The influence of murine macrophage-conditioned medium on cloning efficiency, antibody synthesis, and growth rate of hybridomas

Production of Antibodies to Peptide Targets Using Hybridoma Technology

Hybridoma technology is a well-established and indispensable tool for generating high-quality monoclonal antibodies and has become one of the most common methods for monoclonal antibody production. In this process, antibody-producing B cells are isolated from mice following immunization of mice with a specific immunogen and fused with an immortal myeloma cell line to form antibody-producing hybridoma cell lines. Hybridoma-derived monoclonal antibodies not only serve as powerful research and diagnostic reagents but have also emerged as the most rapidly expanding class of therapeutic biologicals. In spite of the development of new high-throughput monoclonal antibody generation technologies, hybridoma technology still is applied for antibody production due to its ability to preserve innate functions of immune cells and to preserve natural cognate antibody paring information. In this chapter, an overview of hybridoma technology and the laboratory procedures used for hybridoma production and antibody screening of peptide-specific antibodies are presented.

Investigation of the immunogenicity of Zika glycan loop

Background

Zika virus (ZIKV) is a major human pathogen and member of the Flavivirus genus. Previous studies have identified neutralizing antibodies from Zika patients that bind to quaternary epitopes across neighboring envelope (E) proteins, called E dimer epitopes (EDE). An asparagine-linked glycan on the “glycan loop” (GL) of the ZIKV envelope protein protects the functionally important “fusion loop” on the opposite E subunit in the dimer, and EDE antibodies have been shown to bind to both of these loops. Human EDE antibodies have been divided into two subclasses based on how they bind to the glycan loop region: EDE1 antibodies do not require glycosylation for binding, while EDE2 antibodies strongly rely on the glycan for binding.

Methods

ZIKV GL was expressed on tobacco mosaic virus nanoparticles. Mice were immunized with GL or full-length monomeric E and the immune response was analyzed by testing the ability of sera and monoclonal antibodies to bind to GL and to neutralize ZIKV in in vitro cellular assay.

Results

We report here the existence of ZIKV moderately neutralizing antibodies that bind to E monomers through epitopes that include the glycan loop. We show that sera from human Zika patients contain antibodies capable of binding to the unglycosylated glycan loop in the absence of the rest of the envelope protein. Furthermore, mice were inoculated with recombinant E monomers and produced neutralizing antibodies that either recognize unglycosylated glycan loop or require glycan for their binding to monomeric E. We demonstrate that both types of antibodies neutralize ZIKV to some extent in a cellular virus neutralization assay.

Conclusions

Analogous to the existing EDE antibody nomenclature, we propose a new classification for antibodies that bind to E monomer epitopes (EME): EME1 and EME2 for those that do not require and those that do require glycan for binding to E, respectively.

A Bioassay for Optimization of Macrophage-Conditioned Medium as a Culture Supplement to Promote Hybridoma Cell Survival and Growth

Macrophage-conditioned medium (MCM) is an important cell culture supplement used to support the survival and growth of newly fused hybridoma cells. The use of macrophage cells, as a part of hybridoma technology, has proven to be an effective and inexpensive source of growth factors that promote the early survival and growth of hybridoma cells. Despite the widespread use of MCM as a hybridoma culture supplement, there is limited guidance and standardization for MCM production to achieve optimal hybridoma support. As an undefined supplement, significant variations in production of MCM may negatively impact hybridoma cell survival and growth. The lack of an available method for standardization of MCM bioactivity has limited validation, optimization, and commercial production. Consequently, variations in batch production of MCM may result in low-quality MCM that limits hybridoma viability and negatively impacts monoclonal antibody production. In this report, we describe a novel bioassay based on the newly generated, MCM-dependent RMH359 hybridoma cell line that can be used to validate MCM bioactivity and standardize production. We demonstrate the utility of the RMH359 bioassay (1) for evaluating MCM hybridoma bioactivity, (2) to define optimal conditions for production of MCM, and (3) as a method for MCM validation and standardization. In conclusion, the RMH359 cell bioassay provides a specific and sensitive assessment of MCM bioactivity in support of hybridoma cell survival and growth.

Production and Screening of Monoclonal Peptide Antibodies

Hybridoma technology is a remarkable and indispensable tool for generating high-quality monoclonal antibodies. Hybridoma-derived monoclonal antibodies not only serve as powerful research and diagnostic reagents, but have also emerged as the most rapidly expanding class of therapeutic biologicals. In this chapter, an overview of hybridoma technology and the laboratory procedures used routinely for hybridoma production and antibody screening are presented, including characterization of peptide antibodies.

Development of monoclonal antibodies and immunoassays for sensitive and specific detection of Shiga toxin Stx2f

Background

Shiga toxin 2 (Stx2) is a major virulence factor in gastrointestinal diseases caused by Escherichia coli. Although Stx2a (prototypical Stx2) is well-studied, all seven subtypes of Stx2 have been associated with disease in mammals. Several subtypes of Stx2, including Stx2f, are difficult to detect immunologically.

Methods And Findings

Four novel monoclonal antibodies (mAbs) against the Stx2f subtype were produced and characterized. These mAbs react exclusively to the Stx2f A subunit, and do not cross-react with other subtypes of Stx2. A Stx2f-specific sandwich ELISA was established and a limit of detection of 0.123 ng/mL was obtained using one pair of the mAbs. The receptor preference of Stx2f was confirmed using this sandwich ELISA. Three out of four mAbs can partially neutralize the toxicity of Stx2f in a cell-based assay. These mAbs were also demonstrated to be highly specific and reactive when applied to colony immunoblot assays.

Conclusions

Novel mAbs specific to Stx2f were developed for the first time, providing new assets for the STEC community. Immunoassays with improved sensitivity and specificity will be useful for the detection of Stx2f present in food, environmental, and clinical samples.

Development and characterization of monoclonal antibodies against Shiga toxin 2 and their application for toxin detection in milk

Human infection by Shiga toxin producing Escherichia coli (STEC) is one of the most prevalent foodborne diseases. Shiga toxin type 2 (Stx2) is the major contributor to hemolytic-uremic syndrome (HUS) and other systemic complications caused by STEC. Although outbreaks of HUS due to the consumption of dairy products occur frequently, very few reports are available on assays for the detection of Stx2 in milk. In this study, we describe the development of five high-affinity monoclonal antibodies (dissociation constants below nM range) against Stx2 using a recombinant toxoid as an immunogen. These antibodies, designated Stx2-1, Stx2-2, Stx2-3, Stx2-4, and Stx2-5 are IgG1 or IgG2a heavy-chain subclass with kappa light-chains, did not cross-react with Stx1 and showed different preferences to variants of Stx2. Western blot analyses demonstrate that mAbs Stx2-2 and Stx2-5 bind both the A- and B-subunits, whereas the other 3 mAbs bind the A-subunit of Stx2a only. All antibodies bound stronger to the native than to the denatured Stx2a except the mAb Stx2-3, which bound equally well to both forms of the toxin. Of the five mAbs, Stx2-5 was capable of neutralizing Stx2a mediated cytotoxicity in Vero cells. Highly sensitive ELISA and immuno-PCR assays, capable of detecting 1 and 0.01 pg/mL of Stx2a in milk, were developed using mAb pair Stx2-1 and Stx2-2. Such assays are useful for routine diagnosis of Stx2 contamination in milk production process, thus reducing the risk of STEC outbreaks.

CB.Hep-1 hybridoma growth and antibody production using protein-free medium in a hollow fiber bioreactor

The protein-free medium TurboDoma HP.1 (THP.1) was used to produce the CB.Hep-1 monoclonal antibody (mAb) in a CP-1000 hollow fiber bioreactor (HFB). This mAb is used for the immunopurification of recombinant hepatitis B surface antigen (rHBsAg), which is included in a vaccine preparation against the Hepatitis B Virus. By using the experimental conditions tested in this work we were able to generate more than 433 mg of IgG in 43 days. The maximum antibody concentration obtained was about 2.4 mg ml(-1)and the IgG production per day was approximately 11 mg of monoclonal antibody, which constitutes a good concentration value in comparison to the results obtained in ascitic fluid, where concentration for this hybridoma was around 3 mg ml(-1). We used different analytical methods to control the quality of mAbs, obtained from the in vitro system. They included affinity constant determination, analysis of N-glycan structures, immunoaffinity chromatography and antigen binding properties. The results obtained suggest that no significant changes occurred in the mean characteristics of the mAb harvested from the bioreactor during the 43 days of cultivation.

Francisella tularensis infection-derived monoclonal antibodies provide detection, protection, and therapy

Francisella tularensis is the causative agent of tularemia and a potential agent of biowarfare. As an easily transmissible infectious agent, rapid detection and treatment are necessary to provide a positive clinical outcome. As an agent of biowarfare, there is an additional need to prevent infection. We made monoclonal antibodies to the F. tularensis subsp. holarctica live vaccine strain (F. tularensis LVS) by infecting mice with a sublethal dose of bacteria and, following recovery, by boosting the mice with sonicated organisms. The response to the initial and primary infection was restricted to immunoglobulin M antibody directed solely against lipopolysaccharide (LPS). After boosting with sonicated organisms, the specificity repertoire broadened against protein antigens, including DnaK, LpnA, FopA, bacterioferritin, the 50S ribosomal protein L7/L12, and metabolic enzymes. These monoclonal antibodies detect F. tularensis LVS by routine immunoassays, including enzyme-linked immunosorbent assay, Western blot analysis, and immunofluorescence. The ability of the antibodies to protect mice from intradermal infection, both prophylactically and therapeutically, was examined. An antibody to LPS which provides complete protection from infection with F. tularensis LVS and partial protection from infection with F. tularensis subsp. tularensis strain SchuS4 was identified. There was no bacteremia and reduced organ burden within the first 24 h when mice were protected from F. tularensis LVS infection with the anti-LPS antibody. No antibody that provided complete protection when administered therapeutically was identified; however, passive transfer of antibodies against LPS, FopA, and LpnA resulted in 40 to 50% survival of mice infected with F. tularensis LVS.

Development and partial characterization of high-affinity monoclonal antibodies for botulinum toxin type A and their use in analysis of milk by sandwich ELISA

Botulinum neurotoxins (BoNT), produced by the anaerobic bacterium Clostridium botulinum, cause severe neuroparalytic disease and are considered the most toxic biological agents known. While botulism is rare in the U.S. it often is fatal if not treated quickly, and recovery is long, requiring intensive treatment. BoNT is synthesized as a 150 kDa precursor protein (holotoxin), which is then enzymatically cleaved to form two subunit chains linked by a single disulfide bond. The 'gold standard' for BoNT detection relies on a mouse bioassay. This is a time consuming (up to 4 days) assay and it lacks specificity, however, it gives a sensitivity (mouse LD(50)) of approximately 10 pg mL(-1). Most BoNT immunoassays are much less sensitive. In this study we describe the development of four high-affinity (dissociation constants (Kd's) in the low pM range) monoclonal antibodies (mAbs) that specifically bind BoNT serotype A (BoNT/A). These antibodies, designated F1-2, F1-5, F1-40, and F2-43 are IgG1 subclass mAbs with kappa light chains and they specifically bind BoNT serotype A. Western blot analyses following SDS-PAGE demonstrate that mAbs F1-2 and F1-5 bind the 100 kDa heavy chain subunit and that mAb F1-40 binds the 50 kDa light chain. The fourth antibody demonstrated strong binding to the 150 kDa holotoxin in the ELISA and on Western blots following electrophoresis on native gels. However binding in Western blot studies was not observed for mAb F2-43 following SDS-PAGE. A highly sensitive sandwich ELISA, capable of detecting as little as 2 pg/mL BoNT/A was developed using mAbs F1-2 and F1-40. Such an assay represents a realistic, high sensitivity alternative to the mouse bioassay.

Biological activity of recombinant chicken interleukin-6 in chicken hybridoma cells

Interleukin-6 (IL-6), a multipotential cytokine that plays roles in regulating immune responses, acute phase reactions and hematopoiesis, induces proliferation and antibody production in hybridoma cells. The biological activities of the recombinant chicken IL-6 (rchIL-6) were determined using murine and chicken hybridoma cells. Cell proliferation and tyrosine phosphorylation of signal transducer and activator of transcription-3 (STAT3) were induced by rchIL-6 in the IL-6-dependent murine hybridoma cell line MH60, whereas the recombinant protein exhibited no significant cell proliferation activity in chicken hybridoma cells but induced antibody production and tyrosine phosphorylation of STAT3. The lack of cell proliferation induced by rchIL-6 in HUC2-13 cells may have been because the cell line was not IL-6-dependent in contrast to MH60 cells. These results suggest that rchIL-6 may be useful for promoting antibody production of chicken hybridoma cells as well as for creating chicken hybridomas by cell fusion.

LcrV capture enzyme-linked immunosorbent assay for detection of Yersinia pestis from human samples

In the United States, there is currently a major gap in the diagnostic capabilities with regard to plague. To address this, we developed an antigen capture assay using an essential virulence factor secreted by Yersinia spp., LcrV, as the target antigen. We generated anti-LcrV monoclonal antibodies (MAbs) and screened them for the ability to bind bacterially secreted native Yersinia pestis LcrV. Anti-LcrV MAb 19.31 was used as a capture antibody, and biotinylated MAb 40.1 was used for detection. The detection limit of this highly sensitive Yersinia LcrV capture enzyme-linked immunosorbent assay is 0.1 ng/ml. The assay detected LcrV from human sputum and blood samples treated with concentrations as low as 0.5 ng/ml of bacterially secreted native Y. pestis LcrV. This assay could be used as a tool to help confirm the diagnosis of plague in patients presenting with pneumonia.

Human DNA polymerase epsilon colocalizes with proliferating cell nuclear antigen and DNA replication late, but not early, in S phase

DNA polymerase epsilon (pol epsilon) has been implicated in DNA replication, DNA repair, and cell cycle control, but its precise roles are unclear. When the subcellular localization of human pol epsilon was examined by indirect immunofluorescence, pol epsilon appeared in discrete nuclear foci that colocalized with proliferating cell nuclear antigen (PCNA) foci and sites of DNA synthesis only late in S phase. Early in S phase, pol epsilon foci were adjacent to PCNA foci. In contrast to PCNA foci that were only present in S phase, pol epsilon foci were present throughout mitosis and the G(1) phase of cycling cells. It is hypothesized from these observations that pol epsilon and PCNA have separate but associated functions early in S phase and that pol epsilon participates with PCNA in DNA replication late in S phase.

Differential effect of estradiol on antibody secretion of murine hybridomas

The need for increased antibody production by hybridomas has been approached by the addition to cell cultures of different growth factors; in vitro addition of estradiol-17beta (E2) to human blood lymphocytes increases the accumulation of plasma-blasts and Ig-secreting cells. Four different murine-murine hybridomas secreting different monoclonal antibodies (MAbs) were treated with E2. Specific antibody concentration was measured by enzyme-linked immunoadsorbent assay (ELISA) in culture supernatants whereas expression of E2-receptor in the hybridoma cells was determined by polymerase chain reaction (PCR). When E2 was added as a growth supplement to alpha-estrogen receptor positive murine-murine hybridomas it enhanced MAb secretion by as much as 255%, in a dose-dependant manner. This effect lasted for as long as the alpha-estrogen receptor was detected in the hybridoma cells, was inhibited by tamoxifen and was not observed in alpha-estrogen receptor negative hybridomas. The synthetic estrogen analogue diethylstilbestrol had no effect. Estradiol-17beta should be added to the list of hybridoma-inducing growth factors.

Generation of murine monoclonal antibodies in serum-free medium

Traditional hybridoma fusion technology requires complete medium with serum supplements to support the growth of hybridoma cells. Serum is also required for subcloning of hybridoma cells to support low density cell growth. IL-6 has been shown to enhance the growth of hybridomas and stimulate antibody production by B cells. We found that the serum requirement in media used for generation of hybridomas can be totally eliminated by substituting with 300 units/ml of IL-6. Stable hybridoma cell lines were generated to peptide and protein antigens using serum-free adapted P3.653 myelomas as the fusion partner and medium containing IL-6. Our results indicate that, in general, the fusion efficiencies of serum-free IL-6 supplemented fusions are lower than the fusions employing serum containing media (40%-60% vs. 80%-100%). However, in spite of the lower fusion efficiency, the number of antigen-specific clones generated using IL-6 was equal to or greater than fusions using serum supplements. The use of IL-6 instead of serum in the generation of monoclonal antibodies (MAbs) has several advantages. We are able to eliminate the costly need for serum in media by using IL-6 that is prepared in house. In addition, we eliminate the need for time-consuming serum-free adaptation of hybridoma cell lines prior to transfer to hollow fiber bioreactors.

Differential DNA damage detected in hybridomas

Monoclonal antibody technology has improved over recent years. However, there remains a serious problem with regard to the stability and antibody production of the hybrid cell lines. In order to investigate the potential increased sensitivity of hybridomas to DNA damage, we produced a monoclonal antibody producing cell line in our laboratory. Three types of cells were analyzed by the single cell gel technique to determine single strand DNA damage, including the fusion partner FO, BALB/c splenocytes and an IgM producing hybridoma. The hybridoma cell line displayed a statistically significant increase in sensitivity to induced DNA damage as compared to the fusion partners used in its establishment. The instability of hybridomas in culture may be associated with their inherent increased susceptibility to DNA damage.

Increased frequency of both total and specific monoclonal antibody producing hybridomas using a fusion partner that constitutively expresses recombinant IL-6

The addition of auxiliary feeder cells or conditioned medium has been shown to augment the yield of mouse hybridomas obtained following the cell-cell fusion of myeloma and B lymphocytes. The addition of one of these factors, interleukin-6 (IL-6) has been found to increase the proportion of hybridomas secreting monoclonal antibodies of desired specificity. As an alternative genetic approach, we have examined the efficacy of a retroviral infectant of Sp2/0 cells that constitutively expresses recombinant murine IL-6 (Sp2/mIL-6) as fusion partner. The results demonstrated that the yields of both viable Ig-secreting hybridomas, and antigen-specific monoclonal antibodies were increased 3-15-fold and 5-9-fold, respectively, with the Sp2/mIL-6 relative to Sp2/0 or Sp2/neo cells as fusion partner. Sp2/mIL-6 cells generated hybridomas with comparable growth rates, stability, and Ig production. The results of staining nascent hybridoma colonies immunohistochemically for Ig production suggest that Sp2/mIL-6 cells as a fusion partner increased the viability and/or stability of nascent hybrid cells that are producing Ig. Thus the Sp2/mIL-6 cells are an improved myeloma parent for the generation of large numbers of antibody-producing hybridomas against specific antigens.

Preparation and characterization of monoclonal antibodies against soybean seed lipoxygenase isoenzymes

Sets of monoclonal antibodies have been prepared using two soybean seed lipoxygenase isoenzymes as the antigens. The antibodies were characterized by ELISA, Western blot analysis, immunoprecipitation, and in kinetic assays. Several antibodies displaying selectivity for the two closely related polypeptides were obtained, while the majority of the antibodies generated were crossreactive. Antibodies specific to the native and denatured forms of the two proteins were also obtained. Two of the monospecific antibodies were shown to immunoprecipitate the appropriate isoenzyme selectively from a mixture. When these antibodies were immobilized on agarose, they were successful in the immunoaffinity purification of the individual isoenzymes. In kinetic experiments certain antibodies were found to influence catalysis upon incubation with lipoxygenase. Antibodies which both inhibited and stimulated catalysis were identified.

Protein growth factor(s) from C6 glioma cells that promote the growth of murine hybridomas

C6 glioma cell conditioned medium (C6CM) has been used as a growth supplement for murine hybridomas. At 10% C6CM has been found to increase cell proliferation by 3-4-fold. This effect is observed in the presence of saturating concentration of FCS. Clonal growth is also enhanced 6.7-fold. No growth promoting effect is seen on murine myelomas or spleen cells. The factor(s) appear to be protein in nature.

Characterization of p51/52, a cell-growth regulated protein of WI-38 cells

A number of proteins have been identified whose expression or activity is regulated by cell growth. We have produced a monoclonal antibody against a new cell-growth regulated protein found in normal human fibroblasts. We have shown that this antibody recognizes a 51/52-kDa doublet (p51/52) found mainly in normal cells. This doublet is sensitive to degradation by the calcium-activated protease, calpain, breaking down to a 37/38-kDa doublet. The relative amount of the two members of the 51/52-kDa doublet changes when serum-starved cells reenter the cell cycle. Quiescent cells express mainly the 51-kDa form; the 52-kDa form becomes more abundant upon refeeding serum-starved cells. Transformed cells express either very small amounts of this doublet, and then predominantly the 52-kDa form, or no detectable amount of either form. These characteristics distinguish this molecule from several other known growth-regulated proteins such as statin and the anti-oncogene p53.

Production of a hybridoma cell line secreting retinoic acid-specific monoclonal antibody

A stabilized hybridoma cell line secreting anti-retinoic acid monoclonal antibodies of subclass IgG1 with kappa chains was produced by fusing NS-1 myeloma cells with the spleen cells from BALB/c female mice immunized with all-trans-4-oxoretinoic acid-oxime-chicken IgG conjugate. The antibody titer of mice ascitic fluid ranged from 1/12,800 to 1/25,600, as determined by competitive indirect enzyme-linked immunosorbent assay (ELISA). 50% inhibition dosage of all-trans-retinoic acid at a 1/20,000 dilution of mice ascitic fluid was 6.6 ng/ml, as determined by ELISA. The anti-retinoic acid monoclonal antibody was generated in mice ascitic fluid and purified by protein G affinity chromatography. Cross-reactivity of the monoclonal antibody was determined at 0.1 microgram/ml concentration of retinoids and indicated high specificity to both all-trans-retinoic acid (86% inhibition) and 13-cis-retinoic acid (87% inhibition), and strong cross-reactivity with 4-oxoretinoic acid (77%) and 4-oxoretinoic acid oxime (109%). Specificity was confirmed by the horseradish peroxidase-linked immunostaining method and immunoradioassay. The affinity constant of the monoclonal antibody, K, was determined to be 3.6 X 10(9) l/mol. A calibration curve for retinoic acid using the monoclonal antibody to retinoic acid was developed; the detection limit for all-trans-retinoic acid is 1 ng/ml in the competitive indirect ELISA. The antibody counteracts the effect of retinoic acid on growth inhibition and differentiation in HL-60 cells.

Rapid screening for cell surface binding monoclonal antibodies

A procedure is described which allows for rapid detection of cell surface binding or cytoskeleton binding monoclonal antibodies. At the same time this procedure ensures that selected antibodies will be useful in Western blot analysis. This procedure including the cytochemistry and Western blot analysis requires only 100 microliters of supernatant and can be done directly from the original 96 well plates into which the fusion was plated. One person can easily assay several hundred supernatants in one day for the ability to stain both cells and selected proteins in Western blot analysis.

Catenin association with E-cadherin changes with the state of polarity of HT-29 cells

Cadherins are transmembrane glycoproteins that mediate the calcium-dependent adhesion of cells to one another. It has been reported that at least two and probably more proteins associate with cadherins in various systems. These proteins have been called catenins. HT-29 cells can be manipulated to express either a polar or a nonpolar phenotype, depending on the growth conditions. We have taken advantage of this feature of HT-29 cells to explore the role catenins may play in cadherin-mediated adhesion. In this paper we report that several catenins co-immune-precipitate with E-cadherin in cultured human cells (HT-29 and JAR PR497) and that the nature of the complex of proteins varies with the physiological state of the HT-29 cells. In addition, we show data suggesting that the proteins that associate with calcium-dependent adhesion molecules may represent a group of proteins, some of which are present in all cells and some of which are cell-type specific.

Fluorescein-specific hybridomas derived from primary mice exhibit more stringent growth requirements than do hybrids from pre-immune animals

Although the generation of antigen-specific hybridoma cell lines from animals which have been multiply immunized is now a routine procedure, the derivation of hybridomas following a single in vivo antigen injection has proven to be much more difficult to accomplish. We show that the addition of an interleukin-containing supernatant derived from rat spleen cells which have been stimulated with concanavalin A (ConA SN) to hybrids after the initial cloning step results in the consistently successful isolation of IgM anti-fluorescein specific hybridomas. However, addition of the same supernatant to fused cultures simultaneously with the addition of the HAT selection medium results in the loss growing cells. In contrast to the situation with primary hybridomas, the growth of secondary hybridomas is inhibited by the addition of ConA SN at the cloning step. Following successful cloning, there is a time-dependent variation in the sensitivity of all cell lines to ConA SN.

Development of a monoclonal antibody for use as an amboceptor in complement fixation tests

A monoclonal antibody for use as a haemolytic amboceptor in complement fixation tests was developed. The monoclonal antibody selected was investigated in parallel with conventional rabbit amboceptor. The results with the monoclonal amboceptor were at least as good as with the rabbit amboceptor. Production of the monoclonal amboceptor was attained provided that hybridoma growth factor was added to the culture medium.

Increased proportion of B cell hybridomas secreting monoclonal antibodies of desired specificity in cultures containing macrophage-derived hybridoma growth factor (IL-6)

The addition of macrophage feeder cells or conditioned medium has been shown to increase the yield of murine hybridomas obtained after the fusion of myeloma cells and activated B lymphocytes. It has been shown recently that the conditioned medium contains a growth factor (HGF) active on newly formed hybridomas and that the human HGF is similar to B cell stimulatory factor 2 which can induce the synthesis of antibodies in transformed B cells. We have compared in several fusion experiments the stimulatory effects of HGF both on the yield of hybridomas and on the number of antibody-secreting hybridomas. The results obtained clearly showed that while the stimulatory effect of HGF on the yield of growth-positive wells was variable and sometimes barely detectable, the proportion of growth-positive wells containing monoclonal antibodies was consistently much higher in the HGF-containing cultures. These results suggest that the majority of the antibody-secreting newly formed hybridomas are sensitive to HGF and indicate that HGF is a very useful culture supplement for the generation of a high number of antibody-producing hybridomas even if it may not increase significantly the yield of viable hybridomas.

Mitomycin C-treated 3T3/B (3T3/A31) cell feeder layers in hybridoma technology

Several methods were compared for their efficiency at supporting the growth of hybridoma cells at low cell densities. Soluble growth factors from different sources gave poor results, whereas actively metabolising syngeneic cells proved to be effective feeder systems. Of the latter, the transformed subline of BALB/c embryo fibroblast 3T3/B cells - 3T3/A31 - were best. Macrophage (peritoneal exudate) feeder layers could be as effective as the 3T3/A31 cells, but were much more variable, probably reflecting the physiological state of the donor mice, the degree of sensitisation of the cells in vitro and the rate of recovery after isolation from the peritoneal cavity. Since the 3T3/A31 cells could replicate more rapidly than the hybridoma cells, division of the feeder cell chromosomes was inhibited using mitomycin C; 1-2 X 10(4) 3T3/A31 cells/ml were treated with 1 microgram/ml mitomycin C for 8-16 h at 37 degrees C, washed, and incubated for 3-7 days at 37 degrees C. The latter incubation was to permit the metabolism and breakdown of unreacted but intracytoplasmic drug, and the establishment of an active feeder layer before use with the hybridoma cells.

The use of rat mixed-thymocyte culture-conditioned medium for hybridoma production, cloning and revival

Allogeneic rat mixed-thymocyte 48 h culture-conditioned medium (MTM) was used successfully in place of feeder cells for hybridoma production with the NS-1 and NS-0 plasmacytoma lines. It permitted lower concentrations of fused cells to be seeded, and supported the transition from 96 to 24 well plates. MTM improved the performance of poor sera during cloning. It also assisted the survival of cells that were sensitive to thawing from liquid nitrogen storage, and cells that had inadvertently been allowed to overgrow. Two rats could produce the equivalent of 1500-5000 ml feeder cell suspension according to the dilution used; 150-500 mice would be required to produce such a quantity of cells. Thus use of MTM entailed a considerable saving in mice and provided a secure supply of 'reagent', since a batch could be prepared, checked for sterility, frozen and stored indefinitely.

A monoclonal-based, two-site enzyme immunoassay of human insulin

A procedure is described for the efficient production of insulin-specific monoclonal antibodies, which involves primary and secondary immunization of BALB/c mice in the hind footpads with bovine or porcine insulin and fusion of lymphocytes from popliteal lymph nodes with a P3x63 murine myeloma line. With this protocol, over 200 positive hybrids were obtained from four separate fusions. Dissociation constants of 31 purified monoclonals, cross-reacting with human insulin, were determined by two different methods and ranged between 4 X 10(-10) and 2 X 10(-6) mol/l. 24 monoclonals were biotinylated, paired in all possible combinations and tested by ELISA for their capacity to simultaneously bind to human insulin in a two-site assay. More than 40 monoclonal pairs were found which formed a sandwich with the hormone. The development of a simple and rapid one-step enzyme immunoassay is described, which involves a first monoclonal bound to the wells of a microtiter plate and a second monoclonal conjugated to alkaline phosphatase. With this assay, insulin can be determined in a range between 0.08 and 7.5 ng/ml in 3-4 h.

Conditioned medium from macrophage cell lines supports the single-cell growth of hybridomas

The aim of this study was to establish whether conditioned medium (CM) from macrophage cell lines would support the growth of hybridomas under conditions commonly used in hybridization experiments and in cloning of antigen-specific hybridomas. The ability of CM from macrophage cell lines J774, WEHI 274, WEHI 265, and PU 5 to support single-cell growth during cloning was compared with CM from cultures of resident mouse peritoneal cells, EL 4 mouse thymoma cells, L929 mouse fibrosarcoma, and feeder layers of resident peritoneal cells. CM from J774, L929, and resident peritoneal cells supported single-cell growth at the same level as the macrophage feeder layer. J774 and L929 CM were most effective at a final concentration of 25% with fresh medium supplemented with 20% fetal calf serum (FCS). The ability of J774 CM to support hybridoma growth was increased by prior stimulation with LPS but not PMA. CM from LPS-stimulated J774 cells used in fusion experiments resulted in increased numbers of hybridomas compared with those obtained with macrophage feeder layers.