Hybridoma technology: new developments of practical interest

Hybridoma technology; advancements, clinical significance, and future aspects

BACKGROUND

Hybridoma technology is one of the most common methods used to produce monoclonal antibodies. In this process, antibody-producing B lymphocytes are isolated from mice after immunizing the mice with specific antigen and are fused with immortal myeloma cell lines to form hybrid cells, called hybridoma cell lines. These hybridoma cells are cultured in a lab to produce monoclonal antibodies, against a specific antigen. This can be achieved by an in vivo or an in vitro method. It is preferred above all the available methods to produce monoclonal antibodies because antibodies thus produced are of high purity and are highly sensitive and specific. Monoclonal antibodies are useful in diagnostic, imaging, and therapeutic purposes and have a very high clinical significance. Once hybridoma cells become stable, these cell lines offer limitless production of homogenized antibodies. This method is also cost-effective. The antibodies produced by this method are highly sensitive and specific to the targeted antigen. It is an important tool used in various fields of research such as in toxicology, animal biotechnology, medicine, pharmacology, cell, and molecular biology. Monoclonal antibodies are used extensively in the diagnosis and therapeutic applications. Radiolabeled monoclonal antibodies are used as probes to detect tumor antigens in the living system; also radioisotope coupled antibodies are used for therapeutic target specific action on oncogenic cells.

SHORT CONCLUSION

Presently, the monoclonal antibodies used are either raised in mice or rats; this poses a risk of disease transfer from mice to humans. There is no guarantee that antibodies thus created are entirely virus-free, despite the purification process. Also, there are some immunogenic responses observed against the antibodies of mice origin. Technologically advanced techniques such as genetic engineering helped in reducing some of these limitations. Advanced methods are under development to make lab-produced monoclonal antibodies as human as possible. This review discusses the advantages and challenges associated with monoclonal antibody production, also enlightens the advancement, clinical significance, and future aspects of this technique.

Molecular organization of recombinant human-Arabidopsis chromosomes in hybrid cell lines

Although plants and animals are evolutionarily distant, the structure and function of their chromosomes are largely conserved. This allowed the establishment of a human-Arabidopsis hybrid cell line in which a neo-chromosome was formed by insertion of segments of Arabidopsis chromosomes into human chromosome 15. We used this unique system to investigate how the introgressed part of a plant genome was maintained in human genetic background. The analysis of the neo-chromosome in 60- and 300-day-old cell cultures by next-generation sequencing and molecular cytogenetics suggested its origin by fusion of DNA fragments of different sizes from Arabidopsis chromosomes 2, 3, 4, and 5, which were randomly intermingled rather than joined end-to-end. The neo-chromosome harbored Arabidopsis centromeric repeats and terminal human telomeres. Arabidopsis centromere wasn’t found to be functional. Most of the introgressed Arabidopsis DNA was eliminated during the culture, and the Arabidopsis genome in 300-day-old culture showed significant variation in copy number as compared with the copy number variation in the 60-day-old culture. Amplified Arabidopsis centromere DNA and satellite repeats were localized at particular loci and some fragments were inserted into various positions of human chromosome. Neo-chromosome reorganization and behavior in somatic cell hybrids between the plant and animal kingdoms are discussed.

Techniques to investigate cellular and molecular interactions in the host response to implanted biomaterials

Evaluation of the host response to implanted materials requires systematic, objective investigations of responses at both the cellular and molecular levels. This article explains the basis behind two technologies: antibody and molecular techniques, which will give valuable information when applied to investigations of cells and molecules involved in the host biomaterial interaction. Such investigations are well underway, and a number of groups are now studying well characterised cell markers or molecules to evaluate the host response to biomaterials. Here we outline current technologies for the development of antibodies as tools to study cell markers or molecules, including those for which reagents are not yet available and DNA based technologies, whose continued application should prove an invaluable adjunct to existing approaches. These technologies may be particularly valuable to investigations focusing on newly characterised cytokines, receptors or cell adhesion molecules and subsequently provide a way forward for the production of advanced biomaterials.

Hybridoma screening using an amplified fluorescence microassay to quantify immunoglobulin concentration

The early identification of antibody-secreting hybridomas significantly reduces the time and resources devoted to unproductive colonies. To quantify the immunoglobulin concentration in hybridoma supernatants within 2 weeks of fusion, we used immunomagnetic microspheres to capture immunoglobulin in the hybridoma culture supernatant. The captured immunoglobulin was detected using a goat anti-mouse second antibody liked to beta-galactosidase. With data transformation to correct for the nonlinear accumulation of the fluorescent reaction product, the enzymatic hydrolysis of fluorescein digalactoside permitted the reliable detection of less than 10 pg of immunoglobulin per milliliter. To determine the value of quantifying immunoglobulin concentration within 2 weeks of fusion, the amplified fluorescence microassay was applied to the evaluation of 3 consecutive fusions and more than 1200 growing hybridoma colonies. Using antibody concentrations greater than 10 ng/ml as a threshold for routine subculture, the selection of hybridoma colonies based on antibody secretion was threefold more efficient than selection based on colony growth alone. These results suggest the utility of the early determination of immunoglobulin concentration in the selection of hybridoma colonies.

Multiparametric analyses of hybridoma growth on glass cylinders in a packed-bed bioreactor system with internal aeration. Serum-supplemented and serum-free media comparison for MAb production

Monoclonal antibodies are one of the most important products of biotechnology and laboratories and companies all over the world are pursuing their large-scale production. Herein we report a protocol for hybridoma cell cultivation over small glass cylinders inside a 3 liter bioreactor vessel which leads to the production and purification--in order of grams--of one MAb intended for human therapeutic use. This protocol proved to be simple, reproducible and cost effective. Three trials are reported: the first two using conventionally serum-supplemented medium culture and producing 3.15 and 2.1 g of purified MAb in 30 and 21 days respectively, and the third one using serum-free medium culture and producing 6 g of purified MAb in 36 days. We have ascertained the stability of the hybridoma by its cloning directly in serum-free medium. The downstream processing of the serum-free trial was done in a single step, concentrating large volumes of supernatant while simultaneously purifying the antibody.

Semi-preparative purification and validation of monoclonal antibodies for immunotherapy in mice

A number of rat hybridomas were adapted to grow in RPMI containing either 5% IgG-depleted FCS or 1% serum-free Nutridoma. Alternatively, protein-free Ultradoma PF was used. Growth in these media allowed purification procedures to be used that are based on tangential ultrafiltration in combination with affinity chromatography on gels linked to protein G or anti-rat L chain coupled antibodies. The isolated antibody preparations were found to be pure and to consist of monomeric intact IgG. The yield and recovery of mAb using this procedure were found to be consistently high. These antibody preparations were analyzed for endotoxin contamination. Whereas during isolation endotoxin contamination increased, the endotoxin content per mg purified protein did not. Affinity chromatography on Detoxi-gel resulted in the efficient removal of this contamination and using this protocol the antibody preparations obtained were found to be of sufficient purity, activity and low endotoxin content to permit their in vivo use in animal models of immunotherapy.

Enhancement of the attachment on microcarriers and tPA production by fibroblast cells in a serum-free medium by the addition of the extracts of Centella asiatica

The addition of ethanol extracts of Centella asiatica showed a remarkable enhancement of fibroblast cells attachment to Cytodex beads in serum-free (SF) medium. It also improves tPA production in both batch and perfusion cultivations. The optimal concentration for SF medium was determined as 2 ppm of the extracts when using Cytodex III. In batch cultivation a high specific tPA production rate was obtained, compared to that from 5% FBS containing medium. However, a fast specific growth rate was observed in 5% FBS medium. In perfusion cultivation a reasonably good cell density and tPA production was achieved at a perfusion rate of 2.4 x 10(6) (viable cell/ml) and 0.65 (micrograms/ml), respectively at 22 ml/min.

Ganglioside alterations in YAC-1 cells cultivated in serum-supplemented and serum-free growth medium

Gangliosides of the 'GM1b-pathway' (GM1b and GalNAc-GM1b) have been found to be highly expressed by the mouse T lymphoma YAC-1 grown in serum-supplemented medium, whereas GM2 and GM1 ('GM1a-pathway') occurred only in low amounts [Müthing, J., Peter-Katalinić, J., Hanisch, F.-G., Neumann, U. (1991) Glycoconjugate J 8:414-23]. Considerable differences in the ganglioside composition of YAC-1 cells grown in serum-supplemented and in well defined serum-free medium were observed. After transfer of the cells from serum-supplemented medium (RPMI 1640 with 10% fetal calf serum) to serum-free medium (RPMI 1640 with well defined supplements), GM1b and GalNAc-GM1b decreased and only low amounts of these gangliosides could be detected in serum-free growing cells. The expression of GM1a was also diminished but not as strongly as that of GM1b and GalNAc-GM1b. These growth medium mediated ganglioside alterations were reversible, and the original ganglioside expression was achieved by readaptation of serum-free growing cells to the initial serum-supplemented medium. On the other hand, a 'new' ganglioside, supposed to represent GalNAc-GD1a and not expressed by serum-supplemented growing cells, was induced during serum-free cultivation, and increased strongly after readaptation. These observations reveal that the ganglioside composition of in vitro cultivated cells can be modified by the extracellular environment due to different supplementation of the basal growth medium.

Influence of somatic cell hybridization and human serum on the generation and stability of human hybridomas

We describe an approach that allows the generation of stable hybridomas secreting antigen specific human IgG antibodies with an efficiency comparable to that of the generation of IgM and IgA secreting hybridomas. This was achieved by evaluating means to increase the frequency of human hybridoma formation and the stability of the generated hybridoma cells when subjected to conditions for large scale growth. To this end, we generated new fusion lines with an increased human DNA content and modified the culture system. However, the application of these new fusion lines primarily resulted in unstable giant cells. As a consequence, we evaluated whether the viability of newly formed hybrids between existing fusion lines and lymphoblastoid cell lines might be improved. In an attempt to provide as many components necessary for the growth of antibody secreting hybridomas as possible, we propagated fused cells in medium supplemented with human serum. Our results show that with this approach the frequency of initially growing hybrids was significantly increased. Furthermore, only in culture medium supplemented with human serum was it possible to obtain stable IgG secreting clones.

Tumour-associated antigens of mammary carcinomas recognized by human monoclonal antibody 1G12

We have reported the production of human monoclonal antibodies (mAb), by the fusion of lymph node lymphocytes from a primary carcinoma patient with murine myeloma cells. Seven heterohybridomas showed reactivity with class III antigens, and five hybridomas (1G12, 2D4, 4H5, 5D10 and 3B10) were reactive with class II antigens. One of these human mAbs (1G12) was intensively studied and results are presented here. 1G12 reacted strongly and specifically with five mammary carcinoma cell lines and showed no cross-reactivity with seven normal fibroblast cells. It continuously produced human mAbs (IgM) at a rate of 4.5-12.5 micrograms/ml over a period of 2 years. Human mAb 1G12 (IgM) was purified by either a combination of anion-exchange chromatography (ABx) and gel filtration (Superose 6) or affinity chromatography (agarose). Immunohistological analysis of frozen tissue sections was performed with biotinylated 1G12. All mammary carcinomas analysed (n = 26) were positive, while the connective tissue of 36 different patients was completely negative with 1G12. In normal breast, endometrium and intestine only a weak or moderate staining of the epithelial cells was observed. Normal oesophagus, small bowel, cervix, uterus, lung and skin were completely negative. Partly purified tumour antigen recognized by 1G12 had a molecular mass of 1-2 MDa and showed strong binding with Ulex europaeus lectin I and Bauhina purpurea agglutinin, indicative for the glucoprotein nature of antigens. These results show that human mAb 1G12 may be useful for the analysis of tumour-associated antigen of mammary carcinoma patients. In further studies the therapeutic and diagnostic application of 1G12 should be analysed in more detail.

Preferential generation of monoclonal IgG-producing hybridomas by use of vesicular stomatitis virus-mediated cell fusion

Vesicular stomatitis virus (VSV)-mediated cell fusion was recently proposed as an alternative fusion technique to generate monoclonal antibody (MAb)-producing hybridomas. In order to further examine this technique, we made direct comparative experiments among VSV, Sendai virus (SV) and polyethylene glycol (PEG)-mediated cell fusion in generating MAb-producing hybridomas. The distribution of immunoglobulin (Ig) isotypes secreted by the hybridomas obtained, as well as hybridoma yield and specific hybridoma yield, was compared. The results show that VSV-fusion yielded almost the same number of specific hybridomas as SV- and PEG-fusion in spite of its lower fusion frequency. In addition, VSV-fusion preferentially gave Ig-producing, especially IgG-producing, hybridomas. SV-fusion yielded both hybridomas and specific hybridomas with similar frequency to PEG-fusion, but IgM-producers predominated. These results demonstrate that fusion method has a considerable influence on the isotypes of obtained antibodies, and also suggest an advantage of VSV-fusion for production of IgG monoclonal antibodies.

Optimization of growth and secretion of human monoclonal antibodies by hybridomas cultured in serum-free media

To facilitate the production and purification of human monoclonal antibodies, we evaluated the ability of human hybridomas to adapt to chemically defined-serum free media. From a panel of human hybridomas secreting antibody against serotype specific lipopolysaccharide determinants of gram-negative bacteria, the growth and secretion properties of the two hybridomas producing antibodies against two strains of Pseudomonas aeruginosa, 4-8KH15 and 4-10KH139, were analysed. Both clones did not grow in protein-free medium. However, it was possible to adapt them to serum-free media consisting of a basal medium supplemented with insulin, transferrin, ethanolamine, and selenite. Antibody secretion rates were equal (4-8KH15: 26-31 micrograms IgM/10(6) cells/day) or higher (4-10KH139: 58-90 micrograms IgM/10(6) cells/day) in serum-free media as compared to conventional serum-supplemented medium. Our studies suggest that adaptation of the described hybridomas to selected serum-free media results in an antibody production which is very high as compared with reports in comparable systems. The establishment of these conditions will significantly facilitate the production of large amounts of human monoclonal antibodies which is a prerequisite for a therapeutical application.

Production of human monoclonal antibodies in dialysis tubing

Human x mouse hybridoma cells were grown in dialysis tubing (DT) to obtain large quantities of human monoclonal antibodies (MAb). Hybridoma cells were grown inside the DT, which was placed in a tissue culture flask containing medium. The medium inside the DT was supplemented with different additives which may be selected depending on the intended use of the MAb. About 10-50 times higher concentrations of immunoglobulin (Ig) were obtained after cultivation in DT compared to conventional tissue culture (CTC) for 2 days. The purity of the MAb was high which facilitated further antibody purification. Production of human MAb in DT proved to be excellent for evaluation studies in laboratory scale. It does not require expensive equipment and several hybridomas can be grown simultaneously.

Production of monoclonal antibodies by the use of pH-dependent vesicular stomatitis virus-mediated cell fusion

To explore an alternative fusion method to generate monoclonal antibody (MAb)-producing hybridomas, we have tested whether pH-dependent vesicular stomatitis virus (VSV)-mediated cell fusion is applicable for generation of hybridomas. VSV-mediated cell fusion induced by acid treatment resulted in several specific MAb-producing hybridomas, almost all of which stably produced MAbs. This method is quite simple and offers a potential alternative to other fusion methods. In addition, the fusogenic proteoliposomes prepared by the reconstitution of the solubilized glycoprotein of VSV were also demonstrated to have the ability to generate MAb-producing hybridomas by the same pH-dependent cell fusion.

Methods for increasing monoclonal antibody production in suspension and entrapped cell cultures: biochemical and flow cytometric analysis as a function of medium serum content

The growth and antibody production of the SP2/0-derived hybridoma HB124 (ATCC) grown in media containing varying amounts of fetal bovine serum (FBS) were monitored using biochemical and flow cytometric methods. Hybridomas grown in 100 ml spinner flasks with RPMI-1640 containing varying amounts of serum demonstrated that cell growth, viability and IgG production show significant changes when serum content is decreased from 10.0 to 5.5 to 1.0 and 0.5%. A longer lag phase resulted when the lower serum content media were used. Cellular rates of glucose uptake showed a significant increase as serum levels were lowered. Similarly, exponential phase IgG production rates increased as the amount of serum was decreased, probably as a result of the decreased rate of exponential growth. Flow cytometric analysis showed a similar increase in cellular IgG content as medium serum levels declined. In contrast, the maximum IgG concentrations were found in flasks containing 1% FBS or above with the lowest concentration in the 0.5% FBS flask being due to the lower numbers of viable cells. Cells grown in microporous hollow fiber reactors were fed with medium containing serum which was decreased stepwise with time. Decreasing medium serum content stepwise from 10 to 2.5% resulted in increased antibody production. However, complete removal of serum from the medium resulted in a significant drop in antibody productivity. Cumulative antibody production was equivalent for cells grown entirely in medium containing 10% FBS and for those which experienced a drop to 2.5% FBS. To compare a defined serum-free medium preparation with medium containing 10% FBS, cells were again grown in batch suspension culture and analyzed. The growth rates were similar but there was a significant difference in IgG production rates. The serum-free culture exhibited both higher cellular production rates and higher IgG concentrations. These results indicate that decreasing medium serum content can adversely affect antibody yield because of lower cell viabilities, not because of lower production rates. Use of a defined serum-free medium, as done in this study, results in higher yields because of a higher IgG production rate as well as good cell growth and viability.

Selective cloning of hybridoma cells for enhanced immunoglobulin production using flow cytometric cell sorting and automated laser nephelometry

Techniques for selective cloning of murine hybridoma cells by flow cytometric cell sorting and use of automated laser nephelometry to determine the resultant clones' immunoglobulin secretion levels are described. Using a commercially available attachment to a fluorescence-activated cell sorter, individual hybridoma cells were successfully distributed into microtiter wells in an automated manner based on their forward angle light scatter properties and their reaction to fluorescein-conjugated anti-mouse-IgG. The techniques were used to estimate successfully the frequency of immunoglobulin-secreting cells in established cultures. In addition, heterogeneity of cell surface immunoglobulin expression was observed and utilized as a criterion for flow sorting of new hybridoma variants. In these studies, clones derived from high (anti-IgG) intensity sorting regions yielded cultures with enhanced immunoglobulin secretion levels, as determined by automated laser nephelometry. Furthermore, the surface immunoglobulin phenotype of the derived clones was conserved in subsequent progeny. Finally, it was established that inclusion of propidium iodide in the hybridoma cell sorting mixtures improved cloning efficiency by facilitating enhanced discrimination and elimination of nonviable cells. Our results indicate that flow cytometric-assisted single cell deposition provides positive attributes of several traditional hybridoma cloning techniques and, in addition, furnishes a tool for steering the cloning process toward selection of enhanced immunoglobulin producing cultures.

In vitro stimulation of nonimmunized, naturally infected rat spleen cells for the production of Mycoplasma pulmonis-specific monoclonal antibodies

Spleen cells derived from rats naturally-infected with Mycoplasma pulmonis were stimulated in vitro, and then fused with a mouse myeloma cell line. The resulting hybridomas were screened for mycoplasma-specific Mabs by ELISA and for hemolysis-blocking activities. Fusions performed with in vitro-treated spleen cells yielded larger numbers of growth-positive wells and antibody secreting cells than untreated spleen cells from the same animals. Hybridomas derived from naturally-infected animals gave a higher percentage of hemolysin-specific monoclonal antibodies than did hyperimmunized animals. This indicated that B cell priming during mucosal infections can produce antigen-primed spleen cells. Stimulation of these cells in vitro can result in monoclonal antibodies against antigens not normally recognized during immunization with in vitro grown pathogenic bacteria.

Localization and immunogenicity of tubulin in the filarial nematodes Brugia malayi and B. pahangi

Tubulin was identified in the filarial nematodes Brugia malayi and B. pahangi by several approaches. Initially, a monoclonal antibody (6D8) was selected for its unusual binding to B. malayi microfilariae in indirect immunofluorescence assays: 6D8 showed granular, heterogeneously dispersed fluorescence on fixed parasites but did not bind to unfixed microfilariae. The microfilarial sheath did not bind 6D8, although it did bind fluoresceinated wheatgerm agglutinin. By Western blotting against microfilarial sonicate, 6D8 reacted with a 50,000-55,000 mol. wt protein, and also bound to purified chicken brain beta-tubulin. Additionally, this monoclonal antibody reacted with a recombinant fusion protein expressed by a clone (Bpa-7) originally isolated from an adult B. pahangi cDNA expression library by its reaction with chronic human filariasis serum. This clone encodes a small 40 amino acid C-terminal segment corresponding to residues 409-449 of beta-tubulin, and shows complete amino acid sequence homology with vertebrate beta-tubulin from 409 to 430 but 55% divergence (six amino acid substitutions, four insertions and one deletion) from human and chicken beta-tubulin over positions 431-449 at the C terminus. Antibody to both parasite and vertebrate (chicken) tubulin was found in filarial infection sera, with higher levels of autoreactive antibody apparent in amicrofilaraemic individuals. Immunogold electron microscopy was then used to localize beta-tubulin in B. malayi microfilariae and adult worms. Tubulin was shown not to be exposed on the microfilarial sheath or in the cuticle of either stage, but was found to be abundant in the somatic tissues. In microfilariae, 6D8 bound myofibril structures under the hypodermal layer, and also bound within cell nuclei. In the adult stage, tubulin was associated with muscle blocks, as well as the intestinal brush border and the embryonic uterine microfilariae.

Human monoclonal antibody against glycoproteins of human immunodeficiency virus

We have established a program to make human monoclonal antibodies to the human immunodeficiency virus (HIV). Lymphocytes of lymph nodes from patients with the acquired immunodeficiency syndrome (AIDS) related complex (ARC) spontaneously produced antibodies to HIV in vitro and their antibody production was suppressed by culturing them in the presence of HIV antigens. Therefore, in vitro stimulation with HIV antigens was not done but rather, donor lymph node or spleen lymphocytes were directly fused with mouse myeloma cells. One of the hybridomas thus generated has been stably producing human monoclonal antibody (MAb) of the IgG1 isotype with a kappa chain. This antibody, MAb86, bound to the surface membrane of HIV-infected cells but not to that of uninfected cells at all. MAb86 reacted in Western blot with both viral glycoproteins of 120,000 daltons (gp120) and 41,000 daltons (gp41). While not neutralizing alone, a combination of MAb86 with another human IgG1 MAb against gp120 showed viral neutralization. Based on these data it seems likely that this approach will result in human MAbs capable of viral neutralization and antibody-dependent cytotoxicity. These may have value for the prevention and/or treatment of AIDS.