Spy chemistry-enabled protein directional immobilization and protein purification

Site-directed protein immobilization allows the homogeneous orientation of proteins with high retention of activity, which is advantageous for many applications. Here, we report a facile, specific, and efficient strategy based on the SpyTag-SpyCatcher chemistry. Two SpyTag-fused model proteins, that is, the monomeric red fluorescent protein (RFP) and the oligomeric glutaryl-7-aminocephalosporanic acid acylase, were easily immobilized onto a SpyCatcher-modified resin directly from cell lysates, with activity recoveries in the range of 85-91%. This strategy was further adapted to protein purification, which proceeded through the selective capture of the SpyCatcher-fused target proteins by a SpyTag-modified resin, with the aid of an intein to generate authentic N-termini. For two model proteins, that is, RFP and a variable domain of a heavy chain antibody, the yields were ∼3-7 mg/L culture with >90% purities. This approach could provide a versatile tool for producing high-performance immobilized protein devices and proteins for industrial and therapeutic uses.

Characterization of ADCs by Capillary Electrophoresis

Capillary electrophoresis (CE) is a highly efficient separation technique that resolves ions based on their electrophoretic mobility in the presence of an applied voltage. It has been broadly applied for characterizing biotherapeutics including ADCs. In this chapter, step-by-step procedures for characterizing ADCs using CE will be described with focus placed on reduced and non-reduced capillary electrophoresis sodium dodecyl sulfate (CE-SDS) for purity determination and imaged capillary isoelectric focusing (iCIEF) for charge heterogeneity analysis.

Identifying Conformation-Selective Heavy-Chain-Only Antibodies Against Membrane Proteins by a Thermal-Shift Scintillation Proximity Assay

Over the last decades, the use of heavy-chain-only antibodies has received growing attention in academia and industry as research and diagnostic tools as well as therapeutics. Their generation has improved with the help of innovative new methods such as the sybody technology; however, identifying conformation-selective compounds against membrane proteins remains a major challenge. In this chapter, we apply a thermal shift scintillation proximity assay (SPA-TS) to identify sybodies from an in vitro display campaign with the ability to selectively stabilize the inhibitor-bound conformation of the human solute carrier (SLC) family transporter SC6A9 (GlyT1). Using detergent-purified GlyT1 protein and a tritium-labeled glycine uptake inhibitor small molecule, we find sybody candidates that increase the apparent melting temperature in SPA-TS by several degrees. The thermal shift stabilizes the GlyT1-inhibitor complex and qualifies the sybodies for structural studies and inhibitor-selective small molecule screening assays. The SPA-TS assay in its current form is adaptable to any antibody discovery campaign for membrane proteins and permits the generation of highly valuable tools in most stages of drug discovery and development.

VHH characterization.Recombinant VHHs: Production, characterization and affinity

Among the biological approaches to therapeutics, are the cells, such as CAR-T cells engineered or not, the antibodies armed or not, and the smaller protein scaffolds that can be modified to render them specific of other proteins, à la façon of antibodies. For several years, we explored ways to substitute antibodies by nanobodies (also known as VHHs), the smallest recognizing part of camelids' heavy-chain antibodies: production of those small proteins in host microorganisms, minute analyses, characterization, and qualification of their affinity towards designed targets. Here, we present three standard VHHs described in the literature: anti-albumin, anti-EGF receptor and anti-HER2, a typical cancer cell surface -associated protein. Because they differ slightly in global structure, they are good models to assess our body of analytical methodologies. The VHHs were expressed in several bacteria strains in order to identify and overcome the bottlenecks to obtain homogeneous preparations of this protein. A large panel of biophysical tools, ranging from spectroscopy to mass spectrometry, was here combined to assess VHH structural features and the impact of the disulfide bond. The routes are now ready to move to more complex VHHs raised against specific targets in numerous areas including oncology.

Isolation and characterization of camelid single-domain antibodies against HER2

OBJECTIVE

To isolate and characterize novel high-affinity llama single-domain antibodies against human HER2.

RESULTS

We immunized a llama with human HER2, constructed a phage-displayed VHH library from the lymphocytes of the animal, and isolated six unique HER2-specific VHHs by panning. All six VHHs were unique at the amino acid level and were clonally unrelated, as reflected by their distinct CDR3 lengths. All six VHHs recognized recombinant human HER2 ectodomain with monovalent affinities ranging from 1 to 51 nM, had comparable affinities for cynomolgus monkey HER2, and bound HER2+ SKOV3 cells by flow cytometry. Three of the VHHs recognized recombinant murine HER2 with no loss of affinity compared with human and cynomolgus monkey HER2. The VHHs recognized three major epitopes on HER2 (including one conserved across the human, simian and murine orthologues), all of which were distinct from that of trastuzumab. These VHHs may be useful in the design of modular cancer immunotherapeutics.

Rapid quantitative analysis of monoclonal antibody heavy and light chain charge heterogeneity

An alternative method to traditional 2-dimensional gel electrophoresis (2D-PAGE) and its application in characterizing the inherent charge heterogeneity of chromatographically isolated monoclonal antibody heavy and light chains is described. This method, referred to as ChromiCE, utilizes analytical size-exclusion chromatography (SEC), performed under reducing and denaturing conditions, followed by imaged capillary isoelectric focusing (icIEF) of the chromatographically separated heavy and light chains. Under conditions suitable for the subsequent icIEF analysis, the absolute and relative SEC elution volumes of the heavy and light chains were found to be highly pH dependent, a phenomenon that can be exploited in optimizing chromatographic separation. Compared to 2D-PAGE, the ChromiCE method substantially decreases the time and labor needed to complete the analysis, improves reproducibility, and provides fully quantitative assessment of charge heterogeneity. The ChromiCE methodology was applied to a set of diverse monoclonal antibodies to demonstrate suitability for quantitative charge variant analysis of heavy and light chains. A typical application of ChromiCE in extended characterization and stability studies of a purified antibody is shown.

Isolation and characterization of recombinant variable domain of heavy chain anti-idiotypic antibodies specific to aflatoxin B1

Some unique subclasses of Camelidae antibodies are devoid of the light chain, and the antigen binding site is comprised exclusively of the variable domain of the heavy chain (VHH). The recombinant VHHs have a high potential as alternative reagents for the next generation of immunoassay. In particular, they might be very useful for molecular mimicry. The present study demonstrated an alpaca immunized with the F(ab')2 fragment of anti-aflatoxin B1 mAb and developed an important anti-idiotypic (anti-Id) responses. Antigen-specific elution method was used for panning private anti-Id VHHs from the constructed alpaca VHH library. The selected VHHs were expressed, renatured, purified, and then identified by a competitive enzyme-linked immunosorbent assay (ELISA). Our findings indicated that the VHH would be an alternative tool for haptens mimicry studies.

Detection of clonal immunoglobulin heavy chain gene rearrangements by the polymerase chain reaction and capillary gel electrophoresis

Although well-established diagnostic criteria exist for mature B-cell neoplasms, a definitive diagnosis of a B-cell lymphoproliferative disorder cannot always be obtained using more conventional techniques such as flow cytometric immunophenotyping, conventional cytogenetics, fluorescence in situ hybridization, or immunohistochemistry. However, because B-cell malignancies contain identically rearranged immunoglobulin heavy chain genes, the polymerase chain reaction (PCR) can be a fast, convenient, and dependable option to identify clonal B-cell processes. This chapter describes the use of PCR and capillary electrophoresis to identify clonal immunoglobulin heavy chain (IGH) variable and joining region (VH-JH) gene rearrangements (IGH VH-JH PCR) using a commercially available method employing multiple multiplex PCR tubes that was originally developed as the result of a large European BIOMED-2 collaborative study (Invivoscribe Technologies). The core protocol involves the use of three separate master mix tubes that target the conserved framework (FR1, FR2, and FR3) and joining (J) regions of the IGH gene. Analysis of these three framework regions can detect approximately 88% of clonal IGH gene rearrangements.

NanoLC Chips MS/MS for the characterization of N-glycopeptides generated from trypsin digestion of a monoclonal antibody

In the field of therapeutic recombinant proteins, monoclonal antibodies (mAbs) have achieved a rising success with more than 30 mAbs that have reached the market in the past 20 years. From a structural standpoint, one of the most important posttranslational modifications affecting antibodies is by far glycosylation. Furthermore, glycosylation of mAbs directly impacts on their biological activity and safety and therefore needs to be well characterized. Glycoprotein analysis requires high-resolution separation techniques that can provide detailed structural analysis able to discriminate between glycoforms of various abundances. This chapter describes a protocol for nanoLC-Chip-MS/MS analysis of a proteolytic digest of the heavy chain of a recombinant mAb. The use of graphitized carbon column instead of classical C18 reversed-phase material is shown to be well suited to detect low abundant glycoforms and to provide in one shot information regarding both the oligosaccharide structure and the amino acid sequence of its peptide moiety.

Serum carbohydrate-binding IgM are present in Vietnamese striped catfish (Pangasianodon hypophthalmus) but not in North African catfish (Clarias gariepinus)

Pangasianodon hypophthalmus serum was fractionated by affinity chromatography on 12 different Sepharose-carbohydrate columns and proteins eluted by the corresponding sugar. Binding to the affinity matrices is dependent on Ca(2+) ions. Upon gel filtration using Superose-12, essentially one fraction was obtained, eluting as a protein with a molecular mass of about 900 kDa. SDS-PAGE in reducing conditions revealed the presence of large (72 kDa) subunits (H-chains) and one up to three small (24, 26 and/or 28-29 kDa) subunits (L-chains). The isolated proteins were shown to be IgM since they bind monoclonal anti-P. hypophthalmus IgM antibodies. Rabbit polyclonal anti-galactose-binding IgM only cross-react with some sugar-binding IgM. The H-chains of the anti-carbohydrate IgM are glycosylated. Circular dichroism studies revealed that the IgMs have an "all-β" type of structure, and that Ca(2+) ions, though essential for carbohydrate-binding activity, are not required for the structural integrity of the molecules. In non-reducing SDS-PAGE, only monomers and halfmers were obtained, showing that there are no disulfide bonds linking the monomers, and that a disulfide bond connecting both H-chains within one monomer is only present in 45% of the molecules. Both the monomers and the halfmers display molecular mass heterogeneity which is indicative for redox forms at the level of the intradomain disulfide bonds. The native carbohydrate-binding IgMs agglutinate erythrocytes from different animals, as well as fish pathogenic bacteria. Similar proteins could not be isolated from another catfish, Clarias gariepinus.

Engineered single-domain antibodies with high protease resistance and thermal stability

The extreme pH and protease-rich environment of the upper gastrointestinal tract is a major obstacle facing orally-administered protein therapeutics, including antibodies. Through protein engineering, several Clostridium difficile toxin A-specific heavy chain antibody variable domains (V_HHs) were expressed with an additional disulfide bond by introducing Ala/Gly54Cys and Ile78Cys mutations. Mutant antibodies were compared to their wild-type counterparts with respect to expression yield, non-aggregation status, affinity for toxin A, circular dichroism (CD) structural signatures, thermal stability, protease resistance, and toxin A-neutralizing capacity. The mutant V_HHs were found to be well expressed, although with lower yields compared to wild-type counterparts, were non-aggregating monomers, retained low nM affinity for toxin A, albeit the majority showed somewhat reduced affinity compared to wild-type counterparts, and were capable of in vitro toxin A neutralization in cell-based assays. Far-UV and near-UV CD spectroscopy consistently showed shifts in peak intensity and selective peak minima for wild-type and mutant V_HH pairs; however, the overall CD profile remained very similar. A significant increase in the thermal unfolding midpoint temperature was observed for all mutants at both neutral and acidic pH. Digestion of the V_HHs with the major gastrointestinal proteases, at biologically relevant concentrations, revealed a significant increase in pepsin resistance for all mutants and an increase in chymotrypsin resistance for the majority of mutants. Mutant V_HH trypsin resistance was similar to that of wild-type V_HHs, although the trypsin resistance of one V_HH mutant was significantly reduced. Therefore, the introduction of a second disulfide bond in the hydrophobic core not only increases V_HH thermal stability at neutral pH, as previously shown, but also represents a generic strategy to increase V_HH stability at low pH and impart protease resistance, with only minor perturbations in target binding affinities. These are all desirable characteristics for the design of protein-based oral therapeutics.

Llama-derived single domain antibodies to build multivalent, superpotent and broadened neutralizing anti-viral molecules

For efficient prevention of viral infections and cross protection, simultaneous targeting of multiple viral epitopes is a powerful strategy. Llama heavy chain antibody fragments (VHH) against the trimeric envelope proteins of Respiratory Syncytial Virus (Fusion protein), Rabies virus (Glycoprotein) and H5N1 Influenza (Hemagglutinin 5) were selected from llama derived immune libraries by phage display. Neutralizing VHH recognizing different epitopes in the receptor binding sites on the spikes with affinities in the low nanomolar range were identified for all the three viruses by viral neutralization assays. By fusion of VHH with variable linker lengths, multimeric constructs were made that improved neutralization potencies up to 4,000-fold for RSV, 1,500-fold for Rabies virus and 75-fold for Influenza H5N1. The potencies of the VHH constructs were similar or better than best performing monoclonal antibodies. The cross protection capacity against different viral strains was also improved for all three viruses, both by multivalent (two or three identical VHH) and biparatopic (two different VHH) constructs. By combining a VHH neutralizing RSV subtype A, but not subtype B with a poorly neutralizing VHH with high affinity for subtype B, a biparatopic construct was made with low nanomolar neutralizing potency against both subtypes. Trivalent anti-H5N1 VHH neutralized both Influenza H5N1 clade1 and 2 in a pseudotype assay and was very potent in neutralizing the NIBRG-14 Influenza H5N1 strain with IC₅₀ of 9 picomolar. Bivalent and biparatopic constructs against Rabies virus cross neutralized both 10 different Genotype 1 strains and Genotype 5.

The results show that multimerization of VHH fragments targeting multiple epitopes on a viral trimeric spike protein is a powerful tool for anti-viral therapy to achieve “best-in-class” and broader neutralization capacity.

[Construction, expression and functional characterization of single chain variable fragments (scFv) against human CD33 antigen]

AIM

To construct and express the single chain variable fragments (scFv) gene against human CD33 antigen, and characterize its bioactivity.

METHODS

The genes encoding the light and heavy chain variable regions were cloned by RT-PCR from a murine hybridoma cell line, which could produce monoclonal antibody(mAb) against human CD33 antigen. Then the light and heavy chain variable regions were fused together by a short peptide linker containing 15 amino acid (Gly(4)Ser)(3) using splice-overlap extensive PCR. The recombinant anti-CD33 scFv was subcloned into the expression vector pET28a(+) and expressed in E.coli Rosetta after induction by IPTG.

RESULTS

SDS-PAGE and Western blot analysis showed that the recombinant anti-CD33 scFv gene was expressed in the form of inclusion body in E.coli Rosetta, and the purified fusion protein was obtained after a series of purification steps including cell lysis, inclusion body solubilization, Ni(2+) metal affinity chromatography and protein refolding. Flow cytometry(FCM) analysis showed that the scFv could react with human CD33 antigen.

CONCLUSION

Recombinant anti-CD33 scFv gene has been successfully constructed and expressed in E.coli Rosetta, which could provide foundation for the future target therapy to the myeloid leukemia.

Electrotransfer of proteins in an environmentally friendly methanol-free transfer buffer

Western blot transfer buffer was modified to substitute the acute poison methanol, with the common rubbing alcohol, isopropanol in concentrations of as low as 5 % for protein electrotransfer. Commercially available molecular weight markers and rabbit serum were run on polyacrylamide gels and shown to be transferred adequately to both nitrocellulose and polyvinylidene difluoride membranes under either wet or semi-dry conditions with similar results in all cases. This procedure was successfully used for immunodetection of the rabbit IgG heavy chain from serum. Therefore, this represents a good alternative for less toxic and environmentally friendly conditions for western immunoblotting of proteins.

[Expression, purification and activity analysis of human single-chain antibody against hepatocellular cancer]

AIM

To express and characterize an active form of a single-chain antibody (scFv) from the gene of human phage antibodies which is specific for hepatocellular cancer.

METHODS

The complementary DNAs encoding the variable regions of the light chain (V(L)) and heavy chain (V(H)) were connected by a (Gly(4)Ser)(3) linker using a splicing by overlap extension polymerase chain reaction. The resultant scFv gene was cloned to the pET28a(+) vector and expressed in E.coli as inclusion bodies. Then the inclusion bodies were solubilized, denatured and renatured. Finally, the affinity constant of scFv was determined by noncompetitive enzyme immunoassay.

RESULTS

The target protein amounted 26% of the total protein in the condition of A(600) at 0.8 for 6 hours. After renatured, the purity of target protein was 95% and the affinity constant of the scFv was 3.6x10(7) mol/L.

CONCLUSION

An active form of scFv which is specific for hepatocellular cancer can bind selectively with hepatocellular cancer cells, which provides a theoretical basis for immunological detection and clinical use of scFv.

Efficient inhibition of EGFR signaling and of tumour growth by antagonistic anti-EFGR Nanobodies

The development of a number of different solid tumours is associated with over-expression of ErbB1, or the epidermal growth factor receptor (EGFR), and this over-expression is often correlated with poor prognosis of patients. Therefore, this receptor tyrosine kinase is considered to be an attractive target for antibody-based therapy. Indeed, antibodies to the EGFR have already proven their value for the treatment of several solid tumours, especially in combination with chemotherapeutic treatment regimens. Variable domains of camelid heavy chain-only antibodies (called Nanobodies) have superior properties compared with classical antibodies in that they are small, very stable, easy to produce in large quantities and easy to re-format into multi-valent or multi-specific proteins. Furthermore, they can specifically be selected for a desired function by phage antibody display. In this report, we describe the successful selection and the characterisation of antagonistic anti-EGFR Nanobodies. By using a functional selection strategy, Nanobodies that specifically competed for EGF binding to the EGFR were isolated from "immune" phage Nanobody repertoires. The selected antibody fragments were found to efficiently inhibit EGF binding to the EGFR without acting as receptor agonists themselves. In addition, they blocked EGF-mediated signalling and EGF-induced cell proliferation. In an in vivo murine xenograft model, the Nanobodies were effective in delaying the outgrowth of A431-derived solid tumours. This is the first report describing the successful use of untagged Nanobodies for the in vivo treatment of solid tumours. The results show that functional phage antibody selection, coupled to the rational design of Nanobodies, permits the rapid development of novel anti-cancer antibody-based therapeutics.

Cloning of idiotype immunoglobulin genes in B cell lymphomas by anchored PCR and production of individual recombinant idiotype vaccines in Escherichia coli

OBJECTIVES

Individual immunoglobulins expressed by B-cell lymphomas represent tumor-specific antigens ('idiotypes'). Immunization with idiotype in follicular lymphoma patients may induce specific immune responses, sustained progression-free survival, and disappearance of minimal residual disease. Manufacturing of idiotype vaccines has mostly relied on heterohybridomas established from viable lymphoma cells. This paper describes the feasibility of production of GMP-grade idiotype vaccines as recombinant Fab fragments in Escherichia coli.

METHODS

IgH and IgL transcripts were analyzed by anchored PCR from 106 lymphoma and nine control biopsies. Lymphoma-derived V segments were inserted into prokaryotic expression plasmids. Recombinant idiotype Fab fragments were expressed in E. coli in a fermentation system.

RESULTS

Idiotype IgH and IgL transcripts were identified in 95% of 106 lymphoma biopsies according to stringent clonality criteria. Large-scale idiotype expression was successful in 69 of 78 cases (89%) and yielded a median of 17 mg (range: 1.2-250 mg) recombinant Fab protein. After affinity chromatography, median vaccine purity was 99% heterodimeric Fab protein (range: 72-100%). Bacterial protein contamination was detectable in one vaccine only. Fab proteins with IgL lambda chains had a tendency for inferior yield and lesser purity than kappa-type Fabs. Among other structural idiotype features (isotype, V family usage, somatic hypermutation pattern, novel glycosylation sites, CDR III net charge), no consistent influences on Fab yield or purity were detected.

CONCLUSIONS

Anchored PCR cloning and subsequent protein expression in E. coli provides a reliable technological basis for clinical idiotype vaccination trials.

Identification of human scFvs targeting atherosclerotic lesions: selection by single round in vivo phage display

Our aim was to investigate by in vivo biopanning the lesions developed early in atherosclerosis and identify human antibodies that home to diseased regions. We have designed a two-step approach for a rapid isolation of human Monoclonal phage-display single-chain antibodies (MoPhabs) reactive with proteins found in lesions developed in an animal model of atherosclerosis. After a single round of in vivo biopanning, the MoPhabs were eluted from diseased sections of rabbit aorta identified by histology and NMR microscopy. MoPhabs expressed in situ were selected by subtractive colony filter screening for their capacity to recognize atherosclerotic but not normal aorta. MoPhabs selected by our method predominantly bind atherosclerotic lesions. Two of them, B3.3G and B3.GER, produced as scFv fragments, recognized an epitope present on the surface in early atherosclerotic lesions and within the intimal thickness in more complex plaques. These human MoPhabs homed to atherosclerotic lesions in ApoE(-/-) mice after in vivo injection. A protein of approximately 56 kDa recognized by B3.3G was affinity-purified and identified by mass spectrometry analysis as vitronectin. This is the first time that single round in vivo biopanning has been used to select human antibodies as candidates for diagnostic imaging and for obtaining insight into targets displayed in atherosclerotic plaques.

Pre-B cell receptor assesses the quality of IgH chains and tunes the pre-B cell repertoire by delivering differential signals

It is well understood how a variety of Ig H and L chains, components of BCR, are generated in the DNA level during B cell development. However, it has remained largely unknown whether and how each component is monitored for its quality and selected before the assembly into the BCR. Here we show that muH chains produced by pre-B cells display a wide spectrum of ability to form the pre-BCR, which is composed of muH and surrogate light (SL) chains and is crucial for B cell development. The level of surface pre-BCR expression varies among pre-B cells, depending on the ability of their muH chains to pair with SL chains. The higher the level of pre-BCR expression by pre-B cells, the stronger their pre-BCR signaling, and the better they proliferate and differentiate. Thus, the extent of survival, proliferation, and differentiation of individual pre-B cells is primarily determined by the SL-pairing ability of their muH chains. Furthermore, IgH chains with higher potential to assemble with IgL chains appear to be positively selected and amplified through the assessment of their ability to pair with SL chains at the pre-BCR checkpoint before the assembly into the BCR. These results indicate that the pre-BCR assesses the quality of muH chains and tunes the pre-B cell repertoire by driving the preferential expansion and differentiation of cells with the higher quality of muH chains.

Immunoglobulin alpha heavy chain derived from human epithelial cancer cells promotes the access of S phase and growth of cancer cells

It is generally believed that under normal conditions only B lymphocytes express immunoglobulin. Interestingly, our previous work demonstrated that epithelial cancer tissues and cancer cell lines also express Ig alpha heavy chain. So we further analyzed the potential function of cancer-derived Ig alpha heavy chain. Here we show that blockade of cancer-derived Ig alpha suppressed the growth and viability of cancer cells. And cancer-derived Ig alpha promotes the malignant proliferation ability of cancer cells. Furthermore, we demonstrated that Ig alpha protein increases the access percentage of S phase from the early mitosis of synchronized cancer cells. Our findings support the important role of cancer-derived Ig alpha as a growth promoter of cancer cells, and reveal a novel molecular mechanism for growth and proliferation of cancer cells.

Identification of a candidate regulatory element within the 5' flanking region of the mouse Igh locus defined by pro-B cell-specific hypersensitivity associated with binding of PU.1, Pax5, and E2A

The Igh locus is controlled by cis-acting elements, including Emu and the 3' IgH regulatory region which flank the C region genes within the well-studied 3' part of the locus. Although the presence of additional control elements has been postulated to regulate rearrangements of the VH gene array that extends to the 5' end of the locus, the 5' border of Igh and its flanking region have not been characterized. To facilitate the analysis of this unexplored region and to identify potential novel control elements, we physically mapped the most D-distal VH segments and scanned 46 kb of the immediate 5' flanking region for DNase I hypersensitive sites. Our studies revealed a cluster of hypersensitive sites 30 kb upstream of the most 5' VH gene. Detection of one site, HS1, is restricted to pro-B cell lines and HS1 is accessible to restriction enzyme digestion exclusively in normal pro-B cells, the stage defined by actively rearranging Igh-V loci. Sequence motifs within HS1 for PU.1, Pax5, and E2A bind these proteins in vitro and these factors are recruited to HS1 sequence only in pro-B cells. Transient transfection assays indicate that the Pax5 binding site is required for the repression of transcriptional activity of HS1-containing constructs. Thus, our characterization of the region 5' of the VH gene cluster demonstrated the presence of a single cluster of DNase I hypersensitive sites within the 5' flanking region, and identified a candidate Igh regulatory region defined by pro-B cell-specific hypersensitivity and interaction with factors implicated in regulating VDJ recombination.

Anti-erythrocyte natural antibody activity in the unconventional ‘heavy chain’ immunoglobulins of Indian desert camel (Camelus dromedarius)

Members of the family Camelidae contain unconventional 'heavy chain' antibodies (HCAbs) that are devoid of light chains (LCs) in their structure and occur under physiological conditions. The spectrum of antigenic specificities in HCAbs and hence their biological significance is not known at present. Recent studies have however indicated that they contribute significantly towards the immunoglobulin (Ig) receptor diversity. The present study was planned to investigate the natural antibody (NAb) activity in camel HCAbs as further indication of the wide spectrum of their antigenic specificities. Detection of NAbs in the sera and isolated HCAbs of Indian Thar desert camels was undertaken against erythrocyte antigens (E-Ags) from eleven animal species including nine mammals, chicken and frog by using direct haemagglutination (HA) and indirect Coombs' test. HCAbs were found to behave as 'incomplete antibodies' and agglutinated erythrocytes of different animal species in indirect Coombs' test using rabbit anti-camel IgG3 (HCAbs) antiserum. Variations were noticed in the Coombs' titres against erythrocytes from different species. HCAbs also reacted against E-Ags in immunoblots. These findings provide further evidence that camelid HCAbs are produced against diverse antigens (Ags) under natural conditions, thereby contributing to camelid Ig receptor diversity.

Isolation of Human Antibody Repertoires with Preservation of the Natural Heavy and Light Chain Pairing

The humoral immune system in higher vertebrates is unique in its ability to generate highly diverse antibody responses against most pathogens as well as against certain malignancies. Several technologies have been developed to exploit this vast source of potentially therapeutic antibodies, including hybridoma technology, phage display and yeast display. Here, we present a novel, high-throughput technology (the Symplex Technology) for rapid direct cloning and identification of human antigen-specific high-affinity antibodies from single antibody-producing cells of immune individuals. The utility of the technology was demonstrated by isolation of diverse sets of unique high-affinity antibodies against tetanus toxoid and influenza virus from immunized volunteers. Hence, the Symplex Technology is a new method for the rapid isolation of high-affinity antibodies directly from humans.

Development and immunochemical evaluation of antibodies Y for the poorly immunogenic polypeptide prothymosin alpha

Since conserved mammalian polypeptides are believed to exhibit enhanced immunogenicity in avian species, hens were immunized against the poorly immunogenic, highly conserved mammalian polypeptide prothymosin alpha (ProTalpha), i.e. against either non-conjugated ProTalpha (isolated from bovine thymus) or ProTalpha conjugated to keyhole limpet hemocyanin (ProTalpha/KLH). The antibodies Y were isolated from the egg yolk and evaluated through suitable dot-blot and ELISA systems in parallel with antibodies G isolated from the antiserum of rabbits immunized against the same immunogens. As revealed, antibodies Y and G of low titer and/or affinity were obtained against non-conjugated ProTalpha, while antibodies Y against ProTalpha/KLH had a better apparent titer, could better discriminate between ProTalpha and the closely related bioactive peptide thymosin alpha 1, and were obtained at much larger quantities than the corresponding antibodies G.

The production and characterization of novel heavy-chain antibodies against the tandem repeat region of MUC1 mucin

Camelidae are known to produce immunoglobulins (Igs) devoid of light chains and constant heavy-chain domains (CH1). Antigen-specific fragments of these heavy-chain IgGs (VHH) are of great interest in biotechnology applications. This paper describes the first example of successfully raised heavy-chain antibodies in Camelus dromedarius (single-humped camel) and Camelus bactrianus (two-humped camel) against a MUC1 related peptide that is found to be an important epitope expressed in cancerous tissue. Camels were immunized against a synthetic peptide corresponding to the tandem repeat region of MUC1 mucin and cancerous tissue preparation obtained from patients suffering from breast carcinoma. Three IgG subclasses with different binding properties to protein A and G were purified by affinity chromatography. Both conventional and heavy-chain IgG antibodies were produced in response to MUC1-related peptide. The elicited antibodies could react specifically with the tandem repeat region of MUC1 mucin in an enzyme linked immunosorbant assay (ELISA). Anti-peptide antibodies were purified after passing antiserum over two affinity chromatography columns. Using ELISA, immunocytochemistry and Western blotting, the interaction of purified antibodies with different antigens was evaluated. The antibodies were observed to be selectively bound to antigens namely: MUC1 peptide (tandem repeat region), human milk fat globule membrane (HMFG), deglycosylated human milk fat globule membrane (D-HMFG), homogenized cancerous breast tissue and a native MUC1 purified from ascitic fluid. Ka values of specific polyclonal antipeptide antibodies were estimated in C. dromedarius and C. bactrianus, as 7 x 10(10) M(-1) and 1.4 x 10(10) M(-1) respectively.

Discovery of a new class of immunoglobulin heavy chain from fugu

In teleosts, the genomic organization of the immunoglobulin (Ig) heavy (H)-chain locus was thought to follow a typical translocon-type multigene structure; however, recent studies have indicated a variation in the structure and this might be teleost specific. Isotypes of the Ig H-chain, namely IgM, IgD, IgZ and IgT, have been identified. In this study, we report the discovery of a new class of IgH from fugu. This isotype was first identified from the genomic sequence of the fugu IgH locus. This novel IgH gene is composed of two constant (C) domains, a hinge region, and two exons encoding membrane regions. Surprisingly, the new IgH gene is present between the variable (V)H and Cmu regions of the locus. The C domains of the new isotype do not show any significant similarity to mammalian or fish IgH genes. The cloned cDNA from the new isotype has typical Ig H-chain characteristics and is expressed as both secretory and membrane form. Transcript analyses suggest that the new IgH from fugu might only use the joining (J)H segments present in front of the new CH domains and that the usage of DH and JH segments is specific to the isotype expressed. The expression pattern of the gene has been confirmed by in situ hybridization and PCR studies.

Production of recombinant humanized anti-HBsAg Fab fragment from Pichia pastoris by fermentation

In this report, we describe the high-yield secretory expression of the recombinant human anti-HBsAg Fab fragment from Pichia pastoris that was achieved by co-integration of the genes encoding the heavy and light chains (both under the control of alcohol oxidase promoter) into the genome of the yeast cells. The fed-batch fermentations were carried out in a 5 L scale. Both chains of the Fab were successfully expressed upon methanol induction. The absorbance (OD600) of the broth can reach 350 approximately 500 at the end of fed-batch phase. After the induction, the expression level of the recombinant Fab (soluble) reached 420 approximately 458 mg/L. The recombinant Fab fragment was purified from the crude culture supernatant by ion exchange chromatography and the purity of the recombinant Fab fragment was over 95%. The affinity activities of the crude fermentation supernatant and the purified Fab were analyzed by indirect ELISA, which showed that the purified recombinant Fab fragment had high affinity activity with hepatitis B surface antigen.

Domain Interactions in the Fab Fragment: A Comparative Evaluation of the Single-chain Fv and Fab Format Engineered with Variable Domains of Different Stability

Recombinant antibody fragments, most notably Fab and scFv, have become important tools in research, diagnostics and therapy. Since different recombinant antibody formats exist, it is crucial to understand the difference in their respective biophysical properties. We assessed the potential stability benefits of changing the scFv into the Fab format, the influence of the variable domains on the stability of the Fab fragment, and the influence of the interchain disulfide bond in the Fab fragment. To analyze domain interactions, the Fab fragment was broken down into its individual domains, several two-domain assemblies and one three-domain assembly. The equilibrium denaturation properties of these constructs were then compared to those of the Fab fragment. It was found that mutual stabilization occurred across the VH/VL and the CH1/CL interface, whereas the direct interaction between the V) and the CL domain had no influence on the stability of either domain. This observation can be explained by the different interfaces used for interaction. In contrast, the whole CH1CL and VHVL unit showed significant mutual stabilization, indicating a high degree of cooperation between the VH/VL and CH1/CL interface. The interchain disulfide bond in the Fab fragment plays an essential role in this stabilization. In addition to the effects of domain association on the thermodynamic (equilibrium) stability, Fab fragments differ from scFv fragments of similar equilibrium stability by having a very slow unfolding rate. This kinetic stabilization may increase significantly the resistance of Fab fragments against short time exposure to adverse conditions.

Over expression of anti-MUC1 single-domain antibody fragments in the yeast Pichia pastoris

The methylotrophic yeast Pichia pastoris has become a highly popular expression host system for the recombinant production of a wide variety of proteins, such as antibody fragments. Camelids produce functional antibodies devoid of light chains and constant heavy-chain domain (CH1). The antigen binding fragments of such heavy chain antibodies are therefore comprised in one single domain, the so-called VH of the camelid heavy chain antibody (VHH). To test the feasibility of expressing VHHs in the yeast, which on account of their small size and antigen recognition properties would have a major impact on antibody engineering strategies, we constructed two VHH genes encoding the single-domain antibody fragments with specificity for a cancer associated mucin, MUC1. The recombinant strains of the yeast P. pastoris were developed which secrete single-domain antibody fragment to the culture supernatant as a biologically active protein. Supplementation of medium with sorbitol (in pre-induction phase) and casamino acid or EDTA (in induction phase) provided ideal condition of increasing the yield of VHH production compared to culture condition devoid of above recipe. The secreted protein was purified following a 80% ammonium sulfate precipitation step, followed by a affinity chromatography column. The specific activity in enzyme-linked immunosorbant assay (ELISA) of the purified yeast VHH was higher than that of a bacterial periplasmic counterpart. These results reaffirm that the yeast P. pastoris is a suitable host for high level and correctly folded production of VHH antibody fragments with potential in vivo diagnostic and therapeutic applications. This is the first report of expression of VHH in P. pastoris.

Restricted IgA repertoire in both B-1 and B-2 cell-derived gut plasmablasts

Mucosal IgA is the most abundantly produced Ig upon colonization of the intestinal tract with commensal organisms in the majority of mammals. The repertoire of these IgA molecules is still largely unknown; a large amount of the mucosal IgA cannot be shown to react with the inducing microorganisms. Analysis of the repertoire of used H chain Ig (V(H)) genes by H-CDR3 spectrotyping, cloning, and sequencing of V(H) genes from murine intestinal IgA-producing plasma cells reveals a very restricted usage of V(H) genes and multiple clonally related sequences. The restricted usage of V(H) genes is a very consistent observation, and is observed for IgA plasma cells derived from B-1 or conventional B-2 cells from different mouse strains. Clonal patterns from all analyzed V(H) gene sequences show mainly independently acquired somatic mutations in contrast to the clonal evolution patterns often observed as a consequence of affinity maturation in germinal center reactions in peripheral lymphoid organs and Peyer's patches. Our data suggest a model of clonal expansion in which many mucosal IgA-producing B cells develop in the absence of affinity maturation. The affinity of most produced IgA might not be the most critical factor for its possible function to control the commensal organisms, but simply the abundance of large amounts of IgA that can bind with relatively unselected affinity to redundant epitopes on such organisms.

Aggregation-resistant domain antibodies selected on phage by heat denaturation

We describe a method for selecting aggregation-resistant proteins by heat denaturation. This is illustrated with antibody heavy chain variable domains (dAbs), which are prone to aggregate. The dAbs were displayed multivalently at the infective tip of filamentous bacteriophage, and heated transiently to induce unfolding and to promote aggregation of the dAbs. After cooling, the dAbs were selected for binding to protein A (a ligand common to these folded dAbs). Phage displaying dAbs that unfold reversibly were thereby enriched with respect to those that do not. From a repertoire of phage dAbs, six dAbs were characterized after selection; they all resisted aggregation, and were soluble, well expressed in bacteria and could be purified in good yields. The method should be useful for making aggregation-resistant proteins and for helping to identify features that promote or prevent protein aggregation, including those responsible for misfolding diseases.

Production of Novel Recombinant Single-Domain Antibodies against Tandem Repeat Region of MUC1 Mucin

Recently, the existence of "heavy-chain" antibody in Camelidae has been described. However, as yet there is no data on the binding of this type of antibody to peptides. In addition, there was not any report of production of single-domain antibodies in two-humped camels (Camelus bactrianus). In the present study, these questions are addressed. We showed the feasibility of immunizing old world camels, cloning the repertoire of the variable domain of their heavy-chain antibodies, panning and selection, leading to the successful identification of minimum-sized antigen binders. Antigen-specific fragments of the heavy-chain IgGs (V(HH)) are of great interest in biotechnology because they are very stable, highly soluble, and react specifically and with high affinity to the antigens. In this study, we immunized two camels (Camelus dromedarius and Camelus bactrianus) with homogenized cancerous tissues, synthetic peptide, and human milk fat globule membrane (HMFG), and generated two V(HH) libraries displayed on phage particles. Some single-domain antibody fragments have been isolated that specifically recognize the tandem repeat region of MUC1. The camels' single-domain V(HH) harbor the original, intact antigen binding site and reacted specifically and with high affinity to the tandem repeat region of MUC1. Indeed soluble, specific antigen binders and good affinities (in the range of 0.2 x 10(9) M(-1) to 0.6 x 10(9) M(-1)) were identified from these libraries. This is the first example of the isolation of camel anti-peptide V(HH) domains.

Characterization of Monoclonal Antibodies against Heavy and Light Chains of Flounder (Paralichthys olivaceus) Immunoglobulin

Flounder (Paralichthys olivaceus) Immunoglobulins (Igs) were purified from the serum of mouse IgG-immunized flounder by using affinity chromatography. Under denaturing conditions in SDS-PAGE, the flounder Igs appeared to be composed of 2 heavy (H) chains (72 and 77 kDa) and two light (L) chains (26 and 28 kDa). Monoclonal antibodies (MAbs) were produced by the fusion of myeloma cells (SP2/0) with Balb/c mouse spleen cells that were previously sensitized against affinity-purified flounder Igs. In a Western blot analysis, the produced MAbs, FIM511, FIM519, and FIM562 recognized both the 72 and 77 kDa H chains, 26 kDa, and 28 kDa L chain, respectively. Mouse antiserum against flounder Igs reacted more strongly with the L chain of 28 kDa than with 26 kDa, suggesting that the 28 kDa molecule is more immunogenic than the 26 kDa L chain molecule. In a FACS analysis, the ratios of the Ig+ cell population in the flounder head kidney and spleen cells were 49% and 24%, respectively. Unexpectedly, however, the ratios of the Ig+ B-like cell population in the flounder were not significantly augmented, even after the immunization of an immunogenic antigen. This suggests that the humoral immune response in fish could be considerably different from that in mammals. The produced MAbs in this study would be useful in characterizing flounder Ig+ B-like cells and in developing flounder Ig detecting an immunoassay system.

Isolation of human monoclonal antibodies that neutralize human rotavirus

A human antibody library constructed by utilizing a phage display system was used for the isolation of human antibodies with neutralizing activity specific for human rotavirus. In the library, the Fab form of an antibody fused to truncated cp3 is expressed on the phage surface. Purified virions of strain KU (G1 serotype and P[8] genotype) were used as antigen. Twelve different clones were isolated. Based on their amino acid sequences, they were classified into three groups. Three representative clones-1-2H, 2-3E, and 2-11G-were characterized. Enzyme-linked immunosorbent assay with virus-like particles (VLP-VP2/6 and VLP-VP2/6/7) and recombinant VP4 protein produced from baculovirus recombinants indicated that 1-2H and 2-3E bind to VP4 and that 2-11G binds to VP7. The neutralization epitope recognized by each of the three human antibodies might be human specific, since all of the antigenic mutants resistant to mouse monoclonal neutralizing antibodies previously prepared were neutralized by the human antibodies obtained here. After conversion from the Fab form of an antibody into immunoglobulin G1, the neutralizing activities of these three clones toward various human rotavirus strains were examined. The 1-2H antibody exhibited neutralizing activity toward human rotaviruses with either the P[4] or P[8] genotype. Similarly, the 2-3E antibody showed cross-reactivity against HRVs with the P[6], as well as the P[8] genotype. In contrast, the 2-11G antibody neutralized only human rotaviruses with the G1 serotype. The concentration of antibodies required for 50% neutralization ranged from 0.8 to 20 micro g/ml.

Identification of CD4 and transferrin receptor antibodies by CXCR4 antibody-guided Pathfinder selection

To generate human antibodies against CXCR4, a seven-transmembrane chemokine receptor and a principal coreceptor for HIV-1, several rounds of Pathfinder and Step-back selection from a large phage display antibody library were performed on Jurkat cells. A mAb against CXCR4 or biotinyated phage antibodies were used as guide molecules. Over 100 pan-Jurkat-cell-positive antibodies were characterized, but none were CXCR4 specific. However, several antibodies against CD4 and the transferrin receptor were identified. Our results indicate that, although Pathfinder and Step-back selection can be used to select phage antibodies on whole cells, the successful selection of certain targets is still complex and limited. The reason is probably, in part, due to the inaccessibility of the targeted extracellular structures and the range of the horseradish peroxidase-labeled guide molecule. Refinements of these techniques are required to improve target specificity and selectivity.

Endopeptidase character of monoclonal antibody i41-7 subunits

We prepared six anti-idiotypic monoclonal antibodies (mAbs) against parent 41S-2 mAb whose light chain is a super catalytic antibody (41S-2-L) capable of degrading targeted HIV-1gp41 molecule. Out of the obtained six mAbs, i41-7 mAb showed the strongest affinity to the parent 41S-2 mAb. The three dimensional structure of i41-7 mAb was created by molecular modeling using the deduced amino acid sequence of the light and heavy chain of i41-7 mAb. It suggests that the light and heavy chain possess catalytic triad-like structure composed of Ser, His and Asp in their conformations. Both chains of i41-7 mAb could cleave peptide bond of some peptides such as a polypeptide, TP41-1 (TPRGPDRPEGIEEEGGERDRD), as anticipated. The cleaving reaction advanced in accordance with Michaelis-Menten equation. The catalytic efficiency (kcat/Km) of light and heavy chain was 9.1 x 10(3) and 1.7 x 10(4) M(-1) x min(-1), respectively, while the intact i41-7 mAb did not exhibit any catalytic activity. The first cleaved bond of the TP41-1 peptide by the light chain was between 14E and 15G in the sequence. It was revealed that both light and heavy chains had endopeptidase characteristics.

Subunits of IgM reconstitute defective contact sensitivity in B-1 cell-deficient xid mice: kappa light chains recruit T cells independent of complement

The elicitation of contact sensitivity (CS) to local skin challenge with the hapten trinitrophenyl (TNP) chloride requires an early process that is necessary for local recruitment of CS-effector T cells. This is called CS initiation and is due to the B-1 subset of B cells activated at immunization to produce circulating IgM Ab. At challenge, the IgM binds hapten Ag in a complex that locally activates C to generate C5a that aids in T cell recruitment. In this study, we present evidence that CS initiation is indeed mediated by C-activating classic IgM anti-TNP pentamer. We further demonstrate the involvement of IgM subunits derived either from hybridomas or from lymphoid cells of actively immunized mice. Thus, reduced and alkylated anti-TNP IgM also initiates CS, likely due to generated H chain-L chain dimers, as does a mixture of separated H and L chains that still could weakly bind hapten, but could not activate C. Remarkably, anti-TNP kappa L chains alone mediated CS initiation that was C-independent, but was dependent on mast cells. Thus, B-1 cell-mediated CS initiation required for T cell recruitment is due to activation of C by specific IgM pentamer, and also subunits of IgM, while kappa L chains act via another C-independent but mast cell-dependent pathway.

Artiodactyl IgD: the missing link

IgD has been suggested to be a recently developed Ig class, only present in rodents and primates. However, in this paper the cow, sheep, and pig Ig delta genes have been identified and shown to be transcriptionally active. The deduced amino acid sequences from their cDNAs show that artiodactyl IgD H chains are structurally similar to human IgD, where the cow, sheep, and pig IgD H chain constant regions all contain three domains and a hinge region, sharing homologies of 43.6, 44, and 46.8% with their human counterpart, respectively. According to a phylogenetic analysis, the Cdelta gene appears to have been duplicated from the Cmu gene >300 million yr ago. The ruminant mu CH1 exon and its upstream region was again duplicated before the speciation of the cow and sheep, approximately 20 million yr ago, inserted upstream of the delta gene hinge regions, and later modified by gene conversion. A short Sdelta (switch delta) sequence resulting from the second duplication, is located immediately upstream of the bovine Cdelta gene and directs regular mu-delta class switch recombination in the cow. The presence of Cdelta genes in artiodactyls, possibly in most mammals, suggests that IgD may have some as yet unknown biological properties, distinct from those of IgM, conferring a survival advantage.

Grafting of "abbreviated" complementarity-determining regions containing specificity-determining residues essential for ligand contact to engineer a less immunogenic humanized monoclonal antibody

Murine mAb COL-1 reacts with carcinoembryonic Ag (CEA), expressed on a wide range of human carcinomas. In preclinical studies in animals and clinical trials in patients, murine COL-1 showed excellent tumor localization. To circumvent the problem of immunogenicity of the murine Ab in patients, a humanized COL-1 (HuCOL-1) was generated by grafting the complementarity-determining regions (CDRs) of COL-1 onto the frameworks of the variable light and variable heavy regions of human mAbs. To minimize anti-V region responses, a variant of HuCOL-1 was generated by grafting onto the human frameworks only the "abbreviated" CDRs, the stretches of CDR residues that contain the specificity-determining residues that are essential for the surface complementarity of the Ab and its ligand. In competition RIAs, the recombinant variant completely inhibited the binding of radiolabeled murine and humanized COL-1 to CEA. The HuCOL-1 and its variant showed no difference in their binding ability to the CEA expressed on the surface of a CEA-transduced tumor cell line. Compared with HuCOL-1, the HuCOL-1 variant showed lower reactivity to patients' sera carrying anti-V region Abs to COL-1. The final variant of the HuCOL-1, which retains its Ag-binding reactivity and shows significantly lower serum reactivity than that of the parental Ab, can serve as a prototype for the development of a potentially useful clinical reagent.

Biophysical properties of camelid V(HH) domains compared to those of human V(H)3 domains

Camelidae possess an unusual form of antibodies lacking the light chains. The variable domain of these heavy chain antibodies (V(HH)) is not paired, while the V(H) domain of all other antibodies forms a heterodimer with the variable domain of the light chain (V(L)), held together by a hydrophobic interface. Here, we analyzed the biophysical properties of four camelid V(HH) fragments (H14, AMD9, RN05, and CA05) and two human consensus V(H)3 domains with different CDR3 loops to gain insight into factors determining stability and aggregation of immunoglobulin domains. We show by denaturant-induced unfolding equilibria that the free energies of unfolding of V(HH) fragments are characterized by Delta G(N-U) values between 21.1 and 35.0 kJ/mol and thus lie in the upper range of values for V(H) fragments from murine and human antibodies. Nevertheless, the V(HH) fragments studied here did not reach the high values between 39.7 and 52.7 kJ/mol of the human consensus V(H)3 domains with which they share the highest degree of sequence similarity. Temperature-induced unfolding of the V(HH) fragments that were studied proved to be reversible, and the binding affinity after cooling was fully retained. The melting temperatures were determined to be between 60.1 and 66.7 degrees C. In contrast, the studied V(H)3 domains aggregated during temperature-induced denaturation at 63-65 degrees C. In summary, the camelid V(HH) fragments are characterized by a favorable but not unusually high stability. Their hallmark is the ability to reversibly melt without aggregation, probably mediated by the surface mutations characterizing the V(HH) domains, which allow them to regain binding activity after heat renaturation.

Interaction of the octapeptide angiotensin II with a high-affinity single-chain Fv and with peptides derived from the antibody paratope

The amino-acid sequence of the very high-affinity anti-angiotensin II monoclonal antibody 4D8 was predicted from the nucleotide sequence of the heavy and light chain variable genes. The single-chain variable fragment (scFv) was constructed and expressed in Escherichia coli as a soluble protein and at the surface of the filamentous M13 phage and was compared with the full-length antibody (Ab). The scFv showed the same specificity profile and affinity constant as the intact antibody (5.0x10(10) and 8.0x10(10) M(-1), respectively, by Scatchard analysis). Several peptides from the set of overlapping dodecapeptides covering the variable domains of 4D8 mAb were found to specifically bind biotinylated angiotensin II: peptides from the L1, L2, L3 and H1 regions had the strongest capacity to bind the antigen.

Production of functional antibodies generated in a nonlytic insect cell expression system

A monoclonal antibody directed against the type 2 adenovirus (Ad2) penton base protein was cloned and expressed in Spodoptera frugiperda (Sf9) cells using a nonlytic vector system. The coding sequences for the immunoglobulin light and heavy chains were placed under the control of the Orgyia pseudotsugata multicapsid nucleopolyhedrosis virus immediate-early 2 (OpIE2) promoter. Transfected Sf9 cells continuously secreted the antibody which retained the ability to recognize both native and recombinant Ad2 penton base proteins. Bifunctional penton base antibodies were also generated by fusing a gene for a growth factor or a cytokine at the 3' end of the Ig constant heavy chain domain. The quantity and activity of recombinant antibodies generated in the nonlytic insect cell system could be determined relatively quickly compared to other expression systems. Moreover, these recombinant proteins were not subjected to proteolytic degradation as frequently occurs during baculovirus-mediated cell lysis and the levels of recombinant antibodies produced in the nonlytic system were comparable to those reported for cytolytic baculovirus vectors.

VH gene replacement in thymocytes

The quasi-monoclonal (QM) mouse has a functionally rearranged H chain gene inserted into its natural position in the IgH locus. In this position, the H chain gene is subject to many of the same activities as normally arranged H chain genes, including somatic hypermutation, V(H) gene replacement, and class switch recombination. Here, we have used this mouse strain to determine some of the rules that govern the V(D)J recombination activity of the IgH locus in thymus. We focused on the requirements for V(H) gene replacement. In normal mice, thymic DJ(H) rearrangements are common, but VDJ(H) rearrangements are not. We found intermediate products of V(H) replacement in double-positive CD4(+)CD8(+) cells of the QM thymus, demonstrating that the inserted V(H) gene was accessible and ruling out the possibility that a V(H) gene per se cannot be rearranged in the thymus. We found transcripts from the knocked-in H chain gene of QM, but no mu H chain protein was detectable in thymocytes. Cloning and sequencing of these transcripts revealed that some had been generated by V(H) gene replacement. Corresponding signal joints could also be identified. These results suggest that neither a B cell-specific signal nor an Ig protein are necessary to activate V(H)-to-VDJ(H) joining in thymocytes. Possible mechanisms remaining to account for overcoming the barrier to V(H) joining in thymocytes include the insertion of a transcriptionally active gene segment and/or the inactivation of a silencer.

Characterization and V(H) sequences of human monoclonal anti-F(ab')(2) autoantibodies from normals and Sjögren's syndrome patients

To investigate the genetic background of anti-F(ab')(2) autoantibodies and the mechanism behind their production we have analyzed 10 human monoclonal antibodies directed against IgG F(ab')(2) and IgG Fab. They were all derived from peripheral blood by the EBV/hybridoma technique. Eight were from three healthy individuals and two from two patients with primary Sjögren's syndrome (pSS). They react with epitopes on distinct regions of IgG, including epitopes present on or near the hinge of IgG, epitopes on the Fd gamma, and an antigenic determinant(s) present on lambda light chains. These determinants are either exposed on the intact IgG molecule or revealed following pepsin or papain digestion. The V(H) germline gene repertoire used is diverse and with considerable overlap with that used by rheumatoid factors (RF). The two IgG antibodies from normals are extensively mutated (13 and 24 mutations/V(H)), but with a replacement to silent mutation ratio in the CDR(H)1 + 2 of only 3.7. The IgM antibodies from normals are also heavily mutated (mean 10 mutations/V(H)). This suggests that anti-F(ab')(2) from normals are generated by an antigen-driven somatic hypermutation mechanism. In contrast, the two IgM antibodies from pSS are virtually unmutated in both V(H) and V(L). Together with published data of pSS RF and anti-Ro 52-kDa sequences (1-3), this suggests that there is an expanded population of naïve B cells with autoantibody specificities in the peripheral blood of pSS patients.

A single 3' alpha hs1,2 enhancer in the rabbit IgH locus

Multiple cis-acting elements including the intronic enhancer and the 3'alpha enhancer (3'alphaE) regulate expression of the Ig heavy chain genes during B cell development. A 3'alphaE is composed of DNase I-hypersensitive sites, hs1,2, hs3a,b, and hs4, found 3' of the murine Calpha gene as well as 3' of both human Calpha genes, Calpha1 and Calpha2. Rabbits have 13 Calpha genes, and we tested whether a 3'alphaE is associated with each of these genes. To identify 3'alphaE regions we developed a rabbit hs1,2 probe and used this to search for enhancer homologues of human hs1,2 in a genomic fosmid library. We identified a single hs1,2 fragment 8-kb downstream of Calpha13, the presumed 3'-most Calpha gene. We also identified and partially sequenced a new Calpha gene, Calpha14, located 6 kb upstream of Calpha13. Genomic Southern blot analysis confirmed that the rabbit genome contains only one hs1,2 enhancer region. We tested the enhancer activity of the hs1,2 with the SV40, V(H), and Ialpha promoters using the luciferase reporter gene in transient transfection assays and found that it significantly enhanced the activity of SV40 and V(H) promoters and slightly enhanced an Ialpha promoter. We conclude that the rabbit has a single hs1,2 enhancer that resides at the 3' end of the IgH gene cluster and may constitute one of the cis-elements regulating the expression of IgH genes.