阅读说明：本技术 从噬菌体抗体库中筛选和验证抗狂犬病病毒中和抗体的方法及筛选试剂盒 (Method for screening and verifying rabies virus resistant neutralizing antibody from phage antibody library and screening kit ) 是由 毛晓燕 陈继军 安晨 赵晓瑞 叶星 于 2019-09-26 设计创作，主要内容包括：本发明涉及生物医药工程技术领域,公开了一种从噬菌体抗体库中筛选和验证抗狂犬病病毒中和抗体的方法,包括A、单克隆噬菌体抗体培养,并取培养上清液；B、定性分析：将步骤A中的培养上清液置于96孔板中,依次经DMEM培养基以及中和用病毒中和、BSR细胞悬液培养、预冷丙酮固定后,与稀释后的FITC标记的抗狂犬病病毒核蛋白抗体共孵育,选择可明显抑制病毒感染的克隆测序,排除重复的序列,初步获得中和活性各不相同的抗狂犬病病毒抗体序列；C、定量分析：挑选不同序列有中和活性的各个克隆,重新制备噬菌体抗体颗粒,纯化并稀释一定倍数后采用RFFIT法测定体外中和活性；以及D、全分子抗体瞬时表达和活性分析。(The invention relates to the technical field of biomedical engineering, and discloses a method for screening and verifying rabies virus resistant neutralizing antibodies from a phage antibody library, which comprises the steps of A, culturing monoclonal phage antibodies, and taking culture supernatant; B. and (3) qualitative analysis: placing the culture supernatant in the step A into a 96-well plate, sequentially performing virus neutralization, BSR cell suspension culture and precooling acetone fixation on the culture supernatant through a DMEM culture medium, and after virus neutralization and BSR cell suspension culture and precooling acetone fixation, performing co-incubation with the diluted FITC-labeled anti-rabies virus nucleoprotein antibody, selecting clone sequencing capable of obviously inhibiting virus infection, eliminating repeated sequences, and primarily obtaining anti-rabies virus antibody sequences with different neutralization activities; C. quantitative analysis: selecting each clone with different sequences and neutralizing activity, preparing phage antibody particles again, purifying and diluting by a certain multiple, and then determining in vitro neutralizing activity by adopting an RFFIT method; and D, transient expression and activity analysis of the whole molecule antibody.)

1. A method for screening and verifying rabies virus neutralizing antibodies from a phage antibody library, which comprises the following steps:

A. culturing monoclonal phage antibody, and taking culture supernatant;

B. and (3) qualitative analysis: RFFIT method for primary screening of antibodies with neutralizing activity

Placing the culture supernatant in the step A into a 96-well plate, sequentially performing virus neutralization, BSR cell suspension culture and precooling acetone fixation on the culture supernatant through a DMEM culture medium, and after virus neutralization and BSR cell suspension culture and precooling acetone fixation, performing co-incubation with the diluted FITC-labeled anti-rabies virus nucleoprotein antibody, selecting clone sequencing capable of obviously inhibiting virus infection, eliminating repeated sequences, and primarily obtaining anti-rabies virus antibody sequences with different neutralization activities;

C. quantitative analysis: monoclonal phage antibody particle Activity assay

Selecting each clone with different sequences and neutralizing activity, preparing phage antibody particles again, purifying and diluting by a certain multiple, and then determining in vitro neutralizing activity by adopting an RFFIT method;

D. whole molecule antibody transient expression and activity analysis

Selecting a clone with the activity of phage antibody particles larger than 0.5IU/ml, amplifying antibody variable region genes, constructing eukaryotic transient expression plasmids, transiently transferring HEK293EBNA1 cells, and determining the specific activity of the anti-rabies virus antibody after the culture supernatant is subjected to Mabselect Sure affinity purification to obtain the anti-rabies virus neutralizing antibody.

2. The method of claim 1 for screening and validating anti-rabies virus neutralizing antibodies from phage antibody libraries is characterized by:

wherein, the monoclonal phage antibody culture is carried out in the step A, and the specific preparation method of the culture supernatant is as follows:

adding the phage antibody subjected to three rounds of screening into E.coli TG1 bacterial liquid, uniformly mixing, and standing and infecting for 30-40 min at room temperature; coating the bacterial liquid on a 2YT-A plate, culturing overnight at 30 ℃, selecting and cloning to a 96-well plate containing 2YT-A, and culturing overnight; and then culturing the culture in a fresh 2YT-A culture medium at 220rpm and 37 ℃ for 1.5h, adding MK1307 helper phage, mixing uniformly, standing and infecting at room temperature for 30-40 min, centrifuging, then resuspending the cells in the 2YT-A/K culture medium, culturing overnight, and centrifuging to collect supernatant containing monoclonal phage antibody particles.

3. The method of screening and validating anti-rabies virus neutralizing antibodies from phage antibody library according to claim 2, characterized in that:

in the step B, the specific method for primarily screening monoclonal phage antibody particles by the RFFIT method is as follows:

putting the supernatant into a 96-well plate, adding 14-15 times of DMEM culture medium and 15-16 times of diluted virus for neutralization into each well, neutralizing for 1h at 37 ℃, and adding 1.0 multiplied by 10 with 15-16 times of volume⁶BSR cell suspension at one/mL, 5% CO₂Culturing at 37 ℃ for 24h, removing the supernatant, washing the cells with PBS, fixing with 80% precooled acetone with the volume of 60-70 times, removing the acetone, and standing at room temperature for 15 min;

diluting an FITC-labeled rabies virus nucleoprotein antibody by 200 times by using PBS (phosphate buffer solution), adding the diluted FITC-labeled rabies virus nucleoprotein antibody into each hole, incubating for 1h at 37 ℃, discarding liquid, washing by using PBS, observing and recording the infection proportion of each hole under a fluorescence microscope, and labeling the hole with obvious inhibition on virus growth as a positive hole;

and C, taking the bacterial liquid from the 96-well plate corresponding to the positive well, adding a 2YT-A culture medium, performing overnight culture at 37 ℃ and 220rpm, then sequencing, selecting a correct scFv sequence, selecting a clone with an unrepeated sequence, and entering the step C.

4. The method of screening and validating anti-rabies virus neutralizing antibodies from phage antibody library according to claim 3, characterized in that:

wherein, the sequencing primer sequence of the phage antibody is shown in SEQ NO. 1.

5. The method of screening and validating anti-rabies virus neutralizing antibodies from phage antibody library according to claim 3, characterized in that:

wherein, the concrete steps of the step C are as follows:

selecting each clone with different sequences and neutralizing activity, culturing the monoclonal phage antibody according to the step A, and taking culture supernatant; adding 20% PEG-8000+2.5mol/LNaCl solution of 1/5 volume into the obtained supernatant, mixing, standing in ice bath for 1h, centrifuging at 10000g for 20min to obtain precipitate as phage antibody particles,

diluting the obtained phage antibody particles by 15 times, respectively adding into 96-well cell culture plates, adding neutralizing virus with the same volume into each well, neutralizing at 37 deg.C for 1h, adding BSR cell suspension with 1.0 × 106/mL and 5% CO with the same volume₂Culturing at 37 deg.C for 24 hr, and removing supernatant; after PBS is used for cleaning cells, adding precooled 80% acetone with four times volume to be fixed for 10min at the temperature of 30 ℃, then removing the acetone, and standing for 15min at room temperature; diluting an FITC-labeled anti-rabies virus nucleoprotein antibody by 200 times by using PBS, adding the volume of the FITC-labeled anti-rabies virus nucleoprotein antibody into each hole by twice, incubating at 37 ℃ for 1h, discarding liquid, and washing by using PBS; the infection ratio of each well was observed and recorded under a fluorescence microscope and the antibody activity was calculated according to the formula in the rabies immunoglobulin titer assay.

6. The method of screening and validating anti-rabies virus neutralizing antibodies from phage antibody library according to claim 5, characterized in that:

when the number of infected cells in a 150-fold dilution well as the highest concentration well in a sample exceeds 50%, the sample is not considered to have significant neutralizing activity against rabies virus, and the result of phage antibody activity is recorded as 0 IU/mL.

7. The method of screening and validating anti-rabies virus neutralizing antibodies from phage antibody library according to claim 1, characterized in that:

in step D, the method for constructing eukaryotic transient expression plasmid is as follows:

comparing antibody variable region sequences to determine antibody subtypes; constructing corresponding light chain expression plasmids by using corresponding kappa and lambda light chain vectors respectively, and constructing respective heavy chain expression plasmids by using the same heavy chain vector for all sequences; and (3) amplifying the variable regions of the light chain and the heavy chain of the antibody from the clone corresponding to the phage particles with the neutralizing activity by using transient expression primers shown in SEQ NO. 2-7, constructing a PCR product into a plasmid, selecting clone sequencing for identification, selecting the clone with the sequencing result conforming to the expectation, and extracting the plasmid.

8. A kit for screening and verifying neutralizing antibodies against rabies virus from a phage antibody library, said kit comprising a monoclonal phage antibody particle preparation system; the RFFIT method is used for measuring the in-vitro neutralizing activity system of the antibody; constructing an extraction system by using the transient expression plasmid; and whole molecule antibody transient expression and purification systems.

Technical Field

The invention relates to the technical field of biomedical engineering, in particular to a method for screening and verifying an anti-rabies virus neutralizing antibody from a phage antibody library and an antibody screening kit.

Background

Rabies is a serious lethal disease, susceptible to infection by humans and all warm-blooded animals. Rabies belongs to rhabdoviridae and is mainly divided into 7 genotypes. Rabies virus is RNA virus, which encodes five structural proteins, namely nucleoprotein (N), phosphoprotein (P), matrix protein (M), RNA-dependent RNA polymerase (L) and Glycoprotein (G), wherein Glycoprotein (Glycoprotein, G) is transmembrane protein, forms a protuberance on the surface of the virus, is a main protective antigen and can induce the generation of protective antibodies. The glycoprotein mainly comprises 3 main antigen epitopes and other minor epitopes, wherein the epitope I is positioned in AA226-331 and is a linear epitope; epitope II is a conformational epitope consisting of AA34-42 and AA 198-200; epitope III is a conformational epitope consisting of AA 330-338; the G5 epitope is a linear epitope consisting of AA 261-264; the G1 epitope consists of AA 341-343.

Rabies still lacks an effective treatment means at present, and once the disease is almost 100% dead, the prevention of rabies is mainly carried out by using rabies virus vaccine, and because the vaccination needs a certain time to generate antibody, the anti-rabies virus immunoglobulin must be used simultaneously for the exposure above level III. Anti-rabies virus immunoglobulins currently on the market all have certain problems or limitations, such as inability to produce large quantities due to blood source problems, potential risk of disease transmission, or seropathy. The anti-rabies virus monoclonal antibody overcomes the defects of the products and is a very promising replacement product for upgrading. The phage antibody library technology is one of the main technologies for obtaining antibody sequences, and is widely applied to antibody screening.

The primary screening of phage antibody libraries is usually performed by using an ELISA method, and the screening is performed firstly on positive clones combined with antigen and sequencing analysis is performed on the positive clones, then prokaryotic expression plasmids are constructed, activity verification is performed after scFv is expressed by escherichia coli, and finally a full molecular antibody is constructed for property analysis, wherein the defects of the screening method are obviously as follows:

first, this method can only evaluate the binding activity of an antibody to an antigen and cannot evaluate the neutralizing activity of an antibody, and therefore the proportion of a neutralizing antibody in a positive clone is low and most of the neutralizing activity is not possessed. Of the 147 sequences obtained from human hyperimmune repertoire by inactivated virus or recombinant glycoprotein screening, e.g., de KruifJ, only 39 were active, 21 of which were constructed for ScFv expression, and 14 were more than 500IU/mg (de Kruif J, Bakker A B, Marissen W E, et al. A human monoclonal antibody conjugate as a novel component of rare and simple substances of nested and spots pro-phyla. J. Annu Rev Med,2007,58: 359. 368.), considering that the specific activity of the antibody scFv form is generally higher than that of the whole molecule form, the activity of 14 antibodies could reach 500IU/mg after only partial expression as a whole molecule antibody. SunL et al in another experiment, ELISA analysis was performed on 1000 clones using aG strain virus as antigen, 260 clones were positive, immunofluorescence analysis showed that 70 of them bound 293T cells expressing aG strain glycoprotein, sequence analysis showed that 11 of them were unique sequences, RFFTI analysis determined that 5 of them had neutralizing activity, and 3 of them had neutralizing activity against rabies virus in vitro of more than 500IU/mg (Sun L, Chen Z, Yu L, et al. Generation and chromatography of neutralizing activity against humanized antibodies and antibodies [ J ]. applied Microbiol technology, 2012,96(2): 357) 366.

Secondly, ELISA in the traditional screening format has three antigens available for selection, namely inactivated virions, glycoproteins expressed from prokaryotes and glycoproteins expressed from eukaryotes. Wherein the inactivated virus particles can obtain neutralizing antibodies against all neutralizing epitopes; however, since the glycoprotein with the neutralizing epitope only accounts for a small part of the glycoprotein, most of the screened antibodies do not aim at the neutralizing epitope; due to lack of glycosylation modification, the glycoprotein expressed by pronucleus influences the formation of space conformation, a neutralizing antibody aiming at conformational epitopes may not be obtained, and simultaneously, a large amount of antibodies aiming at non-neutralizing epitopes exist; the glycoprotein expressed by the eukaryon can be screened to be an antibody aiming at all neutralizing epitopes, but a large amount of antibodies combined with the non-neutralizing epitopes of the glycoprotein still exist, and the proportion of the neutralizing antibodies is still low; meanwhile, the eukaryotic expression and purification of rabies virus glycoprotein are difficult, and many laboratories do not have related technical capacity.

In addition, another difficulty faced by the conventional screening method is how to perform preliminary activity verification on the screened antibody, and since the proportion of sequences with neutralizing activity in the screened antibody is low, hundreds of sequences are usually required to be verified to obtain an antibody with high in vitro neutralizing activity. The verification is generally to adjust an ScFv sequence, express the ScFv sequence in escherichia coli, purify the ScFv sequence and analyze the neutralizing activity of the rabies virus in vitro. Since part of the protein is expressed in E.coli as inclusion bodies, which is difficult to renature, the general strategy is to discard the antibody sequence expressed in the form of inclusion bodies, which may result in the rejection of part of the highly neutralizing antibody in this step; meanwhile, due to the numerous sequences, the verification process needs to be performed by investing a large amount of resources and time.

Therefore, the traditional primary screening method of the phage antibody library has low screening efficiency and large investment, only a small amount of antibodies can enter next step of analysis in each step, and many positive clones are lost because scFv cannot be successfully expressed or precipitates are generated, and the neutralization activity of the finally obtained full-molecular antibody is difficult to ensure, so that a new method for efficiently screening the rabies virus resistant neutralizing antibody is urgently needed.

Disclosure of Invention

The invention aims to overcome the defects of the traditional ELISA screening method applied to the phage antibody library by relying on the research background, and develops a new method for screening and verifying the rabies virus resistant neutralizing antibody from the phage antibody library and an rabies virus resistant neutralizing antibody screening kit prepared by the method. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

in a first aspect of the invention, a method is provided for screening and validating anti-rabies virus neutralizing antibodies from phage antibody libraries.

The screening and verification method abandons the thought in the existing ELISA screening method, and directly carries out antibody screening and function verification by qualitative analysis and quantitative analysis by using an immunofluorescence focus method (RFFIT) on the level of phage antibody particles, thereby realizing high throughput of antibody screening and verification, and the main thought is as follows:

1) and (3) qualitative analysis: carrying out serial dilution on an anti-rabies virus ScFv phage antibody library, coating a plate, selecting a monoclonal antibody from the anti-rabies virus ScFv phage antibody library, culturing the monoclonal antibody in a 96-well plate, and preparing phage antibody particles of the corresponding monoclonal antibody; and (3) diluting phage antibody particles by 15 times, performing a fluorescence focus inhibition test (RFFIT), selecting clone sequencing capable of obviously inhibiting virus infection, eliminating repeated sequences, and primarily obtaining antibody sequences with different neutralization activities. 2) Quantitative analysis: selecting each clone with different sequences and neutralizing activity, preparing phage antibody particles again, and performing RFFIT analysis after purification; selecting a clone with the specific activity of phage antibody particles larger than 0.5IU/ml, amplifying antibody variable region genes, constructing eukaryotic transient expression plasmids, transiently transferring HEK293EBNA1 cells, and determining the specific activity of the antibody after the culture supernatant is subjected to Mabselect Sure affinity purification.

The specific screening steps are as follows:

A. culturing monoclonal phage antibody, and taking culture supernatant;

B. and (3) qualitative analysis: RFFIT method for primary screening of antibodies with neutralizing activity

Placing the culture supernatant in the step A into a 96-well plate, sequentially performing virus neutralization, BSR cell suspension culture and precooling acetone fixation on the culture supernatant through a DMEM culture medium, and after virus neutralization and BSR cell suspension culture and precooling acetone fixation, performing co-incubation with the diluted FITC-labeled anti-rabies virus nucleoprotein antibody, selecting clone sequencing capable of obviously inhibiting virus infection, eliminating repeated sequences, and primarily obtaining anti-rabies virus antibody sequences with different neutralization activities;

C. quantitative analysis: monoclonal phage antibody particle Activity assay

Selecting each clone with different sequences and neutralizing activity, preparing phage antibody particles again, purifying and diluting by a certain multiple, and then determining in vitro neutralizing activity by adopting an RFFIT method;

D. whole molecule antibody transient expression and activity analysis

Selecting a clone with the activity of phage antibody particles larger than 0.5IU/ml, amplifying antibody variable region genes, constructing eukaryotic transient expression plasmids, transiently transferring HEK293EBNA1 cells, and determining the specific activity of the anti-rabies virus antibody after the culture supernatant is subjected to Mabselect Sure affinity purification to obtain the anti-rabies virus neutralizing antibody.

Preferably, the monoclonal phage antibody culture in step a is performed, and the specific preparation method of the culture supernatant is as follows: adding the phage antibody subjected to three rounds of screening into E.coli TG1 bacterial liquid, uniformly mixing, and standing and infecting for 30-40 min at room temperature; coating the bacterial liquid on a 2YT-A plate, culturing overnight at 30 ℃, selecting and cloning to a 96-well plate containing 2YT-A, and culturing overnight; and then culturing the culture in a fresh 2YT-A culture medium at 220rpm and 37 ℃ for 1.5h, adding MK1307 helper phage, mixing uniformly, standing and infecting at room temperature for 30-40 min, centrifuging, then resuspending the cells in the 2YT-A/K culture medium, culturing overnight, and centrifuging to collect supernatant containing monoclonal phage antibody particles.

Preferably, in step B, the RFFIT method is used for primary screening of monoclonal phage antibody particles as follows:

putting the supernatant into a 96-well plate, adding 14-15 times of DMEM culture medium and 15-16 times of diluted virus for neutralization into each well, neutralizing for 1h at 37 ℃, and adding 1.0 multiplied by 10 with 15-16 times of volume⁶BSR cell suspension at one/mL, 5% CO₂Culturing at 37 ℃ for 24h, removing the supernatant, washing the cells with PBS, fixing with 80% precooled acetone with the volume of 60-70 times, removing the acetone, and standing at room temperature for 15 min;

diluting an FITC-labeled rabies virus nucleoprotein antibody by 200 times by using PBS (phosphate buffer solution), adding the diluted FITC-labeled rabies virus nucleoprotein antibody into each hole, incubating for 1h at 37 ℃, discarding liquid, washing by using PBS, observing and recording the infection proportion of each hole under a fluorescence microscope, and labeling the hole with obvious inhibition on virus growth as a positive hole;

and C, taking the bacterial liquid from the 96-well plate corresponding to the positive well, adding a 2YT-A culture medium, performing overnight culture at 37 ℃ and 220rpm, then sequencing, selecting a correct scFv sequence, selecting a clone with an unrepeated sequence, and entering the step C. The sequencing primer sequence of the phage antibody is shown as CGAAGGAGACAGTCATAATG (SEQ NO. 1).

Preferably, the specific steps of step C are as follows:

selecting each clone with different sequences and neutralizing activity, culturing the monoclonal phage antibody according to the step A, and taking culture supernatant; adding 20% PEG-8000+2.5mol/LNaCl solution of 1/5 volume into the obtained supernatant, mixing, standing in ice bath for 1h, centrifuging at 10000g for 20min to obtain precipitate as phage antibody particles,

diluting the obtained phage antibody particles by 15 times, respectively adding into 96-well cell culture plates, adding neutralizing virus with the same volume into each well, neutralizing at 37 deg.C for 1h, adding BSR cell suspension with 1.0 × 106/mL and 5% CO with the same volume₂Culturing at 37 deg.C for 24 hr, and removing supernatant; after PBS is used for cleaning cells, adding precooled 80% acetone with four times volume to be fixed for 10min at the temperature of 30 ℃, then removing the acetone, and standing for 15min at room temperature; diluting an FITC-labeled anti-rabies virus nucleoprotein antibody by 200 times by using PBS, adding the volume of the FITC-labeled anti-rabies virus nucleoprotein antibody into each hole by twice, incubating at 37 ℃ for 1h, discarding liquid, and washing by using PBS; the infection ratio of each well was observed and recorded under a fluorescence microscope and the antibody activity was calculated according to the formula in the rabies immunoglobulin titer assay.

Preferably, when calculating the antibody activity, if the number of infected cells in a 150-fold dilution well as the highest concentration well in a sample exceeds 50%, the sample is considered to have no significant neutralizing activity against rabies virus, and the result of the phage antibody activity is recorded as 0 IU/mL.

Preferably, in step D, the method for constructing eukaryotic transient expression plasmid is as follows: comparing antibody variable region sequences to determine antibody subtypes; constructing corresponding light chain expression plasmids by using corresponding kappa and lambda light chain vectors respectively, and constructing respective heavy chain expression plasmids by using the same heavy chain vector for all sequences; and (3) amplifying the variable regions of the light chain and the heavy chain of the antibody from the clone corresponding to the phage particles with the neutralizing activity by using transient expression primers shown in SEQ NO. 2-7, constructing a PCR product into a plasmid, selecting clone sequencing for identification, selecting the clone with the sequencing result conforming to the expectation, and extracting the plasmid.

Primer types	Cleavage site at 5' end of primer	Serial number
			Kappa light chain upstream	GGTCTCAGTGC+18～22	SEQNO.2
Downstream of kappa light chain	GGTCTCATTCG	SEQNO.3
			Lambda light chain upstream	GGTCTCAGGCC	SEQNO.4
Downstream of lambda light chain	GGTCTCAGACC	SEQNO.5
			Upstream of the heavy chain	GGTCTCAGTGT	SEQNO.6
Downstream of the heavy chain	GGTCTCACACT	SEQNO.7

In the screening method of the invention, phage antibody particles obtained by qualitative analysis (containing low-activity sequences in the qualitative analysis) are obviously related to the in vitro neutralizing activity of the whole molecular antibody; after the low-activity sequences are removed, the phage antibody particles with the activity higher than 0.5IU/ml and the in-vitro neutralizing activity of the whole molecular antibody thereof have no obvious correlation; all purified phage antibody particles with activity greater than 0.5IU/ml have in vitro neutralizing activity greater than 500 IU/ml.

The second aspect of the invention provides a kit for screening and verifying rabies virus neutralizing antibodies from a phage antibody library, which comprises a monoclonal phage antibody particle preparation system; the RFFIT method is used for measuring the in-vitro neutralizing activity system of the antibody; constructing an extraction system by using the transient expression plasmid; and whole molecule antibody transient expression and purification systems.

The invention has the following beneficial guarantee and effects:

the screening method of the anti-rabies virus neutralizing antibody does not need ScFv prokaryotic expression of the antibody, and the antibody with high in vitro anti-rabies virus neutralizing activity can be screened and obtained by using the phage, and the obtained antibody has very high in vitro anti-rabies virus activity at the level of the whole molecular antibody, thereby meeting the requirement of the anti-rabies virus monoclonal antibody on the antibody activity.

Compared with the traditional screening technology of the anti-rabies virus phage antibody library, the method for directly detecting the neutralizing activity of the anti-rabies virus is used for primary qualitative screening to replace an ELISA method, so that the efficiency of quickly obtaining a neutralizing antibody is greatly improved; meanwhile, in quantitative analysis, phage antibody particles are used for replacing scFv to perform in-vitro neutralization activity analysis of the antibody, the process of prokaryotic construction and expression is omitted, the phenomenon of antibody omission caused by protein expression problems is avoided, the analysis result of the method has greater correlation with the activity of the full-molecular antibody, and the activity of the sequence constructed into the full-molecular antibody can be predicted.

In addition, most of the positive clones obtained by the traditional method are non-neutralizing active antibodies, the activity analysis needs to be further carried out through prokaryotic expression, the operation of the subsequent steps is complicated, the time is long, and part of the antibodies are non-soluble expression, so that the comprehensive evaluation of the antibody sequence is influenced.

In conclusion, the screening method of the human anti-rabies virus phage antibody library established by the invention overcomes a plurality of problems in the traditional screening method, and has the advantages that: 1. the inactivated whole virus particles are further screened in a phage antibody library to obtain a neutralizing antibody, and the antigen is easy to prepare; 2. the RFFIT method is used for primary quantitative screening, non-neutralizing antibodies are eliminated, the obtained clones have neutralizing activity, the screening efficiency is greatly improved, and the later verification work is reduced; 3. the activity of the antibody at the phage level is positively correlated with the activity at the full molecular level, and the antibody with low neutralization activity can be excluded at an early stage. After the positive clones obtained by screening are expressed in a full molecular antibody form, the specific activity is more than 500IU/ml, and the requirement of the anti-rabies virus monoclonal antibody on the activity is met; 4. the screening process is simplified, and prokaryotic expression ScFv is not needed for activity verification, so that the screening process is simplified. 5. Avoids the problems of incapability of expression, non-soluble expression and the like in the expression of ScFv.

Drawings

FIG. 1 is a comparison of the process of screening neutralizing anti-rabies virus antibodies in the phage antibody library of the present invention and the conventional phage antibody library.

Detailed Description

The following examples and experimental examples further illustrate the present invention and should not be construed as limiting the present invention. The examples do not include detailed descriptions of conventional methods, such as those used to construct vectors and plasmids, methods of inserting genes encoding proteins into such vectors and plasmids, or methods of introducing plasmids into host cells. A Laboratory Manual, 2^ndedition，Cold spring Harbor Laboratory Press。

Materials and methods

1.1 cell, virus and phage antibody libraries

Baby hamster kidney cells (BSR) and a rabies virus standard challenge strain (CVS) are from the viral disease prevention and control institute of the Chinese disease prevention and control center; pGP5-con transient expression vector was purchased from Hangzhou Tianjian biological LLC; HEK-293EBNA1 was purchased from Beijing coordination cell resources center; the screened rabies virus phage library was provided by the fourth institute of Biotechnology, Lanzhou, using purified, inactivated CVS-11 as antigen, obtained after three rounds of screening.

1.2 Primary reagents and apparatus

The primer entrusts to be synthesized by Shanghai biological engineering Co., Ltd; vent DNA polymerase was purchased from NEB; restriction enzymes and T4 DNA ligase were purchased from Promega; plasmid extraction kit was purchased from Qiagen; polyetherimide (PEI) and horseradish peroxidase-labeled anti-rabbit anti-human Fc antibodies were purchased from Sigma company; the human anti-rabies virus immunoglobulin national standard is purchased from China food and drug testing research institute; fluorescein Isothiocyanate (FITC) labeled anti-rabies virus nucleoprotein antibody was purchased from the medical research center of beijing kangsaitai; DMEM, FreeStyle F17 and newborn bovine serum were purchased from Thermo; the helper phage M13K07 was supplied by the Lambda Biometrics institute, Inc.; the Mabselect SuRe affinity purification media were purchased from GE. Fluorescence microscopy was from olympus IX 71; capillary electrophoresis apparatus and PA 800plus SDS-MW analysis kit were purchased from Beckmann corporation; high performance liquid chromatography was purchased from waters; ImageQuant gel imaging systems were purchased from GE.

1.3 primer sequences

The phage sequencing primer sequence is CGA AGGAGACAGTCATAATG (SEQ NO. 1). The variable region primer of the transient expression antibody is determined according to a sequencing result, about 18-22 nucleotides are intercepted from the first base at the upstream or the last base at the downstream of a variable region sequence, the Tm value is enabled to be 58-62 ℃, and enzyme cutting sites are added at two ends of the primer according to the rule of Table 1.

TABLE 1 amplification of antibody variable region primers 5' terminal addition of base sequence

Primer types	Cleavage site at 5' end of primer	Serial number
			Kappa light chain upstream	GGTCTCAGTGC+18～22	SEQNO.2
Downstream of kappa light chain	GGTCTCATTCG	SEQNO.3
			Lambda light chain upstream	GGTCTCAGGCC	SEQNO.4
Downstream of lambda light chain	GGTCTCAGACC	SEQNO.5
			Upstream of the heavy chain	GGTCTCAGTGT	SEQNO.6
Downstream of the heavy chain	GGTCTCACACT	SEQNO.7

1.4 in vitro Activity assay against rabies Virus

1.4.1 neutralization was determined by dilution of the virus

Continuously diluting rabies virus CVS-11 to be detected with 10% calf serum-containing DMEM medium 3 times, and collecting 50 μ LThe diluted virus was added to 96-well plates in 2 wells per dilution as replicates, and 1.0X 10 was added⁶one/mL BSR cell suspension 50. mu.L, then each well was supplemented with 50. mu.L of medium, 5% CO₂Culturing at 37 deg.C for 24 hr, centrifuging, and removing supernatant; the cells were washed with PBS 1 time, fixed with 200. mu.L of pre-cooled 80% acetone for 10min, the acetone was discarded, and allowed to stand at room temperature for 15 min. After the FITC-labeled anti-rabies virus nucleoprotein antibody was diluted 200-fold with PBS, 100. mu.L of the FITC-labeled anti-rabies virus nucleoprotein antibody was added to each well, incubated at 37 ℃ for 1 hour, the liquid was discarded, and washed 3 times with PBS. And observing the infection ratio of the cells with different dilutions under a fluorescence microscope.

The virus dilution for neutralization is the virus dilution with 80% -95% of cells infected by virus.

1.4.2 determination of in vitro neutralizing Activity by RFFIT method

The sample to be tested and the national standard of rabies human immunoglobulin are diluted by 1:3 times from 10 times, and the total dilution is 8, and a culture medium is used as a negative control. Adding 50 μ L of each sample, standard and negative control to 96-well cell culture plate, adding 50 μ L of neutralizing virus to each well, neutralizing at 37 deg.C for 1 hr, adding 1.0 × 10⁶one/mL BSR cell suspension 50. mu.L, 5% CO₂And culturing at 37 ℃ for 24 h. Centrifuging to remove supernatant, washing cells with PBS for 1 time, adding 200 μ L pre-cooled 80% acetone, fixing at-30 deg.C for 10min, removing acetone, and standing at room temperature for 15 min.

After the FITC-labeled anti-rabies virus nucleoprotein antibody was diluted 200-fold with PBS, 100. mu.L of the FITC-labeled anti-rabies virus nucleoprotein antibody was added to each well, incubated at 37 ℃ for 1 hour, the liquid was discarded, and washed 3 times with PBS. The infection rate of each well was observed and recorded under a fluorescence microscope. The antibody activity was calculated according to the formula in the titer determination of rabies immunoglobulin in the pharmacopoeia of the people's republic of China (three parts) 2015 edition.

Second, screening and verification of neutralizing antibody against rabies virus

FIG. 1 shows the flow of the present invention and the conventional screening methods, which overlap the early phage antibody culture and the later antibody property verification, and the distinction is focused on the screening step of neutralizing antibody, and the present invention employs a completely different method.

2.1 qualitative analysis: RFFIT method for analyzing primary screening monoclonal phage antibody particles

2.1.1 monoclonal phage antibody culture

And (3) adding 100 mu L of phage subjected to three rounds of screening into 1ml of E.coli TG1 bacterial liquid (OD600 is 0.5-0.7), uniformly mixing, and standing at room temperature for infection for 30 min. The bacterial suspension was spread on 4 150mm 2YT-A plates overnight at 30 ℃. The clones were picked and cultured, and each clone was added to a 96-well plate containing 100. mu.L of 2YT-A and cultured overnight at 37 ℃ and 220 rpm. 10 μ L of the culture was added to 140 μ L of fresh 2YT-A medium, cultured at 220rpm at 37 ℃ for 1.5h, 15 μ L of MK1307 helper phage was added, mixed well, and left to infect at room temperature for 30 min. Centrifuging at 4 deg.C and 4000g for 10min, resuspending cells in 150 μ L2 YT-A/K culture medium, culturing overnight at 30 deg.C and 220 rpm; the supernatant was collected by centrifugation at 4000g for 20min at 4 ℃.

2.1.2 analysis of monoclonal phage antibody particles by RFFIT

Collecting 3.3 μ L culture supernatant, adding 46.7 μ L DMEM medium and diluted 50 μ L virus for neutralization, neutralizing at 37 deg.C for 1 hr, adding 1.0 × 10⁶one/mL BSR cell suspension 50. mu.L, 5% CO₂Incubated at 37 ℃ for 24 hours, centrifuged and the supernatant discarded. Washing cells with PBS for 1 time, adding 200 μ L pre-cooled 80% acetone, and fixing for 10 min; the acetone was discarded and allowed to stand at room temperature for 15 min.

After the FITC-labeled anti-rabies virus nucleoprotein antibody was diluted 200-fold with PBS, 100. mu.L of the FITC-labeled anti-rabies virus nucleoprotein antibody was added to each well, incubated at 37 ℃ for 1 hour, the liquid was discarded, and washed 3 times with PBS. The infection ratio of each well was observed and recorded under a fluorescence microscope, and wells with significant inhibition of virus growth were labeled as positive wells.

50. mu.L of the bacterial suspension was collected from the 96-well plate corresponding to the positive well, and 1ml of 2YT-A medium was added thereto, followed by overnight culture at 37 ℃ and 220 rpm. Adding 300 μ L of sterilized glycerol into 300 μ L of the bacterial liquid, and preserving at-70 deg.C; another 300. mu.L of the bacterial solution was sequenced. Determining whether the sequencing result is a correct scFv sequence by using Vbase2 online alignment; the correct sequences were aligned using DNASTAR 7.1 and clones with non-overlapping sequences were selected for further testing.

2.2 quantitative analysis: purification and Activity assay of monoclonal phage antibody particles

mu.L of the preserved bacterial suspension was added to 1.5mL of 2YT-A G medium, and phage antibody culture was performed at 2.1.1. Adding 1/5 volume 20% PEG-8000+2.5mol/L NaCl solution into the obtained supernatant, mixing, standing in ice bath for 1h, centrifuging at 10000g for 20min, and precipitating to obtain phage antibody particles. 1.0ml PBS-1% BSA heavy suspension precipitation, 12000rpm centrifugation for 5min, abandon the precipitation, -70 degrees C frozen storage.

The in vitro neutralizing activity of the obtained phage antibody particles was measured according to item 1.4.2 after 15-fold dilution. If the number of infected cells in the wells with the highest concentration of a certain sample exceeds 50%, the sample is considered to have no significant neutralizing activity against rabies virus, and the result of phage antibody activity is recorded as 0 IU/ml.

2.3 transient expression and Activity analysis of Whole-molecule antibodies

2.3.1 transient expression plasmid construction and extraction

Antibody subtypes were determined using alignment of antibody variable region sequences with vbase 2. Constructing corresponding light chain expression plasmids by using corresponding kappa and lambda light chain vectors in the table 1 respectively; all sequences the same heavy chain vector was used to construct the respective heavy chain expression plasmids. The variable regions of the antibody light and heavy chains were amplified from clones corresponding to phage particles with neutralizing activity using transient expression primers. BSAI is used for enzyme digestion of PCR products and plasmids, 2% agarose gel electrophoresis is used for identification, gel cutting and recovery are carried out, and the size of the light and heavy chain fragments of the antibody after enzyme digestion is about 350 bp. And (3) carrying out enzyme digestion on the recovered product and the light and heavy chain vectors of the antibody after enzyme digestion by BsaI enzyme according to the product specification, connecting T4 DNA ligase overnight according to the specification, adopting a 10-microliter connection system, containing 0.1 microliter of T4 DNA ligase and 1 microliter of buffer solution, transfecting escherichia coli Top10, coating an LB agar plate containing kanamycin, and selecting, sequencing and identifying. Clones with the expected sequencing result are selected, and plasmids are extracted by using a plasmid maxi Kit after amplification culture according to the instructions.

2.3.2 Whole-molecule antibodies transient expression, purification and Activity determination

HEK293EBNA1 cells were diluted to 1.0X 10 using medium⁶one/mL. Adding 0.4 μ g light chain plasmid and 0.2 μ g heavy chain plasmid into 100 μ L culture medium, mixing, and adding 2.37 mu g PEI, mixing, standing at room temperature for 15min, adding to 1ml diluted cells, 5% CO₂Culturing at 37 deg.C for 120h at 220 r/min; then 10000g are centrifuged for 10min, the supernatant is taken, and the expressed antibody is purified by using Mabselect Sure medium; after washing impurities with PBS solution, eluting with sodium acetate solution with pH 3.5 to obtain the purified rabies virus resistant whole-molecule monoclonal antibody. Purified antibodies were assayed for protein concentration using a GE navue microspectrophotometer.

After purification the antibody was subjected to 150-fold dilution in cell culture medium and the in vitro neutralizing activity was determined as in item 1.4.2. If the number of infected cells in the highest concentration well (150-fold dilution well) of a sample exceeds 50%, the sample is considered to have no significant anti-rabies virus neutralizing activity, and the in vitro anti-rabies virus neutralizing activity result is recorded as 0 IU/ml.

2.4 correlation analysis of phage antibody particle RFFIT results with in vitro neutralization Activity of transiently expressed Whole molecule antibodies

The correlation between the activity of the phage antibody and the activity of the transient expression full-molecule antibody is analyzed by using SPSS software, the analysis method is bivariate correlation analysis, and the single-side significance level alpha is 0.05; meanwhile, after eliminating the data with the activity of phage antibody particles being "0", the remaining samples were analyzed for correlation, the analysis method is bivariate correlation analysis, and the single-side significance level alpha is 0.05.

3 results

3.1 qualitative analysis- -Primary screening of monoclonal phage antibody particles RFFIT

About 564 clones are preliminarily screened, wherein 180 positive clones are screened, the sequencing result shows that all positive clones are correct antibody variable region sequences, the sequence alignment result shows that 35 different antibody variable region sequences are obtained, and the result is summarized as shown in table 2:

TABLE 2 Positive clone sequencing results

Verification of clone number	Number of positive clones	Correct number of scFv	Accuracy rate	Number of clones of different variable regions
					564	180	180	100％	35

3.2 quantitative analysis: preparation, purification and activity determination of monoclonal phage antibody particles

One clone was picked for each different variable region sequence to prepare phage antibody particles and their titers and in vitro anti-rabies virus activity were determined, and the results are shown in table 3.

TABLE 3 summary of phage antibody Activity

*: an activity of 0IU/ml represents that phage diluted 15 times showed no significant inhibition of the infected dose of rabies virus CVS-11 in the RFFIT assay for an equal volume of 80% cells.

3.3 full-molecular antibody transient expression and Activity assay

3.3.1 expression and purification of Whole-molecule antibodies

The variable region sequence of the antibody light and heavy chains is called from the clone of the positive result of the phage antibody particle RFFIT, eukaryotic homeotropic expression plasmids are constructed, and 35 pairs of plasmids are constructed in total.

3.3.2 determination of neutralizing Activity of Whole-molecule antibodies in vitro

The results of in vitro anti-rabies virus activity detection after purification of the whole molecule antibody are shown in table 4.

TABLE 4 specific Activity of Whole molecular anti-rabies Virus antibodies

*: activity 0IU/mg represents 150-fold dilution of the antibody in the RFFIT assay did not show significant inhibition of an equal volume of 80% cells by the infecting dose of rabies virus CVS-11.

3.4 correlation of phage antibody RFFIT results with in vitro neutralizing Activity of Whole molecule antibodies

Bivariate correlation analysis showed that both phage activity and specific activity of whole antibody were significantly correlated at the unilateral α -0.05 level, sig-0.339, p-0.025; the data with zero phage activity were rejected and then subjected to bivariate correlation analysis, which showed no significant correlation at a single α -0.05 level, sig-0.083, and p-0.361.

As can be seen from the above method and results, the method of this example screens about 564 clones, 180 of which are positive clones, to obtain 35 unique sequences, 22 of which have a neutralizing activity greater than 500IU/mg in the form of a whole molecule antibody, and the method has a significant advantage in neutralizing antibody screening.

The phage antibody particles obtained by qualitative analysis (containing low-activity sequences in the qualitative analysis) are obviously related to the in vitro neutralizing activity of the whole molecular antibody; after the low-activity sequences are removed, the phage antibody particles with the activity higher than 0.5IU/ml and the in-vitro neutralizing activity of the whole molecular antibody thereof have no obvious correlation; all purified phage antibody particles with activity greater than 0.5IU/ml have in vitro neutralizing activity greater than 500 IU/ml. Therefore, the method for screening and verifying the neutralizing antibody from the anti-rabies virus phage library, which is constructed by the invention, can obtain the anti-rabies virus antibody with neutralizing activity without performing prokaryotic expression and verification of the antibody on each sequence, thereby realizing high throughput.

In addition, the activity of the phage antibody particles and the activity of the whole molecule antibody are analyzed to determine that the phage antibody particles and the whole molecule antibody have a significant correlation. Analysis of samples positive for phage antibody activity showed that the activity of the antibody at the phage level was not correlated with its activity at the full molecular level, and therefore the method of the invention was only suitable for preliminary screening and preliminary activity validation of phage antibody libraries for the rejection of non-neutralizing antibodies and low neutralizing activity antibodies. The activity at phage level was marked as "-" for a total of 13 antibodies, of which 9 neutralizing activities were still not detected after construction as full molecule antibodies, and 3 had lower in vitro anti-rabies virus activity, 57, 12 and 18IU/ml respectively; 22 antibodies with activity of more than 0.5IU/ml at the phage level all show higher in vitro anti-rabies virus activity (>500IU/mg) after being constructed into a full-molecular antibody.

In conclusion, the invention describes a method for screening the rabies virus neutralizing antibody in a phage antibody library, the method does not need ScFv prokaryotic expression of the antibody, and the phage can be used for screening the antibody with high in vitro rabies virus neutralizing activity, and the obtained antibody has very high in vitro rabies virus resisting activity at the level of the whole molecular antibody, thereby meeting the requirement of the rabies virus resisting monoclonal antibody on the antibody activity.

According to the figure 1, compared with the traditional screening technology of the anti-rabies virus phage antibody library, the method uses a method capable of directly detecting the neutralizing activity of the anti-rabies virus in primary qualitative screening to replace an ELISA method, so that the efficiency of quickly obtaining a neutralizing antibody is greatly improved; meanwhile, in quantitative analysis, phage antibody particles are used for replacing scFv to perform in-vitro neutralization activity analysis of the antibody, the process of prokaryotic construction and expression is omitted, the phenomenon of antibody omission caused by protein expression problems is avoided, the analysis result of the method has greater correlation with the activity of the full-molecular antibody, and the activity of the sequence constructed into the full-molecular antibody can be predicted.

Sequence listing

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