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

Fc engineered anti-virus therapeutic human IgG1 expressed in plants with altered binding to the neonatal Fc receptor

Production of therapeutic monoclonal antibody (mAb) in transgenic plants has several advantages such as large-scale production and the absence of pathogenic animal contaminants. However, mAb with high mannose (HM) type glycans has shown a faster clearance compared to antibodies produced in animal cells. The neonatal Fc receptor (FcRn) regulates the persistence of immunoglobulin G (IgG) by the FcRn-mediated recycling pathway, which salvages IgG from lysosomal degradation within cells. In this study, Fc-engineering of antirabies virus therapeutic mAb SO57 with the endoplasmic reticulum (ER)-retention peptide signal (Lys-Asp-Glu-Leu; KDEL) (mAbpK SO57) in plant cell was conducted to enhance its binding activity to human neonatal Fc receptor (hFcRn), consequently improve its serum half-life. Enzyme-linked immunosorbent assay (ELISA) and Surface plasmon resonance assay showed altered binding affinity of the Fc region of three different mAbpK SO57 variants [M252Y/S254T/T256E (MST), M428L/N434S (MN), H433K/N434F (HN)] to hFcRn compared to wild type (WT) of mAbpK SO57. Molecular modeling data visualized the structural alterations in these mAbpK SO57. All of the mAbpK SO57 variants had HM type glycan structures similar to the WT mAbpK SO57. In addition, the neutralizing activity of the three variants against the rabies virus CVS-11 was effective as the WT mAbpK SO57. These results indicate that the binding affinity of mAbpK SO57 variants to hFcRn can be modified without alteration of N-glycan structure and neutralization activity. Taken together, this study suggests that Fc-engineering of antirabies virus mAb can be applied to enhance the efficacy of therapeutic mAbs in plant expression systems.

Impact of structural modifications of IgG antibodies on effector functions

Immunoglobulin G (IgG) antibodies are a critical component of the adaptive immune system, binding to and neutralizing pathogens and other foreign substances. Recent advances in molecular antibody biology and structural protein engineering enabled the modification of IgG antibodies to enhance their therapeutic potential. This review summarizes recent progress in both natural and engineered structural modifications of IgG antibodies, including allotypic variation, glycosylation, Fc engineering, and Fc gamma receptor binding optimization. We discuss the functional consequences of these modifications to highlight their potential for therapeutical applications.

Fc-Engineered Therapeutic Antibodies: Recent Advances and Future Directions

Monoclonal therapeutic antibodies have revolutionized the treatment of cancer and other diseases. Fc engineering aims to enhance the effector functions or half-life of therapeutic antibodies by modifying their Fc regions. Recent advances in the Fc engineering of modern therapeutic antibodies can be considered the next generation of antibody therapy. Various strategies are employed, including altering glycosylation patterns via glycoengineering and introducing mutations to the Fc region, thereby enhancing Fc receptor or complement interactions. Further, Fc engineering strategies enable the generation of bispecific IgG-based heterodimeric antibodies. As Fc engineering techniques continue to evolve, an expanding portfolio of Fc-engineered antibodies is advancing through clinical development, with several already approved for medical use. Despite the plethora of Fc-based mutations that have been analyzed in in vitro and in vivo models, we focus here in this review on the relevant Fc engineering strategies of approved therapeutic antibodies to finetune effector functions, to modify half-life and to stabilize asymmetric bispecific IgGs.

Pharmaceutical Strategies to Improve Druggability of Potential Drug Candidates in Nonalcoholic Fatty Liver Disease Therapy

Nonalcoholic fatty liver disease (NAFLD) has become globally prevalent and is the leading cause of chronic liver disease. Although NAFLD is reversible without medical intervention in the early stage, the condition could be sequentially worsened to nonalcoholic steatohepatitis (NASH) and, eventually, cirrhosis and hepatic cancer. The progression of NAFLD is related to various factors such as genetics, pre-disposed metabolic disorders, and immunologic factors. Thankfully, to date, there have been accumulating research efforts and, as a result, different classes of potent drug candidates have been discovered. In addition, there have also been various attempts to explore pharmaceutical strategies to improve the druggability of drug candidates. In this review, we provided a brief overview of the drug candidates that have undergone clinical trials. In the latter part, strategies for developing better drugs are discussed.

Antibody-mediated protection against symptomatic COVID-19 can be achieved at low serum neutralizing titers

Multiple studies of vaccinated and convalescent cohorts have demonstrated that serum neutralizing antibody (nAb) titers correlate with protection against coronavirus disease 2019 (COVID-19). However, the induction of multiple layers of immunity after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exposure has complicated the establishment of nAbs as a mechanistic correlate of protection (CoP) and hindered the definition of a protective nAb threshold. Here, we show that a half-life-extended monoclonal antibody (adintrevimab) provides about 50% protection against symptomatic COVID-19 in SARS-CoV-2-naïve adults at serum nAb titers on the order of 1:30. Vaccine modeling results support a similar 50% protective nAb threshold, suggesting that low titers of serum nAbs protect in both passive antibody prophylaxis and vaccination settings. Extrapolation of adintrevimab pharmacokinetic data suggests that protection against susceptible variants could be maintained for about 3 years. The results provide a benchmark for the selection of next-generation vaccine candidates and support the use of broad, long-acting monoclonal antibodies as alternatives or supplements to vaccination in high-risk populations.

Harnessing Fc/FcRn Affinity Data from Patents with Different Machine Learning Methods

Monoclonal antibodies are biopharmaceuticals with a very long half-life due to the binding of their Fc portion to the neonatal receptor (FcRn), a pharmacokinetic property that can be further improved through engineering of the Fc portion, as demonstrated by the approval of several new drugs. Many Fc variants with increased binding to FcRn have been found using different methods, such as structure-guided design, random mutagenesis, or a combination of both, and are described in the literature as well as in patents. Our hypothesis is that this material could be subjected to a machine learning approach in order to generate new variants with similar properties. We therefore compiled 1323 Fc variants affecting the affinity for FcRn, which were disclosed in twenty patents. These data were used to train several algorithms, with two different models, in order to predict the affinity for FcRn of new randomly generated Fc variants. To determine which algorithm was the most robust, we first assessed the correlation between measured and predicted affinity in a 10-fold cross-validation test. We then generated variants by in silico random mutagenesis and compared the prediction made by the different algorithms. As a final validation, we produced variants, not described in any patents, and compared the predicted affinity with the experimental binding affinities measured by surface plasmon resonance (SPR). The best mean absolute error (MAE) between predicted and experimental values was obtained with a support vector regressor (SVR) using six features and trained on 1251 examples. With this setting, the error on the log(KD) was less than 0.17. The obtained results show that such an approach could be used to find new variants with better half-life properties that are different from those already extensively used in therapeutic antibody development.

Preclinical in vitro evaluation of immune suppression induced by GYM329, Fc-engineered sweeping antibody

Fc-engineering is commonly used to improve the therapeutic potency of antibody (Ab) treatments. Because FcγRIIb is the only inhibitory FcγR that contains an immunoreceptor tyrosine-based inhibition motif (ITIM), Fc-engineered Abs with enhanced binding affinity to FcγRIIb might provide immune suppression in clinical contexts. GYM329 is an anti-latent myostatin Fc-engineered Ab with increased affinity to FcγRIIb which is expected to improve muscle strength in patients with muscular disorders. Cross-linking of FcγRIIb by immune complex (IC) results in phosphorylation of ITIM to inhibit immune activation and apoptosis in B cells. We examined whether the IC of Fc-engineered Abs with enhanced binding affinity to FcγRIIb causes phosphorylation of ITIM or B cell apoptosis using GYM329 and its Fc variant Abs in human and cynomolgus-monkey (cyno) immune cells in vitro. IC of GYM329 with enhanced binding affinity to human FcγRIIb (×5) induced neither ITIM phosphorylation nor B cell apoptosis. As for GYM329, FcγRIIb should work as an endocytic receptor of small IC to sweep latent myostatin, so it is preferable that GYM329 induces neither ITIM phosphorylation nor B cell apoptosis to prevent immune suppression. In contrast, IC of myo-HuCy2b, the Ab with enhanced binding affinity to human FcγRIIb (×4), induced ITIM phosphorylation and B cell apoptosis. The result of the present study demonstrated that Fc-engineered Abs with similar binding affinity to FcγRIIb had different effects. Thus, it is important to also investigate FcγR-mediated immune functions other than binding to fully understand the biological effects of Fc-engineered Abs.

Functionalized FcRn-targeted nanosystems for oral drug delivery: A new approach to colorectal cancer treatment

Colorectal cancer (CRC) is the second type of cancer with the highest lethality rate. The current chemotherapy to treat CRC causes systemic toxicity, unsatisfying response rate, and low tumor-specific selectivity, which is mainly administered by invasive routes. The chronic and aggressive nature of cancers may require long-term regimens. Thus, the oral route is preferred. However, the orally administered drugs still need to surpass the harsh environment of the gastrointestinal tract and the biological barriers. Nanotechnology is a promising strategy to overcome the oral route limitations. Targeted nanoparticle systems decorated with functional groups can enhance the delivery of anticancer agents to tumor sites. It is described in the literature that the neonatal Fc receptor (FcRn) is expressed in cancer tissue and overexpressed in CRC epithelial cells. However, the impact of FcRn-targeted nanosystems in the treatment of CRC has been poorly investigated. This review article discusses the current knowledge on the involvement of the FcRn in CRC, as well as to critically assess its relevance as a target for further localization of oral nanocarriers in CRC tumor cells. Finally, a brief overview of cancer therapeutics, strategies to design the nanoparticles of anticancer drugs and a review of decorated nanoparticles with FcRn moieties are explored.

Monoclonal Antibody Engineering and Design to Modulate FcRn Activities: A Comprehensive Review

Understanding the biological mechanisms underlying the pH-dependent nature of FcRn binding, as well as the various factors influencing the affinity to FcRn, was concurrent with the arrival of the first recombinant IgG monoclonal antibodies (mAbs) and IgG Fc-fusion proteins in clinical practice. IgG Fc–FcRn became a central subject of interest for the development of these drugs for the comfort of patients and good clinical responses. In this review, we describe (i) mAb mutations close to and outside the FcRn binding site, increasing the affinity for FcRn at acidic pH and leading to enhanced mAb half-life and biodistribution, and (ii) mAb mutations increasing the affinity for FcRn at acidic and neutral pH, blocking FcRn binding and resulting, in vivo, in endogenous IgG degradation. Mutations modifying FcRn binding are discussed in association with pH-dependent modulation of antigen binding and (iii) anti-FcRn mAbs, two of the latest innovations in anti-FcRn mAbs leading to endogenous IgG depletion. We discuss the pharmacological effects, the biological consequences, and advantages of targeting IgG–FcRn interactions and their application in human therapeutics.

Anticalin N- or C-Terminal on a Monoclonal Antibody Affects Both Production and In Vitro Functionality

Bispecific antibodies (BsAbs) represent an important advance in innovative therapeutic strategies. Among the countless formats of BsAbs, fusion with molecules such as anticalins linked to a monoclonal antibody (mAb), represents an easy and low-cost way to obtain innovative molecules. We fused an anticalin against human fibronectin to a molecule biosimilar to trastuzumab (H0) or rituximab (R0), in four different positions, two on the N terminal region of heavy or light chains and two on the C terminal region. The eight BsAbs (H family (HF) 1 to 4 and R family (RF) 1 to 4) were produced and their affinity parameters and functional properties evaluated. The presence of anticalin did not change the glycosylation of the BsAb, shape or yield. The antigenic recognition of each BsAb family, Her2 for HF1 to 4 and CD20 for RF1 to 4, was slightly decreased (HF) or absent (RF) for the anticalin N-terminal in the light chain position. The anticalin recognition of FN was slightly decreased for the HF family, but a dramatic decrease was observed for RF members with lowest affinity for RF1. Moreover, functional properties of Abs, such as CD16 activation of NK, CD32-dependent phagocytosis and FcRn transcytosis, confirmed that this anticalin position leads to less efficient BsAbs, more so for RF than HF molecules. Nevertheless, all BsAbs demonstrated affinities for CD16, CD32 and FcRn, which suggests that more than affinity for FcRs is needed for a functioning antibody. Our strategy using anticalin and Abs allows for rapid generation of BsAbs, but as suggested by our results, some positions of anticalins on Abs result in less functionality.

Evaluation of strategies to modify Anti-SARS-CoV-2 monoclonal antibodies for optimal functionality as therapeutics

The current global COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in a public health crisis with more than 168 million cases reported globally and more than 4.5 million deaths at the time of writing. In addition to the direct impact of the disease, the economic impact has been significant as public health measures to contain or reduce the spread have led to country wide lockdowns resulting in near closure of many sectors of the economy. Antibodies are a principal determinant of the humoral immune response to COVID-19 infections and may have the potential to reduce disease and spread of the virus. The development of monoclonal antibodies (mAbs) represents a therapeutic option that can be produced at large quantity and high quality. In the present study, a mAb combination mixture therapy was investigated for its capability to specifically neutralize SARS-CoV-2. We demonstrate that each of the antibodies bind the spike protein and neutralize the virus, preventing it from infecting cells in an in vitro cell-based assay, including multiple viral variants that are currently circulating in the human population. In addition, we investigated the effects of two different mutations in the Fc portion (YTE and LALA) of the antibody on Fc effector function and the ability to alleviate potential antibody-dependent enhancement of disease. These data demonstrate the potential of a combination of two mAbs that target two different epitopes on the SARS-CoV2 spike protein to provide protection against SARS-CoV-2 infection in humans while extending serum half-life and preventing antibody-dependent enhancement of disease.

Neonatal Fc Receptor-Targeted Therapies in Neurology

Autoantibodies are increasingly recognized for their pathogenic potential in a growing number of neurological diseases. While myasthenia gravis represents the prototypic antibody (Ab)-mediated neurological disease, many more disorders characterized by Abs targeting neuronal or glial antigens have been identified over the past two decades. Depletion of humoral immune components including immunoglobulin G (IgG) through plasma exchange or immunoadsorption is a successful therapeutic strategy in most of these disease conditions. The neonatal Fc receptor (FcRn), primarily expressed by endothelial and myeloid cells, facilitates IgG recycling and extends the half-life of IgG molecules. FcRn blockade prevents binding of endogenous IgG to FcRn, which forces these antibodies into lysosomal degradation, leading to IgG depletion. Enhancing the degradation of endogenous IgG by FcRn-targeted therapies proved to be a powerful therapeutic approach in patients with generalized MG and is currently being tested in clinical trials for several other neurological diseases including autoimmune encephalopathies, neuromyelitis optica spectrum disorders, and inflammatory neuropathies. This review illustrates mechanisms of FcRn-targeted therapies and appraises their potential to treat neurological diseases.

The Dual Targeting of FcRn and FcγRs via Monomeric Fc Fragments Results in Strong Inhibition of IgG-Dependent Autoimmune Pathologies

Novel molecules that directly target the neonatal Fc receptor (FcRn) and/or Fc gamma receptors (FcγRs) are emerging as promising treatments for immunoglobulin G (IgG)-dependent autoimmune pathologies. Mutated Fc regions and monoclonal antibodies that target FcRn are currently in clinical development and hold promise for reducing the levels of circulating IgG. Additionally, engineered structures containing multimeric Fc regions allow the dual targeting of FcRn and FcγRs; however, their tolerance needs to first be validated in phase I clinical studies. Here, for the first time, we have developed a modified monomeric recombinant Fc optimized for binding to all FcRns and FcγRs without the drawback of possible tolerance associated with FcγR cross-linking. A rational approach using Fc engineering allowed the selection of LFBD192, an Fc with a combination of six mutations that exhibits improved binding to human FcRn and FcγR as well as mouse FcRn and FcγRIV. The potency of LFBD192 was compared with that of intravenous immunoglobulin (IVIg), an FcRn blocker (Fc-MST-HN), and a trimeric Fc that blocks FcRn and/or immune complex-mediated cell activation through FcγR without triggering an immune reaction in several in vitro tests and validated in three mouse models of autoimmune disease.

In Translation: FcRn across the Therapeutic Spectrum

As an essential modulator of IgG disposition, the neonatal Fc receptor (FcRn) governs the pharmacokinetics and functions many therapeutic modalities. In this review, we thoroughly reexamine the hitherto elucidated biological and thermodynamic properties of FcRn to provide context for our assessment of more recent advances, which covers antigen-binding fragment (Fab) determinants of FcRn affinity, transgenic preclinical models, and FcRn targeting as an immune-complex (IC)-clearing strategy. We further comment on therapeutic antibodies authorized for treating SARS-CoV-2 (bamlanivimab, casirivimab, and imdevimab) and evaluate their potential to saturate FcRn-mediated recycling. Finally, we discuss modeling and simulation studies that probe the quantitative relationship between in vivo IgG persistence and in vitro FcRn binding, emphasizing the importance of endosomal transit parameters.

A general Fc engineering platform for the next generation of antibody therapeutics

Rationale: Fc engineering has become the focus of antibody drug development. The current mutagenesis and in silico protein design methods are confined by the limited throughput and high cost, while the high-throughput phage display and yeast display technologies are not suitable for screening glycosylated Fc variants. Here we developed a mammalian cell display-based Fc engineering platform. Methods: By using mammalian cell display and next generation sequencing, we screened millions of Fc variants for optimized affinity and specificity for FcγRIIIa or FcγRIIb. The identified Fc variants with improved binding to FcγRIIIa were substituted into trastuzumab and rituximab and the effector function of antibodies were examined in the PBMC-based assay. On the other hand, the identified Fc variants with selectively enhanced FcγRIIb binding were applied to CD40 agonist antibody and the activities of the antibodies were measured on different cell assays. The immunostimulatory activity of CD40 antibodies was also evaluated by OVA-specific CD8+ T cell response model in FcγR/CD40-humanized mice. Results: Using this approach, we screened millions of Fc variant and successfully identified several novel Fc variants with enhanced FcγRIIIa or FcγRIIb binding. These identified Fc variants displayed a dramatic increase in antibody-dependent cellular cytotoxicity in PBMC-based assay. Novel variants with selectively enhanced FcγRIIb binding were also identified. CD40 agonist antibodies substituted with these Fc variants displayed activity more potent than the parental antibody in the in vitro and in vivo models.Conclusions: This approach increased the throughput of Fc variant screening from thousands to millions magnitude, enabled screening variants containing multiple mutations and could be integrated with glycoengineering technology, represents an ideal platform for Fc engineering. The initial efforts demonstrated the capability of the platform and the novel Fc variants could be substituted into nearly any antibody for the next generation of antibody therapeutics.

Brain Delivery of Nanomedicines: Trojan Horse Liposomes for Plasmid DNA Gene Therapy of the Brain

Non-viral gene therapy of the brain is enabled by the development of plasmid DNA brain delivery technology, which requires the engineering and manufacturing of nanomedicines that cross the blood-brain barrier (BBB). The development of such nanomedicines is a multi-faceted problem that requires progress at multiple levels. First, the type of nanocontainer, e.g., nanoparticle or liposome, which encapsulates the plasmid DNA, must be developed. Second, the type of molecular Trojan horse, e.g., peptide or receptor-specific monoclonal antibody (MAb), must be selected for incorporation on the surface of the nanomedicine, as this Trojan horse engages specific receptors expressed on the BBB, and the brain cell membrane, to trigger transport of the nanomedicine from blood into brain cells beyond the BBB. Third, the plasmid DNA must be engineered without bacterial elements, such as antibiotic resistance genes, to enable administration to humans; the plasmid DNA must also be engineered with tissue-specific gene promoters upstream of the therapeutic gene, to insure gene expression in the target organ with minimal off-target expression. Fourth, upstream manufacturing of the nanomedicine must be developed and scalable so as to meet market demand for the target disease, e.g., annual long-term treatment of 1,000 patients with an orphan disease, short term treatment of 10,000 patients with malignant glioma, or 100,000 patients with new onset Parkinson's disease. Fifth, downstream manufacturing problems, such as nanomedicine lyophilization, must be solved to ensure the nanomedicine has a commercially viable shelf-life for treatment of CNS disease in humans.

Eliminating Fc N-Linked Glycosylation and Its Impact on Dosing Consideration for a Transferrin Receptor Antibody-Erythropoietin Fusion Protein in Mice

Erythropoietin (EPO), a hematopoietic growth factor and a promising therapy for Alzheimer's disease, has low permeability across the blood-brain barrier. The transferrin receptor antibody fused to EPO (TfRMAb-EPO) is a chimeric monoclonal antibody that ferries EPO into the brain via the transvascular route. However, TfRMAbs have Fc-effector function-related adverse effects including reticulocyte suppression. To overcome this, we recently developed an effectorless TfRMAb-EPO fusion protein, designated TfRMAb-N292G-EPO, by eliminating the Fc N-linked glycosylation site at position 292 of the antibody heavy chain. The mutant fusion protein showed enhanced plasma clearance and dramatically reduced plasma concentrations compared with the wild-type (WT) nonmutant fusion protein. This increased clearance of the aglycosylated TfRMAb is expected to increase the injection dose of the mutant fusion protein. To provide a basis for future therapeutic uses of this IgG-neurotrophin fusion protein, the current study aimed to characterize the pharmacokinetic profile of this effectorless TfRMAb-N292G-EPO at different doses following different routes of administration in the mouse. Adult C57BL/6J male mice were injected with a single dose (3, 6, 9, or 20 mg/kg; n = 3-6 per dose) of TfRMAb-N292G-EPO through either the subcutaneous (SQ) or intraperitoneal (IP) route. TfRMAb-N292G-EPO plasma concentrations were determined using an enzyme-linked immunosorbent assay. Mice were sacrificed 24 h after injection, and terminal blood was used for a complete blood count. Brain concentrations in the WT- and mutant fusion protein-treated mice were compared. We observed stark differences in the plasma pharmacokinetics of TfRMAb-N292G-EPO between the IP and SQ routes of administration. Dose escalation from 3 to 20 mg/kg increased the plasma C_max only 3.5-fold for the SQ route, compared with a 35-fold increase for the IP route. The plasma C_max was 15.0 ± 2.0, 21.3 ± 4.1, 21.3 ± 6.4, and 52.8 ± 27.9 ng/mL following SQ injection and 288 ± 47, 389 ± 154, 633 ± 194, and 10,066 ± 7059 ng/mL following IP injection for 3, 6, 9, and 20 mg/kg doses, respectively. The plasma C_max following the SQ route was therefore 19- to 190-fold lower than that following the IP route. This finding is consistent with a 31-fold higher apparent clearance following the SQ route compared with the IP route at the highest dose administered. The brain concentrations in the mice treated with a 3 mg/kg dose of the mutant fusion protein were lower than those in the nonmutant WT-treated mice. No reticulocyte suppression was observed at the 3 mg/kg SQ dose of TfRMAb-N292G-EPO. However, reticulocyte suppression increased with an increase in dose and area under the plasma concentration-time curve (AUC) for both the IP and SQ routes. Overall, elimination of Fc N-linked glycosylation, to mitigate TfRMAb effector function side effects, has a profound effect on the plasma exposure of TfRMAb-N292G-EPO at therapeutic as well as high doses (3-20 mg/kg). This effect is more pronounced following SQ injection. The low plasma concentrations of the mutant fusion protein following a 3 mg/kg dose resulted in negligible brain uptake. The beneficial rescue of reticulocyte reduction by the N292G mutation is a function of AUC and is negated at high doses of the N292G mutant.

The covalent SNAP tag for protein display quantification and low-pH protein engineering

Yeast display has become an important tool for modern biotechnology with many advantages for eukaryotic protein engineering. Antibody-based peptide interactions are often used to quantify yeast surface expression (e.g., by fusing a target protein to a FLAG, Myc, polyhistidine, or other peptide tag). However, antibody-antigen interactions require high stability for accurate quantification, and conventional tag systems based on such interactions may not be compatible with a low pH environment. In this study, a SNAP tag was introduced to a yeast display platform to circumvent disadvantages of conventional antibody display tags at low pH. SNAP forms a covalent bond with its small-molecule substrate, enabling precise and pH-independent protein display tagging. We compared the SNAP tag to conventional antibody-based peptide fusion and to direct fluorescent domain fusion using antibody fragment crystallizable (Fc) gene libraries as a case study in low pH protein engineering. Our results demonstrated that covalent SNAP tags can effectively quantify protein-surface expression at low pH, enabling the enrichment of Fc variants with increased affinity at pH 6.0 to the neonatal Fc receptor (FcRn). Incorporation of a covalent SNAP tag thus overcomes disadvantages of conventional antibody-based expression tags and enables protein-engineering applications outside of physiological pH.

An engineered human Fc domain that behaves like a pH-toggle switch for ultra-long circulation persistence

The pharmacokinetic properties of antibodies are largely dictated by the pH-dependent binding of the IgG fragment crystallizable (Fc) domain to the human neonatal Fc receptor (hFcRn). Engineered Fc domains that confer a longer circulation half-life by virtue of more favorable pH-dependent binding to hFcRn are of great therapeutic interest. Here we developed a pH Toggle switch Fc variant containing the L309D/Q311H/N434S (DHS) substitutions, which exhibits markedly improved pharmacokinetics relative to both native IgG1 and widely used half-life extension variants, both in conventional hFcRn transgenic mice and in new knock-in mouse strains. engineered specifically to recapitulate all the key processes relevant to human antibody persistence in circulation, namely: (i) physiological expression of hFcRn, (ii) the impact of hFcγRs on antibody clearance and (iii) the role of competing endogenous IgG. DHS-IgG retains intact effector functions, which are important for the clearance of target pathogenic cells and also has favorable developability.

DuoMab: a novel CrossMab-based IgG-derived antibody format for enhanced antibody-dependent cell-mediated cytotoxicity

High specificity accompanied with the ability to recruit immune cells has made recombinant therapeutic antibodies an integral part of drug development. Here we present a generic approach to generate two novel IgG-derived antibody formats that are based on a modification of the CrossMab technology. MoAbs harbor two heavy chains (HCs) resulting in one binding entity and one fragment crystallizable region (Fc), whereas DuoMabs are composed of four HCs harboring two binding entities and two Fc regions linked at a disulfide-bridged hinge. The latter bivalent format is characterized by avidity-enhanced target cell binding while simultaneously increasing the 'Fc-load' on the surface. DuoMabs were shown to be producible in high yield and purity and bind to surface cells with affinities comparable to IgGs. The increased Fc load directed at the surface of target cells by DuoMabs modulates their antibody-dependent cell-mediated cytotoxicity competency toward target cells, making them attractive for applications that require or are modulated by FcR interactions.

Plasma Pharmacokinetics of High-Affinity Transferrin Receptor Antibody-Erythropoietin Fusion Protein is a Function of Effector Attenuation in Mice

Erythropoietin (EPO) is a potential therapeutic for Alzheimer's disease (AD); however, limited blood-brain barrier (BBB) penetration reduces its applicability as a CNS therapeutic. Antibodies against the BBB transferrin receptor (TfRMAbs) act as molecular Trojan horses for brain drug delivery, and a fusion protein of EPO and TfRMAb, designated TfRMAb-EPO, is protective in a mouse model of AD. TfRMAbs have Fc effector function side effects, and removal of the Fc N-linked glycosylation site by substituting Asn with Gly reduces the Fc effector function. However, the effect of such Fc mutations on the pharmacokinetics (PK) of plasma clearance of TfRMAb-based fusion proteins, such as TfRMAb-EPO, is unknown. To examine this, the plasma PK of TfRMAb-EPO (wild-type), which expresses the mouse IgG1 constant heavy chain region and includes the Asn residue at position 292, was compared to the mutant TfRMAb-N292G-EPO, in which the Asn residue at position 292 is mutated to Gly. Plasma PK was compared following IV, IP, and SQ administration for doses between 0.3 and 3 mg/kg in adult male C57 mice. The results show a profound increase in clearance (6- to 8-fold) of the TfRMAb-N292G-EPO compared with the wild-type TfRMAb-EPO following IV administration. The clearance of both the wild-type and mutant TfRMAb-EPO fusion proteins followed nonlinear PK, and a 10-fold increase in dose resulted in a 7- to 11-fold decrease in plasma clearance. Following IP and SQ administration, the C_max values of the TfRMAb-N292G-EPO mutant were profoundly (37- to 114-fold) reduced compared with the wild-type TfRMAb-EPO, owing to comparable increases in plasma clearance of the mutant fusion protein. The wild-type TfRMAb fusion protein was associated with reticulocyte suppression, and the N292G mutation mitigated this suppression of reticulocytes. Overall, the beneficial suppression of effector function via the N292G mutation may be offset by the deleterious effect this mutation has on the plasma levels of the TfRMAb-EPO fusion protein, especially following SQ administration, which is the preferred route of administration in humans for chronic neurodegenerative diseases including AD.

In-Use Physicochemical and Biological Stability of the Trastuzumab Biosimilar CT-P6 Upon Preparation for Intravenous Infusion

BACKGROUND

CT-P6 is a biosimilar of trastuzumab, a monoclonal antibody targeting human epidermal growth factor 2 (HER2), that is used in the treatment of breast and gastric cancers.

OBJECTIVE

The aim of this study was to evaluate the in-use physicochemical and biological stability of CT-P6 following preparation for intravenous (IV) infusion.

METHODS

One batch of CT-P6 within the final month of its 48-month shelf life was used to simulate sub-optimal administration conditions. CT-P6 dilutions of 0.4, 1.0, and 4.0 mg/mL, representative of actual use scenarios, were prepared in 0.9% saline solution in either polypropylene (PP) or polyvinylchloride (PVC) infusion bags. Following refrigeration at 2-8 °C for 1 month, samples were incubated at room temperature for 24 h. Physicochemical and biological stability were evaluated according to presence of sub-visible particles, pH, proportion of molecular weight variants, oxidation level of methionine residues 107, 255/256 and 432/433, and binding affinity to the Fc neonatal receptor and HER2.

RESULTS

Analyses of CT-P6 preparations at all concentrations tested and in both PP and PVC infusion bags revealed no changes in sub-visible particles, pH, molecular weight variants, oxidation, or potency after 1 month at 2-8 °C followed by exposure to room temperature for 24 h.

CONCLUSION

These analyses demonstrate the extended stability, after refrigerated storage for 1 month followed by 24-h exposure to room temperature, of CT-P6 under the dilution conditions required for IV infusion. This stability was sustained for all dilution factors and both infusion bag materials tested.

The Ligands for Human IgG and Their Effector Functions

Activation of the humoral immune system is initiated when antibodies recognize an antigen and trigger effector functions through the interaction with Fc engaging molecules. The most abundant immunoglobulin isotype in serum is Immunoglobulin G (IgG), which is involved in many humoral immune responses, strongly interacting with effector molecules. The IgG subclass, allotype, and glycosylation pattern, among other factors, determine the interaction strength of the IgG-Fc domain with these Fc engaging molecules, and thereby the potential strength of their effector potential. The molecules responsible for the effector phase include the classical IgG-Fc receptors (FcγR), the neonatal Fc-receptor (FcRn), the Tripartite motif-containing protein 21 (TRIM21), the first component of the classical complement cascade (C1), and possibly, the Fc-receptor-like receptors (FcRL4/5). Here we provide an overview of the interactions of IgG with effector molecules and discuss how natural variation on the antibody and effector molecule side shapes the biological activities of antibodies. The increasing knowledge on the Fc-mediated effector functions of antibodies drives the development of better therapeutic antibodies for cancer immunotherapy or treatment of autoimmune diseases.

Fc Sialylation Prolongs Serum Half-Life of Therapeutic Antibodies

The long serum t _1/2 of IgGs is ensured by their interaction with the neonatal Fc receptor (FcRn), which salvages IgG from intracellular degradation. Fc glycosylation is thought not to influence FcRn binding and IgG longevity in vivo. In this article, we demonstrate that hypersialylation of asparagine 297 (N297) enhances IgG serum persistence. This polarized glycosylation is achieved using a novel Fc mutation, a glutamate residue deletion at position 294 (Del) that endows IgGs with an up to 9-fold increase in serum lifespan. The strongest impact was observed when the Del was combined with Fc mutations improving FcRn binding (Del-FcRn⁺). Enzymatic desialylation of a Del-FcRn⁺ mutant or its production in a cell line unable to hypersialylate reduced the in vivo serum t _1/2 of the desialylated mutants to that of native FcRn⁺ mutants. Consequently, our study proves that sialylation of the N297 sugar moiety has a direct impact on human IgG serum persistence.

Improvement of pharmacokinetic properties of therapeutic antibodies by antibody engineering

Monoclonal antibodies (mAbs) have become an important therapeutic option for several diseases. Since several mAbs have shown promising efficacy in clinic, the competition to develop mAbs has become severe. In efforts to gain a competitive advantage over other mAbs and provide significant benefits to patients, innovations in antibody engineering have aimed at improving the pharmacokinetic properties of mAbs. Because engineering can provide therapeutics that are more convenient, safer, and more efficacious for patients in several disease areas, it is an attractive approach to provide significant benefits to patients. Further advances in engineering mAbs to modulate their pharmacokinetics were driven by the increase of total soluble target antigen concentration that is often observed after injecting a mAb, which then requires a high dosage to antagonize. To decrease the required dosage, several antibody engineering techniques have been invented that reduce the total concentration of soluble target antigen. Here, we review the various ways that antibody engineering can improve the pharmacokinetic properties of mAbs.

Extending human IgG half-life using structure-guided design

Engineering of antibodies for improved pharmacokinetics through enhanced binding to the neonatal Fc receptor (FcRn) has been demonstrated in transgenic mice, non-human primates and humans. Traditionally, such approaches have largely relied on random mutagenesis and display formats, which fail to address related critical attributes of the antibody, such as effector functions or biophysical stability. We have developed a structure- and network-based framework to interrogate the engagement of IgG with multiple Fc receptors (FcRn, C1q, TRIM21, FcγRI, FcγRIIa/b, FcγRIIIa) simultaneously. Using this framework, we identified features that govern Fc-FcRn interactions and identified multiple distinct pathways for enhancing FcRn binding in a pH-specific manner. Network analysis provided a novel lens to study the allosteric impact of half-life-enhancing Fc mutations on FcγR engagement, which occurs distal to the FcRn binding site. Applying these principles, we engineered a panel of unique Fc variants that enhance FcRn binding while maintaining robust biophysical properties and wild type-like binding to activating receptors. An antibody harboring representative Fc designs demonstrates a half-life improvement of > 9 fold in transgenic mice and > 3.5 fold in cynomolgus monkeys, and maintains robust effector functions such as antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity.

Efficacy and Mechanism of Antitumor Activity of an Antibody Targeting Transferrin Receptor 1 in Mouse Models of Human Multiple Myeloma

The transferrin receptor 1 (TfR1) is an attractive target for Ab-mediated cancer therapy. We previously developed a mouse/human chimeric IgG3 Ab (ch128.1) targeting human TfR1, which exhibits direct in vitro cytotoxicity against certain human malignant B cells through TfR1 degradation and iron deprivation. ch128.1 also demonstrates exceptional antitumor activity against the B cell malignancy multiple myeloma (MM) in xenograft models of SCID-Beige mice bearing either disseminated ARH-77 or KMS-11 cells in an early disease setting. Interestingly, this activity is observed even against KMS-11 cells, which show no sensitivity to the direct cytotoxic activity of ch128.1 in vitro. To understand the contributions of the Fc fragment, we generated a ch128.1 mutant with impaired binding to FcγRs and to the complement component C1q, which retains binding to the neonatal Fc receptor. We now report that this mutant Ab does not show antitumor activity in these two MM models, indicating a crucial role of the Fc fragment in the antitumor activity of ch128.1, which can be attributed to effector functions (Ab-dependent cell-mediated cytotoxicity, Ab-dependent cell-mediated phagocytosis, and/or complement-dependent cytotoxicity). Interestingly, in the KMS-11 model, complement depletion does not affect protection, whereas macrophage depletion does. Consistent with this observation, we found that ch128.1 induces Ab-dependent cell-mediated cytotoxicity and Ab-dependent cell-mediated phagocytosis against KMS-11 cells in the presence of murine bone marrow-derived macrophages. Finally, we found that ch128.1 therapy effectively increases survival in a late MM disease setting. Our results suggest that macrophages play a major role in ch128.1-mediated antitumor protection in our models and that ch128.1 can be effective against human B cell malignancies such as MM.

Progress and Challenges in the Design and Clinical Development of Antibodies for Cancer Therapy

The remarkable progress in engineering and clinical development of therapeutic antibodies in the last 40 years, after the seminal work by Köhler and Milstein, has led to the approval by the United States Food and Drug Administration (FDA) of 21 antibodies for cancer immunotherapy. We review here these approved antibodies, with emphasis on the methods used for their discovery, engineering, and optimization for therapeutic settings. These methods include antibody engineering via chimerization and humanization of non-human antibodies, as well as selection and further optimization of fully human antibodies isolated from human antibody phage-displayed libraries and immunization of transgenic mice capable of generating human antibodies. These technology platforms have progressively led to the development of therapeutic antibodies with higher human content and, thus, less immunogenicity. We also discuss the genetic engineering approaches that have allowed isotype switching and Fc modifications to modulate effector functions and bioavailability (half-life), which together with the technologies for engineering the Fv fragment, have been pivotal in generating more efficacious and better tolerated therapeutic antibodies to treat cancer.

Insertion of scFv into the hinge domain of full-length IgG1 monoclonal antibody results in tetravalent bispecific molecule with robust properties

By simultaneous binding two disease mediators, bispecific antibodies offer the opportunity to broaden the utility of antibody-based therapies. Herein, we describe the design and characterization of Bs4Ab, an innovative and generic bispecific tetravalent antibody platform. The Bs4Ab format comprises a full-length IgG1 monoclonal antibody with a scFv inserted into the hinge domain. The Bs4Ab design demonstrates robust manufacturability as evidenced by MEDI3902, which is currently in clinical development. To further demonstrate the applicability of the Bs4Ab technology, we describe the molecular engineering, biochemical, biophysical, and in vivo characterization of a bispecific tetravalent Bs4Ab that, by simultaneously binding vascular endothelial growth factor and angiopoietin-2, inhibits their function. We also demonstrate that the Bs4Ab platform allows Fc-engineering similar to that achieved with IgG1 antibodies, such as mutations to extend half-life or modulate effector functions.

Correlation of FCGRT genomic structure with serum immunoglobulin, albumin and farletuzumab pharmacokinetics in patients with first relapsed ovarian cancer

Farletuzumab (FAR) is a humanized monoclonal antibody (mAb) that binds to folate receptor alpha. A Ph3 trial in ovarian cancer patients treated with carboplatin/taxane plus FAR or placebo did not meet the primary statistical endpoint. Subgroup analysis demonstrated that subjects with high FAR exposure levels (Cmin>57.6μg/mL) showed statistically significant improvements in PFS and OS. The neonatal Fc receptor (fcgrt) plays a central role in albumin/IgG stasis and mAb pharmacokinetics (PK). Here we evaluated fcgrt sequence and association of its promoter variable number tandem repeats (VNTR) and coding single nucleotide variants (SNV) with albumin/IgG levels and FAR PK in the Ph3 patients. A statistical correlation existed between high FAR Cmin and AUC in patients with the highest quartile of albumin and lowest quartile of IgG1. Analysis of fcgrt identified 5 different VNTRs in the promoter region and 9 SNVs within the coding region, 4 which are novel.

Rethinking the INN system for therapeutic antibodies

In the context of a possible revision of the International Nonproprietary Names (INN) system of recombinant monoclonal antibodies, which is saturated, we propose several avenues of reflection driven by the primary goal of the INN, information of health-care professionals. Clinical considerations argue for an abandon of the substems A (target category) and B (origin category), which lengthen the INN without real added-value. On the contrary, new substems or suffixes are required to alert on the absence/presence of an Fc portion and/or multispecificity, which are essential from a pharmacological point of view. Moreover, we think it necessary to explicitly mention Fc variations since they could influence the pharmacology of these biopharmaceuticals, and hence their efficacy and side-effects. Besides indicating the subclass/isotype in the documents easily accessible to health care professionals, we propose to systematically describe both the natural variations (allotypes) by using the Gm (G marker) system, and the artificial variations by using a Ge (G engineering) system that is discussed here and could apply to all IgG constant domains (tentatively called the Fy portion).

Biology of anti-TNF agents in immune-mediated inflammatory diseases: therapeutic implications

Biologics are increasingly being used to modify the course of immune-mediated inflammatory diseases. Some main agents are monoclonal antibodies and a fusion-protein that target TNF. This group includes adalimumab, infliximab, certolizumab pegol, golimumab and etanercept. Although the efficacy of anti-TNFs is supported by numerous randomized clinical trials, their pharmacokinetics depend on many factors, in particular immunogenicity, which can cause marked and rapid clearance and a consequent decrease in efficacy. Kinetics involve receptors that recognize the Fc fragment of the antibody and are responsible for various processes. Pharmacological advances permit optimizing the pharmacokinetics of anti-TNFs. In this review, we examine the kinetics of anti-TNF biologics, and consequent therapeutic implications, and overview some latest developments in the field. First draftsubmitted: 17 May 2016; Accepted for publication: 15 September2016; Published online: 14 October 2016.

Utility of immunodeficient mouse models for characterizing the preclinical pharmacokinetics of immunogenic antibody therapeutics

Prior to clinical studies, the pharmacokinetics (PK) of antibody-based therapeutics are characterized in preclinical species; however, those species can elicit immunogenic responses that can lead to an inaccurate estimation of PK parameters. Immunodeficient (SCID) transgenic hFcRn and C57BL/6 mice were used to characterize the PK of three antibodies that were previously shown to be immunogenic in mice and cynomolgus monkeys. Four mouse strains, Tg32 hFcRn SCID, Tg32 hFcRn, SCID and C57BL/6, were administered adalimumab (Humira®), mAbX and mAbX-YTE at 1 mg/kg, and in SCID strains there was no incidence of immunogenicity. In non-SCID strains, drug-clearing ADAs appeared after 4-7 days, which affected the ability to accurately calculate PK parameters. Single species allometric scaling of PK data for Humira® in SCID and hFcRn SCID mice resulted in improved human PK predictions compared to C57BL/6 mice. Thus, the SCID mouse model was demonstrated to be a useful tool for assessing the preclinical PK of immunogenic therapeutics.

Engineering antibody therapeutics

The successful introduction of antibody-based protein therapeutics into the arsenal of treatments for patients has within a few decades fostered intense innovation in the production and engineering of antibodies. Reviewed here are the methods currently used to produce antibodies along with how our knowledge of the structural and functional characterization of immunoglobulins has resulted in the engineering of antibodies to produce protein therapeutics with unique properties, both biological and biophysical, that are leading to novel therapeutic approaches. Antibody engineering includes the introduction of the antibody combining site (variable regions) into a host of architectures including bi and multi-specific formats that further impact the therapeutic properties leading to further advantages and successes in patient treatment.

IgG1 Allotypes Influence the Pharmacokinetics of Therapeutic Monoclonal Antibodies through FcRn Binding

Because IgG1 allotypes might have different half-lives, their influence on infliximab (G1m17,1 allotype) pharmacokinetics was investigated in a group of spondyloarthritis patients. Infliximab was found to have a shorter half-life in patients homozygous for the G1m17,1 allotypes than in those carrying the G1m3 with no G1m1 (G1m3,-1) allotype. Because the neonatal FcR (FcRn) is involved in the pharmacokinetics of mAbs, the interaction of different IgG1 allotypes with FcRn was examined using cellular assays and surface plasmon resonance. G1m17,1 mAbs, such as infliximab and rituximab, were shown to bind more efficiently to FcRn and to be transcytosed better than the G1m3,-1 mAb cetuximab, which explains why infliximab is a better competitor for endogenous IgG1 in G1m3,-1 allotype-bearing patients. A set of four allotype variants of adalimumab (G1m17,1; G1m17,-1; G1m3,1; and G1m3,-1) was also tested for its binding to FcRn, revealing that the G1m3,1 variant, not present in commercial mAbs, binds more efficiently to FcRn and is transcytosed better than the other three variants, all of which are found in therapeutic mAbs.

Conformational Destabilization of Immunoglobulin G Increases the Low pH Binding Affinity with the Neonatal Fc Receptor

Crystallographic evidence suggests that the pH-dependent affinity of IgG molecules for the neonatal Fc receptor (FcRn) receptor primarily arises from salt bridges involving IgG histidine residues, resulting in moderate affinity at mildly acidic conditions. However, this view does not explain the diversity in affinity found in IgG variants, such as the YTE mutant (M252Y,S254T,T256E), which increases affinity to FcRn by up to 10×. Here we compare hydrogen exchange measurements at pH 7.0 and pH 5.5 with and without FcRn bound with surface plasmon resonance estimates of dissociation constants and FcRn affinity chromatography. The combination of experimental results demonstrates that differences between an IgG and its cognate YTE mutant vary with their pH-sensitive dynamics prior to binding FcRn. The conformational dynamics of these two molecules are nearly indistinguishable upon binding FcRn. We present evidence that pH-induced destabilization in the CH2/3 domain interface of IgG increases binding affinity by breaking intramolecular H-bonds and increases side-chain adaptability in sites that form intermolecular contacts with FcRn. Our results provide new insights into the mechanism of pH-dependent affinity in IgG-FcRn interactions and exemplify the important and often ignored role of intrinsic conformational dynamics in a protein ligand, to dictate affinity for biologically important receptors.