Elimination of Fc receptor-dependent effector functions of a modified IgG4 monoclonal antibody to human CD4

Activating Inducible T-cell Costimulator Yields Antitumor Activity Alone and in Combination with Anti-PD-1 Checkpoint Blockade

In recent years, there has been considerable interest in mAb-based induction of costimulatory receptor signaling as an approach to combat cancer. However, promising nonclinical data have yet to translate to a meaningful clinical benefit. Inducible T-cell costimulator (ICOS) is a costimulatory receptor important for immune responses. Using a novel clinical-stage anti-ICOS immunoglobulin G4 mAb (feladilimab), which induces but does not deplete ICOS+ T cells and their rodent analogs, we provide an end-to-end evaluation of the antitumor potential of antibody-mediated ICOS costimulation alone and in combination with programmed cell death protein 1 (PD-1) blockade. We demonstrate, consistently, that ICOS is expressed in a range of cancers, and its induction can stimulate growth of antitumor reactive T cells. Furthermore, feladilimab, alone and with a PD-1 inhibitor, induced antitumor activity in mouse and humanized tumor models. In addition to nonclinical evaluation, we present three patient case studies from a first-time-in-human, phase I, open-label, dose-escalation and dose-expansion clinical trial (INDUCE-1; ClinicalTrials.gov: NCT02723955), evaluating feladilimab alone and in combination with pembrolizumab in patients with advanced solid tumors. Preliminary data showing clinical benefit in patients with cancer treated with feladilimab alone or in combination with pembrolizumab was reported previously; with example cases described here. Additional work is needed to further validate the translation to the clinic, which includes identifying select patient populations that will benefit from this therapeutic approach, and randomized data with survival endpoints to illustrate its potential, similar to that shown with CTLA-4 and PD-1 blocking antibodies.

Significance

Stimulation of the T-cell activation marker ICOS with the anti-ICOS agonist mAb feladilimab, alone and in combination with PD-1 inhibition, induces antitumor activity across nonclinical models as well as select patients with advanced solid tumors.

Nonclinical Characterization of Bexmarilimab, a Clever-1-Targeting Antibody for Supporting Immune Defense Against Cancers

Common lymphatic endothelial and vascular endothelial receptor-1 (Clever-1) is a multifunctional type-1 transmembrane protein that plays an important role in immunosuppression against tumors. Clever-1 is highly expressed in a subset of human tumor-associated macrophages and associated with poor survival. In mice, Clever-1 supports tumor growth and metastasis formation, and its deficiency or blockage induces T-cell-dependent killing of cancer cells. Therefore, targeting Clever-1 could lead to T-cell activation and restoration of immune response also in patients with cancer. This is studied in an on-going clinical trial [Macrophage Antibody To INhibit immune Suppression (MATINS); NCT03733990] in patients with advanced solid tumors where bexmarilimab, a humanized IgG4 antibody against human Clever-1, shows promising safety and efficacy. Here, we report the humanization and nonclinical characterization of physicochemical properties, biological potency, and safety profile of bexmarilimab. Bexmarilimab showed high affinity to Clever-1 on KG-1 cells and bound to Clever-1 on the surface of classical and intermediate monocytes derived from healthy human blood. Bexmarilimab inhibited the internalization of its natural ligand acetylated low-density lipoprotein into KG-1 cells and increased TNFα secretion from macrophages but did not impair phagocytic clearance. Bexmarilimab did not induce significant cytokine release in human whole-blood cultures, did not contain nonsafe immunogenic glycans, or show any significant binding to human Fcγ receptors or complement pathway component C1q. In vivo, bexmarilimab showed dose-dependent duration of monocyte Clever-1 receptor occupancy in cynomolgus monkeys but did not induce a cytokine storm up to a dose of 100 mg/kg. In conclusion, these data support the clinical development of bexmarilimab for the restoration of immune response in cancers.

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

Phase 1 study of anti-CD47 monoclonal antibody CC-90002 in patients with relapsed/refractory acute myeloid leukemia and high-risk myelodysplastic syndromes

CC-90002 is an anti-CD47 antibody that inhibits CD47-SIRPα interaction and enables macrophage-mediated killing of tumor cells in hematological cancer cell lines. In this first clinical, phase 1, dose-escalation and -expansion study (CC-90002-AML-001; NCT02641002), we evaluated CC-90002 in patients with relapsed/refractory acute myeloid leukemia (AML) or high-risk myelodysplastic syndromes (MDS). CC-90002 was administered in escalating doses of 0.1-4.0 mg/kg, using a modified 3 + 3 design. Primary endpoints included dose-limiting toxicities (DLTs), non-tolerated dose (NTD), maximum tolerated dose (MTD), and recommended phase 2 dose. Secondary endpoints included preliminary efficacy, pharmacokinetics, and presence/frequency of anti-drug antibodies (ADAs). Between March 2016 and July 2018, 28 patients were enrolled (24 with AML and 4 with MDS) at 6 sites across the USA. As of July 18, 2018, all patients had discontinued, mainly due to death or progressive disease. The most common treatment-emergent adverse events were diarrhea (46.4%), thrombocytopenia (39.3%), febrile neutropenia (35.7%), and aspartate aminotransferase increase (35.7%). Four patients experienced DLTs (1 patient had grade 4 disseminated intravascular coagulation and grade 5 cerebral hemorrhage, 1 had grade 3 purpura, 1 had grade 4 congestive cardiac failure and grade 5 acute respiratory failure, and another had grade 5 sepsis). The NTD and MTD were not reached. No objective responses occurred. CC-90002 serum exposure was dose-dependent. ADAs were present across all doses, and the proportion of ADA-positive patients in cycle 1 increased over time. Despite no unexpected safety findings, the CC-90002-AML-001 study was discontinued in dose escalation for lack of monotherapy activity and evidence of ADAs. However, as other anti-CD47 agents in clinical trials are showing promising early results for AML and MDS, understanding preclinical and clinical differences between individual agents in this class will be of high importance.

Anti-CD40 Antibody Fused to CD40 Ligand Is a Superagonist Platform for Adjuvant Intrinsic DC-Targeting Vaccines

CD40 is a potent activating receptor expressed on antigen-presenting cells (APCs) of the immune system. CD40 regulates many aspects of B and T cell immunity via interaction with CD40L expressed on activated T cells. Targeting antigens to CD40 via agonistic anti-CD40 antibody fusions promotes both humoral and cellular immunity, but current anti-CD40 antibody-antigen vaccine prototypes require co-adjuvant administration for significant in vivo efficacy. This may be a consequence of dulling of anti-CD40 agonist activity via antigen fusion. We previously demonstrated that direct fusion of CD40L to anti-CD40 antibodies confers superagonist properties. Here we show that anti-CD40-CD40L-antigen fusion constructs retain strong agonist activity, particularly for activation of dendritic cells (DCs). Therefore, we tested anti-CD40-CD40L antibody fused to antigens for eliciting immune responses in vitro and in vivo. In PBMC cultures from HIV-1-infected donors, anti-CD40-CD40L fused to HIV-1 antigens preferentially expanded HIV-1-specific CD8⁺ T cells versus CD4⁺ T cells compared to analogous anti-CD40-antigen constructs. In normal donors, anti-CD40-CD40L-mediated delivery of Influenza M1 protein elicited M1-specific T cell expansion at lower doses compared to anti-CD40-mediated delivery. Also, on human myeloid-derived dendritic cells, anti-CD40-CD40L-melanoma gp100 peptide induced more sustained Class I antigen presentation compared to anti-CD40-gp100 peptide. In human CD40 transgenic mice, anti-CD40-CD40L-HIV-1 gp140 administered without adjuvant elicited superior antibody responses compared to anti-CD40-gp140 antigen without fused CD40L. In human CD40 mice, compared to the anti-CD40 vehicle, anti-CD40-CD40L delivery of Eα 52-68 peptide elicited proliferating of TCR I-Eα 52-68 CD4⁺ T cells producing cytokine IFNγ. Also, compared to controls, only anti-CD40-CD40L-Cyclin D1 vaccination of human CD40 mice reduced implanted EO771.LMB breast tumor cell growth. These data demonstrate that human CD40-CD40L antibody fused to antigens maintains highly agonistic activity and generates immune responses distinct from existing low agonist anti-CD40 targeting formats. These advantages were in vitro skewing responses towards CD8⁺ T cells, increased efficacy at low doses, and longevity of MHC Class I peptide display; and in mouse models, a more robust humoral response, more activated CD4⁺ T cells, and control of tumor growth. Thus, the anti-CD40-CD40L format offers an alternate DC-targeting platform with unique properties, including intrinsic adjuvant activity.

Anti-CD40 Antibodies Fused to CD40 Ligand Have Superagonist Properties

CD40 is a potent activating receptor within the TNFR family expressed on APCs of the immune system, and it regulates many aspects of B and T cell immunity via interaction with CD40 ligand (CD40L; CD154) expressed on the surface of activated T cells. Soluble CD40L and agonistic mAbs directed to CD40 are being explored as adjuvants in therapeutic or vaccination settings. Some anti-CD40 Abs can synergize with soluble monomeric CD40L. We show that direct fusion of CD40L to certain agonistic anti-CD40 Abs confers superagonist properties, reducing the dose required for efficacy, notably greatly increasing total cytokine secretion by human dendritic cells. The tetravalent configuration of anti-CD40-CD40L Abs promotes CD40 cell surface clustering and internalization and is the likely mechanism of increased receptor activation. CD40L fused to either the L or H chain C termini, with or without flexible linkers, were all superagonists with greater potency than CD40L trimer. The increased anti-CD40-CD40L Ab potency was independent of higher order aggregation. Moreover, the anti-CD40-CD40L Ab showed higher potency in vivo in human CD40 transgenic mice compared with the parental anti-CD40 Ab. To broaden the concept of fusing agonistic Ab to natural ligand, we fused OX40L to an agonistic OX40 Ab, and this resulted in dramatically increased efficacy for proliferation and cytokine production of activated human CD4⁺ T cells as well as releasing the Ab from dependency on cross-linking. This work shows that directly fusing antireceptor Abs to ligand is a useful strategy to dramatically increase agonist potency.

Systemic Blockade of Clever-1 Elicits Lymphocyte Activation Alongside Checkpoint Molecule Downregulation in Patients with Solid Tumors: Results from a Phase I/II Clinical Trial

PURPOSE

Macrophages are critical in driving an immunosuppressive tumor microenvironment that counteracts the efficacy of T-cell-targeting therapies. Thus, agents able to reprogram macrophages toward a proinflammatory state hold promise as novel immunotherapies for solid cancers. Inhibition of the macrophage scavenger receptor Clever-1 has shown benefit in inducing CD8+ T-cell-mediated antitumor responses in mouse models of cancer, which supports the clinical development of Clever-1-targeting antibodies for cancer treatment.

PATIENTS AND METHODS

In this study, we analyzed the mode of action of a humanized IgG4 anti-Clever-1 antibody, FP-1305 (bexmarilimab), both in vitro and in patients with heavily pretreated metastatic cancer (n = 30) participating in part 1 (dose-finding) of a phase I/II open-label trial (NCT03733990). We studied the Clever-1 interactome in primary human macrophages in antibody pull-down assays and utilized mass cytometry, RNA sequencing, and cytokine profiling to evaluate FP-1305-induced systemic immune activation in patients with cancer.

RESULTS

Our pull-down assays and functional studies indicated that FP-1305 impaired multiprotein vacuolar ATPase-mediated endosomal acidification and improved the ability of macrophages to activate CD8+ T-cells. In patients with cancer, FP-1305 administration led to suppression of nuclear lipid signaling pathways and a proinflammatory phenotypic switch in blood monocytes. These effects were accompanied by a significant increase and activation of peripheral T-cells with indications of antitumor responses in some patients.

CONCLUSIONS

Our results reveal a nonredundant role played by the receptor Clever-1 in suppressing adaptive immune cells in humans. We provide evidence that targeting macrophage scavenging activity can promote an immune switch, potentially leading to intratumoral proinflammatory responses in patients with metastatic cancer.

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.

A bispecific antibody agonist of the IL-2 heterodimeric receptor preferentially promotes in vivo expansion of CD8 and NK cells

The use of recombinant interleukin-2 (IL-2) as a therapeutic protein has been limited by significant toxicities despite its demonstrated ability to induce durable tumor-regression in cancer patients. The adverse events and limited efficacy of IL-2 treatment are due to the preferential binding of IL-2 to cells that express the high-affinity, trimeric receptor, IL-2Rαβγ such as endothelial cells and T-regulatory cells, respectively. Here, we describe a novel bispecific heavy-chain only antibody which binds to and activates signaling through the heterodimeric IL-2Rβγ receptor complex that is expressed on resting T-cells and NK cells. By avoiding binding to IL-2Rα, this molecule circumvents the preferential T-reg activation of native IL-2, while maintaining the robust stimulatory effects on T-cells and NK-cells in vitro. In vivo studies in both mice and cynomolgus monkeys confirm the molecule's in vivo biological activity, extended pharmacodynamics due to the Fc portion of the molecule, and enhanced safety profile. Together, these results demonstrate that the bispecific antibody is a safe and effective IL-2R agonist that harnesses the benefits of the IL-2 signaling pathway as a potential anti-cancer therapy.

Small Molecule Cyclotriazadisulfonamide Abrogates the Upregulation of the Human Receptors CD4 and 4-1BB and Suppresses In Vitro Activation and Proliferation of T Lymphocytes

The small molecule cyclotriazadisulfonamide (CADA) down-modulates the human CD4 receptor, an important factor in T cell activation. Here, we addressed the immunosuppressive potential of CADA using different activation models. CADA inhibited lymphocyte proliferation with low cellular toxicity in a mixed lymphocyte reaction, and when human PBMCs were stimulated with CD3/CD28 beads, phytohemagglutinin or anti-CD3 antibodies. The immunosuppressive effect of CADA involved both CD4⁺ and CD8⁺ T cells but was, surprisingly, most prominent in the CD8⁺ T cell subpopulation where it inhibited cell-mediated lympholysis. Immunosuppression by CADA was characterized by suppressed secretion of various cytokines, and reduced CD25, phosphoSTAT5 and CTPS-1 levels. We discovered a direct down-modulatory effect of CADA on 4-1BB (CD137) expression, a survival factor for activated CD8⁺ T cells. More specifically, CADA blocked 4‑1BB protein biosynthesis by inhibition of its co-translational translocation into the ER in a signal peptide-dependent way. Taken together, this study demonstrates that CADA, as potent down-modulator of human CD4 and 4‑1BB receptor, has promising immunomodulatory characteristics. This would open up new avenues toward chemotherapeutics that act as selective protein down-modulators to treat various human immunological disorders.

Passive immunotherapies targeting Aβ and tau in Alzheimer's disease

Amyloid-β (Aβ) and tau proteins currently represent the two most promising targets to treat Alzheimer's disease. The most extensively developed method to treat the pathologic forms of these proteins is through the administration of exogenous antibodies, or passive immunotherapy. In this review, we discuss the molecular-level strategies that researchers are using to design an effective therapeutic antibody, given the challenges in treating this disease. These challenges include selectively targeting a protein that has misfolded or is pathological rather than the more abundant, healthy protein, designing strategic constructs for immunizing an animal to raise an antibody that has the appropriate conformational selectivity to achieve this end, and clearing the pathological protein species before prion-like cell-to-cell spread of misfolded protein has irreparably damaged neurons, without invoking damaging inflammatory responses in the brain that naturally arise when the innate immune system is clearing foreign agents. The various solutions to these problems in current clinical trials will be discussed.

Tetravalent Bispecific Tandem Antibodies Improve Brain Exposure and Efficacy in an Amyloid Transgenic Mouse Model

Most antibodies display very low brain exposure due to the blood-brain barrier (BBB) preventing their entry into brain parenchyma. Transferrin receptor (TfR) has been used previously to ferry antibodies to the brain by using different formats of bispecific constructs. Tetravalent bispecific tandem immunoglobulin Gs (IgGs) (TBTIs) containing two paratopes for both TfR and protofibrillar forms of amyloid-beta (Aβ) peptide were constructed and shown to display higher brain penetration than the parent anti-Aβ antibody. Additional structure-based mutations on the TfR paratopes further increased brain exposure, with maximal enhancement up to 13-fold in wild-type mice and an additional 4–5-fold in transgenic (Tg) mice harboring amyloid plaques, the main target of our amyloid antibody. Parenchymal target engagement of extracellular amyloid plaques was demonstrated using in vivo and ex vivo fluorescence imaging as well as histological methods. The best candidates were selected for a chronic study in an amyloid precursor protein (APP) Tg mouse model showing efficacy at reducing brain amyloid load at a lower dose than the corresponding monospecific antibody. TBTIs represent a promising format for enhancing IgG brain penetration using a symmetrical construct and keeping bivalency of the payload antibody.

Cancer Immunotherapeutic Potential of NKTT320, a Novel, Invariant, Natural Killer T Cell-Activating, Humanized Monoclonal Antibody

Invariant natural killer T cells (iNKTs) directly kill tumor cells and trans-activate the anti-tumor functions of dendritic cells (DC), natural killer (NK) cells, and T and B cells. As such, iNKTs serve as a powerful tool for use in cell-based cancer immunotherapy. iNKT cell activation commonly requires engagement of the invariant T cell receptor (iTCR) by CD1d presenting glycolipid antigens. However, transformed cells often down-regulate CD1d expression, which results in a reduction of iNKT cell anti-tumor functions. One approach to circumvent this critical barrier to iNKT cell activation is to develop an agonistic antibody that binds directly to the iTCR without the requirement for CD1d-mediated antigen presentation. To this end, we have characterized the iNKT cell stimulatory properties of NKTT320, a novel, recombinant, humanized, monoclonal antibody that binds selectively and with high affinity to human iTCRs. Strikingly, immobilized NKTT320 mediated robust iNKT cell activation (upregulation of CD25 and CD69) and proliferation (carboxyfluorescein succinimidyl ester (CFSE) dilution), as well as Th1 and Th2 cytokine production. Additionally, iNKTs stimulated by plate-bound NKTT320 exhibited increased intracellular levels of granzyme B and degranulation (exposure of CD107 on the cell surface). Furthermore, both soluble and immobilized NKTT320 induced iNKT cell-mediated activation of bystander immune cells, suggesting that this novel anti-iTCR antibody facilitates both direct and indirect iNKT cell cytotoxicity. These studies are significant, as they provide a framework by which iNKT cell anti-cancer functions could be enhanced for therapeutic purposes.

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.

Gene delivery of a modified antibody to Aβ reduces progression of murine Alzheimer's disease

Antibody therapies for Alzheimer’s Disease (AD) hold promise but have been limited by the inability of these proteins to migrate efficiently across the blood brain barrier (BBB). Central nervous system (CNS) gene transfer by vectors like adeno-associated virus (AAV) overcome this barrier by allowing the bodies’ own cells to produce the therapeutic protein, but previous studies using this method to target amyloid-β have shown success only with truncated single chain antibodies (Abs) lacking an Fc domain. The Fc region mediates effector function and enhances antigen clearance from the brain by neonatal Fc receptor (FcRn)-mediated reverse transcytosis and is therefore desirable to include for such treatments. Here, we show that single chain Abs fused to an Fc domain retaining FcRn binding, but lacking Fc gamma receptor (FcγR) binding, termed a silent scFv-IgG, can be expressed and released into the CNS following gene transfer with AAV. While expression of canonical IgG in the brain led to signs of neurotoxicity, this modified Ab was efficiently secreted from neuronal cells and retained target specificity. Steady state levels in the brain exceeded peak levels obtained by intravenous injection of IgG. AAV-mediated expression of this scFv-IgG reduced cortical and hippocampal plaque load in a transgenic mouse model of progressive β-amyloid plaque accumulation. These findings suggest that CNS gene delivery of a silent anti-Aβ scFv-IgG was well-tolerated, durably expressed and functional in a relevant disease model, demonstrating the potential of this modality for the treatment of Alzheimer’s disease.

Antibody Structure and Function: The Basis for Engineering Therapeutics

Antibodies and antibody-derived macromolecules have established themselves as the mainstay in protein-based therapeutic molecules (biologics). Our knowledge of the structure–function relationships of antibodies provides a platform for protein engineering that has been exploited to generate a wide range of biologics for a host of therapeutic indications. In this review, our basic understanding of the antibody structure is described along with how that knowledge has leveraged the engineering of antibody and antibody-related therapeutics having the appropriate antigen affinity, effector function, and biophysical properties. The platforms examined include the development of antibodies, antibody fragments, bispecific antibody, and antibody fusion products, whose efficacy and manufacturability can be improved via humanization, affinity modulation, and stability enhancement. We also review the design and selection of binding arms, and avidity modulation. Different strategies of preparing bispecific and multispecific molecules for an array of therapeutic applications are included.

Efficient tumor killing and minimal cytokine release with novel T-cell agonist bispecific antibodies

T-cell-recruiting bispecific antibodies (T-BsAbs) have shown potent tumor killing activity in humans, but cytokine release-related toxicities have affected their clinical utility. The use of novel anti-CD3 binding domains with more favorable properties could aid in the creation of T-BsAbs with improved therapeutic windows. Using a sequence-based discovery platform, we identified new anti-CD3 antibodies from humanized rats that bind to multiple epitopes and elicit varying levels of T-cell activation. In T-BsAb format, 12 different anti-CD3 arms induce equivalent levels of tumor cell lysis by primary T-cells, but potency varies by a thousand-fold. Our lead CD3-targeting arm stimulates very low levels of cytokine release, but drives robust tumor antigen-specific killing in vitro and in a mouse xenograft model. This new CD3-targeting antibody underpins a next-generation T-BsAb platform in which potent cytotoxicity is uncoupled from high levels of cytokine release, which may lead to a wider therapeutic window in the clinic.

SAR228810: an antibody for protofibrillar amyloid β peptide designed to reduce the risk of amyloid-related imaging abnormalities (ARIA)

BACKGROUND

Anti-amyloid β (Aβ) immunotherapy represents a major area of drug development for Alzheimer's disease (AD). However, Aβ peptide adopts multiple conformations and the pathological forms to be specifically targeted have not been identified. Aβ immunotherapy-related vasogenic edema has also been severely dose limiting for antibodies with effector functions binding vascular amyloid such as bapineuzumab. These two factors might have contributed to the limited efficacy demonstrated so far in clinical studies.

METHODS

To address these limitations, we have engineered SAR228810, a humanized monoclonal antibody (mAb) with limited Fc effector functions that binds specifically to soluble protofibrillar and fibrillar forms of Aβ peptide and we tested it together with its murine precursor SAR255952 in vitro and in vivo.

RESULTS

Unlike gantenerumab and BAN2401, SAR228810 and SAR255952 do not bind to Aβ monomers, low molecular weight Aβ oligomers or, in human brain sections, to Aβ diffuse deposits which are not specific of AD pathology. Both antibodies prevent Aβ42 oligomer neurotoxicity in primary neuronal cultures. In vivo, SAR255952, a mouse aglycosylated IgG1, dose-dependently prevented brain amyloid plaque formation and plaque-related inflammation with a minimal active dose of 3 mg/kg/week by the intraperitoneal route. No increase in plasma Aβ levels was observed with SAR255952 treatment, in line with its lack of affinity for monomeric Aβ. The effects of SAR255952 translated into synaptic functional improvement in ex-vivo hippocampal slices. Brain penetration and decoration of cerebral amyloid plaques was documented in live animals and postmortem. SAR255952 (up to 50 mg/kg/week intravenously) did not increase brain microhemorrhages and/or microscopic changes in meningeal and cerebral arteries in old APPSL mice while 3D6, the murine version of bapineuzumab, did. In immunotolerized mice, the clinical candidate SAR228810 demonstrated the same level of efficacy as the murine SAR255952.

CONCLUSION

Based on the improved efficacy/safety profile in non-clinical models of SAR228810, a first-in-man single and multiple dose administration clinical study has been initiated in AD patients.

Ibalizumab Targeting CD4 Receptors, An Emerging Molecule in HIV Therapy

The HIV infection is responsible for the most devastating global pandemic of the last century. More than 39 million people have died of HIV/AIDS since 1981. The development of the antiretroviral (ARV) treatment begins with the discovery of zidovudine a nucleoside reverse transcriptase inhibitor. This breakthrough was followed by other ARV drug classes and representatives. Presently, HIV treatment employs 27 ARV representatives belonging to five different classes. Despite the proven benefits of ARV treatment and its long-term control of the HIV infection, there is an increasing concern about the numerous adverse effects and resistance to current ARV drugs. Therefore, the new HIV treatment strategies focus on the development of new ARV agents with a high genetic barrier to resistance and low toxicity. Monoclonal antibodies (MAbs) belong to a new drug class with encouraging results in the treatment of cancer, autoimmune disorders and most recently against HIV infection. The advantages of using MAbs for HIV treatment are related to their antiviral effect, lack of toxicity, good resistance profile, additional synergy with other ARV drug classes and ability to restore CD4 T-cell responses. The current article is a short summary of ibalizumab, an anti-CD4 monoclonal antibody that interferes with HIV viral entry. Current studies on ibalizumab have underlined its antiviral potential, minimal adverse effects, and lack of crossed resistance with other ARV agents thus supporting its further therapeutic use in multidrug resistant HIV-infected patients.

Checkpoint Inhibition of KIR2D with the Monoclonal Antibody IPH2101 Induces Contraction and Hyporesponsiveness of NK Cells in Patients with Myeloma

PURPOSE

Immune checkpoint inhibitors have recently revolutionized cancer immunotherapy. On the basis of data showing KIR-ligand mismatched natural killer (NK) cells reduce the risk of leukemia and multiple myeloma relapse following allogeneic hematopoietic stem cell transplantation, investigators have developed a checkpoint inhibition antibody that blocks KIR on NK cells. Although in vitro studies suggest the KIR2D-specific antibody IPH2101 induces KIR-ligand mismatched tumor killing by NK cells, our single-arm phase II clinical trial in patients with smoldering multiple myeloma was prematurely terminated due to lack of clinical efficacy. This study aimed at unveiling the underlying mechanisms behind the lack of clinical efficacy.

EXPERIMENTAL DESIGN

Treatment-naïve patients received an intravenous infusion of 1 mg/kg IPH2101 every other month for up to a year. Peripheral blood was collected at baseline and 24 hours after first infusion, followed by weekly samples for the first month and monthly samples thereafter. NK cell phenotype and function was analyzed using high-resolution flow cytometry.

RESULTS

Unexpectedly, infusion of IPH2101 resulted in rapid reduction in both NK cell responsiveness and KIR2D expression on the NK cell surface. In vitro assays revealed KIR2D molecules are removed from the surface of IPH2101-treated NK cells by trogocytosis, with reductions in NK cell function directly correlating with loss of free KIR2D surface molecules. Although IPH2101 marginally augmented the antimyeloma cytotoxicity of remaining KIR2D^dull patient NK cells, the overall response was diminished by significant contraction and reduced function of KIR2D-expressing NK cells.

CONCLUSIONS

These data raise concerns that the unexpected biological events reported in this study could compromise antibody-based strategies designed at augmenting NK cell tumor killing via checkpoint inhibition. Clin Cancer Res; 22(21); 5211-22. ©2016 AACRSee related commentary by Felices and Miller, p. 5161.

Human IgG4: a structural perspective

IgG4, the least represented human IgG subclass in serum, is an intriguing antibody with unique biological properties, such as the ability to undergo Fab-arm exchange and limit immune complex formation. The lack of effector functions, such as antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity, is desirable for therapeutic purposes. IgG4 plays a protective role in allergy by acting as a blocking antibody, and inhibiting mast cell degranulation, but a deleterious role in malignant melanoma, by impeding IgG1-mediated anti-tumor immunity. These findings highlight the importance of understanding the interaction between IgG4 and Fcγ receptors. Despite a wealth of structural information for the IgG1 subclass, including complexes with Fcγ receptors, and structures for intact antibodies, high-resolution crystal structures were not reported for IgG4-Fc until recently. Here, we highlight some of the biological properties of human IgG4, and review the recent crystal structures of IgG4-Fc. We discuss the unexpected conformations adopted by functionally important Cγ2 domain loops, and speculate about potential implications for the interaction between IgG4 and FcγRs.

Therapeutic HPV Cancer Vaccine Targeted to CD40 Elicits Effective CD8+ T-cell Immunity

Human papillomavirus (HPV), particularly HPV16 and HPV18, can cause cancers in diverse anatomical sites, including the anogenital and oropharyngeal (throat) regions. Therefore, development of safe and clinically effective therapeutic vaccines is an important goal. Herein, we show that a recombinant fusion protein of a humanized antibody to CD40 fused to HPV16.E6/7 (αCD40-HPV16.E6/7) can evoke HPV16.E6/7-specific CD8⁺ and CD4⁺ T-cell responses in head-and-neck cancer patients in vitro and in human CD40 transgenic (hCD40Tg) mice in vivo The combination of αCD40-HPV16.E6/7 and poly(I:C) efficiently primed HPV16.E6/7-specific T cells, particularly CD8⁺ T cells, in hCD40Tg mice. Inclusion of montanide enhanced HPV16.E6/7-specific CD4⁺, but not CD8⁺, T-cell responses. Poly(I:C) plus αCD40-HPV16.E6/7 was sufficient to mount both preventative and therapeutic immunity against TC-1 tumors in hCD40Tg mice, significantly increasing the frequency of HPV16-specific CD8⁺ CTLs in the tumors, but not in peripheral blood. In line with this, tumor volume inversely correlated with the frequency of HPV16.E6/7-specific CD8⁺ T cells in tumors, but not in blood. These data suggest that CD40-targeting vaccines for HPV-associated malignancies can provide a highly immunogenic platform with a strong likelihood of clinical benefit. Data from this study offer strong support for the development of CD40-targeting vaccines for other cancers in the future. Cancer Immunol Res; 4(10); 823-34. ©2016 AACR.

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.

Clinical Decision Support Tools: The Evolution of a Revolution

Dashboard systems for clinical decision support integrate data from multiple sources. These systems, the newest in a long line of dose calculators and other decision support tools, utilize Bayesian approaches to fully individualize dosing using information gathered through therapeutic drug monitoring. In the treatment of inflammatory bowel disease patients with infliximab, dashboards may reduce therapeutic failures and treatment costs. The history and future development of modern Bayesian dashboard systems is described.

Functional Specialty of CD40 and Dendritic Cell Surface Lectins for Exogenous Antigen Presentation to CD8(+) and CD4(+) T Cells

Dendritic cells (DCs) are major antigen-presenting cells that can efficiently prime and cross-prime antigen-specific T cells. Delivering antigen to DCs via surface receptors is thus an appealing strategy to evoke cellular immunity. Nonetheless, which DC surface receptor to target to yield the optimal CD8⁺ and CD4⁺ T cell responses remains elusive. Herein, we report the superiority of CD40 over 9 different lectins and scavenger receptors at evoking antigen-specific CD8⁺ T cell responses. However, lectins (e.g., LOX-1 and Dectin-1) were more efficient than CD40 at eliciting CD4⁺ T cell responses. Common and distinct patterns of subcellular and intracellular localization of receptor-bound αCD40, αLOX-1 and αDectin-1 further support their functional specialization at enhancing antigen presentation to either CD8⁺ or CD4⁺ T cells. Lastly, we demonstrate that antigen targeting to CD40 can evoke potent antigen-specific CD8⁺ T cell responses in human CD40 transgenic mice. This study provides fundamental information for the rational design of vaccines against cancers and viral infections.

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Antigen delivery to DCs via CD40 is more efficient than through nine other receptors at eliciting CD8 T⁺ cell response.

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Antigen delivery via lectins (e.g., LOX-1 and Dectin-1) is more efficient than CD40 at eliciting CD4⁺ T cell responses.

The success of an immunotherapeutic vaccine for cancer is largely dependent on its ability to evoke potent cellular immunity. Although targeting antigens to dendritic cells (DCs) has been known to be an efficient strategy to evoke cellular immunity, which targeted receptors yield the optimal cellular immunity remained elusive. We report that targeting CD40, compared to 9 other DC receptors, results in the greatest levels of CD8⁺ cytotoxic T cell responses, while targeting lectins results in enhanced CD4⁺ helper T cell responses. The findings of this study will assist us in the rational design of immunotherapeutic vaccines against cancers.

Tregalizumab - A Monoclonal Antibody to Target Regulatory T Cells

Regulatory T cells (Tregs) represent a subpopulation of CD4⁺ T cells, which are essential for the maintenance of immunological tolerance. The absence or dysfunction of Tregs can lead to autoimmunity and allergies. The restoration of functional Tregs and/or Treg cell numbers represents a novel and attractive approach for the treatment of autoimmune diseases, e.g., rheumatoid arthritis (RA). The CD4 cell surface receptor is a target for modulation of T cell function. Monoclonal antibodies (mAbs) against CD4 have previously been tested for the treatment of autoimmune diseases, including RA. Furthermore, in model systems, anti-CD4 antibodies are able to induce tolerance and mediate immunomodulatory effects through a variety of mechanisms. Despite the availability of innovative and effective therapies for RA, many patients still have persistently active disease or experience adverse events that can limit use. A growing body of evidence suggests that Treg modulation could offer a new therapeutic strategy in RA and other autoimmune disorders. Here, we describe tregalizumab (BT-061), which is a novel, non-depleting IgG1 mAb that binds to a unique epitope of CD4. Tregalizumab represents the first humanized anti-CD4 mAb that selectively induces Treg activation.

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

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

Dashboard systems: Pharmacokinetic/pharmacodynamic mediated dose optimization for monoclonal antibodies

Many marketed drugs exhibit high variability in exposure and response. While these drugs are efficacious in their approved indications, finding appropriate dose regimens for individual patients is not straightforward. Similar dose adjustment problems are also seen with drugs that have a complex relationship between exposure and response and/or a narrow therapeutic window. This is particularly true for monoclonal antibodies, where prolonged dosing at a sub-therapeutic dose can also elicit anti-drug antibodies which will further compromise safety and efficacy. Thus, finding appropriate doses quickly would represent a substantial improvement in healthcare. Dashboard systems, which are decision-support tools, offer an improved, convenient means of tailoring treatment for individual patients. This article reviews the clinical need for this approach, particularly with monoclonal antibodies, the design, development, and testing of such systems, and the likely benefits of dashboard systems in clinical practice. We focus on infliximab for reference.

Fc Engineering of Human IgG1 for Altered Binding to the Neonatal Fc Receptor Affects Fc Effector Functions

Engineering of the constant Fc part of monoclonal human IgG1 (hIgG1) Abs is an approach to improve effector functions and clinical efficacy of next-generation IgG1-based therapeutics. A main focus in such development is tailoring of in vivo half-life and transport properties by engineering the pH-dependent interaction between IgG and the neonatal Fc receptor (FcRn), as FcRn is the main homeostatic regulator of hIgG1 half-life. However, whether such engineering affects binding to other Fc-binding molecules, such as the classical FcγRs and complement factor C1q, has not been studied in detail. These effector molecules bind to IgG1 in the lower hinge-CH2 region, structurally distant from the binding site for FcRn at the CH2-CH3 elbow region. However, alterations of the structural composition of the Fc may have long-distance effects. Indeed, in this study we show that Fc engineering of hIgG1 for altered binding to FcRn also influences binding to both the classical FcγRs and complement factor C1q, which ultimately results in alterations of cellular mechanisms such as Ab-dependent cell-mediated cytotoxicity, Ab-dependent cellular phagocytosis, and Ab-dependent complement-mediated cell lysis. Thus, engineering of the FcRn-IgG1 interaction may greatly influence effector functions, which has implications for the therapeutic efficacy and use of Fc-engineered hIgG1 variants.

Chimeric antigen receptors with mutated IgG4 Fc spacer avoid fc receptor binding and improve T cell persistence and antitumor efficacy

The success of adoptive therapy using chimeric antigen receptor (CAR)-expressing T cells partly depends on optimal CAR design. CARs frequently incorporate a spacer/linker region based on the constant region of either IgG1 or IgG4 to connect extracellular ligand-binding with intracellular signaling domains. Here, we evaluated the potential for the IgG4-Fc linker to result in off-target interactions with Fc gamma receptors (FcγRs). As proof-of-principle, we focused on a CD19-specific scFv-IgG4-CD28-zeta CAR and found that, in contrast to CAR-negative cells, CAR+ T cells bound soluble FcγRs in vitro and did not engraft in NSG mice. We hypothesized that mutations to avoid FcγR binding would improve CAR+ T cell engraftment and antitumor efficacy. Thus, we generated CD19-specific CARs with IgG4-Fc spacers that had either been mutated at two sites (L235E; N297Q) within the CH2 region (CD19R(EQ)) or incorporated a CH2 deletion (CD19Rch2Δ). These mutations reduced binding to soluble FcγRs without altering the ability of the CAR to mediate antigen-specific lysis. Importantly, CD19R(EQ) and CD19Rch2Δ T cells exhibited improved persistence and more potent CD19-specific antilymphoma efficacy in NSG mice. Together, these studies suggest that optimal CAR function may require the elimination of cellular FcγR interactions to improve T cell persistence and antitumor responses.

Driving CAR-based T-cell therapy to success

T cells that have been genetically modified, activated, and propagated ex vivo can be infused to control tumor progression in patients who are refractory to conventional treatments. Early-phase clinical trials demonstrate that the tumor-associated antigen (TAA) CD19 can be therapeutically engaged through the enforced expression of a chimeric antigen receptor (CAR) on clinical-grade T cells. Advances in vector design, the architecture of the CAR molecule especially as associated with T-cell co-stimulatory pathways, and understanding of the tumor microenvironment, play significant roles in the successful treatment of medically fragile patients. However, some recipients of CAR(+) T cells demonstrate incomplete responses. Understanding the potential for treatment failure provides a pathway to improve the potency of adoptive transfer of CAR(+) T cells. High throughput single-cell analyses to understand the complexity of the inoculum coupled with animal models may provide insight into the therapeutic potential of genetically modified T cells. This review focuses on recent advances regarding the human application of CD19-specific CAR(+) T cells and explores how their success for hematologic cancers can provide a framework for investigational treatment of solid tumor malignancies.

Induction and activation of human Th17 by targeting antigens to dendritic cells via dectin-1

Recent compelling evidence indicates that Th17 confer host immunity against a variety of microbes, including extracellular and intracellular pathogens. Therefore, understanding mechanisms for the induction and activation of Ag-specific Th17 is important for the rational design of vaccines against pathogens. To study this, we employed an in vitro system in which influenza hemagglutinin (HA) 1 was delivered to dendritic cells (DCs) via Dectin-1 using anti-human Dectin-1 (hDectin-1)-HA1 recombinant fusion proteins. We found that healthy individuals maintained broad ranges of HA1-specific memory Th17 that were efficiently activated by DCs targeted with anti-hDectin-1-HA1. Nonetheless, these DCs were not able to induce a significant level of HA1-specific Th17 responses even in the presence of the Th17-promoting cytokines IL-1β and IL-6. We further found that the induction of surface IL-1R1 expression by signals via TCRs and common γ-chain receptors was essential for naive CD4(+) T cell differentiation into HA1-specific Th17. This process was dependent on MyD88, but not IL-1R-associated kinase 1/4. Thus, interruptions in STAT3 or MyD88 signaling led to substantially diminished HA1-specific Th17 induction. Taken together, the de novo generation of pathogen-specific human Th17 requires complex, but complementary, actions of multiple signals. Data from this study will help us design a new and effective vaccine strategy that can promote Th17-mediated immunity against microbial pathogens.

Formation, Clearance, Deposition, Pathogenicity, and Identification of Biopharmaceutical-related Immune Complexes

Vascular inflammation, infusion reactions, glomerulopathies, and other potentially adverse effects may be observed in laboratory animals, including monkeys, on toxicity studies of therapeutic monoclonal antibodies and recombinant human protein drugs. Histopathologic and immunohistochemical (IHC) evaluation suggests these effects may be mediated by deposition of immune complexes (ICs) containing the drug, endogenous immunoglobulin, and/or complement components in the affected tissues. ICs may be observed in glomerulus, blood vessels, synovium, lung, liver, skin, eye, choroid plexus, or other tissues or bound to neutrophils, monocytes/macrophages, or platelets. IC deposition may activate complement, kinin, and/or coagulation/fibrinolytic pathways and result in a systemic proinflammatory response. IC clearance is biphasic in humans and monkeys (first from plasma to liver and/or spleen, second from liver or spleen). IC deposition/clearance is affected by IC composition, immunomodulation, and/or complement activation. Case studies are presented from toxicity study monkeys or rats and indicate IHC-IC deposition patterns similar to those predicted by experimental studies of IC-mediated reactions to heterologous protein administration to monkeys and other species. The IHC-staining patterns are consistent with findings associated with generalized and localized IC-associated pathology in humans. However, manifestations of immunogenicity in preclinical species are generally not considered predictive to humans.

Effects of subclass change on the structural stability of chimeric, humanized, and human antibodies under thermal stress

To address how changes in the subclass of antibody molecules affect their thermodynamic stability, we prepared three types of four monoclonal antibody molecules (chimeric, humanized, and human) and analyzed their structural stability under thermal stress by using size-exclusion chromatography, differential scanning calorimetry (DSC), circular dichroism (CD), and differential scanning fluoroscopy (DSF) with SYPRO Orange as a dye probe. All four molecules showed the same trend in change of structural stability; the order of the total amount of aggregates was IgG1 < IgG2 < IgG4. We thus successfully cross-validated the effects of subclass change on the structural stability of antibodies under thermal stress by using four methods. The T(h) values obtained with DSF were well correlated with the onset temperatures obtained with DSC and CD, suggesting that structural perturbation of the CH2 region could be monitored by using DSF. Our results suggested that variable domains dominated changes in structural stability and that the physicochemical properties of the constant regions of IgG were not altered, regardless of the variable regions fused.

Noncovalent assembly of anti-dendritic cell antibodies and antigens for evoking immune responses in vitro and in vivo

Targeting of Ags directly to dendritic cells (DCs) through anti-DC receptor Ab fused to Ag proteins is a promising approach to vaccine development. However, not all Ags can be expressed as a rAb directly fused to a protein Ag. In this study, we show that noncovalent assembly of Ab-Ag complexes, mediated by interaction between dockerin and cohesin domains from cellulose-degrading bacteria, can greatly expand the range of Ags for this DC-targeting vaccine technology. rAbs with a dockerin domain fused to the rAb H chain C terminus are efficiently secreted by mammalian cells, and many Ags not secreted as rAb fusion proteins are readily expressed as cohesin directly fused to Ag either via secretion from mammalian cells or as soluble cytoplasmic Escherichia coli products. These form very stable and homogeneous complexes with rAb fused to dockerin. In vitro, these complexes can efficiently bind to human DC receptors followed by presentation to Ag-specific CD4⁺ and CD8⁺ T cells. Low doses of the HA1 subunit of influenza hemagglutinin conjugated through this means to anti-Langerin rAbs elicited Flu HA1-specific Ab and T cell responses in mice. Thus, the noncovalent assembly of rAb and Ag through dockerin and cohesin interaction provides a useful modular strategy for development and testing of prototype vaccines for elicitation of Ag-specific T and B cell responses, particularly when direct rAb fusions to Ag cannot be expressed.

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.

Targeting self- and foreign antigens to dendritic cells via DC-ASGPR generates IL-10-producing suppressive CD4+ T cells

Targeting antigens to the lectinlike DC-ASGPR receptor on human DCs and in nonhuman primates results in the induction of antigen-specific IL-10–producing CD4⁺ T cells.

Dendritic cells (DCs) can initiate and shape host immune responses toward either immunity or tolerance by their effects on antigen-specific CD4⁺ T cells. DC-asialoglycoprotein receptor (DC-ASGPR), a lectinlike receptor, is a known scavenger receptor. Here, we report that targeting antigens to human DCs via DC-ASGPR, but not lectin-like oxidized-LDL receptor, Dectin-1, or DC-specific ICAM-3–grabbing nonintegrin favors the generation of antigen-specific suppressive CD4⁺ T cells that produce interleukin 10 (IL-10). These findings apply to both self- and foreign antigens, as well as memory and naive CD4⁺ T cells. The generation of such IL-10–producing CD4⁺ T cells requires p38/extracellular signal-regulated kinase phosphorylation and IL-10 induction in DCs. We further demonstrate that immunization of nonhuman primates with antigens fused to anti–DC-ASGPR monoclonal antibody generates antigen-specific CD4⁺ T cells that produce IL-10 in vivo. This study provides a new strategy for the establishment of antigen-specific IL-10–producing suppressive T cells in vivo by targeting whole protein antigens to DCs via DC-ASGPR.

Pre-clinical strategies and safety issues in developing therapeutic monoclonal antibodies

Although mAbs present a different set of challenges from other product classes, and the pre-clinical safety evaluation may need to be more extensive than for other medicinal products to overcome the limited predictive value of conventional pre-clinical test systems, the level of risk associated with first administration to human subjects can be effectively mitigated. This article seeks to provide a systematic approach to identifying and addressing the pertinent risks relative to the characteristics of the particular mAb product before the first administration to human subjects.

Monoclonal antibodies: interspecies scaling with minimal preclinical information

Interspecies scaling for predicting human pharmacokinetics with information from multiple animal species is an established approach for small-molecule drugs. However, in general, the strategy is not a viable approach for therapeutic monoclonal antibodies, since relevant preclinical information is often limited due to highly specific biological activity and unique disposition mechanisms of these biologic agents. Existing data from a limited database indicates that applying minimal but relevant preclinical information and an appropriate approach; for example, fixed-exponent, provides a pragmatic and reasonably accurate prediction of human pharmacokinetics. This article briefly reviews the factors that affect the disposition of monoclonal antibodies and reiterates the importance of biological similarities between animal species and humans when selecting preclinical information for interspecies scaling. The article outlines the rationalization for utilizing the one-species with fixed-exponent approach, with discussions focused on the assumptions in allometry and monoclonal antibodies disposition mechanisms, and provides specific considerations related to practically applying such an approach.

Combined administration of a mutant TGF-beta1/Fc and rapamycin promotes induction of regulatory T cells and islet allograft tolerance

The critical roles of TGF-β in the reciprocal differentiation of tolerance-promoting CD4(+)Foxp3(+) regulatory T cells (Tregs) and proinflammatory Th17 effector cells affect alloimmune reactivity and transplant outcome. We reasoned that a strategy to harness TGF-β and block proinflammatory cytokines would inhibit the differentiation of Th17 cells and strengthen the cadre of Tregs to promote tolerance induction and long-term allograft survival. In this study, we report the development of a long-lasting autoactive human mutant TGF-β1/Fc fusion protein that acts in conjunction with rapamycin to inhibit T cell proliferation and induce the de novo generation of Foxp3(+) Treg in the periphery, while at the same time inhibiting IL-6-mediated Th17 cell differentiation. Short-term combined treatment with TGF-β1/Fc and rapamycin achieved long-term pancreatic islet allograft survival and donor-specific tolerance in a mouse model. This effect was accompanied by expansion of Foxp3(+) Tregs, enhanced alloantigen-specific Treg function, and modulation of transcript levels of Foxp3, IL-6, and IL-17. Our strategy of combined TGF-β1/Fc and rapamycin to target the IL-6-related Tregs and Th17 signaling pathways provides a promising approach for inducing transplant tolerance and its clinical application.

Concomitant activation and antigen uptake via human dectin-1 results in potent antigen-specific CD8+ T cell responses

Dectin-1, a C-type lectin recognizing fungal and mycobacterial pathogens, can deliver intracellular signals that activate dendritic cells (DCs), resulting in initiation of immune responses and expansion of Th17 CD4(+) T cell responses. In this paper, we studied the roles of human Dectin-1 (hDectin-1) expressed on DCs in the induction and activation of Ag-specific CD8(+) T cell responses. We first generated an agonistic anti-hDectin-1 mAb, which recognizes the hDectin-1 Glu(143)-Ile(162) region. It bound to in vitro monocyte-derived DCs and to in vivo CD1c(+)CD1a(+) dermal DCs but not to epidermal Langerhans cells. Anti-hDectin-1-mediated DC activation resulted in upregulation of costimulatory molecules and secretion of multiple cytokines and chemokines in a Syk-dependent manner. DCs activated with the anti-hDectin-1 mAb could significantly enhance both neo and foreign Ag-specific CD8(+) T cell responses by promoting both the expansion of CD8(+) T cells and their functional activities. We further demonstrated that delivering Ags to DCs via hDectin-1 using anti-hDectin-1-Ag conjugates resulted in potent Ag-specific CD8(+) T cell responses. Thus, hDectin-1 expressed on DCs can contribute to the induction and activation of cellular immunity against intracellular pathogens, such as mycobacteria, that are recognized by DCs via Dectin-1. Vaccines based on delivering Ags to DCs with an agonistic anti-hDectin-1 mAb could elicit CD8(+) T cell-mediated immunity.

Overview of novel therapeutic targets for asthma and chronic obstructive pulmonary disease

Obstructive lung diseases, in particular asthma and chronic obstructive pulmonary disease, are a worldwide health problem that is increasing in incidence. While significant progress has been made in the control of symptoms, further advances must be made in modifying the clinical situation in terms of disease progression. Numerous pathogenetic studies have demonstrated that inflammatory responses play a crucial role in the development of chronic lung obstruction, while current molecular findings have provided a myriad of new and promising therapeutic targets. The aim of this article is to provide an overview of clinically and pharmacologically relevant targets for asthma and chronic obstructive pulmonary diseases, considering currently investigated therapeutic approaches.

Cross-priming CD8+ T cells by targeting antigens to human dendritic cells through DCIR

We evaluated human CD8(+) T-cell responses generated by targeting antigens to dendritic cells (DCs) through various lectin receptors. We found the immunoreceptor tyrosine-based inhibitory motif-containing DC immunoreceptor (DCIR) to mediate potent cross-presentation. A single exposure to a low dose of anti-DCIR-antigen conjugate initiated antigen-specific CD8(+) T-cell immunity by all human DC subsets including ex vivo-generated DCs, skin-isolated Langerhans cells, and blood myeloid DCs and plasmacytoid DCs. The delivery of influenza matrix protein (FluMP) through DCIR resulted in expansion of FluMP-specific memory CD8(+) T cells. Enhanced specific CD8(+) T-cell responses were observed when an antigen was delivered to the DCs via DCIR, compared with those induced by a free antigen, or antigen conjugated to a control monoclonal antibody or delivered via DC-SIGN, another lectin receptor. DCIR targeting also induced primary CD8(+) T-cell responses against self (MART-1) and viral (HIV gag) antigens. Addition of Toll-like receptor (TLR) 7/8 agonist enhanced DCIR-mediated cross-presentation as well as cross-priming, particularly when combined with a CD40 signal. TLR7/8 activation was associated with increased expansion of the primed CD8(+) T cells, high production of interferon-γ and tumor necrosis factor-α, and reduced levels of type 2-associated cytokines. Thus, antigen targeting via the human DCIR receptor allows activation of specific CD8(+) T-cell immunity.

Therapeutic antibodies for autoimmunity and inflammation

The development of therapeutic antibodies has evolved over the past decade into a mainstay of therapeutic options for patients with autoimmune and inflammatory diseases. Substantial advances in understanding the biology of human diseases have been made and tremendous benefit to patients has been gained with the first generation of therapeutic antibodies. The lessons learnt from these antibodies have provided the foundation for the discovery and development of future therapeutic antibodies. Here we review how key insights obtained from the development of therapeutic antibodies complemented by newer antibody engineering technologies are delivering a second generation of therapeutic antibodies with promise for greater clinical efficacy and safety.