in the antigenic

prefusion configuration and capable of exciting protective neutralizing antibody responses.

[0018] The glycoprotein of arenaviruses, GPC, is the sole antigen expressed on the viral surface and the critical target for antibody -mediated neutralization. Most neutralizing antibodies against arenaviruses (e.g., LASV) bind to quaternary epitopes involving multiple domains and/or trimerization of the GPC. These antibodies further require the GPC to be in a pre-fusion conformation. A requisite for trimerization is proper processing of the GPC. Large-scale production of the protein for

commercialization necessitates the removal of stabilizing domains such as the stable signal peptide and the GP2 transmembrane domain. The resulting GP1 and GP2 ectodomains do not remain associated with one another and the GP quickly reverts to the post-fusion form.

[0019] The present invention is predicated in part on the development by the inventors of engineered ectodomain polypeptides of arenaviral GPCs. With extensive efforts and experimentations over a decade, the inventors have completed glycoprotein engineering studies that have resulted in stable prefusion GPC for LASV, LCMV, LUJV, MACV, and JUNV. Importantly, the inventors have determined several high- resolution structures of the different, engineered LASV GPC in complex with human neutralizing antibodies from survivors. The crystal structures of the inventions described here are the first available high-resolution structures of the relevant, viral- surface assembly for any arenavirus. These studies have thus shown the architecture of the viral surface assembly, demonstrated why formation and stability of the correct trimeric structure are critical for eliciting a potent neutralizing antibody response, why previous LASV vaccine efforts have failed to elicit potent neutralizing antibodies, why using the natural GPC for other arenaviruses may similarly lead to elicitation of a less potent antibody response.

[0020] The inventors' studies demonstrate that the most effective antibodies bind "quaternary" epitopes, which are formed only when the different subunits assemble together, and which are faithfully represented by the engineered proteins described here. The crystal structures also showed that the quaternary epitopes formed by the engineered GPCs involve the rare surfaces that are not cloaked by carbohydrate and that are thus available for immune surveillance. If the glycoprotein is not stabilized as described herein, these quaternary, unglycosylated epitopes are not presented, and a neutralizing antibody response is not elicited. In the absence of a neutralizing antibody response, vaccine makers have instead previously focused on cell-mediated immunity as the correlate of protection. The engineered proteins described herein, however, yield stabilized native, oligomeric GPC that is reactive with the most potent neutralizing antibodies and is able to improve efficacy of vaccines and quality of protection.

[0021] Thus, the inventors' studies demonstrate that the modifications hold the polypeptide in its "pre-fusion" state which is relevant for vaccine design and for identification and evaluation of vaccines and immunotherapeutics. The viral glycoprotein changes conformation as the virus enters low pH and fuses with the host membrane. Expression of the glycoprotein GPC fails to yield material that remains stably in its prefusion conformation. Instead, all or a portion springs irreversibly into a different post-fusion conformation which is not relevant for binding of the most effective antibodies. As detailed herein, the inventors have engineered the GPC of multiple arenaviruses to maintain the proper pre-fusion configuration.

[0022] As detailed herein, engineered "pre-fusion" state GPC polypeptides were generated with GPC ectodomains from various arenaviruses. Using LASV as an example, the resulting engineered trimeric GPC polypeptide is able to bind to a neutralizing antibody from a human survivor of LASV infection, and suggest that the antibody neutralizes by inhibiting conformational changes required for binding its intracellular receptor and for membrane fusion. Specifically, the inventors found that the engineered prefusion GPC trimer of LASV ("GPCysR4") is in its native, pre-fusion state. This engineered LASV GPC ectodomain polypeptide is recognized by neutralizing antibodies that require native association between the GP1 and GP2 subunits, and is not recognized by antibodies against post-fusion GP2. The inventors obtained a 3.2A crystal structure of the engineered prefusion GPC trimer of LASV (GPCysR4), in complex with the human neutralizing antibody 37.7H directed against the quaternary GPC-B epitope. This structure reveals the first look at the prefusion arenavirus GP trimer, suggests that conformational changes occur in the receptor- binding subunit as well as the fusion subunit upon exposure to low pH, and illuminates reasons why GPC must be processed to oligomerize and bind one of its extracellular receptors. It also illuminates what appears to be the most vulnerable region on the LASV trimer targeted for antibody -mediated neutralization and suggests that such antibodies function by blocking conformational changes required for binding an intracellular receptor and for fusion. These studies demonstrate the feasibility of using the engineered LASV ectodomain polypeptide and related variants for producing vaccines against LASV infections.

[0023] In accordance with these exemplified studies, the invention provides various arenaviral vaccine immunogens, e.g., immunogens derived from the GPC of LASV, LCMV, MACV, JUNV and LUJV. Also provided in the invention are clinical applications of the vaccine immunogens, including therapeutic and preventive uses of the vaccine compositions of the invention. The invention further provides a general method for engineering the arenavirus glycoprotein into a conformation suitable for use as an immunogen or to identify or evaluate antibody therapeutics. The genetically engineered GPC ectodomain polypeptides of the invention provide high quantities of fully processed pre-fusion GP that binds to neutralizing antibodies but not those specific for the post-fusion form of GP, as exemplified herein with LASV immunogen polypeptide. Proteins produced with the expression constructs of the invention can form native-like GP molecules. As specific exemplification, some vaccine

immunogens of the invention are derived from an engineered soluble GPC ectodomain of LASV strain Josiah. These GPC immunogens contain an engineered disulfide bond to covalently link GP1 and GP2, an E329P mutation in the metastable region of HR1 of GP2, and replacement of the native SIP GP1-GP2 cleavage site with a furin cleavage site.

[0024] Unless otherwise specified herein, the arenavirus immunogen polypeptides or vaccine compositions of the invention, the encoding polynucleotides, expression vectors and host cells, as well as the related therapeutic applications, can all be generated or performed in accordance with the procedures exemplified herein or routinely practiced methods well known in the art. See, e.g., Methods in Enzymology, Volume 289: Solid-Phase Peptide Synthesis, J. N. Abelson, M. I. Simon, G. B. Fields (Editors), Academic Press; 1st edition (1997) (ISBN-13: 978-0121821906); U.S. Pat. Nos. 4,965,343, and 5,849,954; Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Press, N.Y., (3^rd ed., 2000); Brent et al., Current Protocols in Molecular Biology, John Wiley & Sons, Inc. (ringbou ed., 2003); Davis et al., Basic Methods in Molecular Biology, Elsevier Science Publishing, Inc., New York, USA (1986); or Methods in Enzymology: Guide to Molecular Cloning Techniques Vol. 152, S. L. Berger and A. R. Kimmerl Eds., Academic Press Inc., San Diego, USA (1987); Current Protocols in Protein Science (CPPS) (John E. Coligan, et. al., ed., John Wiley and Sons, Inc.), Current Protocols in Cell Biology (CPCB) (Juan S. Bonifacino et. al. ed., John Wiley and Sons, Inc.), and Culture of Animal Cells: A Manual of Basic Technique by R. Ian Freshney, Publisher: Wiley -Liss; 5th edition (2005), Animal Cell Culture Methods (Methods in Cell Biology, Vol. 57, Jennie P. Mather and David Barnes editors, Academic Press, 1st edition, 1998). The following sections provide additional guidance for practicing the compositions and methods of the present invention.

II. Definitions [0025] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. The following references provide one of skill with a general definition of many of the terms used in this invention: Academic Press Dictionary of Science and Technology, Morris (Ed.), Academic Press (1^st ed., 1992); Oxford Dictionary of Biochemistry and Molecular Biology, Smith et al. (Eds.), Oxford University Press (revised ed., 2000); Encyclopaedic Dictionary of Chemistry, Kumar (Ed.), Anmol Publications Pvt. Ltd. (2002); Dictionary of Microbiology andMolecular Biology, Singleton et al. (Eds.), John Wiley & Sons (3^rd ed., 2002); Dictionary of Chemistry, Hunt (Ed.), Routledge (1^st ed., 1999); Dictionary of Pharmaceutical Medicine, Nahler (Ed.), Springer-Verlag Telos (1994); Dictionary of Organic

Chemistry, Kumar and Anandand (Eds.), Anmol Publications Pvt. Ltd. (2002); and^l Dictionary of Biology (Oxford Paperback Reference), Martin and Hine (Eds.), Oxford University Press (4^th ed., 2000). Further clarifications of some of these terms as they apply specifically to this invention are provided herein.

[0026] As used herein, the singular forms "a," "an," and "the," refer to both the singular as well as plural, unless the context clearly indicates otherwise. For example, "an LASV GPC-derived trimer" can refer to both single or plural LASV GPC-derived trimer molecules, and can be considered equivalent to the phrase "at least one LASV GPC-derived trimer."

[0027] As used herein, the terms "antigen" or "immunogen" are used

interchangeably to refer to a substance, typically a protein, which is capable of inducing an immune response in a subject. The term also refers to proteins that are

immunologically active in the sense that once administered to a subject (either directly or by administering to the subject a nucleotide sequence or vector that encodes the protein) is able to evoke an immune response of the humoral and/or cellular type directed against that protein.

[0028] An arenavirus refers to any of the Old or New World arenaviruses.

Specific examples of arenaviruses suitable for the invention include, but are not limited to, LASV, LCMV, MACV, JUNV and LUJV. LASV is the etiologic agent of Lassa fever, which is an acute and often fatal illness endemic to West Africa. MACV is the etiologic agent of Bolivian hemorrhagic fever. JUNV is the etiologic agent of Argentinian hemorrhagic fever. LCMV causes neurological disease in adults, birth defects when infecting pregnant women, and is lethal for transplant recipients. It occurs with a 2-5% seroprevalence throughout North American and Europe. LUJV is an 80% lethal hemorrhage fever virus discovered in southern Africa Typically, an arenaviral genome is comprised of two ambisense, single-stranded RNA molecules, designated small (S) and large (L). Two genes on the S segment encode the nucleoprotein (NP) and two envelope glycoproteins (GP1 and GP2); whereas, the L segment encodes the viral polymerase (L protein) and RING finger Z matrix protein. GP1 and GP2 subunits result from post-translational cleavage of a precursor glycoprotein (GPC) by the protease SKI-1/S1P. GP1 serves a putative role in receptor binding, while GP2 has the structural features characteristic of class I viral fusion proteins.

[0029] Conservative amino acid substitutions providing functionally similar amino acids are well known in the art. The following six groups each contain amino acids that are conservative substitutions for one another: 1) Alanine (A), Serine (S), Threonine (T); 2) Aspartic acid (D), Glutamic acid (E); 3) Asparagine (N), Glutamine (Q);

Arginine (R), Lysine (K); 5) Isoleucine (I), Leucine (L), Methionine (M), Valine (V); and 6) Phenylalanine (F), Tyrosine (Y), Tryptophan (W). Not all residue positions within a protein will tolerate an otherwise "conservative" substitution. For instance, if an amino acid residue is essential for a function of the protein, even an otherwise conservative substitution may disrupt that activity, for example the specific binding of an antibody to a target epitope may be disrupted by a conservative mutation in the target epitope.

[0030] Epitope refers to an antigenic determinant. These are particular chemical groups or peptide sequences on a molecule that are antigenic, such that they elicit a specific immune response, for example, an epitope is the region of an antigen to which B and/or T cells respond. Epitopes can be formed both from contiguous amino acids or noncontiguous amino acids juxtaposed by tertiary folding of a protein.

[0031] Effective amount of a vaccine or other agent that is sufficient to generate a desired response, such as reduce or eliminate a sign or symptom of a condition or disease, such as Lassa fever. For instance, this can be the amount necessary to inhibit viral entry into host cells or to measurably alter outward symptoms of the viral infection. In general, this amount will be sufficient to measurably inhibit virus (for example, LASV) replication or infectivity. When administered to a subject, a dosage will generally be used that will achieve target tissue concentrations that has been shown to achieve in vitro inhibition of viral replication. In some examples, an "effective amount" is one that treats (including prophylaxis) one or more symptoms and/or underlying causes of any of a disorder or disease, for example to treat Lassa fever. In one example, an effective amount is a therapeutically effective amount. In one example, an effective amount is an amount that prevents one or more signs or symptoms of a particular disease or condition from developing, such as one or more signs or symptoms associated with Lassa fever.

[0032] As used herein, a fusion protein is a recombinant protein containing amino acid sequence from at least two unrelated proteins that have been joined together, via a peptide bond, to make a single protein. The unrelated amino acid sequences can be joined directly to each other or they can be joined using a linker sequence. As used herein, proteins are unrelated, if their amino acid sequences are not normally found joined together via a peptide bond in their natural environment(s) (e.g., inside a cell).

[0033] Immunogen is a protein or a portion thereof that is capable of inducing an immune response in a mammal, such as a mammal infected or at risk of infection with a pathogen. Administration of an immunogen can lead to protective immunity and/or proactive immunity against a pathogen of interest.

[0034] Immunogenic surface is a surface of a molecule, for example a protein such as an arenaviral GPC, capable of eliciting an immune response. An immunogenic surface includes the defining features of that surface, for example the three-dimensional shape and the surface charge. In some examples, an immunogenic surface is defined by the amino acids on the surface of a protein or peptide that are in contact with an antibody, such as a neutralizing antibody, when the protein and the antibody are bound together. A target epitope includes an immunogenic surface. Immunogenic surface is synonymous with antigenic surface.

[0035] Immune response refers to a response of a cell of the immune system, such as a B cell, T cell, or monocyte, to a stimulus. In some embodiment, the response is specific for a particular antigen (an "antigen-specific response"). In some embodiments, an immune response is a T cell response, such as a CD4+ response or a CD8+ response. In some other embodiments, the response is a B cell response, and results in the production of specific antibodies. [0036] Immunogenic composition refers to a composition comprising an immunogenic polypeptide that induces a measurable CTL response against virus expressing the immunogenic polypeptide, or induces a measurable B cell response (such as production of antibodies) against the immunogenic polypeptide.

[0037] Sequence identity or similarity between two or more nucleic acid sequences, or two or more amino acid sequences, is expressed in terms of the identity or similarity between the sequences. Sequence identity can be measured in terms of percentage identity; the higher the percentage, the more identical the sequences are. Homologs or orthologs of nucleic acid or amino acid sequences possess a relatively high degree of sequence identity/similarity when aligned using standard methods.

Methods of alignment of sequences for comparison are well known in the art. Various programs and alignment algorithms are described in: Smith & Waterman, Adv. Appl. Math. 2:482, 1981; Needleman & Wunsch, J. Mol. Biol. 48:443, 1970; Pearson & Lipman, Proc. Natl. Acad. Sci. USA 85:2444, 1988; Higgins & Sharp, Gene, 73:237- 44, 1988; Higgins & Sharp, CABIOS 5:151-3, 1989; Corpet et al., Nuc. Acids Res. 16:10881-90, 1988; Huang et al. Computer Appls. in the Biosciences 8, 155-65, 1992; and Pearson et al., Meth. Mol. Bio. 24:307-31, 1994. Altschul et al., J. Mol. Biol. 215:403-10, 1990, presents a detailed consideration of sequence alignment methods and homology calculations.

[0038] The term "subject" refers to any animal classified as a mammal, e.g., human and non-human mammals. Examples of non-human animals include dogs, cats, cattle, horses, sheep, pigs, goats, rabbits, and etc. Unless otherwise noted, the terms "patient" or "subject" are used herein interchangeably. Preferably, the subject is human.

[0039] The term "treating" or "alleviating" includes the administration of compounds or agents to a subject to prevent or delay the onset of the symptoms, complications, or biochemical indicia of a disease (e.g., a LASV infection), alleviating the symptoms or arresting or inhibiting further development of the disease, condition, or disorder. Subjects in need of treatment include those already suffering from the disease or disorder as well as those being at risk of developing the disorder. Treatment may be prophylactic (to prevent or delay the onset of the disease, or to prevent the manifestation of clinical or subclinical symptoms thereof) or therapeutic suppression or alleviation of symptoms after the manifestation of the disease. [0040] Vaccine refers to a pharmaceutical composition that elicits a prophylactic or therapeutic immune response in a subject. In some cases, the immune response is a protective immune response. Typically, a vaccine elicits an antigen-specific immune response to an antigen of a pathogen, for example a viral pathogen, or to a cellular constituent correlated with a pathological condition. A vaccine may include a polynucleotide (such as a nucleic acid encoding a disclosed antigen), a peptide or polypeptide (such as a disclosed antigen), a virus, a cell or one or more cellular constituents. III. Modified arenaviral GPC ectodomain polypeptides and immunogens

[0041] As the sole antigen on the viral surface, the arenavirus glycoprotein complex (GPC) is the primary target of protective humoral immune responses and a focus for vaccine design efforts. Using LASV as an illustrative example, the virion form of GPC is a trimer of heterodimers, each containing the receptor-binding subunit GP1 and the transmembrane, fusion-mediating subunit GP2. GPC also encodes an unusual stable signal peptide (SSP) that is required for proper processing of GPC and is retained in the virion as part of the complex. The GPC precursor is trafficked from the endoplasmic reticulum to the Golgi where it is heavily N-glycosylated and processed by cellular proteases (SPase, SKI1/SP1) into its mature form, which is comprised of non- covalently linked GP1, GP2 and SSP. The GPC trimer engages several host receptors to mediate viral entry. GPC of LASV binds to a xylose-glucaronic acid sugar, called matriglycan, on alpha-dystroglycan (a-DG) or alternative receptors at the cell surface, and then enters the endocytic pathway where it binds to lysosome-associated membrane protein 1 (LAMP1), upon reaching the highly acidic interior of the lysosome, before membrane fusion. The GPC of pathogenic New World arenaviruses bind to Transferrin Receptor 1 as their cellular receptor.

[0042] The engineered arenavirus immunogen polypeptides of the invention are modified polypeptides that are derived from the soluble ectodomain of arenaviral GPC. As exemplification, a LASV GPC ectodomain is shown in SEQ ID NO:l, which contains residues 1-424 of the glycoprotein of LASV Josiah strain. The complete GPC sequence of LASV Josiah strain is known in the art. See, e.g., sequence accession number AAA46286, and Auperin and McCormick, Virol. 168:421-425, 1989. Other than the exemplified LASV GPC ectodomain sequence, soluble GPC ectodomain sequences from other LASV strains can also be used for generating the engineered LASV immunogen polypeptides of the invention. As demonstrated for other arenaviruses, the method described herein for generating arenaviral vaccine

immunogens is suitable for production of profusion GPC polypeptides for any arenavirus. Specifically, similar substitutions have been made in the GPC of LCMV, LUJV, MACV and JUNV. As detailed herein, the engineered immunogens contain several variations in some conserved positions in the arenaviral GPC ectodomain. Via sequence alignment, similar immunogens can also be obtained from the GPC ectodomains of other LASV strains or other arenaviruses by introducing the same mutations at corresponding positions.

[0043] As exemplified herein with the LASV Josiah strain, the engineered arenavirus GPC polypeptides of the invention typically contain at least one of the three structural modifications described herein in the ectodomain. First, the modified polypeptides can be a soluble arenaviral (e.g., LASV) GPC ectodomain that harbors an engineered disulfide bond that covalently links the GP1 and GP2 subunits. Second, the polypeptides can also contain a helix-breaking mutation in the metastable region of HR1 of GP2 to limit conversion from the prefusion to the postfusion form. Finally, the native SP1 cleavage site for separating GP1 and GP2 in the precursor protein can be replaced with a furin cleavage site. In some embodiments, the modified polypeptides can contain at least two of these mutations. In some preferred embodiments, the arenaviral ectodomain derived polypeptides can contain all three of these modifications. In the case of polypeptides derived from the GPC ectodomain of LASV Josiah strain as exemplified herein, these modifications include mutations to introduce a disulfide bond, a E329P mutation in the metastable region of HR1 of GP2, and an RRLL^256"259 (SEQ ID NO:6) to RRRR^256"259 (SEQ ID NO:7) replacement of the protease cleavage site. Four pairs of substitutions have been demonstrated to form a disulfide bond that links GP1 to GP2 and anchors LASV GPC in its prefusion conformation: (a) R207C in GP1 and G360C in GP2, (b) G243C in GP1 and I350C in GP2, (c) G98C in GP1 and A330C in GP2, or (d) A132C in GP1 and Q331C in GP2. Examples of some of the modified LASV ectodomain polypeptides (including "GPCysR4") that contain these mutations are shown in SEQ ID NOs:2-5.

[0044] As further exemplifications, similar vaccine immunogens for other arenaviruses have been produced by the same design strategy. These include, e.g., (1) LCMV ectodomain immunogen: containing an engineered R249C-L356C disulfide bond, a Q334P stabilizing mutation, and an RRLA^262"265 (SEQ ID NO: 12) to RRRR^{262" 265} (SEQ ID NO:7) replacement of the protease cleavage site, (2) MACV ectodomain immunogen: containing an engineered H246C-L353C disulfide bond, an N330P stabilizing mutation, and an RSLK^259"262 (SEQ ID NO: 13) to RRRR^259"262 (SEQ ID NO:7) replacement of the protease cleavage site, (3) JUNV ectodomain immunogen: containing an engineered H235C-L342C disulfide bond, an N319P stabilizing mutation and an RSLK^248"251 (SEQ ID NO: 13) to RRRR^248"251 (SEQ ID NO:7) replacement of the protease cleavage site, and (4) LUJV ectodomain immunogen: containing an R205C- L312C disulfide bond, an R289P stabilizing mutation, and an RSLK^218"221 (SEQ ID NO: 13) to RRRR^218"221 (SEQ ID NO:7) replacement of the protease cleavage site. Amino acid sequence of some of these modified ectodomain polypeptides from these other arenaviruses are shown in SEQ ID NOs:8-ll.

[0045] In some embodiments, the starting or base soluble ectodomain polypeptide into which one or more of these mutations are to be introduced is a variant of the soluble GPC ectodomain of an arenavirus, such as the LASV strain Josiah as exemplified herein (SEQ ID NO: 1). The variant typically has an amino acid sequence that is substantially identical to wildtype soluble GPC ectodomain (e.g., SEQ ID NO:l). In various embodiments, the base ectodomain polypeptide can have an amino acid sequence that is at least 85%, 90%, 91&, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identical to the wildtype sequence of the ectodomain of an arenavirus. In some other embodiments, the base soluble ectodomain polypeptide has an amino acid sequence that is identical to the wildtype sequence (e.g., SEQ ID NO:l) except for one or more conservative substituted residues. In any of these embodiments, the resulting engineered arenavirus GPC polypeptides can have one or more of the mutations introduced at positions corresponding to that of the mutations described herein (e.g., mutations for LASV as shown in SEQ ID NO:2). In some of these embodiments, the engineered arenavirus GPC polypeptides have a sequence that is substantially identical to the wildtype sequence (e.g., SEQ ID NO: 1 for LASV) but contain all three mutations corresponding to the mutations exemplified herein for LASV as shown in SEQ ID NO:2.

[0046] The arenavirus immunogen polypeptides of the invention include variants of the engineered arenavirus ectodomain polypeptides exemplified herein. For example, while the exemplified engineered LASV ectodomain polypeptides can have an amino acid sequence shown in SEQ ID NO: 2 (GPCysR4) and SEQ ID NOs:3-5, the LAS V immunogen polypeptides of the invention also encompass variants of the exemplified sequences. Thus, in some embodiments, the engineered LASV glycoprotein immunogen can have an amino acid sequence that is at least 90%, 95% or 99% identical to any one of SEQ ID NOs:2-5. Some of these immunogen polypeptides contain the same or substantially identical mutations as shown in any one of SEQ ID NOs:2-5, i.e., (1) substitutions R207C in GP1 and G360C in GP2 (as shown in SEQ ID NO:2), G243C in GP1 and I350C in GP2 (as shown in SEQ ID NO:3), G98C in GP1 and A330C in GP2 (as shown in SEQ ID NO:4), or A132C in GP1 and Q331C in GP2 (as shown in SEQ ID NO:5), (2) Asp→ Pro mutation E329P or a conservative substitution thereof, and (3)

mutation or conservative substitutions thereof. In some embodiments, the engineered LASV GPC ectodomain immunogen polypeptides can contain all three mutations shown in any one of SEQ ID NOs:2-5. Similarly, the invention provides vaccine immunogen polypeptides derived from the other arenaviruses that can contain the same sequence as or a substantially identical sequence to one shown in SEQ ID NO:8 (for LCMV), SEQ ID NO:9 (for JUNV), SEQ ID NO: 10 (for MACV) and SEQID NO: 11 (for LUJV), plus one or more of the mutations noted above. In some embodiments, the engineered arenavirus glycoprotein immunogen can have an amino acid sequence that is at least 90%, 95% or 99% identical to any one of SEQ ID NOs:8-l 1 plus all three mutations noted above for each of the arenaviruses (LCMV, JUNV, MACV or LUJV).

[0047] The engineered arenavirus ectodomain polypeptides of the invention can be readily used to prepare vaccines for the respective viruses (e.g., LASV). The invention accordingly provides arenavirus vaccine compositions. As detailed below, in addition to an engineered arenavirus glycoprotein immunogen described herein, the vaccine compositions of the invention can additionally contain other ingredients that are typically present in vaccines, e.g., adjuvants and pharmaceutically acceptable carriers. In some embodiments, the vaccine compositions of the invention contain the soluble ectodomain of an arenavirus (e.g., LASV) GPC except for at least one modifications described herein. Using LASV as example, these include mutations selected from the group consisting of (1) an engineered disulfide bond to covalently link GP1 and GP2 as described herein, (2) a proline substitution in the metastable region of HR1 of GP2, and (3) substitution of the native SIP cleavage site between GP1 and GP2 with a furin cleavage site. Immunogen polypeptides for the other arenaviruses can be similarly designed to contain one or more of the specific mutations detailed above for the various viruses. In some embodiments, the engineered arenavirus GPC polypeptide has an amino acid sequence that is at least 90% identical to one of the arenavirus ectodomain sequences exemplified herein (e.g., SEQ ID NO:l for LASV) and also contains an engineered disulfide bond between modified residues R207C in GP1 and G360C in GP2, a Glu→ Pro substitution (E329P), and a SIP to furin cleavage site substitution (RRLL^256"259→RRRR^256"259). In some vaccine compositions, the engineered arenavirus glycoprotein immunogen has an amino acid sequence that is at least 99% identical to one of the exemplified variant sequences (e.g., SEQ ID NOs:2-5 for LASV or SEQ ID Nos:8-ll). In some embodiments, the vaccine compositions contain the soluble GPC ectodomain polypeptide as shown in one of the exemplified variant sequences (e.g., SEQ ID NOs:2-5 and SEQ ID NOs:8-ll).

[0048] As noted above, in addition to the exemplified ectodomain sequence of LASV strain Josiah, the engineered arenavirus GPC immunogen polypeptides and related vaccine compositions can also be generated from the GPC ectodomain of other arenaviruses (such as LCMV, LUJV, MACV and JUNV) and other strains of a given arenavirus. The emplifi cations herein indicate that the general structure and design strategy described herein can be applied to create vaccines against other arenaviruses or combinations of arenaviruses. As described herein, genomic structures and GPC sequences of many other arenaviruses are all known and well characterized in the art. See, e.g., NCBI protien databank; Abraham et al., Nat. Struc. Mo. Biol. 17, 438-444, 2010; Bowden et al., J. Viol. 83, 8259-8265, 2009; Briese et al., PLoS Pathog. 5, el000455, 2009; Cohen-Dvashi et al., J. Virol. 89, 7584-7592, 2015; Hastie et al., Nat. Struc. Mo. Biol. 17, 23, 513-521, 2016; Igonet et al., Proc. Natl. Acad. Sci. USA, 108, 19967-19972, 2011; and Mahmutovic et al., Cell Host Microbe 18, 705-713, 2015. Similarly, sequences of different strains of a specific areanvirus have also been delineated in the literature. For exampe, sequences of a number of the other LASV strains are well known and can be readily employed in the practice of the invention. See, e.g., Bowen et al., J. Virol. 74: 6992-7004, 2000. Since the mutations introduced into the exemplified ectodomain sequences are all located at conserved positions, corresponding mutations to the ectodomain of the other arenavirus (e.g., LASV) strains can be easily devised by sequence alignment.

[0049] The various arenavirus (e.g., LASV) ectodomain-derived polypeptides and immunogens used in the invention can be obtained or generated in accordance with the protocols exemplified herein or methods well known in the art. Upon recombinant expression (e.g., in Drosophila S2 cells as detailed herein), the proteins can be purified by any of the routinely practiced procedures or the protocols exemplified herein (e.g., streptactin-affinity chromatography as exemplified herein). General techniques for protein purification are described in, e.g., Guide to Protein Purification, ed. Deutscher, Meth. Enzymol. 185, Academic Press, San Diego, 1990; and Scopes, Protein

Purification: Principles and Practice, Springer Verlag, New York, 1982. Substantial purification denotes purification from other proteins or cellular components. A substantially purified protein is at least 60%, 70%, 80%, 90%, 95% or 98% pure. Once purified, antigenicity and other properties of the immunogens can also be readily examined with standard methods, e.g., antigenic profiling using known bNAbs and non-Nabs, differential scanning calorimetry (DSC), electron microscopy, binding analysis via ELISA and Biolayer Light Interferometry (BLI), and co-crystallography analysis as exemplified herein.

[0050] In some related embodiments, the invention provides substantially purified polynucleotides (DNA or RNA) which encode the engineered arenavirus (e.g., LASV, LUJV, LCMV, MACV, or JUNV) ectodomain polypeptides described herein, as well as expression vectors (e.g., pMTpuro derived vectors as exemplified herein) that harbor such polynucleotides and host cells for producing the arenavirus (e.g., LASV) immunogen polypeptides (e.g., Drosophila S2 cells noted above). The polynucleotides and related vectors can be readily generated with standard molecular biology techniques or the protocols exemplified herein. For example, introducing mutations to a polynucleotide sequence by PCR can be performed as described in, e.g., PCR Technology: Principles and Applications for DNA Amplification, H.A. Erlich (Ed.), Freeman Press, NY, NY, 1992; PCR Protocols: A Guide to Methods and Applications, Innis et al. (Ed.), Academic Press, San Diego, CA, 1990; Mattila et al., Nucleic Acids Res. 19:967, 1991; and Eckert etal, PCR Methods and Applications 1:17, 1991. Both viral-based and nonviral expression vectors can be used to produce the antibodies in a mammalian host cell. Nonviral vectors and systems include plasmids, episomal vectors, typically with an expression cassette for expressing a protein or RNA, and human artificial chromosomes (see, e.g., Harrington et al., Nat. Genet. 15:345, 1997). Useful viral vectors include vectors based on lentiviruses or other retroviruses, adenoviruses, adenoassociated viruses, herpes viruses, vectors based on SV40, papilloma virus, HBP Epstein Barr virus, vaccinia virus vectors and Semliki Forest virus (SFV). See, Brent et al., supra; Smith, Annu. Rev. Microbiol. 49:807, 1995; and Rosenfeld et al., Cell 68:143, 1992. rv. Pharmaceutical compositions and therapeutic applications

[0051] The invention provides pharmaceutical compositions and related methods of using the LASV immunogens (e.g., engineered soluble GPC ectodomain polypeptide shown in SEQ ID NO:2) described herein for preventing and treating LASV infections. In some embodiments, the immunogens disclosed herein are included in a

pharmaceutical composition. The pharmaceutical composition can be either a therapeutic formulation or a prophylactic formulation. Typically, the composition additionally includes one or more pharmaceutically acceptable vehicles and, optionally, other therapeutic ingredients (for example, antibiotics or antiviral drugs). Various pharmaceutically acceptable additives can also be used in the compositions.

[0052] Some of the pharmaceutical compositions of the invention are vaccines. For vaccine compositions, appropriate adjuvants can be additionally included.

Examples of suitable adjuvants include, e.g., aluminum hydroxide, lecithin, Freund's adjuvant, MPL™ and IL-12. In some embodiments, the LASV immunogens disclosed herein can be formulated as a controlled-release or time-release formulation. This can be achieved in a composition that contains a slow release polymer or via a

microencapsulated delivery system or bioadhesive gel. The various pharmaceutical compositions can be prepared in accordance with standard procedures well known in the art. See, e.g., Remington's Pharmaceutical Sciences, 19^th Ed., Mack Publishing Company, Easton, Pa, 1995; Sustained and Controlled Release Drug Delivery Systems, J. R. Robinson, ed., Marcel Dekker, Inc., New York, 1978); U.S. Pat. Nos. 4,652,441 and 4,917,893; U.S. Pat. Nos. 4,677,191 and 4,728,721; and U.S. Pat. No. 4,675,189.

[0053] The pharmaceutical compositions of the invention can be readily employed in a variety of therapeutic or prophylactic applications for treating an arenavirus (e.g., LASV) infection or eliciting an immune response against the arenavirus in a subject. For example, the composition can be administered to a subject to induce an immune response to the arenavirus, e.g., to induce production of broadly neutralizing antibodies to LASV. For subjects at risk of developing an arenavirus infection, a vaccine composition of the invention can be administered to provide prophylactic protection against viral infection. Depending on the specific subject and conditions, the pharmaceutical compositions of the invention can be administered to subjects by a variety of administration modes known to the person of ordinary skill in the art, for example, intramuscular, subcutaneous, intravenous, intra-arterial, intra-articular, intraperitoneal, or parenteral routes. In general, the pharmaceutical composition is administered to a subject in need of such treatment for a time and under conditions sufficient to prevent, inhibit, and/or ameliorate a selected disease or condition or one or more symptom(s) thereof. The immunogenic composition is administered in an amount sufficient to induce an immune response against an arenavirus. For therapeutic applications, the compositions should contain a therapeutically effective amount of the arenaviral immunogen described herein. For prophylactic applications, the

compositions should contain a prophylactically effective amount of the arenaviral immunogen described herein. The appropriate amount of the immunogen can be determined based on the specific disease or condition to be treated or prevented, severity, age of the subject, and other personal attributes of the specific subject (e.g., the general state of the subject's health and the robustness of the subject's immune system). Determination of effective dosages is additionally guided with animal model studies followed up by human clinical trials and is guided by administration protocols that significantly reduce the occurrence or severity of targeted disease symptoms or conditions in the subject.

[0054] For prophylactic applications, the immunogenic composition is provided in advance of any symptom, for example in advance of infection. The prophylactic administration of the immunogenic compositions serves to prevent or ameliorate any subsequent infection. Thus, in some embodiments, a subject to be treated is one who has, or is at risk for developing, an arenaviral infection, for example because of exposure or the possibility of exposure to the virus. Following administration of a therapeutically effective amount of the disclosed therapeutic compositions, the subject can be monitored for an arenaviral infection, symptoms associated with an arenaviral infection, or both. [0055] For therapeutic applications, the immunogenic composition is provided at or after the onset of a symptom of disease or infection, for example after development of a symptom of an arenaviral infection, or after diagnosis of an renaviral infection. The immunogenic composition can thus be provided prior to the anticipated exposure to an arenavirus so as to attenuate the anticipated severity, duration or extent of an infection and/or associated disease symptoms, after exposure or suspected exposure to the virus, or after the actual initiation of an infection.

[0056] The pharmaceutical composition of the invention can be combined with other agents known in the art for treating or preventing an arenaviral infections. These include, e.g., antibodies or other antiviral agents such as ribavirin. Administration of the pharmaceutical composition and the known anti-an arenaviral agents can be either concurrently or sequentially.

[0057] The arenaviral vaccine or pharmaceutical compositions of the invention can be provided as components of a kit. Optionally, such a kit includes additional components including packaging, instructions and various other reagents, such as buffers, substrates, antibodies or ligands, such as control antibodies or ligands, and detection reagents. An optional instruction sheet can be additionally provided in the kits.

[0058] The engineered arenaviral immunogens of the invention can also be used as essential tools in many other clinical or research applications. These include, e.g., (a) discovering antibodies against ideal, conformational epitopes, (b) characterizing the desired types of antibodies in a discovery effort for immunotherapeutics or diagnostics, and (c) characterizing the desired types of antibody responses elicited by a vaccine or a natural infection. The most effective neutralizing and protective antibodies only bind pre-fusion GP. Without GPC stably engineered to be pre-fusion, one will not be able to identify or find those kinds of antibodies. The lack of this type of GPC is the reason why the skilled artisans in the field feel that T cell responses are the key correlate of immunity - they have never had stable prefusion GPC with which they might elicit the right antibody, nor did they have stable prefusion GPC by which they might evaluate if that kind of antibody had been generated in a patient or a vaccine. As a result, the artisans could only identify mediocre antibodies which don't provide sufficient protection. The engineered GPC of the present invention provide much better vaccines and tools that can be used to identify much better immunotherapeutics. EXAMPLES

[0059] The following examples are offered to illustrate, but not to limit the present invention.

Example 1 Engineered LASV GPC ectodomain mutant polypeptide GPCvsR4

[0060] Structure determination of an arenavirus GPC trimer has been previously hindered by metastability of the protein: the propensity of GP1 and GP2 to separate and for GP2 to spring into its post-fusion, six-helix bundle conformation. We genetically modified the LASV glycoprotein ectodomain by (1) making the point mutations R207C and G360C to covalently link GP1 and GP2 together, (2) introduction of a proline via an E329P mutation in the metastable region of HR1 of GP2, and (3) by replacing the native SIP GP1-GP2 cleavage site with a furin site (RRLL to RRRR) to enable efficient processing of the GP in Drosophila S2 cells (Fig. 1A). Among hundreds of modifications screened over ten years, these three, in combination, provided stable, crystallizable protein. Size-exclusion chromatography coupled to multiangle light scattering (SEC-MALS) and SDS-PAGE analysis of the resulting protein (termed GPCysR4) demonstrates the GP elutes as a monomer and that the protein is efficiently processed into GP1 and GP2 subunits, but that the two subunits remain associated (Fig. IB, C). Further, ELISA analysis with a panel of human antibodies demonstrates that GPCysR4 is recognized by neutralizing antibodies that require native association between the GP1 and GP2 subunits, and is not recognized by antibodies against post- fusion GP2 (Fig. ID). Together, these results suggest that GPCysR4 is in its native, precision state.

[0061] Monomelic GPCysR4 was incubated with excess Fab 37.7H and subjected to SEC-MALS analysis. SEC-MALS indicated the formation of trimeric GP-Fab complexes in addition to monomeric GP-Fab complexes (Fig. IB). Crystals of both the monomeric and trimeric fractions of the GPCysR4-Fab 37.7H complex formed in space group P0!22 and diffract to 3.2A with a trimer of GP bound to three Fabs in the asymmetric unit (Table 1). Phases were determined with an iterative approach using molecular replacement with a related Fab structure and the LCMV GP crystal structure. [0062] In addition to the R207C and G360C disulfide bond as seen in LASV GPCysR4 polypeptide (SEQ ID NO:2), other engineered disulfide pairs were also chosen based on the pre-fusion trimeric structure of LASV GP and chosen to meet bond angle and distance requirements for cysteine bond pairs. These include a G243C and I350C pair of mutations in polypeptide GPCysl3R4 (SEQ ID NO:3), a G98C and A330C pair of mutations in polypeptide GPCyslOR4 (SEQ ID NO:4), and an A132C and Q331C pair of mutations in polypeptide GPCysllR4 (SEQ ID NO:5).

Table 1. Data collection and refinement statistics for the LASV GPCysR4-Fab 37.7H complex structure

Example 2 Architecture of the trimer soluble LASV GPCvsR4 trimer

[0063] In the crystal structure the soluble LASV GPCysR4 trimer adopts a compact tripod shape that closely matches the tomographic reconstruction of the trimeric GPC spike from authentic Lassa virions. Notably, the arenavirus GP lacks a central three-helix fusion subunit core evident in other class I glycoproteins such as Ebola virus GP, HIV-1 Env and Influenza HA. Instead, the 1,775 A² of surface area buried on each LASV GP monomer at the trimeric interface arises from interactions between both the GP1 and GP2 subunits between monomers, particularly a-helices 1, 2 and 3; the C-terminal tail of GP1; and heptad repeat 1 (HR1) of GP2. Our recent work demonstrated that mutation of either S138 or LI 43 (Lassa numbering) to arginine prevented rescue of recombinant LCMV virions. In LASV, these residues lie at the trimeric interface on a2 and contact the GP1 C-terminus of the neighboring monomer. Hence, contacts observed to form the trimer interface in the crystal structure are essential for virus viability.

[0064] GPs of the arenavirus family are heavily glycosylated. Lassa GP has eleven potential N-linked glycosylation sites on each monomer, which together comprise -25% of the total mass of the protein. In the trimeric structure presented here, we can now visualize the location of each of these glycans. The 33 glycans in total shield the side and lower portions of the trimer, leaving only a few regions vulnerable to antibody binding ~ specifically, the β -sheet face where LAMP-1 and the New World arenavirus receptor Transferrin Receptor 1 (TfRl) bind, the fusion peptide and fusion loop and HR2 of GP2, and the trimeric interface. Modeling of the larger, complex-type glycans that would be present on the viral surface reinforces the significant effect glycosylation has on the neutralizing antibody evasion noted for the arenavirus family as a whole (McCormick et al., J. Med. Virol. 37, 1-7, 1992; Sommerstein et al, PLoS Pathog. 11, el 005276, 2015). Further, analysis of gly can-protein interactions in this structure reveals the molecular basis for the specific and strong influences of glycosylation on viral fitness. For example, Bonhomme et al. found that recombinant LCMV bearing a mutation to remove the N79 gly can site (Lassa numbering) was unable to be rescued. We find here that this glycan packs against the fusion peptide and may shield and provide stability to this highly hydrophobic region.

Example 3 Receptor binding in the context of the soluble LASV GPCvsR4 trimer

[0065] The overall structure of LASV GPCysR4 aligns well with the previously determined structure of the LCMV GP monomer with a 2A r.ms.d. over the entire structure and lA r.ms.d. over the core elements (β-sheets and a-helices of GP1 and all of GP2). Differences between the two structures outside the core can be mapped to three main regions: (1) the flexible loops connecting the upper, β-sheet face and the lower a-helical face of GP1, (2) the -20 C-terminal residues of GP1, and (3) the fusion peptide. In LCMV, the C-terminus of GP1 lies in close apposition to the N-terminus of GP2. In the LASV trimer, the C-terminus is translated 30 A, points away from GP2 into the apex of the trimer, and packs against al and ct2 of the neighboring monomer. Note that the ectodomain of LCMV GP (strain WE-HPI) assembled an unexpected, antiparallel dimer in solution and in crystals instead of a trimer. The location of the GP1 C terminus in the dimer is incompatible with trimerization. If a dimer form of the envelope glycoprotein exists during the arenavirus life cycle, for example during maturation, rearrangement of the GP1 C terminus would be necessary for GP to adopt its ultimate, trimeric assembly on the viral surface. Another difference between the dimeric LCMV and trimeric LASV structures is that in the dimer, the fusion peptide packs into the dimer interface and adopts a different conformation from that observed in the trimer.

[0066] Lassa virus employs extracellular and intracellular receptors for efficient entry into host cells. On the cell surface, the virus engages matriglycan on a- dystroglycan (a-DG) and other receptors. Residues involved in binding to a-DG (Hastie et al., Nat. Struc. Mo. Biol. 17, 23, 513-521, 2016; Smelt et al., J. Virol. 75, 448-457, 2001; Sullivan et al., Proc. Natl. Acad. Sci. USA, 108, 2969-2974, 2011; and Teng et al., J. Virol. 70, 8438-8443, 1996) can now be mapped in the context of the trimer. Interestingly, all of these residues are found at the trimeric interfaces, suggesting that LASV GP may need to be a trimer to interact with a-DG. Indeed, we previously observed that a-DG does not bind to the monomelic LCMV GP1 alone, although transferrin receptor 1 (TfRl) can bind to MACV GP1 alone. [0067] Once inside the cell, LASV binds to the lysosomal receptor LAMP1. A histidine triad (H92, H93 and H230) has been identified as important for pH-sensing and LAMP1 binding, and is located on the β-sheet face of GP1, which we locate on the upper and outer surfaces of the trimer. Comparison of this structure, of LASV GP1 in this prefusion assembly solved at pH 8, to the structure of LASV GP1, solved as an isolated subunit at pH 5, shows differences in the positions and interactions made by the three histidines. In this neutral-pH, prefusion complex, H92 is located on the underside of a β-sheet and makes a hydrogen bond with the main-chain oxygen of N90. In the low-pH structure of GP1 alone, H92 is instead oriented 180 degrees away from its location in the GP trimer and is unable to make the same hydrogen bond. In the neutral-pH, prefusion complex, H93 packs against N89, another glycan identified by Bonhomme, et al. as essential for LCMV rescue. In the low-pH structure of GP1 alone, H93 is in essentially the same location, but its interaction partner, N89, is shifted ~10A away. Presumably, the local environment experienced by these residues at neutral and low pH may alter the structural stability of the entire GP1 subunit and release its hold on GP2.

[0068] Other significant structural differences between the neutral pH complex and the low pH GP1 include elongation and rotation of al and ct2 from two antiparallel helices in GP1 of the neutral-pH prefusion complex to a single helix in the low-pH GP1 monomer, as well as rearrangement of residues 200-214 from a helix/loop structure in the prefusion complex to a two-stranded β-sheet in the low-pH monomer. Further, in the low pH GP1, the visible termini are T77 and S237, and both are oriented upwards, away from where GP2 would be. In the prefusion complex, residues 59-75 in the N- terminus form an extended β-strand, which assembles with strand β8 of the GP2 T loop, while residue S237 continues on to form a4 in the GP1 C-terminus. Hence, the helices, loops and C terminus of GP1 are flexible and adopt alternate positions when not bound by GP2.

[0069] Conformational changes in GP2 are well known during fusion. Based on these structural data however, is tempting to speculate that significant conformational changes also occur in GP1 during low pH-mediated LASV entry. Old and New World arenaviruses do not share a high sequence similarity for the GP1 subunit. They are, however, -60% identical in GP2, and share a similar structural organization of each GP1 and GP2 core. The similar organization of each subunit allows modeling of other arenavirus-receptor interactions in the context of the GPC trimer. Arenaviruses in the New World category bind TfRl as their cellular receptor, and a structure of MACV GP1 in complex with a TfRl monomer is available. MACV GP1 aligns with this prefusion LASV GP1 with 2.5 A r.ms.d. for the core, and modeling illustrates the relative positions of the TfRl binding sites relative to each other in the arenavirus trimer. Neutralizing antibodies are known against this TfRl -binding site for JUNV, and modeling of the JUNV-Fab complex into the LASV trimer assembly suggests that three such Fab fragments could bind in the context of the JUNV GPC trimer. Example 4 Structural definition of the anti-LASV 37.7H epitope

[0070] 37.7H is an antibody isolated from a Sierra Leonean survivor of Lassa fever. This antibody neutralizes viruses representing all four known lineages of LASV in vitro and offers protection from lethal LASV challenge in guinea pig models. The antibody simultaneously binds two GP monomers at the base of the GP trimer where it engages four discontinuous regions of LASV GP, two in "site A" and two in "site B". Site A contains residues 62-63 of the N-terminal loop of GP1 and residues 387-408 in the T-loop and HR2 of GP2. Site B contains residues 269-275 of the fusion peptide and residues 324-325 of HR1 of GP2. Antibody contacts here are numerous. At site A, CDR H2 contacts GP1, CDRs H2 and H3 together sandwich GP2 HR2, and CDR H3 projects a long finger into the groove between GP protomers. Further, at site A, CDRs LI and L3 also contact the loop between the T-loop and HR2. At site B, CDRs HI and H3 contact the fusion loop, while CDR L2 contacts both the fusion loop and HR1. In total, 37.7H buries 1620 A² of GP: ~1000A² of GP at site A and ~62θΑ² of GP at site B. Although nearly the entire surface buried on GP belongs to GP2, the presence of both GP1 and GP2 is critical for 37.7H recognition, likely because GP1 is required to maintain the proper prefusion conformation of GP2 for 37.7H binding.

Example 5 Antibody 37.7H neutralizes by stabilizing the pre-fusion GP 37

[0071] The quaternary nature and the involvement of the fusion peptide in the 37.7H epitope suggests this antibody neutralizes the virus by stabilizing GPC in the prefusion conformation, thereby preventing the conformational changes required for infection. To test this hypothesis, we analyzed the ability of LASV GP-pseudotyped VSV (rVSV-LASV GP) to mediate fusion with cell membranes. We first confirmed the ability of 37.7H to neutralize rVSV-LASV GP. Similar to previously published results, 37.7H effectively prevented cellular infection by rVSV-LASV GP, as did the antibody 12. IF, which binds to the upper, β-sheet face of LAS V GP1 and is presumed to block cell attachment. In contrast, antibodies 13.4E, which binds a linear epitope in the T- loop, and 9.7A, which is a non-neutralizing GPC-B antibody, did not prevent viral infection. Next, we determined whether 37.7H could prevent fusion of rVSV-LASV GP with cell membranes when exposed to low pH. Unlike the non-neutralizing antibodies 9.7A and 13.4E, which were not effective in preventing fusion, 37.7H reduced fusion by nearly 80% as compared to rVSV-LASV GP alone. In contrast, the neutralizing anti-GPl antibody 12. IF showed only a slight reduction in infectivity, suggesting the effect of 37.7H was strictly due to disruption in fusogenicity of the GPC and not attachment to cells.

[0072] Prior to exposure of the GP2 fusion peptide and loop and subsequent fusion of the viral and host-cell membranes, LASV GP1 engages LAMPl. Engagement of this receptor is thought to require conformational changes in GP1 that are triggered by exposure to the low pH in the endosome. Tomography of LASV spikes in the presence of low pH and LAMPl indeed shows an opening of the trimer compared to its neutral pH conformation. To determine whether or not 37.7H could prevent these

conformational changes, we analyzed the ability of GPCysR4 to bind to a soluble LAMPl-Fc fusion alone and when bound to Fab 37.7H. In the absence of Fab 37.7H, GPCysR4 effectively bound to LAMPl when exposed to low pH. In the presence of Fab 37.7H, however, interaction between GPCysR4 and LAMPl was markedly reduced. Note that the footprint of 37.7H and the footprint of LAMPl are separated by ~50A, and the angle adopted by the bound Fab fragments of 37.7H suggests it is unlikely to sterically interfere with LAMPl. Certainly, the Fc domain of a 37.7H IgG could provide potential steric hindrance to LAMPl interaction, but the reduction in LAMPl binding in the presence of the 37.7H Fab fragment alone suggests that it is the conformation of GP forced by Fab fragment binding which is not conducive to LAMPl interaction. Thus, there are likely to be conformational changes in GP1 required for LAMPl binding that are prevented by this human survivor antibody.

Taken together, these results demonstrate the probable mechanism of action for 37.7H, and probably other antibodies in its potent GPC-B competition group, is stabilization of the pre-fusion GPC trimer and prevention of the conformational changes required for binding of LAMP 1 and triggering of the GP2 fusion peptide and fusion loop in the endosome.

Example 6 GPC ectodomain based immunofiens for other arenaviruses

[0073] Employing the same structure-based design strategy used for producing engineered LASV immunogens as described above, we also created pre-fusion arenavirus GPC trimers from some other arenaviruses. These studies utilized sequence alignments and the Swiss-Model server (https://swissmodel.expasy.org; see also, e.g., Biasini et al., Nucl. Acids Res. 42:W252-8, 2014; and Schwede et al., Nucl. Acids Res. 31: 3381-3385, 2003). Regions of high sequence conservation were targeted and mutations chosen based upon appropriate bond angles and distances for cysteine pairs. Successful engineering for MACV includes H246C-L353C and N330P mutations. Successful engineering for JUNV includes H235C-L342C and N319P mutations. Successful engineering for LUJV includes R205C-L312C and R289P mutations.

Successful engineering for LCMV includes R249C-L356C and Q334P mutations. In some of the engineered polypeptides, a further modification is made to the protease cleavage site, similar to that introduced in LASV derived mutant GPC ectodomain polypeptide. Example 7 Material and methods

[0074] Expression and purification of LASV GPCysR4: The soluble ectodomain (residues 1-424) of the LASV GPC strain Josiah was modified to bear the dicysteine mutations R207C and G360C, the helix-breaking mutation E329P and the mutations L258R and L259R to alter the native SIP cleavage site to a furin protease cleavage site (termed LASV GPCysR4). GPCysR4 was fused to an enterokinase cleavage site followed by a dual strep II tag and cloned into the pMTpuro vector for stable expression in Drosophila S2 cells (Invitrogen, negative for mycoplasma). Cells were grown in shaker flasks to a density of 6-8x10⁶ cells/mL and expression was induced with 500μΜ CuSCk Expression was carried out for 4-6 days and protein was purified from the supernatant via streptactin-affinity chromatography. Streptactin-purified

GPCysR4 was treated overnight with EKMax (Invitrogen, catalog #E180-01, 0.5 units EKMax/mg GP) to remove the strepll tags, and then further purified by size-exclusion chromatography (SEC) using an S200increase column (GE Healthcare). [0075] Expression and purification of Fab 37.7H: 37.7H was produced in stable NS0 cells (ECACC 851 10503, negative for mycoplasma) as an IgGl as previously described (48) and purified from the supernatant via protein A-affinity chromatography. IgG was digested with 5% w/w papain for 4 hrs at 37C. The resulting Fab was purified from the Fc via a lambda select column (GE Healthcare) and F(ab')2 removed through SEC purification over a S75 10/300 column (GE Healthcare).

[0076] Antibody-GP complex formation: GPCysR4 was mixed in a 1:1.2 molar ratio with Fab 37.7H, allowed to form complexes for lhr and then purified by SEC using an S200increase column. Fractions corresponding to trimeric or monomelic complexes were pooled separately and used in subsequent crystallization trials.

[0077] Structure determination and refinement: Crystal screening of monomeric and trimeric GPCysR4-Fab 37.7H complexes, at 8-10 mg/mL, were carried out independently using sparse matrix screens and an Oryx crystallization robot (Douglas Instruments). Initial hits were further optimized in larger-scale formats and conditions refined. Notably, monomeric complexes formed in the same crystal condition as trimeric complexes. Final crystallization conditions of 0.1M Tris pH 8, 15-18% PEG 3350 and 0.1M-0.3M magnesium acetate produced hexagonal spears within 4-6hrs, growing to 0.3-0.5 μΜ overnight. Crystals were dehydrated by sequential soaking in increasing concentrations of PEG 3350 to a final PEG concentration of 25%. Crystals were then cryoprotected by sequential soaks in glycerol to a final concentration of 15% and flash-cooled in liquid nitrogen. Additional crystals of Cysl3-Fab 37.7H were grown in 0.1M Tris pH, 16% PEG 3350 and 0.2M magnesium acetate, screened at APS beamline 23-ID-D and diffract to 3.5A.

[0078] An initial data set at 3.8 A was collected at APS beamline 23-ID-D and later extended to 3.2A with data collected at SSRL beamline 12-2. Data were processed with XDS (49) (Table 1). Crystals were indexed in space group Ρ6Ϊ22 and contain a trimer of GP-Fab complexes in the asymmetric unit. Phases were obtained by an iterative approach using molecular replacement. The non-neutralizing anti-HIV-1 antibody N5- i5 (PDB: 3TNN) was identified as a suitable molecular replacement model through a blast search of the PDB database using the light chain of 37.7H. The trimmed variable domains of N5-i5 were placed first, followed by the constant domains. Lastly, a trimmed, poly-alanine model of LCMV GP (PDB: SINE) was used as a molecular search model for LASV GPCysR4. Rebuilding and refinement were performed using Coot, Phenix and Buster TnT. MolProbity and composite omit electron-density maps were used to validate the quality of the model. Privateer and PDBcare were used to detect discrepancies in glycan connectivity, nomenclature and glycosidic torsion angles. The final model contains residues 59-416 of GP monomer A, with disordered regions from 171-179, 209-210, 256-259 and 329-330; residues 59-418 of GP monomers B and C, with disordered regions from 170-179, 209-210, 256-259, 268-269 and 329-330 and Fab 37.7H residues 2-226 of the heavy chain (chains D, F and H), with a disordered region from 159-165 and residues 2-211 of the light chain (chains E, G and L).

Modeling of large glycans on the GP trimer was performed using the GlyProt server . Molecular surface and ribbon diagrams were generated using MacPyMOL.

Segmentation of the LASV GPC tomographic density, fitting of crystal structures into the tomographic maps were done in UCSF Chimera

[0079] SEC-MALS: Approximately 250ug of GP or GP-Fab complex was separated on an S200increase column (GE Healthcare) using an AKTA FPLC system (GE Healthcare). Size exclusion chromatography (SEC) was coupled in-line with the following calibrated detectors: 1) a MiniDawn Treos multi-angle light scattering (MALS) detector (Wyatt Corporation): and 2) an Optilab T-reX refractive index (RI) detector (Wyatt Corporation). The Astra VI software (Wyatt Corporation) was used to combine these measurements and allow the absolute molar mass of the eluting gl coprotein or glycoprotein-Fab complex to be determined.

[0080] Recombinant expression of LAMPl-Fc: Residues 29-351 of human LAMPl, fused to the rabbit Fc domain were cloned into the pHCMV3 vector, which was modified to contain an IgK signal sequence at the N-terminus (LAMPl-RbFc, a gift of S. Whelan, Harvard Medical School). LAMPl-RbFc was produced by transient transfection of 293T cells (ATCC CRL-3216, negative for mycoplasma). Protein was purified from the supernatant via protein A-affinity chromatography and subsequently dialyzed into 10 mM Tris pH 7.5, 150 mM NaCl.

[0081] ELISA analysis of LAMPl binding: LASV GPCysR4, either alone or in complex with Fab 37.7H, was diluted to O.Olmg/mL in 50mM NaCitrate pH 5, 150mM NaCl and incubated for lhr at RT prior to coating on ELISA plates (Corning,

Kennebunk, ME). After blocking with 3% BSA''50mM NaCitrate pH 5, 150mM NaCl, a dilution series of LAMPl-RbFc in 50mM NaCitrate pH 5, 150mM NaCl was bound to the coated protein for lhr. Wells were washed extensively with 50mM NaCitrate pH 5, 150mM NaCl and bound LAMPl-Fc was detected using a goat anti-Rabbit- IgG(H+L), mouse/Truman ads-HRP antibody (Southern Biotech, cat# 4050-05). \

[0082] Cells and Viruses: Human osteosarcoma U20S cells (ATCC HTB-96, negative for mycoplasma) were cultured at 37°C with 5% C02 in modified McCoy's 5 A medium (Thermo Fisher, Waltham, MA) supplemented with 10% fetal bovine serum (Gemini Bio-Products, Broderick, CA), 1% GlutaMAX (Thermo Fisher), and 1% penicillin-streptomycin (Thermo Fisher). Recombinant VSVs bearing the VSV G glycoprotein or the LASV GP glycoprotein were propagated on Vero cells (ATCC CRL-1586, negative for mycoplasma), as previously described (61, 62).

[0083] Neutralization Assay : Pre-titrated amounts of rVSV-LASV GP or rVSV G (MOI ~ 0.0125) were incubated in indicated concentrations of antibody at 37°C for lhr before addition to confluent U20S monolayers. Infection proceeded for 12-16hrs at 37°C in 5% C02 before cells were fixed in 4% paraformaldehyde. Cells were imaged using a Celllnsight CX5 imager (Thermo Fisher) and infection was quantitated by automated enumeration of cells expressing GFP.

[0084]

[0085] Some specific soluble LASV ectodomain polypeptide exemplified herein are listed below.

[0086] Sequence of soluble ectodomain (residues 1-424) of LASV GPC strain Josiah) (SEQ ID NO:l):

1 mgqivtffqe vphvieevmn ivlialsvla vlkglynfat cglvglvtfl llcgrsctts

61 lykgvyelqt lelnmetlnm tmplsctknn shhyimvgne tgleltltnt siinhkfcnl

121 sdahkknlyd halmsiistf hlsipnfnqy eamscdfhgg kisvqynlsh syagdaanhc 181 gtvang lqt fmrmawggsy ialdsgrgnw dcimtsyqyl iiqnttwedh cqfsrpspig 241 ylgllsqrtr diyisrrllg tftwtlsdse gkdtpggycl trwmlieael kcfgntavak

301 cnekhdeefc dmlrlfdf k qaiqrlkaea qmsiqlinka vnalindqli mknhlrdimg

361 ipycnysky w ylnhtttgrt slpkcwlvsn gsylnethfs ddieqqadnm itemlqkeym

421 erqg

[0087] Sequence of engineered soluble GPC immunogen (GPCysR4) (SEQ ID NO:2):

1 mgqivtffqe vphvieevmn ivlialsvla vlkglynfat cglvglvtfl llcgrsctts

61 lykgvyelqt lelnmetlnm tmplsctknn shhyimvgne tgleltltnt siinhkfcnl

121 sdahkknlyd halmsiistf hlsipnfnqy eamscdfhgg kisvqynlsh syagdaanhc 181 gtvang lqt fmrmawggsy ialdsgcgnw dcimtsyqyl iiqnttwedh cqfsrpspig 241 ylgllsqrtr diyisrrrrg tftwtlsdse gkdtpggycl trwmlieael kcfgntavak 301 cnekhdeefc dmlrlfdfhk qaiqrlkaga qmsiqlinka vnalindqli mknhlrdimc

361 ipycnysky w ylnhtttgrt slpkcwlvsn gsylnethfs ddieqqadnm itemlqkeym

421 erqg

[0088] Sequence of engineered soluble GPC immunogen (GPCy s 13R4) (SEQ ID NO:3):

1 mgqivtffqe vphvieevmn ivlialsvla vlkglynfat cglvglvtfl llcgrsctts

61 lykgvyelqt lelnmetlnm tmplsctknn shhyimvgne tgleltltnt siinhkfcnl

121 sdahkknlyd halmsiistf hlsipnfnqy eamscdfngg kisvqynlsh syagdaanhc 181 gtvangvlqt fmrmawggsy ialdsgrgnw dcimtsyqyl iiqnttwedh cqfsrpspig 241 ylcllsqrtr diyisrrrrg tftwtlsdse gkdtpggycl trwmlieael kcfgntavak

301 cnekhdeefc dmlrlfdfhk qaiqrlkaga qmsiqlinka vnalindqlc mknhlrdimg 361 ipycnysky w ylnhtttgrt slpkcwlvsn gsylnethfs ddieqqadnm itemlqkeym

421 erqg

[0089] Sequence of engineered soluble GPC immunogen (GPCy s 10R4) (SEQ ID NO:4):

1 mgqivtffqe vphvieevmn ivlialsvla vlkglynfat cglvglvtfl llcgrsctts

61 lykgvyelqt lelnmetlnm tmplsctknn shhyimvcne tgleltltnt siinhkfcnl

121 sdahkknlyd halmsiistf hlsipnfnqy eamscdfngg kisvqynlsh syagdaanhc 181 gtvangvlqt fmrmawggsy ialdsgrgnw dcimtsyqyl iiqnttwedh cqfsrpspig 241 ylgllsqrtr diyisrrrrg tftwtlsdse gkdtpggycl trwmlieael kcfgntavak

301 cnekhdeefc dmlrlfdfhk qaiqrlkapc qmsiqlinka vnalindqli mknhlrdimg

361 ipycnysky w ylnhtttgrt slpkcwlvsn gsylnethfs ddieqqadnm itemlqkeym

421 erqg

[0090] Sequence of engineered soluble GPC immunogen (GPCysl 1R4) (SEQ ID NO:5):

1 mgqivtffqe vphvieevmn ivlialsvla vlkglynfat cglvglvtfl llcgrsctts

61 lykgvyelqt lelnmetlnm tmplsctknn shhyimvgne tgleltltnt siinhkfcnl

121 sdahkknlyd hclmsiistf hlsipnfnqy eamscdfngg kisvqynlsh syagdaanhc 181 gtvangvlqt fmrmawggsy ialdsgrgnw dcimtsyqyl iiqnttwedh cqfsrpspig 241 ylgllsqrtr diyisrrrrg tftwtlsdse gkdtpggycl trwmlieael kcfgntavak

301 cnekhdeefc dmlrlfdfhk qaiqrlkaga cmsiqlinka vnalindqli mknhlrdimg

361 ipycnysky w ylnhtttgrt slpkcwlvsn gsylnethfs ddieqqadnm itemlqkeym

421 erqg quence of engineered soluble GPC immunogen (LCMV GPCysR4) (SEQ

[0092] Sequence of engineered soluble GPC immunogen (LUJV GPCysR4) (SEQ ID NO:9):

[0093] Sequence of engineered soluble GPC immunogen (MACV GPCysR4) (SEQ ID NO: 10):

[0094] Sequence of engineered soluble GPC immunogen (JUNV GPCysR4) (SEQ ID NO: 11):

***

[0095] The invention thus has been disclosed broadly and illustrated in reference to representative embodiments described above. It is understood that various

modifications can be made to the present invention without departing from the spirit and scope thereof. [0096] It is further noted that all publications, patents and patent applications cited herein are hereby expressly incorporated by reference in their entirety and for all purposes as if each is individually so denoted. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

Claims

WHAT IS CLAIMED IS:

1. An engineered arenavirus glycoprotein polypeptide, comprising the soluble ectodomain of an arenaviral GPC except for at least one modifications selected from the group consisting of (1) an engineered disulfide bond to covalently link GP1 and GP2, (2) a stabilizing missense substitution in the metastable region of HR1 of GP2, and (3) substitution of the native SIP cleavage site between GP1 and GP2 with a furin cleavage site.

2. The engineered arenavirus glycoprotein polypeptide of claim 1, comprising all three of said modifications.

3. The engineered arenavirus glycoprotein polypeptide of claim 1, wherein the stabilizing substitution is substitution with a Pro residue.

4. The engineered arenavirus glycoprotein polypeptide of claim 1, wherein the arenavirus is LASV.

5. The engineered arenavirus glycoprotein polypeptide of claim 4, wherein the soluble ectodomain is derived from LASV GPC strain Josiah and comprises a sequence that is at least 90% identical to SEQ ID NO: 1.

6. The engineered arenavirus glycoprotein polypeptide of claim 5, wherein the soluble ectodomain comprises a sequence shown in SEQ ID NO: 1 except for at least one modifications selected from the group consisting of (1) an engineered disulfide bond between modified residues R207C in GP1 and G360C in GP2, G243C in GP1 and I350C in GP2, G98C in GP1 and A330C in GP2, or A132C in GP1 and Q331C in GP2, (2) a Pro substitution E329P, and (3) SIP to furin cleavage site substitution

_RRLL256-₂59_→RRRR256-₂59

7. The engineered arenavirus glycoprotein polypeptide of claim 6, comprising all three of said modifications.

8. The engineered arenavirus glycoprotein polypeptide of claim 5, comprising a sequence that is at least 99% identical to a sequence selected from SEQ ID NOs:2-5.

9. The engineered arenavirus glycoprotein polypeptide of claim 5, comprising (1) mutations R207C in GP1 and G360C in GP2, G243C in GP1 and I350C in GP2, G98C in GP1 and A330C in GP2, or A132C in GP1 and Q331C in GP2, (2) mutation E329P or a conservative substitution thereof, and (3)

mutation or conservative substitutions thereof.

10. The engineered arenavirus glycoprotein polypeptide of claim 1, wherein the arenavirus is LCMV, wherein the stabilizing substitution is Gln→Pro, and wherein the SIP cleavage site substitution is

11. The engineered arenavirus glycoprotein polypeptide of claim 10, comprising (1) mutations R249C in GP1 and L356C in GP2, (2) mutation Q334P or a conservative substitution thereof, and (3) SIP cleavage site substitution RRLA^262"

12. The engineered arenavirus glycoprotein polypeptide of claim 11, comprising a sequence that is at least 90% identical to SEQ ID NO: 8.

13. The engineered arenavirus glycoprotein polypeptide of claim 1, wherein the arenavirus is JUNV, wherein the stabilizing substitution is Asn→Pro, and wherein the SIP cleavage site substitution is

14. The engineered arenavirus glycoprotein polypeptide of claim 13, comprising (1) mutations H235C in GP1 and L342C in GP2, (2) mutation N319P or a conservative substitution thereof, and (3) SIP cleavage site substitution RSLK^248"

15. The engineered arenavirus glycoprotein polypeptide of claim 14, comprising a sequence that is at least 90% identical to SEQ ID NO:9.

16. The engineered arenavirus glycoprotein polypeptide of claim 1, wherein the arenavirus is MACV, wherein the stabilizing substitution is Asn→Pro, and wherein the SIP cleavage site substitution is

17. The engineered arenavirus glycoprotein polypeptide of claim 16, comprising (1) mutations H246C in GP1 and L353C in GP2, (2) N330P or a conservative substitution thereof, and (3) SIP cleavage site substitution

18. The engineered arenavirus glycoprotein polypeptide of claim 17, comprising a sequence that is at least 90% identical to SEQ ID NO: 10.

19. The engineered arenavirus glycoprotein polypeptide of claim 1, wherein the arenavirus is LUJV, wherein the stabilizing substitution is Arg→Pro, and wherein the SIP cleavage site substitution is RSLK^218"221→RRRR²¹⁸-²²¹.

20. The engineered arenavirus glycoprotein polypeptide of claim 19, comprising (1) mutations R205C in GP1 and L312C in GP2, (2) mutation R289P or a conservative substitution thereof, and (3) SIP cleavage site substitution RSLK^{218" 221}→RRRR^218"221

21. The engineered arenavirus glycoprotein polypeptide of claim 20, comprising a sequence that is at least 90% identical to SEQ ID NO: 11.

22. A purified or isolated polynucleotide encoding the engineered arenavirus glycoprotein polypeptide of claim 1.

23. An expression vector harboring the polynucleotide of claim 22.

24. An arenavirus vaccine composition, comprising an engineered arenavirus glycoprotein immunogen, wherein the engineered arenavirus glycoprotein immunogen comprises the soluble ectodomain of an arenavirus GPC except for at least one modifications selected from the group consisting of (1) an engineered disulfide bond to covalently link GP1 and GP2, (2) a stabilizing missense substitution in the metastable region of HR1 of GP2, and (3) substitution of the native SIP cleavage site between GP1 and GP2 with a furin cleavage site.

25. The arenavirus vaccine composition of claim 24, wherein the soluble ectodomain consists of a sequence that is at least 90% identical to SEQ ID NO: 1, and wherein the engineered disulfide bond is between modified residues R207C in GP1 and G360C in GP2, G243C in GP1 and I350C in GP2, G98C in GP1 and A330C in GP2, or A132C in GP1 and Q331C in GP2, wherein the stabilizing substitution is E329P, and wherein the SIP to furin cleavage site substitution is RRLL²⁵⁶-²⁵⁹→RRRR²⁵⁶-²⁵⁹.

26. The arenavirus vaccine composition of claim 24, wherein the engineered arenavirus glycoprotein immunogen comprises all three of said modifications and a sequence that is at least 90% identical to a sequence selected from SEQ ID NOs:2- 5.

27. The arenavirus vaccine composition of claim 24, wherein the engineered arenavirus glycoprotein immunogen comprises (1) the soluble ectodomain of LCMV GPC, wherein the engineered disulfide bond is between modified residues R249C-L356C, the stabilizing substitution is Q334P, and the SIP to furin cleavage site substitution is RRLA^{262 265} to RRRR^{262 265}, (2) the soluble ectodomain of MACV GPC, wherein the engineered disulfide bond is between modified residues H246C-L353C, the stabilizing substitution is N330P, and the SIP to furin cleavage site substitution is RSLK^259"262 to RRRR^259"262, (3) the soluble ectodomain of JU V GPC, wherein the engineered disulfide bond is between modified residues H235C-L342C, the stabilizing substitution is N319P, and the SIP to furin cleavage site substitution is RSLK^248"251 to RRRR^248"251, or (4) the soluble ectodomain of LUJV GPC, wherein the engineered disulfide bond is between modified residues R205C-L312C, the stabilizing substitution is R289P, and the SIP to furin cleavage site substitution is RSLK^218"221 (SEQ ID NO:13) to RRRR^{218 221}.

28. The arenavirus vaccine composition of claim 24, wherein the engineered arenavirus glycoprotein immunogen comprises all three of said modifications and a sequence that is at least 90% identical to a sequence selected from SEQ ID NOs:8- 11.

29. A method of preventing an arenavirus infection in a subject, comprising administering to the subject a therapeutically effective amount of the immunogen of claim 1 or the vaccine composition of claim 24, thereby preventing arenavirus infection in the subject.

30. A method of treating an arenavirus infection or eliciting an immune response against an arenavirus in a subject, comprising administering to the subject a pharmaceutical composition comprising a therapeutically effective amount of the immunogen of claim 1 or the vaccine composition of claim 24, thereby treating the arenavirus infection or eliciting an immune response against the arenavirus in the subject.

31. The method of claim 30, wherein the arenavirus is LASV, LCMV, JUNV, MACV or LUJV.