C‐terminal lysine processing of human immunoglobulin G2 heavy chain in vivo

Although human IgG heavy chain genes encode a C‐terminal lysine, this residue is mostly absent from the endogenous antibodies isolated from serum. Some low but variable level of C‐terminal lysine is present on therapeutic antibodies expressed in mammalian cell culture systems. Here, we monitored the C‐terminal lysine processing of a recombinant human IgG2 antibody after intravenous injection into human subjects. Peptide mapping of the therapeutic antibody isolated from serum samples by affinity purification was used to quantify the C‐terminal lysine levels over time in vivo. The C‐terminal lysine residue was found to be rapidly lost in vivo with a half life of about an hour (62 min). In vivo C‐terminal lysine processing could be reproduced in vitro, but at a faster rate, by incubating in human serum. Pretreated serum, under conditions used to inactivate carboxypeptidase U, generated in vitro C‐terminal lysine processing rates that more closely matched those in vivo. Endogenous IgG, isolated from human blood, contained very low levels of C‐terminal lysine (～0.02%), consistent with the expected circulating half life of antibodies and the calculated C‐terminal lysine processing rate. Thus, the low residual IgG2 C‐terminal lysine is rapidly processed in vivo and such processing likely occurs on endogenous antibodies in circulation. Biotechnol. Bioeng. 2011;108: 404–412. © 2010 Wiley Periodicals, Inc.     

Effect of copper variation in yeast hydrolysate on C‐terminal lysine levels of a monoclonal antibody

The ability to control charge heterogeneity in monoclonal antibodies is important to demonstrate product quality comparability and consistency. This article addresses the control of C‐terminal lysine processing through copper supplementation to yeast hydrolysate powder, a raw material used in the cell culture process. Large‐scale production of a murine cell line exhibited variation in the C‐terminal lysine levels of the monoclonal antibody. Analysis of process data showed that this variation correlated well with shifts in cell lactate metabolism and pH levels of the production culture. Small‐scale studies demonstrated sensitivity of the cells to copper, where a single low dose of copper to the culture impacted cell lactate metabolism and C‐terminal lysine processing. Subsequent analytical tests indicated that the yeast hydrolysate powder, added to the basal media and nutrient feed in the process, contained varying levels of trace copper across lots. The measured copper concentrations in yeast hydrolysate lots correlated well with the variation in lactate and pH trends and C‐terminal lysine levels of the batches in manufacturing. Small‐scale studies further demonstrated that copper supplementation to yeast hydrolysate lots with low concentrations of copper can shift the metabolic performance and C‐terminal lysine levels of these cultures to match the control, high copper cultures. Hence, a strategy of monitoring, and if necessary supplementing, copper in yeast‐hydrolysate powders resulted in the ability to control and ensure product quality consistency. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:463–468, 2017     

Non-random Escape Pathways from a Broadly Neutralizing Human Monoclonal Antibody Map to a Highly Conserved Region on the Hepatitis C Virus E2 Glycoprotein Encompassing Amino Acids 412–423

A challenge for hepatitis C virus (HCV) vaccine development is to define epitopes that are able to elicit protective antibodies against this highly diverse virus. The E2 glycoprotein region located at residues 412–423 is conserved and antibodies to 412–423 have broadly neutralizing activities. However, an adaptive mutation, N417S, is associated with a glycan shift in a variant that cannot be neutralized by a murine but by human monoclonal antibodies (HMAbs) against 412–423. To determine whether HCV escapes from these antibodies, we analyzed variants that emerged when cell culture infectious HCV virions (HCVcc) were passaged under increasing concentrations of a specific HMAb, HC33.1. Multiple nonrandom escape pathways were identified. Two pathways occurred in the context of an N-glycan shift mutation at N417T. At low antibody concentrations, substitutions of two residues outside of the epitope, N434D and K610R, led to variants having improved in vitro viral fitness and reduced sensitivity to HC33.1 binding and neutralization. At moderate concentrations, a S419N mutation occurred within 412–423 in escape variants that have greatly reduced sensitivity to HC33.1 but compromised viral fitness. Importantly, the variants generated from these pathways differed in their stability. N434D and K610R-associated variants were stable and became dominant as the virions were passaged. The S419N mutation reverted back to N419S when immune pressure was reduced by removing HC33.1. At high antibody concentrations, a mutation at L413I was observed in variants that were resistant to HC33.1 neutralization. Collectively, the combination of multiple escape pathways enabled the virus to persist under a wide range of antibody concentrations. Moreover, these findings pose a different challenge to vaccine development beyond the identification of highly conserved epitopes. It will be necessary for a vaccine to induce high potency antibodies that prevent the formation of escape variants, which can co-exist with lower potency or levels of neutralizing activities.     

Arginine‐ but not alanine‐rich carboxy‐termini trigger nuclear translocation of mutant keratin 10 in ichthyosis with confetti

Ichthyosis with confetti (IWC) is a genodermatosis associated with dominant‐negative variants in keratin 10 (KRT10) or keratin 1 (KRT1). These frameshift variants result in extended aberrant proteins, localized to the nucleus rather than the cytoplasm. This mislocalization is thought to occur as a result of the altered carboxy (C)‐terminus, from poly‐glycine to either a poly‐arginine or ‐alanine tail. Previous studies on the type of C‐terminus and subcellular localization of the respective mutant protein are divergent. In order to fully elucidate the pathomechanism of IWC, a greater understanding is critical. This study aimed to establish the consequences for localization and intermediate filament formation of altered keratin 10 (K10) C‐termini. To achieve this, plasmids expressing distinct KRT10 variants were generated. Sequences encoded all possible reading frames of the K10 C‐terminus as well as a nonsense variant. A keratinocyte line was transfected with these plasmids. Additionally, gene editing was utilized to introduce frameshift variants in exon 6 and exon 7 at the endogenous KRT10 locus. Cellular localization of aberrant K10 was observed via immunofluorescence using various antibodies. In each setting, immunofluorescence analysis demonstrated aberrant nuclear localization of K10 featuring an arginine‐rich C‐terminus. However, this was not observed with K10 featuring an alanine‐rich C‐terminus. Instead, the protein displayed cytoplasmic localization, consistent with wild‐type and truncated forms of K10. This study demonstrates that, of the various 3′ frameshift variants of KRT10, exclusively arginine‐rich C‐termini lead to nuclear localization of K10.     

Investigation of the correlation between charge and glycosylation of IgG1 variants by liquid chromatography–mass spectrometry

A recombinant IgG1 monoclonal antibody (mAb) showed multiple charge variants in a cation exchange chromatography profile. To better understand the correlation between charge heterogeneity and glycosylation, a rapid reversed phase ultra-performance liquid chromatography–mass spectrometry (UPLC–MS) method with integrated mass analysis has been developed for simultaneous determination of N-terminal pyroglutamate, C-terminal lysine truncation, and Fc glycosylation. The results show that various degrees and/or types of N-terminal pyroglutamate formation and C-terminal lysine (Lys) cleavage account for the majority of charge heterogeneity; and the charge variants showed Fc glycosylation patterns in relation to their terminal modifications. The amount of G1F decreased in the basic variants, whereas Man5 and G0F-GN increased. The complement-dependent cytotoxicity (CDC) activity of purified charge variants also suggested the potential impact of the charge differences on the glycosylation profile.     

The effect of low intensity ultraviolet‐C light on monoclonal antibodies

As part of an investigation to identify potential new viral reduction strategies, ultraviolet‐C (UV‐C) light was examined. Although this technology has been known for decades to possess excellent virus inactivation capabilities, UV‐C light can also introduce significant unwanted damage to proteins. To study the effect on monoclonal antibodies, three different antibodies were subjected to varying levels of UV‐C light using a novel dosing device from Bayer Technology Services GmbH. The range of fluencies (or doses) covered was between 0 and 300 J/m² at a wavelength of 254 nm. Product quality data generated from the processed pools showed only minimal damage done to the antibodies. Aggregate formation was low for two of the three antibodies tested. Acidic and basic variants increased for all three antibodies, with the basic species increasing more than the acidic species. Peptide maps made for the three sets of pools showed no damage to two of the three antibody backbones, whereas the third antibody had very low levels of methionine oxidation evident. Samples held at 2–8°C for 33 days showed no increase in aggregates or charge variants, indicating that the proteins did not degrade and were not damaged further by reactive or catalytic species that may have been created on exposure to UV‐C light. Overall, UV‐C light was shown to induce very little damage to monoclonal antibodies at lower fluencies and appears to be a viable option for viral inactivation in biotechnology applications. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Isolation of B subunit‐specific monoclonal antibody clones that strongly neutralize the toxicity of Shiga toxin 2

Shiga toxin 2 (Stx2)‐specific mAb‐producing hybridoma clones were generated from mice. Because mice tend to produce small amounts of B subunit (Stx2B)‐specific antibodies at the polyclonal antibody level after immunization via the parenteral route, mice were immunized intranasally with Stx2 toxoids with a mutant heat‐labile enterotoxin as a mucosal adjuvant; 11 different hybridoma clones were obtained in two trials. Six of them were A subunit (Stx2A)‐specific whereas five were Stx2B‐specific antibody‐producing clones. The in vitro neutralization activity of Stx2B‐specific mAbs against Stx2 was greater than that of Stx2A‐specific mAbs on HeLa229 cells. Furthermore, even at low concentrations two of the Stx2B‐specific mAbs (45 and 75D9) completely inhibited receptor binding and showed in vivo neutralization activity against a fivefold median lethal dose of Stx2 in mice. In western blot analysis, these Stx2B‐specific neutralization antibodies did not react to three different mutant forms of Stx2, each amino acid residue of which was associated with receptor binding. Additionally, the nucleotide sequences of the V_H and V_L regions of clones 45 and 75D9 were determined. Our Stx2B‐specific mAbs may be new candidates for the development of mouse‐human chimeric Stx2‐neutralizing antibodies which have fewer adverse effects than animal antibodies for enterohemorrhagic Escherichia coli infection.     

A strategically positioned cation is crucial for efficient catalysis by chorismate mutase

Combinatorial mutagenesis and in vivo selection experiments previously afforded functional variants of the AroH class Bacillus subtilis chorismate mutase lacking the otherwise highly conserved active site residue Arg(90). Here, we present a detailed kinetic and crystallographic study of several such variants. Removing the arginine side chain (R90G and R90A) reduced catalytic efficiency by more than 5 orders of magnitude. Reintroducing a positive charge to the active site through lysine substitutions restored more than a factor of a thousand in k(cat). Remarkably, the lysine could be placed at position 90 or at the more remote position 88 provided a sterically suitable residue was present at the partner site. Crystal structures of the double mutants C88S/R90K and C88K/R90S show that the lysine adopts an extended conformation that would place its epsilon-ammonium group within hydrogen-bonding distance of the ether oxygen of bound chorismate in the transition state. These results provide support for the hypothesis that developing negative charge in the highly polarized transition state is stabilized electrostatically by a strategically placed cation. The implications of this finding for the mechanism of all natural chorismate mutases and for the design of artificial catalysts are discussed.     

Potent inhibitors of human matriptase‐1 based on the scaffold of sunflower trypsin inhibitor

Sunflower trypsin inhibitor‐1 (SFTI‐1), a bicyclic tetradecapeptide, has become a versatile tool as a scaffold for the development of the inhibitors of therapeutically relevant serine proteases, among them matriptase and kallikreins. Herein, we report the rational design of potent monocyclic and bicyclic inhibitors of human matriptase‐1. We found that the presence of positive charge and lack of bulky residues at the peptide N‐terminus is required for the maintenance of inhibitory activity. Replacement of the N‐terminal glycine residue by lysine allowed for the chemical conjugation with a fluorophor via the ε‐amino group without significant loss of inhibitory activity. Head‐to‐tail and side‐chain‐to‐tail cyclization resulted in potent inhibitors with comparable activities against matriptase‐1. The most potent synthetic bicyclic inhibitor found in this study (K_i = 2.6 nM at pH 7.6) is a truncated version of SFTI‐1 (cyclo‐KRCTKSIPPRCH) lacking a C‐terminal proline and aspartate residue. It combines an internal disulfide bond with a peptide macrocycle that is formed through side‐chain‐to‐tail cyclization of the ε‐amino group of an N‐terminal lysine and a C‐terminal proline. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Novel single-chain Fv' formats for the generation of immunoliposomes by site-directed coupling

Immunoliposomes generated by coupling of antibodies to the liposomal surface allow for an active targeting of entrapped compounds to diseased areas. Single-chain Fv fragments (scFv) represent the smallest part of an antibody containing the entire antigen-binding site. They can be coupled in a defined and site-directed manner through genetically engineered cysteine residues, for example, those added at the C-terminus. Here, we have performed a comparative analysis of various scFv' variants with cysteine residues present at the end of a C-terminal extension of varying length and composition (HC variants) or introduced in the linker sequence connecting the variable heavy and light chain domain (LC variants). Using a scFv fragment directed against fibroblast activation protein (FAP) as a model antibody, we could show that all variants can be employed for the generation of active immunoliposomes, although the presence of three additional cysteine residues in one scFv' molecule resulted in decreased binding of immunoliposomes compared to that of immunoliposomes generated with scFv' molecules containing only one additional cysteine residue. In order to further improve the scFv' format by reducing the number of additional amino acid residues, we also generated molecules with the hexahistidyl-tag incorporated into the linker sequence together with a cysteine residue either at position 1 or 3 of the linker sequence (LCH variants). These newly designed scFv' molecules may be particularly suitable for the generation of immunoliposomes and other antibody conjugates, limiting the number of additional residues in these antibody molecules to a minimum.     

Antigenic variants of herpes simplex virus selected with glycoprotein-specific monoclonal antibodies.

Monoclonal antibodies specific for herpes simplex virus type 1 (HSV-1) glycoproteins were used to demonstrate that HSV undergoes mutagen-induced and spontaneous antigenic variation. Hybridomas were produced by polyethylene glycol-mediated fusion of P3-X63-Ag8.653 myeloma cells with spleen cells from BALB/c mice infected with HSV-1 (strain KOS). Hybrid clones were screened for production of HSV-specific neutralizing antibody. The glycoprotein specificities of the antibodies were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immunoprecipitates of radiolabeled infected-cell extracts. Seven hybridomas producing antibodies specific for gC, one for gB, and one for gD were characterized. All antibodies neutralized HSV-1 but not HSV-2. Two antibodies, one specific for gB and one specific for gC, were used to select viral variants resistant to neutralization by monoclonal antibody plus complement. Selections were made from untreated and bromodeoxyuridine- and nitrosoguanidine-mutagenized stocks of a plaque-purified isolate of strain KOS. After neutralization with monoclonal antibody plus complement, surviving virus was plaque purified by plating at limiting dilution and tested for resistance to neutralization with the selecting antibody. The frequency of neutralization-resistant antigenic variants selected with monoclonal antibody ranged from 4 X 10(-4) in nonmutagenized stocks to 1 X 10(-2) in mutagenized stocks. Four gC and four gB antigenic variants were isolated. Two variants resistant to neutralization by gC-specific antibodies failed to express gC, accounting for their resistant phenotype. The two other gC antigenic variants and the four gB variants expressed antigenically altered glycoproteins and were designated monoclonal-antibody-resistant, mar, mutants. The two mar C mutants were tested for resistance to neutralization with a panel of seven gC-specific monoclonal antibodies. The resulting patterns of resistance provided evidence for at least two antigenic sites on glycoprotein gC.     

Efficient Internalization of MHC I Requires Lysine‐11 and Lysine‐63 Mixed Linkage Polyubiquitin Chains

The downregulation of cell surface receptors by endocytosis is a fundamental requirement for the termination of signalling responses and ubiquitination is a critical regulatory step in receptor regulation. The K5 gene product of Kaposi's sarcoma‐associated herpesvirus is an E3 ligase that ubiquitinates and downregulates several cell surface immunoreceptors, including major histocompatibility complex (MHC) class I molecules. Here, we show that K5 targets the membrane proximal lysine of MHC I for conjugation with mixed linkage polyubiquitin chains. Quantitative mass spectrometry revealed an increase in lysine‐11, as well as lysine‐63, linked polyubiquitin chains on MHC I in K5‐expressing cells. Using a combination of mutant ubiquitins and MHC I molecules expressing a single cytosolic lysine residue, we confirm a functional role for lysines‐11 and ‐63 in K5‐mediated MHC I endocytosis. We show that lysine‐11 linkages are important for receptor endocytosis, and that complex mixed linkage polyubiquitin chains are generated in vivo.     

Development of at‐line assay to monitor charge variants of MAbs during production

One major challenge currently facing the biopharmaceutical industry is to understand how MAb microheterogeneity affects therapeutic efficacy, potency, immunogenicity, and clearance. MAb micro‐heterogeneity can result from post‐translational modifications such as sialylation, galactosylation, C‐terminal lysine cleavage, glycine amidation, and tryptophan oxidation, each of which can generate MAb charge variants; such heterogeneity can affect pharmacokinetics (PK) considerably. Implementation of appropriate on‐line quality control strategies may help to regulate bioprocesses, thus enabling more homogenous material with desired post‐translational modifications and PK behavior. However, one major restriction to implementation of quality control strategies is the availability of techniques for obtaining on‐line or at‐line measurements of these attributes. In this work, we describe the development of an at‐line assay to separate MAb charge variants in near real‐time, which could ultimately be used to implement on‐line quality control strategies for MAb production. The assay consists of a 2D‐HPLC method with sequential in‐line Protein A and WCX‐10 HPLC column steps. To perform the 2D‐HPLC assay at‐line, the two columns steps were integrated into a single method using a novel system configuration that allowed parallel flow over column 1 or column 2 or sequential flow from column 1 to column 2. A bioreactor system was also developed such that media samples could be removed automatically from bioreactor vessels during production and delivered to the 2D‐HPLC for analysis. With this at‐line HPLC assay, we have demonstrated that MAb microheterogeneity occurs throughout the cell cycle whether the host cell line is grown under different or the same nominal culture conditions. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:249–255, 2014     

Measurements of auto‐antibodies to α‐synuclein in the serum and cerebral spinal fluids of patients with Parkinson's disease

Biomarkers for α‐synuclein are needed for diagnosis and prognosis in Parkinson's disease (PD ). Endogenous auto‐antibodies to α‐synuclein could serve as biomarkers for underlying synucleinopathy, but previous assessments of auto‐antibodies have shown variability and inconsistent clinical correlations. We hypothesized that auto‐antibodies to α‐synuclein could be diagnostic for PD and explain its clinical heterogeneity. To test this hypothesis, we developed an enzyme‐linked immunosorbent assay for measuring α‐synuclein auto‐antibodies in human samples. We evaluated 69 serum samples (16 healthy controls (HC ) and 53 PD patients) and 145 CSF samples (52 HC and 93 PD patients) from our Institution. Both serum and CSF were available for 24 participants. Males had higher auto‐antibody levels than females in both fluids. CSF auto‐antibody levels were significantly higher in PD patients as compared with HC , whereas serum levels were not significantly different. CSF auto‐antibody levels did not associate with amyloid‐β_1–42, total tau, or phosphorylated tau. CSF auto‐antibody levels correlated with performance on the Montreal Cognitive Assessment, even when controlled for CSF amyloidβ_1–42. CSF hemoglobin levels, as a proxy for contamination of CSF by blood during lumbar puncture, did not influence these observations. Using recombinant α‐synuclein with N‐ and C‐terminal truncations, we found that CSF auto‐antibodies target amino acids 100 through 120 of α‐synuclein. We conclude that endogenous CSF auto‐antibodies are significantly higher in PD patients as compared with HC , suggesting that they could indicate the presence of underlying synucleinopathy. These auto‐antibodies associate with poor cognition, independently of CSF amyloidβ_1–42, and target a select C‐terminal region of α‐synuclein.

Read the Editorial Highlight for this article on page 433 .

     

miRNA engineering of CHO cells facilitates production of difficult‐to‐express proteins and increases success in cell line development

In recent years, coherent with growing biologics portfolios also the number of complex and thus difficult‐to‐express (DTE) therapeutic proteins has increased considerably. DTE proteins challenge bioprocess development and can include various therapeutic protein formats such as monoclonal antibodies (mAbs), multi‐specific affinity scaffolds (e.g., bispecific antibodies), cytokines, or fusion proteins. Hence, the availability of robust and versatile Chinese hamster ovary (CHO) host cell factories is fundamental for high‐yielding bioprocesses. MicroRNAs (miRNAs) have emerged as potent cell engineering tools to improve process performance of CHO manufacturing cell lines. However, there has not been any report demonstrating the impact of beneficial miRNAs on industrial cell line development (CLD) yet. To address this question, we established novel CHO host cells constitutively expressing a pro‐productive miRNA: miR‐557. Novel host cells were tested in two independent CLD campaigns using two different mAb candidates including a normal as well as a DTE antibody. Presence of miR‐557 significantly enhanced each process step during CLD in a product independent manner. Stable expression of miR‐557 increased the probability to identify high‐producing cell clones. Furthermore, production cell lines derived from miR‐557 expressing host cells exhibited significantly increased final product yields in fed‐batch cultivation processes without compromising product quality. Strikingly, cells co‐expressing miR‐557 and a DTE antibody achieved a twofold increase in product titer compared to clones co‐expressing a negative control miRNA. Thus, host cell engineering using miRNAs represents a promising tool to overcome limitations in industrial CLD especially with regard to DTE proteins. Biotechnol. Bioeng. 2017;114: 1495–1510. © 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.     

离子交换色谱对抗VEGFR2单抗的电荷异质性分析

目的采用离子交换高效液相色谱(CEX-HPLC)分析抗VEGFR2(抗血管内皮生长因子受体2)单抗制品的电荷异质性。方法应用CEX-HPLC技术,对VEGFR2单抗进行电荷异质性分析,并结合羧肽酶B(CpB)和N-糖酰胺酶F(EndoF2)酶切,初步研究其电荷异质性的成因。结果用CEX-HPLC分析CpB酶切前后单抗,证明其碱性变异体主要由C末端赖氨酸不均一性引起;分析EndoF2酶切前后处理的单抗,证明其酸性变异体部分由N-糖末端上的唾液酸修饰所引起。通过2种酶的顺序酶切可相对准确地分析含C-末端赖氨酸以及含唾液酸单抗的比例。结论采用CEX-HPLC可较好地分析单抗的电荷异质性;并结合合适的酶切处理,可判断单抗主要电荷异质性的来源,为保证单抗制品生产工艺的稳定性及质量控制提供了有效手段。     

A novel strategy for the generation of T cell lines lacking expression of endogenous alpha- and/or beta-chain T cell receptor genes

Mutant T cell lines that do not express the endogenous alpha- and/or beta-chain genes of the TCR were generated from the alpha beta TCR/CD3+ tumor cell line C6VL with a combination of classical mutagenesis methods and selection of somatic hybrid variants. This novel strategy obviated the need for repeated mutagenesis and screening of a large number of individual clones. The loss of either the alpha- or the beta-chain expression in the mutant cells was associated with the loss of surface TCR/CD3 complex, which could be rescued by the transfection of appropriate exogenous alpha- and/or beta-chain gene constructs. Because these cells express a single TCR molecule on the cell surface, they are useful for the study of the assembly and function of the alpha beta TCR. This strategy is also generally applicable for the generation of homozygous mutant cell lines lacking other gene products.     

Mechanism of antigenic drift in influenza virus. Amino acid sequence changes in an antigenically active region of Hong Kong (H3N2) influenza virus hemagglutinin

During antigenic drift in influenza viruses, changes in antigenicity are associated with changes in amino acid sequence of the large hemagglutinin polypeptide, HA1. In ten variants of Hong Kong (H3N2) influenza virus selected with monoclonal antibodies, the proline residue at position 143 in HA1 changed to serine, threonine, leucine or histidine. In other variants, asparagine 133 changed to lysine, glycine 144 to aspartic acid and serine 145 to lysine. All these changes are possible by single base changes in the RNA except the last, which requires a double base change. Residues 142 to 146 also changed in field strains of Hong Kong influenza isolated between 1968 and 1977 (Laver et al., 1980). The single amino acid sequence changes in HA1 of the monoclonal variants were detected by comparing the compositions of the soluble tryptic peptides from the variants with the known sequences of these peptides from wild-type virus. Two insoluble tryptic peptides, comprising residues 110 to 140 and 230 to 255 in the HA1 molecule, were not examined and we do not know if additional changes occurred in these regions.In order to determine whether sequential changes at the same position occurred during antigenic drift, antibody prepared against the new antigenic site on the variants in which proline 143 changed to histidine or threonine was used to select second generation variants of these variants. In the first case, the glycine residue (144) next to the histidine changed to aspartic acid, and in the second, the threonine residue at position 143 reverted to proline and the virus regained the antigenicity of wild-type.Although monoclonal antibodies revealed dramatic antigenic differences between the variants and wild-type virus, only those variants with changes at position 144 of glycine to aspartic acid or at position 145 of serine to lysine could be distinguished from wild-type virus using heterogeneous rabbit or ferret antisera. The other variants, including those which showed sequence changes in widely separated positions of HA1, could not be distinguished from wild-type with heterogeneous antisera.These findings suggest that sequence changes in the region comprising residues 142 to 146 of HA1 affect an important antigenic site on the hemagglutinin molecule, but how these changes affect the antigenic properties, or whether this region actually forms part of the antigenic site is not known.     

Monoclonal antibodies against neoantigens of the terminal C5b-9 complex of human complement

Assembly of the terminal C5b-C9 complement components into the cytolytic C5b-9 complex is accompanied by exposure of characteristic neoantigens on the macromolecule. We report the production and characterization of mouse monoclonal antibodies to C9-dependent neoantigens of human C5b-9. Binding-inhibition assays with EDTA-human plasma and micro-ELISA assays with purified C9 showed that the antibodies did not react with native complement components and thus confirmed the specificity of the antibodies for the neoantigens. The monoclonal antibodies did, however, cross-react with cytolyticaIly inactive, fluid-phase C5b-9 complexes, Thus, expression of the neoantigenic determinants was not dependent on the formation of high molecular weight C9 polymers with the complex, since these are absent in fluid-phase C5b-9. Radioiodinated antibodies could be utilized in immunoradiometric assays for the detection and quantitation of C5b-9 on cell membranes. Cross-reactivities of the antibodies with C9-dependent neoantigens of several other animal species were examined and antibody clones cross-reacting with rabbit (clones 3BI, 3Dg, and 2F3), sheep (clones 3Dg and 2F3) and guinea-pig (clone 3D8) neoantigens were identified . Three of four tested clones (3D8, 2F3, IA12) precipitated C5b-9 complexes in double-diffusion assays, probably due to their interaction with multiple and repeating C9-epitopes on the terminal complexes. The monoclonal antibodies will be of value for definitive identification and quantitation of C5b-9 on cell membranes and in tissues, and for establishing immunoassays for detection and quantitation of terminal fluid-phase C5b-9 complexes in plasma.