Human monoclonal antibodies

New technologies in therapeutic antibody development: The next frontier for treating infectious diseases

Adaptive immunity to viral infections requires time to neutralize and clear viruses to resolve infection. Fast growing and pathogenic viruses are quickly established, are highly transmissible and cause significant disease burden making it difficult to mount effective responses, thereby prolonging infection. Antibody-based passive immunotherapies can provide initial protection during acute infection, assist in mounting an adaptive immune response, or provide protection for those who are immune suppressed or immune deficient. Historically, plasma-derived antibodies have demonstrated some success in treating diseases caused by viral pathogens; nonetheless, limitations in access to product and antibody titer reduce success of this treatment modality. Monoclonal antibodies (mAbs) have proven an effective alternative, as it is possible to manufacture highly potent and specific mAbs against viral targets on an industrial scale. As a result, innovative technologies to discover, engineer and manufacture specific and potent antibodies have become an essential part of the first line of treatment in pathogenic viral infections. However, a mAb targeting a specific epitope will allow escape variants to outgrow, causing new variant strains to become dominant and resistant to treatment with that mAb. Methods to mitigate escape have included combining mAbs into cocktails, creating bi-specific or antibody drug conjugates but these strategies have also been challenged by the potential development of escape mutations. New technologies in developing antibodies made as recombinant polyclonal drugs can integrate the strength of poly-specific antibody responses to prevent mutational escape, while also incorporating antibody engineering to prevent antibody dependent enhancement and direct adaptive immune responses.

Developing Recombinant Antibodies by Phage Display Against Infectious Diseases and Toxins for Diagnostics and Therapy

Antibodies are essential molecules for diagnosis and treatment of diseases caused by pathogens and their toxins. Antibodies were integrated in our medical repertoire against infectious diseases more than hundred years ago by using animal sera to treat tetanus and diphtheria. In these days, most developed therapeutic antibodies target cancer or autoimmune diseases. The COVID-19 pandemic was a reminder about the importance of antibodies for therapy against infectious diseases. While monoclonal antibodies could be generated by hybridoma technology since the 70ies of the former century, nowadays antibody phage display, among other display technologies, is robustly established to discover new human monoclonal antibodies. Phage display is an in vitro technology which confers the potential for generating antibodies from universal libraries against any conceivable molecule of sufficient size and omits the limitations of the immune systems. If convalescent patients or immunized/infected animals are available, it is possible to construct immune phage display libraries to select in vivo affinity-matured antibodies. A further advantage is the availability of the DNA sequence encoding the phage displayed antibody fragment, which is packaged in the phage particles. Therefore, the selected antibody fragments can be rapidly further engineered in any needed antibody format according to the requirements of the final application. In this review, we present an overview of phage display derived recombinant antibodies against bacterial, viral and eukaryotic pathogens, as well as microbial toxins, intended for diagnostic and therapeutic applications.

Trends in Monoclonal Antibody Production Using Various Bioreactor Syst

Monoclonal antibodies are widely used as diagnostic reagents and for therapeutic purposes, and their demand is increasing extensively. To produce these proteins in sufficient quantities for commercial use, it is necessary to raise the output by scaling up the production processes. This review describes recent trends in high-density cell culture systems established for monoclonal antibody production that are excellent methods to scale up from the lab-scale cell culture. Among the reactors, hollow fiber bioreactors contribute to a major part of high-density cell culture as they can provide a tremendous amount of surface area in a small volume for cell growth. As an alternative to hollow fiber reactors, a novel disposable bioreactor has been developed, which consists of a polymer-based supermacroporous material, cryogel, as a matrix for cell growth. Packed bed systems and disposable wave bioreactors have also been introduced for high cell density culture. These developments in high-density cell culture systems have led to the monoclonal antibody production in an economically favourable manner and made monoclonal antibodies one of the dominant therapeutic and diagnostic proteins in biopharmaceutical industry.

Development of Whole-Porcine Monoclonal Antibodies with Potent Neutralization Activity against Classical Swine Fever Virus from Single B Cells

Classical swine fever (CSF) is a highly contagious swine disease that causes devastating economic losses. However, there are few efficacious therapeutic antibodies against the CSF virus (CSFV). Accordingly, we isolated two whole-porcine anti-CSFV neutralizing antibodies (NAbs) directly from single B cells sorted using the conserved linear epitope of the CSFV E2 protein and goat anti-pig IgG. These mAbs, termed HK24 and HK44, can bind to the E2 protein by recognizing sites within the conserved linear epitope of E2. In addition, these two mAbs can detect virus infection with high specificity and possess potent neutralizing activity. HK24 and HK44 protect PK-15 cells from CSFV infections in vitro with potent IC₅₀ values of 9.3 and 0.62 μg/mL, respectively. We anticipate that these antibodies can be used as diagnostic and antiviral agents for CSFV and that the method we describe here will accelerate the production of therapeutic antibodies for other viruses.

Recombinant antibodies for diagnostics and therapy against pathogens and toxins generated by phage display

Antibodies are valuable molecules for the diagnostic and treatment of diseases caused by pathogens and toxins. Traditionally, these antibodies are generated by hybridoma technology. An alternative to hybridoma technology is the use of antibody phage display to generate recombinant antibodies. This in vitro technology circumvents the limitations of the immune system and allows—in theory—the generation of antibodies against all conceivable molecules. Phage display technology enables obtaining human antibodies from naïve antibody gene libraries when either patients are not available or immunization is not ethically feasible. On the other hand, if patients or immunized/infected animals are available, it is common to construct immune phage display libraries to select in vivo affinity‐matured antibodies. Because the phage packaged DNA sequence encoding the antibodies is directly available, the antibodies can be smoothly engineered according to the requirements of the final application. In this review, an overview of phage display derived recombinant antibodies against bacterial, viral, and eukaryotic pathogens as well as toxins for diagnostics and therapy is given.

Generation of Recombinant Antibodies Against Toxins and Viruses by Phage Display for Diagnostics and Therapy

Antibody phage display is an in vitro technology to generate recombinant antibodies. In particular for pathogens like viruses or toxins, antibody phage display is an alternative to hybridoma technology, since it circumvents the limitations of the immune system. Phage display allows the generation of human antibodies from naive antibody gene libraries when either immunized patients are not available or immunization is not ethically feasible. This technology also allows the construction of immune libraries to select in vivo affinity matured antibodies if immunized patients or animals are available.In this review, we describe the generation of human and human-like antibodies from naive antibody gene libraries and antibodies from immune antibody gene libraries. Furthermore, we give an overview about phage display derived recombinant antibodies against viruses and toxins for diagnostics and therapy.

Antibody-drug conjugates for cancer therapy: The technological and regulatory challenges of developing drug-biologic hybrids

Antibody-drug conjugates (ADCs) are a new class of therapeutic agents that combine the targeting ability of monoclonal antibodies (mAbs) with small molecule drugs. The combination of a mAb targeting a cancer-specific antigen with a cytotoxin has tremendous promise as a new type of targeted cancer therapy. Two ADCs have been approved and many more are in clinical development, suggesting that this new class of drugs is coming to the forefront. Because of their unique nature as biologic-small drug hybrids, ADCs are challenging to develop, from both the scientific and regulatory perspectives. This review discusses both these aspects in current practice, and surveys the current state of the art of ADC drug development.

Tools to therapeutically harness the human antibody response

The natural human antibody response is a rich source of highly specific, neutralizing and self-tolerant therapeutic reagents. Recent advances have been made in isolating and characterizing monoclonal antibodies that are generated in response to natural infection or vaccination. Studies of the human antibody response have led to the discovery of crucial epitopes that could serve as new targets in vaccine design and in the creation of potentially powerful immunotherapies. With a focus on influenza virus and HIV, herein we summarize the technological tools used to identify and characterize human monoclonal antibodies and describe how these tools might be used to fight infectious diseases.

Advances in the field of lentivector-based transduction of T and B lymphocytes for gene therapy

Efficient gene transfer into quiescent T and B lymphocytes for gene therapy or immunotherapy purposes may allow the treatment of several genetic dysfunctions of the hematopoietic system, such as immunodeficiencies, and the development of novel therapeutic strategies for cancers and acquired diseases. Lentiviral vectors (LVs) can transduce many types of nonproliferating cells, with the exception of some particular quiescent cell types such as resting T and B cells. In T cells, completion of reverse transcription (RT), nuclear import, and subsequent integration of the vesicular stomatitis virus G protein pseudotyped LV (VSVG-LV) genome does not occur efficiently unless they are activated via the T-cell receptor (TCR) or by survival-cytokines inducing them to enter into the G(1b) phase of the cell cycle. Lentiviral transduction of B cells is another matter because even B-cell receptor-stimulation inducing proliferation is not sufficient to allow efficient VSVG-LV transduction. Recently, a new LV carrying the glycoproteins of measles virus (MV) at its surface was able to overcome vector restrictions in both quiescent T and B cells. Importantly, naive as well as memory T and B cells were efficiently transduced while no apparent activation, cell-cycle entry, or phenotypic switch were detected, which opens the door to a multitude of gene therapy and immunotherapy applications as reported here.

Clonal diversification in OspA-specific antibodies from peripheral circulation of a chronic Lyme arthritis patient

Chronic, antibiotic treatment-resistant Lyme arthritis develops in a subset of patients following infection with the tick-borne spirochete Borrelia burgdorferi and persists after apparent microbial clearance. IgG responses to Outer Surface Protein (Osp) A, an abundant spirochetal lipoprotein, correlate with both severity and duration of joint inflammation. Characterization of this OspA-directed antibody response is, therefore, important for understanding some of the mechanisms that sustain persistent pathology. Such analyses in Lyme arthritis patients have been previously hampered by relatively small amounts of clinical blood samples, as well as the general intractability and low success rates of B-cell immortalization procedures. Here we describe a robust method for generation of OspA-specific monoclonal antibody fragments from archival cell samples employing a three-step procedure -- isolation of single OspA-specific B-cells, their ex vivo clonal expansion and production of expressed immunoglobulins as single chain variable region fragments (scFvs). Interestingly, two of three scFvs generated from a single patient were of a common clonal origin, additional somatic mutations in the downstream member resulting in a concomitant modulation of antigen binding affinity. Computational docking of OspA into corresponding Fv domains, generated by molecular modeling, reveals subtle binding site differences which could account for the observed alteration in ligand binding. Besides their utility as standards in routine diagnostic assays, being the first described OspA-specific human monoclonal reagents, these scFvs are useful tools for analysis of the anti-OspA repertoire in patients and for identification of putative human mimics of the bacterial protein.

Monoclonal antibody successes in the clinic

Most monoclonal antibodies in clinical trials are owned by small biotech companies. But with blockbuster-sized revenues and approval rates higher than those for small-molecule drugs, that all may be set to change.

Molecular characterization of human monoclonal antibodies derived from fusions of tonsil lymphocytes with a human myeloma cell line

Recently a new human myeloma cell line (Karpas 707H) has been developed for the efficient generation of stable human hybridomas. Here we describe the first molecular characterization of human monoclonal antibodies (MAbs) produced by a human counterpart to mouse myeloma cells. We studied 30 of the hybridomas generated by fusions to tonsil lymphocytes by DNA sequencing of rearranged V-genes, and have analyzed germ-line diversity, somatic hypermutation, and heavy- and light-chain pairings. Our results suggest that the hybridoma-derived antibodies are representative of antibodies from populations of human lymphocytes and at different stages in the maturation of the response; the use of Karpas 707H myeloma for human hybridoma fusions may therefore provide a valuable tool for analysis of the human antibody responses.

Generation of native bovine mAbs by phage display

Modeling of disease pathogenesis and immunity often is carried out in large animals that are natural targets for pathogens of human or economic relevance. Although murine mAbs are a valuable tool in identifying certain host/pathogen interactions, progress in comparative immunology would be enhanced by the use of mAbs isolated from the host species. Such antibodies would reflect an authentic host immune response to infection or vaccination, and as they are host derived, would allow the application of in vivo experiments that previously have been unrealizable in large animals because of induction of an antispecies immune response. The advent of antibody phage display technology provides a way of producing host-derived mAbs in animals where the molecular genetics of Ig formation are known. Exploiting recent advances in the molecular immunology of cattle, we report here the design of an optimized phage display vector, pComBov, for the construction of combinatorial libraries of bovine Ig antigen-binding fragments (Fab) of native sequence. By using this system, we initially have generated and characterized a panel of bovine mAbs against a model antigen glutathione S-transferase. The isolated mAbs showed features typical of bovine Igs and recognized glutathione S-transferase with high specificity in ELISA and by Western blotting. The pComBov expression system can be readily adapted for the preparation of libraries from related ruminant species and advances the use of monoclonal reagents derived in this way for comparative studies in animals of economic importance.

Characterization of an established mouse-human heterohybridoma and its application for production of (mouse-human)-human triple hybridoma secreting human immunoglobulin

We report the construction of a mouse-human (M-H) heterohybridoma by fusion of the murine myeloma cell line NS-1 and human spleen cells from a 17 week old fetus. The nonsecreting, cloned hybridoma cell line II was resistant to 8-azaguanine (8-AG) and sensitive to hypoxanthine, aminopterin and thymidine (HAT) medium. It grew rapidly in 8-AG containing medium (doubling time 20 hrs.), but did not grow in HAT medium or in non-serum medium. It had a high fusion frequency with human lymphocytes from regional lymph nodes. Five human chromosomes were retained stably for over 6 months by this cell line II. Nine (mouse-human)-human ((M-H)-H) triple hybridomas secreting human IgG 1 or IgM were established by the fusion of this parental cell line II and human lymphocytes from regional lymph nodes. Immunoglobulin secretion was stable and has been maintained for over 8-10 months without recloning in these hybridomas. Secretion of immunoglobulin varies from 2.1-3.0 micrograms/10(6) cells/day, and these hybridomas contain from 3 to 16 human chromosomes, including No. 14. So, this M-H heterohybridoma II is an excellent useful parental cell line for the production of hybridomas secreting human immunoglobulin.

Production of baboon (Papio hamadryas) monoclonal antibodies by herpesvirus papio immortalized baboon lymph node cells

Baboon monoclonal antibodies specific for monomorphic determinants of baboon apolipoprotein B were produced from in vivo primed lymph node cells immortalized by herpesvirus papio (HVP). Two cell lines from the immortalized cells were readily stabilized and grew rapidly. Since Epstein-Barr virus (EBV) cannot be used to immortalize baboon or macaque cells, HVP expands the potential sources of monoclonal antibodies to include baboons, and is the immortalizing agent of choice for macaques as well.

Human x human hybridomas from patients with myasthenia gravis: possible tools for idiotypic therapy for myasthenia

Hybridomas secreting monoclonal antibodies directed against the nicotinic acetylcholine receptor have been developed from rats with experimental autoimmune myasthenia gravis and from a patient with myasthenia gravis. Rat monoclonal antibodies were characterized by their ability to bind to electroblotted acetylcholine receptor subunits. Of 34 tested, 22 bound to the alpha subunit. Three bound to other subunits, and the remainder appeared to bind only to the native molecule. The human monoclonal antibodies were analyzed with respect to their binding to membrane-bound and solubilized acetylcholine receptor. Many bound with greater affinity to the membrane-bound form of the antigen. Two rat monoclonal antibodies capable of passively transferring experimental autoimmune myasthenia gravis, and with reactivities to the alpha subunit of the acetylcholine receptor, were employed to produce isogeneic monoclonal antiidiotypic antibodies. When they were injected prior to immunization with acetylcholine receptor, two of the antiidiotypic antibodies directed against framework determinants prevented the development of experimental autoimmune myasthenia gravis. This observation raises the possibility that the human monoclonal antibodies will be useful in the development of idiotypic treatment of the human disease.

Improvement in the basic technology of electrofusion for generation of antibody-producing hybridomas

In order to define the optimum conditions of electrofusion technique for the generation of antibody-producing hybridomas, mouse spleen cells or EBV-transformed human B cells were fused with mouse myeloma cells (SP2/0) or human fusion partner cells (KR-4 or KR-12), respectively, by electric field pulse under various conditions. The results confirm reports that the presence of both Ca2+ and Mg2+ in fusion medium and pretreatment of mixed cells with proteases improve hybridoma yield. Moreover, the presence of liposome or hydrophobic protein in the fusion medium greatly enhanced the yield. Under optimum conditions, hybridoma yields of mouse cells and human cells were 2.5 X 10(-4) and 1 X 10(-4), respectively. These efficiencies were about ten times higher than those obtained by the conventional polyethylene glycol technique. Microscopic observation of the fusion-process revealed that in a human cell system 20%-50% of the cells were physically fused, although only one in 5000 physically fused human cells grew as a hybridoma after hypoxanthine-aminopterin-thymidine selection.

Hybridomas producing human monoclonal antibodies against varicella-zoster virus

Hybridomas producing human monoclonal antibodies (mAb) against varicella-zoster virus (VZV) were generated by fusing human splenic lymphocytes with mouse myeloma cells. Before cell fusion, lymphocytes were stimulated in vitro with viral antigens and pokeweed mitogen. This combination synergistically increased the generation of VZV-specific hybridomas. Five established hybridomas have been stably producing mAb for at least 9 months. These mAb, designated V1, V2, V6, V8 and V9, were of the IgG1, lambda isotype. They bound to all 6 tested VZV strains but not to other herpes viruses, with the exception that V1 bound to herpes simplex virus (HSV) as well as VZV. Immunoprecipitation analysis showed that V1, V6 and V9 recognized glycoprotein gpII, whereas V2 and V8 recognized gpI. In addition, V1 reacted with the gB glycoprotein of HSV. All these mAb neutralized viral infectivity. The neutralizations by V2 and V8 were more effective and more complement dependent than those by V1, V6 and V9. Immunofluorescence tests revealed that all these mAb bound to the surface membrane of VZV-infected cells. These results suggest that cell fusion between in vitro stimulated lymphocytes and mouse myeloma cells is a reliable method for the generation of hybridomas capable of stable production of human mAb. The human mAb thus developed may provide a new means of passive immunization of humans against VZV infection.

Growth of human x human hybridomas in protein-free medium supplemented with ethanolamine

A protein-free medium was developed which supports the growth of human X human hybridomas derived from the fusion partner KR-4. This medium consists of a 1:1 mixture of Iscove's modified Dulbecco's medium and Ham's F-12 medium supplemented with 300 microM ethanolamine. The addition of ethanolamine was essential to maintain cell viability and proliferation. Phosphoethanolamine could not substitute for ethanolamine. Although the maximal cell density achieved in protein-free medium was lower than that in medium supplemented with albumin and transferrin, immunoglobulin production was still supported. This protein-free medium may be useful for large-scale cultivation and for metabolic and immunologic studies of human hybridomas.

Generation of hybridomas producing human monoclonal antibodies against herpes simplex virus after in vitro stimulation

Hybridomas producing human monoclonal antibodies against herpes simplex virus were generated by in vitro antigen stimulation before cell fusion. The cell fusion with tonsillar lymphocytes which were stimulated with antigen and/or pokeweed mitogen generated many hybridomas producing human IgG against the virus. A combination of antigen and pokeweed mitogen synergistically enhanced the generation of virus-specific hybridomas. Furthermore, the higher the antibody response of the tonsil, the more virus-specific hybridomas were generated by the cell fusion. These results suggest that cell fusion with in vitro stimulated lymphocytes can be applied to a variety of clinically relevant viruses.