Enhanced potency of a fucose-free monoclonal antibody being developed as an Ebola virus immunoprotectant

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

Background

The ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014–2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle.

Results

In this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized.

Conclusions

This study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0745-2) contains supplementary material, which is available to authorized users.

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

BACKGROUND

The ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014-2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle.

RESULTS

In this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized.

CONCLUSIONS

This study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle.

Therapeutic treatment of Marburg and Ravn virus infection in nonhuman primates with a human monoclonal antibody

As observed during the 2013-2016 Ebola virus disease epidemic, containment of filovirus outbreaks is challenging and made more difficult by the lack of approved vaccine or therapeutic options. Marburg and Ravn viruses are highly virulent and cause severe and frequently lethal disease in humans. Monoclonal antibodies (mAbs) are a platform technology in wide use for autoimmune and oncology indications. Previously, we described human mAbs that can protect mice from lethal challenge with Marburg virus. We demonstrate that one of these mAbs, MR191-N, can confer a survival benefit of up to 100% to Marburg or Ravn virus-infected rhesus macaques when treatment is initiated up to 5 days post-inoculation. These findings extend the small but growing body of evidence that mAbs can impart therapeutic benefit during advanced stages of disease with highly virulent viruses and could be useful in epidemic settings.

Plant-produced biopharmaceuticals: A case of technical developments driving clinical deployment

The ability to express heterologous proteins in plants has led to the concept of using plants as "bioreactors" or "biofactories" for the production of pharmaceutical proteins. Although initial studies were promising, the pathway to commercialization and deployment in a clinical setting has proven to be a somewhat rocky road. This Review examines the technical developments that have led to the current increase in interest in the use of plants for the production of pharmaceutical proteins, particularly in the context of clinical trials.

Anti-Ebola therapies based on monoclonal antibodies: current state and challenges ahead

The 2014 Ebola outbreak, the largest recorded, took us largely unprepared, with no available vaccine or specific treatment. In this context, the World Health Organization declared that the humanitarian use of experimental therapies against Ebola Virus (EBOV) is ethical. In particular, an experimental treatment consisting of a cocktail of three monoclonal antibodies (mAbs) produced in tobacco plants and specifically directed to the EBOV glycoprotein (GP) was tested in humans, apparently with good results. Several mAbs with high affinity to the GP have been described. This review discusses our current knowledge on this topic. Particular emphasis is devoted to those mAbs that have been assayed in animal models or humans as possible therapies against Ebola. Engineering aspects and challenges for the production of anti-Ebola mAbs are also briefly discussed; current platforms for the design and production of full-length mAbs are cumbersome and costly.

Identification of a Guinea Pig Fcγ Receptor that Exhibits Enhanced Binding to Afucosylated Human and Mouse IgG

Glyco-engineered recombinant antibodies are currently being developed as the next generation therapeutics to treat human diseases, including cancer, autoimmunity and infection. Antibodies lacking core fucosylation show great increase in affinity for FcγRIIIA, leading to an improved receptor-mediated effector function. While afucosyl human IgG1 exhibits 50-100-fold increase in antibody-mediated cellular cytotoxicity (ADCC), a key immune effector mechanism underlying the anti-cancer effect of some approved therapeutic antibodies, it is not clear whether such glyco-engineered antibodies would find similar use for infectious disease. Due to the species difference, human antibodies may have different binding properties towards corresponding IgG receptors from animals used for modeling infection and intoxication. During the course of studying a recombinant human IgG1 in neutralizing diphtheria toxin (DT) in Guinea pigs (Cavia porcellus), we identified a previously uncharacterized Guinea pig protein H0VDZ8 from UNIPROT database that shows high sequence homologies to human FcγRIIIA and mouse FcγRIV. This Fcγ receptor, which we named as gpFcγRIV, also demonstrates functional similarity although not to the same extent as the human and mouse counterparts, in that it binds to afucosyl human and mouse IgG much stronger than to the wild type antibodies. Thus, Guinea pigs can be used to compare the efficacies of wild type vs. afucosyl anti-DT human IgG1 in toxin removal and animal protection. Molecular and functional characterization of human FcγRIIIA and mouse FcγRIV equivalents in other species could expand the list of preclinical animal models for testing afucosyl human antibodies in treating various human diseases.

Two-mAb cocktail protects macaques against the Makona variant of Ebola virus

The 2014-2015 Ebola virus (EBOV) outbreak in West Africa highlighted the urgent need for specific therapeutic interventions for infected patients. The human-mouse chimeric monoclonal antibody (mAb) cocktail ZMapp, previously shown to be efficacious in EBOV (variant Kikwit) lethally infected nonhuman primates (NHPs) when administration was initiated up to 5 days, was used in some patients during the outbreak. We show that a two-antibody cocktail, MIL77E, is fully protective in NHPs when administered at 50 mg/kg 3 days after challenge with a lethal dose of EBOV variant Makona, the virus responsible for the ongoing 2014-2015 outbreak, whereas a similar formulation of ZMapp protected two of three NHPs. The chimeric MIL77E mAb cocktail is produced in engineered Chinese hamster ovary cells and is based on mAbs c13C6 and c2G4 from ZMapp. The use of only two antibodies in MIL77E opens the door to a pan-ebolavirus cocktail.

Plant-produced anti-dengue virus monoclonal antibodies exhibit reduced antibody-dependent enhancement of infection activity

The mAb E60 has the potential to be a desirable therapeutic molecule since it efficiently neutralizes all four serotypes of dengue virus (DENV). However, mammalian-cell-produced E60 exhibits antibody-dependent enhancement of infection (ADE) activity, rendering it inefficacious in vivo, and treated animals more susceptible to developing more severe diseases during secondary infection. In this study, we evaluated a plant-based expression system for the production of therapeutically suitable E60. The mAb was transiently expressed in Nicotiana benthamianaWT and a ∆XFT line, a glycosylation mutant lacking plant-specific N-glycan residues. The mAb was efficiently expressed and assembled in leaves and exhibited highly homogenous N-glycosylation profiles, i.e. GnGnXF3 or GnGn structures, depending on the expression host. Both E60 glycovariants demonstrated equivalent antigen-binding specificity and in vitro neutralization potency against DENV serotypes 2 and 4 compared with their mammalian-cell-produced counterpart. By contrast, plant-produced E60 exhibited reduced ADE activity in Fc gamma receptor expressing human cells. Our results suggest the ability of plant-produced antibodies to minimize ADE, which may lead to the development of safe and highly efficacious antibody-based therapeutics against DENV and other ADE-prone viral diseases. Our study provides so far unknown insight into the relationship between mAb N-glycosylation and ADE, which contributes to our understanding of how sugar moieties of antibodies modulate Fc-mediated functions and viral pathogenesis.

Fc receptor-mediated phagocytosis in tissues as a potent mechanism for preventive and therapeutic HIV vaccine strategies

Although the development of a fully protective HIV vaccine is the ultimate goal of HIV research, to date only one HIV vaccine trial, the RV144, has successfully induced a weakly protective response. The 31% protection from infection achieved in the RV144 trial was linked to the induction of nonneutralizing antibodies, able to mediate antibody-dependent cell-mediated cytotoxicity (ADCC), suggestive of an important role of Fc-mediated functions in protection. Similarly, Fc-mediated antiviral activity was recently shown to play a critical role in actively suppressing the viral reservoir, but the Fc effector mechanisms within tissues that provide protection from or after infection are largely unknown. Here we aimed to define the landscape of effector cells and Fc receptors present within vulnerable tissues. We found negligible Fc receptor-expressing natural killer cells in the female reproductive and gastrointestinal mucosa. Conversely, Fc receptor-expressing macrophages were highly enriched in most tissues, but neutrophils mediated superior antibody-mediated phagocytosis. Modifications in Fc domain of VRC01 antibody increased phagocytic responses in both phagocytes. These data suggest that non-ADCC-mediated mechanisms, such as phagocytosis and neutrophil activation, are more likely to play a role in preventative vaccine or reservoir-eliminating therapeutic approaches.

Modulating Antibody Functionality in Infectious Disease and Vaccination

Induction of pathogen-specific binding antibodies has long been considered a signature of protective immunity following vaccination and infection. The humoral immune response is a complex network of antibodies that target different specificities and drive different functions, collectively acting to limit and clear infection either directly, via pathogen neutralization, or indirectly, via pathogen clearance by the innate immune system. Emerging data suggest that not all antibody responses are equal, and qualitative features of antibodies may be key to defining protective immune profiles. Here, we review the most recent advances in our understanding of protective functional antibody responses in natural infection, vaccination, and monoclonal antibody therapeutics. Moreover, we highlight opportunities to augment or modulate antibody-mediated protection through enhancement of antibody functionality.

Structures of Ebola virus GP and sGP in complex with therapeutic antibodies

The Ebola virus (EBOV) GP gene encodes two glycoproteins. The major product is a soluble, dimeric glycoprotein termed sGP that is secreted abundantly. Despite the abundance of sGP during infection, little is known regarding its structure or functional role. A minor product, resulting from transcriptional editing, is the transmembrane-anchored, trimeric viral surface glycoprotein termed GP. GP mediates attachment to and entry into host cells, and is the intended target of antibody therapeutics. Because large portions of sequence are shared between GP and sGP, it has been hypothesized that sGP may potentially subvert the immune response or may contribute to pathogenicity. In this study, we present cryo-EM structures of GP and sGP in complex with GP-specific and GP/sGP cross-reactive antibodies undergoing human clinical trials. The structure of the sGP dimer presented here, in complex with both an sGP-specific antibody and a GP/sGP cross-reactive antibody, permits us to unambiguously assign the oligomeric arrangement of sGP and compare its structure and epitope presentation to those of GP. Further, we provide biophysical evaluation of naturally occurring GP/sGP mutations that fall within the footprints identified by our high-resolution structures. Taken together, our data provide a detailed and more complete picture of the accessible Ebolavirus glycoprotein landscape and a structural basis to evaluate patient and vaccine antibody responses toward differently structured products of the GP gene.

Ebola Virus Infection: Review of the Pharmacokinetic and Pharmacodynamic Properties of Drugs Considered for Testing in Human Efficacy Trials

The 2014-2015 outbreak of Ebola virus disease is the largest epidemic to date in terms of the number of cases, deaths, and affected areas. In October 2015, no antiviral agents had proven antiviral efficacy in patients. However, in September 2014, the World Health Organization inventoried and has since regularly updated a list of potential drug candidates with demonstrated antiviral efficacy in in vitro or animal models. This includes agents belonging to various therapeutic classes, namely direct antiviral agents (favipiravir and BCX4430), a combination of antibodies (ZMapp), type I interferons, RNA interference-based drugs (TKM-Ebola and AVI-7537), and anticoagulant drugs (rNAPc2). Here, we review the pharmacokinetic and pharmacodynamic information presently available for these drugs, using data obtained in healthy volunteers for pharmacokinetics and data obtained in human clinical trials or animal models for pharmacodynamics. Future studies evaluating these drugs in clinical trials are critical to confirm their efficacy in humans, propose appropriate doses, and evaluate the possibility of treatment combinations.

Post-exposure treatment of Ebola virus disease in guinea pigs using EBOTAb, an ovine antibody-based therapeutic

Ebola virus (EBOV) is highly pathogenic, with a predisposition to cause outbreaks in human populations accompanied by significant mortality. An ovine polyclonal antibody therapy has been developed against EBOV, named EBOTAb. When tested in the stringent guinea pig model of EBOV disease, EBOTAb has been shown to confer protection at levels of 83.3%, 50% and 33.3% when treatment was first started on days 3, 4 and 5 post-challenge, respectively. These timepoints of when EBOTAb treatment was initiated correspond to when levels of EBOV are detectable in the circulation and thus mimic when treatment would likely be initiated in human infection. The effects of EBOTAb were compared with those of a monoclonal antibody cocktail, ZMapp, when delivered on day 3 post-challenge. Results showed ZMapp to confer complete protection against lethal EBOV challenge in the guinea pig model at this timepoint. The data reported demonstrate that EBOTAb is an effective treatment against EBOV disease, even when delivered late after infection.

Ebola Virus Disease: Therapeutic and Potential Preventative Opportunities

The 2014 Ebola virus disease (EVD) epidemic in West Africa was unprecedented in its geographical distribution, scale, and toll on public health infrastructure. Standard public health measures were rapidly overwhelmed, and many projections on outbreak progression through the region were dire. At the beginning of the outbreak there were no treatments or vaccines that had been shown to be safe and effective for treating or preventing EVD, limiting health care providers to offer supportive care under extremely challenging circumstances and at great risk to themselves. Over time, however, drugs and vaccines in the development pipeline were prioritized based on all available research data and were moved forward for evaluation in clinical trials to demonstrate safety and efficacy. The armamentarium against EVD eventually included biologics such as monoclonal antibodies, convalescent plasma, and vaccines as well as small molecule therapeutics such as small interfering RNAs and nucleoside analogs. This article provides a high-level overview of the interventions and prophylactics considered for use in the outbreak and discusses the challenges faced when attempting to deploy investigational countermeasures in the midst of an evolving epidemic.

The potential of plants as a system for the development and production of human biologics

The growing promise of plant-made biologics is highlighted by the success story of ZMapp™ as a potentially life-saving drug during the Ebola outbreak of 2014-2016. Current plant expression platforms offer features beyond the traditional advantages of low cost, high scalability, increased safety, and eukaryotic protein modification. Novel transient expression vectors have been developed that allow the production of vaccines and therapeutics at unprecedented speed to control potential pandemics or bioterrorism attacks. Plant-host engineering provides a method for producing proteins with unique and uniform mammalian post-translational modifications, providing opportunities to develop biologics with increased efficacy relative to their mammalian cell-produced counterparts. Recent demonstrations that plant-made proteins can function as biocontrol agents of foodborne pathogens further exemplify the potential utility of plant-based protein production. However, resolving the technical and regulatory challenges of commercial-scale production, garnering acceptance from large pharmaceutical companies, and obtaining U.S. Food and Drug Administration approval for several major classes of biologics are essential steps to fulfilling the untapped potential of this technology.

Structures of the Zika Virus Envelope Protein and Its Complex with a Flavivirus Broadly Protective Antibody

Zika virus (ZIKV), a mosquito-borne flavivirus, is a current global public health concern. The flavivirus envelope (E) glycoprotein is responsible for virus entry and represents a major target of neutralizing antibodies for other flaviviruses. Here, we report the structures of ZIKV E protein at 2.0 Å and in complex with a flavivirus broadly neutralizing murine antibody 2A10G6 at 3.0 Å. ZIKV-E resembles all the known flavivirus E structures but contains a unique, positively charged patch adjacent to the fusion loop region of the juxtaposed monomer, which may influence host attachment. The ZIKV-E-2A10G6 complex structure reveals antibody recognition of a highly conserved fusion loop. 2A10G6 binds to ZIKV-E with high affinity in vitro and neutralizes currently circulating ZIKV strains in vitro and in mice. The E protein fusion loop epitope represents a potential candidate for therapeutic antibodies against ZIKV.

Antibody Production in Plants and Green Algae

Monoclonal antibodies (mAbs) have a wide range of modern applications, including research, diagnostic, therapeutic, and industrial uses. Market demand for mAbs is high and continues to grow. Although mammalian systems, which currently dominate the biomanufacturing industry, produce effective and safe recombinant mAbs, they have a limited manufacturing capacity and high costs. Bacteria, yeast, and insect cell systems are highly scalable and cost effective but vary in their ability to produce appropriate posttranslationally modified mAbs. Plants and green algae are emerging as promising production platforms because of their time and cost efficiencies, scalability, lack of mammalian pathogens, and eukaryotic posttranslational protein modification machinery. So far, plant- and algae-derived mAbs have been produced predominantly as candidate therapeutics for infectious diseases and cancer. These candidates have been extensively evaluated in animal models, and some have shown efficacy in clinical trials. Here, we review ongoing efforts to advance the production of mAbs in plants and algae.

Isotype-specific glycosylation analysis of mouse IgG by LC-MS

With mice being the top model organism in immunology and with Fc glycosylation being increasingly recognized as important modulator of antibody function, the time has come to take a look at the glycosylation of mouse IgG isotypes. Tryptic glycopeptides of mouse IgG1, IgG2, and IgG3 differ in mass and so these three isoforms can be easily discriminated by MS. Commercial IgG contained a rare IgG1 variant but no IgG3, which, however, was found in sera of C57BL/6 and BALB/c mice. These strains deviated with regard to IgG2a and IgG2b alleles. The Ig2a B allele was not observed in any of the four samples investigated. All a/c isotypes contain the same glycopeptide sequence, which deviates from that of IgG2b by containing Leu instead of Ile. The Leu/Ile glycopeptide variants were separated by RP chromatography and the order of elution was determined. The major glycoforms on all isotypes were fucosylated with no and one galactose (GnGnF and GnAF) followed by fully galactosylated AAF and smaller amounts of mono- and disialylated N-glycans. In the commercial serum pool, the relative ratios of glycans differed between isotypes. Sialic acid exclusively occurred as N-glycolylneuraminic acid. Fucosylation was essentially complete. No bisected and no α1,3-galactosylated glycans were found.

Antiviral Monoclonal Antibodies: Can They Be More Than Simple Neutralizing Agents?

Monoclonal antibodies (mAbs) are increasingly being considered as agents to fight severe viral diseases. So far, they have essentially been selected and used on the basis of their virus-neutralizing activity and/or cell-killing activity to blunt viral propagation via direct mechanisms. There is, however, accumulating evidence that they can also induce long-lasting protective antiviral immunity by recruiting the endogenous immune system of infected individuals during the period of immunotherapy. Exploiting this property may revolutionize antiviral mAb-based immunotherapies, with benefits for both patients and healthcare systems.

Antiviral monoclonal antibodies (mAbs) are promising, high-added-value biotherapeutics. During recent years, the number of antiviral mAbs developed against both acute and chronic viruses has grown exponentially, some of them being currently tested in clinical trials.

Antiviral mAbs can be used to blunt viral propagation through direct effects. They can also engage the host's immune system, leading to the induction of long-lasting protective vaccine-like effects.

The assessment of mechanisms at play in the induction of vaccine-like effects by antiviral mAbs will help in improving antiviral treatments.

Exploiting this effect will translate into therapeutic benefit for patients. The benefit will also help healthcare systems through the reduction of treatment costs.

Monoclonal antibody therapy for Junin virus infection

Countermeasures against potential biothreat agents remain important to US Homeland Security, and many of these pharmaceuticals could have dual use in the improvement of global public health. Junin virus, the causative agent of Argentine hemorrhagic fever (AHF), is an arenavirus identified as a category A high-priority agent. There are no Food and Drug Administration (FDA) approved drugs available for preventing or treating AHF, and the current treatment option is limited to administration of immune plasma. Whereas immune plasma demonstrates the feasibility of passive immunotherapy, it is limited in quantity, variable in quality, and poses safety risks such as transmission of transfusion-borne diseases. In an effort to develop a monoclonal antibody (mAb)-based alternative to plasma, three previously described neutralizing murine mAbs were expressed as mouse-human chimeric antibodies and evaluated in the guinea pig model of AHF. These mAbs provided 100% protection against lethal challenge when administered 2 d after infection (dpi), and one of them (J199) was capable of providing 100% protection when treatment was initiated 6 dpi and 92% protection when initiated 7 dpi. The efficacy of J199 is superior to that previously described for all other evaluated drugs, and its high potency suggests that mAbs like J199 offer an economical alternative to immune plasma and an effective dual use (bioterrorism/public health) therapeutic.

Cell-targeting antibodies in immunity to Ebola

As the 2014-15 Ebola virus epidemic in West Africa evolved from emergency to lesson, developers of both vaccines and therapeutic antibodies were left with the puzzlement of what kinds of anti-Ebola antibodies are predictably desirable in treating the afflicted, and what antibodies might account for the specific and lasting protection elicited by the more effective vaccines. The facile answer in virology is that neutralizing antibody (NAb) is desired and required. However, with Ebola and other filoviruses (as with many prior viral examples), there are multiple discordances in which neutralizing antibodies fail to protect animals, and others in which antibody-mediated protection is observed in the absence of measured virus neutralization. Explanation presumably resides in the protective role of antibodies that bind and functionally 'target' virus-infected cells, here called 'cell-targeting antibody', or CTAb. To be clear, many NAbs are also CTAbs, and in the case of Ebola the great majority of NAbs are likely CTAbs. Isotype, glycosylation, and other features of CTAbs are likely crucial in their capacity to mediate protection. Overall, results and analysis invite an increasingly complex view of antibody-mediated immunity to enveloped viruses.

Antigen-Specific Antibody Glycosylation Is Regulated via Vaccination

Antibody effector functions, such as antibody-dependent cellular cytotoxicity, complement deposition, and antibody-dependent phagocytosis, play a critical role in immunity against multiple pathogens, particularly in the absence of neutralizing activity. Two modifications to the IgG constant domain (Fc domain) regulate antibody functionality: changes in antibody subclass and changes in a single N-linked glycan located in the CH2 domain of the IgG Fc. Together, these modifications provide a specific set of instructions to the innate immune system to direct the elimination of antibody-bound antigens. While it is clear that subclass selection is actively regulated during the course of natural infection, it is unclear whether antibody glycosylation can be tuned, in a signal-specific or pathogen-specific manner. Here, we show that antibody glycosylation is determined in an antigen- and pathogen-specific manner during HIV infection. Moreover, while dramatic differences exist in bulk IgG glycosylation among individuals in distinct geographical locations, immunization is able to overcome these differences and elicit antigen-specific antibodies with similar antibody glycosylation patterns. Additionally, distinct vaccine regimens induced different antigen-specific IgG glycosylation profiles, suggesting that antibody glycosylation is not only programmable but can be manipulated via the delivery of distinct inflammatory signals during B cell priming. These data strongly suggest that the immune system naturally drives antibody glycosylation in an antigen-specific manner and highlights a promising means by which next-generation therapeutics and vaccines can harness the antiviral activity of the innate immune system via directed alterations in antibody glycosylation in vivo.  .

Potential Cancer Prevention and Treatment by Silencing the Killer Cell Immunoglobulin-like Receptor Gene in Natural Killer Cells Derived from Induced Pluripotent Stem Cells

Cancer immunosurveillance is an important host protection process, monitoring the presence of irregular cells that could potentially transform into tumor cells, effectively clearing the body of transformed tumor cells at their earliest stages, and thus maintaining regular cellular homeostasis. Natural killer (NK) cells are effector lymphocytes of the innate immune system, playing a critical role in surveillance for tumor cells, while also eliminating virally infected cells. The significance of the anti-tumor role of NK cells was recently further verified by findings that immunosuppression in most cancer patients is not perceptible until late stages. NK cells express the low-affinity Fc-activating receptor, CD16, and the inhibitory receptor, killer cell immunoglobulin-like receptor (KIR). Consequently, activation of NK cells is determined by the balance of inhibitory and activating receptor stimulation. Here, we propose establishing an induced pluripotent stem cell (iPSC)-derived NK cell line with KIR gene knockout or knockdown as a possible regimen to treat and prevent cancer. We further postulate that an optimal mixture of NK iPSCs with and without KIR gene knockout, would reach a maximum antitumor activity, with minimal side effects. We also discuss the possible advantages of KIR-knockout NK iPSCs for adoptive immunotherapy in patients with cancer.

Antibody therapeutics for Ebola virus disease

With the unprecedented scale of the 2014-2016 West Africa outbreak, the clinical and scientific community scrambled to identify potential therapeutics for Ebola virus disease (EVD). Passive administration of antibodies has a long successful history for prophylaxis and therapy of a variety of infectious diseases, but the importance of antibodies in EVD has been unclear and is the subject of some debate. Recent studies in non-human primates have renewed interest in the potential of antibodies to impact EVD. Currently ongoing clinical evaluation of polyclonal and monoclonal antibody therapy in EVD patients in West Africa may finally offer a definitive answer to this debate.

Profiling N-linked oligosaccharides from IgG by high-performance anion-exchange chromatography with pulsed amperometric detection

Understanding and characterizing protein therapeutic glycosylation is important with growing evidence that glycosylation impacts biological efficacy, pharmacokinetics and cellular toxicity. Protein expression systems and reactor conditions can impact glycosylation, leading to potentially undesirable glycosylation. For example, high-mannose species may be present, which are atypical of human antibody glycosylation. Their presence in the Fc domain has been linked to increased serum clearance of immunoglobulin G (IgG) antibodies. High-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) is an effective tool for determining glycans present in glycoprotein therapeutics. We report an improved HPAE-PAD method for IgG oligosaccharide separation. The neutral glycans are well resolved, including separation of high-mannose species from typical human IgG glycans. Oligosaccharide identification was performed by comparison to known standards in conjunction with selective exoglycosidase digestion of both standards and released glycans. Retention times (RTs) of known glycans were compared with the retention times of maltose, maltotriose and maltotetraose standards to define a retention index value for each glycan. These retention indices were used to aid identification of glycans from an example monoclonal antibody sample of unknown glycosylation. Method ruggedness was evaluated across duplicate systems, analysts and triplicate column lots. Comparing two systems with different analysts and columns, retention time precision relative standard deviations (RSDs) were between 0.63 and 4.0% while retention indices precision RSDs ranged from 0.27 to 0.56%. The separation is orthogonal to capillary electrophoresis-based separation of labeled IgG oligosaccharides.

The potential of plants as a system for the development and production of human biologics

The growing promise of plant-made biologics is highlighted by the success story of ZMapp™ as a potentially life-saving drug during the Ebola outbreak of 2014-2016. Current plant expression platforms offer features beyond the traditional advantages of low cost, high scalability, increased safety, and eukaryotic protein modification. Novel transient expression vectors have been developed that allow the production of vaccines and therapeutics at unprecedented speed to control potential pandemics or bioterrorism attacks. Plant-host engineering provides a method for producing proteins with unique and uniform mammalian post-translational modifications, providing opportunities to develop biologics with increased efficacy relative to their mammalian cell-produced counterparts. Recent demonstrations that plant-made proteins can function as biocontrol agents of foodborne pathogens further exemplify the potential utility of plant-based protein production. However, resolving the technical and regulatory challenges of commercial-scale production, garnering acceptance from large pharmaceutical companies, and obtaining U.S. Food and Drug Administration approval for several major classes of biologics are essential steps to fulfilling the untapped potential of this technology.

Efficient Production of a Bioactive Bevacizumab Monoclonal Antibody Using the 2A Self-cleavage Peptide in Transgenic Rice Callus

Bevacizumab, a humanized monoclonal antibody (mAb) targeting to the vascular endothelial growth factor (VEGF), has been widely used in clinical practice for the treatment of multiple cancers. Bevacizumab was mostly produced by the mammalian cell expression system. We here reported the first plant-derived Bevacizumab by using transgenic rice callus as an alternative gene expression system. Codon-optimized Bevacizumab light chain (BLC) and Bevacizumab heavy chain (BHC) genes were designed, synthesized as a polyprotein with a 2A self-cleavage linker peptide from the Foot-and-mouth disease virus, cloned into a plant binary vector under a constitutive maize ubiquitin promoter, and transformed into rice nuclear genome through Agrobacterium-mediated transformation. Southern blot and western blot analyses confirmed the integration and expression of BLC and BHC genes in transgenic rice callus. Enzyme-linked immunosorbent assay (ELISA) analysis indicated that the rice-derived Bevacizumab mAb was biologically active and the recombinant mAb was expressed at high levels (160.7-242.8 mg/Kg) in transgenic rice callus. The mAb was purified by using protein A affinity chromatography and the purified antibody was tested for its binding affinity with its target human VEGF (hVEGF) antigen by ELISA. Rice callus produced Bevacizumab and a commercial Bevacizumab (Avastin) were shown to have similar binding affinity to hVEGF. These results indicated that rice callus produced Bevacizumab could have similar biological activity and might potentially be used as a cost-effective biosimilar molecule in future cancer treatment.

Plant-Derived Monoclonal Antibodies for Prevention and Treatment of Infectious Disease

Numerous monoclonal antibodies (MAbs) that recognize and neutralize infectious pathogens have been isolated and developed over the years. The fact that infectious diseases can involve large populations of infected individuals is an important factor that has motivated the search for both cost-effective and scalable methods of antibody production. The current technologies for production of antibodies in plants allow for very rapid expression and evaluation that can also be readily scaled for multikilogram production runs. In addition, recent progress in manipulating glycosylation in plant production systems has allowed for the evaluation of antibodies containing glycans that are nearly homogeneous, are mammalian in structure, and have enhanced neutralizing capabilities. Among the anti-infectious disease antibodies that have been produced in plants are included those intended for prevention or treatment of anthrax, Clostridium perfringens, Ebola virus, human immunodeficiency virus, herpes simplex virus, rabies, respiratory syncytial virus, staphylococcal enterotoxin, West Nile virus, and tooth decay. Animal and human efficacy data for these MAbs are discussed.

Enhancing the Quality of Antibodies to HIV-1 Envelope by GagPol-Specific Th Cells

The importance of Fc-dependent effector functions of Abs induced by vaccination is increasingly recognized. However, vaccination of mice against HIV envelope (Env) induced a skewed Th cell response leading to Env-specific Abs with reduced effector function. To overcome this bias, GagPol-specific Th cells were harnessed to provide intrastructural help for Env-specific B cells after immunization with virus-like particles containing GagPol and Env. This led to a balanced Env-specific humoral immune response with a more inflammatory Fc glycan profile. The increased quality in the Ab response against Env was confirmed by FcγR activation assays. Because the Env-specific Th cell response was also biased in human vaccinees, intrastructural help is an attractive novel approach to increase the efficacy of prophylactic HIV Env-based vaccines and may also be applicable to other particulate vaccines.

Glycan modulation and sulfoengineering of anti-HIV-1 monoclonal antibody PG9 in plants

Broadly neutralizing anti-HIV-1 monoclonal antibodies, such as PG9, and its derivative RSH hold great promise in AIDS therapy and prevention. An important feature related to the exceptional efficacy of PG9 and RSH is the presence of sulfated tyrosine residues in their antigen-binding regions. To maximize antibody functionalities, we have now produced glycan-optimized, fucose-free versions of PG9 and RSH in Nicotiana benthamiana. Both antibodies were efficiently sulfated in planta on coexpression of an engineered human tyrosylprotein sulfotransferase, resulting in antigen-binding and virus neutralization activities equivalent to PG9 synthesized by mammalian cells ((CHO)PG9). Based on the controlled production of both sulfated and nonsulfated variants in plants, we could unequivocally prove that tyrosine sulfation is critical for the potency of PG9 and RSH. Moreover, the fucose-free antibodies generated in N. benthamiana are capable of inducing antibody-dependent cellular cytotoxicity, an activity not observed for (CHO)PG9. Thus, tailoring of the antigen-binding site combined with glycan modulation and sulfoengineering yielded plant-produced anti-HIV-1 antibodies with effector functions superior to PG9 made in CHO cells.

Plant-produced candidate countermeasures against emerging and reemerging infections and bioterror agents

Despite progress in the prevention and treatment of infectious diseases, they continue to present a major threat to public health. The frequency of emerging and reemerging infections and the risk of bioterrorism warrant significant efforts towards the development of prophylactic and therapeutic countermeasures. Vaccines are the mainstay of infectious disease prophylaxis. Traditional vaccines, however, are failing to satisfy the global demand because of limited scalability of production systems, long production timelines and product safety concerns. Subunit vaccines are a highly promising alternative to traditional vaccines. Subunit vaccines, as well as monoclonal antibodies and other therapeutic proteins, can be produced in heterologous expression systems based on bacteria, yeast, insect cells or mammalian cells, in shorter times and at higher quantities, and are efficacious and safe. However, current recombinant systems have certain limitations associated with production capacity and cost. Plants are emerging as a promising platform for recombinant protein production due to time and cost efficiency, scalability, lack of harboured mammalian pathogens and possession of the machinery for eukaryotic post-translational protein modification. So far, a variety of subunit vaccines, monoclonal antibodies and therapeutic proteins (antivirals) have been produced in plants as candidate countermeasures against emerging, reemerging and bioterrorism-related infections. Many of these have been extensively evaluated in animal models and some have shown safety and immunogenicity in clinical trials. Here, we overview ongoing efforts to producing such plant-based countermeasures.

Human Polyclonal Antibodies Produced through DNA Vaccination of Transchromosomal Cattle Provide Mice with Post-Exposure Protection against Lethal Zaire and Sudan Ebolaviruses

DNA vaccination of transchromosomal bovines (TcBs) with DNA vaccines expressing the codon-optimized (co) glycoprotein (GP) genes of Ebola virus (EBOV) and Sudan virus (SUDV) produce fully human polyclonal antibodies (pAbs) that recognize both viruses and demonstrate robust neutralizing activity. Each TcB was vaccinated by intramuscular electroporation (IM-EP) a total of four times and at each administration received 10 mg of the EBOV-GP_co DNA vaccine and 10 mg of the SUDV-GP_co DNA vaccine at two sites on the left and right sides, respectively. After two vaccinations, robust antibody responses (titers > 1000) were detected by ELISA against whole irradiated EBOV or SUDV and recombinant EBOV-GP or SUDV-GP (rGP) antigens, with higher titers observed for the rGP antigens. Strong, virus neutralizing antibody responses (titers >1000) were detected after three vaccinations when measured by vesicular stomatitis virus-based pseudovirion neutralization assay (PsVNA). Maximal neutralizing antibody responses were identified by traditional plaque reduction neutralization tests (PRNT) after four vaccinations. Neutralizing activity of human immunoglobulins (IgG) purified from TcB plasma collected after three vaccinations and injected intraperitoneally (IP) into mice at a 100 mg/kg dose was detected in the serum by PsVNA up to 14 days after administration. Passive transfer by IP injection of the purified IgG (100 mg/kg) to groups of BALB/c mice one day after IP challenge with mouse adapted (ma) EBOV resulted in 80% protection while all mice treated with non-specific pAbs succumbed. Similarly, interferon receptor 1 knockout (IFNAR ^-/-) mice receiving the purified IgG (100 mg/kg) by IP injection one day after IP challenge with wild type SUDV resulted in 89% survival. These results are the first to demonstrate that filovirus GP DNA vaccines administered to TcBs by IM-EP can elicit neutralizing antibodies that provide post-exposure protection. Additionally, these data describe production of fully human IgG in a large animal system, a system which is capable of producing large quantities of a clinical grade therapeutic product.

Cross-protection conferred by filovirus virus-like particles containing trimeric hybrid glycoprotein

Filoviruses are causative agents of hemorrhagic fever, and to date no effective vaccine or therapeutic has been approved to combat infection. Filovirus glycoprotein (GP) is the critical immunogenic component of filovirus vaccines, eliciting high levels of antibody after successful vaccination. Previous work has shown that protection against both Ebola virus (EBOV) and Marburg virus (MARV) can be achieved by vaccinating with a mixture of virus-like particles (VLPs) expressing either EBOV GP or MARV GP. In this study, the potential for eliciting effective immune responses against EBOV, Sudan virus, and MARV with a single GP construct was tested. Trimeric hybrid GPs were produced that expressed the sequence of Marburg GP2 in conjunction with a hybrid GP1 composed EBOV and Sudan virus GP sequences. VLPs expressing these constructs, along with EBOV VP40, provided comparable protection against MARV challenge, resulting in 75 or 100% protection. Protection from EBOV challenge differed depending upon the hybrid used, however, with one conferring 75% protection and one conferring no protection. By comparing the overall antibody titers and the neutralizing antibody titers specific for each virus, it is shown that higher antibody responses were elicited by the C terminal region of GP1 than by the N terminal region, and this correlated with protection. These data collectively suggest that GP2 and the C terminal region of GP1 are highly immunogenic, and they advance progress toward the development of a pan-filovirus vaccine.

Mechanism of Binding to Ebola Virus Glycoprotein by the ZMapp, ZMAb, and MB-003 Cocktail Antibodies

Cocktails of monoclonal antibodies (MAbs) that target the surface glycoprotein (GP) of Ebola virus (EBOV) are effective in nonhuman primate models and have been used under emergency compassionate-treatment protocols in human patients. However, the amino acids that form the detailed binding epitopes for the MAbs in the ZMapp, ZMAb, and the related MB-003 cocktails have yet to be identified. Other binding properties that define how each MAb functionally interacts with GP—such as affinity, epitope conservation, and epitope accessibility—also remain largely unknown. To help define how each MAb interacts with GP, here we used comprehensive alanine-scanning mutagenesis (shotgun mutagenesis), neutralization escape, and whole virion binding to define each MAb's specific epitope, epitope accessibility, epitope conservation, and apparent affinity. Each of the six therapeutic MAbs binds nonidentical epitopes in the GP base, glycan cap, or mucin-like domain. Their apparent affinity, epitope complementarity, and epitope accessibility helps explain why MAbs 4G7 and 13C6 are more protective than 2G4 and 1H3. The mucin-like domain MAbs 6D8 and 13F6 bind with the strongest apparent affinity, helping to explain their effectiveness in vivo despite their inability to neutralize virus.

IMPORTANCE

Ebola virus disease (EVD) can be caused by four different filovirus family members, including Ebola virus (EBOV), which infected 10 times more people in western Africa over the last year than all previous EVD outbreaks combined, with a number of cases distributed across the globe by travelers. Cocktails of inhibitory monoclonal antibodies (MAbs), such as ZMAb, MB-003, and in particular ZMapp, have demonstrated in animal models some of the most significant therapeutic potential for treating EVD, and in 2014, 15 patients were treated with ZMapp or ZMAb under compassionate-use protocols. Here, we have defined the epitope features for the most important therapeutic MAbs against EBOV developed to date. Defining the epitopes and binding characteristics for these MAbs, as well as the commonly used reference MAb KZ52, helps explain their breadth of reactivity against different ebolavirus species, predict viral evasion against these MAbs, and design new cocktails of MAbs with improved complementarity.

Using glyco-engineering to produce therapeutic proteins

INTRODUCTION

Glycans are increasingly important in the development of new biopharmaceuticals with optimized efficacy, half-life, and antigenicity. Current expression platforms for recombinant glycoprotein therapeutics typically do not produce homogeneous glycans and frequently display non-human glycans which may cause unwanted side effects. To circumvent these issues, glyco-engineering has been applied to different expression systems including mammalian cells, insect cells, yeast, and plants.

AREAS COVERED

This review summarizes recent developments in glyco-engineering focusing mainly on in vivo expression systems for recombinant proteins. The highlighted strategies aim at producing glycoproteins with homogeneous N- and O-linked glycans of defined composition.

EXPERT OPINION

Glyco-engineering of expression platforms is increasingly recognized as an important strategy to improve biopharmaceuticals. A better understanding and control of the factors leading to glycan heterogeneity will allow simplified production of recombinant glycoprotein therapeutics with less variation in terms of glycosylation. Further technological advances will have a major impact on manufacturing processes and may provide a completely new class of glycoprotein therapeutics with customized functions.

Microscale purification of antigen-specific antibodies

Glycosylation of the Fc domain is an important driver of antibody effector function. While assessment of antibody glycoform compositions observed across total plasma IgG has identified differences associated with a variety of clinical conditions, in many cases it is the glycosylation state of only antibodies against a specific antigen or set of antigens that may be of interest, for example, in defining the potential effector function of antibodies produced during disease or after vaccination. Historically, glycoprofiling such antigen-specific antibodies in clinical samples has been challenging due to their low prevalence, the high sample requirement for most methods of glycan determination, and the lack of high-throughput purification methods. New methods of glycoprofiling with lower sample requirements and higher throughput have motivated the development of microscale and automatable methods for purification of antigen-specific antibodies from polyclonal sources such as clinical serum samples. In this work, we present a robot-compatible 96-well plate-based method for purification of antigen-specific antibodies, suitable for such population level glycosylation screening. We demonstrate the utility of this method across multiple antibody sources, using both purified plasma IgG and plasma, and across multiple different antigen types, with enrichment factors greater than 1000-fold observed. Using an on-column IdeS protease treatment, we further describe staged release of Fc and Fab domains, allowing for glycoprofiling of each domain.

Development of experimental and early investigational drugs for the treatment of Ebola virus infections

INTRODUCTION

Ebola virus (EBOV) causes severe hemorrhagic fever in humans, and due to the aggressive nature of infection it has been difficult to develop effective medical countermeasures. Total casualties from past outbreaks numbered fewer than 1500 cases, but EBOV unexpectedly emerged from Guinea in late 2013 and infected over 25,000 people in nine countries spanning Africa, Europe and North America. Concern among the public and authorities helped spark an unprecedented push to fast-track experimental drugs for clinical use.

AREAS COVERED

The authors provide a historical timeline of the progress in developing a licensed post-exposure EBOV drug for use in humans. Furthermore, they summarize and discuss the published data with different in light of their potential to play a role during outbreak times.

EXPERT OPINION

Monoclonal antibody-based therapy is able to reverse advanced EBOV disease, but the outbreak of an antigenically divergent filovirus would require the reformulation and possibly redevelopment of the most promising candidates. Immunocompetent small animal models have not yet been developed for screening drugs against other filoviruses aside from Ravn and Marburg virus, and thus the number of prophylactic and therapeutic candidates lag behind that of EBOV. There is an urgent need for the proactive development of drugs against other neglected pathogens before the next major outbreak.

NMR-based structural validation of therapeutic antibody produced in Nicotiana benthamiana

KEY MESSAGE

We successfully developed a method for metabolic isotope labeling of recombinant proteins produced in transgenic tobacco. This enabled assessment of structural integrity of plant-derived therapeutic antibodies by NMR analysis. A variety of expression vehicles have been developed for the production of promising biologics, including plants, fungi, bacteria, insects, and mammals. Glycoprotein biologics often experience altered folding and post-translational modifications that are typified by variant glycosylation patterns. These differences can dramatically affect their efficacy, as exemplified by therapeutic antibodies. However, it is generally difficult to validate the structural integrity of biologics produced using different expression vehicles. To address this issue, we have developed and applied a stable-isotope-assisted nuclear magnetic resonance (NMR) spectroscopy method for the conformational characterization of recombinant antibodies produced in plants. Nicotiana benthamiana used as a vehicle for the production of recombinant immunoglobulin G (IgG) was grown in a (15)N-enriched plant growth medium. The Fc fragment derived from the (15)N-labeled antibody thus prepared was subjected to heteronuclear two-dimensional (2D) NMR measurements. This approach enabled assessment of the structural integrity of the plant-derived therapeutic antibodies by comparing their NMR spectral properties with those of an authentic IgG-Fc derived from mammalian cells.

Gene delivery into plant cells for recombinant protein production

Recombinant proteins are primarily produced from cultures of mammalian, insect, and bacteria cells. In recent years, the development of deconstructed virus-based vectors has allowed plants to become a viable platform for recombinant protein production, with advantages in versatility, speed, cost, scalability, and safety over the current production paradigms. In this paper, we review the recent progress in the methodology of agroinfiltration, a solution to overcome the challenge of transgene delivery into plant cells for large-scale manufacturing of recombinant proteins. General gene delivery methodologies in plants are first summarized, followed by extensive discussion on the application and scalability of each agroinfiltration method. New development of a spray-based agroinfiltration and its application on field-grown plants is highlighted. The discussion of agroinfiltration vectors focuses on their applications for producing complex and heteromultimeric proteins and is updated with the development of bridge vectors. Progress on agroinfiltration in Nicotiana and non-Nicotiana plant hosts is subsequently showcased in context of their applications for producing high-value human biologics and low-cost and high-volume industrial enzymes. These new advancements in agroinfiltration greatly enhance the robustness and scalability of transgene delivery in plants, facilitating the adoption of plant transient expression systems for manufacturing recombinant proteins with a broad range of applications.

Expression of bioactive anti-CD20 antibody fragments and induction of ER stress response in Arabidopsis seeds

Seed-based expression system is an attractive platform for the production of recombinant proteins in molecular farming. Despite the many advantages of molecular farming, little is known about the effect of the different subcellular accumulation of recombinant proteins on the endoplasmic reticulum (ER) quality control system in host plants. In this study, we analyzed the expression of anti-CD20 antibody fragments in seeds of Arabidopsis thaliana (ecotype Columbia) and corresponding glycosylation mutants, and evaluated the influence of three different signal sequences on the expression levels of scFv-Fc of C2B8. The highest protein accumulation level, with a maximum of 6.12 % total soluble proteins, was observed upon fusing proteins to the signal peptide of Arabidopsis seed storage albumin 2. The ER stress responses in developing seeds at 13 days post-anthesis were also compared across different transgenic lines under normal and heat shock conditions. Based on the gene expression profiles of ER stress transducers, our results suggest that accumulation of antibody fragments in the ER exerts more stress on ER homeostasis. In addition, quantitative PCR results also implicate enhanced activation of ER-associated degradation in transgenic lines. Last but not the least, we also demonstrate the anti-tumor potency of plant-derived proteins by showing the anti-tumor activity of purified scFv-Fc proteins against Daudi cells. Together, our data implies that better understanding of the interaction between exogenous protein production and the cellular quality control system of the host plant is necessary for the development of an optimal expression strategy that will be especially beneficial to commercial protein manufacturing.

Current and emerging strategies for the diagnosis, prevention and treatment of Lassa fever

ABSTRACT 

Lassa fever (LF) is a potentially fatal disease that affects an estimated 300,000–500,000 people in endemic areas of west Africa each year. Though past studies have identified fatality rates of 5–20% in patients suspected to have contracted Lassa virus (LASV), new studies using more precise clinical diagnoses and modern diagnostic assays show fatalities rates above 60% in acutely ill patients from endemic regions. Currently, there are no approved vaccines or therapeutics, and only one Comformité Européenne (CE) marked rapid immunodiagnostic for acute LASV infection. Therefore, preventing LASV transmission is the primary goal in endemic regions. Development of rapid immunodiagnostics and research into the efficacy of current treatment options continues toward saving lives in west Africa as well as creating a line of defense against the nefarious use of LASV in bioterrorism settings.

Leishmania tarentolae: an alternative approach to the production of monoclonal antibodies to treat emerging viral infections

Background

Monoclonal antibody therapy has an important role to play as a post-exposure prophylactic and therapeutic for the treatment of viral infections, including emerging infections. For example, several patients of the present Ebola virus outbreak in West Africa were treated with ZMapp, a cocktail of three monoclonal antibodies which are expressed in Nicotiana benthamiana.

Discussion

The majority of monoclonal antibodies in clinical use are expressed in mammalian cell lines which offer native folding and glycosylation of the expressed antibody. Monoclonal antibody expression in vegetal systems offers advantages over expression in mammalian cell lines, including improved potential for scale up and reduced costs. In this paper, I highlight the advantages of an upcoming protozoal system for the expression of recombinant antibody formats. Leishmania tarentolae offers a robust, economical expression of proteins with mammalian glycosylation patterns expressed in stable cell lines and grown in suspension culture. Several advantages of this system make it particularly suited for use in developing contexts.

Summary

Given the potential importance of monoclonal antibody therapy in the containment of emerging viral infections, novel and alternative strategies to improve production must be explored.

Electronic supplementary material

The online version of this article (doi:10.1186/2049-9957-4-8) contains supplementary material, which is available to authorized users.

Selection of IgG Variants with Increased FcRn Binding Using Random and Directed Mutagenesis: Impact on Effector Functions

Despite the reasonably long half-life of immunoglogulin G (IgGs), market pressure for higher patient convenience while conserving efficacy continues to drive IgG half-life improvement. IgG half-life is dependent on the neonatal Fc receptor (FcRn), which among other functions, protects IgG from catabolism. FcRn binds the Fc domain of IgG at an acidic pH ensuring that endocytosed IgG will not be degraded in lysosomal compartments and will then be released into the bloodstream. Consistent with this mechanism of action, several Fc-engineered IgG with increased FcRn affinity and conserved pH dependency were designed and resulted in longer half-life in vivo in human FcRn-transgenic mice (hFcRn), cynomolgus monkeys, and recently in healthy humans. These IgG variants were usually obtained by in silico approaches or directed mutagenesis in the FcRn-binding site. Using random mutagenesis, combined with a pH-dependent phage display selection process, we isolated IgG variants with improved FcRn-binding, which exhibited longer in vivo half-life in hFcRn mice. Interestingly, many mutations enhancing Fc/FcRn interaction were located at a distance from the FcRn-binding site validating our random molecular approach. Directed mutagenesis was then applied to generate new variants to further characterize our IgG variants and the effect of the mutations selected. Since these mutations are distributed over the whole Fc sequence, binding to other Fc effectors, such as complement C1q and FcγRs, was dramatically modified, even by mutations distant from these effectors’ binding sites. Hence, we obtained numerous IgG variants with increased FcRn-binding and different binding patterns to other Fc effectors, including variants without any effector function, providing distinct “fit-for-purpose” Fc molecules. We therefore provide evidence that half-life and effector functions should be optimized simultaneously as mutations can have unexpected effects on all Fc receptors that are critical for IgG therapeutic efficacy.

Chemical and Structural Aspects of Ebola Virus Entry Inhibitors

The Ebolaviruses are members of the family Filoviridae (“filoviruses”) and cause severe hemhorragic fever with human case fatality rates as high as 90%. Infection requires attachment of the viral particle to cells and triggering of membrane fusion between the host and viral membranes, a process that occurs in the host endosome and is facilitated by the envelope glycoprotein (GP). One potential strategy for therapeutic intervention is the development of agents (antibodies, peptides, and small molecules) that can interfere with viral entry aspects such as attachment, uptake, priming, or membrane fusion. This paper highlights recent developments in the discovery and evaluation of therapeutic entry inhibitors and identifies opportunities moving forward.