Abstract:
Provided are novel methods for expressing antigens in a vaccine vector strain, a live oral vaccine designed to prevent clostridium difficile-associated disease and methods for delivering antigens to the mucosal immune system of a subject.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/712,923, filed Oct. 12, 2012, which is hereby incorporated by reference in its entirety. 
     
    
     GOVERNMENT FUNDING 
       [0002]    The present invention was made with government support under USDA Grant No. CSREES20053520115345 for development of the vector strain ZCR533, start-up funds from the Biomedical Research Institute of New Mexico (BRINM) for the preparation of the ZCR533 expression plasmids and VA Merit Review award entitled “Attaching/Effacing  E. coli  as Vaccine Vectors” (Boedeker, PI). The Government has certain rights to this invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]      Clostridium Difficile  infection (CDI) can range in severity from asymptomatic to severe and life-threatening, especially among the elderly. People are most often infected in hospitals, nursing home, or other medical institutions, although CDI in the outpatient setting is increasing. Indeed, since 1996 the incidence of CDI has more than doubled resulting in up to three million cases each year in the United States and making CDI the most common bacterial cause of diarrhea in the United States. With the rising incidence, there is also a higher mortality associated with the disease. This mortality is related to at least two factors: (1) increasing virulence of the  C. difficile  strains; and (2) increasing host vulnerability. 
         [0004]    The increase in occurrences of  Clostridium Difficile  associated diarrhea (CDAD) in hospitalized patients leads to high incremental costs for individuals who develop the disease. In the Veterans Administration Hospital System, over the last decade the cases of CDI have doubled to an estimated number of 10/1000 discharges for persons under 65 years of age and to 20/1000 discharges for persons over 65 years of age in the year 2004. Additional treatment costs due to CDI are estimated at $3600 per case. In addition, following treatment of the primary infection with antibiotics, the recurrence rate of the disease is very high. In the U.S., incremental costs per hospitalization were estimated to be $3,000 to $5,000 for primary infections and $13,000 to $18,000 for recurrent infections. 
         [0005]    With an aging population, increasing levels of co-morbidity and widespread use of broad-spectrum antibiotics are predicted to expand the current epidemic of nosocomial CDI. 
         [0006]    Some of the most troublesome aspects of the current CDI epidemic are the emergence of decreasing effectiveness of the frontline antibiotic metronidizole and the appearance of a more virulent strain of  C. difficile  with enhanced toxigenic potential which emerges because of floroquinolone resistance. Increasingly, oral vancomycin has become the treatment of choice for nosocomial CDI, though cost and emergence of decreasing effectiveness of vancomycin resistance limit this approach and result in frequent relapses. 
         [0007]    Accordingly, as both the incidence and complexity are increasing there is an urgent need for novel therapeutic and prophylactic approaches to CDI. The vaccine disclosed herein provides for local mucosal immune responses in the intestine and meets this unmet need. 
       SUMMARY OF THE INVENTION 
       [0008]    Provided herein is a live oral vaccine designed to induce protective mucosal, and systemic, immunity to  Clostridium difficile  toxins in order to prevent CDAD. CDAD is usually manifest as severe pseudomembranous colitis in hospitalized patients receiving antibiotics. We previously developed a live attenuated Enterohemorrhagic  Escherichia coli  (EHEC) bacteria in which the Shiga toxin coding sequences were deleted to abolish Shiga toxin production and one or more of the nucleotide sequences for the bacterial adhesion protein intimin, the locus of enterocyte effacement encoded regulator, and the translocated intimin receptor were mutated to inactivate the encoded protein(s)—referred to herein as the “ZCR533 vector strain”. See, U.S. Publication No. 2008/0286310, incorporated by reference herein in its entirety, 
         [0009]    In the present invention, the ZCR533 vector strain has been engineered to express the immunogenic C-terminal receptor binding portions of the major virulence determinants of  C. Difficile , the A and B toxins (TcdA and TcdB). To express these protective toxin antigens in an immunogenic form in the  E. coli  vector strain, TcdA and TcdB were incorporated into the passenger domain of the autotransporter protein EspP. See, e.g., Greenberg, R. N., et al., Phase I dose finding studies of an adjuvant  Clostridium difficile  toxoid vaccine, Vaccine 30:2245-2249 (2012), incorporated by reference herein in its entirety. Molecular cloning techniques were used to express the C terminal repeats, comprising the binding domains of the TcdA and TcdB toxins, in the passenger domain of the EspP autotransporter on a multicopy plasmid. 
         [0010]    When expressed this way, using immuno-fluorescent anti-toxin antibody, the toxin antigens were found to be displayed on the surface of the vector strain. Mucosal immunization with this new strain should induce anti-toxin immunity in the intestine and provide protection against the toxins of  C. difficile.    
         [0011]    The studies described herein confirm the validity of our approach to immunization against toxin antigens. For example, shiga toxin B subunit antigen was immunogenic, and protective against shiga toxin producing  E. coli  (STEC) infection, when expressed in the autotransporter EspP either on the surface of the organism, or secreted into the medium. 
         [0012]    Provided herein is a method for delivering an antigen to the mucosal immune system of a subject. In some embodiments, the method comprises administering to the subject a live attenuated Enterohemorrhagic  Escherichia Coli  (EHEC) comprising an antigen of another pathogen. In some embodiments, the antigen of another pathogen is an antigen of  Clostridium Difficile . In specific embodiments, the live attenuated Enterohemorrhagic  Escherichia Coli  (EHEC) has been engineered to express the immunogenic C-terminal receptor binding portions of TcdA and TcdB. 
         [0013]    Also provided herein is a method of treating, preventing or ameliorating a Clostridium Difficile Associated Disease. In some embodiments, the method comprises administering to a subject a live attenuated Enterohemorrhagic  Escherichia Coli  (EHEC) comprising an antigen of another pathogen. In various embodiments, the antigen is delivered to the mucosal immune system of the subject. In specific embodiments, the antigen of another pathogen is an antigen of  Clostridium Difficile . In other specific embodiments, the  Clostridium Difficile  Associated Disease comprises diarrhea, fever, nausea, loss of appetite, or abdominal pain. 
         [0014]    Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0015]    The details of the present invention, both as to its structure and function, may be cleaned in part by study of the accompanying drawings, in which: 
           [0016]      FIG. 1  illustrates the homologous  C. Difficile  Toxins TcdA and TcdB and their three major domains: (1) an N Terminus with glycosyltransferase activity; (2) a central translocation domain; and (3) a C Terminus of polypeptide repeats with receptor binding activity. The C terminal polypeptide repeat units are the target of the vaccine according to one embodiment. 
           [0017]      FIG. 2A  illustrates the four functional domains of the autotransporter proteins and  FIG. 2B  illustrates the autotransporter secretion mechanism. Autotransporters form a pore in the bacterial outer membrane, then transfer their passenger domain through the pore to the surface of the cell where it is released by proteolytic cleavage. According to some embodiments, these autotransporters are modified to express antigen (i) in the cytoplasm (signal sequence deletion), (ii) in the periplasm (translocator mutation), (iii) at the cell surface (cleavage site mutation) and/or (iv) secreted into the external milieu (native conformation). 
           [0018]      FIG. 3  illustrates a cloning scheme for the introduction of TcdA and TcdB target antigens into the EspP passenger domain of expression plasmids pFR103 and pFR111 according to one embodiment. As illustrated, PCR-1 amplifies the target antigens from  C. Difficile  genomic DNA flanked with EspP specific sequences, PCR-2 replaces Stx1B in the passenger domain of EspP with either TcdA or TcdB antigenic fragments, and PCR-3 confirms the insertion of TcdA and TcdB antigen sequences into the expression plasmids. 
           [0019]      FIG. 4  illustrates Agarose gel electrophoresis confirmation of the cloning of TcdA ( FIGS. 4A and 4C ) and TcdB ( FIGS. 4B and 4D ) into the autotransporter EspP of pFR103 (secreted— FIGS. 4A and 4B ) and pFR111 (surface— FIGS. 4C and 4D ) by Colony PCR according to one embodiment. 
           [0020]      FIG. 5  illustrates a Western blot of  E. coli  whole cell extracts showing expression of TcdA ( FIG. 5A ) or TcdB ( FIG. 5B ) antigens by pFR103 (secreted) and pFR111 (surface) according to one embodiment. 
           [0021]      FIG. 6  illustrates surface expression of TcdA and TcdB with EspP according to one embodiment. 
           [0022]      FIG. 7  illustrates a cloning scheme for expression of both TcdA and TcdB in a single autotransporter. This illustrates tandem insertion of TcdB 70 aa target sequence while simultaneously maintaining the proximal 58 aa TcdA sequence from pFR103-TcdA or pFR111-TcdA. 
           [0023]      FIG. 8  illustrates cloning of TcdB 70 aa fragment into pFR103-TcdA. The agarose gel electrophoresis shows the insertion of TcdB 70 aa fragment into pFR103-TcdA according to one embodiment. 
           [0024]      FIG. 9  illustrates cloning of TcdB 70 aa fragment into pFR111-TcdA. The agarose gel electrophoresis shows the insertion of TcdB 70 aa fragment into pFR111-TcdA according to one embodiment. 
           [0025]      FIG. 10  illustrates expression of TcdA-TcdB fusion anti-gens by secretion and surface expression-enabled EspP plasmids. Western blot of ZCR-533 whole cell extracts containing pFR103-TcdB-TcdA Or pFR111-TcdB-TcdA. Polyclonal antibody to TcdA recognizes TcdB-TcdA fusions in both constructs according to one embodiment. 
           [0026]      FIG. 11  provides the complete sequence of TcdAl27aa with EspP (SEQID 1), where the bracketed section from 723-1108 is the TcdA insertion. 
           [0027]      FIG. 12  provides the complete sequence of TcdB160aa with EspP (SEQID 2), where the bracketed section from 724-1204 is the TcdB insertion. 
           [0028]      FIG. 13  provides the complete sequence of TcdA-TcdB fused with EspP (SEQID 3), where the bracketed section from 723-934 is the TcdB insertion and the bracketed section from 935-1144 is the TcdA insertion. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary Vaccine Compositions 
       [0029]    The vaccine described herein is based on a genetically attenuated strain of  E. coli  0157:H7 which serves as vector to deliver antigens of other important pathogens such as  C. difficile . This vaccine strain contains no toxin activity, but retains antigenic components of important  E. coli  0157:H7 virulence determinants (intimin and the 0157 lipopolysaccharide) such that the vector itself serves as a vaccine for 0157  E.coli  strains. 
         [0030]    Into the vector strain ZCR533, antigenic components of the most important virulence factors of  C. difficile , i.e. the clostridial toxins A and B (TcdA and TcdB) were introduced. The C-terminal binding regions of the toxins were incorporated as fusions with the passenger domain of the autotransporter EspP and introduced on a medium copy number plasmid. In their native form, these autotransporter constructs allow the antigenic determinants of TcdA and TcdB to be displayed on the surface or secreted by the vector organism. Surface displayed antigens have been determined to be the best location for inducing mucosal immunity. 
       Exemplary Animal Study Procedure 
       [0031]    C57BL/6 mice, female, 6-8 weeks of age and Golden Syrian hamster, female, 4-5 weeks of age are obtained from commercial vendor. The animals are housed in micro-isolator cages and provided with food and water ad libitum. The animals are randomly distributed into 2 groups each group with 10 animals for each group. 
         [0032]    The present invention is illustrated by the following examples. It is to be understood that the particular examples, materials, amounts, and procedures are to be interpreted broadly in accordance with the scope and spirit of the invention set forth herein. 
       EXAMPLES 
     Example 1 
       [0033]    Tandem insertion of TcdA and TcdB 70 aa C terminal target antigens. 
         [0034]    The 70 aa C terminal target antigens of TcdA and TcdB were tandemly inserted by PCR cloning method as depicted in  FIG. 7 . DNA encoding C terminal target antigens of TcdB were amplified by PCR flanked with 30 by sequences complementary to the insertion site in plasmids pFR103-TcdA or pFR111-TcdA. These PCR products were used for the second PCR using pFR103-TcdA and pFR111-TcdA as templates which resulted in insertion of 70 aa target sequence of TcdB, while simultaneously replacing the proximal 58 aa coding sequence from pFR103-TcdA or pFR111-TcdA. 
         [0035]    The resultant plasmids consisted 70 aa C- terminal coding sequence of TcdB fused to 70 aa C terminal coding sequence of TcdA fused altogether with the passenger domains of EspP of expression plasmids pFR103 or pFR111. These plasmids were then introduced into ZCR-533 by electroporation and the colonies were screened for the presence of inserts ( FIG. 8  and  FIG. 9 ). The positive clones were further analyzed for the expression of TcdA-TcdB fusion antigens. 
       Example 2 
       [0036]    Expression of TcdA-TcdB Fusion Antigens by Secretion and Surface Expression-Enabled Autotransporter Plasmids pFR103 Or pFR111. 
         [0037]    Total cell extracts of the positive clones of ZCR 533 harboring TcdB-TcdA target-fusion antigens were subjected to western blot with TcdA polyclonal antibodies. The Western blot ( FIG. 10 ) clearly shows expression of target fusion antigens by both the plasmids. 
       Example 3 
       [0038]    Immunization of Mice and Hamsters with  E. Coli  Vaccine Strains Expressing a Fusion TcdA:TcdB Construct 
         [0039]    A culture of the vaccine construct strain expressing a detoxified  C. Difficile  TcdA:TcdB fusion construct (ZCR533-TcdA:TcdB) is adjusted to a concentration (using PBS) allowing for 1×10 7 −1×10 8  bacteria to be administered intranasally to each anesthetized animal using a micro-pipettor (in a 20 μl volume for mice and in a 50 μl volume for hamsters, half of the dose into each nostril). 
         [0040]    The dose is administered to the external nares of anesthetized animals and allowed to completely inhale the vaccine dose. The hybrid vaccine strains are administered twice (a priming dose and booster dose) two-weeks apart. An equal volume of the PBS diluent is likewise administered to the control (non-immunized) mice. The animals are observed daily for any clinical signs of distress to assure the safety of the vaccine constructs. 
       Example 4 
     Measurement of Antibody Immune Response Following Intranasal Administration of  E. Coli  Vaccine Strains Expressing a Fusion TcdA:TcdB Construct to Mice and Hamsters. 
       [0041]    The mice are bled, pre-immunization and post-immunization, from the tail vein with the serum collected and stored at −80° C. The hamsters are bled from the retro-orbital sinus under isoflurane anesthesia with the serum collected and stored at −80° C. An enzyme linked Immunosorbent assay (ELISA) is performed to measure the level of serum antibody response to the TcdA and TcbB antigens. 
       Example 5 
       [0042]    Challenge of Immunized Mice with  C. difficile  Wild-Type 
         [0043]    The immunized (with the ZCR533-TcdA:TcdB fusion construct vaccine strain) C57BL/6 mice are challenged intragastrically with a  C. Difficile  Wild-Type Strain. The mice are administered intragastrically 0.5 mg/ml of cefoperazone in sterile drinking water for 10 days (antibiotic water will be refreshed every other day to avoid antibiotic break down). 
         [0044]    After 10 days, mice are taken off antibiotic water and given regular sterile water for 2 days. The mice are then administered intragastrically a lethal dose of  C. Difficile  vegetative bacterial cells. Weights, diarrhea, clinical signs of illness, morbidity and mortality are measured daily post-challenge for 7-14 days. The severity of diarrhea in the hamsters is scored as follows: 0, no diarrhea; +1, loose feces; +2, tail region wet; +3, tail, paws and lower abdomen wet. 
       Example 6 
       [0045]    Challenge of Immunized Hamsters with  C. Difficile  Wild-Type 
         [0046]    The immunized (with the ZCR533-TcdA:TcdB fusion construct vaccine strain) Golden Syrian hamsters are challenged intragastrically with a  C. Difficile  wild-type. Initially, the hamsters are administered clindamycin-HCL (3 mg/100 grams body weight) intragastrically followed 3 hours later with a lethal dose of C. Difficile vegetative bacterial cells administered intragastrically (previously washed in PBS to eliminate any residual free clostridial toxin). Weights, clinical signs of illness, morbidity and mortality are measured daily post-challenge for 7-14 days. 
       Example 7 
     Evaluation of Colonization of the  C. Difficile  Wild-Type Strain in Immunized Mice and Hamsters 
       [0047]    After challenge with a  C. difficile  wild-type bacterial strain of the immunized mice and hamsters, fecal samples are collected every other day and the degree of colonization is evaluated by performing a ten-fold serial dilution colony forming unit counts on taurocholatecycloserine-cefoxitin agar plates. 
       Example 8 
     Animal (Mice and Hamsters) Immunization and Challenge 
       [0048]    Group 1: Mice immunized intranasally with the fusion construct vaccine strain (ZCR533-TcdA:TcdB). Group 2: Mice administered intranasally PBS diluent. 
         [0049]    Group 3: Hamsters immunized intranasally with the fusion construct vaccine strain (ZCR533-TcdA:TcdB). Group 4: Hamsters administered intranasally PBS diluent. 
         [0050]    The immunized (Group 1) and non-immunized control (Group 2) mice are challenged orogastrically two-weeks following the booster immunization with a lethal dose of a  C. difficile  wild-type strain with morbidity/mortality being measured daily for 7-14 days post challenge. 
         [0051]    The immunized (Group 3) and non-immunized control (Group 4) hamsters are challenged orogastrically two-weeks following the booster immunization with a lethal dose of a  C. difficile  wild-type strain with morbidity/mortality being measured daily for 7-14 days post challenge. 
         [0052]    These immunization/challenge trials demonstrate immunoprotection induced by antibodies to the TcdA:TcdB antigens expressed by the fusion construct vaccine strain (ZCR533-TcdA:TcdB) against a normally lethal dose of a  C. difficile  wild-type challenge. 
         [0053]    A two-sided test for independent samples (GraphPad Prism) is used to compare the mean serum and fecal antibody values of the vaccinated mice with those of the non-immune mice (antibody values will be log transformed). A two-sided test for independent samples (GraphPad Prism) is used to compare the colonization of the intestines of the vaccinated mice with those of the non-immune mice. The Fisher exact probability test is used to compare the mortality and morbidity rates of the vaccinated mice with those of non-immune mice. Standard deviations (SD) are calculated using GraphPad Prism. Differences in P values of &lt;0.05 are considered to be significant. 
       Example 9 
     Treatment/Prevention of CDAD in Hospitalized or At Risk Patients 
       [0054]    The vaccine described herein is administered patients at risk of developing CDAD on hospital admission. Recipients of the presently described vaccine are placed into two main categories: (1) CDI are particularly likely to occur in patients with advanced age and coexisting medical conditions, and when individuals are admitted to the hospital to receive antibiotics which disrupt their intestinal microbiota; and (2) Patients that have been treated for a primary episode of CDAD and are at risk for development of recurrent disease. Such patients are likely to continue to have disruption of their intestinal microbiota because of antibiotic treatment. 
         [0055]    The above description of the disclosed embodiments is provided to enable any persons skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing form the spirit or scope of the invention. Thus, it is to be understood that the description and figures presented herein represent a presently preferred embodiments of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly not limited.