Patent Application
20230279079
The present invention relates to novel monoclonal antibodies (MAbs) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and/or antigen-binding fragments thereof, especially to novel MAbs binding to the spike (S) protein or the nucleocapsid (N) protein of SARS-COV-2. The present invention also provides a pharmaceutical composition comprising the novel MAbs or antigen-binding fragments thereof. In addition, the present invention provides a kit and method for detecting SARS-CoV-2 and a method for preventing or treating SARS-CoV-2 or a disease mediated by a disease mediated by ACE2, using the novel MAbs or antigen-binding fragments thereof as described herein.
In the end of 2019, a novel coronavirus emerged and was identified as a cause of a cluster of respiratory infection cases. It spread quickly throughout the world. It spread quickly throughout the China and the world. In March of 2020, it has been declared a pandemic by the World Health Organization, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for the coronavirus disease of 2019 (COVID-19). As of 6 May 2021, there have been 154,815,600 total confirmed cases of SARS-CoV-2 infection including 3,236,104 deaths in the ongoing pandemic (World Health Organization).
Although several SARS-CoV-2 vaccines are available, the average worldwide vaccination rate is still low. Besides that, some of the SARS-CoV-2 vaccines currently available require extremely low temperature for storage, while some of the other available vaccines raise concerns about safety and/or low efficacy. As a result, the emergence of the novel coronaviruses in human population remains a continuing threat. In addition, antiviral drugs for SARS-CoV-2 are unavailable in the present (Rome 2020). Conservative treatment is still considered the mainstay of treatment for the SARS-CoV-2 infection in humans. Previous reports indicated that passive immunotherapy with convalescent plasma, serum, or hyperimmune immunoglobulin containing virus-specific polyclonal antibodies may be alternative therapeutic approach toward reduction of mortality of severe respiratory viral infections (Mair-Jenkins 2015). It is also realized for the need of monoclonal antibody (MAb) preparations for the treatment or prophylaxis of viral infectious disease, since polyclonal immunoglobulins may have limited potency and disease scope (Casadevall 2004).
The present invention provides a panel of SARS-CoV-2 spike and nucleocapsid-reactive human monoclonal antibodies, which has been produced from peripheral B cells derived from adult patients with laboratory-confirmed SARS-CoV-2 infection. The antigenic specificity of MAbs and the genetic usage in their variable domains of heavy and light chains were characterized in detail. These SARS-CoV-2-antigen-specific human MAbs offer templates for the development of diagnostic reagents and candidate prophylactic and therapeutic agents against SARS-CoV-2.
Thus, in one aspect, the present invention provides an isolated antibody against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) or antigen-binding fragment thereof, comprising
In some embodiments, the heavy chain variable region (VH) comprises an amino acid sequence about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 67, SEQ ID NO: 273, SEQ ID NO: 275, SEQ ID NO: 277, SEQ ID NO: 279, SEQ ID NO: 281, SEQ ID NO: 283, SEQ ID NO: 285, SEQ ID NO: 287, SEQ ID NO: 289, SEQ ID NO: 291, SEQ ID NO: 293, SEQ ID NO: 295, SEQ ID NO: 297, SEQ ID NO: 299, SEQ ID NO: 301, SEQ ID NO: 303, SEQ ID NO: 305, SEQ ID NO: 307, SEQ ID NO: 309, SEQ ID NO: 311, SEQ ID NO: 313, SEQ ID NO: 315, SEQ ID NO: 317, SEQ ID NO: 319, SEQ ID NO: 321, SEQ ID NO: 323, SEQ ID NO: 325, SEQ ID NO: 327, SEQ ID NO: 329, or SEQ ID NO: 331.
In some embodiments, the light chain variable region (VL) comprises an amino acid sequence about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO: 22, SEQ ID NO: 24, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 274, SEQ ID NO: 276, SEQ ID NO: 278, SEQ ID NO: 280, SEQ ID NO: 282, SEQ ID NO: 284, SEQ ID NO: 286, SEQ ID NO: 288, SEQ ID NO: 290, SEQ ID NO: 292, SEQ ID NO: 294, SEQ ID NO: 296, SEQ ID NO: 298, SEQ ID NO: 300, SEQ ID NO: 302, SEQ ID NO: 304, SEQ ID NO: 306, SEQ ID NO: 308, SEQ ID NO: 310, SEQ ID NO: 312, SEQ ID NO: 314, SEQ ID NO: 316, SEQ ID NO: 318, SEQ ID NO: 320, SEQ ID NO: 322, SEQ ID NO: 324, SEQ ID NO: 326, SEQ ID NO: 328, SEQ ID NO: 330, or SEQ ID NO: 332.
In another aspect, the present invention provides a pharmaceutical composition, comprising at least one of the isolated antibodies, or antigen-binding fragments thereof, of the present invention.
In some embodiments, the pharmaceutical composition further comprises at least one pharmaceutically acceptable carrier.
In another aspect, the present invention provides a kit for detecting the presence of SARS-CoV-2 in a sample, comprising at least one of the isolated antibodies, or antigen-binding fragments thereof, of the present invention.
In some embodiments, the at least one of the isolated antibodies, or antigen-binding fragments thereof, of the present invention comprises a detectable label.
In some embodiments, the detectable label is selected from an enzymatic label, a fluorescent label, a metal label, and a radio label.
In some embodiments, the detectable label is selected from gold nanoparticles, colored latex beads, magnetic particles, carbon nanoparticles, and selenium nanoparticles.
In some embodiments, the kit is an immunoassay kit.
In some embodiments, the immunoassay kit is selected from ELISA (enzyme-linked immunosorbent assay), RIA (radioimmunoassay), FIA (fluorescence immunoassay), LIA (luminescence immunoassay), and ILMA (immunoluminometric assay).
In some embodiments, the immunoassay is a sandwich assay.
In some embodiments, the immunoassay is in a lateral flow assay format.
In yet another aspect, the present invention provides a method for detecting SARS-CoV-2 in a sample suspected of containing said SARS-CoV-2, comprising contacting the sample with at least one of the isolated antibodies, or antigen-binding fragments thereof, of the present invention, and assaying binding of the antibody with the sample.
In some embodiments, the sample is urine, stool, or taken from respiratory tract.
In some embodiments, the sample taken from the respiratory tract is a nasopharyngeal (NP) or nasal (NS) swab.
In some embodiments, the SARS-COV-2 is detected by a sandwich immunoassay or lateral flow assay.
In a further aspect, the present invention provides a method for preventing or treating a disease mediated by angiotensin-converting enzyme 2 (ACE2) in a subject, comprising a step of administering an effective amount of at least one of the isolated antibodies, or antigen-binding fragments thereof, of the present invention.
In some embodiments, the disease mediated by ACE2 is SARS-CoV-2 infection.
In still another aspect, the present invention provides a nucleic acid comprising a nucleotide sequence encoding a heavy chain variable region (VH), a light chain variable region (VL) or both, wherein the VH and VL are as described herein.
In further another aspect, the present invention provides a vector (e.g. an expression vector) comprising any of the nucleic acids described herein and a host cell comprising such a vector.
The details of one or more embodiments of the invention are set forth in the description below. Other features or advantages of the present invention will be apparent from the following detailed description of several embodiments, and also from the appending claims.
The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
In the drawings:
The present invention relates to novel MAbs that bind to the spike (S) protein or the nucleocapsid (N) protein of SARS-COV-2. The present invention provides such antibodies and antigen-binding fragments thereof, which are useful for detection or prevention and/or treatment of SARS-CoV-2 or a disease mediated by angiotensin-converting enzyme 2 (ACE2). The present invention also provides a pharmaceutical composition comprising the novel MAbs or antigen-binding fragments thereof. In addition, the present invention provides a kit and method for detecting SARS-CoV-2 and a method for preventing or treating SARS-CoV-2 or a disease mediated by a disease mediated by ACE2, using the novel MAbs or antigen-binding fragments thereof as described herein.
The following description is merely intended to illustrate various embodiments of the invention. As such, specific embodiments or modifications discussed herein are not to be construed as limitations to the scope of the invention. It will be apparent to one skilled in the art that various changes or equivalents may be made without departing from the scope of the invention.
In order to provide a clear and ready understanding of the present invention, certain terms are first defined. Additional definitions are set forth throughout the detailed description. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as is commonly understood by one of skill in the art to which this invention belongs.
As used herein, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component” includes a plurality of such components and equivalents thereof known to those skilled in the art.
The term “comprise” or “comprising” is generally used in the sense of include/including which means permitting the presence of one or more features, ingredients or components. The term “comprise” or “comprising” encompasses the term “consists” or “consisting of.”
As used herein, the term “about,” “around,” or “approximately” refers to a degree of acceptable deviation that will be understood by persons of ordinary skill in the art, which may vary to some extent depending on the context in which it is used. In general, “about,” “around,” or “approximately” may mean a numeric value having a range of 10% around the cited value. All numbers herein may be understood as modified by “about,” “around,” or “approximately.”
The term “antibody” as used herein refers to immunoglobulin molecules and immunologically active portions of immunoglobulin molecules, i.e., molecules that contain an antigen binding portion that immunospecifically binds a glycoprotein. As such, the term antibody encompasses not only whole antibody molecules, but also antibody fragments as well as variants (including derivatives) of antibodies and antibody fragments. In natural antibodies, two heavy chains are linked to each other by disulfide bonds and each heavy chain is linked to a light chain by a disulfide bond. There are two types of light chain, lambda (l) and kappa (κ). There are five main heavy chain classes (or isotypes) which determine the functional activity of an antibody molecule: IgM, IgD, IgG, IgA and IgE. Each chain contains distinct sequence domains. The light chain includes two domains, a variable domain (VL) and a constant domain (CL). The heavy chain includes four domains, a variable domain (VH) and three constant domains (CH1, CH2 and CH3, collectively referred to as CH). The variable regions of both light (VL) and heavy (VH) chains determine binding recognition and specificity to the stem cell surface glycoprotein. The light and heavy chains of an antibody each have three complementarity determining regions (CDRs), designated LCDR1, LCDR2, LCDR3 and HCDR1, HCDR2, HCDR3, respectively. An antigen-binding site, therefore, includes six CDRs, comprising the CDR set from each of a heavy and a light chain variable region. Framework Regions (FRs) refer to amino acid sequences interposed between CDRs.
Identity or homology with respect to a specified amino acid sequence of this invention is defined herein as the percentage of amino acid residues in a candidate sequence that are identical with the specified residues, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent homology or identity, and not considering any conservative substitutions as part of the sequence homology or identity. None of N-terminal, C-terminal or internal extensions, deletions, or insertions into the specified sequence shall be construed as affecting homology or identity. Methods of alignment of sequences for comparison are well known in the art. While such alignments may be done by hand using conventional methods, various programs and alignment algorithms are described in: Smith and Waterman, Adv. Appl. Math. 2:482, 1981; Needleman and Wunsch, J. Mol. Biol. 48:443, 1970; Pearson and Lipman, Proc. Natl. Acad. Sci. U.S.A. 85:2444, 1988; Higgins and Sharp, Gene 73:237, 1988; Higgins and Sharp, CABIOS 5:151, 1989; Corpet et al, Nucleic Acids Research 16:10881, 1988; and Pearson and Lipman, Proc. Natl. Acad. Sci. U.S.A. 85:2444, 1988. Altschul et al., Nature Genet. 6:119, 1994, present a detailed consideration of sequence alignment methods and homology/identity calculations. The NCBI Basic Local Alignment Search Tool (BLAST (Altschul et al, J. Mol. Biol. 215:403, 1990) is available from several sources, including the National Center for Biotechnology Information (NCBI, Bethesda, Md., USA) and on the internet, for use in connection with the sequence analysis programs blastp, blastn, blastx, tblastn and tblastx. A description of how to determine sequence identity or homology using this program is available on the NCBI website.
Antibodies of the present invention also include chimerized or humanized monoclonal antibodies generated from antibodies of the present invention. In one embodiment, humanized antibodies are antibody molecules from non-human species having one, two or all CDRs from the non-human species and one, two or all three framework regions from a human immunoglobulin molecule. A chimeric antibody is a molecule in which different portions are derived from different animal species. For example, an antibody may contain a variable region derived from a murine mAb and a human immunoglobulin constant region. Chimeric antibodies can be produced by recombinant DNA techniques. Morrison, et al., Proc Natl Acad Sci, 81:6851-6855 (1984). For example, a gene encoding a murine (or other species) antibody molecule is digested with restriction enzymes to remove the region encoding the murine Fc, and the equivalent portion of a gene encoding a human Fc constant region is then substituted into the recombinant DNA molecule. Chimeric antibodies can also be created by recombinant DNA techniques where DNA encoding murine V regions can be ligated to DNA encoding the human constant regions. Better et al., Science, 1988, 240:1041-1043. Liu et al. PNAS, 1987 84:3439-3443. Liu et al., J. Immunol., 1987, 139:3521-3526. Sun et al. PNAS, 1987, 84:214-218. Nishimura et al., Canc. Res., 1987, 47:999-1005. Wood et al. Nature, 1985, 314:446-449. Shaw et al., J. Natl. Cancer Inst., 1988, 80:1553-1559. International Patent Publication Nos. WO1987002671 and WO 86/01533. European Patent Application Nos. 184,187; 171,496; 125,023; and 173,494. U.S. Pat. No. 4,816,567.
Thus, SARS-CoV-2 antibodies of the present invention include in combination with a heavy chain or light chain variable region, a heavy chain or light chain constant region, a framework region, or any portion thereof, of non-murine origin, preferably of human origin, which can be incorporated into an antibody of the present invention.
Antibodies of the present invention are capable of modulating, decreasing, antagonizing, mitigating, alleviating, blocking, inhibiting, abrogating and/or interfering with the SARS-CoV-2 virus.
As used herein, the term “antigen-binding domain” or “antigen-binding fragment” refers to a portion or region of an intact antibody molecule that is responsible for antigen binding. An antigen-binding fragment is capable of binding to the same antigen to which the parent antibody binds. Examples of antigen-binding fragments include, but are not limited to: (i) a Fab fragment, which can be a monovalent fragment composed of a VH-CH1 chain and a VL-CL chain; (ii) a F(ab′)2 fragment which can be a bivalent fragment composed of two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fv fragment, composed of the VH and VL domains of an antibody molecule associated together by noncovalent interaction; (iv) a single chain Fv (scFv), which can be a single polypeptide chain composed of a VH domain and a VL domain through a peptide linker; and (v) a (scFv)2, which can comprise two VH domains linked by a peptide linker and two VL domains, which are associated with the two VH domains via disulfide bridges.
The antibody can be administered in a single dose treatment or in multiple dose treatments on a schedule and over a time period appropriate to the age, weight and condition of the subject, the particular composition used, and the route of administration, for prophylactic or curative purposes, etc. For example, in one embodiment, the antibody according to the invention is administered once per month, twice per month, three times per month, every other week (qow), once per week (qw), twice per week (biw), three times per week (tiw), four times per week, five times per week, six times per week, every other day (qod), daily (qd), twice a day (qid), three times a day (tid), four times a day (qid) or 6 times a day.
For ease of administration and uniformity of dosage, parenteral dosage unit form may be used. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the subject to be treated; each unit containing a predetermined quantity of antibody calculated to produce the desired therapeutic effect.
An “effective amount,” as used herein, refers to a dose of the antibody that is sufficient to reduce the symptoms and signs of SARS-CoV-2, such as cough, fever shortness of breath, viral shedding, or pneumonia which is detectable, either clinically or radiologically through various imaging means. The term “effective amount” and “therapeutically effective amount” are used interchangeably.
The effective amount of the antibody or the conjugate depends on the subject and the condition to be treated. The specific dose level for any particular subject depends upon a variety of factors including the activity of the specific peptide, the age, body weight, general health, sex, diet, time of administration, route of administration, and rate of excretion, drug combination and the severity of the particular disease undergoing therapy and can be determined by one of ordinary skill in the art without undue experimentation.
The term “subject” may refer to a vertebrate suspected of having SARS-CoV-2 or has confirmed SARS-CoV-2 infection. Subjects include warm-blooded animals, such as mammals, such as a primate, and, more preferably, a human. Non-human primates are subjects as well. The term subject includes domesticated animals, such as cats, dogs, etc., livestock (for example, cattle, horses, pigs, sheep, goats, etc.) and laboratory animals (for example, mouse, rabbit, rat, gerbil, guinea pig, etc.).
The term “treating” as used herein refers to the application or administration of a composition including one or more active agents to a subject afflicted with a disorder, a symptom or conditions of the disorder, or a progression of the disorder, with the purpose to cure, heal, alleviate, relieve, alter, remedy, ameliorate, improve, or affect the disorder, the symptoms or conditions of the disorder, the disabilities induced by the disorder, or the progression of the disorder or the symptom or condition thereof.
As used herein, “pharmaceutically acceptable” means that the carrier is compatible with the active ingredient in the composition, and preferably can stabilize said active ingredient and is safe to the individual receiving the treatment. Said carrier may be a diluent, vehicle, excipient, or matrix to the active ingredient. Some examples of appropriate excipients include lactose, dextrose, sucrose, sorbose, mannose, starch, Arabic gum, calcium phosphate, alginates, tragacanth gum, gelatin, calcium silicate, microcrystalline cellulose, polyvinyl pyrrolidone, cellulose, sterilized water, syrup, and methylcellulose. The composition may additionally comprise lubricants, such as talc, magnesium stearate, and mineral oil; wetting agents; emulsifying and suspending agents; preservatives, such as methyl and propyl hydroxybenzoates; sweeteners; and flavoring agents. The composition of the present invention can provide the effect of rapid, continued, or delayed release of the active ingredient after administration to the patient.
According to the present invention, the form of said pharmaceutical composition may be tablets, pills, powder, lozenges, packets, troches, elixirs, suspensions, lotions, solutions, syrups, soft and hard gelatin capsules, suppositories, sterilized injection fluid, and packaged powder.
As used herein, the term “polypeptide” refers to a polymer composed of amino acid residues linked via peptide bonds. The term “protein” typically refers to relatively large polypeptides. The term “peptide” typically refers to relatively short polypeptides (e.g., containing up to 100, 90, 70, 50, 30, or 20 amino acid residues).
As used herein, an “isolated” substance means that it has been altered by the hand of man from the natural state. In some embodiments, the polypeptide (e.g. antibody) or nucleic acids of the present invention can be said to be “isolated” or “purified” if they are substantially free of cellular material or chemical precursors or other chemicals/components that may be involved in the process of peptides/nucleic acids preparation. It is understood that the term “isolated” or “purified” does not necessarily reflect the extent to which the peptide has been “absolutely” isolated or purified e.g. by removing all other substances (e.g., impurities or cellular components). In some cases, for example, an isolated or purified polypeptide includes a preparation containing the polypeptide having less than 50%, 40%, 30%, 20% or 10% (by weight) of other proteins (e.g. cellular proteins), having less than 50%, 40%, 30%, 20% or 10% (by volume) of culture medium, or having less than 50%, 40%, 30%, 20% or 10% (by weight) of chemical precursors or other chemicals/components involved in synthesis procedures.
As used herein, the term “specific binds” or “specifically binding” refers to a non-random binding reaction between two molecules, such as the binding of the antibody to an epitope of its target antigen. An antibody that “specifically binds” to a target antigen or an epitope is a term well understood in the art, and methods to determine such specific binding are also well known in the art. A molecule is said to exhibit “specific binding” if it reacts or associates more frequently, more rapidly, with greater duration and/or with greater affinity with a particular target antigen or an epitope than it does with other targets/epitopes. An antibody “specifically binds” to a target antigen if it binds with greater affinity, avidity, more readily, and/or with greater duration than it binds to other substances. In other words, it is also understood by reading this definition that, for example, an antibody that specifically binds to a first target antigen may or may not specifically or preferentially bind to a second target antigen. As such, “specific binding” or “preferential binding” does not necessarily require (although it can include) exclusive binding. Generally, but not necessarily, reference to binding means specific/preferential binding. The affinity of the binding is defined in terms of a dissociation constant (Kd). Typically, specifically binding when used with respect to an antibody can refer to an antibody that specifically binds to (recognize) its target with an Kd value less than about 10−7 M, such as about 10−8 M or less, such as about 10−9 M or less, about 10−10 M or less, about 10−11 M or less, about 10−12 M or less, or even less, and binds to the specific target with an affinity corresponding to a Kd that is at least ten-fold lower than its affinity for binding to a non-specific antigen (such as BSA or casein), such as at least 100 fold lower, for instance at least 1,000 fold lower, such as at least 10,000 fold lower.
As used herein, the term “Coronavirus” refers to viruses belonging to the family Coronavirinae. Coronaviruses are enveloped RNA viruses that are spherical in shape and characterized by crown-like spikes on the surface under an electron microscope, hence the name. This type of virus can be further divided into four subgroups: alpha (α), beta (β), gamma (γ), and delta (δ). There are seven human coronavirus strains, including two alpha coronaviruses (HCov-229E and HCoV-NL63), two beta coronaviruses (HCov-HKU1 and HCov-OC43), Middle East respiratory syndrome coronavirus (MERS-CoV), SARS-CoV, and the newly discovered SARS-CoV-2.
As used herein, the term “severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)” refers to the strain of coronavirus that causes Coronavirus disease 2019 (COVID-19). SARS-CoV-2 is a positive-sense single-stranded RNA virus that is a member of the genus Betacoronavirus of the family Coronavirinae. The RNA sequence of SARS-CoV-2 is approximately 30,000 bases in length. Each SARS-CoV-2 virion is 50-200 nanometres in diameter. Like other coronaviruses, SARS-CoV-2 has four structural proteins, known as the S (spike), E (envelope), M (membrane), and N (nucleocapsid) proteins; the N protein holds the RNA genome, and the S, E, and M proteins together create the viral envelope.
As used herein, the term “spike protein,” “S polypeptide,” “S protein,” “SARS-CoV-2 spike,” or “SARS-CoV-2 S protein,” which can be used interchangeably, refers to a surface structure glycoprotein on SARS CoV-2 and is responsible for allowing the virus to attach to and fuse with the membrane of a host cell. Each monomer of trimeric S protein is about 180 kDa, and contains two subunits, S1 and S2, mediating attachment and membrane fusion, respectively. Spike protein mainly enters human cells by binding to the receptor angiotensin converting enzyme 2 (ACE2).
As used herein, the term “nucleocapsid protein,” “N polypeptide,” “N protein,” “SARS-CoV-2 nucleocapsid,” or “SARS-CoV-2 N protein,” which can be used interchangeably, refers to the multi-domain RNA-binding protein of SARS CoV-2 and is critical for viral genome packaging. N protein contains three dynamic disordered regions that house putative transiently-helical binding motifs; and the two folded domains interact minimally such that full-length N protein is a flexible and multivalent RNA-binding protein. (Cubuk 2021).
The term “nucleic acid” or “polynucleotide” can refer to a polymer composed of nucleotide units. Polynucleotides include naturally occurring nucleic acids, such as deoxyribonucleic acid (“DNA”) and ribonucleic acid (“RNA”) as well as nucleic acid analogs including those which have non-naturally occurring nucleotides. Polynucleotides can be synthesized, for example, using an automated DNA synthesizer. It will be understood that when a nucleotide sequence is represented by a DNA sequence (i.e., A, T, G, C), this also includes an RNA sequence (i.e., A, U, G, C) in which “U” replaces “T.” The term “cDNA” refers to a DNA that is complementary or identical to an mRNA, in either single stranded or double stranded form.
The term “encoding” refers to the inherent property of specific sequences of nucleotides in a polynucleotide (e.g., a gene, a cDNA, or an mRNA) to serve as templates for synthesis of other polymers and macromolecules in biological processes having either a given sequence of nucleotides (i.e., rRNA, tRNA and mRNA) or a given sequence of amino acids and the biological properties resulting therefrom. Therefore, a gene encodes a protein if transcription and translation of mRNA produced by that gene produces the protein in a cell or other biological system. It is understood by a skilled person that numerous different polynucleotides and nucleic acids can encode the same polypeptide as a result of the degeneracy of the genetic code. It is also understood that skilled persons may, using routine techniques, make nucleotide substitutions that do not affect the polypeptide sequence encoded by the polynucleotides described there to reflect the codon usage of any particular host organism in which the polypeptides are to be expressed. Therefore, unless otherwise specified, a “nucleotide sequence encoding an amino acid sequence” encompasses all nucleotide sequences that are degenerate versions of each other and that encode the same amino acid sequence.
Numerous methods conventional in this art are available for obtaining monoclonal antibodies or antigen-binding fragments thereof. In some embodiments, the monoclonal antibodies provided herein may be made by the conventional hybridoma technology. In some embodiments, the monoclonal antibodies provided herein may be prepared via recombinant technology. In some embodiments, the monoclonal antibodies provided herein may be prepared by single cell expression system based on flow cytometry and PCR cloning of antigen specific B cells (Huang 2015, Huang 2017, Huang 2019).
When a full-length antibody is desired, coding sequences of any of the VH and VL chains described herein can be linked to the coding sequences of the Fc region of an immunoglobulin and the resultant gene encoding a full-length antibody heavy and light chains can be expressed and assembled in a suitable host cell, e.g., a plant cell, a mammalian cell, a yeast cell, or an insect cell.
Antigen-binding fragments can be prepared via routine methods. For example, F(ab′)2 fragments can be generated by pepsin digestion of a full-length antibody molecule, and Fab fragments that can be made by reducing the disulfide bridges of F(ab′)2 fragments. Alternatively, such fragments can also be prepared via recombinant technology by expressing the heavy and light chain fragments in suitable host cells and have them assembled to form the desired antigen-binding fragments either in vivo or in vitro. A single-chain antibody can be prepared via recombinant technology by linking a nucleotide sequence coding for a heavy chain variable region and a nucleotide sequence coding for a light chain variable region. Preferably, a flexible linker is incorporated between the two variable regions.
In general, the method of the present invention for detecting SARS-CoV-2 in a sample suspected of containing said SARS-CoV-2 comprises contacting the sample with any of the disclosed monoclonal antibodies or any combination thereof and assaying binding of the antibody with said sample.
There are various assay formats known to those of ordinary skill in the art for using antibodies to detect an antigen or pathogen in a sample. These assays that use antibodies specific to target antigens/pathogens are generally called immunoassays. Examples of immunoassays include but are not limited to ELISA (enzyme-linked immunosorbent assay), RIA (radioimmunoassay), FIA (fluorescence immunoassay), LIA (luminescence immunoassay), or immunoluminometric assay (ILMA). Such assays can be employed to detect the presence of SARS-CoV-2 in biological samples including blood, serum, plasma, saliva, cerebrospinal fluid, urine, stool, samples taken from respiratory tract, and other tissue specimens.
In some embodiments, the samples taken from the respiratory tract are nasopharyngeal (NP) or nasal (NS) swabs.
In some embodiments, the immunoassay is a sandwich assay or in a lateral flow assay format.
The following examples of specific aspects for carrying out the present invention are offered for illustrative purposes only, and are not intended to limit the scope of the present invention in any way.
1. Study Design
In this Example, SARS-CoV-2 antigen-specific human MAbs were isolated from peripheral plasmablasts in humans with natural SARS-CoV-2 infection, and then the antigenic specificity and phenotypic activities of human MAbs were characterized. The diagnosis of acute SARS-CoV-2 infection was based on positive real-time reverse transcriptase polymerase chain reaction (PCR) results of respiratory samples. The study protocol and informed consent were approved by the ethics committee at the Chang Gung Medical Foundation (Taoyuan, Taiwan) and the Taoyuan General Hospital, Ministry of Health and Welfare (Taoyuan, Taiwan). Each patient provided signed informed consent. The study and all associated methods were carried out in accordance with the approved protocol, the Declaration of Helsinki and Good Clinical Practice guidelines.
2. Staining and Sorting of Plasmablasts
Fresh peripheral blood mononuclear cells (PBMCs) were separated from whole blood by density gradient centrifugation and cryopreserved PBMCs were thawed. PBMCs were stained with a mix of fluorescent-labeled antibodies to cellular surface markers, including anti-CD3 (BD Biosciences, USA), anti-CD19 (BD Biosciences, USA), anti-CD27 (BD Biosciences, USA), anti-CD20 (BD Biosciences, USA), anti-CD38 (BD Biosciences, USA), anti-IgG (BD Biosciences, USA) and anti-IgM (BD Biosciences, USA). Plasmablasts were selected by gating on CD3− CD20−CD19+CD27hiCD38hiIgG+IgM− events and were isolated in chamber as single cell as previously described (Huang 2015, Huang 2017, Huang 2019).
3. Production of Human IgG 1 Monoclonal Antibodies
Sorted single cells were used to produce human IgG monoclonal antibodies as previously described (Huang 2015, Huang 2017, Huang 2019). Briefly, single cells were sorted directly to catch buffer and the variable region genes from each cell were amplified in a reverse transcriptase PCR (QIAGEN, Germany) using a cocktail of sense primers specific for the leader region and antisense primers to the Cγ constant region for heavy chain and Cκ and Cλ for light chain. The reverse transcriptase PCR products were amplified in separate PCR reactions for the individual heavy and light chain gene families using nested primers to incorporate restriction sites at the ends of the variable gene as previously described (Huang 2015, Huang 2017, Huang 2019). These variable genes were then cloned into expression vectors for the heavy and light chains. Plasmids were transfected into the 293T cell line for expression of recombinant full-length human IgG monoclonal antibodies in serum-free transfection medium (
To determine the individual gene segments employed by VDJ and VJ rearrangements and the number of nucleotide mutations and amino acid replacements, the variable domain sequences were aligned with germline gene segments using the international ImMunoGeneTics (IMGT) alignment tool (http://www.imgt.org/IMGT_vquest/input).
4. Enzyme-Linked Immunosorbent Assay (ELISA)
The ELISA plates (Corning® 96-well Clear Polystyrene High Bind Stripwell™ Microplate, USA) were coated with SARS-CoV-2 antigen (Spike extracellular domain or spike S1 subunit or spike receptor binding domain (RBD) or spike S2 subunit or nucleocapsid, Sino Biological, China) or SARS antigen (Spike S1 subunit, Sino Biological, China) or Middle East respiratory syndrome coronavirus (MERS) antigen (Spike extracellular domain, Sino Biological, China) or human coronavirus OC43 antigen (Spike extracellular domain, Sino Biological, China) at optimal concentration in carbonate buffer and incubated at 4° C. overnight. The next day unbound antigens were removed by pipetting to avoid risk of forming aerosols. Nonspecific binding was blocked with the solution of phosphate-buffered saline (PBS) with 3% bovine serum albumin (BSA) at room temperature for 1 hour on a shaker. After removing blocking buffer, monoclonal antibody-containing cell culture supernatant or purified monoclonal antibody preparation were added and incubated at 37° C. for 1 hour. The non-transfected cell culture supernatant and anti-influenza human monoclonal antibody BS 1A (in house) were used as negative antibody controls for each experiment. The anti-SARS spike monoclonal antibody CR3022 and convalescent serum were used as positive antibody controls for each experiment. After incubation, the plate was washed and incubated with horseradish peroxidase-conjugated rabbit anti-human IgG (Rockland Immunochemicals, USA) as secondary antibody. After incubation, the plate was washed and developed with 3,3′,5,5′-Tetramethylbenzidine (TMB) substrate reagent (BD Biosciences, USA). Reaction was stopped by 0.5M Hydrochloric acid and the optical density was measured at OD450 on a microplate reader. The well that yielded an OD value four times the mean absorbance of negative controls (BS 1A) was considered positive.
5. Immunofluorescence Assay
Under biosafety level 3 (BSL-3) conditions, cells were infected with 100 TCID50 (median tissue culture infectious dose) SARS-CoV-2 (hCoV-19/Taiwan/CGMH-CGU-01/2020, EPI_ISL_411915). Infected cells were placed on coverslips and, and fixed with acetone at room temperature for 10 minutes. After blocking with 1% BSA at room temperature for 1 hour and washing, fixed cells were incubated with MAb-containing cell culture supernatant. The anti-influenza human monoclonal antibody BS 1A was used as negative antibody controls for each experiment. The anti-SARS spike glycoprotein MAb CR3022 and convalescent serum were used as positive antibody controls for each experiment. Following incubation and wash, cells were stained with FITC-conjugated anti-human IgG secondary antibody and Evans blue dye as counterstain. Antibody-bound infected cells demonstrated an apple-green fluorescence against a background of red fluorescing material stained by the Evans Blue counterstain. Images were acquired with original magnification 40×, scale bar 20 μm.
6. Flow Cytometry Assay
SARS-CoV-2 receptor-binding domain (RBD)-expressed Madin-Darby Canine Kidney (MDCK) cells (RBD cells) were prepared and resuspended. RBD Cells were probed with purified MAbs in 3% BSA. Bound primary antibodies were detected with FITC-conjugated anti-IgG secondary antibody. The binding activities were analyzed by BD FACSCanto™ II flow cytometer (BD Biosciences, USA). The nonlinear regression analysis was performed to obtain the Kd value of MAb against SARS-CoV-2 RBD.
7. Results
Peripheral blood samples were obtained from convalescent patients with laboratory-confirmed SARS-CoV-2 infections and circulating plasmablasts were identified by flow cytometry (Huang 2015, Huang 2017, Huang 2019). Sorted single cells were used to generate SARS-CoV-2 human monoclonal antibodies (
Among spike-reactive antibodies, 15 recognize the S1 subunit and 10 recognize the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein (Table 1,
Variable domain sequences were obtained from the 34 SARS-CoV-2 spike-reactive monoclonal antibodies, each of which was unique and harbored somatic mutations (Table 2, Table 3, Table 4). Table 2 shows that SARS-CoV-2 spike-reactive monoclonal antibodies were evolved from 25 clonal groups defined by their heavy chain VDJ and light chain VJ rearrangements. Their average nucleotide somatic mutations are 6±9 in the heavy chain variable regions and 4±6 in the light chain variable regions. It was noted that 14 SARS-CoV-2 spike-reactive antibodies carry low number (less than 2) of somatic mutations in the heavy chain variable region, suggesting a de-novo B cell response to the SARS-CoV-2 virus in humans. Table 3 shows the nucleotide and amino acid sequences of the heavy chain variable regions and the light chain variable regions of the 34 SARS-CoV-2 spike-reactive monoclonal antibodies and Table 4 shows the amino acid sequences of complementarity-determining regions (CDRs) of the heavy chain variable regions and the light chain variable regions of the 34 SARS-CoV-2 spike-reactive human monoclonal antibodies.
Tables 5 and 6 show that SARS-CoV-2 nucleocapsid-reactive monoclonal antibodies were evolved from 32 clonal groups defined by their heavy chain VDJ and light chain VJ rearrangements. Their average nucleotide somatic mutations are 22±30 in the heavy chain variable regions and 13±18 in the light chain variable regions.
Table 6 shows the nucleotide and amino acid sequences of the heavy chain variable regions and the light chain variable regions of the 32 SARS-CoV-2 nucleocapsid-reactive monoclonal antibodies. Table 7 shows the amino acid sequences of complementarity-determining regions (CDRs) of the heavy chain variable regions and the light chain variable regions of the SARS-CoV-2 nucleocapsid-reactive human monoclonal antibodies.
SARS-CoV-2 nucleocapsid-reactive antibodies EW 4C, EY 2A and EY 3B bound to paraformaldehyde-fixed and Triton X-100-permeabilised SARS-CoV-2 infected cells by immunofluorescence assay.
1. Quantitative PCR-Based Neutralization Assay
Neutralization activity of MAb-containing supernatant was measured using a SARS-CoV-2 infection of Vero E6 cells. Briefly, Vero E6 cells were pre-seeded in a 96 well plate at a concentration of 104 cells per well. In the following day, monoclonal antibody-containing supernatant were mixed with an equal volume of 100 TCID50 virus preparation and incubated at 37° C. for 1 hour. The mixture was added into seeded Vero E6 cells and incubated at 37° C. for 5 days. The cell control, virus control, and virus back-titration were setup for each experiment. At day 5, the culture supernatant was harvested from each well and the viral RNA was extracted and determined by real-time RT-PCR targeting the E gene of SARS-CoV-2. The cycle threshold values of real-time RT-PCR were used as indicators of the copy number of SARS-CoV-2 RNA in samples with lower cycle threshold values corresponding to higher viral copy numbers.
2. Cytopathic Effect (CPE)-Based Neutralization Assay
Vero E6 cells in Dulbecco's Modified Eagle's Medium (DMEM) containing 10% FBS were added into 96-well plates and incubated at 37° C. with 5% CO2 overnight to reach confluence. After washing with virus growth medium (VGM: DMEM containing 2% FBS), two-fold serially diluted MAbs in VGM starting at 100 μg/ml were added to each duplicated well. The plates were immediately transferred to a BSL-3 laboratory and 100 TCID50 SARS-CoV-2 in VGM was added. The plates were further incubated at 37° C. with 5% CO2 for three days and the cytopathic morphology of the cells was recorded using an ImageXpress Nano Automated Cellular Imaging System.
3. Plaque Reduction Neutralization Test (PRNT)
Confluent monolayers of Vero E6 cells in 96-well plates were incubated with SARS CoV-2 and antibodies in a 2-fold dilution series (triplicates) for 3 hours at room temperature. Inoculum was then removed, and cells were overlaid with plaque assay overlay. Cells were incubated at 37° C., 5% CO2 for 24 hours prior to fixation with 4% paraformaldehyde at 4° C. for 30 minutes. Fixed cells were then permeabilised with 0.2% Triton-X-100 and stained with a horseradish peroxidase conjugated-antibody against virus protein for 1 hour at room temperature. TMB substrate was then added to visualize virus plaques as described previously for influenza virus. Convalescent serum from COVID-19 patients was used as a control.
4. Fluorescent Focus-Forming Units Microneutralization Assay (FMNT)
In brief, this rapid, high-throughput assay determines the concentration of antibody that produces a 50% reduction in infectious focus-forming units of authentic SARS-CoV-2 in Vero cells, as follows. Triplicate serial dilutions of antibody are pre-incubated with a fixed dose of SARS-CoV-2 in triplicate before incubation with Vero cells. A carboxymethyl cellulose-containing overlay is used to prevent satellite focus formation. Twenty hours post-infection, the monolayers are fixed with paraformaldehyde and stained for N antigen using MAb EY 2A. After development with a peroxidase-conjugated antibody and substrate, foci are enumerated by enzyme-linked immune absorbent spot reader. Data are analyzed using four-parameter logistic regression (Hill equation) in GraphPad Prism.
5. Competitive Binding Assays
Competitive binding assays were performed as described previously (Rijal 2019) with slight modifications for epitope mapping of the anti-RBD MAbs. Briefly, 0.5 μg/ml of RBD-virus like particles (VLPs) were coated on NUNC plates (50 μl per well) overnight at 4° C., washed and blocked with 300 μl of 5% (w/v) dried skimmed milk in PBS for 1 hour at room temperature prior to the assays. Antibody was biotinylated using EZ-Link Sulfo-NHS-LC-biotin (21237; Life Technologies) and then mixed with competing MAb (in at least 10-fold excess) and transferred to the blocked NUNC plates for 1 hour. A second layer Streptavidin-HRP (S911, Life Technologies) diluted 1:1,600 in PBS/0.1% BSA (37525; Thermo Fisher Scientific) was then added and incubated for another 1 hour. Plates were then washed, and signal was developed by adding POD substrate (11484281001, Roche) for 5 minutes before stopping the reaction with 1 M H2SO4. Absorbance (OD450) was measured using a Clariostar plate reader (BMG, Labtech). Mean and 95% confidence interval of 4 replicate measurements were calculated. Competition was measured as: (X-minimum binding/(maximum binding-minimum binding), where X is the binding of the biotinylated MAb in the presence of competing MAb. Minimum binding is the self-blocking of the biotinylated MAb or background binding. Maximum binding is binding of biotinylated MAb in the presence of non-competing MAb (anti-influenza N1 neuraminidase MAb).
6. ACE2 Blocking Assays
Two assays were used to determine the blocking of binding of ACE2 to RBD by MAbs. RBD was anchored on the plate in the first assay whereas ACE2 was anchored for the second assay.
In the first ACE2 blocking assay, RBD-VLP (Spycatcher-mi3 VLP-particles conjugated with Spytagged-RBD recombinant protein) (Bruun 2018) was coated on ELISA plates as described for the competitive binding assay. Recombinant ACE2-Fc (18-615) protein expressed in Expi293F (Life Technologies) cells was chemically biotinylated using EZ-link Sulfo-NHS-Biotin (A39256; Life Technologies) and buffer exchanged to PBS using a Zebaspin desalting column (Thermo Fischer). MAbs were titrated in duplicate or triplicate as half-log serial dilution, 8-point series starting at 1 μM in 30 μl volume with PBS/0.1% BSA buffer. Thirty (30) μl of biotinylated ACE2-Fc at approx. 0.2 nM (40 ng/ml) was added to the antibodies. Fifty (50) μl of the mixture was transferred to the PBS-washed RBD-VLP coated plates and incubated for 1 hour at room temperature. Secondary Streptavidin-HRP antibody (S911, Life Technologies) diluted to 1:1600 was then added to the PBS-washed plates and incubated for 1 hour at room temperature. Plates were then washed four times with PBS and signal was developed by adding POD substrate (11484281001, Roche) for 5 minutes before stopping with 1 M H2SO4. OD450 was measured using a Clariostar plate reader (BMG, Labtech). The control antibody (a non-blocking anti-influenza N1 MAb) or ACE2-Fc without antibody used to obtain the maximum signal and wells with PBS/BSA buffer only were used to determine the minimum signal. Graphs were plotted as % binding of biotinylated ACE2 to RBD. Binding %={(X−Min)/(Max−Min)}*100, where X=measurement of the antibody, Min=buffer only, Max=biotinylated ACE2-Fc alone. The 50% inhibitory concentrations of the antibodies against ACE2 was determined using non-linear regression curve fit using GraphPad Prism 8.
The second ACE2 blocking assay was performed as described previously (Huo 2020; Zhou 2020). Briefly, MDCK-SIAT1 cells were stably transfected to overexpress codon-optimised human ACE2 cDNA (NM_021804.1) using lentiviral vector and FACS sorted (MDCK-ACE2). Cells (3×104 per well) were seeded on a flat-bottomed 96-well plate the day before the assay. RBD-6H (340-538; NITN.GPKK) was chemically biotinylated using EZ-link Sulfo-NHS-Biotin (A39256; Life Technologies). Serial half-log dilutions (starting at 1 μM) of antibodies and controls were performed in a U-bottomed 96 well plate in 30 μl volume. Thirty (30) μl of biotinylated RBD (25 nM) were mixed and 50 μl of the mixture was then transferred to the MDCK-ACE2 cells. After 1 hour a second layer Streptavidin-HRP antibody (S911, Life Technologies) diluted 1:1,600 in PBS/0.1% BSA (37525; Thermo Fisher Scientific) was added and incubated for another 1 hour. Plates were then washed four times with PBS and signal was developed by adding POD substrate (11484281001, Roche) before stopping with 1 M H2SO4 after 5 minutes. OD450 was measured using a Clariostar plate reader (BMG, Labtech). The control antibody (a non-blocking anti-influenza N1 antibody) was used to obtain maximum signal and PBS only wells were used to determine background. Graphs were plotted as % binding of biotinylated RBD to ACE2. The 50% inhibitory concentration of the blocking antibody was determined as described above.
7. Statistics
The two-tailed Mann-Whitney test was performed to compare differences between two independent groups. The 50% effective concentration (EC50) was determined using linear regression analysis. A p value of less than 0.05 was considered significant. Graphs were presented by Microsoft Excel and GraphPad Prism software.
8. Results
A neutralization test for EW 9C, EY 6A, FD 5D, FD 11A and FI 3A MAbs based on quantitative PCR detection of SARS-CoV-2 in the supernatant bathing infected Vero E6 cells after 5 days of culture, showed a substantial reduction in virus signal (
All anti-spike glycoprotein MAbs were systematically screened by plaque reduction neutralization (PRNT) assay for neutralization of wild type SARS-CoV-2 virus (Table 10). A total of 14 neutralizing antibodies distributed between different regions of the spike glycoprotein were identified: three of 13 to S1 (non-RBD), six of nine to S2, five of 10 to RBD. The EC50 concentrations, as a measure of potency, ranged from 0.05 nM to around 133.33 nM (8 ng/ml-around 20 μg/ml). Neutralization was corroborated by a microneutralization test (FMNT), that measured a reduction in fluorescent focus-forming units, summarised in Table 10,
Five neutralizing MAbs (FD 11A, FI 3A, FI 1C, FD 5D and EY 6A) target the RBD and all of these partially or completely blocked the interaction between RBD and ACE2 in one or the other type of assay (Table 10,
Six MAbs specific for SARS-CoV-2 S2 subunit showed moderate neutralization in the PRNT assay (Table 10). The antibodies FB 1E, FJ 4E and EW 9C, are moderately neutralizing (EC50 36-133.33 nM), cross-react on the spike glycoprotein from the common cold betacoronavirus OC43, and show sequence characteristics of memory cells with high numbers of somatic mutations. This indicates that memory B cells, likely primed by an endemic or epidemic betacoronavirus related to OC43, can give rise to antibodies that neutralize SARS-CoV-2, albeit modestly. The other three neutralizing antibodies specific for SARS-CoV-2 S2 subunit, FD 10A, FG 7A and FM 1A were close to germline in sequence and did not cross-react strongly with other betacoronaviruses (Table 1). FD 10A exhibits the most potent neutralizing activity in the PRNT assay and completely inhibits SARS-CoV-2-induced cytopathic effect at 8.33 nM.
Thirteen MAbs were defined that bound the non-RBD S1 region (Table 1) and three, close to germline in sequence, were neutralizing. FJ 1C showed strong neutralization (EC50 55.5 nM), whilst FD 11E (EC50 70 nM) and FD 1E (EC50 110 nM) were moderately neutralizing (Table 10).
SARS-CoV-2 nucleocapsid-reactive antibodies were also screened for binding to fixed and permeabilised infected cells for use in scoring wells in microneutralisation assays (FMNT). Antibody EY 2A performed well for this purpose.
aThe plaque reduction neutralization (PRNT) assay was performed with wild type SARS-CoV-2 and the half maximal effective concentration (EC50) was determined using linear regression analysis.
bThe fluorescent focus-forming units microneutralization (FMNT) assay was performed with wild type SARS-CoV-2 and the half maximal effective concentration (EC50) was determined using logistic regression model. Partial: MAb neutralizes at least ~40% viruses at 100 nM (hightest concentration tested).
cACE2 blocking activity of anti-RBD antibody compared to ACE2-Fc: +, partial; ++, IC50 > ACE2-Fc; +++, IC50 ~= ACE2-Fc; ++++, IC50 < ACE2-Fc.
aCompetitive inhibition: values are shown for percentage inhibition and those with ≥75% blocking, 50-74% blocking, and <50% blocking are highlighted in black, gray and light gray, respectively.
bNeutralization of antibody against wild type SARS-COV-2 was analysed in the PRNT assay (+ = positive, − = negative).
1. Test Aminals and Study Design
The prophylactic and therapeutic efficacies of a cocktail of the MAbs of the present invention (hereinafter referred to as antibody cocktail) against SARS-CoV-2 were evaluated in the Syrian hamster model. Briefly, 32 female Golden Syrian hamsters (National Laboratory Aminal Center, Taipei, Taiwan) of 8 weeks old were randomly divided into 8 groups (n=4), 4 groups for the prophylactic experiment, and the other 4 groups for the therapeutic experiment.
In the prophylactic experiment, one day prior to intranasal challenge with 1×105 TCID50/hamster SARS-CoV-2 (hCoV-19/Taiwan/4/2020), animals were treated with a single dose (0.4 mg/kg, 4 mg/kg, or 40 mg/kg) of the antibody cocktail or 40 mg/kg of an isotype negative control (Z3B2, anti-influenza haemagglutinin human IgG1 monoclonal antibody (Huang et al., 2019)) via intraperitoneal injection. Body weight of each animal was measured daily after challenge, and data were normalized to the initial weight of each animal. Animals were sacrificed on day 4 after viral challenge, and the right lung and trachea were collected for histopathological evaluation and viral load and titer.
In the therapeutic experiment, animals were treated with single dose (0.4 mg/kg, 4 mg/kg, or 40 mg/kg) of the antibody cocktail or 40 mg/kg of the isotype negative control via intraperitoneal injection three hours after intranasal challenge with 1×105 TCID50/hamster SARS-CoV-2 (hCoV-19/Taiwan/4/2020). Body weight of each animal was measured daily after challenge, and data were normalized to the initial weight of each animal. Animals were sacrificed on 4 dpi for histopathology, viral load and titer.
2. Viral load and virus titer (median tissue culture infectious dose (TCID50) Assays)
The right lung tissues were weighed and homogenized in 2 ml of PBS. After centrifugation at 600×g for 5 minutes, the clarified supernatant was harvested for viral load detection and live virus titration (TCID50 assay). For viral load detection, total RNAs in the tissue homogenate were extracted with RNeasy Mini kit (Qiagen). Quantitative reverse transcription PCR (qRT-PCR) for detection of SARS-CoV-2 envelope (E) and nucleocapsid (N) genes was performed to determine viral loads. For TCID50 assay, serial 10-fold dilutions of each sample were inoculated in a Vero E6 cell monolayer and cultured for 4 to 7 days for observation of cytopathic effects (CPE). Viral titer was calculated with the Reed-Munch method.
3. Histopathology
Lungs and tracheas were collected and fixed in 10% PBS buffered formaldehyde for 24 hours, then processed into paraffin-embedded tissues blocks. The tissue sections in 4 μm were stained with haematoxylin and eosin (H&E) for microscopy examination.
4. Statistics
Statistical significance between groups was calculated by an unpaired two-sided t test.
5. Results
In the prophylactic experiment, administration of antibody cocktail at 40 or 4 mg/kg prior to SARS-CoV-2 challenge resulted in complete protection from weight loss (
In the therapeutic experiment, animals of all doses gradually gained weight and those treated with isotype negative control had no significant weight loss (
In the prophylactic experiment, there was a significantly lower amount of pulmonary inflammation or necrosis in animals treated with 40 or 4 mg/kg of the antibody cocktail when compared to those treated with 0.4 mg/kg of the antibody cocktail or isotype negative control (
4/44
1Prophylactic experiment: isotype control or antibody cocktail via intraperitoneal injection 1 day before SARS-CoV-2 infection.
2Therapeutic experiment: isotype control or antibody cocktail via intraperitoneal injection 3 hours after SARS-CoV-2 infection.
3Degree of lesions was graded from one to five depending on severity: 1 = minimal (<1%); 2 = slight (1-25%); 3 = moderate (26-50%); 4 = moderate/severe (51-75%); 5 = severe/high (76-100%).
4Incidence: Affected hamsters/Total examined hamsters (n = 3-4).
1.1 ± 0.64
1Prophylactic experiment: isotype negative control or antibody cocktail via intraperitoneal injection 1 day before SARS-CoV-2 infection.
2Therapeutic experiment: isotype control or antibody cocktail via intraperitoneal injection 3 hours after SARS-CoV-2 infection.
3The final numerical score was calculated by dividing the sum of the number per grade of affected hamsters by the total number of examined hamsters (n = 4).
4The subtotal mean score was calculated by dividing the sum of the number per grade of each lesion of affected hamsters by the total number of examined hamsters (n = 4).
*Statistically significant difference compared to the isotype control group each at p < 0.05.
aStatistically significant difference between the 0.4 mg/kg antibody cocktail-treated group and the 4 or 40 mg/kg antibody cocktail-treated groups in the prophylactic and therapeutic experiments each at p < 0.05.
bStatistically significant difference between the 4 mg/kg antibody cocktail-treated group and the 40 mg/kg antibody cocktail-treated groups in the prophylactic and therapeutic experiments each at p < 0.05.
Taken together, the Syrian hamster study shows that the prophylactic or therapeutic treatment with either 40 or 4 mg/kg of antibody cocktail could significantly reduce lung viral load and attenuate SARS-COV-2 virus-induced pulmonary inflammation according to histopathological examination.
In summary, a panel of SARS-CoV-2 spike and nucleocapsid-reactive human monoclonal antibodies was produced and characterized their antigenic specificities and genetic information in the variable domains of heavy and light chains. These human MAbs have held great potential for use as prophylactic or therapeutic molecules against SARS-CoV-2 and diagnostic reagents for detection of virus in the clinical samples.
Many changes and modifications in the above described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, to promote the progress in science and the useful arts, the invention is disclosed and is intended to be limited only by the scope of the appended claims.
This application is a continuation application of International Patent Application No. PCT/CN2021/093083, filed on May 11, 2021, which itself claims priority to U.S. Provisional Application No. 63/022,944, filed on May 11, 2020; U.S. Provisional Application No. 63/029,980, filed on May 26, 2020; and U.S. Provisional Application No. 63/070,560, filed on Aug. 26, 2020. The disclosures of the above applications are incorporated herein in their entireties by reference. The sequence information contained in the Sequence Listing XML file, with the file name “P22-0214US.xml” created on Nov. 8, 2022 and having a file size of 791,199 bytes, is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63022844 | May 2020 | US | |
| 63029980 | May 2020 | US | |
| 63070560 | Aug 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2021/093083 | May 2021 | US |
| Child | 18054594 | US |
