CN114249820A

CN114249820A - Alpaca source nano antibody combined with SARS-CoV-2RBD

Info

Publication number: CN114249820A
Application number: CN202011037584.1A
Authority: CN
Inventors: 金腾川; 马欢; 曾威红
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2020-09-25
Filing date: 2020-09-25
Publication date: 2022-03-29
Anticipated expiration: 2040-09-25
Also published as: CN114249820B

Abstract

The present disclosure relates to alpaca-derived antibodies or antigen-binding fragments thereof that bind to SARS-CoV-2RBD, and in particular, to alpaca-derived nanobodies or antigen-binding fragments thereof that bind to the receptor-binding Region (RBD) of the novel coronavirus (SARS-CoV-2) with high affinity, which can be used for the prevention, treatment and/or diagnosis of SARS-CoV-2 infection.

Description

Alpaca source nano antibody combined with SARS-CoV-2RBD

Technical Field

The present invention belongs to the field of biotechnology, and is especially the nanometer antibody sequence for resisting SARS-CoV-2RBD for treatment and diagnosis.

Background

SARS-CoV-2 belongs to the coronavirus, and the pneumonia that it causes is called COVID-19. SARS-CoV-2 enters the cell after binding with angiotensin converting enzyme 2(ACE2) on the surface of epithelial cell via the receptor binding Region (RBD) of its surface spike protein (spike), completing the infection.

Fully human antibodies isolated from convalescent patients have been shown to have excellent antiviral effects, but these are classical monoclonal antibodies consisting of 2 heavy chains and 2 light chains. Has the limitations of large molecular weight, complex production process, difficult processing and reconstruction and the like.

In camelids there is an antibody naturally lacking the light chain, i.e. a heavy chain antibody, the variable region of which consists only of heavy chains, abbreviated VHH, and the variable region protein is less than 10nm in diameter and is therefore also referred to as nanobody. The nano antibody has the advantages of small molecular weight, strong penetrability, easy expression, easy gene modification, easy combination of a plurality of epitopes and the like.

No natural nano-antibody derived from alpaca that is resistant to SARS-CoV-2RBD is currently approved for the treatment of COVID 19.

Disclosure of Invention

The present disclosure provides alpaca heavy chain antibody variable region Sequences (VHHs), also known as nanobodies, that can bind with high affinity to the receptor binding Region (RBD) of the novel coronavirus (SARS-CoV-2), which can be used for the prevention, treatment and/or diagnosis of SARS-CoV-2 infection.

The inventor adopts SARS-CoV-2RBD protein expressed by in vitro recombination to immunize 2-head alpaca for 3 times, then separates out peripheral blood lymphocyte and extracts total RNA of the cell, and then reverse transcribes the total RNA into cDNA. Then using the cDNA as a template and using a specific primer to amplify a nano antibody sequence. We isolated 7 strains of nanobodies. Are respectively named as aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42 and aRBD-54, and the amino acid sequences are respectively as follows:

amino acid sequence of aRBD-2:

amino acid sequence of aRBD-3:

amino acid sequence of aRBD-5:

amino acid sequence of aRBD-7:

amino acid sequence of aRBD-41:

amino acid sequence of aRBD-42:

amino acid sequence of aRBD-54:

the 3 antigen complementarity determining regions (CDR1, CDR2 and CDR3) of the 7 nanobodies are shown in underlined section, specifically:

aRBD-2：

CDR1：GRTYTM(SEQ ID NO：1)

CDR2：EFVAAMRWSDTD(SEQ ID NO：2)

CDR3：AGEAWLARSTHHYDY(SEQ ID NO：3)

aRBD-3：

CDR1：GLTLDYYAI(SEQ ID NO：4)

CDR2：EGVSCISHPGGSTN(SEQ ID NO：5)

CDR3：ASPLALFRLCVLPSPLPYDY(SEQ ID NO：6)

aRBD-5：

CDR1：GFTLDYYAI(SEQ ID NO：7)

CDR2：EGVSCISGSGGITN(SEQ ID NO：8)

CDR3：PVSHTVVAGCAFEAWTDFGS(SEQ ID NO：9)

aRBD-7：

CDR1：ERTFSGGVM(SEQ ID NO：10)

CDR2：EFVAAIRWNGASTF(SEQ ID NO：11)

CDR3：RAVRTYASSDYYFQERTYDY(SEQ ID NO：12)

aRBD-41：

CDR1：GFTSGHYAI(SEQ ID NO：13)

CDR2：EGVSCIGSSDGSTY(SEQ ID NO：14)

CDR3：AGLWYGRSLNSFDYDY(SEQ ID NO：15)

aRBD-42：

CDR1：GRTFSSATM(SEQ ID NO：16)

CDR2：EFVAAISWSGLSRY(SEQ ID NO：17)

CDR3：DSWGCSGLGC(SEQ ID NO：18)

aRBD-54：

CDR1：GRTFGSFM(SEQ ID NO：19)

CDR2：DFVAAITWSGGSTY(SEQ ID NO：20)

CDR3：ARISSAYYTRSSSYAY(SEQ ID NO：21)。

then, the inventors found that the nano antibodies aRBD-2 and aRBD-5 bind to different epitopes, and the aRBD-2 and aRBD-7 bind to different epitopes, so that the corresponding two double epitope specific antibodies aRBD-2-5 and aRBD-2-7 are respectively constructed by combining the nano antibodies aRBD-2 and aRBD-5.

As used herein, a bi-epitope specific antibody refers to an antibody that is constructed to bind two epitopes on a SARS-CoV-2RBD by linking two nanobodies that are capable of binding two separate epitopes on the RBD with a flexible polypeptide chain.

Specifically, the invention provides the following technical schemes:

1. an alpaca-derived antibody or antigen-binding fragment thereof that binds to SARS-CoV-2RBD having a VHH with a composition selected from the group consisting of:

as shown in SEQ ID NO: 1 of the CDR1 shown in FIG. 1,

such as SEO ID NO:2 CDR2 and

as shown in SEQ ID NO:3, CDR 3;

as shown in SEQ ID NO:4 of the CDR1 shown in figure 4,

as shown in SEQ ID NO: CDR2 and shown in FIG. 5

As shown in SEQ ID NO:6 CDR 3;

as shown in SEQ ID NO: the CDR1 shown in figure 7 is,

as shown in SEQ ID NO: CDR2 and 8 shown in

As shown in SEQ ID NO: 9, CDR 3;

as shown in SEQ ID NO: 10 of the CDR1 shown in figure 10,

as shown in SEQ ID NO: 11 and CDR2 and

as shown in SEQ ID NO: CDR3 shown in fig. 12;

as shown in SEQ ID NO: 13 is shown in the figure 13 as a CDR1,

as shown in SEQ ID NO: CDR2 and CDR 14

As shown in SEQ ID NO: 15, CDR 3;

as shown in SEQ ID NO: 16 is shown in the figure as CDR1,

as shown in SEQ ID NO: 17 and CDR2 and

as shown in SEQ ID NO: 18 CDR3 shown in fig. 18; and/or

As shown in SEQ ID NO: 19 is shown in the figure as CDR1,

as shown in SEQ ID NO: 20 CDR2 and

as shown in SEQ ID NO: 21, CDR3 shown.

2. The antibody or antigen-binding fragment thereof of item 1, wherein the VHH comprises:

as shown in SEQ ID NO: 22, or a pharmaceutically acceptable salt thereof, wherein,

as shown in SEQ ID NO:23, or a pharmaceutically acceptable salt thereof

As shown in SEQ ID NO: 24.

As shown in SEQ ID NO: 25, or a pharmaceutically acceptable salt thereof, wherein,

as shown in SEQ ID NO: 26, or a pharmaceutically acceptable salt thereof, wherein,

as shown in SEQ ID NO: 27, and/or

As shown in SEQ ID NO: 28, or a pharmaceutically acceptable salt thereof.

3. The antibody or antigen-binding fragment thereof of

item

1 or 2, which is a bi-epitope-specific antibody comprising, in order (e.g., in N-terminal to C-terminal order), SEQ ID NO: 22 and SEQ ID NO: 24, or SEQ ID NO: 22 and SEQ ID NO: 25, preferably wherein SEQ ID NO: 22 and SEQ ID NO: 24 or SEQ ID NO: 22 and SEQ ID NO: 25 are connected by a linker (e.g., a flexible polypeptide chain, such as a GS linker).

4. The antibody or antigen binding fragment thereof of any one of items 1-3, further having an Fc domain, preferably an IgG1 Fc domain, more preferably a human IgG1 Fc domain, the sequence of the human IgG1 Fc domain being, for example, as set forth in SEQ ID NO:30, the nucleotide sequence of the gene encoding the sequence of the Fc domain of human IgG1 is shown as SEQ ID NO: shown at 31.

5. A polynucleotide encoding the antibody or antigen-binding fragment thereof of any one of items 1-4.

6. An expression vector, for example one based on one or more promoters and host cells, comprising the polynucleotide of item 5.

7. A host cell comprising the expression vector of item 6, said host cell being a host cell for the expression of a foreign protein, such as a bacterium, yeast, insect cell, mammalian cell.

8. A pharmaceutical composition comprising the antibody or antigen-binding fragment thereof of any one of claims 1-4 and a pharmaceutically acceptable carrier.

9. Use of the antibody or antigen-binding fragment thereof of any one of items 1-4 in the manufacture of a kit or medicament for the prevention, treatment and/or diagnosis of SARS-CoV-2 infection.

Advantages and positive effects of the disclosure

The nano antibody (VHH) is derived from a natural alpaca heavy chain antibody, so that the nano antibody has the characteristics of high stability, high expression level and high affinity.

The circular dichroism experiments show that the half-dissolving temperatures (Tm values) of the 7-strain nanometer antibodies are all above 70 ℃.

After the 7 strains of the nano-antibodies are fused with an Fc segment of human IgG1, the fusion proteins are cloned to a pTT5 vector, secretory expression is carried out by adopting mammalian cells 293F, and after 3 days of expression, the fusion proteins in the supernatant of a culture medium are purified by adopting a Protein A column, so that the yield of the 7 strains of the antibodies is over 90 mg/L.

The 7 antibodies can bind to SARS-CoV-2RBD with high affinity. The detection of ELISA experiments shows that the affinity of the Fc fusion protein of other antibodies of the disclosure for binding to the extracellular domain of SARS-CoV-2 spike protein (S1+ S2) is higher than that of ACE2 except aRBD-42. The Surface Plasmon Resonance (SPR) experiment shows that the affinity dissociation constants (K) of aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42 and aRBD-54 and SARS-CoV-2RBD_D) Values were 2.60, 3.33, 16.3, 3.31, 21.9, 113 and 5.49nM (nanomoles per liter), respectively.

Besides aRBD-42, the other 6 strains of the nano-antibodies disclosed by the invention can well inhibit the combination of human ACE2 and SARS-CoV-2RBD after being fused with human IgG1 Fc. Competitive ELISA experiments showed that the Fc fusion proteins of aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41 and aRBD-54 all competed with 10nM ACE2-Fc for SARS-CoV-2RBD, IC₅₀2.68, 2.59, 1.89, 1.42, 5.76 and 2.07nM, respectively.

The nano antibodies aRBD-2 and aRBD-5 of the disclosure are combined with different epitopes, and aRBD-2 and aRBD-7 are combined with different epitopes, so that two double epitope specific antibodies aRBD-2-5 and aRBD-2-7 are constructed, SPR shows that the affinity of the antibodies with SARS-CoV-2RBD is greatly enhanced, and K is greatly improved_DValues were 59.2pM (picomoles per liter) and 0.25nM, respectively.

The Fc fusion proteins of the nano antibodies aRBD-2, aRBD-5 and aRBD-7 disclosed by the invention can neutralize SARS-CoV-2 infected Vero E6 cells in vitro. Fc fusion proteins of aRBD-2, aRBD-5 and aRBD-7 neutralized 200 PFU SARS-CoV-2 infection Vero E6 concentration ND in 100. mu.L system₅₀0.092, 0.413 and 0.591. mu.g/mL, respectively. Double epitope specific antibody aRFc fusion protein of BD-2-5 and aRBD-2-7 neutralized 200 PFU SARS-CoV-2 infection Vero E6 concentration ND in 100. mu.L system₅₀0.0104 and 0.0067. mu.g/mL, respectively.

Drawings

FIG. 1 results of phage display screening of 7 nanobodies of the present disclosure. (A) The phase counting results of two rounds of panning; (B) is the result of monoclonal phage ELISA.

FIG. 2 shows the SDS-PAGE gel electrophoresis results of the Nanobody Fc fusion protein (A) and the Nanobody (B). Lane M is marker, lanes 1 to 7 are aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42 and aRBD-54 fusion proteins (A) and their respective Fc-cleaved nanobody proteins (B).

Figure 3 is a graph of results of Circular Dichroism (CD) experiments testing denaturation temperatures of 7 nanobodies of the present disclosure. (A) - (G) are the results of detection of aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42 and aRBD-54 in this order.

FIG. 4 is a graph showing the results of detecting the binding between the Fc fusion protein of the nanobody and the extracellular domain protein of SARS-CoV-2 spike protein (S1+ S2) by ELISA.

FIG. 5 shows the detection of the affinity between the nanobody and SARS-CoV-2RBD by SPR. (A) And (I) sequentially detecting the dynamic curve of the combination between the nano antibodies aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42, aRBD-54, aRBD-2-5 and aRBD-2-7 and SARS-CoV-2RBD protein by using an SPR method. Where the solid line is the kinetic curve monitored in real time and the dashed line is the curve fitted using biacore evaluation software. The kinetic curves for the different antibody concentration gradients correspond in order from top to bottom to the top to bottom concentrations indicated on the right.

FIG. 6 is a graph showing the results of detecting that the Fc fusion protein of the nanobody blocks the binding of ACE2 and SARS-CoV-2RBD by competitive ELISA.

Figure 7 in vitro virus neutralization experiments demonstrate the function of the antibodies of the disclosure. And (3) analyzing the experimental data of the Fc fusion proteins of the nano antibodies aRBD-2, aRBD-5 and aRBD-7, the double epitope specific antibodies aRBD-2-5 and aRBD-2-7 and the Fc fusion protein thereof in vitro and the experiment data of SARS-CoV-2 virus infected Vero E6 cells.

Detailed Description

In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

EXAMPLE 1 immunization of alpaca with SARS-CoV-2RBD and screening of Nanobodies

1) A total of 2 first 6 month-sized llamas were immunized by mixing purified SARS-CoV-2RBD (QKV42562.1, aa 321-591) expressed in HEK293F cells (ATCC, CBP60437) with Freund's adjuvant and injecting the immunized llama three times subcutaneously at a dose of 500. mu.g/time, each time with 2 weeks intervals.

2) After 2 weeks of the third immunization, blood was taken intravenously and leukocytes in the blood were isolated. Total RNA was extracted using an RNA extraction kit from omegabiotek, and genomic DNA was removed using DNase. PrimeScript by TAKARA^TMII 1st Strand cDNA Synthesis Kit reverse transcription of RNA, reverse transcription of RNA into cDNA.

3) Preparing a nano antibody phagemid library: and (2) amplifying by using the cDNA as a template to obtain a VHH coding gene fragment by using an alpaca VHH specific primer designed by us, cloning the amplified VHH sequence into NcoI and NotI sites of phagemid pR2 by using a Gibson assembly method, and obtaining a Gibson assembly product which is an initial nano antibody phagemid library.

4) Electrotransformation TG1 amplified the nanobody phagemid library: escherichia coli TG1 competent cells were prepared by 10% glycerol washing, and the above Gibson assembly product was then electro-transformed into TG1 competent cells, spread on 5 150mm LB (LB/2% G/Amp) plates containing 2% glucose and 100. mu.g/mL ampicillin to amplify the phagemid library.

5) Amplification of Nanobody phage library: taking a proper amount of bacterial liquid after scraping, inoculating 200mL of 2TY (containing 2% glucose and 100 mu g/mL ampicillin) to culture until logarithmic phase, adding 10¹²pfu of KM13 helper phage (purchased from MRC Laboratory of Molecular Biology), infected at 37 ℃ for 45min, 100mL of the inoculum was centrifuged, the cells were resuspended in 200mL of 2TY (containing 0.1% glucose, 100. mu.g/mL and 50. mu.g/mL kanamycin), and incubated at 25 ℃ for 20h to amplify the displayPhase of nanobody. The phase was concentrated by PEG precipitation and finally resuspended in PBS and stored on ice.

6) Panning (Panning)

A. A first round: the SARS-CoV-2RBD expressed and purified in example 1 was diluted to 0.1mg/mL with PBS, 100. mu.L of the diluted solution was added to one well of a 96-well immunoplate (Nunc maxsorp plate), and the plate was coated overnight at 4 ℃ while one well of a no-antigen control was set. Wash 3 times with PBS and add 300 μ L MPBS (5% skim milk in PBS) per well and block for 2h at room temperature. Wash 3 times with PBS and add 1 x 10 per well¹¹pfu phage library phase (dissolved in 100. mu.L MPBS) was prepared above and incubated at 80rpm for 1h at room temperature. Washed 30 times with PBST (0.1% Tween 20). After adding 100. mu.L of trypsin with a concentration of 0.5mg/mL to each well, the bound phase was eluted after 1h of digestion at room temperature. 10 μ L of eluted phase was used to infect 1mL of log phase TG1 bacteria in a 37 ℃ water bath for 45 min. 100. mu.L, 10. mu.L and 1. mu.L of LB-coated/2% G/Amp plates were counted, respectively. The remaining phase solution was totally infected with 3mL of log phase TG1 bacteria, water-bathed at 37 ℃ for 45min, coated on 1 piece of 150mm LB/2% G/Amp plate, and cultured overnight at 37 ℃.

B. And a second round: adding the mixture into a plate with the diameter of between 4 and 2TY and above 150mm, scraping the bacterial colony, uniformly mixing the bacterial liquid, inoculating the mixture into a culture medium with the diameter of between 100 and 100mL of 2TY/2 percent G/Amp, culturing the mixture until the logarithmic growth phase is completed, and adding KM13 to infect the mixture to prepare the nano antibody displayed phase. SARS-CoV-2RBD was then diluted to 0.02mg/mL with PBS, 100. mu.L was added to one well of a 96-well immunoplate, coated overnight at 4 ℃ while a well no antigen control was set. Wash 3 times with PBS and add 300 μ L MPBS (5% skim milk in PBS) per well and block for 2h at room temperature. Wash 3 times with PBS and add 1 x 10 per well⁸pfu first round of amplified phase (dissolved in 100. mu.L MPBS) and incubated at 80rpm for 1h at room temperature. Washed 30 times with PBST (0.2% Tween 20). After adding 100. mu.L of trypsin with a concentration of 0.5mg/mL to each well, the bound phase was eluted after 1h of digestion at room temperature. 10 μ L of eluted phase was used to infect 1mL of log phase TG1 bacteria in a 37 ℃ water bath for 45 min. 100. mu.L, 10. mu.L and 1. mu.L of LB-coated/2% G/Amp plates were counted, respectively.

C. The phase counts of two rounds of panning elution are shown in FIG. 1A. Compared with the control wells, the RBD-coated wells eluted a significantly greater number of phases, the number of phases eluted in the first round of RBD-coated wells was more than 70 times that of the control wells, and the ratio was higher in the second round. Indicating that the phage specific for RBD were successfully isolated and enriched.

7) Phage ELISA screening of monoclonal antibody against SARS-CoV-2 RBD.

A. Preparation of monoclonal phase: 31 single clones were picked from the plates counted after the 2 rounds of selection elution above and inoculated into 96-well cell culture plates containing 100. mu.L of 2TY medium (containing 2% glucose and 100. mu.g/mL ampicillin) per well, and 1 clone was cultured in 1 well at 37 ℃ for 12 hours with shaking at 250 rpm. Transfer 5. mu.L of the above inoculum to a new 96-well plate containing 200. mu.l of 2TY medium (containing 2% glucose and 100. mu.g/mL Ampicillin) per well for culturing (15% glycerol final concentration was added to the remaining inoculum; storage at-80 ℃), shake culture at 37 ℃ and 250rpm for 1.5h to an OD600 of about 0.5, and aspirate 100. mu.L of inoculum per well. Adding 50 μ L of the solution containing 4X 10⁸pfu KM13 phage 2TY, mixed well and incubated at 37 ℃ for 45 min. 3500g were centrifuged for 10min, the supernatant was discarded, and the pellet was resuspended in 200. mu.L of 2TY containing 0.1% glucose, 100. mu.g/mL ampicilin and 50. mu.g/mL Kanamycin and shake-cultured at 25 ℃ and 250rpm for 20 h. 3500g centrifugation is carried out for 10min, 75 mu L of supernatant is taken and transferred to the hole of a 96-hole plate containing 225 mu L MPBS per hole, and the mixture is evenly mixed and temporarily stored at 4 ℃ for standby, so that the preparation of the monoclonal phage is completed.

B, phage phase ELISA detection: diluting SARS-CoV-2RBD protein to 1 μ g/mL with PBS, coating 96-well immunoplates with 100 μ L/well, setting blank control (PBS well, coating overnight at 4 deg.C, washing with PBS 3 times, adding 300 μ L MPBS into each well, sealing at room temperature for 2h, adding 100 μ L of the above prepared mixture to each well, incubating at room temperature for 1h, washing plate with PBST for 4 times, diluting HRP-anti M13 antibody (Yiqian Shenzhou) with MPBS, adding 100 μ L to each well of the above immunoplates, incubating at room temperature for 1h, washing plate with PBST for 4 times, adding 100 μ L of TMB chromogenic substrate (Biyunyan day) into each well, covering with aluminum foil paper to prevent light, reacting at room temperature for 5min, adding 50 μ L of 1M H μ L into each well, and coating 96 μ L of immunoplates with PBS, and adding₂SO₄The reaction was terminated and OD was measured_450nmThe value is obtained. The results are shown in FIG. 1B.

C. All OD will be_450nmPositive clones with a value greater than 1 were sent to the company for sequencing, and the results of the sequencing were analyzed and aligned to finally determine 7 positive single clones, which were named as aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42 and aRBD-54, respectively, as described above.

Example 2 expression and purification of the resulting Nanobodies and Fc fusion proteins thereof

1) Designing a primer, fusing an IFN alpha protein signal peptide at the N end of a gene sequence of the nano antibody to guide secretion expression, fusing a human IgG1 Fc at the C end of the gene sequence of the nano antibody, introducing a TEV enzyme cutting site between the C end and the human IgG1 Fc, and then cloning into a mammalian expression vector pTT 5. The construction carrier is transiently transfected into mammalian cells HEK293F by PEI, supernatant is collected after 3 days of culture, fusion Protein in the supernatant is purified by a Protein A column and is subjected to SDS-PAGE electrophoresis, and as a result, as shown in FIG. 2A, high-purity nano antibody Fc fusion Protein is obtained from the supernatant.

2) And (2) carrying out enzyme digestion on the fusion Protein by using TEV, then enabling enzyme digestion products to respectively flow through a Protein G column and a nickel column, so as to respectively remove proteins, Fc and TEV which are not completely digested by enzyme, collecting flow-through, concentrating and carrying out SDS-PAGE electrophoresis, wherein the result is shown in figure 2B, and the high-purity nano antibody Protein is obtained from the flow-through.

Example 3 characterization of the Nanobodies

1) The stability of the nanobody was characterized by Circular Dichroism (CD): the nano antibody solutions of the examples were replaced with PBS and diluted to QD_280nmAbout 0.6, and detecting with circular dichroism chromatograph at wavelength of 280-180 nm and temperature of 20-95 deg.C. Each test was repeated twice. And processing data by Prism software, selecting the change condition of the spectral value at 205nm along with the temperature, and further fitting to obtain the Tm value. As shown in FIG. 3, the Tm values of aRBD-2-Fc, aRBD-3-Fc, aRBD-5-Fc, aRBD-7-Fc, aRBD-41-Fc, aRBD-42-Fc and aRBD-54-Fc were 72.33, 75.44, 73.37, 78.98, 71.26, 98.23 and 71.07 ℃.

2) Preliminarily characterizing the binding condition of the nano-antibody Fc fusion protein and SARS-CoV-2 spike protein (S1+ S2) extracellular domain by adopting non-competitive ELISA: will be provided withSARS-CoV-2SARS-CoV-2 spike Protein (S1+ S2) extracellular segment (Val 16-Pro 1213, Beijing Yiqianshengzhou) was diluted to 2. mu.g/mL with PBS, 100. mu.L of each well was added for coating, after conventional washing and blocking, a 1: 2.5 gradient diluted solution of Nanobody Fc fusion Protein and ACE2-Fc Protein (after fusing aa 19-615 segment of human ACE2 to human IgG1 Fc, HEK293F cells were used for secretory expression, followed by Protein A purification) was added in sequence, and incubated at room temperature for 1 hour. After washing, bound VHH-Fc and ACE2-Fc were detected by adding HRP-conjugated anti-IgG 1 Fc antibody (Beijing Okawa), and the results are shown in FIG. 4, except aRBD-42-Fc, other 6 nanobody Fc fusion proteins, i.e., aRBD-2-Fc, aRBD-3-Fc, aRBD-5-Fc, aRBD-7-Fc, aRBD-41-Fc and aRBD-54-Fc, all had higher affinities than ACE2-Fc, and their EC were₅₀0.256, 0.098, 0.077, 0.105, 0.226, 0.164nM, respectively.

3) The affinity between the nanobody and SARS-CoV-2RBD was characterized by SPR: RBD protein is dissolved in sodium acetate with pH 4.5, coupled to a channel of CM5 chip, and a control channel without coupled protein is set and blocked by ethanolamine. The 7 nanobodies were diluted 1: 1 with PBS for 5 gradients, and then flowed through the above 2 channels at 30. mu.L/min, respectively, while detecting signal values (RU). After one cycle was completed, the bound antibody was aspirated off with 50mM NaOH to regenerate the chip. All operations were done on the Biacore T200 system. Results are shown in FIG. 5, and the results were analyzed by Biacore evaluation program, and the binding affinities K of aRBD-2, aRBD-3, aRBD-5, aRBD-7, aRBD-41, aRBD-42 and aRBD-54_DValues were 2.60, 3.33, 16.3, 3.31, 21.9, 113 and 5.49nM, respectively. Meanwhile, according to competition experiments among antibodies, 2 double epitope specific antibodies aRBD-2-5 (aRBD-2 and aRBD-5 are connected end to end by a GS joint with a sequence shown as SEQ ID NO: 29 (GGGGSGGGGSGGGGS)) and aRBD-2-7 (aRBD-2 and aRBD-7 are connected end to end by a GS joint with a sequence shown as SEQ ID NO: 29 (GGGGSGGGGSGGS) are designed, compared with a monomer, the affinity of the double epitope specific antibodies is greatly improved, and the affinity K of the aRBD-2-5 and the aRBD-2-7 is greatly improved_DValues were 59.2pM and 0.25nM, respectively.

Example 4 characterization of the Nanobodies inhibits the binding function of ACE2 and RBD

And (3) adopting a competitive ELISA method to characterize the blocking function of the nano antibody obtained by screening. SARS-CoV-2RBD was diluted to 1. mu.g/mL with PBS and 100. mu.L of each well was added for coating, washed routinely and blocked. Biotinylated ACE2-Fc was diluted to 10nM, and the Nanobody Fc fusion protein was then diluted in 1: 3 gradient with the ACE2-Fc solution, 100. mu.L of each gradient mixture was added to antigen-coated wells separately and incubated at room temperature for 1 hour. After 4 times of PBST washing, bound biotinylated ACE2-Fc was detected by adding HRP-conjugated Streptavidin (Byunnan), and the results are shown in FIG. 6, except aRBD-42, other 6 selected Nanobody Fc fusion proteins aRBD-2-Fc, aRBD-3-Fc, aRBD-5-Fc, aRBD-7-Fc, aRBD-41-Fc and aRBD-54-Fc all have the function of inhibiting the binding of ACE2-Fc and SARS-CoV-2RBD, and the IC of 10nM ACE2-Fc and SARS-CoV-2RBD₅₀2.68, 2.59, 1.89, 1.42, 5.76 and 2.07nM, respectively.

EXAMPLE 5 characterization of the Nanobodies in vitro neutralization SARS-CoV-2 invasive cell assay

1) Vero E6 cells (ATCC CBP60972) were seeded in 96-well plates in DMEM + 10% FBS at 37 ℃ in 5% CO₂Incubate overnight. The Fc fusion protein of the Nanobody aRBD-2 is diluted from 10. mu.g/mL to 0.041. mu.g/mL according to a gradient of 1: 3, the Fc fusion proteins of aRBD-5 and aRBD-7 are diluted from 30. mu.g/mL to 0.123. mu.g/mL according to a gradient of 1: 3, the dual epitope-specific antibodies aRBD-2-5 and aRBD-2-7 and the Fc fusion protein thereof are diluted from 1. mu.g/mL to 0.0041. mu.g/mL according to a gradient of 1: 3, the dilutions are DMEM + 1% FBS, and then 50. mu.L of each is added to a 96-well plate. SARS-CoV-2(USA-WA1/2020 isolate) WAs diluted to 4000 PFU/mL in DMEM + 1% FBS, and then 50. mu.L of SARS-CoV-2 dilution WAs added to wells containing antibody in gradient dilution, while no antibody control WAs set, mixed well and incubated at 37 ℃ for half an hour. The culture medium of Vero E6 cells was aspirated, and 100. mu.L of the above antibody and virus incubations were transferred to wells inoculated with Vero E6 cells, respectively, at 37 ℃ with 5% CO₂Incubate for 1 h. Incubations were aspirated, washed 2 times with PBS, 100. mu.L DMEM (10% FBS + 0.5% methylcellulose) was added to each well,culturing at 37 deg.C under 5% CO2 for 48 h. Each antibody concentration contained 2 replicate wells.

2) The medium supernatant was aspirated off, washed 2 times with PBS, 50. mu.L of 4% paraformaldehyde-containing PBS was added to each well, fixed for 15 minutes, and washed twice with PBS. The samples were incubated with PBS containing 0.1% Triton X-100 for 10 minutes, the cell membranes were perforated and washed 3 times with PBS. DMEM with 10% FBS was added to block non-specific binding sites and left at room temperature for 30 min. PBS was washed 2 times, diluted anti-SARS-CoV-2N protein antibody (GeneTex, GTX635679) was added to a suitable concentration, 50. mu.L was added to each well, and incubated at room temperature for 1 hour. PBST 3 times washing. Diluted Alexa Fluor 488-conjugated secondary antibody (Thermo) was added to the appropriate concentration, 50. mu.L was added per well, and incubated at room temperature for 1 hour. Nuclei were stained with Hoechst 33342. Fluorescence images of the entire well were obtained using a 4-fold objective lens in the cell imager rotation 5(BioTek), and the total number of cells (as indicated by nuclear staining) and the total number of infected cells (as indicated by N protein staining) were quantified using the cell analysis module of Gen5 software (BioTek) to calculate the percentage of infected cells. Neutralization rate is 100 × (1-percentage of infected cells in antibody wells/percentage of infected cells in antibody-free wells). The data were analyzed using Prism software and, as shown in FIG. 7, fitting showed that aRBD-2-Fc, aRBD-5-Fc, aRBD-7-Fc, aRBD-2-5-Fc and aRBD-2-7-Fc neutralized ND-CoV-2 infecting VeroE6 cells₅₀(half-neutralizing dose concentrations) were 0.092, 0.413, 0.591, 0.0104 and 0.0067. mu.g/mL, respectively, versus ND for aRBD-2-5 and aRBD-2-7₅₀Then less than 0.004. mu.g/mL can be seen, and the virus neutralization capacity of the double epitope specific antibody is obviously better than that of a single nano antibody. .

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An alpaca-derived antibody or antigen-binding fragment thereof that binds to SARS-CoV-2RBD, having a VHH with

CDR1 shown in SEQ ID NO. 4,

CDR2 as shown in SEQ ID NO. 5, and

CDR3 shown in SEQ ID NO. 6.

2. The antibody or antigen-binding fragment thereof of claim 1, wherein the VHH comprises: the amino acid sequence shown as SEQ ID NO. 23.

3. The antibody or antigen binding fragment thereof of claim 1 or 2, further having an Fc domain, preferably an IgG1 Fc domain, more preferably a human IgG1 Fc domain, the amino acid sequence of said human IgG1 Fc domain being for example as set forth in SEQ ID No. 30.

4. A polynucleotide encoding the antibody or antigen-binding fragment thereof of any one of claims 1-3.

5. An expression vector comprising the polynucleotide of claim 4.

6. A host cell comprising the expression vector of claim 5, said host cell being a host cell for the expression of a foreign protein, such as a bacterium, yeast, insect cell, mammalian cell.

7. A pharmaceutical composition comprising the antibody or antigen-binding fragment thereof of any one of claims 1-3 and a pharmaceutically acceptable carrier.

8. Use of the antibody or antigen-binding fragment thereof of any one of claims 1-3 in the manufacture of a kit or medicament for the prevention, treatment and/or diagnosis of SARS-CoV-2 infection.