IdeS, a novel streptococcal cysteine proteinase with unique specificity for immunoglobulin G

Pharmacokinetic and Pharmacodynamic Considerations for the Use of Monoclonal Antibodies in the Treatment of Bacterial Infections

Antibiotic-resistant bacterial pathogens are increasingly implicated in hospital- and community-acquired infections. Recent advances in monoclonal antibody (mAb) production and engineering have led to renewed interest in the development of antibody-based therapies for treatment of drug-resistant bacterial infections. Currently, there are three antibacterial mAb products approved by the Food and Drug Administration (FDA) and at least nine mAbs are in clinical trials. Antibacterial mAbs are typically developed to kill bacteria or to attenuate bacterial pathological activity through neutralization of bacterial toxins and virulence factors. Antibodies exhibit distinct pharmacological mechanisms from traditional antimicrobials and, hence, cross-resistance between small molecule antimicrobials and antibacterial mAbs is unlikely. Additionally, the long biological half-lives typically found for mAbs may allow convenient dosing and vaccine-like prophylaxis from infection. However, the high affinity of mAbs and the involvement of the host immune system in their pharmacological actions may lead to complex and nonlinear pharmacokinetics and pharmacodynamics. In this review, we summarize the pharmacokinetics and pharmacodynamics of the FDA-approved antibacterial mAbs and those are currently in clinical trials. Challenges in the development of antibacterial mAbs are also discussed.

Pharmacokinetics, biodistribution and brain retention of a bispecific antibody-based PET radioligand for imaging of amyloid-β

Monoclonal antibodies (mAbs) have not been used as positron emission tomography (PET) ligands for in vivo imaging of the brain because of their limited passage across the blood-brain barrier (BBB). However, due to their high affinity and specificity, mAbs may be an attractive option for brain PET if their brain distribution can be facilitated. In the present study, a F(ab’)₂ fragment of the amyloid-beta (Aβ) protofibril selective mAb158 was chemically conjugated to the transferrin receptor (TfR) antibody 8D3 to enable TfR mediated transcytosis across the BBB. The generated bispecific protein, 8D3-F(ab’)₂-h158, was subsequently radiolabeled and used for microPET imaging of Aβ pathology in two mouse models of AD. [¹²⁴I]8D3-F(ab’)₂-h158 was distributed across the BBB several fold more than unmodified mAbs in general and its accumulation in the brain reflected disease progression, while its concentration in blood and other organs remained stable across all age groups studied. Cerebellum was largely devoid of 8D3-F(ab’)₂-h158 in young and middle aged mice, while mice older than 18 months also showed some accumulation in cerebellum. In a longer perspective, the use of bispecific antibodies as PET ligands may enable in vivo ‘immunohistochemistry’ also of other proteins in the brain for which PET radioligands are lacking.

GingisKHAN™ protease cleavage allows a high-throughput antibody to Fab conversion enabling direct functional assessment during lead identification of human monoclonal and bispecific IgG1 antibodies

The determination of the binding strength of immunoglobulins (IgGs) to targets can be influenced by avidity when the targets are soluble di- or multimeric proteins, or associated to cell surfaces, including surfaces introduced from heterogeneous assays. However, for the understanding of the contribution of a second drug-to-target binding site in molecular design, or for ranking of monovalent binders during lead identification, affinity-based assessment of the binding strength is required. Typically, monovalent binders like antigen-binding fragments (Fabs) are generated by proteolytic cleavage with papain, which often results in a combination of under- and over-digestion, and requires specific optimization and chromatographic purification of the desired Fabs. Alternatively, the Fabs are produced by recombinant approaches. Here, we report a lean approach for the functional assessment of human IgG1s during lead identification based on an in-solution digestion with the GingisKHAN™ protease, generating a homogenous pool of intact Fabs and Fcs and enabling direct assaying of the Fab in the digestion mixture. The digest with GingisKHAN™ is highly specific and quantitative, does not require much optimization, and the protease does not interfere with methods typically applied for lead identification, such as surface plasmon resonance or cell-based assays. GingisKHAN™ is highly suited to differentiate between affinity and avidity driven binding of human IgG1 monoclonal and bispecific antibodies during lead identification.

IgG Endopeptidase in Highly Sensitized Patients Undergoing Transplantation

BACKGROUND

Donor-specific antibodies create an immunologic barrier to transplantation. Current therapies to modify donor-specific antibodies are limited and ineffective in the most highly HLA-sensitized patients. The IgG-degrading enzyme derived from Streptococcus pyogenes (IdeS), an endopeptidase, cleaves human IgG into F(ab')₂ and Fc fragments inhibiting complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity, which suggests that IdeS might be useful for desensitization. We report on the combined experience of two independently performed open-label, phase 1-2 trials (conducted in Sweden and the United States) that assessed the efficacy of IdeS with regard to desensitization and transplantation of a kidney from an HLA-incompatible donor.

METHODS

We administered IdeS to 25 highly HLA-sensitized patients (11 patients in Uppsala or Stockholm, Sweden, and 14 in Los Angeles) before the transplantation of a kidney from an HLA-incompatible donor. Frequent monitoring for adverse events, outcomes, donor-specific antibodies, and renal function was performed, as were renal biopsies. Immunosuppression after transplantation consisted of tacrolimus, mycophenolate mofetil, and glucocorticoids. Patients in the U.S. study also received intravenous immune globulin and rituximab after transplantation to prevent antibody rebound.

RESULTS

Recipients in the U.S. study had a significantly longer cold ischemia time (the time elapsed between procurement of the organ and transplantation), a significantly higher rate of delayed graft function, and significantly higher levels of class I donor-specific antibodies than those in the Swedish study. A total of 38 serious adverse events occurred in 15 patients (5 events were adjudicated as being possibly related to IdeS). At transplantation, total IgG and HLA antibodies were eliminated. A total of 24 of 25 patients had perfusion of allografts after transplantation. Antibody-mediated rejection occurred in 10 patients (7 patients in the U.S. study and 3 in the Swedish study) at 2 weeks to 5 months after transplantation; all these patients had a response to treatment. One graft loss, mediated by non-HLA IgM and IgA antibodies, occurred.

CONCLUSIONS

IdeS reduced or eliminated donor-specific antibodies and permitted HLA-incompatible transplantation in 24 of 25 patients. (Funded by Hansa Medical; ClinicalTrials.gov numbers, NCT02224820 , NCT02426684 , and NCT02475551 .).

Antibody-mediated rejection across solid organ transplants: manifestations, mechanisms, and therapies

Solid organ transplantation is a curative therapy for hundreds of thousands of patients with end-stage organ failure. However, long-term outcomes have not improved, and nearly half of transplant recipients will lose their allografts by 10 years after transplant. One of the major challenges facing clinical transplantation is antibody-mediated rejection (AMR) caused by anti-donor HLA antibodies. AMR is highly associated with graft loss, but unfortunately there are few efficacious therapies to prevent and reverse AMR. This Review describes the clinical and histological manifestations of AMR, and discusses the immunopathological mechanisms contributing to antibody-mediated allograft injury as well as current and emerging therapies.

IgG-degrading enzyme of Streptococcus pyogenes (IdeS) prevents disease progression and facilitates improvement in a rabbit model of Guillain-Barré syndrome

Autoantibodies binding to peripheral nerves followed by complement deposition and membrane attack complex formation results in nerve damage in Guillain-Barré syndrome (GBS). Strategies to remove the pathogenic autoantibodies or block the complement deposition benefit most patients with GBS. Immunoglobulin G-degrading enzyme of Streptococcus pyogenes (IdeS) is a cysteine protease which cleaves IgG antibodies into F(ab')₂ and Fc fragments. In this study, using a rabbit model of axonal GBS, acute motor axonal neuropathy (AMAN), we demonstrated that IdeS treatment significantly reduced the disruption of Nav channels as well as activated C3 deposition at the anterior spinal root nodes of Ranvier in AMAN rabbits. IdeS significantly promoted the clinical recovery of AMAN rabbits and there were significant lower frequencies of axonal degeneration in anterior spinal roots of AMAN rabbits with IdeS treatment compared to the saline controls. Our data support that IdeS treatment is a promising therapeutic strategy for GBS.

BspK, a Serine Protease from the Predatory Bacterium Bdellovibrio bacteriovorus with Utility for Analysis of Therapeutic Antibodies

The development of therapeutic and diagnostic antibodies is a rapidly growing field of research, being the fastest expanding group of products on the pharmaceutical market, and appropriate quality controls are crucial for their application. We have identified and characterized the serine protease termed BspK (Bdellovibrio serine protease K) from Bdellovibrio bacteriovorus and here show its activity on antibodies. Mutation of the serine residue at position 230 rendered the protease inactive. Further investigations of BspK enzymatic characteristics revealed autoproteolytic activity, resulting in numerous cleavage products. Two of the autoproteolytic cleavage sites in the BspK fusion protein were investigated in more detail and corresponded to cleavage after K₂₈ and K₂₁₀ in the N- and C-terminal parts of BspK, respectively. Further, BspK displayed stable enzymatic activity on IgG within the pH range of 6.0 to 9.5 and was inhibited in the presence of ZnCl₂. BspK demonstrated preferential hydrolysis of human IgG1 compared to other immunoglobulins and isotypes, with hydrolysis of the heavy chain at position K₂₂₆ generating two separate Fab fragments and an intact IgG Fc domain. Finally, we show that BspK preferentially cleaves its substrates C-terminally to lysines similar to the protease LysC. However, BspK displays a unique cleavage profile compared to several currently used proteases on the market.

IMPORTANCE The rapid development of novel therapeutic antibodies is partly hindered by difficulties in assessing their quality and safety. The lack of tools and methods facilitating such quality controls obstructs and delays the process of product approval, eventually affecting the patients in need of treatment. These difficulties in product evaluations indicate a need for new and comprehensive tools for such analysis. Additionally, recent concerns raised regarding the limitations of established products on the market (e.g., trypsin) further highlight a general need for a larger array of proteases with novel cleavage profiles to meet current and future needs, within both the life science industry and the academic research community.

bisFabs: Tools for rapidly screening hybridoma IgGs for their activities as bispecific antibodies

Bispecific antibodies are a growing class of therapeutic molecules. Many of the current bispecific formats require DNA engineering to convert the parental monoclonal antibodies into the final bispecific molecules. We describe here a method to generate bispecific molecules from hybridoma IgGs in 3-4 d using chemical conjugation of antigen-binding fragments (Fabs) (bisFabs). Proteolytic digestion conditions for each IgG isotype were analyzed to optimize the yield and quality of the final conjugates. The resulting bisFabs showed no significant amounts of homodimers or aggregates. The predictive value of murine bisFabs was tested by comparing the T-cell redirected cytotoxic activity of a panel of antibodies in either the bisFab or full-length IgG formats. A variety of antigens with different structures and expression levels was used to extend the comparison to a wide range of binding geometries and antigen densities. The activity observed for different murine bisFabs correlated with those observed for the full-length IgG format across multiple different antigen targets, supporting the use of bisFabs as a screening tool. Our method may also be used for the screening of bispecific antibodies with other mechanisms of action, allowing for a more rapid selection of lead therapeutic candidates.

Subunit mass analysis for monitoring antibody oxidation

Methionine oxidation is a common posttranslational modification (PTM) of monoclonal antibodies (mAbs). Oxidation can reduce the in-vivo half-life, efficacy and stability of the product. Peptide mapping is commonly used to monitor the levels of oxidation, but this is a relatively time-consuming method. A high-throughput, automated subunit mass analysis method was developed to monitor antibody methionine oxidation. In this method, samples were treated with IdeS, EndoS and dithiothreitol to generate three individual IgG subunits (light chain, Fd’ and single chain Fc). These subunits were analyzed by reversed phase-ultra performance liquid chromatography coupled with an online quadrupole time-of-flight mass spectrometer and the levels of oxidation on each subunit were quantitated based on the deconvoluted mass spectra using the UNIFI software. The oxidation results obtained by subunit mass analysis correlated well with the results obtained by peptide mapping. Method qualification demonstrated that this subunit method had excellent repeatability and intermediate precision. In addition, UNIFI software used in this application allows automated data acquisition and processing, which makes this method suitable for high-throughput process monitoring and product characterization. Finally, subunit mass analysis revealed the different patterns of Fc methionine oxidation induced by chemical and photo stress, which makes it attractive for investigating the root cause of oxidation.

Identification of a novel host-specific IgG protease in Streptococcus phocae subsp. phocae

Streptococcus (S.) phocae subsp. phocae causes bronchopneumonia and septicemia in a variety of marine mammals. Especially in harbor seals infected with phocine distemper virus it plays an important role as an opportunistic pathogen. This study was initiated by the detection of IgG cleavage products in Western blot analysis after incubation of bacterial supernatant with harbor seal serum. Hence, the objectives of this study were the identification and characterization of a secreted IgG cleaving protease in S. phocae subsp. phocae isolated from marine mammals. To further identify the responsible factor of IgG cleavage a protease inhibitor profile was generated. Inhibition of the IgG cleaving activity by iodoacetamide and Z-LVG-CHN₂ indicated that a cysteine protease is involved. Moreover, an anti-IdeS antibody directed against the IgG endopeptidase IdeS of S. pyogenes showed cross reactivity with the putative IgG protease of S. phocae subsp. phocae. The IgG cleaving factor of S. phocae subsp. phocae was identified through an inverse PCR approach and designated IdeP (Immunoglobulin G degrading enzyme of S. phocae subsp. phocae) in analogy to the cysteine protease IdeS. Notably, recombinant (r) IdeP is a host and substrate specific protease as it cleaves IgG from grey and harbor seals but not IgG from harbor porpoises or non-marine mammals. The identification of IdeP represents the first description of a protein in S. phocae subsp. phocae involved in immune evasion. Furthermore, the fact that IdeP cleaves solely IgG of certain marine mammals reflects functional adaption of S. phocae subsp. phocae to grey and harbor seals as its main hosts.

Toward Clinical use of the IgG Specific Enzymes IdeS and EndoS against Antibody-Mediated Diseases

The endoglycosidase EndoS and the protease IdeS from the human pathogen Streptococcus pyogenes are immunomodulating enzymes hydrolyzing human IgG. IdeS cleaves IgG in the lower hinge region, while EndoS hydrolyzes the conserved N-linked glycan in the Fc region. Both enzymes are remarkably specific for human IgG that after hydrolysis loses most of its effector functions, such as binding to leukocytes and complement activation, all contributing to bacterial evasion of adaptive immunity. However, taken out of their infectious context, we and others have shown that IdeS and EndoS can alleviate autoimmune disease in a number of animal models of antibody-mediated disorders. In this chapter, we will briefly describe the discovery and characterization of these unique enzymes, present the findings from a number of animal models of autoimmunity where the enzymes have been tested, and outline the ongoing clinical testing of IdeS. Furthermore, we will discuss the rationale for further development of IdeS and EndoS into novel pharmaceuticals against diseases where IgG antibodies contribute to the pathology, including, but not restricted to, chronic and acute autoimmunity, transplant rejection, and antidrug antibody reactions.

Generating and Purifying Fab Fragments from Human and Mouse IgG Using the Bacterial Enzymes IdeS, SpeB and Kgp

Fab fragments are valuable research tools in various areas of science including applications in imaging, binding studies, removal of Fc-mediated effector functions, mass spectrometry, infection biology, and many others. The enzymatic tools for the generation of Fab fragments have been discovered through basic research within the field of molecular bacterial pathogenesis. Today, these enzymes are widely applied as research tools and in this chapter, we describe methodologies based on bacterial enzymes to generate Fab fragments from both human and mouse IgG. For all human IgG subclasses, the IdeS enzyme from Streptococcus pyogenes has been applied to generate F(ab')2 fragments that subsequently can be reduced under mild conditions to generate a homogenous pool of Fab' fragments. The enzyme Kgp from Porphyromonas gingivalis has been applied to generate intact Fab fragments from human IgG1 and the Fab fragments can be purified using a CH1-specific affinity resin. The SpeB protease, also from S. pyogenes, is able to digest mouse IgGs and has been applied to digest antibodies and Fab fragments can be purified on light chain affinity resins. In this chapter, we describe methodologies that can be used to obtain Fab fragments from human and mouse IgG using bacterial proteases.

Measuring Antibody Orientation at the Bacterial Surface

Many bacteria have the ability to interact with antibodies as a means to circumvent the immune response. This includes binding to the Fc portion of antibodies, effectively reversing the antibody orientation and thus decreasing the Fc-mediated immune signaling. Since antibody orientation at the bacterial surface has been shown to be important in human disease, it is valuable to be able to assess how antibodies are interacting with bacterial pathogens. Here, we describe a method to measure the proportion of human IgG that are bound via their Fc or Fabs to a bacterial surface. This is achieved by treating antibody-coated bacteria with the bacterial enzyme IdeS - which will cleave IgG into Fc and Fab fragments - and subsequently detect remaining fragments with fluorescent Fabs. The method is easy and fast, and the principle is most likely also applicable to other systems where distinguishing between antibody Fc and Fab binding is important.

Anti-Hinge Antibodies Recognize IgG Subclass- and Protease-Restricted Neoepitopes

Anti-hinge Abs (AHAs) target neoepitopes exposed after proteolytic cleavage of IgG. In this study, we explored the diversity of protease- and IgG subclass-restricted AHAs and their potential as immunological markers in healthy donors (HDs) and patients with rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE). AHA reactivity against IgG-degrading enzyme of Streptococcus pyogenes (IdeS)- or pepsin-generated F(ab')₂ fragments of all four human IgG subclasses was determined. AHA reactivity against one or more out of eight F(ab')₂ targets was found in 68% (68 of 100) of HDs, 69% (68 of 99) of SLE patients, and 81% (79 of 97) of RA patients. Specific recognition of hinge epitopes was dependent on IgG subclass and protease used to create the F(ab')₂ targets, as confirmed by inhibition experiments with F(ab')₂ fragments and hinge peptides. Reactivity against IdeS-generated F(ab')₂ targets was found most frequently, whereas reactivity against pepsin-generated F(ab')₂ targets better discriminated between RA and HDs or SLE, with significantly higher AHA levels against IgG1/3/4. In contrast, AHA levels against pepsin-cleaved IgG2 were comparable. No reactivity against IdeS-generated IgG2-F(ab')₂s was detected. The most discriminatory AHA reactivity in RA was against pepsin-cleaved IgG4, with a 35% prevalence, ≥5.8-fold higher than in HDs/SLE, and significantly higher levels (p < 0.0001). Cross-reactivity for F(ab')₂s generated from different IgG subclasses was only observed for subclasses having homologous F(ab')₂ C termini (IgG1/3/4). For IgG2, two pepsin cleavage sites were identified; anti-hinge reactivity was restricted to only one of these. In conclusion, AHAs specifically recognize IgG subclass- and protease-restricted hinge neoepitopes. Their protease-restricted specificity suggests that different AHA responses developed under distinct inflammatory or infectious conditions and may be markers of, and participants in, such processes.

Mac Protein is not an Essential Virulence Factor for the Virulent Reference Strain Streptococcus suis P1/7

Streptococcus suis is a major pathogen of pigs and also an important zoonotic agent for humans. A S. suis protein containing Mac-1 domain (designated Mac) is a protective antigen, exclusively cleaves porcine IgM, and contributes to complement evasion with the presence of high titers of specific porcine anti-S. suis IgM, but its role in S. suis virulence has not been investigated in natural healthy host without specific IgM. In this study, a mac deletion mutant was constructed by homologous recombination in S. suis serotype 2 virulent reference strain P1/7. Deletion of mac did not significantly influence phagocytosis or intracellular survival within murine macrophages RAW264.7, or the oxidative-burst induction of RAW264.7 and murine neutrophils. Furthermore, the mutant is as virulent as the wild-type strain in pig, mouse, and zebrafish infection models. Our data suggest that Mac is not essential for S. suis virulence in strain P1/7 in natural healthy host without specific IgM, and the immunogenicity of Mac does not appear to correlate with its significance for virulence.

De Novo MS/MS Sequencing of Native Human Antibodies

One direct route for the discovery of therapeutic human monoclonal antibodies (mAbs) involves the isolation of peripheral B cells from survivors/sero-positive individuals after exposure to an infectious reagent or disease etiology, followed by single-cell sequencing or hybridoma generation. Peripheral B cells, however, are not always easy to obtain and represent only a small percentage of the total B-cell population across all bodily tissues. Although it has been demonstrated that tandem mass spectrometry (MS/MS) techniques can interrogate the full polyclonal antibody (pAb) response to an antigen in vivo, all current approaches identify MS/MS spectra against databases derived from genetic sequencing of B cells from the same patient. In this proof-of-concept study, we demonstrate the feasibility of a novel MS/MS antibody discovery approach in which only serum antibodies are required without the need for sequencing of genetic material. Peripheral pAbs from a cytomegalovirus-exposed individual were purified by glycoprotein B antigen affinity and de novo sequenced from MS/MS data. Purely MS-derived mAbs were then manufactured in mammalian cells to validate potency via antigen-binding ELISA. Interestingly, we found that these mAbs accounted for 1 to 2% of total donor IgG but were not detected in parallel sequencing of memory B cells from the same patient.

Novel IgG-Degrading Enzymes of the IgdE Protease Family Link Substrate Specificity to Host Tropism of Streptococcus Species

Recently we have discovered an IgG degrading enzyme of the endemic pig pathogen S. suis designated IgdE that is highly specific for porcine IgG. This protease is the founding member of a novel cysteine protease family assigned C113 in the MEROPS peptidase database. Bioinformatical analyses revealed putative members of the IgdE protease family in eight other Streptococcus species. The genes of the putative IgdE family proteases of S. agalactiae, S. porcinus, S. pseudoporcinus and S. equi subsp. zooepidemicus were cloned for production of recombinant protein into expression vectors. Recombinant proteins of all four IgdE family proteases were proteolytically active against IgG of the respective Streptococcus species hosts, but not against IgG from other tested species or other classes of immunoglobulins, thereby linking the substrate specificity to the known host tropism. The novel IgdE family proteases of S. agalactiae, S. pseudoporcinus and S. equi showed IgG subtype specificity, i.e. IgdE from S. agalactiae and S. pseudoporcinus cleaved human IgG1, while IgdE from S. equi was subtype specific for equine IgG7. Porcine IgG subtype specificities of the IgdE family proteases of S. porcinus and S. pseudoporcinus remain to be determined. Cleavage of porcine IgG by IgdE of S. pseudoporcinus is suggested to be an evolutionary remaining activity reflecting ancestry of the human pathogen to the porcine pathogen S. porcinus. The IgG subtype specificity of bacterial proteases indicates the special importance of these IgG subtypes in counteracting infection or colonization and opportunistic streptococci neutralize such antibodies through expression of IgdE family proteases as putative immune evasion factors. We suggest that IgdE family proteases might be valid vaccine targets against streptococci of both human and veterinary medical concerns and could also be of therapeutic as well as biotechnological use.

Orthogonal Assessment of Biotherapeutic Glycosylation: A Case Study Correlating N-Glycan Core Afucosylation of Herceptin with Mechanism of Action

In the development of therapeutic antibodies and biosimilars, an appropriate biopharmaceutical CMC control strategy that connects critical quality attributes with mechanism of action should enable product assessment at an early stage of development in order to mitigate risk. Here we demonstrate a new analytical workflow using trastuzumab which comprises "middle-up" analysis using a combination of IdeS and the endoglycosidases EndoS and EndoS2 to comprehensively map the glycan content. Enzymatic cleavage between the two N-acetyl glucosamine residues of the chitobiose core of N-glycans significantly simplifies the oligosaccharide component enabling facile distinction of GlcNAc from GlcNAc with core fucose. This approach facilitates quantitative determination of total Fc-glycan core-afucosylation, which was in turn correlated with receptor binding affinity by surface plasmon resonance and in vitro ADCC potency with a cell based bioassay. The strategy also quantifies Fc-glycan occupancy and the relative contribution from high mannose glycans.

Evading pre-existing anti-hinge antibody binding by hinge engineering

Antigen-binding fragments (Fab) and F(ab')₂ antibodies serve as alternative formats to full-length anti-bodies in therapeutic and immune assays. They provide the advantage of small size, short serum half-life, and lack of effector function. Several proteases associated with invasive diseases are known to cleave antibodies in the hinge-region, and this results in anti-hinge antibodies (AHA) toward the neoepitopes. The AHA can act as surrogate Fc and reintroduce the properties of the Fc that are otherwise lacking in antibody fragments. While this response is desired during the natural process of fighting disease, it is commonly unwanted for therapeutic antibody fragments. In our study, we identify a truncation in the lower hinge region of the antibody that maintains efficient proteolytic cleavage by IdeS protease. The resulting neoepitope at the F(ab')₂ C-terminus does not have detectable binding of pre-existing AHA, providing a practical route to produce F(ab')₂ in vitro by proteolytic digestion when the binding of pre-existing AHA is undesired. We extend our studies to the upper hinge region of the antibody and provide a detailed analysis of the contribution of C-terminal residues of the upper hinge of human IgG1, IgG2 and IgG4 to pre-existing AHA reactivity in human serum. While no pre-existing antibodies are observed toward the Fab of IgG2 and IgG4 isotype, a significant response is observed toward most residues of the upper hinge of human IgG1. We identify a T₂₂₅L variant and the natural C-terminal D₂₂₁ as solutions with minimal serum reactivity. Our work now enables the production of Fab and F(ab')₂ for therapeutic and diagnostic immune assays that have minimal reactivity toward pre-existing AHA.

A hingeless Fc fusion system for site-specific cleavage by IdeS

Fusion of proteins to the Fc region of IgG is widely used to express cellular receptors and other extracellular proteins, but cleavage of the fusion partner is sometimes required for downstream applications. Immunoglobulin G-degrading enzyme of Streptococcus pyogenes (IdeS) is a protease with exquisite specificity for human IgG, and it can also cleave Fc-fusion proteins at a single site in the N-terminal region of the CH2 domain. However, the site of IdeS cleavage results in the disulfide-linked hinge region partitioning with the released protein, complicating downstream usage of the cleaved product. To tailor the Fc fragment for release of partner proteins by IdeS treatment, we investigated the effect of deleting regions of IgG-derived sequence that are upstream of the cleavage site. Elimination of the IgG-derived hinge sequence along with several residues of the CH2 domain had negligible effects on expression and purity of the fusion protein, while retaining efficient processing by IdeS. An optimal Fc fragment comprising residues 235-447 of the human IgG1 heavy chain sufficed for efficient production of fusion proteins and minimized the amount of residual Ig-derived sequence on the cleavage product following IdeS treatment. Pairing of this truncated Fc fragment with IdeS cleavage enables highly specific cleavage of Fc-fusion proteins, thus eliminating the need to engineer extraneous cleavage sequences. This system should be helpful for producing Fc-fusion proteins requiring downstream cleavage, particularly those that are sensitive to internal miscleavage if treated with alternative proteases.

Characterization of alanine to valine sequence variants in the Fc region of nivolumab biosimilar produced in Chinese hamster ovary cells

Nivolumab is a therapeutic fully human IgG4 antibody to programmed death 1 (PD-1). In this study, a nivolumab biosimilar, which was produced in our laboratory, was analyzed and characterized. Sequence variants that contain undesired amino acid sequences may cause concern during biosimilar bioprocess development. We found that low levels of sequence variants were detected in the heavy chain of the nivolumab biosimilar by ultra performance liquid chromatography (UPLC) and tandem mass spectrometry. It was further identified with UPLC-MS/MS by IdeS or trypsin digestion. The sequence variant was confirmed through addition of synthetic mutant peptide. Subsequently, the mixing base signal of normal and mutant sequence was detected through DNA sequencing. The relative levels of mutant A424V in the Fc region of the heavy chain have been detected and demonstrated to be 12.25% and 13.54%, via base peak intensity (BPI) and UV chromatography of the tryptic peptide mapping, respectively. A424V variant was also quantified by real-time PCR (RT-PCR) at the DNA and RNA level, which was 19.2% and 16.8%, respectively. The relative content of the mutant was consistent at the DNA, RNA and protein level, indicating that the A424V mutation may have little influence at transcriptional or translational levels. These results demonstrate that orthogonal state-of-the-art techniques such as LC- UV- MS and RT-PCR should be implemented to characterize recombinant proteins and cell lines for development of biosimilars. Our study suggests that it is important to establish an integrated and effective analytical method to monitor and characterize sequence variants during antibody drug development, especially for antibody biosimilar products.

Modification of the classical Lancefield assay of group A streptococcal killing to reduce inter-donor variation

The lack of a surrogate-of-immunity assay presents a major barrier to Streptococcus pyogenes research. Modification of the Lancefield assay to include an antibody digestion step reduced inter-donor variation and permitted detection of the anti-streptococcal activity of intravenous immunoglobulin and convalescent serum, thus facilitating retrospective evaluation of immunity using stored samples.

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The lack of a surrogate-of-immunity assay is a major barrier to S. pyogenes research.

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Pre-treatment of whole blood with IdeS standardised bacterial growth between donors.

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IdeS was subsequently inhibited using a non-cytotoxic iodoacetamide derivative.

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The bactericidal action of stored samples could then be measured by Lancefield assay.

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The modified assay facilitates retrospective dissection of anti-S. pyogenes immunity.

Naturally Occurring IgG Antibodies Provide Innate Protection against Vibrio cholerae Bacteremia by Recognition of the Outer Membrane Protein U

Cholera epidemics are caused by Vibrio cholerae serogroups O1 and O139, whereas strains collectively known as non-O1/non-O139 V. cholerae are found in cases of extraintestinal infections and bacteremia. The mechanisms and factors influencing the occurrence of bacteremia and survival of V. cholerae in normal human serum have remained unclear. We found that naturally occurring IgG recognizing V. cholerae outer membrane protein U (OmpU) mediates a serum-killing effect in a complement C1q-dependent manner. Moreover, outer membrane vesicles (OMVs) containing OmpU caused enhanced survival of highly serum-sensitive classical V. cholerae in a dose-dependent manner. OMVs from wild-type and ompU mutant V. cholerae thereby provided a novel means to verify by extracellular transcomplementation the involvement of OmpU. Our data conclusively indicate that loss, or reduced expression, of OmpU imparts resistance to V. cholerae towards serum killing. We propose that the difference in OmpU protein levels is a plausible reason for differences in serum resistance and the ability to cause bacteremia observed among V. cholerae biotypes. Our findings provide a new perspective on how naturally occurring antibodies, perhaps induced by members of the microbiome, may play a role in the recognition of pathogens and the provocation of innate immune defense against bacteremia.

Sialylated IgG-Fc: a novel biomarker of chronic inflammatory demyelinating polyneuropathy

OBJECTIVE

Sialylation in Fc portion of IgG plays a crucial role in the pathogenesis of autoimmune diseases and the working mechanism of intravenous immunoglobulin (IVIG). We aim to test whether IgG-Fc sialylation is a biomarker of disease activity for chronic inflammatory demyelinating polyneuropathy (CIDP).

METHODS

By using specific lectins for sialylation, galactosylation and agalactosylation, lectin-enzyme assay and lectin blotting with pretreatment of IgG degradating enzyme of Streptococcus pyogenes were performed to compare the glycosylation levels of serum IgG-Fc (1) between patients of untreated CIDP (n=107) and normal control subjects (n=27), (2) among patients with untreated CIDP of different clinical severities and (3) before and after IVIG treatment of patients with CIDP (n=12).

RESULTS

Sialylation and galactosylation of IgG-Fc were significantly reduced in patients with CIDP than normal control subjects (p=0.003 and 0.033, respectively), whereas agalactosylation was increased in CIDP (p=0.21). Ratios of sialylated/agalactosylated IgG-Fc levels were significantly reduced in CIDP (p<0.001) and inversely related to disease severity (p=0.044). After IVIG treatment, levels of sialylated IgG-Fc significantly increased (p=0.003).

CONCLUSIONS

Sialylation of IgG-Fc is reduced in CIDP. Its level correlated with clinical severity and increased after IVIG treatment. Sialylated as well as ratio of sialylated/agalactosylated IgG-Fc could be new measures to monitor the disease severity and treatment status in CIDP.

Antibody-based PET imaging of amyloid beta in mouse models of Alzheimer's disease

Owing to their specificity and high-affinity binding, monoclonal antibodies have potential as positron emission tomography (PET) radioligands and are currently used to image various targets in peripheral organs. However, in the central nervous system, antibody uptake is limited by the blood-brain barrier (BBB). Here we present a PET ligand to be used for diagnosis and evaluation of treatment effects in Alzheimer's disease. The amyloid β (Aβ) antibody mAb158 is radiolabelled and conjugated to a transferrin receptor antibody to enable receptor-mediated transcytosis across the BBB. PET imaging of two different mouse models with Aβ pathology clearly visualize Aβ in the brain. The PET signal increases with age and correlates closely with brain Aβ levels. Thus, we demonstrate that antibody-based PET ligands can be successfully used for brain imaging.

Protection from experimental autoimmune encephalomyelitis by polyclonal IgG requires adjuvant-induced inflammation

Background

Intravenous immunoglobulin (IVIG) proved to be an efficient anti-inflammatory treatment for a growing number of neuroinflammatory diseases and protects against the development of experimental autoimmune encephalomyelitis (EAE), a widely used animal model for multiple sclerosis (MS).

Methods

The clinical efficacy of IVIG and IVIG-derived F(ab’)₂ fragments, generated using the streptococcal cysteine proteinase Ide-S, was evaluated in EAE induced by active immunization and by adoptive transfer of myelin-specific T cells. Frequency, phenotype, and functional characteristics of T cell subsets and myeloid cells were determined by flow cytometry. Antibody binding to microbial antigen and cytokine production by innate immune cells was assessed by ELISA.

Results

We report that the protective effect of IVIG is lost in the adoptive transfer model of EAE and requires prophylactic administration during disease induction. IVIG-derived Fc fragments are not required for protection against EAE, since administration of F(ab’)₂ fragments fully recapitulated the clinical efficacy of IVIG. F(ab’)₂-treated mice showed a substantial decrease in splenic effector T cell expansion and cytokine production (GM-CSF, IFN-γ, IL-17A) 9 days after immunization. Inhibition of effector T cell responses was not associated with an increase in total numbers of Tregs but with decreased activation of innate myeloid cells such as neutrophils, monocytes, and dendritic cells. Therapeutically effective IVIG-derived F(ab’)₂ fragments inhibited adjuvant-induced innate immune cell activation as determined by IL-12/23 p40 production and recognized mycobacterial antigens contained in Freund’s complete adjuvant which is required for induction of active EAE.

Conclusions

Our data indicate that F(ab’)₂-mediated neutralization of adjuvant contributes to the therapeutic efficacy of anti-inflammatory IgG. These findings might partly explain the discrepancy of IVIG efficacy in EAE and MS.

Identification and Characterization of IgdE, a Novel IgG-degrading Protease of Streptococcus suis with Unique Specificity for Porcine IgG

Streptococcus suisis a major endemic pathogen of pigs causing meningitis, arthritis, and other diseases. ZoonoticS. suisinfections are emerging in humans causing similar pathologies as well as severe conditions such as toxic shock-like syndrome. Recently, we discovered an IdeS family protease ofS. suisthat exclusively cleaves porcine IgM and represents the first virulence factor described, linkingS. suisto pigs as their natural host. Here we report the identification and characterization of a novel, unrelated protease ofS. suisthat exclusively targets porcine IgG. This enzyme, designated IgdE forimmunoglobulinG-degradingenzyme ofS. suis, is a cysteine protease distinct from previous characterized streptococcal immunoglobulin degrading proteases of the IdeS family and mediates efficient cleavage of the hinge region of porcine IgG with a high degree of specificity. The findings that allS. suisstrains investigated possess the IgG proteolytic activity and that piglet serum samples contain specific antibodies against IgdE strongly indicate that the protease is expressedin vivoduring infection and represents a novel and putative important bacterial virulence/colonization determinant, and a thus potential therapeutic target.

Full validation of therapeutic antibody sequences by middle-up mass measurements and middle-down protein sequencing

The regulatory bodies request full sequence data assessment both for innovator and biosimilar monoclonal antibodies (mAbs). Full sequence coverage is typically used to verify the integrity of the analytical data obtained following the combination of multiple LC-MS/MS datasets from orthogonal protease digests (so called “bottom-up” approaches). Top-down or middle-down mass spectrometric approaches have the potential to minimize artifacts, reduce overall analysis time and provide orthogonality to this traditional approach. In this work we report a new combined approach involving middle-up LC-QTOF and middle-down LC-MALDI in-source decay (ISD) mass spectrometry. This was applied to cetuximab, panitumumab and natalizumab, selected as representative US Food and Drug Administration- and European Medicines Agency-approved mAbs. The goal was to unambiguously confirm their reference sequences and examine the general applicability of this approach. Furthermore, a new measure for assessing the integrity and validity of results from middle-down approaches is introduced – the “Sequence Validation Percentage.” Full sequence data assessment of the 3 antibodies was achieved enabling all 3 sequences to be fully validated by a combination of middle-up molecular weight determination and middle-down protein sequencing. Three errors in the reference amino acid sequence of natalizumab, causing a cumulative mass shift of only −2 Da in the natalizumab Fd domain, were corrected as a result of this work.

Rapid and improved characterization of therapeutic antibodies and antibody related products using IdeS digestion and subunit analysis

Antibody subunits LC, Fd and Fc/2, generated by IdeS digestion has been applied in analytical methodologies to characterize antibody quality attributes such as glycosylation, oxidation, deamidation, and identity.

Reformatting Rituximab into Human IgG2 and IgG4 Isotypes Dramatically Improves Apoptosis Induction In Vitro

The direct induction of cell death, or apoptosis, in target cells is one of the effector mechanisms for the anti CD20 antibody Rituximab. Here we provide evidence that Rituximab’s apoptotic ability is linked to the antibody IgG isotype. Reformatting Rituximab from the standard human IgG1 heavy chain into IgG2 or IgG4 boosted in vitro apoptosis induction in the Burkitt’s lymphoma B cell line Ramos five and four-fold respectively. The determinants for this behavior are located in the hinge region and CH1 domain of the heavy chain. By transplanting individual IgG2 or IgG4 specific amino acid residues onto otherwise IgG1 like backbones, thereby creating hybrid antibodies, the same enhancement of apoptosis induction could be achieved. The cysteines at position 131 of the CH1 domain and 219 in the hinge region, involved in IgG2 and IgG4 disulfide formation, were found to be of particular structural importance. Our data indicates that the hybrid antibodies possess a different CD20 binding mode than standard Rituximab, which appears to be key in enhancing apoptotic ability. The presented work opens up an interesting engineering route for enhancing the direct cytotoxic ability of therapeutic antibodies.

The Bacterial Enzyme IdeS Cleaves the IgG-Type of B Cell Receptor (BCR), Abolishes BCR-Mediated Cell Signaling, and Inhibits Memory B Cell Activation

Ag binding to the BCR is a critical step in B cell development and activation, initiating a cascade of signaling events ultimately leading to proliferation, differentiation, or cell death. A bacterial enzyme, IgG-degrading enzyme of Streptococcus pyogenes (IdeS), was shown to specifically cleave IgG molecules below the hinge region of soluble IgG and when IgG is bound to Ag, resulting in one F(ab')2 molecule and one homodimeric Fc fragment. Whether IdeS could also cleave the IgG molecule when it is present in the BCR attached to the B cell membrane in a complex with CD79a and CD79b is unknown. In this article, we present human in vitro and ex vivo data showing that IdeS cleaves the IgG present in the BCR complex and very efficiently blocks Ag binding to the BCR. As a consequence of IdeS cleaving the BCR, signaling cascades downstream of the BCR are blocked, and memory B cells are temporarily silenced, preventing them from responding to antigenic stimulation and their transition into Ab-producing cells.

Streptococcal toxins: role in pathogenesis and disease

Group A Streptococcus (Streptococcus pyogenes), group B Streptococcus (Streptococcus agalactiae) and Streptococcus pneumoniae (pneumococcus) are host-adapted bacterial pathogens among the leading infectious causes of human morbidity and mortality. These microbes and related members of the genus Streptococcus produce an array of toxins that act against human cells or tissues, resulting in impaired immune responses and subversion of host physiological processes to benefit the invading microorganism. This toxin repertoire includes haemolysins, proteases, superantigens and other agents that ultimately enhance colonization and survival within the host and promote dissemination of the pathogen.

Localization-triggered bacterial pathogenesis

Bacterial infections are becoming an increasing problem worldwide and there is a need for a deeper understanding of how bacteria turn pathogenic. Here, we suggest that one answer may be found by taking into account the localization of the bacteria, both at an anatomical level and at a microenvironment level. Both commensals and traditional pathogens alter their interaction with the human host depending on the local surroundings--turning either more or less virulent. These localization effects could derive from the characteristics of different anatomical sites but also from local differences within a microenvironment. In order to understand the adaptive functions of bacterial virulence factors, we need to study the bacteria in the environments where they have evolved.

Streptococcal IdeS: therapeutic potential for Guillain-Barré syndrome

Plasma exchange and intravenous immunoglobulin are effective in treating Guillain–Barré syndrome (GBS) probably because the former removes IgG autoantibodies and complement and the latter inhibits complement activation subsequent to the autoantibody binding to peripheral nerve antigens. IgG degrading enzyme of Streptococcus pyogenes (IdeS) can cleave the pathogenic autoantibodies into F(ab’)₂ and Fc. The purpose of this study is to show whether IdeS has novel therapeutic potential for GBS. Sera with anti-ganglioside IgG antibodies from 15 patients with GBS or Miller Fisher syndrome were used. We tested whether IdeS cleaved the anti-ganglioside IgG antibodies and inhibited deposition of activated complement component on ELISA plates. IdeS efficiently cleaved IgG and blocked complement activation mediated by anti-GM1, anti-GD1a and anti-GQ1b IgG antibodies. IdeS has therapeutic potential for GBS and related conditions.