Modification of the Fc region of a primatized IgG antibody to human CD4 retains its ability to modulate CD4 receptors but does not deplete CD4(+) T cells in chimpanzees

Monoclonal Antibody Therapies Against SARS-CoV-2: Promises and Realities

Monoclonal antibodies targeting the Spike protein of SARS-CoV-2 have been widely deployed in the ongoing COVID-19 pandemic. I review here the impact of those therapeutics in the early pandemic, ranging from structural classification to outcomes in clinical trials to in vitro and in vivo evidence of basal and treatment-emergent immune escape. Unfortunately, the Omicron variant of concern has completely reset all achievements so far in mAb therapy for COVID-19. Despite the intrinsic limitations of this strategy, future developments such as respiratory delivery of further engineered mAb cocktails could lead to improved outcomes.

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.

Monoclonal antibody therapies against SARS-CoV-2

Monoclonal antibodies (mAbs) targeting the spike protein of SARS-CoV-2 have been widely used in the ongoing COVID-19 pandemic. In this paper, we review the properties of mAbs and their effect as therapeutics in the pandemic, including structural classification, outcomes in clinical trials that led to the authorisation of mAbs, and baseline and treatment-emergent immune escape. We show how the omicron (B.1.1.529) variant of concern has reset treatment strategies so far, discuss future developments that could lead to improved outcomes, and report the intrinsic limitations of using mAbs as therapeutic agents.

The clinical significance of allergen-specific IgG4 in allergic diseases

IgG4 is a subclass of IgG antibody with a unique molecular feature of (Fragment antigen- binding) Fab-arm exchange, allowing bispecific antigen binding in a mono-valent manner. With low binding affinity to C1q and Fcγreceptors, IgG4 is incapable of forming immune complexes and activating the complement pathway, exhibiting a non-inflammatory feature. IgG4 is produced similarly to IgE and is considered a modified reaction to IgE class-switching response under certain conditions. It could also counteract IgE-activated inflammation. However, the clinical significance of IgG4 in allergic diseases is complex and controversial. Three viewpoints have been suggested to describe the role of IgG4. IgG4 can act as a tolerance-inducer to play a protective role under repeated and rapid incremental dosing of allergen exposure in allergen immunotherapy (AIT), supported by allergies in cat raisers and venom desensitization in beekeepers. Another viewpoint accepted by mainstream specialists and guidelines of Food Allergy and Management in different countries points out that food-specific IgG4 is a bystander in food allergy and should not be used as a diagnostic tool in clinical work. However, eosinophilic esophagitis (EoE) investigation revealed a direct clinical relevance between physiopathology and serum IgG4 in cow milk and wheat. These factors indicate that allergen-specific IgG4 plays a multifaceted role in allergic diseases that is protective or pathogenic depending on different allergens or exposure conditions.

Immunomodulatory potential of in vivo natural killer T (NKT) activation by NKTT320 in Mauritian-origin cynomolgus macaques

Invariant natural killer T-lymphocytes (iNKT) are unique immunomodulatory innate T cells with an invariant TCRα recognizing glycolipids presented on MHC class-I-like CD1d molecules. Activated iNKT rapidly secrete pro-and anti-inflammatory cytokines, potentiate immunity, and modulate inflammation. Here, we report the effects of in vivo iNKT activation in Mauritian-origin cynomolgus macaques by a humanized monoclonal antibody, NKTT320, that binds to the invariant region of the iNKT TCR. NKTT320 led to rapid iNKT activation, increased polyfunctionality, and elevation of multiple plasma analytes within 24 hours. Flow cytometry and RNA-Seq confirmed downstream activation of multiple immune subsets, enrichment of JAK/STAT and PI3K/AKT pathway genes, and upregulation of inflammation-modulating genes. NKTT320 also increased iNKT frequency in adipose tissue and did not cause iNKT anergy. Our data indicate that NKTT320 has a sustained effect on in vivo iNKT activation, potentiation of innate and adaptive immunity, and resolution of inflammation, which supports its future use as an immunotherapeutic.

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NKTT320 rapidly activates iNKT in vivo, modulating downstream immune function

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In vivo NKTT320 treatment modulates pro- and anti-inflammatory genes

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NKTT320 treatment results in activation of innate and adaptive immune subsets

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NKTT320 has promise as an immunotherapeutic with translational potential

Engineered Fc-glycosylation switch to eliminate antibody effector function

Antibodies mediate effector functions through Fcγ receptor (FcγR) interactions and complement activation, causing cytokine release, degranulation, phagocytosis, and cell death. They are often undesired for development of therapeutic antibodies where only antigen binding or neutralization would be ideal. Effector elimination has been successful with extensive mutagenesis, but these approaches can potentially lead to manufacturability and immunogenicity issues. By switching the native glycosylation site from position 297 to 298, we created alternative antibody glycosylation variants in the receptor interaction interface as a novel strategy to eliminate the effector functions. The engineered glycosylation site at Asn298 was confirmed by SDS-PAGE, mass spectrometry, and X-ray crystallography (PDB code 6X3I). The lead NNAS mutant (S298N/T299A/Y300S) shows no detectable binding to mouse or human FcγRs by surface plasmon resonance analyses. The effector functions of the mutant are completely eliminated when measured in antibody-dependent cell-meditated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays. In vivo, the NNAS mutant made on an antibody against a human lymphocyte antigen does not deplete T cells or B cells in transgenic mice, in contrast to wild-type antibody. Structural study confirms the successful glycosylation switch to the engineered Asn298 site. The engineered glycosylation would clash with approaching FcγRs based on reported Fc-FcγR co-crystal structures. In addition, the NNAS mutants of multiple antibodies retain binding to antigens and neonatal Fc receptor, exhibit comparable purification yields and thermal stability, and display normal circulation half-life in mice and non-human primate. Our work provides a novel approach for generating therapeutic antibodies devoid of any ADCC and CDC activities with potentially lower immunogenicity.

Fc-Engineering for Modulated Effector Functions-Improving Antibodies for Cancer Treatment

The majority of monoclonal antibody (mAb) therapeutics possess the ability to engage innate immune effectors through interactions mediated by their fragment crystallizable (Fc) domain. By delivering Fc-Fc gamma receptor (FcγR) and Fc-C1q interactions, mAb are able to link exquisite specificity to powerful cellular and complement-mediated effector functions. Fc interactions can also facilitate enhanced target clustering to evoke potent receptor signaling. These observations have driven decades-long research to delineate the properties within the Fc that elicit these various activities, identifying key amino acid residues and elucidating the important role of glycosylation. They have also fostered a growing interest in Fc-engineering whereby this knowledge is exploited to modulate Fc effector function to suit specific mechanisms of action and therapeutic purposes. In this review, we document the insight that has been generated through the study of the Fc domain; revealing the underpinning structure-function relationships and how the Fc has been engineered to produce an increasing number of antibodies that are appearing in the clinic with augmented abilities to treat cancer.

Antibody-based strategies in HIV therapy

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Antibody therapies offer a unique mechanism of action, decreased resistance and improved safety.

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Ibalizumab is a CD4 post-attachment inhibitor and leronlimab is a CCR5 inhibitor.

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Ibalizumab is approved for multi-drug-resistant human immunodeficiency virus (MDR HIV) treatment in combination with antiretroviral therapy.

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Leronlimab is being studied for treatment of MDR HIV and as maintenance monotherapy.

Antibody-based strategies have been introduced for a number of disease states, but represent a novel approach in the management of human immunodeficiency virus (HIV). Ibalizumab and leronlimab are monoclonal antibodies with unique mechanisms as a CD4-directed post-attachment inhibitor and a C-C chemokine receptor type 5-directed inhibitor, respectively. These antibody-based strategies are generally well tolerated, have a favourable pharmacokinetic profile allowing for less-frequent dosing, and have a high barrier to resistance. Ibalizumab is currently approved by the US Food and Drug Administration (US FDA) for management of multi-drug-resistant (MDR) HIV infection in patients who are failing their current regimens. Clinical data demonstrated impressive antiretroviral activity with ibalizumab among a complex HIV population in combination with an optimized background regimen, where limited therapeutic options exist. To date, leronlimab has not been granted approval by the US FDA, but has been designated fast-track status. Leronlimab is being studied as a maintenance monotherapy agent in virologically suppressed patients, as well as for treatment of MDR HIV infection in patients who are failing their current regimens. Currently available data in both of these potential areas appear promising for leronlimab. The mechanism of action, pharmacokinetic profile, efficacy and safety of these novel antibody-based strategies represent an advance in the management of HIV. Future studies and post-marketing experience will further determine longer-term clinical efficacy, safety and resistance data for ibalizumab and leronlimab.

R409K mutation prevents acid-induced aggregation of human IgG4

Human immunoglobulin G isotype 4 (IgG4) antibodies are suitable for use in either the antagonist or agonist format because their low effector functions prevent target cytotoxicity or unwanted cytokine secretion. However, while manufacturing therapeutic antibodies, they are exposed to low pH during purification, and IgG4 is more susceptible to low-pH-induced aggregation than IgG1. Therefore, we investigated the underlying mechanisms of IgG4 aggregation at low pH and engineered an IgG4 with enhanced stability. By swapping the constant regions of IgG1 and IgG4, we determined that the constant heavy chain (CH3) domain is critical for aggregate formation, but a core-hinge-stabilizing S228P mutation in IgG4 is insufficient for preventing aggregation. To identify the aggregation-prone amino acid, we substituted the CH3 domain of IgG4 with that of IgG1, changing IgG4 Arg409 to a Lys, thereby preventing the aggregation of the IgG4 variant as effectively as in IgG1. A stabilizing effect was also recorded with other variable-region variants. Analysis of thermal stability using differential scanning calorimetry revealed that the R409K substitution increased the Tm value of CH3, suggesting that the R409K mutation contributed to the structural strengthening of the CH3-CH3 interaction. The R409K mutation did not influence the binding to antigens/human Fcγ receptors; whereas, the concurrent S228P and R409K mutations in IgG4 suppressed Fab-arm exchange drastically and as effectively as in IgG1, in both in vitro and in vivo in mice models. Our findings suggest that the IgG4 R409K variant represents a potential therapeutic IgG for use in low-effector-activity format that exhibits increased stability.

Conceptual Approaches to Modulating Antibody Effector Functions and Circulation Half-Life

Antibodies and Fc-fusion antibody-like proteins have become successful biologics developed for cancer treatment, passive immunity against infection, addiction, and autoimmune diseases. In general these biopharmaceuticals can be used for blocking protein:protein interactions, crosslinking host receptors to induce signaling, recruiting effector cells to targets, and fixing complement. With the vast capability of antibodies to affect infectious and genetic diseases much effort has been placed on improving and tailoring antibodies for specific functions. While antibody:antigen engagement is critical for an efficacious antibody biologic, equally as important are the hinge and constant domains of the heavy chain. It is the hinge and constant domains of the antibody that engage host receptors or complement protein to mediate a myriad of effector functions and regulate antibody circulation. Molecular and structural studies have provided insight into how the hinge and constant domains from antibodies across different species, isotypes, subclasses, and alleles are recognized by host cell receptors and complement protein C1q. The molecular details of these interactions have led to manipulation of the sequences and glycosylation of hinge and constant domains to enhance or reduce antibody effector functions and circulating half-life. This review will describe the concepts being applied to optimize the hinge and crystallizable fragment of antibodies, and it will detail how these interactions can be tuned up or down to mediate a biological function that confers a desired disease outcome.

Ibalizumab, a Novel Monoclonal Antibody for the Management of Multidrug-Resistant HIV-1 Infection

Limited antiretrovirals are currently available for the management of multidrug-resistant (MDR) HIV-1 infection. Ibalizumab, a recombinant humanized monoclonal antibody, represents the first novel agent for HIV-1 management in over a decade and is the first monoclonal antibody for the treatment of MDR HIV-1 infection in combination with other forms of antiretroviral therapy in heavily treatment-experienced adults who are failing their current antiretroviral regimen. Ibalizumab demonstrates a novel mechanism of action as a CD4-directed postattachment inhibitor and has a favorable pharmacokinetic profile that allows for a dosing interval of every 14 days after an initial loading dose. Clinical studies have demonstrated reasonably substantial antiretroviral activity with ibalizumab among a complex patient population with advanced HIV-1 infection who are receiving an optimized background regimen, where limited therapeutic options exist. Ibalizumab was well tolerated in clinical trials, and the most common adverse effects included diarrhea, nausea, dizziness, fatigue, pyrexia, and rash. Resistance to ibalizumab has also been observed via reduced expression or loss of the potential N-linked glycosylation sites in the V5 loop of the envelope glycoprotein 120. The mechanism of action, pharmacokinetic parameters, efficacy, and safety of ibalizumab present an advance in the management of MDR HIV-1 infection. Future studies and postmarketing experience will further determine longer-term clinical efficacy, safety, and resistance data for ibalizumab.

A new technology for increasing therapeutic protein levels in the brain over extended periods

Effective delivery of protein therapeutics into the brain remains challenging because of difficulties associated with crossing the blood-brain barrier (BBB). To overcome this problem, many researchers have focused on antibodies binding the transferrin receptor (TfR), which is expressed in endothelial cells, including those of the BBB, and is involved in receptor-mediated transcytosis (RMT). RMT and anti-TfR antibodies provide a useful means of delivering therapeutics into the brain, but the anti-TfR antibody has a short half-life in blood because of its broad expression throughout the body. As a result, anti-TfR antibodies are only maintained at high concentrations in the brain for a short time. To overcome this problem, we developed a different approach which slows down the export of therapeutic antibodies from the brain by binding them to a brain-specific antigen. Here we report a new technology, named AccumuBrain, that achieves both high antibody concentration in the brain and a long half-life in blood by binding to myelin oligodendrocyte glycoprotein (MOG), which is specifically expressed in oligodendrocytes. We report that, using our technology, anti-MOG antibody levels in the brains of mice (Mus musculus) and rats (Rattus norvegicus) were increased several tens of times for a period of one month. The mechanism of this technology is different from that of RMT technologies like TfR and would constitute a breakthrough for central nervous system disease therapeutics.

Ibalizumab

PURPOSE OF REVIEW

Antiretroviral options for patients infected with multiclass resistant HIV-1 warrant the development of new agents with unique mechanisms of action and modes of delivery. Here we review one such agent, ibalizumab, a parenteral CD4 postattachment inhibitor that has demonstrated efficacy as part of combination antiretroviral therapy in the treatment of HIV-1.

RECENT FINDINGS

In a phase III clinical trial in HIV-infected participants with multiclass antiretroviral drug resistance, the intravenous administration of ibalizumab led to declines in plasma HIV-1 RNA more than 0.5 log in 83% of participants at 1 week. An optimized background antiretroviral regimen was then added, and plasma HIV-1 RNA became less than 50 copies/ml in 43% of participants at 24 weeks. Adverse effects of ibalizumab were uncommon and generally low grade. Ibalizumab was approved by the US Food and Drug Administration on March 16, 2018, under the trade name Trogarzo.

SUMMARY

Ibalizumab has demonstrated both safety and efficacy in the treatment of HIV-1 infection. Its primary use will be in the setting of multidrug resistant virus as part of combination antiretroviral therapy. Further enhancements of ibalizumab to prolong its clearance and broaden its activity are in development.

Glycation, oxidation and glycoxidation of IgG: a biophysical, biochemical, immunological and hematological study

Glycation and oxidation induce structural alterations in the proteins in an interdependent manner with consequent pathological implications. The published literature presents wide range of modifications in conformational characteristics of proteins by glycation and oxidation; however, there is little data that could elaborate the cumulative effect of both the processes. This study has analysed the modifications in IgG by methylglyoxal (MG) (glycative stress), hydroxyl radical ([Formula: see text]) (oxidative stress) and by their combined action i.e. [Formula: see text] treatment of MG glycated IgG (glycoxidation). It further addresses the implications of the altered structural integrity of IgG on its immunological characteristics and impact on haematological parameters in rabbits. Using circular dichroism, FTIR, SDS-PAGE analysis, thioflavin-T fluorescence assay, congo red absorbance analysis, dynamic light scattering, transmission electron microscopy, ELISA, blood cell counts and rectal temperature studies, we report that the glycoxidative modification caused maximum alteration in the IgG as compared to the glycatively and oxidatively modified protein. Far-UV CD results confirmed the highest decline in the beta-pleated sheet content of the protein by glycoxidation. The damage led to the reduced flexibility and enhanced electronic interactions in IgG as observed by near-UV CD. Modifications caused cross-linking and adduct formation in the serum protein. The electron micrograph confirmed amorphous aggregation in modified IgG. The modifications increased the hydrodynamic radius of IgG by allowing the attachment of [Formula: see text] and MG residues. The glycoxidatively modified IgG induced the maximum antibody titres that showed high specificity towards the altered IgG. The glycoxidation of IgG leads to activation of inflammatory pathways.

Combined OX40L and mTOR blockade controls effector T cell activation while preserving Treg reconstitution after transplant

A critical question facing the field of transplantation is how to control effector T cell (T_eff) activation while preserving regulatory T cell (T_reg) function. Standard calcineurin inhibitor-based strategies can partially control T_effs, but breakthrough activation still occurs, and these agents are antagonistic to T_reg function. Conversely, mechanistic target of rapamycin (mTOR) inhibition with sirolimus is more T_reg-compatible but is inadequate to fully control T_eff activation. In contrast, blockade of OX40L signaling has the capacity to partially control T_eff activation despite maintaining T_reg function. We used the nonhuman primate graft-versus-host disease (GVHD) model to probe the efficacy of combinatorial immunomodulation with sirolimus and the OX40L-blocking antibody KY1005. Our results demonstrate significant biologic activity of KY1005 alone (prolonging median GVHD-free survival from 8 to 19.5 days), as well as marked, synergistic control of GVHD with KY1005 + sirolimus (median survival time, >100 days; P < 0.01 compared to all other regimens), which was associated with potent control of both T_H/T_C1 (T helper cell 1/cytotoxic T cell 1) and T_H/T_C17 activation. Combined administration also maintained T_reg reconstitution [resulting in an enhanced T_reg/T_eff ratio (40% over baseline) in the KY1005/sirolimus cohort compared to a 2.9-fold decrease in the unprophylaxed GVHD cohort]. This unique immunologic signature resulted in transplant recipients that were able to control GVHD for the length of analysis and to down-regulate donor/recipient alloreactivity despite maintaining anti-third-party responses. These data indicate that combined OX40L blockade and sirolimus represents a promising strategy to induce immune balance after transplant and is an important candidate regimen for clinical translation.

Asymmetric Fc Engineering for Bispecific Antibodies with Reduced Effector Function

Asymmetric bispecific antibodies are a rapidly expanding therapeutic antibody class, designed to recognize two different target epitopes concurrently to achieve novel functions not available with normal antibodies. Many therapeutic designs require antibodies with reduced or silenced effector function. Although many solutions have been described in the literature to knockout effector function, to date all of them have involved the use of a specific antibody subtype (e.g., IgG2 or IgG4), or symmetric mutations in the lower hinge or CH2 domain of traditional homodimeric monospecific antibodies. In the context of a heterodimeric Fc, we describe novel asymmetric Fc mutations with reduced or silenced effector function in this article. These heteromultimeric designs contain asymmetric charged mutations in the lower hinge and the CH2 domain of the Fc. Surface plasmon resonance showed that the designed mutations display much reduced binding to all of the Fc gamma receptors and C1q. Ex vivo ADCC and CDC assays showed a consistent reduction in activity. Differential scanning calorimetry showed increased thermal stability for some of the designs. Finally, the asymmetric nature of the introduced charged mutations allowed for separation of homodimeric impurities by ion exchange chromatography, providing, as an added benefit, a purification strategy for the production of bispecific antibodies with reduced or silenced effector function.

Novel human IgG1 and IgG4 Fc-engineered antibodies with completely abolished immune effector functions

Recombinant human IgG antibodies (hIgGs) completely devoid of binding to Fcγ receptors (FcγRs) and complement protein C1q, and thus with abolished immune effector functions, are of use for various therapeutic applications in order to reduce FcγR activation and Fc-mediated toxicity. Fc engineering approaches described to date only partially achieve this goal or employ a large number of mutations, which may increase the risk of anti-drug antibody generation. We describe here two new, engineered hIgG Fc domains, hIgG1-P329G LALA and hIgG4-P329G SPLE, with completely abolished FcγR and C1q interactions, containing a limited number of mutations and with unaffected FcRn interactions and Fc stability. Both 'effector-silent' Fc variants are based on a novel Fc mutation, P329G that disrupts the formation of a proline sandwich motif with the FcγRs. As this motif is present in the interface of all IgG Fc/FcγR complexes, its disruption can be applied to all human and most of the other mammalian IgG subclasses in order to create effector silent IgG molecules.

Targeting CLEC9A delivers antigen to human CD141+ DC for CD4+ and CD8+T cell recognition

DC-based vaccines that initiate T cell responses are well tolerated and have demonstrated efficacy for tumor immunotherapy, with the potential to be combined with other therapies. Targeting vaccine antigens (Ag) directly to the DCs in vivo is more effective than cell-based therapies in mouse models and is therefore a promising strategy to translate to humans. The human CD141⁺ DCs are considered the most clinically relevant for initiating CD8⁺ T cell responses critical for killing tumors or infected cells, and they specifically express the C-type lectin-like receptor CLEC9A that facilitates presentation of Ag by these DCs. We have therefore developed a human chimeric Ab that specifically targets CLEC9A on CD141⁺ DCs in vitro and in vivo. These human chimeric Abs are highly effective at delivering Ag to DCs for recognition by both CD4⁺ and CD8⁺ T cells. Given the importance of these cellular responses for antitumor or antiviral immunity, and the superior specificity of anti-CLEC9A Abs for this DC subset, this approach warrants further development for vaccines.

IgG4 Characteristics and Functions in Cancer Immunity

IgG4 is the least abundant subclass of IgG in normal human serum, but elevated IgG4 levels are triggered in response to a chronic antigenic stimulus and inflammation. Since the immune system is exposed to tumor-associated antigens over a relatively long period of time, and tumors notoriously promote inflammation, it is unsurprising that IgG4 has been implicated in certain tumor types. Despite differing from other IgG subclasses by only a few amino acids, IgG4 possesses unique structural characteristics that may be responsible for its poor effector function potency and immunomodulatory properties. We describe the unique attributes of IgG4 that may be responsible for these regulatory functions, particularly in the cancer context. We discuss the inflammatory conditions in tumors that support IgG4, the emerging and proposed mechanisms by which IgG4 may contribute to tumor-associated escape from immune surveillance and implications for cancer immunotherapy.

Ageing Is Associated with Decreases in Appetite and Energy Intake--A Meta-Analysis in Healthy Adults

It is not well recognized that in the elderly weight loss is more common than weight gain. The aim of this analysis was to determine the effect of ageing on appetite (hunger/fullness) and energy intake, after overnight fasting and in a postprandial state, by meta-analyses of trials that included at least two age groups (>18 years). We hypothesized that appetite and energy intake would be less in healthy older compared with younger adults. Following a PubMed-database systematic search up to 30 June 2015, 59 studies were included in the random-effects-model meta-analyses. Energy intake was 16%-20% lower in older (n = 3574/~70 years/~71 kg/~25 kg/m²) than younger (n = 4111/~26 years/~69 kg/~23 kg/m²) adults (standardized mean difference: -0.77 (95% confidence interval -0.90 to -0.64)). Hunger was 25% (after overnight fasting; weighted mean difference (WMD): -17 (-22 to -13) mm) to 39% (in a postprandial state; WMD: -14 (-19 to -9) mm) lower, and fullness 37% (after overnight fasting; WMD: 6 mm (95% CI: 1 to 11 mm)) greater in older than younger adults. In conclusion, appetite and energy intake are less in healthy older than younger adults, suggesting that ageing per se affects food intake.

Monoclonal antibody-based therapies in cancer: advances and challenges

Conventional anticancer therapeutics often suffer from lack of specificity, resulting in toxicities to normal healthy tissues and poor therapeutic index. Antibody-mediated delivery of anticancer drugs or toxins to tumor cells through tumor selective or overexpressed antigens is progressively being recognized as an effective strategy for increasing the therapeutic index of anticancer drugs. In this review we focus on three therapeutic modalities in the field of antibody-mediated targeting, including antibody-drug conjugates (ADCs), immunotoxins (ITs) and immunoliposomes (ILs). Design considerations for development of each of the above therapeutic modalities are discussed. Furthermore, an overview of ADCs, ITs or ILs approved for use in clinical oncology and those currently in clinical development is provided. Challenges encountered by the field of antibody-based targeting are discussed and concepts around development of the next generation of antibody therapeutics are presented.

Development and validation of an antibody-dependent cell-mediated cytotoxicity-reporter gene assay

Humanized monoclonal antibodies (mAbs) are the fastest growing class of biological therapeutics that are being developed for various medical indications, and more than 30 mAbs are already approved and in the market place. Antibody-dependent cell-mediated cytotoxicity (ADCC) is an important biological function attributed to the mechanism of action of several therapeutic antibodies, particularly oncology targeting mAbs. The ADCC assay is a complicated and highly variable assay. Thus, the use of an ADCC assay as a lot release test or a stability test for clinical trial batches of mAbs has been a substantial challenge to install in quality control laboratories. We describe here the development and validation of an alternate approach, an ADCC-reporter gene assay that is based on the key attributes of the PBMC-based ADCC assay. We tested the biological relevance of this assay using an anti-CD20 based model and demonstrated that this ADCC-reporter assay correlated well with standard ADCC assays when induced with the drugable human isotypes [IgG1, IgG2, IgG4, IgG4S > P (S228P) and IgG4PAA (S228P, F234A, L235A)] and with IgG1 isotype variants with varying amounts of fucosylation. This data demonstrates that the ADCC-reporter gene assay has performance characteristics (accuracy, precision and robustness) to be used not only as a potency assay for lot release and stability testing for antibody therapeutics, but also as a key assay for the characterization and process development of therapeutic molecules.

What is IgG4? A review of the biology of a unique immunoglobulin subtype

PURPOSE OF REVIEW

Recent descriptions of the group of clinical disorders collectively defined as IgG4-related systemic disease (IgG4-RSD) have prompted this review of the unique biology of the IgG4 antibody. This article will discuss IgG4 structure and function, the unique phenomenon of half-antibody exchange, and the implications of IgG4 biology for its proposed role in immunologic diseases.

RECENT FINDINGS

IgG4 antibodies have unique structural and functional properties and undergo 'half-antibody exchange' in vivo, resulting in recombined antibodies composed of two different binding specificities. The production of IgG4 antibodies appears to be driven in part by T helper 2 (Th2) cytokines that mediate allergic responses and IgE production. Although serum IgG4 levels in healthy individuals vary significantly, data from multiple sclerosis (MS) patients suggest tight regulation of individual IgG4 levels over time. IgG4-RSD represents a diverse group of clinical disorders unified by elevated IgG4 levels and specific histopathologic findings. A key unanswered question is whether IgG4, a relatively weak activator of effector cells, is pathogenic in these disorders.

SUMMARY

IgG4 is a unique antibody biologically and structurally. Increased understanding of its precise role in the clinical syndromes that comprise IgG4-RSD may ultimately elucidate the underlying pathogenesis.

Combination of two insulin-like growth factor-I receptor inhibitory antibodies targeting distinct epitopes leads to an enhanced antitumor response

The insulin-like growth factor-I receptor (IGF-IR) is a cell surface receptor tyrosine kinase that mediates cell survival signaling and supports tumor progression in multiple tumor types. We identified a spectrum of inhibitory IGF-IR antibodies with diverse binding epitopes and ligand-blocking properties. By binding distinct inhibitory epitopes, two of these antibodies, BIIB4 and BIIB5, block both IGF-I and IGF-II binding to IGF-IR using competitive and allosteric mechanisms, respectively. Here, we explored the inhibitory effects of combining BIIB4 and BIIB5. In biochemical assays, the combination of BIIB4 and BIIB5 improved both the potency and extent of IGF-I and IGF-II blockade compared with either antibody alone. In tumor cells, the combination of BIIB4 and BIIB5 accelerated IGF-IR downregulation and more efficiently inhibited IGF-IR activation as well as downstream signaling, particularly AKT phosphorylation. In several carcinoma cell lines, the antibody combination more effectively inhibited ligand-driven cell growth than either BIIB4 or BIIB5 alone. Notably, the enhanced tumor growth-inhibitory activity of the BIIB4 and BIIB5 combination was much more pronounced at high ligand concentrations, where the individual antibodies exhibited substantially reduced activity. Compared with single antibodies, the BIIB4 and BIIB5 combination also significantly further enhanced the antitumor activity of the epidermal growth factor receptor inhibitor erlotinib and the mTOR inhibitor rapamycin. Moreover, in osteosarcoma and hepatocellular carcinoma xenograft models, the BIIB4 and BIIB5 combination significantly reduced tumor growth to a greater degree than each single antibody. Taken together, our results suggest that targeting multiple distinct inhibitory epitopes on IGF-IR may be a more effective strategy of affecting the IGF-IR pathway in cancer.

Monoclonal antibody-induced cytokine-release syndrome

Monoclonal antibodies (mAbs) are widely used in anti-inflammatory and tumor therapy. Although effective, mAbs can cause a variety of adverse effects. An important toxicity seen with a few mAbs is cytokine-release syndrome (CRS). These mAbs include: alemtuzumab, muromonab-CD3, rituximab, tosituzumab, CP-870,893, LO-CD2a/BTI-322 and TGN1412. By contrast, over 30 mAbs used clinically are not associated with CRS. In this review, the clinical aspects of CRS, the mAbs associated with CRS, the cytokines involved and putative mechanisms mediating cytokine release will be discussed. This will be followed by a discussion of the poor predictive value of studies in animals and the prospects for creating in vitro screens. Finally, approaches to decreasing the probability of CRS, decreasing the severity or treating CRS, should it occur, will be described.

Therapeutic IgG4 antibodies engage in Fab-arm exchange with endogenous human IgG4 in vivo

Two humanized IgG4 antibodies, natalizumab and gemtuzumab, are approved for human use, and several others, like TGN1412, are or have been in clinical development. Although IgG4 antibodies can dynamically exchange half-molecules, Fab-arm exchange with therapeutic antibodies has not been demonstrated in humans. Here, we show that natalizumab exchanges Fab arms with endogenous human IgG4 in natalizumab-treated individuals. Gemtuzumab, in contrast, contains an IgG4 core-hinge mutation that blocks Fab-arm exchange to undetectable levels both in vitro and in a mouse model. The ability of IgG4 therapeutics to recombine with endogenous IgG4 may affect their pharmacokinetics and pharmacodynamics. Although pharmacokinetic modeling lessens concerns about undesired cross-linking under normal conditions, unpredictability remains and mutations that completely prevent Fab-arm exchange in vivo should be considered when designing therapeutic IgG4 antibodies.

T cell targeted immunotherapy for autoimmune disease

Much emphasis has been placed on the so-called "biologics" in the treatment of immune disorders within the last few years. Here we discuss the expanding horizon of potential strategies for immunotherapies targeting T lymphocytes as key effectors and regulators of autoimmunity. We review emerging reagents in a variety of animal models and human disorders that may offer new therapeutic options in current or modified iterations.

Human immunodeficiency virus type 1 escape from cyclotriazadisulfonamide-induced CD4-targeted entry inhibition is associated with increased neutralizing antibody susceptibility

Continuous specific downmodulation of CD4 receptor expression in T lymphocytes by the small molecule cyclotriazadisulfonamide (CADA) selected for the CADA-resistant human immunodeficiency virus type 1 (HIV-1) NL4.3 virus containing unique mutations in the C4 and V5 regions of gp120, likely stabilizing the CD4-binding conformation. The amino acid changes in Env were associated with decreased susceptibility to anti-CD4 monoclonal antibody treatment of the cells and with higher susceptibility of the virus to soluble CD4. In addition, the acquired ability of a CADA-resistant virus to infect cells with low CD4 expression was associated with an increased susceptibility of the virus to neutralizing antibodies from sera of several HIV-1-infected patients.

Safety, pharmacokinetics, and antiretroviral activity of multiple doses of ibalizumab (formerly TNX-355), an anti-CD4 monoclonal antibody, in human immunodeficiency virus type 1-infected adults

Ibalizumab (formerly TNX-355) is a humanized monoclonal antibody that binds CD4, the primary receptor for human immunodeficiency virus type 1 (HIV-1), and inhibits the viral entry process. A phase lb multidose study of the safety, pharmacokinetics, and antiviral activity of ibalizumab was conducted with 22 HIV-1-infected patients. Nineteen patients were randomized to receive either 10 mg/kg of body weight weekly (arm A) or a 10-mg/kg loading dose followed by 6 mg/kg every 2 weeks (arm B) intravenously for 9 weeks. Three patients were assigned to receive 25 mg/kg every 2 weeks for five doses (arm C). During the study, the patients remained off other antiretrovirals or continued a stable failing regimen. Treatment with ibalizumab resulted in substantial reductions in HIV-1 RNA levels (0.5 to 1.7 log(10)) in 20 of 22 subjects. In most patients, HIV-1 RNA fell to nadir levels after 1 to 2 weeks of treatment and then returned to baseline despite continued treatment. Baseline viral isolates were susceptible to ibalizumab in vitro, regardless of coreceptor tropism. Emerging resistance to ibalizumab was manifested by reduced maximal percent inhibition in a single-cycle HIV infectivity assay. Resistant isolates remained CD4 dependent and were susceptible to enfuvirtide in vitro. Complete coating of CD4(+) T-cell receptors was correlated with serum ibalizumab concentrations. There was no evidence of CD4(+) T-cell depletion in ibalizumab-treated patients. Ibalizumab was not immunogenic, and no serious drug-related adverse effects occurred. In conclusion, ibalizumab administered either weekly or biweekly was safe and well tolerated and demonstrated antiviral activity. Further studies with ibalizumab in combination with standard antiretroviral treatments are warranted.

When binding is enough: nonactivating antibody formats

Most therapeutic antibodies currently used in the clinic are based on the human IgG1 format, which is a bivalent molecule that efficiently interacts with the immune system's effector functions. In clinical applications where binding to the target alone is sufficient for therapeutic efficacy; however, engagement of the immune system is not required and may even cause unwanted side-effects. Likewise, bivalent binding to the target may negatively influence the therapeutic efficacy of an antibody. Here we discuss the state of the art for antibody-based therapeutics, designed to be nonactivating (i.e. do not engage the innate immune system's effector functions), in both monovalent and bivalent formats.

The poor contribution of chimpanzee experiments to biomedical progress

Biomedical research on captive chimpanzees incurs substantial nonhuman animal welfare, ethical, and financial costs that advocates claim resultin substantial advancements in biomedical knowledge. However, demonstrating minimal contribution toward the advancement of biomedical knowledge generally, subsequent papers did not cite 49.5% (47/95), of 95 experiments randomly selected from a population of 749 published worldwide between 1995 and 2004. Only 14.7% (14/95) were cited by 27 papers that abstracts indicated described well-developed methods for combating human diseases. However, detailed examination of these medical papers revealed that in vitrostudies, human clinical and epidemiological studies, molecular assays and methods, and genomic studies contributed most to their development. No chimpanzee study made an essential contribution, or, in most cases, a significant contribution of any kind, to the development of the medical method described. The approval of these experiments indicates a failure of the ethics committee system. The demonstrable lack of benefit of most chimpanzee experimentation and its profound animal welfare and bioethical costs indicate that a ban is warranted in those remaining countries - notably the United States - that continue to conduct it.

New reagents on the horizon for immune tolerance

Recent advances in immunology and a growing arsenal of new drugs are bringing the focus of tolerance research from animal models into the clinical setting. The conceptual framework for therapeutic tolerance induction has shifted from a "sledgehammer" approach that relies solely on cellular depletion and cytokine targeting, to a strategy directed toward restoring a functional balance across the immune system, namely the different populations of naive cells, effector and memory cells, and regulatory cells. Unlocking the key to tolerance induction in the future will likely depend on our ability to harness the functions of T regulatory cells. Also, dendritic cells are strategically positioned at the interface between innate and adaptive immunity and may be subject to deliberate medical intervention in a way that can control a chronic inflammatory response. Many reagents with tolerance-inducing potential are currently undergoing clinical testing in transplantation, autoimmune diseases, and allergic diseases, and even more that are on the horizon promise to offer enormous benefits to human health.

Engineering of therapeutic antibodies to minimize immunogenicity and optimize function

One of the first difficulties in developing monoclonal antibody therapeutics was the recognition that human anti-mouse antibody (HAMA) response limited the administration of murine antibodies. Creative science has lead to a number of ways to counter the immunogenicity of non-human antibodies, primarily through chimeric, humanized, de-immunized, and most recently, human-sequence therapeutic antibodies. Once therapeutic antibodies of low or no immunogenicity were available, the creativity then turned to engineering both the antigen-binding domains (e.g., affinity maturation, stability) and altering the effector functions (e.g. antibody-dependent cellular cytotoxicity, complement-dependent cellular cytotoxicity, and clearance rate).

Clinical trials of transplant tolerance: slow but steady progress

The search for tolerance therapies that would thwart the alloimmune response following organ transplantation while preserving a patient's protective immune response has been a formidable goal for clinical immunologists. Over the past few decades, a more detailed understanding of the molecular events associated with T-cell recognition and activation has demonstrated the feasibility of various tolerance approaches, such as costimulation blockade, in numerous animal models of both autoimmunity and transplantation. Yet, only a few promising new therapies have reached the early stages of human clinical development. In contrast, the use of T-cell depleting induction therapy has become widespread, and new trials have been designed with immunosuppressive drug withdrawal in mind. Furthermore, nonmyeloablative mixed chimeric approaches have allowed complete immunosuppressive withdrawal in some limited cases. In the course of these investigations, however, what has become increasingly clear is that the distinctions between immunosuppression and tolerance have been blurred as the success and durability of the therapies rely as much on the state of the organ and organism as they do the mechanism of action of the drug. In this review, we provide a summary of the progress and lessons in promoting clinical transplant tolerance and an overview of promising agents.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.

CD4 mAb induced apoptosis of peripheral T cells: multiparameter subpopulation analysis by flow cytometry using Attractors

Studies describing the induction of apoptosis for CD4 mAbs do not delineate between epitope-dependent and Fc-driven epitope cross-linking induced cell death. Keliximab and clenoliximab are two CD4 mAbs that differ only in their heavy chain isotypes, being an IgG1 and a modified IgG4, respectively. These antibodies suppress CD4 T cell responses in vitro and in vivo and have been in human clinical trials for the treatment of RA and asthma. Here we compared the apoptotic activity of these mAbs to differentiate between the contributions of epitope-dependent vs. Fc-driven epitope cross-linking induced cell death in vitro as a link to differential CD4 cell depletion in vivo. We developed a simple flow cytometry procedure that measures apoptosis within intact and compromised subpopulations of PBMCs within a few hours of culture. Attractors software was used to quantitate the percentage of apoptotic CD4 T cells, which generate reactive oxygen species (ROS), express external phosphatidyl serine (PS) and cleaved fluorescein diacetate (FDA), within the intact and compromised lymphocyte populations. Treatment of freshly isolated PBMCs with keliximab resulted in the appearance of characteristic apoptotic condensed CD4 T cells that contained reactive oxygen species, were annexin V positive and had intact esterase activity. Apoptosis was evident within 3 h and continued throughout the 72-h culture period. In contrast, clenoliximab alone did not induce apoptosis. The use of multiparameter flow cytometry and Attractors to analyze subpopulations based on scatter properties and biochemical processes during apoptosis provides a sensitive assay in which to quantitate and characterize the induction of cell death. Depletion of CD4 T cells in vivo by keliximab may reflect, in part, antibody-mediated apoptosis of these cells that is dependent on Fcgamma receptors.