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.

Effects of Hemodialysis Therapy Using Dialyzers with Medium Cut-Off Membranes on Middle Molecules

The removal of larger middle molecules, such as free immunoglobulin light chains (FLC), is poor with most currently used dialysis technologies. While hemodiafiltration (HDF) provides enhanced clearance of middle molecules compared to high-flux hemodialysis (HD), this technique is currently not approved in some regions and, hence, not accessible for all patients. The retention of middle molecules is thought to be one factor, which contributes to excessive morbidity and mortality in HD patients. The development of medium cut-off (MCO) dialysis membranes is aimed at a more efficient clearance of larger uremic toxins while retaining albumin and may extend the benefit of enhanced solute removal to more patients. In 2 pilot studies, the removal of middle molecules using HD with an MCO dialyzer prototype was compared to (1) high-flux HD and (2) high-flux HD and HDF. The primary outcome was the overall clearance of λ FLC, and the secondary outcome was the clearance of other middle molecules and safety. Pre-to-post reduction ratios and instantaneous clearances during HD were also assessed. In both trials, the overall λ FLC clearance with MCO HD was significantly larger than with high-flux HD and HDF. Accordingly, instantaneous clearances at 30 and 120 min showed significantly higher removal of λ FLC compared to high-flux HD and HDF. MCO HD provides a more efficient removal of larger middle molecules compared to high-flux HD and HDF. A potential drawback is slightly increased albumin loss, yet preliminary data suggest that this does not lead to permanently decreased albumin levels. Thus, MCO HD may present a promising approach to further improve middle molecule removal in maintenance dialysis patients and to extend its benefit to more patients.

Plant expression systems for early stage discovery and development of lead therapeutic antibodies

BACKGROUND

Antibodies for human clinical applications are predominantly produced in mammalian expression systems, with Chinese hamster ovary (CHO) cells being the gold standard. CHO cells are ideal for the manufacturing of the IgG class of antibodies, but not for the production of complex antibodies like secretory IgAs (SIgAs) and IgMs, which remain unavailable for clinical use. In contrast, plant seeds and leaves hold the promise to produce SIgAs, IgMs and similar complex antibody formats to scalable amounts. Using transient transformation of Nicotiana benthamiana leaves, complex antibody formats can be produced up to milligram amounts in less than a month.

OBJECTIVE

Based on these merits, we propose a model for early-phase exploration and designing of innovative antibody formats for therapeutic application. Further in this essay, we elaborate how the model was followed during the selection of novel antibodies for seed-based production.

RESULT

This exploratory model led to the engineering of novel light-chain devoid porcinized-llama antibodies (VHH-Fc) of the IgG (VHH-IgG) and IgA (VHH-IgA) isotypes and also tetravalent dimeric and SIgAs.

CONCLUSION

The proposed strategy may lead to plant-based rapid engineering of innovative antibodies more apt and efficacious for therapy, and in the coarse also add to the understanding of their mode of action.

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.

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.

[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.

Characterization of lower molecular weight artifact bands of recombinant monoclonal IgG1 antibodies on non-reducing SDS-PAGE

SDS-PAGE under non-reducing conditions is one of the most commonly used techniques for recombinant monoclonal antibody purity and stability indicating assay. On non-reducing SDS-PAGE, bands with a lower molecular weight than the intact antibody are routinely observed and is a common feature of IgG molecules. These fragments were analyzed by in-gel digestion followed by matrix-assisted-laser-desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry, Western blot and by comparing the banding pattern of sample prepared in the presence of a reducing reagent. The fragments bands were identified as antibody lacking one light chain, two heavy chains, one light chain and one heavy chain, free heavy chain and free light chain. Sensitivity of fragmentation to sample buffer pH, incubation time, reducing reagent and alkylation reagents indicated that fragments were formed during sample preparation, but not present in the samples analyzed. Disulfide bond scrambling and beta-elimination are the two major mechanisms of the formation antibody fragments. Mass spectrometry analysis suggested that disulfide bond scrambling can be prevented by specifically modifying free sulhydryl using alkylation and thus reduced the amount of artifacts on non-reducing SDS-PAGE. Breakage of disulfide bonds by beta-elimination was evidenced by the detection of dehydroalanine using mass spectrometry.

[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.

Light-chain removal by plasmapheresis in myeloma-associated renal failure

BACKGROUND

Although plasmapheresis has been recommended to reverse nephrotoxic elevations of serum free light chains (sFLCs), there are scant published data on removal of sFLC measured with modern assays.

STUDY DESIGN AND METHODS

sFLC levels were recorded in two patients with myeloma-associated renal failure receiving multiple plasmapheresis procedures.

RESULTS

In one patient, presenting with acute renal failure 8 months after diagnosis of kappa-LC myeloma, 16 plasmapheresis procedures neither reduced sFLC levels (percent removal ranging from -70% to +40%) nor improved renal function. In another patient who presented with leukemic immunoglobulin A-lambda myeloma and acute renal failure, sFLC decreased by 30 to 60 percent after each plasmapheresis procedure, but rebounded within 5 to 10 hours. Renal failure occurred despite plasmapheresis, and hemodialysis was required.

CONCLUSIONS

In both patients, plasmapheresis failed to effectively lower sFLC levels. The results provide initial biologic data supporting the conclusions of a recent randomized multicenter clinical trial in which plasmapheresis was an ineffective adjunct to chemotherapy for myeloma-associated acute renal failure.

How lab staff and the estimation of free light chains can combine to aid the diagnosis of light chain disease

The diagnosis and monitoring of free light chain abnormalities and disease has always been a challenging area for laboratory and clinical staff because urine electrophoresis is often overlooked in the investigations requested. We present here three case reports which illustrate first, the role of the laboratory staff and second, the use of serum free light chain estimations in the diagnosis and monitoring of patients with light chain paraproteinaemia and myeloma.

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.

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.

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.

Cellular response of cardiac fibroblasts to amyloidogenic light chains

Amyloidoses are a group of disorders characterized by abnormal folding of proteins that impair organ function. We investigated the cellular response of primary cardiac fibroblasts to amyloidogenic light chains and determined the corresponding change in proteoglycan expression and localization. The cellular response to 11 urinary immunoglobulin light chains of kappa1, lambda6, and lambda 3 subtypes was evaluated. The localization of the light chains was monitored by conjugating them to Oregon Green 488 and performing live cell confocal microscopy. Sulfation of the proteoglycans was determined after elution over Q1-columns with a single-step salt gradient (1.5 mol/L NaCl) via dimethylmethylene blue. Light chains were detected inside cells within 4 hours and demonstrated perinuclear localization. Over 80% of the cells showed intracellular localization of the amyloid light chains. The light chains induced sulfation of the secreted glycosaminoglycans, but the cell fraction possessed only minimal sulfation. Furthermore, the light chains caused a translocation of heparan sulfate proteoglycan to the nucleus. The conformation and thermal stability of light chains was altered when they were incubated in the presence of heparan sulfate and destabilization of the amyloid light chains was detected. These studies indicate that internalization of the light chains mediates the expression and localization of heparan sulfate proteoglycans.

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.

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.

Infusion of light chains from patients with cardiac amyloidosis causes diastolic dysfunction in isolated mouse hearts

BACKGROUND

Primary (AL) amyloidosis is a plasma cell dyscrasia characterized by clonal production of immunoglobulin light chains (LC) resulting in the subsequent systemic deposition of extracellular amyloid fibrils. Cardiac involvement is marked by the hemodynamic pattern of impaired diastolic filling and restrictive cardiomyopathy. Although cardiac death in patients with AL amyloidosis is usually associated with extensive myocardial infiltration, the infiltration alone does not correlated with the degree of heart failure or survival. We hypothesized that circulating monoclonal LC may directly impair cardiac function, in addition to any mechanical effects of amyloid fibril deposition. Therefore, we examined the effects of amyloid LC proteins on diastolic and systolic cardiac function, as measured in an isolated mouse heart model.

METHODS AND RESULTS

LC were obtained from patients with nonamyloid disease or from those with noncardiac, mild cardiac, and severe cardiac involved AL amyloidosis. Saline or LC (100 microgram/mL) was infused into a Langendorff-perfused, isovolumically contracting mouse heart. Saline and control, noncardiac, and mild-cardiac LC infusions did not alter ex vivo cardiac function. In contrast, infusion of sever cardiac LC resulted in marked impairment of ventricular relaxation with preservation of contractile function.

CONCLUSION

These results demonstrate that infusion of LC from patients with AL amyloidosis result in diastolic dysfunction similar to that observed in patients with cardiac involved AL amyloidosis, and they suggest that amyloid LC proteins may contribute directly to the pathogenesis and the rapid progression of amyloid cardiomyopathy, independent of extracellular fibril deposition.

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.

Monoclonal light chain--mesangial cell interactions: early signaling events and subsequent pathologic effects

Glomerulopathic monoclonal light chains (G-LC) interact with mesangial cells (MC), resulting in alterations of mesangial homeostasis. Early signaling events control mitogenic activities and cytokine production, which in turn participate in the subsequent pathologic events. Mesangial homeostasis is affected in two very different ways, depending on whether the G-LC is from a patient with light chain deposition disease (LCDD) or light chain-related amyloidosis (AL-Am). In contrast, tubulopathic (T)-LC chains from patients with myeloma cast nephropathy do not significantly interact with MC and result in no alterations in mesangial homeostasis. Therefore, understanding early events in the monoclonal LC-MC interactions is fundamental. MC in culture were exposed to LC obtained and purified from the urine of patients with plasma cell dyscrasias and biopsy-proven renal disease, including LCDD, AL-Am, and myeloma cast nephropathy. Incubation of MC with G-LC, but not T-LC, resulted in cytoskeletal and cell shape changes, activation of platelet-derived growth factor-beta (PDGF-beta) and its corresponding receptor, cytoplasmic to nuclear migration of c-fos and NF-kappa beta signals, and production of monocyte chemoattractant protein-1 (MCP-1), as well as increased expression of Ki-67, a proliferation marker. Although NF-kappa beta activation was directly related to MCP-1 production, c-fos activation regulated proliferative signals and cytoskeletal changes in MC. Amyloidogenic LC were avidly internalized by the MC, whereas LCDD-LC effector targets were located at the MC surface. These cellular events are likely initiated as a result of interactions of the G-LC with yet-uncharacterized MC surface receptors. Dissecting the events taking place when G-LC interact with MC may define potential important targets for selective therapeutic manipulation to ameliorate or prevent the glomerular injury that ensues.

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.

Site-specific photobiotinylation of antibodies, light chains, and immunoglobulin fragments

The high affinity of biotin for avidin has been exploited for many antibody-based assays. This requires that biotin is covalently conjugated to the antibody molecule. Several chemically reactive biotinylation reagents are commercially available. Except for the attachment via sulfhydryl groups in the immunoglobulin (Ig) molecule, these reagents attach biotin randomly to various amino acid side chains. Although non-site-specific modification of antibodies does not interfere in most immunoassays, specific application and sensitive antibodies would benefit from site-specific biotinylation. Here we describe an affinity biotinylation technique based on a photoreactive biotin reagent. The design of this reaction was possible from the discovery of a conserved binding site in the variable Ig domain for nucleotides and nucleosides. The described photoaffinity biotinylation offers the advantages of ease, convenience, and production of a reproducible and defined biotinylated antibody preparation.

Production and functional characterization of two mouse/human chimeric antibodies with specificity for the tumor-associated Tn-antigen

In this work, we have constructed two functional mouse/human chimeric antibodies (IgMkappa and IgG1kappa isotypes) by inserting genomic DNA fragments encoding VH and Vkappa variable regions of the murine monoclonal antibody IgMK-83D4 into mammalian expression vectors containing human mu, gamma1, and kappa constant exons, and by transfecting them into the nonsecreting mouse myeloma X-63 cell line. In previous works, we have demonstrated that 83D4 murine mAb reacts with Tn determinant (GalNAcalpha-O-Ser/Thr) expressed in 90% of breast, ovary, and colon carcinomas. Both expressed chimeric antibodies were purified from the transfected cell line supernatant by affinity chromatography, and their reactivities against Tn antigen were confirmed by ELISA on asialo ovine submaxilar mucin and immunofluorescence studies on MCF-7 breast carcinoma cell line. We have demonstrated by gel filtration chromatography, that the principal secreted forms were monomers for IgG1kappa and pentamers for IgMkappa. The binding affinities of these chimeric antibodies against synthetic Tn glycopeptides, were evaluated by surface plasmon resonance showing an affinity constant similar to that of 83D4 native antibody for IgMkappa and a lower affinity constant for IgG1kappa chimeric antibody. On the other hand, the replacement of mouse C regions with human C regions confers both chimeric antibodies the ability to activate human complement. These mouse/human chimeric antibodies should be much less immunogenic and could play an important role in the lysis of tumor cell expressing Tn-antigen. Therefore, these anti-Tn chimeric antibodies could be considered as potential tools for human in vivo studies.

Monoclonal antibody light chain with prothrombinase activity

Prothrombin is the precursor of thrombin, a central enzyme in coagulation. Autoantibodies to prothrombin are associated with thromboembolism, but the mechanisms by which the antibodies modulate the coagulation processes are not understood. We screened a panel of 34 monoclonal antibody light chains isolated from patients with multiple myeloma for prothrombinase activity by an electrophoresis method. Two light chains with the activity were identified, and one of the light chains was characterized further. The prothrombinase activity eluted from a gel-filtration column run in denaturing solvent (6 M guanidine hydrochloride) at the characteristic positions of the light chain dimer and monomer. A constant level of catalytic activity was observed across the width of the light chain monomer peak, assessed as the cleavage of IEGR-methylcoumarinamide, a peptide substrate corresponding to residues 268-271 of prothrombin. Hydrolysis of this peptide by the light chain was saturable and consistent with Michaelis-Menten-Henri kinetics (K(m) 103 microM; k(cat) of 2.62 x 10(-)(2)/min). Four cleavage sites in prothrombin were identified by N-terminal sequencing of the fragments: Arg(155)-Ser(156), Arg(271)-Thr(272), Arg(284)-Thr(285), and Arg(393)-Ser(394). The light chain did not cleave radiolabeled albumin, thyroglobulin, and annexin V under conditions that readily permitted detectable prothrombin cleavage. Two prothrombin fragments (M(r) 55 000 and 38 000), were isolated by anion-exchange chromatography and were observed to cleave a thrombin substrate, tosyl-GPR-nitroanilide. Conversion of fibrinogen to fibrin was accelerated by the prothrombin fragments generated by the light chain. These finding suggest a novel mechanism whereby antibodies can induce a procoagulant state, i.e., prothrombin activation via cleavage of the molecule.

Secretory immunoglobulin A from healthy human mothers' milk catalyzes nucleic acid hydrolysis

The human milk secretory immune system is the first line of protection for the newborn infant against various pathogens. Secretory IgA (sIgA), the typical immunoglobulin found in secretions, can fight infections through many mechanisms. Using different methods, we have shown that sIgA from the milk of healthy women possesses DNAse and RNAse activities. The catalytic center is localized in the light chain of catalytic sIgA, while the DNA-binding center is predominantly formed by its heavy chain. The enzymic properties and substrate specificity of catalytic sIgA distinguish it from other known DNases and RNases. It is reasonable to assume that the milk DNA- and RNA-hydrolyzing antibodies are capable not only of neutralizing viral and bacterial nucleic acids by binding these antigens as well as by hydrolyzing them. The DNA-hydrolyzing activity of Abs raises the possibility that these catalytic Abs may provide protective functions for the newborn through the hydrolysis of viral and bacterial nucleic acids.

The importance of the light chain for the epitope specificity of human anti-U1 small nuclear RNA autoantibodies present in systemic lupus erythematosus patients

Abs to U1 RNA are frequently found in patients suffering from systemic lupus erythematosus overlap syndromes and Ab titers correlate with disease activity. We describe the isolation of the first human anti-U1 RNA autoantibodies from a combinatorial IgG library made from the bone marrow of a systemic lupus erythematosus patient. With the use of phage display technology, two anti-U1 RNA single-chain variable fragment (scFv) Abs were selected. Both high affinity anti-U1 RNA Ab fragments (Kd approximately 1 nM) recognize stem II of U1 RNA and were derived from the same heavy chain gene (VH3-11) and the same lambda (3r) light chain gene although somatic mutations, predominantly present in the complementarity-determining regions, are different. Experiments, in which the heavy chain genes of both anti-U1 RNA scFvs were reshuffled with the original light chain repertoire of the patient resulted, after selection on stem loop II, in a large number of RNA-binding Ab fragments. All these stem loop II-specific RNA binding clones used a similar, but not identical, 3r lambda light chain. When scFvs were selected from the reshuffled libraries by stem loop IV, representing the other autoantigenic site of U1 RNA, most selected Ab clones did react with stem loop IV, but no longer with stem loop II. The stem loop IV-reactive Ab clones contained different, not 3r-related, light chains. These results point to a major role for the light chain in determining the sequence specificity of these disease-related anti-U1 RNA Abs. The possibility that secondary light chain rearrangements are involved in this autoimmune response is discussed.

Intrabody construction and expression. II. A synthetic catalytic Fv fragment

In general, proteins with structural disulfides cannot be expressed in the reducing environment of the cellular cytoplasm. To overcome this folding problem, we have previously engineered stabilizing mutations, predicted from a consensus sequence analysis, into isolated immunoglobulin VL domains. Here we show that such domains can be used as a framework in the construction of a functional heterodimeric Fv fragment, which was expressed solubly, with high yield in the cytoplasm of Escherichia coli. This designed catalytic intrabody, obtained from grafting the combining site of the esterolytic antibody 17E8, is active in the oxidized and the reduced state. Its construction required no special features on the part of the immunoglobulin, no single-chain linker and introduced no non-natural sequence motifs. The potential to design intrabodies with the recognition sequences of arbitrary immunoglobulins opens novel opportunities for gene therapy, cell biology, metabolic engineering and antibody biotechnology.

Generation of anti-p53 Fab fragments from individuals with colorectal cancer using phage display

Although many individuals with malignancy develop Abs against p53, little is currently known of the structural features, V gene usage, and degree of somatic mutation of these Abs. Such information is critical to any meaningful understanding of the nature and significance of this humoral immune response to p53. We have constructed phage display libraries from six individuals with colorectal cancer and a demonstrable serum immune response against p53. Following panning with recombinant p53, a total of 43 binding Fab were identified. Four of these Abs bound with high affinity to wild-type denatured p53 (1.19 x 10-8 - 1.57 x 10-8), as determined by BIAcore analysis, and were highly specific for both recombinant and cell line-derived p53, as determined by ELISA and immunoprecipitation. Epitope mapping showed they were reactive with the N terminus of human p53 between residues 27 and 44. Sequence analysis showed that the heavy chains were derived from the VH1 gene family, and the light chains from VL4. The pattern of replacement and silent mutations in the Fab sequence indicated that negative selection had occurred in the framework regions of all the VH genes. We show that lymphocytes from individuals with cancer represent a valuable source of high affinity human Abs against p53. This approach provides an opportunity to examine the genetic structure of these naturally occurring Abs, and to draw inferences regarding the nature of the immune response that produced them. Abs identified in this way have a number of potential therapeutic applications.

In vitro modulation of AL-amyloid formation by human mesangial cells exposed to amyloidogenic light chains

We have shown in vitro AL-amyloid formation by human mesangial cells (HMCs). AL-amyloid formation may require lysosomal processing of the light chains (LCs) by HMCs for amyloidogenesis to occur. Chloroquine inhibits lysosomal activity. TGF-beta mediates extracellular matrix formation in many glomerulopathies. Thrombospondin (TSP) has been proposed as a mediator of cell proliferation and a marker of early fibrosis. We investigated amyloid formation by HMCs exposed to AL-LCs in the absence of amyloid enhancing factor (AEF). The effects of TGF-beta, TSP and chloroquine on in vitro amyloid formation were studied. HMCs were incubated with two AL-LCs, a light chain deposition disease (LCDD)-LC, or one of two tubulopathic LCs (T-LCs). Additional cells were treated with an AL-LC and chloroquine, TGF-beta, or TSP. Amyloid formation was evaluated microscopically using hematoxylin and eosin, Congo red and Thioflavin-T stains, as well as ultrastructurally. Amyloid was formed only when HMCs were incubated with AL-LCs. Addition of TSP significantly enhanced amyloid formation. In contrast, exogenous TGF-beta and chloroquine significantly attenuated amyloid formation. These findings show that some AL-LCs do not require AEF for amyloidogenesis to occur, and that chloroquine, TGF-beta and sTSP modulate in vitro AL-amyloidosis.

Expressed immunoglobulin repertoire of LPS-stimulated splenocytes of unimmunized mice as studied by two-dimensional gel electrophoresis

The repertoire of isolated immunoglobulin polypeptide chains synthesized by LPS-stimulated splenic B cells from unimmunized 6 weeks old mice was studied by two-dimensional gel electrophoresis. These B cells formed mainly mu heavy chains, while only a small amount of gamma chains was detected on two-dimensional electrophoregrams. The number and character of spots corresponding to each class and type of H and L chains were analyzed. Most of the detected 52 spots, which corresponded to L chains, were well resolved with clearly defined round boundaries. Six of them belonged to two isotypes of lambda chains and the rest to the kappa chain. About 25 clusters corresponded to mu chains. They had different appearance from those of L chains and their characteristic elliptic form with prolonged vertical axes indicated the presence of several H chain variants of slightly different length (due probably to the length variations of CDR3 and carbohydrate heterogeneity) in each cluster. The limited number of spots both of H and L chains is explained as being due to restrictions in the expressed repertoire of preimmune splenic B cells, which have no somatic mutations in the immunoglobulin genes. The concept of macrorepertoire (referring to the relatively small number of detected molecular species) and microrepertoire (describing the mutationally altered molecules) is introduced.

Mutual stabilization of VL and VH in single-chain antibody fragments, investigated with mutants engineered for stability

A set of six mutants of the levan binding single-chain Fv (scFv) fragment A48 (ABPC48), which have the identical light chain but differ gradually in the stability of the heavy chain, was generated. This was achieved by introducing one or both of the stabilizing mutations H-K66R and H-N52S into the VH domain of the A48 wild-type protein, which is naturally missing the conserved disulfide bridge in VH, and into the cysteine-restored variant A48cys scFv. The stabilizing effects of these two mutations in VH, which had been selected in the context of a disulfide-free derivative of this scFv fragment [Proba, K., et al. (1998) J. Mol. Biol. 275, 245-253], were found to be additive and transferable to the cysteine-restored variant of the A48 scFv, thereby generating extremely stable VH domains. The equilibrium denaturation of these scFv fragments was compared with the corresponding isolated VL domain and two of the different isolated VH domains. In the scFv fragment, the VL domain was found to be stabilized by a more stable VH domain, and, conversely, the VH domain was stabilized by a more stable VL domain. A folding intermediate with nativelike VH and denatured VL was found at equilibrium, if VH was significantly more stable than VL. In all other cases, a cooperative unfolding of the scFv was observed. We explain this observation with different contributions of intrinsic domain stability and extrinsic stabilization provided by the partner domain in the single-chain antibodies.

Myeloma light chains are ligands for cubilin (gp280)

Although myeloma light chains are known to undergo receptor-mediated endocytosis in the kidney, the molecular identity of the receptor has not been characterized. We examined the interaction between cubilin (gp280) and four species of light chains isolated from the urine of patients with multiple myeloma. Four lines of evidence identify cubilin, a giant glycoprotein receptor, which is restricted in distribution to endocytic scavenger pathways and which has potent effects on endosomal trafficking, as a potentially physiologically relevant binding site for light chains: 1) light chains coeluted during immunoaffinity purification of cubilin; 2) polyclonal antisera to cubilin but not control sera, displaced human light chain binding from rat renal brush-border membranes; 3) cubilin bound to multiple species of light chains during surface plasmon resonance; 4) anti-cubilin antiserum interfered with light chain endocytosis by visceral yolk sac epithelial cells. However, both binding of light chains to brush-border membranes and endocytosis of light chains by yolk sac epithelial cells were only partially inhibited by anticubilin antibodies, suggesting presence of additional or alternate binding sites for light chains. Excess light chain had a potent inhibitory effect on endosomal fusion in vitro. Binding showed dose and time-dependent saturability with low-affinity, high-capacity equilibrium binding parameters. These data demonstrate that cubilin plays a role in the endocytosis and trafficking of light chains in renal proximal tubule cells.

An intrinsically stable antibody scFv fragment can tolerate the loss of both disulfide bonds and fold correctly

A fully functional cysteine-free derivative of the intrinsically stable anti-HER2 scFv fragment hu4D5-8 was generated by replacing the disulfide forming cysteine residues in VH and VL with the amino acid combination valine-alanine in both domains. The antigen binding properties, determined by ELISA and BIAcore measurements, were not affected by removal of the disulfide bonds. The thermodynamic stability of the disulfide-containing scFv of 8.1 kcal/mol is decreased upon complete reduction of both disulfides to 2.7 kcal/mol, while that of the valine-alanine variant is somewhat higher (about 3.8 kcal/ mol). Our results suggest that, in principle, a disulfide-free fully functional derivative of any scFv can be obtained, as long as the corresponding disulfide-containing scFv has a high enough thermodynamic stability.

Immunological and molecular analysis of three monoclonal lupus anticoagulant antibodies from a patient with systemic lupus erythematosus

Antiphospholipid antibodies (APA), including lupus anticoagulants (LAC; as detected by in vitro blood clotting tests) and anti-cardiolipin antibodies (ACA; as assayed by solid-phase immunoassay), are strongly associated with recurrent thrombosis, thrombocytopenia, and recurrent fetal loss in some patients with systemic lupus erythematosus (SLE). The combined presence of APA and these clinical manifestations is termed antiphospholipid syndrome (APS). LAC and ACA comprise heterogeneous and somewhat overlapping autoantibody subsets. To date, it is unclear what degree of heterogeneity is present in an individual patient and between patients. To begin to address these issues, we generated three monoclonal LAC antibodies from a patient with SLE and APS. These antibodies were studied for their binding specificities and variable (V) region nucleotide sequences. All three LAC were unreactive with DNA, cardiolipin or other phospholipids. Sequence analysis of these antibodies revealed extensive overlap in their Ig V genes with anti-DNA antibodies and other autoantibodies characteristic of lupus. These data provide the first V gene sequence information on a group of SLE-derived LAC without ACA activity, representative of a similar subset of LAC found in patients with APS.

DNA-hydrolyzing activity of the light chain of IgG antibodies from milk of healthy human mothers

Various catalytically active antibodies or abzymes have been detected recently in the sera of patients with several autoimmune pathologies, where their presence is most probably associated with autoimmunization. Normal humans are generally considered to have no abzymes, since no obvious immunizing factors are present. Recently we have shown that IgG (its Fab and F(ab)2 fragments) from the milk of normal humans possesses DNase activity. Here we demonstrate for the first time that the light chain of IgG catalyzes the reaction of DNA hydrolysis. These findings speak in favor of the generation of abzymes in the tissue of healthy mothers, and since a mother's breast milk protects her infant from infections until the immune system is developed, they raise the possibility that these abzymes may contribute to this protective role.