Abstract:
The present invention relates to a super-antigen fusion protein, comprising: a peptide fragment whose sequence corresponds to a partial SARS E2 spike protein; and a translocating peptide fragment for transporting a protein into a cell and translocating the protein in cytosol; wherein, the amino acid sequence of the peptide fragment corresponding to the partial SARS E2 spike protein includes SEQ ID NO. 1, SEQ ID NO. 2, SEQ ID NO. 3 or SEQ ID NO. 4. The present invention further relates to DNA sequences corresponding to the partial SARS E2 spike protein includes SEQ ID NO. 5, SEQ ID NO. 6, SEQ ID NO. 7, or SEQ ID NO. 8; wherein the DNA sequences are able to express specific proteins in an  E. Coli  expression system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a super-antigen fusion protein and the use thereof and, more particularly, to a fusion protein which binds to an antigen-presenting cell for inducing antibodies effectively, so as to suppress the virus infection and block the super-antigen response. 
     2. Description of Related Art 
     A virus is too small to propagate independently, and has to survive in a host cells by way of parasitism. Hence, viruses are classified in a species between organism and non-organism. Coronavirus is a single-strand RNA virus, and the way it enters cells is by binding to a target cell receptor and forming a cyst, then the virus enters host cells through endocytosis. The viral ribonucleic acid (RNA) reverses to DNA via reverse transcription, and further inserts into chromosomes of the host cell. Therefore, the proteins and genetic materials required for virus growth are produced by the host cell. Under the enzyme catalysis, proteins and genetic materials are assembled and released from the cell, thus the host cell is destroyed. 
     The virus recognizes the receptors on a cell surface, for example, HIV recognizes CD4 and CCR5 antigens on T lymphocyte surface and then enters the cell. However, coronavirus recognizes aminopeptidase-N on lung or kidney cell surfaces, which is the structure of CD13 receptor, for invasion. Therefore, the main direction in developing biotechnology against viruses is to design a drug to interrupt the interaction between virus and surface antigens, so as to prevent virus invasion. However, besides the structure of the above-mentioned for pathogenesis, some virus has another portion just like a super-antigen to interact with host immune system, which directly binds to a T lymphocyte surface receptor, and then induces interleukin or γ-interferon production heavily from T lymphocyte, resulting in drastically inflammatory response and even triggering the linked T lymphocyte to death (such as programmed cell death apoptosis). Therefore, by elimination of the binding elements of a binding event between super-antigen and cell surface antigen, the viral invasion is suppressed, and the infection symptoms is possibly prevented or alleviated. 
     T lymphocyte cell membrane exhibits its own T lymphocyte receptor (TCR) in the immune system. There are approximately one million mature T lymphocytes patrolling in the human body. Therefore, TCR is used for monitoring the messages from cells or antigen-presenting cell membranes in the body. An antigen-presenting cell exhibits a Major Histocompatibility Complex (MHC), which is capable of recognizing foreign proteins. MHC and a peptide fragment bind together to form a complex, which is then presented on the surface of cell membrane. Thus, the complex formed by MHC and the peptide will specifically release a message to TCR, which acts as a mediator for self and non-self recognition. However, from the scientific research, it has been found that a certain part of the SARS (severe acute respiratory syndrome) virus envelope spike protein binds to a T lymphocyte receptor after invasion. Moreover, the message of mis-recognizing the immune cell results in a release of cytokines immediately without the involvement of MHC molecule through an antigen-presenting cell system. Therefore, T lymphocytes are induced to largely proliferate or produce a vast amount of cytokines, which attack vigorously back to cells and result in inflammatory response. Based on the above study, it is sure that the SARS spike protein exhibits the “super-antigen” property. However, the position of amino acid sequence where the super-antigen fragment is located is still under investigation. Recently, it has been speculated that the super-antigen position is located at the SARS spike protein amino acid sequence 680 to 1050, however, the exactitude needs to be further confirmed. 
     To prevent the autoimmunological response resulting from SARS virus invasion, a vaccine-like protection system can be utilized. The key point of vaccination is to trigger the originally existing antibody of the infected host with the lymph cell that carries memories of invasion for response. The inventor of the present invention found that the strategy of “induction antibody effectively with a fusion protein” can proceed to a “partial immunization of a super-antigen”. The strategy is designed to provide a fusion protein with partial super-antigen of the SARS virus to a healthy human, and a higher titer of antibody is anticipated, wherein the antibody is induced from the immune cells which are capable of recognizing SARS virus super-antigen regions. During infection, the antibody will capture the super-antigen region of SARS virus and this results in alleviating super-antigen induction or inflammatory response without over-stimulating T lymphocyte proliferation. The inventor of the present invention also utilizes the prior investigation of “fusion protein transporting system”, to find out the “antibody induction of CD13 cell receptor binding region”. Thus, the induced antibody can suppress SARS virus invasion and the SARS infection is prevented. 
     To begin the experiments for SARS virus investigation, the first concern is to obtain the SARS virus. However, the virus is transmitted by droplet contact, thus the highly infectious virus must be isolated in an appropriately-equipped laboratory. Even though scientists have already sequenced the wild-type SARS virus genome, an ex vivo synthesis of vast amount of viruses is still dependent on a specific host system, which limits the investigation. In the present invention, the inventor translates the amino acid sequence of SARS wild-type virus into specific protein which is published via the Internet. The codons in the amino acid sequence of the SARS virus are modified with translating-effective codons of the ordinary  E. Coli  host system, and the modified sequence is synthesized by sequential PCR. SARS proteins are further expressed effectively by a conventional  E. Coli  host system. The present invention aims to acquire a SARS antigen without adopting a virus gene entity, which is beneficial for SARS virus research. 
     SUMMARY OF THE INVENTION 
     The present invention provides a super-antigen fusion protein and the application method thereof, wherein the super-antigen fusion protein comprises a peptide fragment encoding the SARS E2 spike protein, and a translocating peptide. In order to ex vivo obtain the SARS E2 spike protein without infection of the highly infectious virus, the present invention further comprises a nucleic acid sequence encoding super-antigen fusion protein to be expressed as the target protein in the  E. Coli  expression system. 
     Another object of the present invention is to provide a super-antigen peptide domain which is able to prevent the binding of SARS virus with a T lymphocyte, especially for a peptide domain targeting the E2 spike protein of the SARS virus. Similar to the way of antibody recognition, an E2 spike protein super-antigen peptide domain binds to the position of T lymphocyte where the invasive SARS virus are expected to bind. As a result, immunological responses and allergic reactions are prevented excessive when the invasive SARS virus binds to the T lymphocyte. 
     Another object of the present invention is to provide a peptide binding domain which prevents the binding of the virus with the T lymphocyte surface receptor CD13, specifically for a peptide targeting the SARS E2 spike protein. Similar to the way of antibody recognition, an E2 spike protein super-antigen peptide domain binds to the position of the T lymphocyte surface receptor CD13 where the invasive SARS virus is expected to bind. The binding mechanism between a virus and the immune T lymphocyte surface receptor CD13 is blocked, which prevents SARS virus invasion through the immune T lymphocyte CD13 binding. 
     The present invention can be used for detecting SARS virus infection. The induced antibody stimulated by the fusion protein of the present invention prevents the host T lymphocyte from being infected by a virus, and reduces the excessive immunological response and allergic reaction resulting from immune T lymphocyte and SARS virus binding. Therefore, the fusion protein of the present invention is also used for relieving or treating the infection symptoms of the SARS virus. 
     To achieve the object, the present invention discloses a super-antigen fusion protein, comprising a peptide fragment whose sequence corresponds to at least a partial SARS E2 spike protein. Moreover, a translocating peptide fragment is disclosed for cell binding and translocation, wherein the peptide fragment sequence corresponding to the SARS E2 spike protein includes SEQ ID NO. 1, SEQ ID NO. 2, SEQ ID NO. 3, or SEQ ID NO. 4. 
     The present invention also comprises a nucleic acid sequence encoding super-antigen fusion protein, the sequence including SEQ ID NO. 5, SEQ ID NO. 6, SEQ ID NO. 7, or SEQ ID NO. 8; wherein, the specific proteins are expressed by the nucleic acid in an  E. Coli  expression system. 
     The present invention further comprises a peptide for T lymphocyte binding, and the peptide contains at least a partial SARS E2 spike protein, including SEQ ID NO. 1, SEQ ID NO. 2, SEQ ID NO. 3, or SEQ ID NO. 4. 
     The present invention also comprises a pharmaceutical composition for a peptide binding to a T lymphocyte, comprising a peptide fragment that corresponds to at least a partial SARS E2 spike protein, wherein the peptide fragment corresponding to the SARS E2 spike protein includes SEQ ID NO. 1, SEQ ID NO. 2, SEQ ID NO. 3, or SEQ ID NO. 4. 
     The peptide sequence of the present invention further comprises a nucleic acid or translocating peptide. The sequence of the translocating peptide is not limited in its category, and mainly has the ability to transport linking peptides into a cell. Preferably, the first and second functional domains of  Pseudomonas  exotoxin A are used for peptide binding and translocating (see U.S. Pat. No. 5,705,163). 
     The pharmaceutical composition of the present invention also comprises a peptide with amino acids sequence of SEQ ID NO. 1, SEQ ID NO. 2, or the combination thereof, and which is used as a vaccine for stimulating a passive immunological response in a subject. A peptide with amino acids sequence of SEQ ID NO. 3, SEQ ID NO. 4, or the combination thereof is used for producing a vaccine for the SARS virus in a subject. 
     The super-antigen fusion protein of the present invention comprises four peptide fragments with their amino acid sequences consensus to SARS E2 spike protein sequence (NP — 828851) from National Center for Biotechnology Information (NCBI) database. In order to synthesize the SARS E2 spike protein ex vivo, the present invention employs the method disclosed in TW 92126644, to modify the nucleic acid without altering the encoded amino acid for the SARS E2 spike protein partial sequence synthesizing. The modified nucleic acid includes SEQ ID NO. 5, SEQ ID NO. 6, SEQ ID NO. 7, or SEQ ID NO. 8. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the plasmid map of the embodiment 1 in the present invention. 1A is pET-PE-SA; 1B is pET-PE-SB; 1C is pET-PE-SC; and 1D is pET-PE-SD. 
         FIG. 2  is the enzyme-linked immunospot assay (ELISPOT assay) of the embodiment 3B in the present invention. The result shows the interactions of the fusion proteins (PE-SA, PE-SB, PE-SC and PE-SD) and the monocytes of human peripheral blood after various incubation periods. A1 is the result with PE-SA fusion protein; A2 is the result with PE-SA fusion protein after 7 days incubation; A3 is the result with PE-SA after 14 days incubation. B1 is the result with PE-SB fusion protein; B2 is the result with PE-SB after 7 days incubation; B3 is the result with PE-SB after 14 days incubation. C1 is the result with PE-SC fusion protein; C2 is the result with PE-SC after 7 days incubation. C3 is the result with PE-SC after 14 days incubation. D1 is the result with PE-SD fusion protein; D2 is the result with PE-SD after 7 days incubation; D3 is the result with PE-SD after 14 days incubation. 
         FIG. 3  is the bar chart illustrating the result of the Embodiment 4, where the spots in  FIG. 2  are counted and shown in the bar chart. 
         FIG. 4  is the antibody titer determination of the Embodiment 4 in the present invention. A, B, C, and D represents the fusion proteins consisting of the PE translocation peptide and SA, SB, SC, or SD peptide fragments respectively. The solid bar represents the present fusion protein, and the hollow bar represents the peptide simply encoding the PE translocation protein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiment 1 
     Synthesis of Peptide Encoding a Partial SARS E2 Spike Protein 
     SARS E2 spike protein sequence (accession number: NP — 828851, SEQ ID No. 9) is found in the National Center for Biotechnology Information (NCBI). Position 680 to 1050 of the amino acid sequence (SEQ ID No. 9) is divided into four fragments (SA (SEQ ID NO:1), SB, (SEQ ID NO:2) SC(SEQ ID NO:3), and SD (SEQ ID NO:4)) for nucleic acid modification, and fragment synthesis and amplification, resulting target amino acid sequences ex vivo. 
     The present invention employs a method disclosed in TW 92126644, and expresses heterogenous virus spike protein in an  E. Coli  expression system. The importance of the modification is to alter a single nucleotide without effecting the original amino acid expression, and further to express specific proteins well in an  E. Coli  host system. 
     The commercial  E. Coli  plasmid pET230 is used as a template for amplifying nucleic acid fragments with polymerase chain reaction (PCR). In the present embodiment, four synthetic nucleotide fragments are SA (SEQ ID NO:5), SB (SEQ ID NO:6), SC(SEQ ID NO:7) and SD (SEQ ID NO:8). There are 29 pairs of primers used in the fragment amplification, and all the primer sequences are listed in Table 1. The forward primers (F1) are homologous to  E. Coli  plasmid pET230 partial sequence. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Primer Sequence Design 
               
             
          
           
               
                   
                   
                 SEQ 
                   
                   
               
               
                 Pep- 
                   
                 ID 
               
               
                 tide 
                 Sequence 
                 NO 
                 Primer Sequence 
               
               
                   
               
               
                 SA 
                 SA-F1 
                 10 
                 5′-CCC TCA GAA TTC GAG AAC ACC ATC 
                   
               
               
                   
                   
                   
                 GCT ATC CCG A-3′ 
               
               
                   
               
               
                   
                 SA-R1 
                 11 
                 5′-GAT GGA GAT GGA GAA GTT GGT CG 
               
               
                   
                   
                   
                 G GAT AGC GAT GGT GTT CTC GAG TGC 
               
               
                   
                   
                   
                 TGA GGG-3′ 
               
               
                   
               
               
                   
                 SA-R2 
                 12 
                 5′-GGA GGT TTT AGC CAT GGA AAC 
               
               
                   
                   
                   
                 CGG CAT AAC TTC GGT GGT GAT GGA 
               
               
                   
                   
                   
                 GAT GGA GAA-3′ 
               
               
                   
               
               
                   
                 SA-R3 
                 13 
                 5′-TTC GGT GGA GTC ACC GCA GAT GTA 
               
               
                   
                   
                   
                 CAT GTT GCA GTC AAC GGA GGT TTT 
               
               
                   
                   
                   
                 AGC CAT-3′ 
               
               
                   
               
               
                   
                 SA-R4 
                 14 
                 5′-GGT GCA GAA GGA ACC GTA CTG 
               
               
                   
                   
                   
                 CAG CAG CAG GTT AGC GCA TTC GGT 
               
               
                   
                   
                   
                 GGA GTC ACC-3′ 
               
               
                   
               
               
                   
                 SA-R5 
                 15 
                 5′-AGC GAT ACC GGA CAG AGC ACG 
               
               
                   
                   
                   
                 GTT CAG CTG GGT GCA GAA GGA 
               
               
                   
                   
                   
                 ACC-3′ 
               
               
                   
               
               
                   
                 SA-R6 
                 16 
                 5′-TTT TGA ATT CAC GGG TGT TAC GGT 
               
               
                   
                   
                   
                 CCT GTT CAG CAG CGA TAC CGG ACA 
               
               
                   
                   
                   
                 G-3′ 
               
               
                   
               
               
                 SB 
                 SB-F1 
                 17 
                 5′-CCC TCA GAA TTC GAG GTT TTC GCT 
               
               
                   
                   
                   
                 CAG GTT AAA-3′ 
               
               
                   
               
               
                   
                 SB-R1 
                 18 
                 5′-GGT CGG GGT TTT GTA CAT CTG TTT 
               
               
                   
                   
                   
                 AAC CTG AGC GAA AAC CTC GAG TGC 
               
               
                   
                   
                   
                 TGA GGG-3′ 
               
               
                   
               
               
                   
                 SB-R2 
                 19 
                 5′-CAG GAT CTG GGA GAA GTT GAA 
               
               
                   
                   
                   
                 ACC ACC GAA GTA TTT CAG GGT CGG 
               
               
                   
                   
                   
                 GGT TTT GTA-3′ 
               
               
                   
               
               
                   
                 SB-R3 
                 20 
                 5′-TTC GAT GAA GGA ACG TTT GGT CGG 
               
               
                   
                   
                   
                 TTT CAG CGG GTC CGG CAG GAT CTG 
               
               
                   
                   
                   
                 GGA GAA-3′ 
               
               
                   
               
               
                   
                 SB-R4 
                 21 
                 5′-ACC AGC GTC AGC CAG GGT AAC TTT 
               
               
                   
                   
                   
                 GTT GAA CAG CAG GTC TTC GAT GAA 
               
               
                   
                   
                   
                 GGA ACG-3′ 
               
               
                   
               
               
                   
                 SB-R5 
                 22 
                 5′-GTT GAT GTC ACC CAG GCA TTC ACC 
               
               
                   
                   
                   
                 GTA CTG TTT CAT GAA ACC AGC GTC 
               
               
                   
                   
                   
                 AGC CAG-3′ 
               
               
                   
               
               
                   
                 SB-R6 
                 23 
                 5′-CAG ACC GTT GAA TTT CTG AGC GCA 
               
               
                   
                   
                   
                 GAT CAG GTC ACG AGC GTT GAT GTC 
               
               
                   
                   
                   
                 ACC CAG-3′ 
               
               
                   
               
               
                   
                 SB-R7 
                 24 
                 5′-CAT GTC GTC GGT CAG CAG CGG 
               
               
                   
                   
                   
                 CGG CAG AAC GGT CAG ACC GTT GAA 
               
               
                   
                   
                   
                 TTT-3′ 
               
               
                   
               
               
                   
                 SB-R8 
                 25 
                 5′-TTT TGA ATT CCA GAG CAG CGG TGT 
               
               
                   
                   
                   
                 AAG CAG CGA TCA TGT CGT CGG 
               
               
                   
                   
                   
                 TCAG-3′ 
               
               
                   
               
               
                 SC 
                 SC-F1 
                 26 
                 5′-CCC TCA GAA TTC GAG GTT TCC GGT 
               
               
                   
                   
                   
                 ACC GCT ACC GCT-3′ 
               
               
                   
               
               
                   
                 SC-R1 
                 27 
                 5′-AGC ACC GAA GGT CCA ACC AGC 
               
               
                   
                   
                   
                 GGT AGC GGT ACC GGA AAC CTC GAG 
               
               
                   
                   
                   
                 TGC TGA GGG-3′ 
               
               
                   
               
               
                   
                 SC-R2 
                 28 
                 5′-AGC CAT CTG CAT AGC GAA CGG 
               
               
                   
                   
                   
                 GAT CTG CAG AGC AGC ACC AGC ACC 
               
               
                   
                   
                   
                 GAA GGT CCA-3′ 
               
               
                   
               
               
                   
                 SC-R3 
                 29 
                 5′-CAG AAC GTT CTG GGT AAC ACC 
               
               
                   
                   
                   
                 GAT ACC GTT GAA ACG GTA AGC CAT 
               
               
                   
                   
                   
                 CTG CAT AGC-3′ 
               
               
                   
               
               
                   
                 SC-R4 
                 30 
                 5′-TTT GTT GAA CTG GTT AGC GAT CTG 
               
               
                   
                   
                   
                 TTT CTG GTT TTC GTA CAG AAC GTT 
               
               
                   
                   
                   
                 CTG GGT-3′ 
               
               
                   
               
               
                   
                 SC-R5 
                 31 
                 5′-GGA GGT GGT GGT CAG GGA TTC 
               
               
                   
                   
                   
                 CTG GAT CTG GGA GAT AGC TTT GTT 
               
               
                   
                   
                   
                 GAA CTG GTT-3′ 
               
               
                   
               
               
                   
                 SC-R6 
                 32 
                 5′-AGC GTT CTG GTT AAC AAC GTC CTG 
               
               
                   
                   
                   
                 CAG TTT ACC CAG AGC GGA GGT GGT 
               
               
                   
                   
                   
                 GGT CAG-3′ 
               
               
                   
               
               
                   
                 SC-R7 
                 33 
                 5′-TTT TGA ATT CGG ACA GCT GTT TAA 
               
               
                   
                   
                   
                 CCA GGG TGT TCA GAG CCT GAG CGT 
               
               
                   
                   
                   
                 TCT GGT TAAC-3′ 
               
               
                   
               
               
                 SD 
                 SD-F1 
                 34 
                 5′-CCC TCA GAA TTC GAG TCC AAC TTC 
               
               
                   
                   
                   
                 GGT GCT ATC TCC T-3′ 
               
               
                   
               
               
                   
                 SD-R1 
                 35 
                 5′-GAT GTC GTT CAG AAC GGA GGA 
               
               
                   
                   
                   
                 GAT AGC ACC GAA GTT GGA CTC GAG 
               
               
                   
                   
                   
                 TGC TGA GGG-3′ 
               
               
                   
               
               
                   
                 SD-R2 
                 36 
                 5′-GAT CTG AAC TTC AGC TTC AAC TTT 
               
               
                   
                   
                   
                 GTC CAG ACG GGA CAG GAT GTC GTT 
               
               
                   
                   
                   
                 CAG AAC-3′ 
               
               
                   
               
               
                   
                 SD-R3 
                 37 
                 5′-GGT CTG CAG GGA CTG CAG ACG 
               
               
                   
                   
                   
                 ACC GGT GAT CAG ACG GTC GAT CTG 
               
               
                   
                   
                   
                 AAC TTC AGC-3′ 
               
               
                   
               
               
                   
                 SD-R4 
                 38 
                 5′-ACG GAT TTC AGC AGC ACG GAT 
               
               
                   
                   
                   
                 CAG CTG CTG GGT AAC GTA GGT CTG 
               
               
                   
                   
                   
                 CAG GGA CTG-3′ 
               
               
                   
               
               
                   
                 SD-R5 
                 39 
                 5′-GCA TTC GGA CAT TTT GGT AGC AGC 
               
               
                   
                   
                   
                 CAG GTT AGC GGA AGC ACG GAT TTC 
               
               
                   
                   
                   
                 AGC AGC-3′ 
               
               
                   
               
               
                   
                 SD-R6 
                 40 
                 5′-TTT ACC GCA GAA GTC AAC ACG TTT 
               
               
                   
                   
                   
                 GGA CTG ACC CAG AAC GCA TTC GGA 
               
               
                   
                   
                   
                 CAT TTT-3′ 
               
               
                   
               
               
                   
                 SD-R7 
                 41 
                 5′-GTG CGG AGC AGC CTG CGG GAA 
               
               
                   
                   
                   
                 GGA CAT CAG GTG GTA ACC TTT ACC 
               
               
                   
                   
                   
                 GCA GAA GTC-3′ 
               
               
                   
               
               
                   
                 SD-R8 
                 42 
                 5′-TTT TGA ATT CAA CGT AGG TAA CGT 
               
               
                   
                   
                   
                 GCA GGA AAA CAA CAC CGT GCG GAG 
               
               
                   
                   
                   
                 CAG CCT G-3′ 
               
               
                   
               
             
          
         
       
     
     These four peptides are amplified for several times (SA for 6 times, SB for 8 times, SC for 7 times, and SD for 8 times) from PCR by coupling the same forwarded primers (SA-F1 (SEQ ID NO: 10), SB-F1 (SEQ ID NO: 17), SC-F1 (SEQ ID NO: 26), and SD-F1 (SEQ ID NO: 34)) with various reversed primers (SA-R1˜R6 (SEQ ID NO: 11-16), SB-R1˜R8 (SEQ ID NO: 18-25), SC-R1˜R7 (SEQ ID NO: 27-33), and SD-R1˜R8 (SEQ ID NO:35-42)). The amplification conditions are: a first cycle for 5 min at 95° C.; a second cycle for 1 min at 94° C., 0.5 min at 55° C., and 1 min at 72° C. of 20 cycles; and a third cycle for 1 min at 72° C. 
     After amplification, the PCR products are visualized in the agarose gel electrophoresis. The representatives are cut and eluted from gel slices. 
     Embodiment 2 
     Plasmid Construction 
     Four nucleotides SA (SEQ ID NO:5), SB (SEQ ID NO:6), SC(SEQ ID NO:7), and SD (SEQ ID NO:8) from PCR, and plasmid pET-PE which contains binding domain and translocating domain of  Pseudomonas  exotoxin A (see Liao C. W. et al., Applied Microbiol Biotechnol 143:498-507, 1995), are ligated together in the restriction enzyme site respectively. Four constructed fusion plasmids are obtained and named pET-PE-SA, pET-PE-SB, pET-PE-SC, and pET-PE-SD ( FIG. 1 ). 
     Embodiment 3 
     Protein Expression and Purification 
     According to the method from Sambrook (Sambrook et al., J. Neuroimmunol. 1991; 32(1):35-41), the four plasmids, pET-PE-SA, pET-PE-SB, pET-PE-SC, and pET-PE-SD, were expressed to obtain fusion proteins by using IPTG induction method. 
     The  E. Coli  strain for protein (peptide) expression was BL21 (DE3) pLysS. First, the picked colony was inoculated into 100 ml of LB medium containing 200 μg/ml of ampicillin until OD 550  reached approximate 0.3. Second, 1 mM IPTG (isopropylthio-β-D-galactoside, Promege, USA) was added into the medium, the incubation was carried on for 90 min, and cells were centrifuged and collected. The membranes of the cells carrying the target protein were loosen by freezing and thawing repeatedly, and then 10 ml lysis buffer (which contains 0.9 mg/ml lysozyme, 1 ml PMSF and 0.064 mg/ml DNaseI) was added for 10 min treatment at room temperature. Then, 1 ml 10% TRITON® X-100 was added for another 10 min treatment at room temperature. The mixture was centrifuged at 12000×g for 10 min to collect the protein. Then, the collected inclusion body was dissolved in 4 ml 8M urea. 
     Furthermore, the commercial pET His-Taq purification system (Novagen, USA) is performed according to the instructions. The cell inclusion body is dissolved in 4 ml ice cold binding buffer (which contains 5 mM imidazole, 0.5 M NaCl, and 20 mM Tris-HCl, pH7.9) with sonication until the inclusion body disperses. Then, the mixture is centrifuged in 1200×g for 15 min at 4° C., and the supernatant is poured into a column (which is the His-Bind metal chelating resin immobilized with Ni 2+ ). Finally, the protein binding to column is eluted and collected with a buffer (which contains 0.5 M imidazole, 0.5 M NaCl, and 20 mM Tris-HCl, pH7.9). 
     Four fusion proteins, i.e. PE-SA (SEQ ID NO:43), PE-SB (SEQ ID NO:44), PE-SC(SEQ ID NO:45), and PE-SD (SEQ ID NO:46), have been expressed from fusion plasmids in the same process. 
     Embodiment 4 
     Cellular Immunity Test 
     A. Isolation of Peripheral Blood Monocytes 
     The blood of a healthy adult was obtained and mixed with the Hanks&#39; balanced salt solution (Hanks&#39; balanced salt solution kit, Life Technologies, Rockville, Md.) at a 1:1 ratio. 
     According to the method from Sacerdote (Sacerdote et al., J. Neuroimmunol 1991; 32(1):35-41), the Ficoll-Paque solution (Amersham Biosciences, Uppsala, Sweden) was used for isolating peripheral blood monocytes. The mixture of blood and Ficoll-Paque solution was centrifuged (600×g, 30 min), and then the solution with monocytes was removed to another centrifuge tube. The mixture was washed twice with Hanks&#39; balanced salt solution and centrifuged at 1200×g for 10 min to obtain the isolated peripheral blood monocytes. 
     According to the method from Gong (Gong et al., J. Immunol., 2000; 165(3):1705-11), the immature peripheral blood monocytes have the potential to proliferate into dendritic cells (DCs). Peripheral blood monocytes were dispersed in the cell culture medium to allow cells to attach to the culture dish, thereafter the cells were incubated for 2 hr at 37° C. Then, the unattached cells were removed. The cells were incubated with 1% human serum RPMI 1640 (Mediatech, Herndon, Va.) medium and GM-CSF (800 IU/ml) and IL-4 (500 U/ml) for 6 days. The cytokines were added on Day 0, Day 2, or Day 4. On Day 6, the unattached cells were collected to analyze the molecular marker of the dendritic cells. 
     The collected dendritic cells are washed with a FACScan buffer consisting of PBS, 0.2% FBS, and 0.5% sodium azide. Further, the FITC- or PE-conjugated anti-human antibodies (CD1a, CD3, CD56, CD80, HLA-A, B, C, and HLA-DR; PharMingen, San Diego, Calif.) are added to the cells for 30 min on ice. Again, the cells are washed with the FACScan buffer. The data is analyzed with FACScalibur flow cytometer (Becton Dickinson, Mountain View, Calif.) and “CellQuest” software. 
     B. IFN-γ Enzyme-Linked Immunospot Assay (Elispot Assay) 
     According to the articles from Miyahira et al. (Miyahira et al., J Immunol Methods, 1995; 181(1):45-54) and Murali-Krishna et al. (Murali-Krishna et al., Immunity, 1998; 8(2): 177-87), enzyme-linked immunospot assay was modified to estimate the specificity for SA, SB, SC, and SD antigens with CD8+ T lymphocytes. 
     A layer of anti-human INF-7 antibody (10 μg/ml; PharMingen) in PBS (50 μl) was covered on a 96-well dish (Millipore, Bedford, Mass.) and cultured at 4° C. for overnight. Then, the cultured wells were washed and coated with 10% fetal bovine serum (FBS) medium. Moreover, different amounts of fresh or cultured peripheral blood monocytes were prepared, and further mixed with proliferated dendritic cells at a 10:1 ratio (as described in the Embodiment 3). An amount of 1×10 6  of dendritic cells were added into each cultured well coated with FBS, wherein the cells were untreated or treated with four fusion proteins PE-SA (SEQ ID NO:43), PE-SB (SEQ ID NO:44), PE-SC (SEQ ID NO:45), and PE-SD (SEQ ID NO:46), for 2 hr, respectively. 
     After incubation, the cultured wells were washed again. A biotin-conjugated rat anti-human INF-γ antibody (5 μg/ml; PharMingen) in PBS (50 μl) was added and incubated overnight at 4° C. Then, the dish was washed for six times. 1.2 μg/ml of avidin-alkaline phosphatase (Sigma, St. Louis, Mo.) in 50 μl PBS was added and incubated for 2 hr at room temperature. Further, 50 μl of 5-bromo-4-chloro-3-indolyl phosphate/nitroblue tetrazolium solution (Boehringer Mannheim, Indianapolis, Ind., USA) was added for 20 min at room temperature, and the spots were observed. The substrate solution was removed, and the cultured wells were washed with water to stop the reaction. Finally, the cultured wells were dried and the spot amount was counted under an anatomic microscopy. 
     An enzyme-linked immunospot assay was used for evaluating the amount of CD8+ T lymphocytes reflected from PE-SA (SEQ ID NO:43), PE-SB (SEQ ID NO:44), PE-SC (SEQ ID NO:45), and PE-SD (SEQ ID NO:46) fusion protein treatment.  FIG. 2  shows the result of enzyme-linked immunospot assay, which represents the reactions from different incubation times. The spots were counted and shown in a bar chart as in  FIG. 3 . From the figure, it was observed that on the seventh day after immunizing, serum IFN-γ production is elevated in mice injected with PE-SA (SEQ ID NO:43), PE-SC (SEQ ID NO:45), and PE-SD (SEQ ID NO:46) fusion protein. On the fourteenth day after immunizing, PE-SC (SEQ ID NO:45) fusion protein elicited a severe immunological response and induced a high amount of IFN-γ in mice. 
     Embodiment 5 
     Animal Immunity Test 
     A. Animal Preparation 
     Six to eight week-old female mice C57BL/6J are purchased from National Taiwan University (Taipei, Taiwan), and are fed in the Animal Center of National Taiwan University Hospital. 
     B. Animal Immunity 
     The fusion proteins, i.e. PE-SA (SEQ ID NO:43), PE-SB (SEQ ID NO:44), PE-SC(SEQ ID NO:45), and PE-SD (SEQ ID NO:46), prepared from Embodiment 2 are injected individually into each mice in an amount of 100 μg for immunological response observation. Meanwhile, another group of mice is prepared for injecting with  Pseudomonas  exotoxin A peptide only as the control. The administering schedule is Day 0, Day 14, and Day 28 while initiating the experiment. 
     C. Antibody Specificity Test 
     According to the method from Cheng (Cheng et al., J. Clin. Invest., 2001; 108(5):669-78), i.e., enzyme-linked immunoabsorbent assay (ELISA), serum PE-SA (SEQ ID NO:43), PE-SB (SEQ ID NO:44), PE-SC (SEQ ID NO:45), and PE-SD (SEQ ID NO:46) antibody is specificities were evaluated, respectively. A 96-well dish was covered with a layer of PE-SA (SEQ ID NO:43), PE-SB (SEQ ID NO:44), PE-SC (SEQ ID NO:45) (5 μg) fusion proteins, respectively, for overnight culturing at 4° C. Then, 20% fetal bovine serum (FBS) in PBS was coated into culture well. Mice serum was obtained after 14 days of immunization, and serially diluted with PBS and then added into cultured wells for 2 hr at 37° C. Furthermore, cultured wells were washed with 0.05% TWEEN® 20 in PBS, and a 1:2000 peroxidase-conjugated rabbit anti-mouse IgG antibody (Zymed, San Francisco, Calif.) was added for 1 hr at room temperature. After washing, 1-STEP™ Turbo TMB-ELISA (Pierce, Rockford, Ill.) was added to develop the color. Finally, the reaction was stopped by adding 1M H 2 SO 4 . The result was read at the 450 nm absorbance spectra in an ELISA reader. 
       FIG. 4  is the titer estimation of specific antibody with the serum diluted serially at the ratio of 1:100, 1:500 and 1:1000. The result shows that the CD8+ cell amount in mice serum injected with PE-SC(SEQ ID NO:45) and PE-SD (SEQ ID NO:46) fusion protein is higher than that of the serum from PE-SA (SEQ ID NO:43) and PE-SB (SEQ ID NO:44) fusion protein injected mice (P&lt;0.01, one-way ANOVA). Herein, it is found that PE-SC(SEQ ID NO:45) and PE-SD (SEQ ID NO:46) fusion protein could stimulate higher antibody in animals. Thus, in clinical tests, a subject accepting PE-SC(SEQ ID NO:45) and PE-SD (SEQ ID NO:46) fusion protein will produce an antibody for the SARS virus and protect oneself form infection. 
     The fusion proteins of the present invention successfully induce antibody production in animals. For large amounts of IFN-γ production induced by PE-SC(SEQ ID NO:45) and PE-SD (SEQ ID NO:46) fusion protein, it is observed that in the present embodiment, the amino sequences of SC and SD peptides are possibly located in the super-antigen positions of SARS virus. Therefore, the excessive immunological response occurs in an antibody-inducting animal injected with PE-SC(SEQ ID NO:45) and PE-SD (SEQ ID NO:46) fusion protein, and the immunological response is not harmful to an animal. For another aspect, the large amount of specific antibodies in animals, induced from PE-SC(SEQ ID NO:45) and PE-SD (SEQ ID NO:46) fusion protein enables the vaccine manufacture in the future and has the potential for SARS therapy. 
     Furthermore, the present PE-SA (SEQ ID NO:43) and PE-SB (SEQ ID NO:44) fusion protein do not induce excessive immunological response in animals. Thus, it is possible to stimulate passive immunity in an animal tending to be infected with the SARS virus. In animals, the binding mechanism of the SARS spike protein and T lymphocyte surface receptor CD13 can be blocked by simply administering PE-SA (SEQ ID NO:43) and PE-SB (SEQ ID NO:44) fusion proteins, and thus prevent the SARS virus infection. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.