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.