EP4626470A2 - Vaccines containing novel nanoparticle scaffolds - Google Patents

Abstract

The present invention provides novel engineered nanoparticle scaffold sequences that are derived from the 13-01 protein. Relative to the known 13-01 protein or variants thereof, the novel 13-01 derived scaffold sequences of the invention contain an extended N-terminal helix. Also provided in the invention are vaccine constructs that contain various immunogenic proteins displayed on the novel nanoparticle scaffold sequences described herein. The vaccine constructs of the invention include, e.g., nanoparticles displaying tandem repeats of influenza M2e proteins or HCV E2 core proteins.

Description

Attorney Docket No.: TSRI 2189.1PC VACCINES CONTAINING NOVEL NANOPARTICLE SCAFFOLDS CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The subject patent application claims the benefit of priority to U.S. Provisional Patent Application Number 63/385,224 (filed November 29, 2022; now pending). The full disclosure of the priority application is incorporated herein by reference in its entirety and for all purposes. SEQUENCE LISTING [0002] This application includes by incorporation of reference a sequence listing in the XML format, 2189_1PC_Sequence Listing, which was created on November 9, 2023 and contains 37 KB in content. BACKGROUND OF THE INVENTION [0003] Influenza viruses (IAVs) belong to the Orthomyxoviridae family and can be classified into four types: A, B, C, and D. All influenza viruses are enveloped negative- sense single-stranded RNA viruses with a segmented genome, with influenza A and B viruses (IAV and IBV) containing 8 gene segments, which encode for at least 17 proteins. The most abundant surface glycoprotein, hemagglutinin (HA), allows the virus to bind to the host cell receptors and mediates the cell entry. Neuraminidase (NA) aids in the release of viral particles through cleavage of residues on the host cell’s surface. Matrix-1 protein (M1) aids in the budding of the virus from the plasma membrane of infected cells, and matrix-2 protein (M2) facilitates the maintenance of pH during viral entry and viral replication in host cells. IAVs can be further classified by subtype, based on the antigenic properties of the two surface glycoproteins, HA (HA1-18) and NA (NA1-11). IAVs can infect many hosts, whereas IBVs are restricted to humans and have diverged into two lineages (Victoria and Yamagata) through the intra-host evolution. Influenza viruses of avian origin recognize α-2,3 sialic acid receptors, whereas human influenza viruses bind preferably to α-2,6 sialic acid receptors in the upper respiratory tract. Influenza virus utilizes two mechanisms to evade the immune system. Antigenic drift consists of small changes introduced into HA and NA under the immune pressure and is the cause of annual epidemics of human influenza. Antigen shift occurs when a complete change in HA and/or NA genes occurs in IAVs due to their large animal reservoirs. Antigen shift results in novel IAV strains with increased transmission in humans and is a major cause of pandemics. [0004] Since the 1940s, seasonal influenza vaccines have been used as an efficient and cost-effect tool to minimize influenza epidemics and improve public health. Current vaccines use inactivated or live-attenuated strains. The most common types of inactivated virus vaccines are referred to as split vaccines where detergents or chemicals are used to disrupt viral particles. Live-attenuated vaccines use cold-adapted live viruses that do not replicate at human body temperature and are generally administered intranasally to induce strong local immunity. Subunit vaccines utilize viral HA or NA proteins that are partially purified after chemical or detergent splitting. Virus strains selected for quadrivalent vaccines, which contain an H1N1, H3N2, and two Flu B strains are produced in chicken eggs. However, due to the influenza virus’ propensity for mutation and immune evasion, current influenza vaccines must be updated yearly to include predicted strains. Strain mismatch often results in low efficacy, highlighting the need for better vaccines. [0005] A strong unmet need exists in the medical field for more reliable and effective influenza vaccines. The instant invention is directed to this and other unmet needs in the art. SUMMARY OF THE INVENTION [0006] In one aspect, the invention provides N-terminally extended I3-01 nanoparticle scaffold sequence. These scaffold sequences contain an extended N- terminal helix relative to the N-terminal helix in the original or wildtype I3-01 scaffold sequence. In some embodiments, the novel I3-01 derived NP scaffold sequences of the invention contain a heterologous helical motif of about 6 to about 12 amino acid residues that is fused to the N-terminus of the I3-01 scaffold sequence set forth in SEQ ID NO:27 (I3-01v9). In some of these embodiments, the inserted heterologous helical motif contains AKLAEELQK (SEQ ID NO:25), a conservatively modified variant or a substantially identical sequence thereof. Some of the N-terminally extended I3-01 nanoparticle scaffold sequences of the invention contain SEQ ID NO:4, a conservatively modified variant or a substantially identical sequence thereof. In a related aspect, the invention provides self-assembling nanoparticles that are formed with the novel N-terminally extended I3-01 nanoparticle scaffold sequences of the invention. [0007] In another aspect, the invention provides nanoparticle vaccine constructs that contain an immunogenic protein or a polypeptide immunogen that is fused to an N- terminally extended I3-01 nanoparticle scaffold sequence. The N-terminally extended I3-01 nanoparticle scaffold sequence in these NP vaccine constructs contains an extended N-terminal helix relative to the N-terminal helix in the original or wildtype I3- 01 scaffold sequence. In some of these vaccine constructs, the N-terminally extended I3-01 nanoparticle scaffold sequence contains a heterologous helical motif of about 6 to about 12 amino acid residues that is fused to the N-terminus of the I3-01 scaffold sequence set forth in SEQ ID NO:27 (I3-01v9). In some embodiments, the extending heterologous helical motif contains AKLAEELQK (SEQ ID NO:25), a conservatively modified variant or a substantially identical sequence thereof. In some vaccine constructs, the N-terminally extended I3-01 nanoparticle scaffold sequence contains SEQ ID NO:4, a conservatively modified variant or a substantially identical sequence thereof. Typically, the displayed immunogenic protein in the vaccine constructs is fused via a linker at its C-terminus to the N-terminus of the N-terminally extended I3-01 nanoparticle scaffold sequence. In some embodiments, the employed linker contains GGGGS (SEQ ID NO:3). [0008] In some vaccine constructs of the invention, the displayed polypeptide immunogen is an influenza fusion polypeptide containing 2 or more tandem repeats of influenza M2 protein ectodomain (M2e). In some other constructs, the displayed polypeptide immunogen is an HCV immunogenic protein. In some embodiments, the displayed tandem influenza M2e repeats are separated by a peptide spacer, e.g., GGGG (SEQ ID NO:9). In some of the influenza vaccine constructs, at least one of the displayed M2e tandem repeats contains missense mutations at the conserved Cys17 and Cys19 residues. In some of these embodiments, the missense mutations contain substitutions of each of the two Cys residues with an amino acid residue with uncharged polar side chains. In various embodiments, each of the Cys residues is independently replaced with an amino acid residue selected from the group consisting of serine, glycine, asparagine, glutamine, threonine and tyrosine. In some preferred embodiments, the two Cys residues in the same M2e sequence are both replaced with Ser. [0009] In some influenza vaccines of the invention, the displayed immunogenic protein contains 3 tandem M2e sequences. In some of these embodiments, the 3 tandem M2e sequences are independently a human M2e sequence, an avian/swine consensus M2e sequence, or a human/swine consensus M2e sequence, except for missense mutations at residues Cys17 and Cys19 in at least 2 of the 3 tandem M2e sequences. In some of these embodiments, the displayed influenza fusion polypeptide contains, in any order, a human M2e (SEQ ID NO:2), an avian/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:30), and a human/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:31). In some embodiments, the displayed influenza M2e tandem repeat fusion polypeptide contains, in any order, a human M2e with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:29), an avian/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:30), and a human/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:31). In some embodiments, the displayed influenza M2e tandem fusion polypeptide contains SEQ ID NO:23, SEQ ID NO:24, a conservatively modified variant or a substantially identical sequence thereof. Some of these influenza vaccine constructs contain a subunit or scaffold sequence shown in SEQ ID NO:11, SEQ ID NO:12, a conservatively modified variant or a substantially identical sequence thereof. [0010] Other than the immunogenic protein sequence, the novel I3-01 scaffold based vaccine constructs of the invention can additionally include a locking domain and a T-cell epitope at the C-terminus. For example, they can contain at the C-terminus the locking domain shown in SEQ ID NO:5 and the T-cell epitope shown in SEQ ID NO:6. Some of these vaccine constructs contain a subunit or scaffold sequence shown in SEQ ID NO:14, SEQ ID NO:15, a conservatively modified variant or a substantially identical sequence thereof. Some vaccine constructs of the invention can additionally include an N-terminal leader sequence. Some of these vaccine constructs contain a subunit or scaffold sequence shown in SEQ ID NO:17, SEQ ID NO:18, a conservatively modified variant or a substantially identical sequence thereof. Some vaccine constructs of the invention can additionally include an N-terminal leader sequence, and a locking domain and a T-cell epitope at the C-terminus. Some of these vaccine constructs contain a subunit or scaffold sequence shown in SEQ ID NO:20, SEQ ID NO:21, a conservatively modified variant or a substantially identical sequence thereof. [0011] In some vaccine constructs of the invention, the displayed immunogenic protein is an HCV immunogen, e.g., an E2 core or an E1E2 dimer protein. In some of these embodiments, the displayed protein contains a HCV E2 core as shown in any one of SEQ ID NOs:32-35. In some embodiments, the displayed HCV immunogenic protein contains a tandem copy of 2 E2 core sequences. In some of these embodiments, the 2 E2 core sequences are from different HCV isolates. For example, the 2 tandem E2 core sequences can respectively contain SEQ ID NOs:32 and 33, or SEQ ID NOs:34 and 35. Some of the HCV vaccine constructs of the invention additionally contain a locking domain and a T-cell epitope at the C-terminus. For example, the vaccine constructs can include the locking domain shown in SEQ ID NO:5, and/or the T-cell epitope shown in SEQ ID NO:6. Some of these HCV vaccines contain a subunit or scaffold sequence that has from the N-terminus to the C-terminus different structural motifs respectively shown in (a) SEQ ID NO:4, SEQ ID NO:32, SEQ ID NO:33, SEQ ID NO:5 and SEQ ID NO:6, or (b) SEQ ID NO:4, SEQ ID NO:34, SEQ ID NO:35, SEQ ID NO:5 and SEQ ID NO:6. Some other constructs contain a subunit or scaffold sequence that is a conservatively modified variant or substantially identical sequence of one of these exemplified scaffold sequences. [0012] In another aspect, the invention provides polynucleotide sequences that encode the subunit or scaffold sequence of one of the nanoparticle vaccine constructs described herein. Vectors or expression constructs harboring one or more of these polynucleotide sequences are also encompassed by the invention. Further provided in the invention are pharmaceutical compositions or kits that contain the nanoparticle vaccine constructs or the encoding polynucleotide sequences described herein. [0013] 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 [0014] Figure 1. Rational design of I3-01v9a to achieve the optimal display of monomeric antigens on the nanoparticle (NP) surface. Full amino acid sequence (SEQ ID NO:4) of the I3-01v9a scaffold is shown. [0015] Figure 2. (A) Construct design of HCV E2 core I3-01v9a nanoparticles. Restriction site and linker between the E2 core and the nanoparticle scaffold are indicated (SEQ ID NO:36). (B) EM images of three HCV E2 core I3-01v9a nanoparticles. (C) Construct design of HCV tandem E2 core I3-01v9a nanoparticles. Connecting sequences between the 2 E2 cores (SEQ ID NO:3) and between the second E2 core and the nanoparticle scaffold (SEQ ID NO:36) are shown. (D) SEC and EM analyses of two tandem E2 core I3-01v9a nanoparticles. SEC profiles for two expression volumes in ExpiCHO cells: 50ml vs 200ml. [0016] Figure 3. (A) M2e-based vaccine construct design. Left: hM2e structure and sequence (SEQ ID NO:2). Middle: model of the hM2e-5GS-1TD0 trimer; Right: models of hM2e-5GS-FR, hM2e-5GS-E2p-LD4-PADRE, and hM2e-5GS-I3-01v9a- LD7-PADRE 1c-SApNPs. (B) Schematic representation of 1c-SApNP expression and purification. (C) SEC profiles of hM2e trimer and 1c-SApNPs. (D) Micrographs of Fab148-purified hM2e 1c-SApNPs by negative-stain EM.. [0017] Figure 4. (A) Mouse immunization/challenge schedule. (B) Survival and weight loss after A/Puerto Rico/8/1934 (PR8) H1N1 virus challenge. (C) Survival and weight loss after A/Hong Kong/1/1968 (HK68) H3N2 virus challenge. (D) ELISA of hM2e-specific antibody responses in mouse sera against an hM2e probe. [0018] Figure 5. (A) Negative-stain EM images of tandem M2e 1c-SApNPs. A M2ex3-5GS-FR sample that was held at 70°C for 10 min showed no visible change in structure and bound to anti-M2e antibodies with nearly identical affinity. (B) Survival and weight loss for the Alum adjuvant groups after A/Puerto Rico/8/1934 (PR8) H1N1 virus challenge. (C) Survival and weight loss for the AddaVax adjuvant groups after A/Puerto Rico/8/1934 (PR8) H1N1 virus challenge. DETAILED DESCRIPTION I Overview [0019] Various antigens and vaccine strategies have been explored to develop universal flu vaccines. The most common antigen is HA, with recent vaccine design effort focusing on the conserved stem region or conserved epitopes within the head domain. These approaches include using headless HA, chimeric HA, and mosaic HA. NA is also an attractive target of broadly neutralizing antibodies (bNAbs) to seasonal and pandemic strains. The ectodomain of M2 protein (M2e) is a highly conserved target for universal IAV vaccines. Although M2e is small (~23 aa) and non-immunogenic, it can be attached to large carriers to elicit cross-protection and reduce virus replication. Internal proteins such as nucleoprotein and M1 have been explored for T cell targeting. The use of adjuvants, such as MF59 and AS03, has been shown to significantly improve the efficacy of influenza vaccines. Therefore, adjuvant effect must be carefully examined in the development of universal flu vaccines to target the subdominant HA stem and M2e. [0020] M2e-based vaccines confer protection via mechanism such as antibody- dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP), which eliminate virus-infected cells. M2e has been attached to various carriers for vaccine development. One of the early M2e vaccines used hepatitis B core protein (HBc) as a carrier. Tobacco mosaic virus (TMV) coat protein, keyhole limpet hemocyanin (KLH), rotavirus NSP4, GCN4, bacterial flagellin, and liposome have since been tested in M2e vaccine development. As the search for better carriers continued, a number of vaccine candidates were advanced to human trials, thus providing critical feedback for future M2e vaccine development. The adjuvanted M2e-HBc fusion protein induced anti-M2e antibodies in 90% of the cases and was well tolerated in the Phase-I trial (clinicaltrials.gov: NCT00819013). However, the vaccine induced anti-M2e antibody response declined rapidly. The M2e-flagellin fusion vaccine was highly immunogenic but caused undesirable side effects, such as fever, diarrhea, fatigue, headache, and muscle pain, at higher doses in the Phase-I trial (clinicaltrials.gov NCT00921206). The vaccine that combines M2e with multiple cytotoxic T lymphocyte (CTL) epitopes could stimulate strong cellular immunity in humans (clinicaltrials.gov: NCT01181336), but the T cell response was narrow and slow, making this vaccine unsuitable in the event of an emerging pandemic. Therefore, the carrier, the adjuvant, and the right balance between antibody and T-cell responses, are the major challenges facing M2e vaccine development. [0021] The present inventors designed multilayered single-component self- assembling protein nanoparticles (1c-SApNP) based on E2p and I3-01, two bacterial proteins that self-assemble into 60-mers of 22-25 nm, as carriers of foreign antigens for vaccine development. These 1c-SApNPs have been applied successfully to HIV-1, HCV, Ebola virus (EBOV), and SARS-CoV-2 to create nanoparticle vaccines. Among the embodiments described herein, the invention encompasses novel I3-01 derived NP platforms that have demonstrated activities for presenting immunogenic proteins such as influenza M2e proteins and HCV immunogens. The invention also encompasses broadly protective vaccines that contain immunogenic proteins (e.g., HCV E2 core proteins and influenza M2e proteins) displayed on the novel NP scaffolds. Details for making and using the compositions and methods encompassed by the invention are described below. [0022] The nanoparticle scaffolds and vaccine constructs described can have various applications in clinical setting. For example, the novel I3-01 derived NP scaffolds described herein, e.g., I3-01v9a (SEQ ID NO:4), can be used to present various other monomeric antigens in addition to HCV and influenza immunogenic proteins exemplified herein. The vaccines thus constructed, such as the HCV vaccines or tandem hM2e vaccines as exemplified herein, can be used as broadly protective vaccines. Using influenza vaccine as an example, they can be added to seasonal vaccines (e.g., HCV or influenzas vaccines) as a “performance enhancer” to improve protection against endemic (human strains) and pandemic (swine and avian strains) influenza viruses. In other applications, the novel I3-01 scaffold based vaccines (e.g., M2e displaying vaccines) can be combined with other vaccine modalities, e.g., hemagglutinin (HA) stem-based vaccines, to create truly universal influenza vaccines. [0023] The vaccines of the invention also have a number of advantageous properties relative to related vaccines known in the art. Using influenza vaccines for illustration, the uniform distribution and the just-above-sea-level exposure of antigen anchoring sites on the surface make the novel I3-01 scaffolds described herein ideal nanoparticle platforms for presenting monomeric antigens. The icosahedral symmetry and dense surface display make 1c-SApNPs ideal carriers for multivalent display of a suitable antigen, e.g., influenza M2e. Being a single segment or a tandem construct design, it can be optimally displayed on the nanoparticle surface and can generate high- quality antibody responses. Additionally, the genetic fusion combined with self- assembly will result in robust production of 1c-SApNPs in laboratory and industrial settings. As demonstrated herein, the vaccines can be produced in ExpiCHO cells with reasonable yield and extremely high purity after immunoaffinity (Fab148) purification. Since CHO is one of the principal mammalian cell lines used for industrial manufacture of protein therapeutics and vaccines and ExpiCHO is a transient version of this CHO cell line, the vaccines obtained from ExpiCHO cells (e.g., influenza M2e vaccines) are expected to have the same properties as those from industrial CHO cell lines. This will enable the GMP manufacturing of the 1c-SApNP vaccines for human use. Furthermore, the multilayered structure will ensure the thermostability of the 1c-SApNPs (e.g., influenza M2e 1c-SApNPs) and allow various delivery routes and combined use with other related vaccines. As exemplified herein, the high-temperature hold at 70°C for 10 min did not cause any structural change and ELISA showed nearly identical binding to M2e-specific antibodies such as Fab65 and Fab148. The superior thermostability of the 1c-SApNPs of the invention (e.g., influenza M2e 1c-SApNPs) will allow them to be used in harsh conditions such as embedded in self-dissolvable microneedles for transdermal immunization. [0024] Unless otherwise specified herein, the various compositions and methods of the invention 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 and Molecular 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 A 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 Env-derived trimer" can refer to both single or plural Env-derived trimer molecules, and can be considered equivalent to the phrase "at least one Env-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. Unless otherwise noted, the term “vaccine immunogen” is used interchangeably with “protein antigen” or “immunogen polypeptide.” [0028] The term "conservatively modified variant" applies to both amino acid and nucleic acid sequences. With respect to particular nucleic acid sequences, conservatively modified variants refers to those nucleic acids which encode identical or essentially identical amino acid sequences, or where the nucleic acid does not encode an amino acid sequence, to essentially identical sequences. Because of the degeneracy of the genetic code, a large number of functionally identical nucleic acids encode any given protein. For polypeptide sequences, “conservatively modified variants” refer to a variant which has conservative amino acid substitutions, amino acid residues replaced with other amino acid residue having a side chain with a similar charge. Families of amino acid residues having side chains with similar charges have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). [0029] 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. [0030] 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 seasonal flu. For instance, this can be the amount necessary to inhibit viral replication or to measurably alter outward symptoms of the viral infection, such as increase of T cell counts in the case of an influenza infection. In general, this amount will be sufficient to measurably inhibit viral replication or infectivity. When administered to a subject, a dosage will generally be used that will achieve target tissue concentrations (for example, in lymphocytes) that has been shown to achieve in vitro inhibition of viral replication. In some embodiments, 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 influenza infection. In some embodiments, an effective amount is a therapeutically effective amount. In some embodiments, 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 the disease. [0031] 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). For example, the amino acid sequence of an enzyme of anaerobic bacteria Thermotoga maritima, from which the I3-01 NP scaffolds are derived, is not naturally joined via a peptide bond to the amino acid sequences of influenza M2e or HCV E2 core. [0032] 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. [0033] 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 embodiments, 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. [0034] 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. [0035] As used herein, amino acid numbering or amino acid numbering system refers to the numbering or linear positions of amino acid residues in an immunogenic protein or polypeptide (e.g., influenza M2e) from a prototype strain or species. With a normalized sequence alignment, it allows comparison of the sequences of different orthologs of the same immunogenic protein (e.g., M2e) from other strains or species, or engineered versions of the same protein described herein with that of the prototype sequence. Utilizing such a standard or normalized amino acid numbering, conserved amino acid residues in the immunogenic proteins from various viral strains or engineered proteins can be readily identified and designated. For example, unless otherwise noted herein, amino acid numbering of the M2e protein can be based on the consensus sequence of human influenza M2e protein. With this numbering, the conserved Cys residues to be mutated are referred to as residues Cys17 and Cys19 for all influenza strains. [0036] 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. Two sequences are "substantially identical" if two sequences have a specified percentage of amino acid residues or nucleotides that are the same (i.e., 60% identity, optionally 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99% identity over a specified region, or, when not specified, over the entire sequence), when compared and aligned for maximum correspondence over a comparison window, or designated region as measured using one of the following sequence comparison algorithms or by manual alignment and visual inspection. Optionally, the identity exists over a region that is at least about 50 nucleotides (or 10 amino acids) in length, or more preferably over a region that is 100 to 500 or 1000 or more nucleotides (or 20, 50, 200 or more amino acids) in length. [0037] 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., an influenza 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. In some embodiments of the invention, vaccines or vaccine immunogens or vaccine compositions are expressed from fusion constructs and self-assemble into nanoparticles displaying an immunogen polypeptide or protein on the surface. [0041] A vaccine (e.g., an influenza or HCV vaccine) refers to an immunogenic composition capable of stimulating an immune response, administered for the prevention, amelioration, or treatment of a disease or infection (e.g., influenza virus infection). A vaccine may include, for example, attenuated or killed (e.g., split) pathogen (e.g., a virus), virus-like particles (VLPs) and/or antigenic polypeptides or DNA derived from them, or any recombinant versions of such immunogenic materials. [0042] Virus-like particle (VLP) refers to a non-replicating, viral shell, derived from any of several viruses. VLPs are generally composed of one or more viral proteins, such as, but not limited to, those proteins referred to as capsid, coat, shell, surface and/or envelope proteins, or particle-forming polypeptides derived from these proteins. VLPs can form spontaneously upon recombinant expression of the protein in an appropriate expression system. Methods for producing particular VLPs are known in the art. The presence of VLPs following recombinant expression of viral proteins can be detected using conventional techniques known in the art, such as by electron microscopy, biophysical characterization, and the like. See, for example, Baker et al. (1991) Biophys. J.60:1445-1456; and Hagensee et al. (1994) J. Virol.68:4503-4505. For example, VLPs can be isolated by density gradient centrifugation and/or identified by characteristic density banding. Alternatively, cryoelectron microscopy can be performed on vitrified aqueous samples of the VLP preparation in question, and images recorded under appropriate exposure conditions. [0043] A self-assembling nanoparticle refers to a ball-shape protein shell with a diameter of tens of nanometers and well-defined surface geometry that is formed by identical copies of a non-viral protein capable of automatically assembling into a nanoparticle with a similar appearance to VLPs. Known examples include ferritin (FR), which is conserved across species and forms a 24-mer, as well as B. stearothermophilus dihydrolipoyl acyltransferase (E2p), Aquifex aeolicus lumazine synthase (LS), I3-01 derived variants, and Thermotoga maritima encapsulin, which all form 60-mers. Self- assembling nanoparticles can form spontaneously upon recombinant expression of the protein in an appropriate expression system. Methods for nanoparticle production, detection, and characterization can be conducted using the same techniques developed for VLPs. III. Novel NP scaffolds with improved activities [0044] The invention provides novel nanoparticle scaffold sequences that are suitable for presenting various viral immunogenic proteins for eliciting potent neutralizing antibody responses. These rationally designed and functionally tested scaffold sequences are based on the I3-01 protein. I3-01 is an engineered protein (SEQ ID NO:22) that can self-assemble into hyperstable nanoparticles. The original (“un- extended” or “wildtype”) I3-01 protein was described in Hsia et al., Nature 535, 136- 139, 2016. Several hyperstable nanoparticle scaffolds derived from I3-01 were previously developed and employed for presenting viral proteins such as that from HIV-1 and HCV. See, e.g., WO21/021603, WO22/035739, US Patent No.10,906,944, and WO19/089817. To identify novel NP scaffolds with improved activities, the inventors rationally designed and functionally tested the known I3-01 variant scaffolds. The original I3-01 protein and variants known in the art (i.e., un-extended I3-01 scaffold sequences) contain a N-terminal helix motif, KMEELFKKHK (SEQ ID NO:26). The novel scaffold sequences of the invention were obtained by extending the N-terminal helix of the existing I3-01 variant scaffolds, e.g., I3-01v9 (SEQ ID NO:27), via grafting a heterologous helical motif, followed by rational design with an ensemble- based protein design program. An example of the novel scaffolds is I3-01v9a (SEQ ID NO:4), as exemplified herein. As described in more detail in the Examples, the resulting novel variant I3-01 scaffolds (e.g., SEQ ID NO:4) are able to provide the optimal surface display of monomeric protein antigens. [0045] I3-01 sequence without the first Met residue (SEQ ID NO:22) (N-terminal helix underlined): KMEELFKKHKIVAVLRANSVEEAKKKALAVFLGGVHLIEITFTVPDADTVIKEL SFLKEMGAIIGAGTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMP GVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNL DNVCEWFKAGVLAVGVGSALVKGTPVEVAEKAKAFVEKIRGCTE [0046] In various embodiments, the novel I3-01 derived NP scaffolds of the invention contains an I3-01 variant sequence (e.g., SEQ ID NO:27) except for the addition of a helix motif of about 6 to about 12 amino acid residues at the N-terminus. This inserted helical motif leads to extension of the original N-terminal helix KMEELFKKHK (SEQ ID NO:26) in the I3-01 protein. In some embodiments, the inserted helical motif contains AKLAEELQK (SEQ ID NO:25), a conservatively modified variant or a substantially identical sequence thereof. [0047] I3-01v9 (SEQ ID NO:27) (N-terminal helix underlined): [0048] KMEELFKKHKIVAVLRANSVEEAKMKALAVFVGGVHLIEITFTVPD ADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEK GVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVP TGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTE [0049] I3-01v9a (SEQ ID NO:4) (extension of N-terminal helix underlined): [0050] AKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFVGGV HLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVSPHL DEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAM KGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKAAAF VEKIRGCTE [0051] In various embodiments, the novel I3-01 derived NP scaffolds of the invention contain SEQ ID NO:4, a conservatively modified variant or a substantially identical sequence thereof (e.g., at least 90%, 95%, 96%, 97%, 98% or 99% identical). In some of these embodiments, the helical motif inserted at the N-terminus is identical to SEQ ID NO:25, while the rest of the scaffold sequence is a conservative modified variant or a substantially identical sequence of SEQ ID NO:27. In some other embodiments, the entire extended N-terminal helix of the novel I3-01 variant scaffold is identical to the N-terminal helix in I3-01v9a, i.e., AKLAEELQKKMEELFKKHK (SEQ ID NO:28), while the remaining sequence is a conservative modified variant or a substantially identical sequence of the corresponding sequence of SEQ ID NO:27 (i.e., SEQ ID NO:27 minus the N-terminal helix). IV. Immunogenic polypeptides or proteins for generating vaccine compositions [0052] The novel I3-01 derived nanoparticle scaffolds described herein can be used to construct vaccines that present many different immunogenic proteins, including monomeric polypeptides and multimeric proteins. These include any proteins or polypeptides from pathogens against which an elicited immune response may be desired. Thus, the vaccine compositions of the invention can utilize immunogenic polypeptides that are derived from any viruses, bacteria or other pathogenic organisms. Suitable immunogenic polypeptides for the invention can also be derived from non- pathogenic species, including human proteins, against which an elicited immune response may have a therapeutic effect, alleviate disease symptoms, or improve general health. In general, the immunogenic polypeptide can be any structural or functional polypeptide or peptide that contains at least about 10 amino acid residues. In some embodiments, the immunogenic polypeptides contains between about 10 to about 10,000 amino acid residues in length. In some embodiments, the immunogenic polypeptides contains between about 25 to about 2,000 amino acid residues in length. In some embodiments, the immunogenic polypeptides contains about 50 to about 500 amino acid residues in length. Thus, the immunogenic polypeptides or proteins suitable for the invention can have a molecular weight of from about 1 kDa to about 1,000 kDa, and preferably from about 2.5 kDa to about 250 kDa. In some more preferred embodiments, the employed immunogenic polypeptide has a molecular weight of about 5 kDa to about 25 kDa or 50 kDa. [0053] In some embodiments, the immunogenic polypeptide or protein used in the vaccine compositions of the invention can be derived from a viral surface or core protein (target polypeptide). There are many known viral proteins that are important for viral infection of host cells. Examples include, but are not limited to, glycoproteins (or surface antigens, e.g., GP120 and GP41) and capsid proteins (or structural proteins, e.g., P24 protein) of HIV; surface antigens or core proteins of hepatitis A, B, C, D or E virus (e.g., small hepatitis B virus surface antigen (S-HBsAg) and the core proteins of hepatitis C virus, NS3, NS4 and NS5 antigens); glycoproteins gp350/220 of Epstein- Barr virus (EBV), glycoprotein (G-protein) or the fusion protein (F-protein) of respiratory syncytial virus (RSV); surface and core proteins of herpes simplex virus HSV-1 and HSV-2 (e.g., glycoprotein D from HSV-2), surface proteins (e.g., gB, gC, gD, gH and gL) of poliovirus, envelope glycoproteins hemagglutinin (H) and fusion protein (F) of measles virus (MV), glycoprotein G of lymphocytic choriomeningitis virus (LCMV), fiber and penton base proteins of adenoviruses, S spikes of coronaviruses, envelope (E) proteins of flaviviruses such as Dengue virus, yellow fever virus, and Zika virus, and non-enveloped capsid proteins of picornaviruses. [0054] In some preferred embodiments, the immunogens or immunogenic proteins displayed on the novel I3-01 NP scaffolds are monomeric proteins. Examples of such proteins include, e.g., influenza M2 ectodomain (M2e) proteins exemplified herein. As detailed below, some embodiments of influenza vaccines of the invention encompass NP vaccines that contain a novel I3-01 scaffold (e.g., SEQ ID NO:4) that displays a tandem repeat (e.g., 2, 3, 4 or more copies) of the M2e protein. In some of these embodiments, one or more of the tandem M2e copies contain substitutions at the conserved Cys17 and Cys19 residues to prevent formation of random disulfide bonds. [0055] Some other embodiments of the invention are directed to HCV vaccines containing the novel I3-01 NP scaffolds (e.g., SEQ ID NO:4) that display an HCV immunogenic protein. Typically, the HCV immunogenic protein to be displayed on the NP scaffold is derived from HCV glycoproteins E1 and E2, which form a heterodimer on the HCV envelope that mediates viral entry into host hepatocytes. In some embodiments, the displayed HCV protein contains E2 core. E2 core as well understood in the art refers to a portion of E2 that forms a 3-dimensional structure that is recognized by broadly neutralizing antibody AR3C Fab (Law et al., Nat. Med. 2008;14:25, 2008). As exemplified herein, the I3-01 variant scaffold of the invention can be used to display either a single copy of the E2 core protein or a tandem E2 core fusion protein. One specific HCV E2 core protein that can be used in the HCV vaccine constructs of the invention is the redesigned E2mc3 protein as described in US Patent No.11,008,368. E2mc3 derived from various HCV subtypes or isolates can be used, including E2mc3 sequences of HCV H77, J6, ED43 and UKN3A1.28c isolates (SEQ ID NOs:32-35, respectively) as exemplified herein. Conservatively modified variants of these exemplified E2 core sequences, or substantially identical sequences, can also be employed in the HCV vaccine constructs of the invention. [0056] In some embodiments, the displayed HCV immunogenic protein is a tandem E2 core fusion protein containing SEQ ID NO:32 and SEQ ID NO:33, in any order. In some other embodiments, the displayed HCV immunogenic protein is a tandem E2 core fusion protein containing SEQ ID NO:34 and SEQ ID NO:35, in any order. In some other embodiments, the HCV immunogenic protein displayed by the NP scaffold contains an E1E2 heterodimer, e.g., a rationally redesigned HCV E1E2 dimer. Other than the HCV derived immunogenic protein, the novel I3-01 scaffold displayed HCV vaccines can additionally contain a locking domain and/or a T cell epitope. For example, the vaccine constructs can have a LD7 motif (SEQ ID NO:5) and a PADRE epitope (SEQ ID NO:6) at the C-terminus, as exemplified herein. [0057] In the construction of the HCV vaccines of the invention, any E2 core protein sequences, tandem E2 core fusion molecules and E1E2 dimers that are known in the art or that can be readily engineered are suitable. Detailed guidance for obtaining such HCV immunogenic proteins and constructing NP vaccines containing the same is provided in, e.g., WO21/021603; McGregor et al., J. Virol.96: e01675-21; Lin et al., Front Immunol.2022; 13: 831285; Wang et al., Proc. Natl. Acad. Sci. USA 119: e2112008119, 2022; Clarke et al., Plant Biotechnol. J.15: 1611-21, 2017; and Sepulveda-Crespo et al., J. Biomed. Sci 27, 78, 2020. The various immunogenic proteins or polypeptides (e.g., tandem influenza M2e fusion proteins or tandem HCV E2 core fusion proteins) for display on the novel I3-01 NP scaffolds of the invention can be obtained or generated in accordance with the protocols exemplified herein or methods well known in the art. See, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Press, N.Y., (3^rd ed., 2000); and Brent et al., Current Protocols in Molecular Biology, John Wiley & Sons, Inc. (ringbou ed., 2003). V. NP vaccines containing novel I3-01 NP scaffolds [0058] The invention provides nanoparticle vaccines bearing the novel I3-01 NP scaffolds disclosed herein. As noted above, some of the vaccine constructs display an HCV immunogenic protein such as a tandem E2 core protein. Some other vaccine constructs of the invention display a single copy of the influenza M2 protein ectodomain (M2e). A few examples of such influenza NP vaccines are exemplified herein. In still some other embodiments, a fusion polypeptide that contains tandem repeats of the influenza M2e protein is displayed on the novel I3-01 derived nanoparticle scaffolds. In these embodiments, the displayed immunogenic protein displayed on the novel I3-01 scaffold sequence is a fusion polypeptide containing 2 or more tandem repeats of influenza M2e sequence. In various embodiments, at least one of the M2e tandem repeats contain missenses mutations at the conserved Cys17 and Cys19 residues to prevent random disulfide bond formation. In some of these influenza NP vaccine constructs, the engineered missense mutations are substitutions of each of the Cys residues with an amino acid residue that contains an uncharged polar side chains. For example, each of the two CYs residues in one or more of the tandem M2e repeats can be independently replaced with serine, glycine, asparagine, glutamine, threonine or tyrosine. In some embodiments, one or both of the Cys residues are replaced with Ser. [0059] Typically, the tandem M2e fusion polypeptide sequence is fused to the N- terminus of the novel I3-01 scaffold sequence, e.g., via a linker motif such as GGGGS (SEQ ID NO:3) as exemplified herein. Preferably, the tandem M2e repeats in the displayed fusion polypeptide are separated by a short linker or spacer. For example, a GGGG (SEQ ID NO:9) spacer herein can be used to separate the different M2e sequences, as exemplified herein. Some influenza NP vaccines of the invention contain 3 tandem M2e repeats. In various embodiments, the tandem M2e repeats displayed on the novel I3-01 scaffolds of the invention can be identical or different. Ortholog M2e sequences from many species and modified versions thereof are known in the art. See, e.g., Mezhenskaya et al., J. Biomed. Sci.26, 76, 2019. Thus, for example, each of the M2e tandem repeats can be independently a human M2e sequence (SEQ ID NO:2), an avian/swine consensus M2e sequence (SEQ ID NO:7), or a human/swine consensus M2e sequence (SEQ ID NO:8). When M2e sequences from different sources are employed in the tandem M2e molecule, the different M2e motifs can be linked in any order. As an example, the tandem M2e repeat sequence in the influenza vaccines of the invention can contain a human M2e sequence, an avian/swine consensus M2e sequence, and a human/swine consensus M2e sequence. In these embodiments, the 3 different Me2 sequences can be linked to the scaffold sequence in any of the 6 possible sequence orders. [0060] In some embodiments, at least 2 of the 3 tandem M2e repeats contain the substitutions at residues Cys17 and Cys19. For example, the human M2e sequence can retain unmutated residues at Cys17 and Cys19, while the avian/swine consensus M2e sequence and the human/swine consensus M2e sequence contain substituted residues (e.g., all with Ser) at Cys17 and Cys19. In some of these embodiments, the mutated Cys residues are all replaced with Ser residues. Thus, the displayed M2e fusion polypeptide can contain, in any order, an unmutated human M2e (SEQ ID NO:2), a mutated avian/swine consensus M2e sequence SLLTEVETPTRNGWESKSSDSSD (SEQ ID NO:30), and a mutated human/swine consensus M2e sequence SLLTEVETPTRSEWESRSSGSSD (SEQ ID NO:31). In some embodiments, all 3 tandem M2e repeats contain the substitutions at residues Cys17 and Cys19. Thus, the displayed M2e fusion polypeptide can contain, in any order, a mutated human M2e SLLTEVETPIRNEWGSRSNDSSD (SEQ ID NO:29), a mutated avian/swine consensus M2e sequence SLLTEVETPTRNGWESKSSDSSD (SEQ ID NO:30), and a mutated human/swine consensus M2e sequence SLLTEVETPTRSEWESRSSGSSD (SEQ ID NO:31). As specific exemplifications, the fusion M2e polypeptide can contain the sequence set forth in SEQ ID NO:23 or SEQ ID NO:24, a conservatively modified variant or a substantially identical sequence thereof. [0061] In some embodiments, the NP vaccines containing the novel I3-01 variant scaffolds of the invention (e.g., tandem influenza M2e vaccines or HCV E2 vaccines) may optionally contain a trimerization motif, e.g., SHP or foldon. Some nanoparticle vaccine compositions can additionally contain other structural components that function to further enhance stability and antigenicity of the displayed immunogen. In some embodiments, a locking protein domain (LD) can be inserted into the nanoparticle construct, e.g., by covalently fused to the C-terminus of the nanoparticle subunit. The locking domain can be any dimeric protein that is capable of forming an interface through specific interactions such as hydrophobic (van der Waals) contacts, hydrogen bonds, and/or salt bridges. One example of locking domains that can be used in the vaccines of the invention is LD7 (SEQ ID NO:5) as exemplified herein. General guidance on selecting locking domains and various other examples (e.g., LD4) are described in the art, e.g., WO19/241483, US Patent NO.10,906,944, and US Patent NO.11,305,004. [0062] In some embodiments, scaffolded influenza vaccines of the invention can also contain a T-cell epitope to promote robust T-cell responses and to steer B cell development towards bNAbs. The T-cell epitope can be located at any position in relation to the other structural components as long as it does not impact presentation of the engineered HA protein on the nanoparticle surface. Any T-cell epitope sequences or peptides known in the art may be employed in the practice of the present invention. They include any polypeptide sequence that contain MHC class-II epitopes and can effectively activate CD4+ and CD8+ T cells upon immunization, e.g., T-helper epitope that activates CD4+ T helper cells. See, e.g., Alexander et al., Immunity 1, 751- 761,1994; Ahlers et al., J. Clin. Invest.108:1677–1685, 2001; Fraser et al., Vaccine 32, 2896-2903, 2014; De Groot et al., Immunol. Cell Biol.8:255–269, 2002; and Gene Ther.21: 225–232, 2014. In some embodiments, the T cell epitope inserted into the nanoparticle vaccine construct is a universal pan DR epitope peptide (PADRE), AKFVAAWTLKAAA (SEQ ID NO:6), as exemplified herein for influenza and HCV vaccines. More detailed information of T-cell epitopes suitable for the invention are described in, e.g., Hung et al., Mole. Ther.15: 1211-19, 2007; Wu et al., J. Biomed. Sci.17: 88, 2010; and Bissati et al., npj Vaccines 2: 24, 2017. Other examples of suitable T-cell epitope are also described in the art, e.g., the D and TpD epitope (Fraser et al., Vaccine 32, 2896-2903, 2014). [0063] The novel I3-01 scaffold based nanoparticle vaccines of the invention can be constructed in accordance with standard recombinant techniques and other methods that have been described in the art, e.g., He et al., Nat. Comm.7, 12041, 2016; Kong et al., Nat. Comm.7, 12040, 2016; He et al., Sci Adv.4(11):eaau6769, 2018; and PCT publications WO2017/192434, WO2019/089817 and WO19/241483. In various embodiments, the novel I3-01 scaffold based nanparticle vaccines can be constructed by fusing an immunogenic protein of interest (e.g., tandem HCV E2 core or tandem influenza M2e polypeptide) to the I3-01 scaffold subunit. Preferably, C-terminus of the immunogenic protein sequence is fused to the N-terminus of the nanoparticle subunit sequence. In some embodiments, a short peptide linker or spacer (e.g., SEQ ID NOs:3 and 9) can be inserted between the immunogenic protein sequence and the nanoparticle subunit sequence or between the tandem copies of the immunogenic protein. [0064] Upon recombinant expression (e.g., in ExpiCHO cells as detailed herein), the nanoparticle vaccines of the invention can be substantially purified by any of the routinely practiced procedures. See, 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 vaccines 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, Biolayer Interferometry (BLI), Surface Plasmon Resonance (SPR), and co- crystallography analysis. Some of these assays are exemplified herein for analyzing the novel I3-01 scaffolded HCV vaccines or influenza vaccines. V. Polynucleotides and expression constructs [0065] The novel I3-01 scaffolds and vaccines based thereon of the invention are typically produced by first generating expression constructs (i.e., expression vectors) that contain operably linked coding sequences of the various structural components described herein. In some embodiments, vaccine compositions of the invention are polynucleotide based (e.g., mRNA based vaccines). Accordingly, in some related aspects, the invention provides polynucleotides (e.g., DNA or RNA) that encode the novel I3-01 scaffolds or the subunit sequence of nanoparticle vaccines based on the scaffolds, expression vectors that harbor such polynucleotides, and host cells for producing the novel NP scaffolds and the vaccines (e.g., ExpiCHO cells as exemplified herein). The fusion polypeptides encoded by the polynucleotides or expressed from the vectors are also encompassed by the invention. [0066] The polynucleotides and related vectors can be readily generated with standard molecular biology techniques or the protocols exemplified herein. For example, general protocols for cloning, transfecting, transient gene expression and obtaining stable transfected cell lines are described in the art, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Press, N.Y., (3^rd ed., 2000); and Brent et al., Current Protocols in Molecular Biology, John Wiley & Sons, Inc. (ringbou edition, 2003). 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 et al., PCR Methods and Applications 1:17, 1991. [0067] The selection of a particular vector depends upon the intended use of the fusion polypeptides. For example, the selected vector must be capable of driving expression of the fusion polypeptide in the desired cell type, whether that cell type be prokaryotic or eukaryotic. Many vectors contain sequences allowing both prokaryotic vector replication and eukaryotic expression of operably linked gene sequences. Vectors useful for the invention may be autonomously replicating, that is, the vector exists extrachromosomally and its replication is not necessarily directly linked to the replication of the host cell's genome. Alternatively, the replication of the vector may be linked to the replication of the host's chromosomal DNA, for example, the vector may be integrated into the chromosome of the host cell as achieved by retroviral vectors and in stably transfected cell lines. Both viral-based and nonviral expression vectors can be used to produce the immunogens 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, cytomegalovirus, 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. [0068] Depending on the specific vector used for expressing the fusion polypeptide, various known cells or cell lines can be employed in the practice of the invention. The host cell can be any cell into which recombinant vectors carrying a fusion of the invention may be introduced and wherein the vectors are permitted to drive the expression of the fusion polypeptide is useful for the invention. It may be prokaryotic, such as any of a number of bacterial strains, or may be eukaryotic, such as yeast or other fungal cells, insect or amphibian cells, or mammalian cells including, for example, rodent, simian or human cells. Cells expressing the fusion polypeptides of the invention may be primary cultured cells or may be an established cell line. Thus, in addition to the cell lines exemplified herein (e.g., CHO cells), a number of other host cell lines capable well known in the art may also be used in the practice of the invention. These include, e.g., various Cos cell lines, HeLa cells, HEK293, AtT20, BV2, and N18 cells, myeloma cell lines, transformed B-cells and hybridomas. [0069] The use of mammalian tissue cell culture to express polypeptides is discussed generally in, e.g., Winnacker, From Genes to Clones, VCH Publishers, N.Y., N.Y., 1987. The fusion polypeptide-expressing vectors may be introduced to the selected host cells by any of a number of suitable methods known to those skilled in the art. For the introduction of fusion polypeptide-encoding vectors to mammalian cells, the method used will depend upon the form of the vector. For plasmid vectors, DNA encoding the fusion polypeptide sequences may be introduced by any of a number of transfection methods, including, for example, lipid-mediated transfection (“lipofection”), DEAE-dextran-mediated transfection, electroporation or calcium phosphate precipitation. These methods are detailed, for example, in Brent et al., supra. Lipofection reagents and methods suitable for transient transfection of a wide variety of transformed and non-transformed or primary cells are widely available, making lipofection an attractive method of introducing constructs to eukaryotic, and particularly mammalian cells in culture. For example, LipofectAMINE™ (Life Technologies) or LipoTaxi™ (Stratagene) kits are available. Other companies offering reagents and methods for lipofection include Bio-Rad Laboratories, Clontech, Glen Research, Life Technologies, JBL Scientific, MBI Fermentas, PanVera, Promega, Quantum Biotechnologies, Sigma-Aldrich, and Wako Chemicals USA. [0070] For long-term, high-yield production of recombinant fusion polypeptides, stable expression is preferred. Rather than using expression vectors which contain viral origins of replication, host cells can be transformed with the fusion polypeptide- encoding sequences controlled by appropriate expression control elements (e.g., promoter, enhancer, sequences, transcription terminators, polyadenylation sites, etc.), and selectable markers. The selectable marker in the recombinant vector confers resistance to the selection and allows cells to stably integrate the vector into their chromosomes. Commonly used selectable markers include neo, which confers resistance to the aminoglycoside G-418 (Colberre-Garapin, et al., J. Mol. Biol., 150:1, 1981); and hygro, which confers resistance to hygromycin (Santerre et al., Gene, 30: 147, 1984). Through appropriate selections, the transfected cells can contain integrated copies of the fusion polypeptide encoding sequence. VI. Pharmaceutical compositions and therapeutic applications [0071] The invention provides pharmaceutical or immunogenic compositions and related therapeutic methods of using the vaccines based on the novel I3-01 scaffolds, e.g., influenza vaccines or HCV vaccines. In some embodiments, the vaccine compositions can be used for preventing and treating a disease or an infection (e.g., HCV infection or flu). In some embodiments, a nanoparticle displaying an immunogenic protein (e.g., tandem M2e or HCV E2 core protein) is included in the 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. [0072] 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^TM and IL-12. In some embodiments, the novel I3-01 scaffold based vaccines of the invention 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 ppharmaceutical compositions can be prepared in accordance with standard procedures well known in the art. See, e.g., Remington’s Pharmaceutical Sciences, 19.sup.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. [0073] Therapeutic methods of the invention involve administering a suitable vaccine (e.g., influenza vaccine or HCV vaccine) of the invention to a subject having or at risk of developing a disease or an infection (e.g., flu or HCV infection). Using influenza vaccine as an example, the immunogenic composition of the invention is typically administered in an amount sufficient to induce an immune response against an influenza virus or a group of viruses. 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 influenza viral infection, for example because of exposure or the possibility of exposure to a virus. Following administration of a therapeutically effective amount of the disclosed therapeutic compositions, the subject can be monitored for viral infection, symptoms associated with viral infection, or both. 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 flu, or after diagnosis of an viral infection. The immunogenic composition can thus be provided prior to the anticipated exposure to a virus in order 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. The appropriate amount of a vaccine 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. [0074] The pharmaceutical composition of the invention can be combined with other agents known in the art for treating or preventing a disease or infection (e.g., influenza viral infection). Administration of the pharmaceutical compositions and the known anti-viral agents can be either concurrently or sequentially. Pharmaceutical compositions containing a suitable vaccine 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. EXAMPLES [0075] The following examples are offered to illustrate, but not to limit the present invention. Example 1 Rational design of a novel I3-01v9a nanoparticle scaffold [0076] We rationally optimized the I3-01v9 nanoparticle scaffold to achieve the optimal surface display of monomeric protein antigens (Fig.1). The N-termini of I3- 01v9 form a wide triangle, which is desirable for displaying monomeric antigens (Fig. 1A). However, the first residue (the antigen anchoring site) is under the nanoparticle surface, and as such, a long linker must be used to connect the antigen to the I3-01v9 N-terminus, which will increase structural instability. Our goal is to extend the I3-01v9 N-terminal helix so that its first residue is at the same level as the nanoparticle surface. To achieve this goal, we selected the helical backbone of residues 953-982 from a c- MYC transcription factor protein (PDB ID: 6G6L) and grafted it onto an I3-01v9 subunit (SEQ ID NO:27) using residues E2 and E3 of I3-01v9 for structural fitting (Fig. 1B). The extended N-terminal helix was then truncated to 11 residues so that its first residue would be just above the nanoparticle surface (Fig.1C). Next, a protein structure sampling program, CONCOORD, was used to generate 1000 slightly perturbed conformations for the modified I3-01v9 subunit (Fig.1D). Afterwards, an ensemble- based protein design program that we previously used to optimize HIV gp140 and HCV E2 antigens was used to predict amino acids for the first 9 of the 11-residue segment using Cα and Cβ-based RAPDF scoring functions (Fig.1E). We selected our final design, I3-01v9a (SEQ ID NO:4), by combining data from predictions using both energy functions (Fig.1F). Example 2 Display of HCV antigens on I3-01v9a nanoparticle scaffold [0077] This Example describes multivalent display of HCV E2 cores and tandem E2 cores on the I3-01v9a nanoparticle scaffold. The newly designed I3-01v9a nanoparticle scaffold (SEQ ID NO:4) has been used to present monomeric HCV E2 cores of diverse genotypes (Fig.2A). In negative-stain EM, E2mc3 I3-01v9a-LD7- PADRE nanoparticles designed for H77 (genotype 1a), HCV1 (genotype 1b), and ED43 (genotype 4) showed well-formed nanoparticles (Fig.2B). Sequences of the different E2mc3 proteins are shown in SEQ ID NOs:32-35, respectively. Based on this success, we designed a tandem E2 core antigen in which two HCV E2 cores of different genotypes are linked in tandem with a 5GS linker and linked this tandem E2 core antigen to I3-01v9a with an enzymatic restriction site “AS” (to facilitate molecular cloning) and another 5GS linker (Fig.2C). Based on this design strategy, we displayed H77 (genotype 1) and J6 (genotype 2) E2 cores together on an I3-01v9a-LD7-PADRE nanoparticle and displayed ED43 (genotype 4) and UKN3A1.28c (genotype 3) E2 cores together on an I3-01v9a-LD7-PADRE nanoparticle. These two nanoparticles were expressed in either 50ml or 200ml ExpiCHO cells and then characterized by size- exclusion chromatography (SEC) on a Superose 6 column and by negative-stain EM (Fig.2D). In summary, I3-01v9a has been successfully used to display monomeric antigens for vaccine development. [0078] E2mc3 of H77 isolate (SEQ ID NO:32): [0079] QLINTNGSWHINSTALNCNESLNTGWLAGLFYQHKFDSSGCPERAS GHYPRPCGIVPAKSVCGPVYCFTPSPVVVGTTDRSGAPTYSWGANDTDVFVLN NTGNWFGCTWMNSTGFTKVCGAPPGGPTDGGSGPWITPRCMVDYPYRLWHY PCTINYTIFKVRMYVGGVEHRLEAACN [0080] E2mc3 of J6 isolate (SEQ ID NO:33): [0081] QLVNTNGSWHINRTALNCNDSLHTGFIASLFYTHSFNSSGCPERASG HYPRQCGVVSAKTVCGPVYCFTPSPVVVGTTDRLGAPTYTWGENETDVFLLNS TGSWFGCTWMNSSGYTKTCGAPPGGPTDGGSGPWLTPRCLIDYPYRLWHYPC TVNYTIFKIRMYVGGVEHRLTAACN [0082] E2mc3 of ED43 isolate (SEQ ID NO:34): [0083] QLINSNGSWHINRTALNCNDSLNTGFLASLFYTHKFNSSGCSERASG HYARPCGIVPASSVCGPVYCFTPSPVVVGTTDHVGVPTYTWGENETDVFLLNS TGAWFGCVWMNSTGFTKTCGAPPGGPTDGGSGPWITPRCLIDYPYRLWHFPCT ANFSVFNIRTFVGGIEHRMQAACN [0084] E2mc3 of UKN3A1.28c isolate (SEQ ID NO:35): [0085] QLVNTNGSWHINRTALNCNESINTGFIAGLFYYHKFNSTGCPQRAS GHYARPCESVPASKVCGPVYCFTPSPVVVGTTDAKGVPTYTWGANETDVFLL NSLGRWFGCTWMNSTGFTKTCGAPPGGPTDGGAGPWLTPRCMVDYPYRLWH YPCTVNFTLFQVRMFVGGFEHRFTAACN Example 3 Design of single hM2e (1c-SApNP) vaccines and characterization [0086] Crystal structures are available for human M2e (hM2e) in complex with monoclonal antibodies Fab65 and Fab148. The Fab65-bound hM2e folds into a compact conformation containing a β-turn (T5-E8) and a 3₁₀ helix (I11-W15). The Fab148-bound hM2e adopts a hook conformation with an N-terminal β-turn (S2-T5). We used a trimeric scaffold (PDB ID: 1TD0) to present hM2e (S2-D24) with a 5GS spacer (Fig.3A), as 1TD0 has been used in our previous study as a C-terminal motif to stabilize EBOV GP trimers. Structural modeling indicates that two hM2e peptides on the 1TD0 scaffold would span 9.1 nm measured at P10. The hM2e peptide was then fused to 24-meric ferritin (FR) and two “multilayered” 1c-SApNPs, E2p-LD4-PADRE (or termed E2p-L4P), and I3-01v9a-LD7-PADRE (also termed I3-01v9a-L7P), resulting in vaccine particles of 20.9 nm, 29.1 nm, and 32.4 nm, respectively (Fig.3A). The four hM2e immunogens, one trimer and three 1c-SApNPs, were transiently expressed in 25ml ExpiCHO cells and purified by immunoaffinity chromatography (IAC) using antibodies Fab65 and Fab148 (Fig.3B). Size-exclusion chromatography (SEC) profiles were obtained for the hM2e scaffold and three 1c-SApNPs on Superdex 75 and Superose 6 columns, respectively (Fig.3C). Although multiple peaks were noted in SEC, IAC-purified 1c-SApNPs displayed high purity in negative-stain EM images collected at the Scripps EM Core, showing well-formed NPs (Fig.3D). Example 4 Immunization and influenza virus challenge of single hM2e vaccines [0087] The immunogenicity and protective efficacy of M2e-based vaccines were assessed in a comprehensive mouse study. Briefly, 10 mice/group were immunized via intradermal injection into the footpads with 10 µg total (2.5 µg/footpad) of hM2e-5GS- 1TD0, hM2e-5GS-FR, hM2e-5GS-E2p-LD4-PADRE, or hM2e-5GS-I3-01v9a-LD7- PADRE mixed with aluminum phosphate. Mice were immunized twice, 3 weeks apart, and blood collected 2 weeks after each injection. In this study, a group of naïve mice was included as a negative control and a second group of mice was immunized with beta-propiolactone (BPL)-inactivated PR8 H1N1 virus (a.k.a. inactivated H1N1 vaccine) to serve as the positive control. Three weeks after the second immunization, mice were challenged intranasally (i.n.) with vaccine-matched A/Puerto Rico/8/1934 (PR8) H1N1 virus at 10×LD₅₀, the median lethal dose (determined in a previous study). Mice were weighed daily and monitored for visible symptoms of infection (including ruffled fur, hunched posture, and/or reduced activity) for 14 days post-infection (dpi). Mice that were visibly in distress or lost 75% of their original body weight were euthanized. After the surviving mice had returned to their post-immunization, pre- challenge baseline, we performed a heterologous IAV challenge with 10×LD₅₀ of A/Hong Kong/1/1968 (HK68) H3N2 virus and monitored for 14 dpi. The immunization/challenge study schedule is shown in Fig.4A. [0088] After the first challenge (Fig.4B), all naïve mice and 8 of 10 mice in the 1TD0 trimer group died by 8 dpi. In contrast, survival rate was 100% for all three 1c- SApNP groups, as well as the group which received the inactivated PR8 H1N1 vaccine. Mice that received the strain-matched PR8 H1N1 vaccine lost the least weight, began regaining weight by 6 dpi, and returned to their starting weight by 14 dpi. Mice that received hM2e-5GS-FR and hM2e-5GS-I3-01v9a-L7P lost more weight and began regaining it at 8 dpi, but also returned to their starting weight by 14dpi. Mice that received the hM2e-5GS-1TD0 trimer lost significantly more weight than those in the 1c-SApNP groups. The two survived mice began regaining weight by 9 dpi and had not returned to their starting weight by 14 dpi. After the second challenge (Fig.4C), 4 of 9 mice in the group which received the inactivated PR8 H1N1 vaccine died, whereas all hM2e-immunized mice survived the H3N2 challenge. Consistently, compared with the hM2e trimer and 1c-SApNP vaccine groups, mice that received the inactivated H1N1 virus vaccine lost notably more weight upon the H3N2 challenge and started to regain their weight one day later (at dpi 6) and with a slower pace. Our challenge data thus highlight the effectiveness and broad protection of M2e 1c-SApNP vaccines. To determine whether the protection of hM2e-immunized mice is correlated with the hM2e-specific antibody response, we performed the enzyme-linked immunosorbent assay (ELISA) on mouse sera at w5, one week before the first challenge (Fig.4D), using an hM2e-5GS-foldon antigen probe. Foldon (PDB ID: 4NCU) was used in this antigen probe to avoid detecting 1TD0-specific antibodies in the hM2e-5GS-1TD0 trimer group. As expected, naïve mice showed no hM2e-specific responses. Notably, mice that received the inactivated H1N1 virus vaccine also showed no signals, consistent with the low abundance of M2 in virions32. While all 1c-SApNP groups showed high hM2e-specific antibody titers, two surviving mice in the 1TD0 trimer group generated detectable hM2e antibody responses. Overall, our results show that 1c- SApNPs displaying M2e can effectively protect mice from lethal challenge with both diverse IAV sand this protection is closely correlated with M2e-specific antibodies. Example 5 Sequences of some of the single hM2e vaccine constructs [0089] We determined the sequences of some of the hM2e vaccines described herein. The full sequences of the I3-01v9a based constructs are shown below. In the sequence, the underlined sequence represents the leader sequence (SEQ ID NO:1). The italicized sequence indicate the 23-residue hM2e (SEQ ID NO:2). The two conserved Cys residues in the hM2e sequence that are mutated in some of the tandem M2e constructs discussed below are also underlined. It is noted that the first Met residue was removed from the hM2e sequence inserted into the NP constructs described herein. As a result, while respectively termed Cys17 and Cys19 herein (and also in the literature) based on the original full hM2e sequence, they are actually the 16^th and 18^th residues in the hM2e sequence present in the vaccine constructs. The two bold and underlined residues show the restriction site for PCR. The double underlined sequence represents the I3-01v9a NP scaffold subunit sequence (SEQ ID NO:4). The constructs can optionally also contain a locking domain and/or a T-cell epitope. As exemplified in the constructs herein, the employed locking domain can be LD7 (SEQ ID NO:5) (shown in double underlined and bold font), and the T-cell epitope can be the PADRE epitope (SEQ ID NO:6) (shown in double underlined and italicized font). Linkers or spacers separating the different structural motifs of the nanoparticle constructs are shown in italicized and underlined residues in the construct sequences herein, e.g., GS, GGGG spacer (SEQ ID NO:9) and the 5GS linker (SEQ ID NO:3). [0090] hM2e-5GS-I3-01v9a-LD7-PADRE construct without N-terminal leader and LD/PADRE motifs (SEQ ID NO:10) [0091] SLLTEVETPIRNEWGCRCNDSSDASGGGGSAKLAEELQKKMEELFKK HKIVAVLRANSVEEAKMKALAVFVGGVHLIEITFTVPDADTVIKELSFLKELGA IIGAGTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMPGVMTPTELV KAMKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNLDNVCEWFKA GVLAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTE [0092] hM2e-5GS-I3-01v9a-LD7-PADRE construct, including C-terminal LD/PADRE motifs (SEQ ID NO:13) [0093] SLLTEVETPIRNEWGCRCNDSSDASGGGGSAKLAEELQKKMEELFKK HKIVAVLRANSVEEAKMKALAVFVGGVHLIEITFTVPDADTVIKELSFLKELGA IIGAGTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMPGVMTPTELV KAMKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNLDNVCEWFKA GVLAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTEGGGGSSPAVDIGDRLDE LEKALEALSAEDGHDDVGQRLESLLRRWNSRRADGSAKFVAAWTLKAAA [0094] hM2e-5GS-I3-01v9a-LD7-PADRE construct, (SEQ ID NO:16) [0095] MGILPSPGMPALLSLVSLLSVLLMGCVAESLLTEVETPIRNEWGCRCN DSSDASGGGGSAKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFV GGVHLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVS PHLDEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVK AMKGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKA AAFVEKIRGCTE [0096] hM2e-5GS-I3-01v9a-LD7-PADRE construct, including N-terminal leader and C-terminal LD/PADRE motifs (SEQ ID NO:19) [0097] MGILPSPGMPALLSLVSLLSVLLMGCVAESLLTEVETPIRNEWGCRCN DSSDASGGGGSAKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFV GGVHLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVS PHLDEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVK AMKGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKA AAFVEKIRGCTEGGGGSSPAVDIGDRLDELEKALEALSAEDGHDDVGQRLES LLRRWNSRRADGSAKFVAAWTLKAAA Example 6 Design, characterization, and challenge study of tandem M2e vaccines [0098] Phylogenetic analysis divides IAVs into several lineages based on their original host species: avian, swine, or human. While M2e is highly conserved, there are small but important sequence differences between IAVs from different species, which have been shown to limit cross-protection. Therefore, an M2e-based universal influenza vaccine must protect against pandemic strains that often arise from avian or swine IAVs, in addition to seasonal endemic strains. Combined use of M2e sequences from multiple species has been previously reported. Here, we designed a tandem M2e×3 construct that contains human, avian/swine, and human/swine M2e sequences, with a GGGG (SEQ ID NO:9) spacer between the consecutive M2e segments. Of note, Cys17 and Cys19 in the second (avian/swine) and third (human/swine) repeats were mutated to Serine to avoid random disulfide bonds. Optionally, Cys17 and Cys19 in all three repeats can be mutated to serine as exemplified herein. This M2e×3 antigen was fused to 1TD0 and three 1c-SApNPs with a 5GS spacer, resulting in four constructs named M2e×3-5GS-1TD0, M2e×3-5GS-FR, M2e×3-5GS-E2p-LD4-PADRE (or M2e×3-5GS- E2p-L4P), and M2e×3-5GS-I3-01v9a-LD7-PADRE (or M2e×3-5GS-I3-01v9a-L7P). These four tandem M2e immunogens were transiently expressed in ExpiCHO cells and purified by IAC using an Fab148 antibody column. The Fab148-purified 1c-SApNP samples were analyzed using negative-stain EM at the Scripps EM Core. Consistent with the hM2e 1c-SApNPs, all tandem M2e 1c-SApNPs showing well-formed NPs (Fig.5A). [0099] The immunogenicity and protective efficacy of tandem M2e vaccines were assessed in a mouse study following a similar schedule to the study of hM2e immunogens (Fig.4A). Two adjuvants, aluminum hydroxide (AH) and an oil-in-water emulsion, AddaVax, were tested in this study. For the AH adjuvant groups (Fig.5B), after the PR8 H1N1 challenge, all naïve mice and 4 of 8 mice in the 1TD0 trimer group died by 9 dpi. In contrast, survival rate was 88% for the FR 1c-SApNP and 100% for the two large, multilayered 1c-SApNP groups, as well as the group which received the inactivated PR8 H1N1 vaccine. In terms of weight loss, the AH-formulated E2p 1c- SApNP appeared to be the closest to the inactivated vaccine and more effective than other tandem M2e immunogens. For the AddaVax adjuvant groups (Fig.5C), after the PR8 H1N1 challenge, all naïve mice and 3 of 8 mice in the 1TD0 trimer group died by 9 dpi. In contrast, survival rate was 100% for all the 1c-SApNP groups, as well as the group which received the inactivated PR8 H1N1 vaccine. In terms of weight loss, the AddaVax-formulated I3-01v9a 1c-SApNP appeared to be the closest to the inactivated vaccine and more effective than other tandem M2e immunogens. This formulation also outperformed the E2p/AH formulation in terms of preventing weight loss (Fig.5B). Overall, the tandem M2e immunogens exhibited broad protection with the tandem M2e-5GS-1TD0 trimer being notably better than its hM2e counterpart and I3-01v9a 1c- SApNP being the best performer among all immunogens when paired with AddaVax. Example 7 Sequences of some tandem M2e×3 immunogen constructs [00100] Amino acid sequences of two exemplified tandem M2e vaccine constructs (M2e×3-5GS-I3-01v9a-LD7-PADRE; aka M2e×3-5GS-I3-01v9a-L7P) are set forth below (SEQ ID NOs:11 and 12). Each of the two constructs contains the rationally designed I3-01v9a variant scaffold (SEQ ID NO:4) and a tandem M2e molecule having 3 M2e sequences (SEQ ID NO:23 or SEQ ID NO:24). The 3 M2e sequences are respectively a human M2e sequence SLLTEVETPIRNEWGCRCNDSSD (SEQ ID NO:2; Cys17 and Cys19 underlined), an avian/swine consensus M2e sequence SLLTEVETPTRNGWECKCSDSSD (SEQ ID NO:7; Cys17 and Cys19 underlined), and a human/swine consensus M2e sequence SLLTEVETPTRSEWECRCSGSSD (SEQ ID NO:8; Cys17 and Cys19 underlined). Additionally, these two constructs respectively have the conserved Cys17 and Cys19 residues in either 2 or all 3 of the M2e tandem repeats replaced with Ser residues. Other than the NP scaffold sequence and the displayed tandem M2e molecule, the constructs also contain a locking domain LD7 (SEQ ID NO:5) and the universal PADRE T-cell epitope (SEQ ID NO:6). Finally, each of the constructs could additionally have a leader sequence at the N-terminus. The leader sequence could contain MGILPSPGMPALLSLVSLLSVLLMGCVAE (SEQ ID NO:1) as exemplified herein. [00101] Tandem M2e polypeptide with conserved CYs residues mutated in Repeats 2 and 3 (SEQ ID NO:23): [00102] SLLTEVETPIRNEWGCRCNDSSDGGGGSLLTEVETPTRNGWESKSS DSSDGGGGSLLTEVETPTRSEWESRSSGSSD [00103] Tandem M2e polypeptide with conserved CYs residues mutated in all 3 repeats (SEQ ID NO:24): [00104] SLLTEVETPIRNEWGSRSNDSSDGGGGSLLTEVETPTRNGWESKSSD SSDGGGGSLLTEVETPTRSEWESRSSGSSD [00105] In each of the two exemplified tandem M2e NP construct sequences shown below, each of the 3 tandem M2e sequences is italicized. The conserved Cys17 and Cys19 residues in the M2e sequences or the replacing Ser residues are also underlined. The two bold and underlined residues show the restriction site for PCR. Linkers or spacers connecting the M2e sequences and/or the different motifs of the constructs are italicized and underlined. These include the 5 aa GS linker GGGGS (SEQ ID NO:3) and the GGGG (SEQ ID NO:9) spacer separating the tandem M2e sequences. The double underlined sequence represents the display I3-01v9a scaffold sequence. Sequence of the locking domain (LD7) is double underlined and bolded. Finally, the PATRE T-cell epitope is indicated with double underlined and italicized font. [00106] Tandem M2e NP construct with Cys17/CYs19 in M2e repeats #2 and #3 mutated to serine, without N-terminal leader and C-terminal LD/PADRE motifs (SEQ ID NO:11): [00107] SLLTEVETPIRNEWGCRCNDSSDGGGGSLLTEVETPTRNGWESKSSDSS DGGGGSLLTEVETPTRSEWESRSSGSSDASGGGGSAKLAEELQKKMEELFKKHKI VAVLRANSVEEAKMKALAVFVGGVHLIEITFTVPDADTVIKELSFLKELGAIIG AGTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMPGVMTPTELVK AMKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNLDNVCEWFKAG VLAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTE [00108] Tandem M2e NP construct with Cys17/CYs19 in M2e repeats #2 and #3 mutated to serine, including C-terminal LD/PADRE motifs (SEQ ID NO:14): [00109] SLLTEVETPIRNEWGCRCNDSSDGGGGSLLTEVETPTRNGWESKSSDSS DGGGGSLLTEVETPTRSEWESRSSGSSDASGGGGSAKLAEELQKKMEELFKKHKI VAVLRANSVEEAKMKALAVFVGGVHLIEITFTVPDADTVIKELSFLKELGAIIG AGTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMPGVMTPTELVK AMKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNLDNVCEWFKAG VLAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTEGGGGSSPAVDIGDRLDELE KALEALSAEDGHDDVGQRLESLLRRWNSRRADGSAKFVAAWTLKAAA [00110] Tandem M2e NP construct with Cys17/CYs19 in 2 M2e repeats mutated, including N-terminal leader sequence (SEQ ID NO:17): [00111] MGILPSPGMPALLSLVSLLSVLLMGCVAESLLTEVETPIRNEWGCRCN DSSDGGGGSLLTEVETPTRNGWESKSSDSSDGGGGSLLTEVETPTRSEWESRSSGSS DASGGGGSAKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFVGG VHLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVSPH LDEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAM KGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKAAAF VEKIRGCTE [00112] Tandem M2e NP construct with Cys17/CYs19 in 2 M2e repeats mutated, including N-terminal leader sequence and C-terminal LD/PADRE motifs (SEQ ID NO:20): [00113] MGILPSPGMPALLSLVSLLSVLLMGCVAESLLTEVETPIRNEWGCRCN DSSDGGGGSLLTEVETPTRNGWESKSSDSSDGGGGSLLTEVETPTRSEWESRSSGSS DASGGGGSAKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFVGG VHLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVSPH LDEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAM KGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKAAAF VEKIRGCTEGGGGSSPAVDIGDRLDELEKALEALSAEDGHDDVGQRLESLLR RWNSRRADGSAKFVAAWTLKAAA [00114] Tandem M2e NP construct with Cys17/CYs19 in all 3 M2e repeats mutated to serine, without N-terminal leader and C-terminal LD/PADRE motifs (SEQ ID NO:12): [00115] SLLTEVETPIRNEWGSRSNDSSDGGGGSLLTEVETPTRNGWESKSSDSSD GGGGSLLTEVETPTRSEWESRSSGSSDASGGGGSAKLAEELQKKMEELFKKHKIV AVLRANSVEEAKMKALAVFVGGVHLIEITFTVPDADTVIKELSFLKELGAIIGA GTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMPGVMTPTELVKA MKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNLDNVCEWFKAGV LAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTE [00116] Tandem M2e NP construct with Cys17/CYs19 in all 3 M2e repeats mutated to serine, including C-terminal LD/PADRE motifs (SEQ ID NO:15): [00117] SLLTEVETPIRNEWGSRSNDSSDGGGGSLLTEVETPTRNGWESKSSDSSD GGGGSLLTEVETPTRSEWESRSSGSSDASGGGGSAKLAEELQKKMEELFKKHKIV AVLRANSVEEAKMKALAVFVGGVHLIEITFTVPDADTVIKELSFLKELGAIIGA GTVTSVEQCRKAVESGAEFIVSPHLDEEISQFCKEKGVFYMPGVMTPTELVKA MKLGHTILKLFPGEVVGPQFVKAMKGPFPNVKFVPTGGVNLDNVCEWFKAGV LAVGVGSALVKGTIAEVAAKAAAFVEKIRGCTEGGGGSSPAVDIGDRLDELE KALEALSAEDGHDDVGQRLESLLRRWNSRRADGSAKFVAAWTLKAAA [00118] Tandem M2e NP construct with Cys17/CYs19 in all 3 M2e repeats mutated to serine, including N-terminal leader sequence (SEQ ID NO:18): [00119] MGILPSPGMPALLSLVSLLSVLLMGCVAESLLTEVETPIRNEWGSRSN DSSDGGGGSLLTEVETPTRNGWESKSSDSSDGGGGSLLTEVETPTRSEWESRSSGSS DASGGGGSAKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFVGG VHLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVSPH LDEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAM KGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKAAAF VEKIRGCTE [00120] Tandem M2e NP construct with Cys17/CYs19 in all 3 M2e repeats mutated to serine, including N-terminal leader sequence and C-terminal LD/PADRE motifs (SEQ ID NO:21): [00121] MGILPSPGMPALLSLVSLLSVLLMGCVAESLLTEVETPIRNEWGSRSN DSSDGGGGSLLTEVETPTRNGWESKSSDSSDGGGGSLLTEVETPTRSEWESRSSGSS DASGGGGSAKLAEELQKKMEELFKKHKIVAVLRANSVEEAKMKALAVFVGG VHLIEITFTVPDADTVIKELSFLKELGAIIGAGTVTSVEQCRKAVESGAEFIVSPH LDEEISQFCKEKGVFYMPGVMTPTELVKAMKLGHTILKLFPGEVVGPQFVKAM KGPFPNVKFVPTGGVNLDNVCEWFKAGVLAVGVGSALVKGTIAEVAAKAAAF VEKIRGCTEGGGGSSPAVDIGDRLDELEKALEALSAEDGHDDVGQRLESLLR RWNSRRADGSAKFVAAWTLKAAA *** [00122] 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. [00123] It is further noted that all publications, sequence accession numbers, 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 N-terminally extended I3-01 nanoparticle scaffold sequence, comprising an extended N-terminal helix relative to the N-terminal helix in the original I3-01 scaffold sequence.

2. The N-terminally extended I3-01 nanoparticle scaffold sequence of claim 1, comprising a heterologous helical motif of about 6 to about 12 amino acid residues that is fused to the N-terminus of the I3-01 scaffold sequence set forth in SEQ ID NO:27.

3. The N-terminally extended I3-01 nanoparticle scaffold sequence of claim 2, wherein the heterologous helical motif comprises AKLAEELQK (SEQ ID NO:25), a conservatively modified variant or a substantially identical sequence thereof.

4. The N-terminally extended I3-01 nanoparticle scaffold sequence of claim 2, comprising SEQ ID NO:4, a conservatively modified variant or a substantially identical sequence thereof.

5. A self-assembling nanoparticle formed with the N-terminally extended I3-01 nanoparticle scaffold sequence of claim 1.

6. A nanoparticle vaccine construct, comprising a polypeptide immunogen that is fused to an N-terminally extended I3-01 nanoparticle scaffold sequence, wherein the N-terminally extended I3-01 nanoparticle scaffold sequence comprises an extended N-terminal helix relative to the N-terminal helix in the original I3-01 scaffold sequence.

7. The nanoparticle vaccine construct of claim 6, wherein the N- terminally extended I3-01 nanoparticle scaffold sequence comprises a heterologous helical motif of about 6 to about 12 amino acid residues that is fused to the N-terminus of the I3-01 scaffold sequence set forth in SEQ ID NO:27.

8. The nanoparticle vaccine construct of claim 6, wherein the heterologous helical motif comprises AKLAEELQK (SEQ ID NO:25), a conservatively modified variant or a substantially identical sequence thereof.

9. The nanoparticle vaccine construct of claim 6, wherein the N- terminally extended I3-01 nanoparticle scaffold sequence comprises SEQ ID NO:4, a conservatively modified variant or a substantially identical sequence thereof.

10. The nanoparticle vaccine construct of claim 6, wherein the polypeptide immunogen is fused via a linker at its C-terminus to the N-terminus of the N-terminally extended I3-01 nanoparticle scaffold sequence.

11. The nanoparticle vaccine construct of claim 10, wherein the linker comprises GGGGS (SEQ ID NO:3)

12. The nanoparticle vaccine construct of claim 6, wherein the polypeptide immunogen comprises (a) an influenza fusion polypeptide containing 2 or more tandem repeats of influenza M2 protein ectodomain (M2e) or (b) an HCV immunogenic protein.

13. The nanoparticle vaccine construct of claim 12, wherein the tandem M2e repeats are separated by a peptide spacer.

14. The nanoparticle displayed immunogenic protein of claim 13, wherein the peptide spacer comprises GGGG (SEQ ID NO:9).

15. The nanoparticle vaccine construct of claim 12, wherein at least one of the M2e tandem repeats comprises missense mutations at the conserved Cys17 and Cys19 residues.

16. The nanoparticle vaccine construct of claim 15, wherein the missense mutations comprise substitutions of each of the two Cys residues with an amino acid residues with uncharged polar side chains.

17. The nanoparticle vaccine construct of claim 15, wherein each of the Cys residues is independently replaced with an amino acid residue selected from the group consisting of serine, glycine, asparagine, glutamine, threonine and tyrosine.

18. The nanoparticle vaccine construct of claim 15, wherein the two Cys residues are both replaced with Ser.

19. The nanoparticle vaccine construct of claim 12, wherein the influenza fusion polypeptide comprises 3 tandem M2e sequences.

20. The nanoparticle vaccine construct of claim 19, wherein the 3 tandem M2e sequences are independently a human M2e sequence, an avian/swine consensus M2e sequence, or a human/swine consensus M2e sequence, except for missense mutations at residues Cys17 and Cys19 in at least 2 of the 3 tandem M2e sequences.

21. The nanoparticle vaccine construct of claim 20, wherein the influenza fusion polypeptide comprises, in any order, a human M2e (SEQ ID NO:2), an avian/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:30), and a human/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:31).

22. The nanoparticle vaccine construct of claim 20, wherein the influenza fusion polypeptide comprises, in any order, a human M2e with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:29), an avian/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:30), and a human/swine consensus M2e sequence with Cys17 and Cys19 each replaced with a Ser residue (SEQ ID NO:31).

23. The nanoparticle vaccine construct of claim 20, wherein the influenza fusion polypeptide comprises SEQ ID NO:23, SEQ ID NO:24, a conservatively modified variant or a substantially identical sequence thereof.

24. The nanoparticle vaccine construct of claim 20, comprising the sequence set forth in SEQ ID NO:11, SEQ ID NO:12, a conservatively modified variant or a substantially identical sequence thereof.

25. The nanoparticle vaccine construct of claim 20, further comprising a locking domain and a T-cell epitope at the C-terminus.

26. The nanoparticle vaccine construct of claim 25, wherein the locking domain comprises SEQ ID NO:5, and the T-cell epitope comprises SEQ ID NO:6.

27. The nanoparticle vaccine construct of claim 25, comprising SEQ ID NO:14, SEQ ID NO:15, a conservatively modified variant or a substantially identical sequence thereof.

28. The nanoparticle vaccine construct of claim 20, further comprising an N-terminal leader sequence.

29. The nanoparticle vaccine construct of claim 28, comprising SEQ ID NO:17, SEQ ID NO:18, a conservatively modified variant or a substantially identical sequence thereof.

30. The nanoparticle vaccine construct of claim 20, further comprising an N-terminal leader sequence, and a locking domain and a T-cell epitope at the C- terminus.

31. The nanoparticle vaccine construct of claim 30, comprising SEQ ID NO:20, SEQ ID NO:21, a conservatively modified variant or a substantially identical sequence thereof.

32. The nanoparticle vaccine construct of claim 12, wherein the HCV immunogenic protein comprises an E2 core or an E1E2 dimer.

33. The nanoparticle vaccine construct of claim 32, wherein the HCV E2 core comprises any one of SEQ ID NOs:32-35.

34. The nanoparticle vaccine construct of claim 32, wherein the HCV immunogenic protein comprises a tandem copy of 2 E2 core sequences.

35. The nanoparticle vaccine construct of claim 34, wherein the 2 E2 core sequences are from different HCV isolates.

36. The nanoparticle vaccine construct of claim 34, wherein the 2 E2 core sequences respectively comprise SEQ ID NOs:32 and 33 or SEQ ID NOs:34 and 35.

37. The nanoparticle vaccine construct of claim 34, further comprising a locking domain and a T-cell epitope at the C-terminus.

38. The nanoparticle vaccine construct of claim 37, wherein the locking domain comprises SEQ ID NO:5, and the T-cell epitope comprises SEQ ID NO:6.

39. The nanoparticle vaccine construct of claim 37, comprising (1) a subunit sequence containing from the N-terminus to the C-terminus: (a) SEQ ID NO:4, SEQ ID NO:32, SEQ ID NO:33, SEQ ID NO:5 and SEQ ID NO:6, or (b) SEQ ID NO:4, SEQ ID NO:34, SEQ ID NO:35, SEQ ID NO:5 and SEQ ID NO:6; or (2) a conservatively modified variant or substantially identical sequence thereof.

40. A polynucleotide sequence, encoding the subunit sequence of the nanoparticle vaccine construct of claim 6.

41. A vector harboring the polynucleotide sequence of claim 40.

42. A pharmaceutical composition comprising the nanoparticle vaccine construct of claim 6 or the polynucleotide sequence of claim 40.