Patent Publication Number: US-10772949-B2

Title: Dengue virus glycoprotein E DIII variants and uses thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage entry under 35 U.S.C. § 371 of PCT International Patent Application No. PCT/US2017/017637, filed Feb. 13, 2017, which claims the benefit of U.S. Provisional Patent Application No. 62/295,634, filed Feb. 16, 2016, the contents of each of which are incorporated herein by reference into the subject application. 
    
    
     STATEMENT OF GOVERNMENT SUPPORT 
     This invention was made with government support under grant numbers AI090249 and AI128090 awarded by the National Institutes of Health. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Throughout this application various publications are referred to in parentheses. Full citations for these references may be found at the end of the specification. The disclosures of these publications are hereby incorporated by reference in their entirety into the subject application to more fully describe the art to which the subject invention pertains. 
     Dengue virus is the leading arthropod-transmitted viral disease in the world with approximately 390 million human infections per year (1). Nearly 3.6 billion people live in at risk areas for infection, and the global distribution of the two mosquito species that carry the virus ( Aedes aegypti  and  Aedes albopictus ) is expanding beyond tropical regions and reaches as far north as New York in North America (2). Primary infection by one of the four Dengue virus serotypes (DENV1-4) typically causes a significant but self-limiting febrile illness, whereas secondary infections can lead to severe disease characterized by hemorrhagic fever and shock syndrome (Severe Dengue or Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS)). These latter syndromes occur in a minor fraction (1% or less) of secondary infections but lead to hospitalization and, in some cases, death. DHF and DSS are thought to arise from a process known as antibody-dependent enhancement (ADE) of infection. In an increasingly accepted model, ADE is caused by antibodies elicited during the course of primary infection that may be potently neutralizing against the primary infection serotype, but also have some cross-reactivity or weak neutralization potential against other serotypes (3). During secondary infection by a heterologous DENV serotype, these antibodies promote uptake and infection of the un-neutralized virus in Fc-γ receptor (FcγR) expressing cells, ultimately increasing viremia. This leads to greater levels of pro-inflammatory cytokines (e.g., IL-1β, TNF-α, IL-6, IFN-γ) and the viral NS1 protein in serum, both of which compromise junctional integrity of capillary endothelial cells (3). Structural proteins encoded by the DENV genome diverge by as much as 40% in amino acid sequence among the four serotypes, and within each of the serotypes, individual genotypes vary by ˜3%. Thus a critical objective for Dengue virus vaccine design is to elicit a broadly neutralizing antibody response against all four serotypes, since weakly cross-reactive antibodies may actually increase the risk of ADE. 
     Three Dengue vaccine candidates are in clinical development, all of which consist of tetravalent mixtures of attenuated or chimeric viruses. In recently published phase III trials, Sanofi&#39;s Dengvaxia®, a tetravalent mixture of yellow-fever virus vector containing DENV1-4 glycoprotein, provided only partial efficacy (&lt;70%) in seropositive cases, and was not effective at all for naïve individuals (4). Nonetheless, Dengvaxia® was recently approved for use in Mexico, the Philippines, Brazil and several other countries in children over the age of 9 who are presumably already flavivirus immune. Two other candidate vaccines are in moving into phase III trials (DENVax, Takeda; and TV003/TV005, NIAID); yet, both also elicited incomplete levels of neutralizing antibody responses (5, 6). Therefore, there is significant rationale for development of alternative vaccine platforms for use either as next-generation primary vaccines, or as boosting agents to improve the efficacy of existing live virus vaccines. 
     The mature, prefusion glycoprotein E exists as a head-to-tail dimer organized into rafts with icosahedral geometry on the viral particle (7, 8). Each E subunit contains three domains, DI, DII, and DIII. DII contains the fusion loop that inserts into the host cell upon initiation of the fusion reaction in the endosome; DI acts as a rigid connector to DIII, which is anchored via the stem and C-terminal TM domain into the viral membrane. The post-fusion E structure is a trimer with the DIII domain and stem region significantly relocated relative to DI and DII, so as to bring the host and viral membranes into proximity to facilitate viral membrane fusion (9). A host receptor has yet to be identified, but there is circumstantial evidence that interactions between cellular components and DIII initiate attachment and infection (10-12). Neutralizing antibodies arising during infection target a variety of epitopes on the E glycoprotein. Potent and cross-neutralizing antibodies appear to be directed toward either complex quaternary epitopes whose constituents involve portions of the E domains on adjacent dimer subunits (13, 14), or toward the lateral ridge on DIII formed by the A and G strands (15, 16). One example of a DIII-specific broadly neutralizing antibody (bNAb) is the murine mAb 4E11 that potently neutralizes DENV1-3 and weakly neutralizes DENV4 (see ref. (15) for the crystal structure of the DIII-4E11 complex). Recently, high-throughput mutagenesis (“combinatorial alanine scanning”) was used to quantify energetic contributions of contact residues on DIII from all four serotypes recognition feature for 4E11 (17). 
     Immunization of mice and non-human primates with recombinant DIII constructs (EDIIIs) leads to strong antibody responses, but these antibodies are poorly neutralizing or limited in breadth (18-28). In mice, the immunodominant regions of DIII appear to be in the AB- and FG-loops; resulting monoclonal antibodies are either cross-reactive and non-neutralizing (AB-loop) or type-specific and variably neutralizing (FG-loop) (26, 27). Antibodies that target other domains or more complex epitopes predominate in the human response during the course of natural infection (13, 14, 29, 30). Immunization of non-human primates with EDIII generates a high DIII-specific antibody titer (19, 23, 28). Other immunogen strategies that focus on more complex epitopes or on mimicking the prefusion E dimer are being explored (31), but EDIII has the advantage of being relatively small and easy to produce in large quantities. Dengue EDIII has high potential as an immunogen target, but previous attempts to improve its qualities have not been successful. One strategy to decrease the complexity of tetravalent cocktails is to produce EDIII fusion proteins linking EDIIIs from the four serotypes by flexible linkers (“beads on a string”), but this approach resulted in an imbalanced neutralizing titer response in mice and only partial protection in a suckling mice model for DENV1, 2, and 4 (25). Another strategy is engineering of a “consensus” DIII, in which conserved segments were emphasized (23). However, this approach led to DENV2-specific responses in non-human primates. 
     The present invention addresses the need for improved methods for preventing and treating Dengue virus infections by providing protein immunogens based on the Dengue virus glycoprotein subunit E domain III (EDIII). 
     SUMMARY OF THE INVENTION 
     Provided are specific Dengue virus glycoprotein subunit E DIII variants and their uses in preventing and treating Dengue virus infection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A-1C . Design of the resurfacing libraries. View down the A/G strand of DENV2 EDIII (inset shows orientation). Some sphere indicate 4E11 contact residues, other spheres indicate positions that were randomized, focusing on the AB- and FG-loops. (B) Phage ELISA of the rsDIIIs for binding to 4E11, all comparable to DENV2 EDIII WT. (C) High point phage ELISA reactivity profiles of rsDIIIs for 4E11 (A/G strand epitope), 2H12 (AB-loop epitope), 3H5-1 (FG-loop epitope), M2 (expression control) and 1% BSA (negative control). 
         FIG. 2A-2B . (A) Sample SDS-PAGE purification of rsDIIIs. A single product at the expected mass (15 kD) is observed. (B) ELISA profile for binding of purified DENV2 EDIII WT or rsDIII-Ser27 to either 4E11 or 1% BSA. 
         FIG. 3A-3C . WT DENV2 DIII (A) and clones rsDIII-Ala11 (B) and rsDIII-Ala30 (C) bind to the model broadly neutralizing antibody 4E11, but the clones do not appreciably bind to 2H12, a prototypic AB-loop antibody (non-neutralizing epitope) or to 3H5-1, a prototypic FG-loop antibody (type-specific). 
         FIG. 4 . rsDIII-A11 binding to mAb 4E11 by biolayer interferometry. 
         FIG. 5A-5B . Serum Ab titers against immunogens. (A) rsDIII-Ala11 and rsDIII-Ala30 immunogens result in similarly robust antibody responses compared to WT DENV-2 DIII. (B) No activity was observed against a negative control (his-tagged). 
         FIG. 6 . Reactivity of rsDIIIs was found to be broad for DIIIs from all four serotypes DENV-1, DENV-2, DENV-3 and DENV-4. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a Dengue virus glycoprotein subunit E DIII variant comprising variant Ser27 (SEQ ID NO:1), variant SerD1 (SEQ ID NO:2), variant Ala1 (SEQ ID NO:3), variant Ala2 (SEQ ID NO:4), variant Ala3 (SEQ ID NO:5), variant Ala5 (SEQ ID NO:6), variant Ala11 (SEQ ID NO:7), or variant Ala30 (SEQ ID NO:8). 
     In one embodiment, the variant consists of the specified variant. In one embodiment, the variant consists essentially of the specified variant, wherein any elements added to the specified variant do not decrease the immunogenic properties of the specified variant. 
     The engineered Dengue virus glycoprotein subunit E DIII variants have the amino acid sequences set forth below. The underlined portions of the sequences below correspond to the amino acid residues set forth for the corresponding sequences in Table 1. 
                    Ser27 (SEQ ID NO: 1):       DYKDDDDKGSGMSYSMCTGKFKIVKEIA STSHG TIVIRVQYEG D GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GVE                   SSQ L S LNWFKKGSSIGQHHHHHHHH               SerD1 (SEQ ID NO: 2):       DYKDDDDKGSGMSYSMCTGKFKIVKEIA ESSSG TIVIRVQYEG Y GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GVE                   SAQ L K LNWFKKGSSIGQHHHHHHHH               Ala1 (SEQ ID NO: 3):       DYKDDDDKGSGMSYSMCTGKFKIVKEI AAAAAG TIVIRVQYEG D GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GVA                   PGQ L E LNWFKKGSSIGQHHHHHHHH               Ala2 (SEQ ID NO: 4):       DYKDDDDKGSGMSYSMCTGKFKIVKEI AAAADA TIVIRVQYEG D GSPC E                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GVE                   AAE L K LNWFKKGSSIGQHHHHHHHH               Ala3 (SEQ ID NO: 5):       DYKDDDDKGSGMSYSMCTGKFKIVKEIA AAQAG TIVIRVQYEG D GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GAA                   AGA L E LNWFKKGSSIGQHHHHHHHH               Ala5 (SEQ ID NO: 6):       DYKDDDDKGSGMSYSMCTGKFKIVKEIA ATADA TIVIRVQYEG D GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GAE                   AAP L T LNWFKKGSSIGQHHHHHHHH               Ala11 (SEQ ID NO: 7):       DYKDDDDKGSGMSYSMCTGKFKIVKEIA EAAPG TIVIRVQYEG D GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GAE                   PGE L T LNWFKKGSSIGQHHHHHHHH               A1a30 (SEQ ID NO: 8):       DYKDDDDKGSGMSYSMCTGKFKIVKEIA ETQDG TIVIRVQYEG D GSPC K                 IPFEIMDLEKRHVLGRLITVNPIVTEKDSPVNIEAEPPFGDSYIII GAE                   PAA L E LNWFKKGSSIGQHHHHHHHH.            
The amino acids are encoded by the following DNA sequences:
 
     
       
         
           
               
               
            
               
                 Ser27 (SEQ ID NO: 9): 
                   
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgcctcgacgtcgcacggtaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgttgagtc 
               
               
                   
               
               
                 tagtcagctgagcctgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 SerD1 (SEQ ID NO: 10): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgagtcgtcgagcggtaccattgtgatccgtgtgcagtatgaaggctacggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgttgagtc 
               
               
                   
               
               
                 tgctcagctgaaactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 Ala1 (SEQ ID NO: 11): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgcagctgcagctggtaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgttgcacc 
               
               
                   
               
               
                 aggtcaactggaactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 Ala2 (SEQ ID NO: 12): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgcagctgcagatgctaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcgaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgttgaagc 
               
               
                   
               
               
                 agctgaactgaaactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 Ala3 (SEQ ID NO: 13): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgcagctcaagctggtaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgctgcagc 
               
               
                   
               
               
                 aggtgcactggaactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 Ala5 (SEQ ID NO: 14): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgcaactgcagatgctaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgctgaagc 
               
               
                   
               
               
                 agctccactgacactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 Ala11 (SEQ ID NO: 15): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgaagctgcacctggtaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgctgaacc 
               
               
                   
               
               
                 aggtgaactgacactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa 
               
               
                   
               
               
                 Ala30 (SEQ ID NO: 16): 
               
               
                 gactacaaggatgatgacgacaaaggcagcggcatgagctatagcatgtgcaccggcaaatttaaaatcgtgaa 
               
               
                   
               
               
                 agagatcgccgaaactcaagatggtaccattgtgatccgtgtgcagtatgaaggcgatggtagcccgtgcaaaa 
               
               
                   
               
               
                 tcccgttcgagatcatggacctggagaaacgccatgtgctgggtcgcctgattaccgtgaacccgattgtgacc 
               
               
                   
               
               
                 gagaaagatagcccggtgaacattgaagccgaaccgccgttcggcgatagctacattatcattggtgctgaacc 
               
               
                   
               
               
                 agctgcactggaactgaactggttcaagaagggcagcagcattggccagcatcatcatcatcatcatcatcatt 
               
               
                   
               
               
                 aa. 
               
            
           
         
       
     
     Shown below are the DIII wildtype amino acid sequences for serotypes DENV-1 (SEQ ID NO:17), DENV-2 (SEQ ID NO:18), DENV-3 (SEQ ID NO:19) and DENV-4 (SEQ ID NO:20). Also shown are the AB loop and FG loop regions. The arrow next to A is the A-strand, and the arrow next to G is the G-strand. The A/G strand is amino acid residues under the A and G arrows. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                 Strands indicated with arrows 
               
            
           
         
       
     
     Also provided are DIII variants encoded by the nucleic acid set forth in SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, SEQ ID NO:14, SEQ ID NO:15, and SEQ ID NO: 16. 
     Further provided are dimers and oligomers comprising any of the variants disclosed herein. The dimer or oligomer can contain a C-terminal disulfide-bonded leucine zipper dimerization domain (41). Stimulation of B-cell receptors (BCRs) for affinity maturation requires cross-linking of BCRs and thus, dimers or higher order oligomers may be beneficial. In addition, the serum stability of dimers and higher order oligomers may be better than monomers because of the increased size, which minimizes renal clearance, and potential resistance to degradation. 
     Also provided is a virion of an isolated, recombinant Dengue virus comprising any of the variants or dimers or oligomers disclosed herein. 
     Also provided is a Dengue virus vaccine composition comprising any of the variants, or dimers or oligomers, or virions disclosed herein. The vaccine composition can further comprise an immunological adjuvant. 
     Also provided is a method of eliciting an immune response in a subject comprising administering to the subject any of the variants, or dimers or oligomers, or virions, or vaccines disclosed herein in an amount effective to elicit an immune response in a subject. 
     Also provided is a method of vaccinating a subject for Dengue virus infection comprising administering to the subject any of the variants, or dimers or oligomers, or virions, or vaccines disclosed herein in an amount effective to vaccinate a subject for Dengue virus. 
     Also provided is a method of immunizing a subject against Dengue virus infection comprising administering to the subject any of the variants, or dimers or oligomers, or virions, or vaccines disclosed herein in an amount effective to immunize a subject against Dengue virus. 
     Also provided is a method of treating a Dengue virus infection in a subject or treating a disease caused by a Dengue virus infection in a subject comprising administering to the subject any of the variants, or dimers or oligomers, or virions, or vaccines disclosed herein in an amount effective to treat a Dengue virus infection or treat a disease caused by a Dengue virus infection in a subject. The subject being treated can have, for example, one or more of Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). 
     Preferably, the variants, dimers, oligomers, virions and vaccines disclosed herein are effective against all Dengue virus serotypes. 
     Also provided is a method of preparing a Dengue virus glycoprotein subunit E DIII variant that is effective as a Dengue virus immunogen, the method comprising 
     a) masking immunodominant, but non-neutralizing or Dengue virus type-specific, AB- and FG-loops of DIII by mutation to obtain a DIII variant, which retains the A/G strand, and 
     b) using phage display to select a DIII variant from step a) that elicits an antibody targeting a broadly neutralizing antibody epitope, 
     thereby preparing a Dengue virus glycoprotein subunit E DIII variant that is effective as a Dengue virus immunogen. 
     In the method, the amino acid positions in DIII can be varied, for example, by substitution with alanine or serine. The variant can be subjected to selection against a DIII-specific broadly neutralizing A/G strand monoclonal antibody. Preferably, the variant binds to a DIII-specific broadly neutralizing A/G strand monoclonal antibody with similar reactivity as wild type DIII, but the variant does not exhibit reactivity to an AB-loop monoclonal antibody or to a FG-loop monoclonal antibody. 
     The vaccine or composition for administration to a subject can be formulated for administration by any routine route of administration, including but not limited to, subcutaneous, intra-muscular, intra-nasal, or mucosal administration. 
     The subject can be any animal, and is preferably a human subject. 
     All combinations of the various elements described herein are within the scope of the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 
     This invention will be better understood from the Experimental Details, which follow. However, one skilled in the art will readily appreciate that the specific methods and results discussed are merely illustrative of the invention as described more fully in the claims that follow thereafter. 
     Experimental Details 
     An attractive strategy for next-generation platforms or boosting agents is the use of subunit vaccines (immunogens) that contain all or parts of the Dengue virus glycoprotein subunit E. The use of recombinant protein immunogens prevents the premature clearance of attenuated or chimeric virus boosters due to pre-existing immunity to vaccine vector components; such clearance would render the boost less effective. Furthermore, subunit vaccines are safer and have lower risk of inducing infection-related side effects because they are replication incompetent. 
     The major challenge to the use of the Dengue virus glycoprotein E domain III (EDIII) as a single immunogen is that the immunodominant regions are focused on non-productive or narrow-spectrum epitopes. Protein engineering was used to identify and characterize EDIII variants that overcome these limitations. Furthermore, by re-engineering EDIII to elicit antibodies targeting a bNAb epitope, the present strategy achieves a single component immunogen that elicits protective antibodies, avoiding the manufacturing and possible safety concerns of multivalent immunogen production. The present application discloses protein immunogens based on the Dengue virus glycoprotein E domain III (EDIII). 
     Major advances in combinatorial and computational protein design have previously permitted engineering of proteins with enhanced function. “Synthetic protein engineering”—defined here as use of phage- or yeast-displayed libraries with restricted diversity elements encoded by designed, synthetic oligonucleotides—in particular has been used in a variety of applications (32-38). The combination of highly specified libraries, coupled with complete control of the binding selections, provides the opportunity to develop reagents that have either enhanced specificity for a single target (e.g., for particular post-translational modifications) or multi-specificity without being non-specific. This method has been used to identify highly specific binding antibodies or proteins that generally would not be accessible by other methods (32-34, 36). For example, specific fusogenic intermediates of virus glycoproteins have been targeted by this approach. 
     In the present studies, phage display and synthetic protein engineering were used to develop novel “resurfaced” variants of DENV2 EDIII (rsDIII) in which the immunodominant AB- and FG-loops, as well as other surface positions, are masked by mutation. DENV2 EDIII was expressed in bivalent format on M13 bacteriophage as a fusion to the minor coat protein (pIII). Based on the structure of EDIIIs from DENV1-4 in complex with 4E11, as well as on previous “functional epitope” mapping to decipher the major contributing residues to binding 4E11, two libraries were designed in which selected positions in DENV2 EDIII were allowed to vary among wild type (WT) and alanine (Ala) (Ala library) or WT and serine (Ser) (Ser library) ( FIG. 1A ). The varied positions included all immunodominant regions of the AB- and FG-loops as well as several surface exposed residues distal to the A/G strands. Alanine was chosen as a substitution because it is statistically disfavored at antibody-antigen interfaces, likely due to the relatively short side chain that is incapable of participating in extended interactions required for large intermolecular interfaces (39). Serine contains a small, flexible, and relatively inert side chain and is also unlikely to form extended interactions with antibody combining sites (40). These two libraries were subjected to selection against 4E11. It was hypothesized that mutants from these libraries that survived selection for 4E11 binding would retain productive conformation for the A/G strand epitope. Clones were sought that had a high content of Ala or Ser in the varied positions, to destroy unproductive epitopes, but retained 4E11 binding thereby maintaining the critical neutralizing epitope. 
     From these selections, eight rsDIII clones were identified (six from the Ala library and two from the Ser library) with desirable reactivity profiles (Table 1). Phage ELISA showed that all rsDIIIs bound to immobilized 4E11 with similar reactivity to WT DENV2 EDIII ( FIG. 1B ). Importantly, none of the rsDIIIs exhibited reactivity at high phage titer to the prototypic AB-loop mAb 2H12 (non-neutralizing) (27) or the prototypic FG-loop mAb 3H5-1 (type-specific) (26), whereas WT DENV2 EDIII did ( FIG. 1C ). The expression levels of all rsDIIIs were similar as determined by reactivity with mAb M2, which specifically recognizes the FLAG epitope that was engineered at the N-terminus of EDIII. 
     The most efficient production protocol was found to involve purification by Nickel affinity chromatography and refolding of rsDIIIs from inclusion bodies, which generally yields high purity material in reasonable yield (see  FIG. 2A , for SDS-PAGE analysis). Importantly, the activity of one refolded rsDIII protein (rsDIII-Ser27) for binding to 4E11 has been confirmed ( FIG. 2B ), indicating that protein behavior off-phage is similar to behavior on-phage. 
                     TABLE 1                  Sequences of Selected rsDIII Clones.                                 Clone/   AB loop           FG loop                                                                         Position   314   315   316   317   318   329   334   381   382   383   384   385   386   388               WT   E   T   Q   H   G   D   K   G   V   E   P   G   Q   K       DENV-2                                                               EDIII                                                                       rsDIII- Ala1     A       A       A       A     G   D   K   G   V     A     P   G   Q                                     rsDIII- Ala2     A       A       A                             A     D                         G   V   E     A       A                           K               rsDIII- Ala3     A       A     Q     A     G   D   K   G     A       A       A     G     A                                       rsDIII- Ala5     A     T     A                             A     D   K   G     A     E     A       A                                                             rsDIII- Ala11   E     A       A                           G   D   K   G     A     E   P   G                                                           rsDIII- Ala30   E   T   Q                         G   D   K   G     A     E   P     A       A                                       rsDIII- SerD1   E     S       S       S     G                         K   G   V   E     S                           Q   K               rsDIII-     S     T     S     H   G   D   K   G   V   E     S       S     Q     S         Ser27                    
Residues substituted for Ala (A) or Ser S) are shown by underlining with a straight line. The combinatorial codon permitted additional variation, in some cases these residues were selected, shown in italics and underlining with a wavy underline. The amino acid residues in Table 1 correspond to the underlined portions of the corresponding parts of the amino acid sequences of the variants disclosed herein above: Ser27 (SEQ ID NO:1), SerD1 (SEQ ID NO:2), Ala1 (SEQ ID NO:3), Ala2 (SEQ ID NO:4), Ala3 (SEQ ID NO:5), Ala5 (SEQ ID NO:6), Ala11 (SEQ ID NO:7), and Ala30 (SEQ ID NO:8). The wildtype DENV-2 DIII sequence is shown in SEQ ID NO:18.
 
     A number of the “resurfaced” DIIIs (rsDIIIs, vaccine candidates) have been expressed, purified, and characterized in greater detail. Among these, the clones rsDIII-Ala11 and rsDIII-Ala30 had favorable properties, and thus additional experiments were conducted with these two clones. 
     Binding of rsDIII-Ala11 and rsDIII-Ala30 to the model broadly neutralizing antibody (bNAb) 4E11 was found to be as good as WT DENV2 DIII, but importantly the rsDIII-Ala11 and rsDIII-Ala30 clones did not exhibit appreciable binding to 2H12, a prototypic AB-loop antibody (non-neutralizing epitope) or 3H5-1, a prototypic FG-loop antibody (type-specific) ( FIG. 3A-3C ). The results in Table 2 were obtained by ELISA. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 EC50 values for binding of DIII domains to DENV mAbs. 
               
            
           
           
               
               
               
               
            
               
                   
                 4E11 
                 2H12 
                 3H5 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 WT DENV2 DIII 
                 2.4 nM 
                 0.32 nM 
                 ~μM 
               
               
                   
                 rsDIII-Ala11 
                 5.7 nM 
                 No binding 
                 No binding 
               
               
                   
                 rsDIII-Ala30 
                 2.5 nM 
                 No binding 
                 No binding 
               
               
                   
               
            
           
         
       
     
     By biolayer interferometry, rsDIII-Ala30 was also found to bind with similar high affinity to 4E11 but not to 2H12 or 3H5-1. Similar results were obtained with rsDIII-Ala11 ( FIG. 4 , Table 3). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 DIII binding to DENV mAbs, by biolayer 
               
               
                 interferometry and ELISA. 
               
            
           
           
               
               
               
               
            
               
                   
                 mAb 4E11 
                 mAb 2H12 
                 mAb 3H5-1 
               
               
                   
                 (A/G strand) 
                 (AB loop) 
                 (FG loop) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 BLI 
                 ELISA 
                 BLI 
                 ELISA 
                 ELISA 
               
               
                 Clone 
                 (K D ) 
                 (EC 50 ) 
                 (K D ) 
                 (EC 50 ) 
                 (EC 50 ) 
               
               
                   
               
               
                 WT DENV2 
                 ~4 pM 
                 2 nM 
                 30 pM 
                 0.3 nM 
                 ~2 mM 
               
               
                 EDIII 
                   
                   
                   
                   
                   
               
               
                 rsDIII-Ala11 
                 &lt;1 pM 
                 6 nM 
                 No 
                 No 
                 No 
               
               
                   
                   
                   
                 binding 
                 binding 
                 binding 
               
               
                   
               
            
           
         
       
     
     NMR experiments were performed with 15N-labeled WT DENV2 EDIII, rsDIII-Ala11, and rsDIII-Ala30. 1H-15N HSQC data shows that many resonances corresponding to “core” residues overlap between WT and either rsDIII-Ala11 or rsDIII-Ala30. These data indicate that the core structures of WT, rsDIII-Ala111 and rsDIII-Ala30 are likely to be very similar, and thus the epitope resurfacing has not affected the core folding structure of the DIII domain. 
     In vivo testing. Groups of 10 BALB/c mice were immunized with three doses of WT DENV2 EDIII, rsDIII-Ala11, or rsDIII-Ala30. Mice were immunized with immuogen at days 0 (20 μg/Complete Freund&#39;s Adjuvant, CFA), day 14 (20 μg/CFA), and day 28 (10 μg/Incomplete Freund&#39;s Adjuvant, IFA). Sera were analyzed at days 0 (naïve, pre-immune sera), 14, 28, 42, 61, and 90. All three immunogens were found to elicit robust antibody responses (high titers) that were specific for DIII (activity against non-specific control bearing a His tag, which is also present in DIII, was not observed) ( FIG. 5A-5B ). Furthermore, the reactivity of rsDIII-Ala11 and rsDIII-Ala30 was found to be broad for DIII from all four serotypes (DENV-1, DENV-2, DENV-3 and DENV-4) ( FIG. 6 ). Notably, this same cross-reactivity was observed with WT DENV2 EDIII, although this has been documented previously as a predominant response to the AB loop, which is extensively mutagenized in rsDIII-Ala11 and rsDIII-Ala30. 
     Examples of purification protocols include the following. 
     rsDIII Expression. 
     From a freshly transformed plate, incubate 1 colony in 50 mL 2×YT media with 50 μL carbenicillin overnight at 37° C., 220 RPM. Transfer 5 mL overnight culture to 100 mL low phosphate media with 100 μL carbenicillin; make up to ten 100 mL cultures. Incubate for 24 hours at 30° C., 220 RPM. Harvest cells via centrifugation at 4,500 RPM, 4° C., for 15 minutes. Weigh cell pellets and freeze at −20° C. until purification. 
     rsDIII Purification. 
     Thaw cells at room temperature. Per gram of wet cell weight add 5 mL of 1×-diluted Bug Buster. Resuspend cells in PBS (20 mM sodium phosphate monobasic+150 mM NaCl) with EDTA-free protease cocktail inhibitor and DNaseI. Add 10× Bug Buster to dilute to 1× and incubate with gentle rocking for 20 minutes at room temperature. Centrifuge at 12,000 RPM (ss-34), for 30 minutes at 4° C. Rinse the pellet (inclusion body fraction) with PBS by vortexing and centrifuge for 30 minutes at 12,000 RPM and 4° C. Discard supernatant. Resuspend pellet in 8M urea/PBS overnight with stirring. Spin down at 15° C. for 30 minutes at 12,000 RPM. Keep the supernatant (solubilized inclusion body). 
     Wash 1 mL Ni-NTA beads (Qiagen) with 8M urea/PBS. Load inclusion body fraction onto the column and collect the flow through. Wash with 7.5 mL 8M urea/PBS, pH 6.0 and collect fraction. Wash with 7.5 mL 8M urea/PBS, pH 5.3/55 mM Imidazole and collect fraction. Elute with 3.8 mL 8M urea/PBS, pH 4.0/250 mM Imidazole and collect elute. Elute with 5 mL 8M urea/PBS, pH 4.0/500 mM Imidazole and collect elute. Run SDS-PAGE to verify purity and pool relevant fractions. 
     rsDIII Refolding. 
     Dilute denatured rsDIII 20-fold into 20 mM Tris-HCl, 500 mM NaCl, pH 7.8—results in a final urea concentration of 0.4M. Dialyze sample in 20 mM Tris-HCl, 500 mM NaCl, pH 7.8 to remove urea. 
     rsDIII Purification and Refolding on Column. 
     Prepare inclusion body fraction as above and wash 1 mL Ni-NTA beads as above. Load inclusion body fraction onto column and collect the flow through. Wash with 5 mL 8M urea/PBS, pH 6.0 and collect fraction. Wash with 5 mL 8M urea/PBS, pH 5.8 and collect fraction. Wash with 10×1 mL refolding buffer (20 mM Tris-HCl, 500 mM NaCl, pH 7.8) and collect fraction. Elute with 5 mL 20 mM Tris/500 mM NaCl/250 mM Imidazole, pH 7.8 and collect elute. Elute with 5 mL 20 mM Tris/500 mM NaCl/500 mM Imidazole, pH 7.8 and collect elute. Run SDS-PAGE and pool relevant fractions. Concentrate to 2-3 mL and dialyze into 20 mM Tris-HCl/500 mM NaCl, pH 7.8 to remove imidazole. 
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