Mutant virus, preparation method therefor and application thereof

Abstract

The present invention relates to a mutated virus. Said virus can be an influenza virus of human or other animal origin. The present invention also relates to a method for preparing the mutated virus, the method comprising introducing UAG codons into positions upstream of the stop codons per se of one or more genes of a viral genome by reverse genetic techniques. The present invention further relates to uses of the mutated virus, for example, as a live attenuated vaccine, or in replication of controllable and safe virus models, and the like.

Claims

1. A pharmaceutical composition comprising a mutated influenza virus, which is characterized in that a coding nucleic acid of at least one protein of the virus comprises one or more UAG codons at a position located one or more codons upstream of a natural, endogenous stop codon of the coding nucleic acid; wherein the at least one protein of the virus is selected from PA, PB1, PB2, or NP protein, and the at least one protein in the virus comprises an unnatural amino acid at the position corresponding to the one or more UAG codons, wherein the influenza virus comprises UAG codon(s) at positions of codon(s) of nucleic acid(s) encoding R266 of PA protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:4, R52 of PB1 protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:3, K33 of PB2 protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:2, and/or D101 of NP protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:6, wherein the composition is an active influenza virus vaccine, wherein the vaccine is capable of eliciting an immune response.

2. The mutated virus according to claim 1, wherein the unnatural amino acid is selected from Lys-diazirine shown in formula ##STR00011##  Lys-azido shown in formula (II) ##STR00012##  or at least one other unnatural amino acid.

3. The mutated virus according to claim 1, wherein UAG stop codons of said natural, endogenous stop codons of the virus are mutated to provide UAA stop codons.

4. The mutated virus according to claim 1 wherein, the amino acid sequence of nonmutated PB2 is identical to the amino acid sequence encoded by the nucleic acid as set forth in SEQ ID NO: 2, the amino acid sequence of nonmutated PB1 is identical to the amino acid sequence encoded by the nucleic acid as set forth in SEQ ID NO: 3, the amino acid sequence of nonmutated PA is identical to the amino acid sequence encoded by the nucleic acid as set forth in SEQ ID NO: 4, or the amino acid sequence of nonmutated NP is identical to the amino acid sequence encoded by the nucleic acid as set forth in SEQ ID NO: 6.

5. The mutated virus according to claim 4, wherein the mutated virus comprises UAG codons at positions of codons coding for R266 of PA protein by reference to a corresponding amino acid encoded by the nucleic acid as set forth in SEQ ID NO:4, R52 of PB1 protein by reference to a corresponding amino acid encoded by the nucleic acid as set forth in SEQ ID NO:3, K33 of PB2 protein by reference to a corresponding amino acid encoded by the nucleic acid as set forth in SEQ ID NO:2 and D101 of NP protein by reference to a corresponding amino acid encoded by the nucleic acid as set forth in SEQ ID NO:6.

6. The mutated virus according to claim 1, wherein the influenza virus is of human or other animal origin, and is an influenza A, B or C virus.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1. A workflow for calculating conservatism of amino acid sequences of various proteins of the influenza virus using the bioinformatics tool Consurf.

(2) FIG. 2A. Effect of rescuing the influenza virus after point mutations of the influenza virus NP protein.

(3) FIG. 2B. Effect of rescuing the influenza virus after point mutations of the influenza virus PA protein.

(4) FIG. 2C. Effect of rescuing the influenza virus after point mutations of the influenza virus PB2 protein.

(5) FIG. 2D. Effect of rescuing the influenza virus after point mutations of the influenza virus PB1 protein.

(6) FIG. 2E. Effect of rescuing the influenza virus after point mutations of HA protein of the influenza virus.

(7) FIG. 2F. Effect of rescuing the influenza virus after point mutations of the influenza virus NA protein.

(8) FIG. 2G. Effect of rescuing the influenza virus after point mutations of the influenza virus NS protein.

(9) FIG. 2H. Effect of rescuing the influenza virus after point mutations of the influenza virus M1 protein.

(10) FIG. 3. Effect of rescuing the influenza virus after point mutations are simultaneously introduced into the NP, PA, PB1, and PB2 of the influenza virus. Specifically, four sites of NP-S3, PA-S1, PB1-S4 and PB2-S4 of the influenza virus are selected and combined, and the four sites are simultaneously mutated, and the resulting plasmid is used to rescue the influenza virus. The resulting influenza virus is named as WSN-RNP-TAG.

(11) FIG. 4. Examination of the genetic stability of the prepared WSN-RNP-TAG indicates that the prepared mutant influenza virus is still stable after multiple passages. During the experiment, the virus is continuously passaged for up to 4 months, and the prepared virus maintains its dependence on the unnatural amino acids.

(12) FIG. 5. The results of qRT-PCR show that the influenza virus produced by using the method of the present invention has a very high yield which is close to that of the wild-type influenza virus.

(13) FIG. 6. By determining antigen erythrocyte agglutination titers of wild-type and of mutant WSN-RNP-TAG viruses, it has been proven that the mutant influenza virus and the wild-type virus have substantially the same antigen erythrocyte agglutination titers, further demonstrating that the yield of mutant influenza virus is very high.

(14) FIG. 7. To test the safety and immunogenicity of the mutant WSN-RNP-TAG virus, animal experimental programs are designed, wherein, the virus is nasally inoculated, and blood is taken from the orbital cavity.

(15) FIG. 8. Safety profile of the mutant WSN-RNP-TAG virus in animals (10 mice per group). (A) All mice have a significantly decreased body weight when inoculated with wild-type influenza virus, while all mice show no significant weight loss when inoculated with mutant WSN-RNP-TAG virus or the inactivated influenza WSN-positive control. (B) All mice die on the 10.sup.th day after inoculation when inoculated with the wild-type influenza virus, while all mice survive during the observation period when inoculated with mutant WSN-RNP-TAG virus or the inactivated influenza virus WSN-positive control. This shows that the mutant WSN-RNP-TAG has good safety in animals.

(16) FIG. 9A. According to the experimental program set out in FIG. 7, lung tissues of mice from each group are taken, and relative amounts of the virus in the lung tissues are detected by qRT-PCR. As shown in the figure, the virus amounts in the lung tissues of the mice are decreased and are immune dose-dependent when mice are immunized with the inactivated virus or the mutant WSN-RNP-TAG. In addition, the immune effect of the mutant WSN-RNP-TAG is better than that of the inactivated virus.

(17) FIG. 9B. The levels of anti-HA antibody in each group of mice before and after immunization are tested by ELISA assay. The results show that the levels of the antibody in mice increased 14 days after the immunization and 21 days after the immunization, and the levels of the antibody on the 21.sup.st day is higher than that on the 14.sup.th day.

(18) FIG. 9C. Following the experimental program set out in FIG. 7, each group of mice is individually immunized, and then infected with 100 LD.sub.50 of WSN. The body weight of the mice is also investigated. It has been found that the mutant WSN-RNP-tag prepared performs well at protecting animals from viral infection. Moreover, the protective effect of the mutant WSN-RNP-tag on mice at a 1-fold dose is comparable to that of the inactivated WSN at a 10-fold dose. This fully demonstrates that the prepared attenuated influenza vaccine is superior to the inactivated vaccine.

(19) FIG. 9D. Following the experimental program set out in FIG. 7, each group of mice is individually immunized, and then infected with 100 LD.sub.50 of WSN. The mortality of the mice is investigated. It has been found that the mutant WSN-RNP-tag prepared can protect animals from viral infection. Moreover, the protective effect of mutant WSN-RNP-tag on mice at a 1-fold dose is comparable to that of the inactivated WSN at a 10-fold dose. This fully demonstrates that the prepared attenuated influenza vaccine is superior to the inactivated vaccine.

(20) FIG. 10. The efficiency of rescuing the mutant influenza virus by using the stable mammalian cell line HEK293-PYL that stably expresses tRNA (tRNA.sup.Pyl) and pyrrolysyl-tRNA synthetase (tRNA.sup.Pyl) is compared with the efficiency of rescuing the mutant influenza virus by using the normal mammalian cell 293T. The results show that efficiency of rescuing the mutant influenza virus by using the cell line HEK293-PYL is much higher than that by using the normal 293T cell.

(21) FIG. 11A. Establishment of a method for screening out the stable cell line HEK293-PYL for orthogonal tRNA/aminoacyl-tRNA synthetase.

(22) FIG. 11B. Construction of a dual viral overexpression system FIG. 11C. Construction of bjmu-12t-zeo vector.

(23) FIG. 12. The levels of antibodies against NA protein and NP protein are determined in mice vaccinated with influenza virus vaccines. The WSN-RNP-tag can induce the mice to produce specific antibodies against NA and specific antibodies against N P.

(24) FIG. 13. Induction of the WSN-RNP-tag to produce virus-specific antibody IgA in lungs of mice. The WSN-RNP-tag can induce production of the IgA at high levels relative to the inactivated WSN.

(25) FIG. 14. The amount of NP-specific CD8+ T cells in lung of mice immunized with the WSN-RNP-tag. The inactivated WSN has minimal affect on the amount of the NP-specific CD8+ T cell, while the amount of the NP-specific CD8+ T cells in lung of the mice immunized with the WSN-RNP-tag is significantly increased.

(26) FIG. 15 shows that the mutant influenza virus containing UAGs prepared by the inventors can inhibit the replication and virulence of wild-type influenza virus. (A) The mutant viruses containing 4 UAGs in the genome inhibit the plaque formation of wild-type virus. Wild type represents a wild-type virus, and CAIV is a cold-adapted attenuated influenza vaccine. (B) The mutant viruses containing UAGs inhibit the plaque formation of the wild-type virus, and the inhibitory activity is enhanced as the number of UAGs increases. (C) In animals, the mutant viruses containing UAGs reduce the animal mortality caused by infection of the wild-type virus. (D) In animals, the mutant viruses containing UAGs reduce the loss of body weight in animals caused by infection of the wild-type virus. (E) In animals, the mutant viruses containing UAGs reduce the titer of virus in lung tissues of animals caused by the infection of the wild-type virus. .star-solid., P<0.05; .star-solid..star-solid., P<0.01; .star-solid..star-solid..star-solid., P<0.001.

(27) To help provide a better understanding of the present invention, the present inventors have described and illustrated specific experiments by using examples, wherein the examples are only used for illustration and do not limit the scope of protection of the present invention. Any variations or embodiments equivalent to the present invention are included in the present invention.

EXAMPLE 1: CONSTRUCTION OF GENETIC VECTOR OF INFLUENZA VIRUS WSN CONTAINING SITE-DIRECTED MUTATIONS

(28) (1) Generation of an Auxiliary Plasmid

(29) The plasmid pACYC-tRNA/PyIRS (hereafter referred to as the “auxiliary plasmid”) was obtained from the Escherichia coli having an Accession number of No. CGMCC No: 4951 (which has been deposited with the China General Microbiological Culture Collection Center, and the strain is deposited in No. 1 of Beichen West Road, Chaoyang District, Beijing City, Institute of Microbiology, Chinese Academy of Sciences; which plasmid was deposited on Jun. 14, 2011; the bacterial cell designated as Escherichia coli contains the plasmid pACYC-tRNA/PyIRS), and the plasmid can express tRNAs and tRNA synthetase that specifically recognize unnatural amino acids Lys-diazirine and Lys-azido.

(30) (2) Generation of Plasmids for Rescuing Wild-Type Influenza Virus WSN

(31) According to the gene sequence of the influenza virus A/WSN/1933 published by Pubmed, genes of various gene fragments of the influenza virus were obtained by whole genome synthesis. The various gene sequences of the influenza virus are shown in SEQ ID NOs: 2-9, respectively. Then, the gene sequences were ligated to pHH21, pCDNA 3 (neo) or pcAAGGS/MCS vector to obtain plasmids for rescuing the wild-type influenza virus WSN. The names and compositions of the plasmids obtained are shown in Table 1.

(32) TABLE-US-00001 TABLE 1 Restriction Sequence No. Name of Key Enzyme Structure of corresponding to Abbreviation plasmid gene cutting site constructed plasmid key gene Ben1 pHH21 PB2 BsmBI pPolI-WSN-PB2 SEQ ID NO: 2 Ben2 pHH21 PB1 BsmBI pPolI-WSN-PB1 SEQ ID NO: 3 Ben3 pHH21 PA BsmBI pPolI-WSN-PA SEQ ID NO: 4 Ben4 pHH21 HA BsmBI pPolI-WSN-HA SEQ ID NO: 5 Ben5 pHH21 NP BsmBI pPolI-WSN-NP SEQ ID NO: 6 Ben6 pHH21 NA BsmBI pPolI-WSN-NA SEQ ID NO: 7 Ben7 pHH21 M BsmBI pPolI-WSN-M SEQ ID NO: 8 Ben8 pHH21 NS BsmBI pPolI-WSN-NS SEQ ID NO: 9 Ben9 pcDNA3 (neo) PB2 EcoRI pcDNA3(neo)-PB2 SEQ ID NO: 2 Ben10 pcDNA3 (neo) PB1 EcoRI pcDNA3(neo)-PB1 SEQ ID NO: 3 Ben11 pcDNA3 (neo) PA EcoRI pcDNA3(neo)-PA SEQ ID NO: 4 Ben13 pcAGGS/MCS NP EcoRI pcAGGS/MCS-NP SEQ ID NO: 6

(33) (3) Selection of Sites for Site-Directed Mutagenesis

(34) The conservatism of amino acids of various proteins of the influenza virus was analyzed using the bioinformatics tool “Consurf”. Sites of conservative, relatively conservative, relatively non-conservative and non-conservative amino acids were selected according to the crystal structure of the analyzed influenza virus proteins (NP-PDB: 2IQH; PA-PDB: 4IUJ; PB1-PDB: 3A1G, 2ZNL; PB2-PDB: 4ENF; NA-PDB: 3TI6; HA-PDB: 1RVT; M-PDB: 4PUS, 2RLF, 3BKD; NS-PDB: 3L4Q) for the mutations. The mutation sites selected at each protein are shown in Table 2a)-Table 2i), respectively.

(35) TABLE-US-00002 TABLE 2a Sites selected within the NP protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) NP-S1 K48 3 NP-S2 L49 7 NP-S3 D101 1 NP-S4 G102 1 NP-S5 G126 6 NP-S6 D127 1 NP-S7 D128 2 NP-S8 Y148 7 NP-S9 S28 9 NP-S10 M32 9 NP-S11 K87 8 NP-S12 K90 8 NP-S13 K113p 9 NP-S14 A123 8 NP-S15 R150 8 NP-S16 T151 8 NP-S17 M163 8 NP-S18 L166 8 NP-S19 G169 9 NP-S20 S170 9 NP-S21 L172 8 NP-S22 R175 8

(36) TABLE-US-00003 TABLE 2b Sites selected within the PB1 protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) PB1-S1 K11 4 PB1-S2 A14 1 PB1-S3 Q15 7 PB1-S4 R52 1 PB1-S5 T105 1 PB1-S6 D685 7 PB1-S7 Y705 3 PB1-S8 K736 1 PB1-S9 I18 9 PB1-S10 S31 9 PB1-S11 A140 9 PB1-S12 I241 9 PB1-S13 A242 9 PB1-S14 I262 9 PB1-S15 Y30 7 PB1-S16 R126 9 PB1-S17 M227 9 PB1-S18 K229 9 PB1-S19 D230 9 PB1-S20 G65 9 PB1-S21 P651 9 PB1-S22 S375 8

(37) TABLE-US-00004 TABLE 2c Sites selected within the PA protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) PA-S1 R266 9 PA-S2 L270 8 PA-S3 D272 4 PA-S4 P274 8 PA-S5 K281 7 PA-S6 K289 6 PA-S7 K318 5 PA-S8 K328 5

(38) TABLE-US-00005 TABLE 2d Sites selected within the PB2 protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) PB2-S1 Q13 7 PB2-S2 T23 7 PB2-S3 T24 8 PB2-S4 K33 9 PB2-S5 T35 8 PB2-S6 S320 3 PB2-S7 D417 5 PB2-S8 A424 7

(39) TABLE-US-00006 TABLE 2e Sites selected within the HA protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) HA-S1 F12 1 HA-S2 T19 4 HA-S3 A26 8 HA-S4 V33 9 HA-S5 K39 3 HA-S6 N48 8 HA-S7 K57 2 HA-S8 K60 1 HA-S9 D18 8 HA-S10 C21 9 HA-S11 G23 8 HA-S12 T35 9 HA-S13 V43 9 HA-S14 F160 8 HA-S15 G300 8 HA-S16 G317 9 HA-S17 C319 9 HA-S18 P320 9 HA-S19 L328 9 HA-S20 G333 9 HA-S21 N336 9 HA-S22 P338 9

(40) TABLE-US-00007 TABLE 2f Sites selected within the NA protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) NA-S1 N2 9 NA-S2 P3 8 NA-S3 N4 9 NA-S4 Q5 8 NA-S5 K6 6 NA-S6 V16 1 NA-S7 N28 7 NA-S8 I29 5 NA-S9 L118 9 NA-S10 L142 9 NA-S11 S144 9 NA-S12 A186 9 NA-S13 Y192 9 NA-S14 S202 9 NA-S15 I7 8 NA-S16 I8 8 NA-S17 G11 8 NA-S18 C14 7 NA-S19 C76 8 NA-S20 K86 9 NA-S21 K244 5 NA-S22 K331 9

(41) TABLE-US-00008 TABLE 2g Sites selected within the NS1 protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) NS-S1 S8 9 NS-S2 Q10 9 NS-S3 S83 9 NS-S4 A86 1 NS-S5 H101 4 NS-S6 F103 1 NS-S7 A122 9 NS-S8 K126 7 NS-S9 T5 9 NS-S10 F9 9 NS-S11 R37 9 NS-S12 K41 8 NS-S13 K110 9 NS-S14 K131 9 NS-S15 M1 1 NS-S16 D2 8 NS-S17 P3 6 NS-S18 N4 7 NS-S19 V6 3 NS-S20 S7 7 NS-S21 L43 9 NS-S22 A132 9

(42) TABLE-US-00009 TABLE 2h Sites selected within the M1 protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) M-S1 P16 7 M-S2 S17 9 M-S3 G18 7 M-S4 K35 2 M-S5 T37 1 M-S6 I51 9 M-S7 R72 3 M-S8 L74 1 M-S9 S13 9 M-S10 V31 9 M-S11 S53 9 M-S12 A96 9 M-S13 V97 9 M-S14 I131 9

(43) TABLE-US-00010 TABLE 2i Sites selected within the M2 protein and conservatism thereof Conservatism (score ranges 1-9, wherein the Site of larger the value, the more Name amino acid conservative) M2-S1 S22 9 M2-S2 S23 9 M2-S3 D24 9 M2-S4 H37 9 M2-S5 W41 7 M2-S6 K49 9 M2-S7 K56 9 M2-S8 K60 9

(44) (4) Design of Site-Directed Mutated Primers and Construction of Mutant Vectors

(45) The coding nucleotides corresponding to the sites of amino acids listed in Tables 2a)-2i) were mutated to amber stop codons, TAG, by using Ben1 pPoll-WSN-PB2, Ben2 pPoll-WSN-PB1, Ben3 pPoll-WSN-PA, Ben4 pPoll-WSN-HA, Ben5 pPoll-WSN-NP, Ben6 pPoll-WSN-NA, Ben7 pPoll-WSN-M or Ben8 pPoll-WSN-NS as a template plasmid, and designing primers according to conventional primer design guidelines by using a site-directed mutagenesis kit (QuikChange® Lightning Site-Directed Mutagenesis Kits (Catalog #210518). The successful mutations were confirmed by means of sequencing.

(46) Mutations at the selected sites in some proteins were performed by using the primer sequences shown in Table 3.

(47) TABLE-US-00011 TABLE 3 Mutated protein Name of primer Sequence of primer (from 5′ to 3′) NP NP-53 For 5′-ggacctatatacaggagagtatagggaaagtggaggagaga-3′ g326t_a327a_t328g Rev 5′-tctctcctccactttccctatactctcctgtatataggtcc-3′ PA PA-S1 5′-gcccatccggaagtctaagtggctatggtgttgatttcaaaaaaggttca-3′ c796t_g797a_a798g 5′-tgaaccttttttgaaatcaacaccatagccacttagacttccggatgggc-3′ PB1 PB1-S4 5′-gtttgttgtccatcttccctattctgagtactgatgtgtcct-3′ a154t_g155a_g156g 5′-aggacacatcagtactcagaatagggaagatggacaacaaac-3′ PB2 PB2-54 5′-ctgtcttcctgatgtgtactacttgattatggccatatg-3′ a97t_a98a_g99g 5′-catatggccataatcaagtagtacacatcaggaagacag-3′

(48) Other mutations could be introduced by using nucleotide sequences upstream and downstream of the mutation sites and mutated primers designed according to conventional design knowledge in the art.

(49) (5) Establishment of the Stable Mammalian Cell Line HEK293-PYL that Stably Expresses tRNA (tRNA.sup.Pyl) and Pyrrolysyl-tRNA Synthetase (tRNA.sup.Pyl)

(50) Two lentiviral overexpression vectors having puromycin resistance and hygromycin resistance and carrying aminoacyl-tRNA synthetase and a GFP reporter gene with a TAG mutation at position 39, respectively was constructed, and a stable cell line pyIRS/GFP.sup.39TAG was obtained by two-rounds of viral transduction of the HEK-293T cells and puromycin/hygromycin screening. After that, a bjmu-zeo-12tRNA vector carrying 12 copies of tRNA and having zeomycin resistance was constructed, then the cell line pyIRS/GFP.sup.39TAG was transfected with the vector via plasmid linearization and subjected to zeomycin screening in the presence of UAA, and GFP positive cells were separated (which cells were green in the presence of UAA, and then became colorless when UAA was removed). The stable cell line HEK293-PYL that stably expresses the orthogonal tRNA/aminoacyl-tRNA synthetase was thereby obtained (FIG. 11A).

(51) a. Construction of Vectors

(52) Starting from the psd31 vector, the sv40-puro.sup.R gene was first replaced with the IRES-puro.sup.R and IRES-hygro.sup.R gene through the BamHI/xbaI restriction enzyme sites, respectively, resulting in two viral vectors psd31-IRES-puro.sup.R and psd31-IRES-hygro.sup.R with different resistance. The IRES is an internal ribosome entry site, and the IRES sequence is typically used for polycistronic gene expression. For example, an IRES sequence was inserted after the gene of interest and followed by a selectable marker gene, so that such a transcribed mRNA could express both proteins simultaneously. Overexpression of a gene of interest by using an IRES system has two advantages: 1. the gene of interest and a marker gene share a promoter, avoiding the occurrence of false positives; 2. efficiency of IRES translation is lower than traditional translation at initiation site, and so the expression level of the gene of interest is higher than that of the marker gene. Accordingly, the CMV-pyIRS sequence and the CMV-GFP.sup.39TAG sequence were respectively introduced in front of the IRES site through the BamHI restriction sites to obtain a dual viral system psd31-CMV-pyIRS-IRES-puro.sup.R/psd31-CMV-GFP.sup.39TAG-IRES-hygro.sup.R which could overexpress two proteins of interest at the same time.

(53) The tRNA was overexpressed by means of stable plasmid transfection. In order to ensure the expression level of tRNA, a bjmu-12t-zeo vector having a sequence as set forth in SEQ ID NO: 1 was constructed and obtained (FIG. 11C).

(54) b. Package and Transduction of Lentivirus

(55) The psd31-CMV-pyIRS-IRES-puro.sup.R virus was packaged and transduced into the HEK293T cell, and puromycin screening was performed at a concentration of 0.6 μg/ml, thereby obtaining a stable cell line “No. 1”. Then, the psd31-CMV-GFP39TAG-IRES-hygro.sup.R virus was added and hygromycin screening was performed at a concentration of 200 μg/ml, thereby obtaining a stable cell line “No. 2”.

(56) c. Stable Plasmid Transfection

(57) A third-round of screening was performed by means of stable plasmid transfection, and a special cell line that stably expresses the orthogonal tRNA/aminoacyl-tRNA synthetase was finally obtained, wherein the steps were as follows:

(58) A. after linearization of the bjmu-12t-zeo vector via enzyme digestion, the stable cell line No. 2 that expresses pyIRS and GFP.sup.39TAG proteins was transfected (10 cm dish, 10 μg plasmid per dish, and transfection was performed in the absence of antibiotics) with the vector;

(59) B. 6 hours after the transfection, the liquid was changed, and the unnatural amino acids were added;

(60) C. forty-eight hours after the transfection, green fluorescence was observed, the liquid was changed, and 400 μg/ml of zeomycin was added;

(61) D. the liquid was changed every 3 days until all blank groups were dead, and clones were formed in transfection groups; and

(62) E. GFP-positive clones were isolated and purified, and continuously subjected to amplification culture with zeomycin at a half of dose to obtain the 12t-zeo stabilized cell line HEK293-PYL.

(63) (6) Rescue of the influenza virus after site-directed mutagenesis

(64) The stable cell line was co-transfected with 12 plasmids used to rescue an influenza virus according to a normal method for rescuing an influenza virus disclosed in Neumann, G. et al. (Proc. Natl. Acad. Sci. USA 1999, 96, 9345-50), wherein only the corresponding plasmids in the 12 plasmids were replaced with the site-directed mutated plasmids. To each well of a six-well plate, 0.1 μg of each plasmid was added. After transfection, the diseased state of the cell was observed, and mutation sites that could rescue the virus and were dependent on the unnatural amino acids were screened out. The screened sites were named according to proteins and mutation sites. For example, the Ben3 pPoll-WSN-PA plasmid was mutated. After the mutation was successfully performed, the stable cell line established in step (5) was co-transfected with the mutated plasmid together with other plasmids that rescue the influenza virus, Ben1 pPoll-WSN-PB2; Ben2 pPoll-WSN-PB1; Ben4 pPoll-WSN-HA; Ben5 pPoll-WSN-NP; Ben6 pPoll-WSN-NA; Ben7 pPoll-WSN-M; Ben8 pPoll-WSN-NS; Ben9 pcDNA 3 (neo)-PB2; Ben10 pcDNA 3 (neo)-PB1; Ben11 pcDNA 3 (neo)-PA; and Ben13 pcAGGS/MCS-NP, thereby rescuing a mutant influenza virus into which the codon TAG was introduced at the S1 site of the PA gene fragment of the influenza virus; wherein the site was designated as PA-S1, and the designation corresponded to the mutation site shown in Table 2a)-Table 2i).

(65) Following the same procedure, mutant influenza viruses into which the TAG codons were introduced at other sites could be obtained, and named according to the mutation sites.

(66) TABLE-US-00012 TABLE 4 Packaging efficiency and escape frequency of mutant viruses Relative Mutant packaging Escape frequency Escape frequency virus name protein TAG site efficiency (%) (1.sup.st generation) (20.sup.th generation ) NP-D101 NP D101 ~80% 2.00E−09 ± 1.20E−09 8.00E−09 ± 7.10E−09 NP-G102 NP G102 ~50% 8.90E−08 ± 5.89E−09 4.10E−07 ± 9.40E−08 NP-D128 NP D128 ~33% 4.16E−07 ± 2.13E−07 5.90E−07 ± 7.26E−08 NP-G126 NP G126 ~40% 3.21E−08 ± 6.50E−09 1.10E−07 ± 5.20E−08 NP-R150 NP R150 ~31% Not measured Not measured NP-M163 NP M163  67% 7.00E−10 ± 1.02E−10  2.00E−9 ± 8.90E−10 NP-G169 NP G169 ~25% Not measured Not measured PB1-R52 PB1 R52 ~67% 7.10E−07 ± 1.10E−07 1.21E−06 ± 4.42E−07 PB1-T105 PB1 T105 ~57% 6.24E−06 ± 3.12E−06 7.35E−05 ± 3.62E−05 PB1-K736 PB1 K736 ~29% Not measured Not measured PB1-K11 PB1 K11 ~25% Not measured Not measured PB1-Y30 PB1 Y30 ~25% Not measured Not measured PB1-G65 PB1 G65 ~31% Not measured Not measured PB1-R126 PB1 R126 ~25% Not measured Not measured PB1-M227 PB1 M227 ~31% Not measured Not measured PB1-K229 PB1 K229 ~25% Not measured Not measured PB1-D230 PB1 D230 ~25% Not measured Not measured PB1-S375 PB1 S375 ~57% 3.20E−07 ± 1.06E−07 5.10E−07 ± 4.25E−07 PB2-S320 PB2 S320 ~36% Not measured Not measured PB2-Q13 PB2 Q13 ~67% 5.80E−04 ± 2.20E−05 8.90E−01 ± 8.90E−02 PB2-T24 PB2 T24 ~50% 6.00E−06 ± 6.12E−07 1.30E−05 ± 1.10E−06 PB2-K33 PB2 K33 ~67% 3.00E−09 ± 1.12E−09 7.00E−09 ± 3.28E−09 PB2-T35 PB2 T35 ~67% 3.50E−04 ± 3.08E−04 9.20E−01 ± 4.25E−02 PA-D272 PA D272 ~80% 9.30E−06 ± 1.00E−06 5.91E−04 ± 2.25E−04 PA-K289 PA K289 ~25% Not measured Not measured PA-K318 PA K318 ~33% Not measured Not measured PA-K328 PA K328 ~67% 1.12E−06 ± 2.45E−07 2.10E−05 ± 6.20E−06 PA-R266 PA R266 ~80% 1.00E−08 ± 1.10E−08 6.80E−08 ± 1.80E−08 PA-L270 PA L270 ~80% 6.70E−07 ± 1.09E−07 3.90E−06 ± 5.13E−07 NA-V16 NA V16 ~31% Not measured Not measured NA-K6 NA K6 ~24% Not measured Not measured NA-I29 NA I29 ~40% 3.10E−06 ± 5.34E−07 6.10E−06 ± 1.11E−06 NA-K244 NA K244 ~36% Not measured Not measured NA-N2 NA N2 ~33% Not measured Not measured NA-I7 NA I7 ~25% Not measured Not measured NA-I8 NA I8 ~33% Not measured Not measured NA-G11 NA G11 ~36% Not measured Not measured NA-N28 NA N28 ~50% 9.30E−05 ± 8.56E−06 1.21E−03 ± 2.12E−04 NA-C76 NA C76 ~25% Not measured Not measured HA-K57 HA K57 ~57% 6.20E−04 ± 1.30E−05 1.80E−01 ± 1.50E−02 HA-G317 HA G317 ~25% Not measured Not measured HA-C319 HA C319 ~25% Not measured Not measured HA-G333 HA G333 ~25% Not measured Not measured HA-N336 HA N336 ~25% Not measured Not measured NS-M1 NS M1 ~25% Not measured Not measured NS-V6 NS V6 ~25% Not measured Not measured NS-A86 NS A86 ~100%  3.00E−06 ± 6.15E−07 2.30E−04 ± 8.29E−05 NS-F103 NS F103 ~67% 8.90E−03 ± 1.12E−03 9.10E−01 ±3.30E−02  NS-H101 NS H101 ~67% 4.50E−06 ± 7.30E−07 6.10E−06 ± 1.08E−06 NS-D2 NS D2 ~25% Not measured Not measured NS-N4 NS N4 ~25% Not measured Not measured NS-S7 NS S7 ~25% Not measured Not measured NS-S8 NS S8 ~33% 8.70E−07 ± 4.50E−07 5.10E−05 ± 8.55E−06 NS-R37 NS R37 ~67% 6.10E−07 ± 7.31E−08 1.20E−06 ± 1.17E−06 NS-K41 NS K41 ~67% 1.20E−06 ± 8.22E−07 7.20E−05 ± 3.96E−05 NS-L43 NS L43 ~67% 6.50E−07 ± 3.27E−07 2.13E−06 ± 7.24E−07 NS-S83 NS S83 ~100%  8.90E−06 ± 6.60E−07 6.89E−03 ± 1.27E−03 NS-K110 NS K110 ~67% 2.10E−06 ± 2.13E−06 5.98E−05 ± 1.02E−05 NS-A122 NS A122 ~44% 2.10E−07 ± 1.13E−08 9.20E−06 ± 2.54E−06 NS-K126 NS K126 ~67% 6.79E−05 ± 1.27E−05 8.21E−04 ± 8.56E−05 NS-K131 NS K131 ~50% 5.60E−07 ± 3.55E−07 7.68E−06 ± 6.05E−07 NS-A132 NS A132 ~25% Not measured Not measured M2-S23 M2 S23 ~25% Not measured Not measured M2-D24 M2 D24 ~25% Not measured Not measured M2-H37 M2 H37 ~50% 8.00E−06 ± 7.75E−07 1.10E−05 ± 3.21E−06 M2-W41 M2 W41 ~25% Not measured Not measured M2-K49 M2 K49 ~57% 7.90E−03 ± 1.11E−03 7.50E−01 ±2.25E−02  M2-K60 M2 K60 ~57% 5.70E−03 ± 3.29E−03 6.30E−01 ±2.13E−01  PTC-2 PA R266 ~67% 1.20E−10 ± 4.46E−11 3.10E−10 ± 6.45E−11 PB2 K33 PTC-3 PA R266 ~67% <1.00E−11 <1.00E−11 PB2 K33 PB1 R52 PTC-4A PA R266 ~67% <1.00E−11 <1.00E−11 PB2 K33 PB1 R52 NP D101 PTC-4B PA R266 ~57% <1.00E−11 <1.00E−11 PB2 K33 PB1 S375 NP M163 PTC-5 PA R266 ~50% <1.00E−11 <1.00E−11 PB2 K33 PB1 R52 NP D101 NS K131 PTC-6 PA R266 ~50% <1.00E−11 <1.00E−11 PB2 K33 PB1 R52 NP D101 NS K131 M2 H37 PTC-7 PA R266 ~50% <1.00E−11 <1.00E−11 PB2 K33 PB1 R52 NP D101 NS K131 M2 H37 NA N28 PTC-8 PA R266 ~50% <1.00E−11 <1.00E−11 PB2 K33 PB1 R52 NP D101 NS K131 M2 H37 NA N28 HA K57

(67) The sites PA-S1, PB1-S4, PB2-S4 and NP-S3 which were in high efficiency for rescuing the influenza virus and were genetically stable were selected and combined. The stable cell line established in step (5) was co-transfected with the four plasmids together with other plasmids that rescue the influenza virus Ben4 pPoll-WSN-HA; Ben6 pPoll-WSN-NA; Ben7 pPoll-WSN-M; Ben8 pPoll-WSN-NS; Ben9 pcDNA 3 (neo)-PB2; Ben10 pcDNA 3 (neo)-PB; Ben11 pcDNA 3 (neo)-PA; Ben13 pcAGGS/MCS-NP, thereby rescuing a mutant influenza virus into which the TAG codons were introduced at the sites PA-S1, PB1-S4, PB2-S4, and BP-S3 simultaneously. The mutant influenza virus was named as WSN-RNP-tag.

EXAMPLE 2: EXPRESSION AND PURIFICATION OF THE SITE-DIRECTED MUTATED INFLUENZA VIRUS

(68) The plasmids constructed in the present invention for rescuing the influenza viruses into which the TAG codons were introduced may be transcribed and expressed in a mammalian stable cell line that could stably express tRNA (tRNA.sup.Pyl) and pyrrolysyl-tRNA synthetase (tRNA.sup.Pyl). These protein translation systems were used to incorporate the unnatural amino acid Lys-diazirine or Lys-azido, an azido unnatural amino acid that is structurally similar to Lys-diazirine, into the corresponding proteins of the influenza virus, resulting in the site-directed mutagenesis of the corresponding protein of the influenza virus.

(69) Next, the successful incorporation of the two unnatural amino acids Lys-diazirine and Lys-azido and the production performance of mutant proteins were tested.

(70) (1) Synthesis and Identification of the Unnatural Amino Acid Lys-Diazirine

(71) The reaction formula for the chemical synthesis of the unnatural amino acid Lys-diazirine is shown below:

(72) ##STR00009##

(73) As shown in the above formula, 15 mL of raw material 1 (5-hydroxy-2-pentanone) and 40 mL of liquid ammonia were subjected to reaction under stirring conditions at −40° C. for 5 h, then cooled to −60° C., and a methanol solution of NH.sub.2OSO.sub.3H was added dropwise slowly, heated to room temperature after the end of the addition, and allowed to react overnight. The precipitate was filtered off, triethylamine was added to the supernatant, and 12 was added slowly to the supernatant under ice-bath conditions until the color of the reaction liquid became dark and no bubbles were formed. After the reaction was complete, the solvent was removed by evaporation and the remainder extracted with ethyl ether, and dried. The ethyl ether was removed by evaporation, and the remaining liquid was distilled under reduced pressure to obtain 25.4 g of colorless viscous liquid “product 2”.

(74) The above product 2 was dissolved in pyridine, to which 11 g of TsCl was added under stirring conditions at 0° C., and allowed to react overnight. After the reaction was complete, the reaction solution was added to a mixture of concentrated hydrochloric acid and ice water and extracted with ethyl ether. The ethyl ether layer was washed with 1N hydrochloric acid and 1N NaOH, respectively. The organic phase was separated on a drying column to give 11.8 g of colorless viscous liquid “product 3”.

(75) The above product 3 was dissolved in DMF, to which NaN.sub.3 was added, allowed to react overnight at room temperature to complete the reaction, to which a large quantity of water was added, and extracted with ethyl ether. The ethyl ether was removed by evaporation. The remaining product was dissolved in a mixture of THF: water (9:1), to which triphenylphosphine was added, and allowed to react at room temperature. After the reaction was complete, 1N HCl was added and mixed homogenously, and THF was removed by spin drying. The unreacted raw materials, PPh3 and O=PPh3 were removed by washing with dichloromethane. 1N NaOH was added to the liquid phase to adjust the pH to 12, and 4.0 g of “product 4” was extracted with methylene chloride.

(76) Reaction of 5.2 g of starting material 5 (Boc-Lys-OMe) with carbonyldiimidazole gave 5.9 g of compound 6. Then, compound 6 was coupled with the above product 4 (4.0 g) to give compound 7. The Boc and the methyl ester were removed by means of two-step deprotection, obtaining 4.5 g of target “product 8”, Lys-diazirine. The results confirmed by spectroscopy were: .sup.1H NMR (400 MHz, D20): δ 3.10 (1H, t, J=6.3 Hz), 2.96 (4H, m), 1.25 (10H, m), 0.90 (3H, s); .sup.13C NMR (100 MHz, D20): 183.63, 160.66, 56.00, 39.80, 39.30, 34.49, 30.84, 29.20, 26.75, 23.92, 22.43, 18.80; HREIMS m/z 308.16937 [M+1]+(calcd for C.sub.12H.sub.22N.sub.5NaO.sub.3, 308.16931), proving that the structure of the prepared Lys-diazirine was correct.

(77) (2) Rescue of the Mutated Influenza Virus by Incorporating the Non-Natural Amino Acid Lys-Diazirine

(78) The stable cell line in step (5) was co-transfected with the influenza virus packaging plasmids, which were obtained in the rescue of the influenza virus after site-directed mutagenesis in step (6) of Example 1; after 6 hours, a new culture medium containing 1% of FBS, 2 μg/ml of TPCK-trypsin, 1 mM of the non-natural amino acid Lys-diazirine was employed; and a culture medium that did not contain the non-native amino acid Lys-diazirine was used as a control. In this rescue experiment, the wild-type influenza virus WSN was used as a positive control, and except for plasmids for rescuing virus, the conditions were the same as those in the rescue of the mutated influenza virus. After the transfection was complete, the state of the cells was observed every day. The influenza virus mutants used to transfect the cells were identified as positive mutants where cells showed lesions when cultured in a medium containing the unnatural amino acid, and did not show any lesion when cultured in a culture medium without the unnatural amino acid. In contrast, the cells infected with the wild-type influenza virus showed lesions when cultured in a culture medium in the presence or absence of unnatural amino acid.

(79) (3) Purification of Lys-Diazirine Mutated Influenza Virus

(80) 1). When the cell line in step (2) that rescued the mutant influenza virus completely lesioned, the cell supernatant was collected and centrifuged at 5000 g for 10 min, and the supernatant was filtered over a 0.45 μm membrane.

(81) 2) The influenza virus was purified by sucrose density gradient centrifugation, as follows: the virus solution of step 1) was centrifuged in a 50 ml centrifuge tube (adapted to withstand high-speed) at 10.sup.5 g for 2 hours to provide a precipitate, followed by resuspension with 1 ml PBS.

(82) 3) Sucrose was dissolved in NTE Buffer (100 mM NaCl, 10 mM Tris-CI, pH 7.4, 1 mM EDTA) to formulate a 20% sucrose solution, and the solution was filtered over a 0.45 μm membrane.

(83) 4) The sucrose solution in step 3) was added to a 50 ml or 15 ml centrifuge tube, the PBS suspension in step 2) was dropped on the sucrose solution, and centrifugation was performed at 11×10.sup.4 g for 2 hours.

(84) 5) About 15 ml NTE buffer was added to the precipitate, and further centrifuged at 11×10.sup.4 g for 2 hours.

(85) 6) The precipitate in step 5) was resuspended with PBS.

(86) (4) Incorporation and Expression of Lys-Azido in the Mutated Influenza Virus and Purification of the Influenza Virus

(87) The reaction formula for the chemical synthesis of the unnatural amino acid Lys-azido is shown below.

(88) ##STR00010##

(89) As shown in the above formula, 2.3 mL of raw material 1 (2-bromoethanol) was dissolved in a mixed solution of 90 mL of acetone and 15 mL of water, and 3.12 g of NaN.sub.3 was added thereto; the mixture was heated to reflux in a 60° C. oil bath for 20 hours, cooled to room temperature, subjected to rotary evaporation to remove acetone, extracted with anhydrous ether (30 mL×8), dried with anhydrous Na.sub.2SO.sub.4, and subjected to rotary evaporation to remove the solvent, giving 2.62 g of colorless liquid product 2.

(90) Product 2 (500 mg, 5.74 mmol) was added to a solution of triphosgene (1.70 g, 5.74 mmol) in THF (10 ml), allowed to react under stirring conditions at 0° C. for 8 hours, and subjected to evaporation to remove the solvent. The residue was dried under vacuum for 1 h to give a colorless oily liquid as the product 3.

(91) Product 3 was dissolved in 1.5 ml THF, slowly added in a solution of Boc-Lys-OH (1.7 g, 6.88 mmol) in 1M NaOH (20 ml)/THF (5 ml), allowed to react under stirring conditions at 0° C. for 12 hours, and gradually heated to room temperature. The reaction solution was cooled to 0° C. again, and the pH of the reaction solution was adjusted to 2-3 by using 1M hydrochloric acid solution at 0° C. The reaction solution was extracted with EtOAc (30 mL×5), and the organic layer was washed with 2×100 mL of a saturated salt solution. The organic layer was dried with anhydrous Na.sub.2SO.sub.4, filtered, and subjected to rotary evaporation to remove the solvent to give 1.65 g of a colorless viscous liquid as product 4 without further being purified.

(92) Product 4 was dissolved in 15 mL CH.sub.2Cl.sub.2, to which 15 mL TFA was slowly added dropwise under stirring, then allowed to react at room temperature for 30 minutes, and subjected to evaporation to remove the solvent. The remaining liquid product was dissolved with 5 mL methanol, to which 100 mL ether was added so as to form a large amount of white solid precipitate, then filtered, and dried to give 1.38 g of white solid as the final product 5: .sup.1H NMR (D20): δ=1.22-1.45 (m, 4H), 1.67-1.73 (m, 2H), 2.99 (m, 2H), 3.38 (m, 2H), 3.70 (m, 1H), 4.09 (m, 2H); .sup.13C NMR (D20): δ=21.4, 28.4, 29.6, 39.5, 53.4, 56.2, 57.8, 116.0 (TFA), 153.1, 162.3 (TFA), 172.9. HRMS: m/z calcd for C.sub.9H.sub.17N.sub.5O.sub.4 [M]+: 259.1281; found: 259.1283, proving that the structure of resulting Lys-azido was correct.

(93) Except that Lys-diazirine was replaced with Lys-azido, the other conditions were the same as those in the previous steps 2-3. The occurrence of cytopathogenesis upon introduction of the mutated virus was observed, in order to confirm whether the mutation was successful, and that a mutant influenza virus into which the UAGs were introduced into the corresponding mutation sites was obtained.

(94) The rescue of a part of the mutant influenza viruses was used as example shown in FIG. 2. The results indicated that the codon UAGs could be introduced in gene segments encoding 8 proteins of influenza virus, and corresponding mutant influenza viruses could be rescued. The four sites of PA-S1, PB1-S4, PB2-S4 and NP-S3 were highly efficient in rescuing influenza viruses and genetically stable, and they were ideal mutation sites. These four sites were combined, that is, the stable cell line established in step (5) was co-transfected with the these four plasmids and other plasmids that rescue influenza virus, Ben4 pPoll-WSN-HA; Ben6 pPoll-WSN-NA; Ben7 pPoll-WSN-M; Ben8 pPoll-WSN-NS; Ben9 pcDNA 3 (neo)-PB2; Ben10 pcDNA 3 (neo)-PB1; Ben11 pcDNA3 (neo)-PA; Ben13 pcAGGS/MCS-NP, thereby rescuing a mutant influenza virus into which the UAG codons were introduced at the sites PA-S1, PB1-S4, PB2-S4, and NP-S3 simultaneously. The mutant influenza virus was named as WSN-RNP-tag (PCT-4A). The rescue efficiency for the mutant influenza virus WSN-RNP-tag was high. The mutant influenza virus had a high yield and it exhibited high genetic stability, and was the final mutation product prepared by the inventors.

(95) 5. Study on Rescue Efficiency for the Mutant Influenza Virus WSN-RNP-Tag

(96) The inventors compared the efficiency for rescuing the mutant influenza virus WSN-RNP-tag with the normal mammalian cell line 293T and that with the stable mammalian cell line HEK293-PYL that stably expresses tRNA (tRNA.sup.Pyl) and pyrrolysyl-tRNA synthetase (tRNA.sup.Pyl).

(97) The experiments were divided into three groups. In the first group, the stable cell line HEK293-PYL was used, and transfected with 1.2 μg of plasmids that express tRNA (tRNA.sup.Pyl) and pyrrolysyl-tRNA synthetase (tRNA.sup.Pyl) and 1.2 μg of plasmids that rescue the mutant influenza virus simultaneously; in the second group, the stable cell line was used, and only transfected with 2.4 μg of plasmids that rescue the mutant influenza virus; and in the third group, the normal 293T cell was used, and transfected with 1.2 μg of plasmids that express tRNA (tRNA.sup.Pyl) and pyrrolysyl-tRNA synthetase (tRNA.sup.Pyl) and 1.2 μg of plasmids that rescue the mutant influenza virus simultaneously. The results shown in FIG. 10 demonstrated that the efficiency of the stable cell line HEK293-PYL for rescuing the influenza virus was much higher than that of the normal 293T cell. (Illustration in the presence of NAEK in FIG. 10).

(98) In addition, the inventors also investigated the yield of the prepared mutant influenza virus WSN-RNP-tag. By measuring the mRNA levels of M gene segments of wild-type and mutant-type viruses prepared under the same conditions, it was demonstrated that the yield of the mutant influenza virus was substantially the same as that of the wild type (FIG. 5). Moreover, by determining antigen erythrocyte agglutination titers of wild-type and of the mutant WSN-RNP-TAG viruses, it was demonstrated that the mutant influenza virus and the wild-type virus had substantially the same antigen erythrocyte agglutination titers, demonstrating that the yield of mutant influenza virus was very high. The specific experimental operations could refer to the experimental steps of qRT-PCR and methods for determining antigen erythrocyte agglutination titer of viruses.

EXAMPLE 3: STUDY ON SAFETY OF THE MUTANT INFLUENZA VIRUS WSN-RNP-TAG AT THE CELLULAR LEVEL

(99) By performing a long-term serial subcultivation of the prepared mutant influenza virus WSN-RNP-tag, the inventors investigated the stability of the UAG codons at the mutation sites of the mutant influenza virus. The specific experiment was as follows: the newly prepared mutant influenza virus WSN-RNP-tag was inoculated into a new medium containing 1% FBS, 2 μg/ml TPCK-trypsin and 1 mM unnatural amino acid NAEK at MOI=0.01, and infected stable cells, and a medium that was free from the unnatural amino acid NAEK served as a controls. After the cells in the 1 mM NAEK medium completely lesioned, the supernatant was removed, filtered over a 0.45 μm membrane, inoculated into a new medium at a ratio of 1/1000, and infected the stable cells, and a medium that was free from the unnatural amino acid NAEK was similarly used as a control. The long-term passage of virus was performed by such repetitions.

(100) It can be seen from FIG. 4 that the mutant influenza virus WSN-RNP-tag had maintained its dependence on the unnatural amino acid after the long-term passage, that is, it could only be reproduced in large-scale in a medium containing an unnatural amino acids to cause cell lesions. This indicated that the UAG codons introduced in the influenza virus gene had been stably present throughout, thus further demonstrating that the selected sites were genetically stable.

EXAMPLE 4: STUDY ON THE SAFETY AND EFFICACY OF THE MUTANT INFLUENZA VIRUS WSN-RNP-TAG IN ANIMALS

(101) Experimental programs could refer to FIG. 7, and the specific implementation was as follows:

(102) 1) 80 mice were divided into 8 groups, with 10 mice in each group.

(103) 2) The mice were fed for one day to adapt to the environment.

(104) 3) The next day, the mice were weighed, 5 mice were selected from each group, the serum thereof was collected (wherein 20-40 μl of blood volume was collected to prevent mice from death due to blood loss, and the serum collected was subjected to cryopreservation at −80° C.).

(105) 4) After feeding for two days (the animals from which the blood was collected returned to normal state), the mice were inoculated with the following corresponding virus solutions according to the groups and tube Nos. of the virus solutions.

(106) Method of inoculating a virus: anesthetized mice were intranasally inoculated with 50 μl of a virus solution by a nasal drip process. The half-lethal dose LD.sub.50 was 10000 virus particles/50 μl. The 1-fold lethal dose was 10*LD.sub.50, which was equivalent to 10.sup.5 virus particles/50 μl. The 10-fold lethal dose was 100*LD.sub.50, which was equivalent to 10.sup.6 virus particles/50 μl.

(107) The first group was inoculated with the virus solution in tube No. 1 (composition: PBS);

(108) The second group was inoculated with the virus solution in tube No. 2 (composition: 1-fold lethal dose of the WSN-wild type);

(109) The third group was inoculated with the virus solution in tube No. 3 (composition: 1-fold lethal dose of the WSN-RNP type);

(110) The fourth group was inoculated with the virus solution in tube No. 4 (composition: 5-fold lethal dose of the WSN-RNP-tag);

(111) The fifth group was inoculated with the virus solution in tube No. 5 (composition: 10-fold lethal dose of the WSN-RNP-tag);

(112) The sixth group was inoculated with the virus solution in tube No. 6 (composition: 1-fold lethal dose of the inactivated WSN);

(113) The seventh group was inoculated with the virus solution in tube No. 7 (composition: 5-fold lethal dose of the inactivated WSN); and

(114) The seventh group was inoculated with the virus solution in tube No. 8 (composition: 10-fold lethal dose of the inactivated WSN).

(115) Cross-infection was prevented among the groups.

(116) 5) On each day after inoculation, the mice were weighed and the body weights thereof were recorded, and the death of the mice was recorded.

(117) 6) On the 14.sup.th and 21.sup.st days after inoculation of the virus solution, the serum of the mice was collected again (wherein 20-40 μl of blood volume was collected, and the serum collected was subjected to cryopreservation at −80° C.).

(118) 7) On the 21.sup.st day after inoculation of the virus solution, each mouse was intranasally infected with 50 μl of a new virus solution at a dose of 100*LD.sub.50.

(119) Then the mice were further observed for 2-3 weeks, weighed, and recorded. The death of the mice was recorded. In addition, on the third day after infection with the virus solution, three mice were taken from each group; the lung tissues thereof were taken out, pulverized, and homogenized; the supernatant was collected (which could be subjected to cryopreservation at −80° C.). The remaining mice were further observed.

(120) As can be seen in FIG. 8, all mice had significantly decreased body weight, and died on the 10.sup.th day after inoculation when inoculated with the wild-type influenza virus, whereas all mice showed no significant weight loss and survived during the observation period when inoculated with mutant WSN-RNP-TAG virus or the inactivated influenza WSN-positive control. This demonstrates that the mutant WSN-RNP-TAG had good safety in animals.

(121) As can be seen in FIG. 9A, according to the experimental program set out in FIG. 7, lung tissues of mice from each group were taken, and relative amounts of the virus in the lung tissues were detected by qRT-PCR. The results showed that the virus amounts in the lung tissues of the mice were decreased and were immune dose-dependent when mice were immunized with the inactivated virus or the mutant WSN-RNP-TAG. In addition, the immune effect of the mutant WSN-RNP-TAG was better than that of the inactivated virus.

(122) As can be seen in FIG. 9B, the levels of anti-HA antibody in each group of mice before and after immunization were tested by ELISA assay. The results showed that the levels of the antibody in the mice increased 14 days after the immunization and 21 days after the immunization, and the levels of the antibody on the 21.sup.st day was higher than that on the 14.sup.th day.

(123) As can be seen in FIG. 9C, following the experimental program set out in FIG. 7, each group of mice was individually immunized, and then infected with 100×LD.sub.50 of WSN. The body weight and death rate of the mice were investigated. It was found that the mutant WSN-RNP-tag strain could protect animals well from viral infection. Moreover, the protective effect of the mutant WSN-RNP-tag on mice at a 1-fold dose was comparable to that of the inactivated WSN at a 10-fold dose. This fully demonstrated that the attenuated influenza vaccine was superior in immunogenicity to the inactivated vaccine.

EXAMPLE 5: DETERMINATION OF THE LEVELS OF ANTI-NA PROTEIN AND OF ANTI-NP PROTEIN IN MICE VACCINATED WITH THE INFLUENZA VIRUS VACCINE

(124) The mice were inoculated with the WSN-RNP-tag and the inactivated WSN according to a method of inoculating a virus described in Example 4.

(125) The amount of the antibody against NA or NP protein in mice was detected by the ELISA method. Specifically, the NA or NP protein was diluted with a coating solution to 30 ng/100 μl. The 96-well plate for the ELISA method was coated with the above diluted solution overnight at 4° C., then washed with the ELISA washing solution, and blocked with 3% BSA washing solution at 37° C. for 1 h. The serum from the mice was diluted with 0.5% BSA washing solution, added to the corresponding wells, incubated at 37° C. for 1 h, washed with a washing solution 5 times after the supernatant was discarded, to which HRP-labeled goat anti-mouse IgG was then added, incubated at 37° C. for 1 h, washed with a washing solution 5 times after the supernatant was discarded, and developed with TMB for 5-10 minutes. The reaction was stopped with an ELISA stop buffer. The OD value was measured at 450 nm.

(126) The results shown in FIG. 12 demonstrate that the WSN-RNP-tag can induce mice to produce specific antibodies against NA at a higher production level than that of the inactivated vaccine, indicating that the vaccine prepared by the inventors had better immunogenicity. More importantly, the WSN-RNP-tag invented by the inventors could also induce mice to produce antibodies against NP, an internal protein of influenza virus, which was beneficial for providing mice with cross-immunity protection.

EXAMPLE 6: INDUCTION OF THE WSN-RNP-TAG TO PRODUCE SPECIFIC IGA AGAINST VIRUS IN MOUSE LUNG

(127) The specific implementation was as follows:

(128) 1) 15 mice were divided into 3 groups, with 5 mice in each group.

(129) 2) The mice were fed for one day to adapt to the environment.

(130) 3) The next day, the mice were inoculated with the following corresponding virus solutions according to the groups and tube Nos. of the virus solutions.

(131) Method of inoculating a virus: anesthetized mice were intranasally inoculated with 50 μl of a virus solution by a nasal drip process. Similarly to Example 4, the half-lethal dose LD.sub.50 was 10000 virus particles/50 μl; the 1-fold lethal dose was 10*LD.sub.50; and the 10-fold lethal dose was 100*LD.sub.50.

(132) The first group was inoculated with the virus solution in tube No. 1 (composition: PBS);

(133) The second group was inoculated with the virus solution in tube No. 2 (composition: 10-fold lethal dose of the WSN-RNP-tag); and

(134) The third group was inoculated with the virus solution in tube No. 3 (composition: 10-fold lethal dose of the inactivated WSN).

(135) Cross-infection was prevented among the groups.

(136) 4) On the 21.sup.st day after inoculation of the virus solution, the lung tissues were taken from the mice in each group and washed with PBS, and the washing solution was collected. The collected washing solution was subjected to cryopreservation at −80° C.

(137) The IgA production was detected by the ELISA method. Specifically, the purified WSN virus was diluted with a coating solution to 0.5 μg/100 μl. The 96-well plate for the ELISA method was coated with the above diluted solution overnight at 4° C., then washed with the ELISA washing solution, and blocked with 3% BSA washing solution at 37° C. for 1 h. The serum from the mice was diluted with 0.5% BSA washing solution, added to the corresponding wells, incubated at 37° C. for 1 h, washed with a washing solution 5 times after the supernatant was discarded, to which HRP-labeled goat anti-mouse IgA was then added, incubated at 37° C. for 1 h, washed with a washing solution 5 times after the supernatant was discarded, and developed with TMB for 5-10 minutes. The reaction was stopped with an ELISA stop buffer. The OD value was measured at 450 nm.

(138) The results shown in FIG. 13 demonstrate that the WSN-RNP-tag could induce production of IgA at a high level relative to the inactivated WSN, which was beneficial for providing mice with cross-immunoprotection.

EXAMPLE 7: CHANGE IN AMOUNT OF NP-SPECIFIC CD8+ T CELLS IN LUNG OF MICE IMMUNIZED WITH THE WSN-RNP-TAG

(139) The test method: three weeks after the mice were immunized, the lung tissues of the mice were extracted, and the T lymphocytes were isolated therefrom. The T lymphocytes were stained with the anti-mouse CD8a-APC antibody and the influenza NP366-374-tetramer-PE. The number (proportion) of influenza-specific CD8+ T cells was measured by flow cytometry, wherein the steps can be found in the reference Budimir, N. et al., Heterosubtypic cross-protection induced by whole inactivated influenza virus vaccine in mice: influence of the route of vaccine administration. Influenza Other Respir Viruses 7, 1202-1209 (2013).

(140) The results shown in FIG. 14 demonstrate that inactivated WSN had minimal affect on the amount of the NP-specific CD8+ T cells, while the amount of the NP-specific CD8+ T cells in lungs of the mice immunized with the WSN-RNP-tag was significantly increased, which was beneficial for providing mice with cross-immunoprotection.

EXAMPLE 8: STUDY OF INHIBITORY EFFECT OF THE VIRUS VACCINE CONTAINING UAG CODONS PREPARED BY THE INVENTORS ON THE WILD-TYPE VIRUS

(141) The effect of the virus containing UAG codons on the replication of the wild-type virus was first investigated at the cellular level. The specific implementation was as follows:

(142) 1. A 6-well plate was provided with MDCK cells at 5×10.sup.5 cells per well.

(143) 2. After 24 hours, the cells were infected with the wild virus (MOI=0.01) or co-infected with a mixture of the wild-type virus and the mutant virus (MOI=0.1 or 1).

(144) 3. After 24 hours, 200 μl of cell supernatant was taken every 12 hours until 72 hours.

(145) 4. The titer of the wild-type virus in the supernatant was measured.

(146) The results as shown in FIGS. 15A and 15B demonstrate that the mutant virus reduced the titer of the progeny virus of the wild type virus, and the increased titer of the mutant virus or increase in number of UAG codons in the genome of the mutant virus resulted in enhancing the inhibitory effect of the mutant virus on the replication of the wild type virus.

(147) The effect of the virus containing the UAG codons on the replication of the wild-type virus was then investigated in animals. The specific implementation was as follows:

(148) 1. 15 Balb/C mice for each group. The Balb/C mice were infected with the wild-type virus (2×10.sup.4 PFU) or a mixture of wild-type virus and mutant virus (2×10.sup.6 PFU) by means of nasal inoculation; or the mice were first infected with wild-type virus (2×10.sup.4 PFU), and after twenty-four hours, the mice were infected with the mutant virus (2×10.sup.6 PFU).

(149) 2. After three days, 5 mice were randomly selected from each group and sacrificed. The lung tissues were taken out. The titer of the wild-type virus in the lung tissues was measured.

(150) 3. The survival rate and body weight of the remaining 10 mice were observed for two weeks.

(151) The results as shown in FIGS. 15 C, D and E demonstrate that: the mice all had reduced body weight and eventually died when inoculated with the wild-type virus alone; when inoculated with the mixture of the wild-type virus and the mutant virus simultaneously, the mice did not display an obvious reduction in body weight, they exhibited a final survival rate of 90%, and displayed obviously reduced virus in the lung tissue; when inoculated with the wild-type virus, and after 24 hours inoculated with the mutant virus, the mice had a reduced body weight, and a survival rate of 40%. This demonstrated that the mutant virus could inhibit the replication of the wild-type virus in mice, thus providing protection for mice. These results also demonstrate that vaccines having therapeutic effects could be prepared by the techniques provided by the present invention.

(152) The above method for preparing a live attenuated influenza virus vaccine could also be applied to any other kind of virus, preferably, hand-foot-mouth disease virus, coxsackievirus, hepatitis C virus HCV, hepatitis B virus HBV, hepatitis A virus, hepatitis D virus, hepatitis E virus, Epstein-Barr virus, human papilloma virus HPV, herpes simplex virus HSV, cytomegalovirus, varicella-zoster virus, vesicular stomatitis virus, respiratory syncytial virus RSV, dengue virus, Ebola virus, Zika virus, SARS, Middle East respiratory syndrome virus, rotavirus, rabies virus, measles virus, adenovirus, human immunodeficiency virus, poliovirus, echovirus, Japanese encephalitis virus, forest encephalitis virus, Hantaan virus, new enterovirus, rubella virus, mumps virus, parainfluenza virus, blue-ear disease virus, swine fever virus, foot-and-mouth disease virus, and parvovirus.

(153) What are described above are only involved in some embodiments of the present invention. For a person skilled in the art, many variations and improvements may be made without departing from the concept of the present invention, all of which are within the scope of protection of the present invention.