Pharmacokinetics and biological activity of atacicept in patients with rheumatoid arthritis

Population pharmacokinetics of atacicept in systemic lupus erythematosus: An analysis of three clinical trials

B cell stimulating factor (BLyS) and a proliferation-inducing ligand (APRIL) are targets for novel treatments in patients with systemic lupus erythematosus (SLE). Atacicept is a recombinant, soluble fusion protein that blocks BLyS and APRIL activity. This study characterized the pharmacokinetic (PK) profile of atacicept using a population PK model and identified covariates explaining the PK variability. Total atacicept concentrations from a phase I study in healthy volunteers and two phase II studies in patients with SLE, using subcutaneous administration, were modeled using a quasi-steady-state approximation of the target-mediated drug disposition model with first-order absorption. The model included 3640 serum atacicept concentration records from 37 healthy volunteers and 503 patients with SLE and described total atacicept concentrations of the three trials, providing precise estimates of all parameters. Body weight and baseline BLyS concentration were the only statistically significant covariates, whereas no differences were found between patients and healthy volunteers. Apparent clearance and volume of the central compartment increased with body weight and initial target concentration increased with baseline BLyS. The change on atacicept exposure was moderate, with a difference in area under the curve compared with the median of 20%-32% for body weight, and 7%-18% for BLyS. Therefore, the effects of these covariates on atacicept exposure are not expected to be clinically relevant. The model described the complete total atacicept concentration-time profiles without finding any differences between healthy subjects and patients with SLE and supports the 150 mg once weekly dose for further trials.

Kinetics of free and ligand-bound atacicept in human serum

BAFF (B cell activation factor of the TNF family/B lymphocyte stimulator, BLyS) and APRIL (a proliferation-inducing ligand) are targeted by atacicept, a decoy receptor consisting of the extracellular domain of TACI (transmembrane activator and calcium-modulator and cyclophilin (CAML) interactor) fused to the Fc portion of human IgG1. The purpose of the study was to characterize free and ligand-bound atacicept in humans. Total and active atacicept in serum of healthy volunteers receiving a single dose of subcutaneous atacicept or in patients treated weekly for one year were measured by ELISA, Western blot, or cell-based assays. Pharmacokinetics of free and bound atacicept were predicted based on total atacicept ELISA results. Persistence of complexes of purified atacicept bound to recombinant ligands was also monitored in mice. Results show that unbound or active atacicept in human serum exceeded 0.1 µg/ml for one week post administration, or throughout a 1-year treatment with weekly administrations. After a single administration of atacicept, endogenous BAFF bound to atacicept was detected after 8 h then increased about 100-fold within 2 to 4 weeks. Endogenous heteromers of BAFF and APRIL bound to atacicept also accumulated, but atacicept-APRIL complexes were not detected. In mice receiving intravenous injections of purified complexes pre-formed in vitro, atacicept-BAFF persisted longer (more than a week) than atacicept-APRIL (less than a day). Thus, only biologically inactive BAFF and BAFF-APRIL heteromers accumulate on atacicept in vivo. The measure of active atacicept provides further support for the once-weekly dosing regimen implemented in the clinical development of atacicept.

Efficacy of long-term repeated rituximab treatment in refractory phospholipase A2 receptor-antibody-related membranous nephropathy

Aims: To evaluate the efficacy of long-term repeated rituximab treatment in refractory PLA2R-Ab-related membranous nephropathy (MN). Materials & methods: Rituximab was administered at a single dose of 375 mg/m² and repeated if peripheral B-cell levels were >5/ul in 46 patients with refractory PLA2R-Ab-related MN. Results: The median frequency of rituximab treatment was 3 (IQR 2.0-4.0). A total of 32 (32/46) patients achieved remission (completed remission [CR] or partial remission [PR]) over a median time of 17.0 months, and 10 patients eventually progressed to CR. The proportion of serum PLA2R-Ab depletion was 73.91% (34/46) over a median time of 9 months. Antibody depletion preceded proteinuria remission. Conclusions: Long-term repeated rituximab treatment achieved high kidney and immunological response rates in refractory PLA2R-Ab related MN, and antibody depletion was a prerequisite for proteinuria remission.

"Old Drugs, New Tricks" - Local controlled drug release systems for treatment of degenerative joint disease

Osteoarthritis (OA) and chronic low back pain (CLBP) caused by intervertebral disc (IVD) degeneration are joint diseases that have become major causes for loss of quality of life worldwide. Despite the unmet need, effective treatments other than invasive, and often ineffective, surgery are lacking. Systemic administration of drugs entails suboptimal local drug exposure in the articular joint and IVD. This review provides an overview of the potency of biomaterial-based drug delivery systems as novel treatment modality, with a focus on the biological effects of drug release systems that have reached translation at the level of in vivo models and relevant ex vivo models. These studies have shown encouraging results of biomaterial-based local delivery of several types of drugs, mostly inhibitors of inflammatory cytokines or other degenerative factors. Prevention of inflammation and degeneration and pain relief was achieved, although mainly in small animal models, with interventions applied at an early disease stage. Less convincing data were obtained with the delivery of regenerative factors. Multidisciplinary efforts towards tackling the discord between in vitro and in vivo release, combined with adaptations in the regulatory landscape may be needed to enhance safe and expeditious introduction of more and more effective controlled release-based treatments with the OA and CLBP patients.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Atacicept in a Randomized Trial in Healthy Caucasian and Japanese Subjects

Background and Objective

Atacicept is an inhibitor of the B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL), and is being studied in relation to immunological disease. Currently, limited data on atacicept are available in non-Caucasian subjects. Pharmacokinetic data from earlier studies of atacicept were derived using an enzyme-linked immunosorbent assay (ELISA), which was subsequently found to have inadequacies. Hence, a new bioanalytical ELISA for total atacicept was developed and validated. We conducted this randomized, double-blind, placebo-controlled phase I study to compare the safety, tolerability, pharmacokinetics, and pharmacodynamics of atacicept in healthy Japanese and Caucasian subjects while generating pharmacokinetic data using the new ELISA.

Methods

Japanese subjects aged ≥ 18 to ≤ 55 years (n  = 24) were randomized (1:1:1:1) to a single subcutaneous dose of atacicept 25, 75, or 150 mg or placebo. Caucasian subjects were then enrolled to match the Japanese subjects’ gender, body weight (± 20%), and height (± 15%).

Results

Atacicept was well tolerated and there were no clinically significant differences in treatment-emergent adverse events (TEAEs), vital signs, or laboratory parameters between the Japanese and Caucasian subjects. Most (90%) TEAEs were mild; no severe or serious TEAEs or deaths occurred. Weight-adjusted atacicept exposure was comparable between ethnicities and across doses: the Japanese/Caucasian ratio of the area under the serum concentration–time curve from time zero to the last sampling point (AUC_0–t) was 107.21% (90% CI 93.42–123.02%) and the Japanese/Caucasian ratio of maximum serum concentration (C_max) was 95.74% (90% CI 74.26–123.43%; ANCOVA). Median time to reach C_max (t_max) was 20–60 h across all subjects. Dose–exposure relationships were comparable for the two ethnicities, with dose-normalized AUC_0–t decreasing with increasing dose, indicating nonlinear pharmacokinetics for the doses examined. There were no statistically significant differences between ethnicities in the pharmacokinetics–dose relationship. Some transient dose-related decreases in mean serum immunoglobulin (Ig)A and IgM, but not IgG, were observed after atacicept administration. There were small transient increases in peripheral B cell numbers in the first 4 days after dosing that were larger with atacicept than with placebo, with no apparent dose relationship. No anti-atacicept antibodies were detected.

Conclusion

The safety, pharmacokinetic, and pharmacodynamic profiles of atacicept in healthy Japanese subjects were comparable to those in healthy Caucasian subjects.

EudraCT-ID: 2013-002703-34.

Electronic supplementary material

The online version of this article (10.1007/s13318-019-00575-7) contains supplementary material, which is available to authorized users.

Hspa13 Promotes Plasma Cell Production and Antibody Secretion

The generation of large numbers of plasma cells (PCs) is a main factor in systemic lupus erythematosus (SLE). We hypothesize that Hspa13, a member of the heat shock protein family, plays a critical role in the control of PC differentiation. To test the hypothesis, we used lipopolysaccharide (LPS)-activated B cells and a newly established mouse line with a CD19^cre-mediated, B cell–specific deletion of Hspa13: Hspa13 cKO mice. We found that Hspa13 mRNA was increased in PCs from atacicept-treated lupus-prone mice and in LPS-stimulated plasmablasts (PBs) and PCs. A critical finding was that PBs and PCs [but not naïve B cells and germinal center (GC) B cells] expressed high levels of Hspa13. In contrast, the Hspa13 cKO mice had a reduction in BPs, PCs, and antibodies induced in vitro by LPS and in vivo by sheep red blood cells (SRCs)- or 4-hydroxy-3-nitrophenylacetyl (NP)-immunization. Accordingly, the Hspa13 cKO mice had reduced class-switched and somatically hypermutated antibodies with defective affinity maturation. Our work also showed that Hspa13 interacts with proteins (e.g., Bcap31) in the endoplasmic reticulum (ER) to positively regulate protein transport from the ER to the cytosol. Importantly, Hspa13 mRNA was increased in B220⁺ cells from patients with multiple myeloma (MM) or SLE, whereas Hspa13 cKO led to reduced autoantibodies and proteinuria in both pristane-induced lupus and lupus-prone MRL/lpr mouse models. Collectively, our data suggest that Hspa13 is critical for PC development and may be a new target for eliminating pathologic PCs.

BC094916 suppressed SP 2/0 xenograft tumor by down-regulating Creb1 and Bcl2 transcription

Background

Both multiple myeloma (MM) and systemic lupus erythematosus (SLE) are associated with abnormal production of plasma cells, although their pathological mechanism of each disease is different. The main characteristic of both diseases is uncontrolled differentiation of B cells into plasmablast/plasma cells. Despite continuous research on prognostic factors and the introduction of new agents for MM and SLE, treatments still do not exist for controlling plasmablast/plasma cells. Thus, it is necessary to identify novel therapeutic targets of plasmablast/plasma cells. Because of its plasmablast-like characteristics, the mus musculus myeloma SP 2/0 cell line was used in this study to test the effect of a novel therapeutic agent (BC094916 overexpression) on plasmablast/plasma cells.

Methods

We first determined gene expression profiles of plasma cells using Affymetrix microarrays and RNA-sequencing. The effect of BC094916 on SP 2/0 cell proliferation, cell cycle, and apoptosis was determined by CCK8 and fluorescence-activated cell sorting. The SP 2/0 xenograft mouse model was used to assess the impact of BC094916 on tumor progression. The luciferase reporter system was used to evaluate the effect of BC094916 on Creb1 and Bcl2 transcription.

Results

We found that BC094916 mRNA was decreased in plasma cells. The mouse myeloma cell line SP 2/0 expressed low levels of BC094916 mRNA, whereas BC094916 overexpression suppressed SP 2/0 cell proliferation by inducing apoptosis. BC094916 overexpression suppressed tumor progression in the SP 2/0 xenograft mouse model. We also found that BC094916 mediate apoptosis by suppressing transcription of the Creb1 and Bcl2 genes, which promote the transcription of eukaryotic translation initiation and elongation factor genes.

Conclusions

BC094916 overexpression suppressed Creb1 and Bcl2 transcription to induce cell apoptosis, which suppressed SP 2/0 proliferation and xenograft tumor progression. Thus, BC094916 overexpression may be a potential therapeutic agent for treatment of MM and autoimmune diseases such as SLE.

Role of Anti-Osteopontin Antibodies in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Osteopontin (OPN) is highly expressed in demyelinating lesions in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). OPN is cleaved by thrombin into N- (OPN-N) and C-terminal (OPN-C) fragments with different ligands and functions. In EAE, administering recombinant OPN induces relapses, whereas treatment with anti-OPN antibodies ameliorates the disease. Anti-OPN autoantibodies (autoAbs) are spontaneously produced during EAE but have never been detected in MS. The aim of the study was to evaluate anti-OPN autoAbs in the serum of MS patients, correlate them with disease course, and recapitulate the human findings in EAE. We performed ELISA in the serum of 122 patients collected cross-sectionally, and 50 patients with relapsing–remitting (RR) disease collected at diagnosis and followed longitudinally for 10 years. In the cross-sectional patients, the autoAb levels were higher in the RR patients than in the primary- and secondary-progressive MS and healthy control groups, and they were highest in the initial stages of the disease. In the longitudinal group, the levels at diagnosis directly correlated with the number of relapses during the following 10 years. Moreover, in patients with active disease, who underwent disease-modifying treatments, autoAbs were higher than in untreated patients and were associated with low MS severity score. The autoAb displayed neutralizing activity and mainly recognized OPN-C rather than OPN-N. To confirm the clinical effect of these autoAbs in vivo, EAE was induced using myelin oligodendrocyte glycoprotein MOG_35–55 in C57BL/6 mice pre-vaccinated with ovalbumin (OVA)-linked OPN or OVA alone. We then evaluated the titer of antibodies to OPN, the clinical scores and in vitro cytokine secretion by spleen lymphocytes. Vaccination significantly induced antibodies against OPN during EAE, decreased disease severity, and the protective effect was correlated with decreased T cell secretion of interleukin 17 and interferon-γ ex vivo. The best effect was obtained with OPN-C, which induced significantly faster and more complete remission than other OPN vaccines. In conclusion, these data suggest that production of anti-OPN autoAbs may favor remission in both MS and EAE. Novel strategies boosting their levels, such as vaccination or passive immunization, may be proposed as a future strategy in personalized MS therapy.

Pharmacokinetics, pharmacodynamics, short term efficacy and safety of RCT-18, a novel BLyS/APRIL fusion protein, in patients with rheumatoid arthritis

AIM

RCT-18 is a recombinant fusion protein that interferes with the selection and survival of mature B-lymphocytes by inhibiting B-lymphocyte stimulator and a proliferation-inducing ligand.

METHODS

This single blind, randomized, placebo controlled, clinical pharmacological study explored the short term efficacy and safety of RCT-18 in 21 rheumatoid arthritis (RA) patients with three different dosing regimens. The pharmacological behaviour of RCT-18 was also characterized through a six level biomarker cascade approach to identify potential predictors for clinical responses.

RESULTS

Nine out of 10 patients (>80%) experienced moderate to good EULAR response at the end of 3 months with once or twice weekly doses of 180 mg RCT-18, whereas weekly administration of 360 mg RCT-18 or placebo, however, only resulted in moderate improvement in one patient in each group. Absence of IgM-type rheumatoid factor reduction, recovery of IgM 2 weeks after drug cessation, lack of decrease in the count of CD27(+) B-lymphocytes and a DAS28 change from baseline <6 in 4-6 weeks after the treatment initiation may indicate poor clinical response. No anti-drug antibody of RCT-18 was detected. The active treatments were well tolerated, although more mild to moderate infections were reported in patients receiving RCT-18.

CONCLUSION

The study results support further development of RCT-18 in RA patients and provide important information for future dose selection.

B-cell survival factors in autoimmune rheumatic disorders

Autoimmune rheumatic disorders have complex etiopathogenetic mechanisms in which B cells play a central role. The importance of factors stimulating B cells, notably the B-cell activating factor (BAFF) and A proliferation inducing ligand (APRIL) axis is now recognized. BAFF and APRIL are cytokines essential for B-cell proliferation and survival from the immature stages to the development of plasma cells. Their levels are increased in some subsets of patients with autoimmune disorders. Several recent biologic drugs have been developed to block this axis, namely belimumab [already licensed for systemic lupus erythematosus (SLE) treatment], tabalumab, atacicept and blisibimod. Many clinical trials to evaluate the safety and efficacy of these drugs in several autoimmune disorders are ongoing, or have been completed recently. This review updates the information on the use of biologic agents blocking BAFF/APRIL for patients with SLE, rheumatoid arthritis, Sjögren's syndrome and myositis.

Atacicept as an investigated therapy for rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic, painful and debilitating autoimmune disease. Although the outcome for patients with RA has improved markedly in the past decades, adequate disease control cannot be achieved in a substantial proportion of patients. Since RA is a syndrome with different biological subsets, new drugs with a novel mechanism of action may represent a valuable addition to the current armamentarium.

AREAS COVERED

This review focuses on the pharmacodynamics and pharmacokinetics of atacicept . Furthermore, the article both summarises and comments on the drug's efficacy and safety profile in RA patients.

EXPERT OPINION

Atacicept is designed to neutralise B-lymphocyte stimulator (BLyS) and a proliferation-inducing ligand, two cytokines involving B-cell function and survival. Two recent Phase II studies have demonstrated that atacicept was not effective in RA patients with an inadequate response to methotrexate or TNF antagonists. However, atacicept displayed significant biological activity, including reduction of Ig and rheumatoid factor levels. Adverse events were slightly more frequent among patients treated with atacicept compared with placebo. In contrast to patients with systemic lupus erythematosus, RA patients receiving atacicept did not show an increased susceptibility to infections. In view of its important impact on immunoglobulin-secreting cells, this drug might be a rational therapy for hematological diseases.

Clinical targeting of the TNF and TNFR superfamilies

Inhibitors of tumour necrosis factor (TNF) are among the most successful protein-based drugs (biologics) and have proven to be clinically efficacious at reducing inflammation associated with several autoimmune diseases. As a result, attention is focusing on the therapeutic potential of additional members of the TNF superfamily of structurally related cytokines. Many of these TNF-related cytokines or their cognate receptors are now in preclinical or clinical development as possible targets for modulating inflammatory diseases and cancer as well as other indications. This Review focuses on the biologics that are currently in clinical trials for immune-related diseases and other syndromes, discusses the successes and failures to date as well as the expanding therapeutic potential of modulating the activity of this superfamily of molecules.

The rationale for BAFF inhibition in systemic lupus erythematosus

BAFF (B-cell-activating factor) is a critical survival factor for transitional and mature B cells and is a promising therapeutic target for systemic lupus erythematosus (SLE). In 2010-2011, two phase 3 clinical trials showed that the addition of the anti-BAFF antibody belimumab to standard-of-care therapy in patients with moderately active SLE results in a better outcome at 52 weeks than standard-of-care therapy alone. Belimumab has been US Food and Drug Administration approved for the treatment of SLE, and other drugs that target BAFF are now in various stages of clinical testing. This review describes the function of BAFF and its homolog APRIL (a proliferation-inducing ligand) and addresses the rationale for the treatment of SLE with BAFF/APRIL inhibitors.

Monoclonal antibodies and recombinant immunoglobulins for the treatment of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory and degenerative disease leading to demyelination and axonal damage in the CNS. Autoimmunity plays a central role in MS pathogenesis. Per definition, monoclonal antibodies are recombinant biological compounds with a well defined target, thus carrying the promise of targeting pathogenic cells or molecules with high specificity, avoiding undesired off-target effects. Natalizumab was the first monoclonal antibody to be approved for the treatment of MS. Several other monoclonal antibodies are in development and have demonstrated promising efficacy in phase II studies. They can be categorized according to their mode of action into compounds targeting (i) leukocyte migration into the CNS (natalizumab); (ii) cytolytic antibodies (rituximab, ocrelizumab, ofatumumab, alemtuzumab); or (iii) antibodies and recombinant proteins targeting cytokines and chemokines and their receptors (daclizumab, ustekinumab, atacicept, tabalumab [Ly-2127399], secukinumab [AIN457]). In this review, we discuss the specific molecular targets, clinical efficacy and safety of these compounds and discuss criteria to anticipate the position of monoclonal antibodies in the diversifying armamentarium of MS therapy in the coming years.

Atacicept in patients with rheumatoid arthritis and an inadequate response to tumor necrosis factor antagonist therapy: results of a phase II, randomized, placebo-controlled, dose-finding trial

OBJECTIVE

To assess the efficacy, safety, and biologic activity of atacicept in patients with rheumatoid arthritis (RA) in whom the response to treatment with tumor necrosis factor antagonists was inadequate.

METHODS

The Atacicept for Reduction of Signs and Symptoms in Rheumatoid Arthritis Trial (AUGUST I) was a multicenter, phase II, double-blind, placebo-controlled dose-finding study involving 256 patients randomized 1:1:1:1 to receive atacicept (25 mg, 75 mg, or 150 mg) or placebo twice weekly for 4 weeks, then weekly for 21 weeks, with a 13-week treatment-free followup period (week 38). The primary end point was a response at week 26 according to the American College of Rheumatology criteria for 20% improvement in disease severity, using the C-reactive protein level.

RESULTS

No statistically significant differences were observed in the efficacy end points at week 26 (P = 0.410 for overall treatment effect). However, atacicept significantly reduced immunoglobulin and rheumatoid factor (RF) levels, but not anti-citrullinated protein antibody levels, in a dose-dependent manner, with levels returning toward baseline values during followup. The effects of treatment on IgG-RF and IgA-RF were more pronounced than the effects on total IgG and IgA. Adverse events (AEs), including serious AEs, leading to withdrawal were more common among patients treated with atacicept compared with placebo. AEs were variable in nature, and no dose-dependent trends were observed. The frequency of infection-related AEs was similar across treatments. No notable effect of treatment on immunization status (protective versus nonprotective titer) was observed after initiation of treatment.

CONCLUSION

This study did not meet the primary efficacy end point. However, clear biologic activity consistent with the proposed mechanism of action was observed. The results suggest that decreasing the expression of RF may not be sufficient to induce clinical improvement in RA. The safety of atacicept was considered acceptable in this patient population.

Atacicept: targeting B cells in multiple sclerosis

Multiple sclerosis (MS) has traditionally been considered to be a T-cell-mediated disease. However, there is an increasing body of evidence for the involvement of B cells and autoantibodies in the pathology of this disease, providing a rationale for treatments directed against B cells. In this paper we summarize evidence for the key role of B cells in the immunopathology of MS and review data supporting the use of a novel B-cell targeted therapy, atacicept, in this condition. Atacicept is a human recombinant fusion protein that comprises the binding portion of a receptor for both BLyS (B-Lymphocyte Stimulator) and APRIL (A PRoliferation-Inducing Ligand), two cytokines that have been identified as important regulators of B-cell maturation, function and survival. Atacicept has shown selective effects on cells of the B-cell lineage, acting on mature B cells and blocking plasma cells and late stages of B-cell development while sparing B-cell progenitors and memory cells. The efficacy of atacicept in animal models of autoimmune disease and the biological activity of atacicept in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) has been demonstrated. Clinical studies were initiated to investigate the safety, tolerability and efficacy of atacicept in patients with MS. An unexpected increase in inflammatory activity in one of the trials, however, led to suspension of all atacicept trials in MS.

BAFF inhibition: a new class of drugs for the treatment of autoimmunity

BAFF (BLyS) and APRIL are TNF-like cytokines that support survival and differentiation of B cells. Recent studies have discovered a role for BAFF in augmenting both innate and adaptive immune responses as well as in collaborating with other inflammatory cytokines to promote the activation and differentiation of effector immune cells. BAFF is an important pathogenic factor in lupus mouse models and BAFF inhibition successfully delays disease onset in these mice, although the responsiveness to BAFF inhibition varies among different strains. These results have led to the development of inhibitors targeting BAFF and APRIL in humans. An anti-BAFF antibody has shown significant but modest efficacy in two Phase III clinical trials for moderately active SLE and other inhibitors are being developed or at early stages of clinical testing.

Pharmacokinetics and immunoglobulin response of subcutaneous and intravenous atacicept in patients with systemic lupus erythematosus

Atacicept, a recombinant fusion protein of the TACI receptor and human IgG, is an inhibitor of B-Lymphocyte Stimulator (BLyS) and APRIL, potent stimulators of B cell maturation, proliferation, and survival. Pharmacokinetics (PKs) and biological activity of intravenous (iv) and subcutaneous (sc) atacicept are described here for patients with systemic lupus erythematosus in two randomized, double-blind, placebo-controlled, Phase Ib studies. Study 1: Six cohorts of eight patients received sc atacicept (single dose: 0.3, 1, 3, or 9 mg/kg; four weekly doses: 1 or 3 mg/kg), or placebo (3:1 ratio). Study 2: Four cohorts of six patients received iv atacicept (single dose: 3, 9, or 18 mg/kg; multiple dose: 2 x 9 mg/kg), or matching placebo (5:1 ratio). PK profiles were determined through serum atacicept and atacicept-BLyS complex, and biological activity through IgA, IgG, and IgM levels. PK profiles of atacicept were influenced by saturable binding between atacicept and its ligands, and were consistent and predictable across doses and regimens. Atacicept's biological activity was compatible with its presumed mechanism of action. Bioavailability was approximately 30-40% following sc or iv administration and similar doses yielded similar biological activity irrespective of administration route. This observation may have a mechanistic foundation and may inform dosing regimen design for future studies.

Immunotherapy of systemic sclerosis

Scleroderma is a multisystem autoimmune disease characterized by an abnormal immune activation associated with the development of underlying vascular and fibrotic disease manifestations. This article highlights the current use of drugs targeting the immune system in scleroderma. Nonselective immunosuppression, and in particular cyclophosphamide, remains the main treatment for progressing skin involvement and active interstitial lung disease. Mycophenolate mofetil is a promising alternative to cyclophosphamide. The use of cyclosporine has been limited by modest efficacy and serious renal toxicity. Newer T-cell (sirolimus and alefacept) and B-cell (rituximab)-targeted therapies have provided some encouraging results in small pilot studies. Hematopoietic stem cell transplantation can be effective for severe fibrotic skin disease, but toxicity remains a concern. Clinical efficacy and safety of antifibrotic treatments (e.g., imatinib) await confirmation. Newer biological agents targeting key molecular or cellular effectors in scleroderma pathogenesis are now available for clinical testing.

Targeting BAFF in autoimmunity

BAFF and APRIL are TNF-like cytokines that support survival and differentiation of B cells. The early appreciation that overexpression of BAFF leads to B cell expansion and a lupus-like syndrome in mice, and the demonstration that BAFF inhibition delays lupus onset in spontaneous mouse models of SLE and other autoimmune diseases has rapidly led to the development of strategies for inhibiting both BAFF and APRIL. The commercialization of this new class of drugs has proceeded in parallel with the continuing elucidation of the biology of the cytokines and their receptors. Recent studies have uncovered a role for BAFF in enhancing both innate and adaptive immune responses and in amplifying aberrant pathways that arise during inflammation. Two phase III studies of an anti-BAFF antibody have yielded positive, although modest, results in SLE and alternate inhibitors are being tested in a variety of autoimmune diseases in which BAFF may play a pathogenic role.

Target-mediated drug disposition model for drugs that bind to more than one target

Until recently, most therapeutic monoclonal antibodies (mAb) were designed to bind only one target. However, several existing mAbs bind to soluble and membrane forms of the same receptor. Moreover, design of bi-specific and multi-specific proteins that bind to more than one target is a promising direction of drug design. The pharmacokinetics and pharmacodynamics of these drugs may be described by the target-mediated drug disposition (TMDD). This work extended the TMDD model to drugs that bind more than one target. The quasi-steady-state (QSS) and Michaelis-Menten (MM) approximations of the model were also derived. Identifiability of model parameters was studied by simulations. The drug and target parameters used in simulations were chosen to imitate a monoclonal antibody that binds to the soluble (S) and membrane-bound (M) targets. The data were simulated for 224 subjects using the full TMDD model and dosing that mimicked typical Phase I and Phase II designs with rich sampling. Four population pharmacokinetic models were fitted to the free (unbound) drug and total (unbound and bound to the drug) S-target data: a one-target QSS model that simultaneously described the free drug and the total S-target (M1), a model with parallel linear and MM elimination that described the free drug combined with a separate S-target model that utilized the free drug concentrations but did not influence them (M2), a two-target QSS model where the S-target was described by the QSS approximation while the contribution of the M-target was described by the MM elimination term (M3), and a two-target full TMDD model (M4). The influence of relative contributions of the S and M-targets to target-mediated elimination on identifiability of the model parameters was investigated. The influence of assay sensitivity and availability of the total rather than free drug concentration measurements were also investigated. The results indicated that for the dosing regimens and system parameters investigated in this work the pharmacokinetic data alone did not allow to distinguish influences of the two targets. When the drug and S-target data were available, the model M1 described the data with the deficiencies of the fit visible only at the lowest dose level. However, the parameter estimates were strongly biased. The model M2 improved the fit and provided the precise estimates of the S-target parameters. However, no information concerning the M-target could be obtained from this model. The model M3 provided an excellent description of the data and the unbiased estimates of all the parameters. It also provided the unbiased estimates of change from baseline of the unobservable M-target concentrations. The models M1-M3 were robust while M4 was unstable despite the prohibitively long run time. The results were similar when the total rather than free drug was measured. The M-target parameters were estimated only when M-target elimination was at least comparable to S-target elimination. Improvement of the assay sensitivity has not resulted in marked improvement of the parameter estimates. In summary, for the cases investigated in this work the QSS approximation of the two-target TMDD model provided the unbiased and robust estimates of all the relevant TMDD parameters.

Management of ANCA-associated vasculitis: Current trends and future prospects

The antineutrophil cytoplasm antibody (ANCA)-associated vasculitides are a spectrum of heterogeneous autoimmune diseases characterized by necrotizing small vessel vasculitis and the presence of ANCA. These chronic multisystem disorders may be life-threatening if there is major organ involvement, such as acute renal failure or pulmonary hemorrhage, and require significant initial immunosuppression and long-term maintenance treatment. Long-established protocols using cyclophosphamide and prednisolone have resulted in dramatically improved outcomes for patients since the 1970s. Subsequently, international collaboration has contributed to a growing evidence base and consensus in the management of these rare disorders. Modifications to traditional treatment protocols by the use of azathioprine or methotrexate rather than cyclophosphamide, and the introduction of newer agents, such as rituximab, has maintained outcomes whilst decreasing toxicity. However, the treatment limitations of incomplete efficacy, infection, and cumulative toxicity persist. These issues have continued to drive the search for safer and more effective modulation of the immune system using targeted immunotherapy. This review will explore the current evidence base for management of ANCA-associated vasculitis and future treatment prospects.

[Atacicept: a new B lymphocyte-targeted therapy for multiple sclerosis]

Multiple sclerosis (MS) has traditionally been considered to be a T cell-mediated disease. However, there is an increasing body of evidence for the involvement of B cells and autoantibodies in the pathology of this disease, providing a rationale for treatment strategies directed against B cells. This paper summarizes the evidence for a key role of B cells in the immunopathology of MS and reviews data supporting the use of a novel B cell-targeted therapy, atacicept, for this condition. Atacicept is a human recombinant fusion protein that comprises the binding portion of a receptor for both BLyS (B Lymphocyte Stimulator) and APRIL (A PRoliferation-Inducing Ligand), two cytokines that have been identified as important regulators of B cell maturation, function and survival. Atacicept has shown selective effects on cells of the B cell lineage, acting on mature B cells and blocking plasma cells and late stages of B cell development while sparing B cell progenitors and memory cells. The efficacy of atacicept in animal models of autoimmune disease and the biological activity of atacicept in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) has been demonstrated. Ongoing clinical studies are investigating the safety, tolerability and efficacy of atacicept in patients with MS, SLE and RA.

Targeting B cells in immune-mediated inflammatory disease: a comprehensive review of mechanisms of action and identification of biomarkers

B cell-depletion therapy, particularly using anti-CD20 treatment, has provided proof of concept that targeting B cells and the humoral response may result in clinical improvements in immune-mediated inflammatory disease. In this review, the mechanisms of action of B cell-targeting drugs are investigated, and potential biomarkers associated with response to treatment in patients with autoimmune diseases are identified. Most available data relate to B cell depletion using anti-CD20 therapy (rituximab) in patients with rheumatoid arthritis (RA). Treatment leads to significant clinical benefit, but apparently fails to deplete long-lived plasma cells, and discontinuation is associated with relapse. Biomarkers commonly used in studies of B cell-targeted therapies include rheumatoid factor, anti-citrullinated peptide antibodies, and immunoglobulin (Ig) levels. More recently, there has been interest in markers such as B cell phenotype analysis, and B lymphocyte stimulator (BLyS)/a proliferation-inducing ligand (APRIL), the latter particularly in studies of the IgG Fc-transmembrane activator and CAML interactor (TACI) fusion protein (atacicept) and anti-BLyS therapy (belimumab). Data from clinical trials of B cell-depleting agents in RA suggest that specific autoantibodies, BLyS, APRIL, and circulating and synovial B lineage cell levels may have potential as biomarkers predictive of response to treatment. Further trials validating these markers against clinical outcomes in RA are required. In patients with systemic lupus erythematosus, Fc receptors and levels of circulating immune cells (including B cells and natural killer cells) may be relevant markers.

Synovial tissues concentrate secreted APRIL

INTRODUCTION

A proliferation-inducing ligand (APRIL) from the TNF family, owing to its role in the generation and survival of plasma cells (PCs), is currently targeted for rheumatoid arthritis (RA) treatment. However, little is known about APRIL expression in RA lesions, hampering our understanding of the way APRIL may modulate this autoimmune disease.

METHODS

We performed immunological staining of human normal, non-RA and RA synovial tissues with a pair of antibodies specifically recognizing APRIL-producing cells and secreted APRIL.

RESULTS

We detected significant amounts of secreted APRIL in normal synovium mostly concentrated around blood vessels and at the lining layer, but no cells producing APRIL. Meanwhile, we observed that blood neutrophils constitutively secrete APRIL, indicating that blood APRIL may diffuse into the synovium via its fenestrated vessels. Synovium from non-RA and RA patients retained similarly secreted APRIL, but in this case APRIL-producing cells, including neutrophils and macrophages, were present in the tissue. Notably, PCs--when present in RA synovium--accumulated in areas of APRIL retention, spreading from blood vessels towards the lining layer.

CONCLUSIONS

PCs accumulate in synovial zones rich in secreted APRIL, consistent with a pro-survival role of APRIL for PCs in RA. The concentration of APRIL by normal synovium indicates that this tissue may constitute a proper environment for PCs even before RA onset.

Anticytokine therapy impacting on B cells in autoimmune diseases

PURPOSE OF REVIEW

To evaluate the impact of particular anticytokine therapies able to indirectly target B cells with emphasis on the tumor necrosis factor (TNF) family members, B cell activating factor/B lymphocyte stimulator (BAFF/BLyS) and a proliferation-inducing ligand (APRIL).

RECENT FINDINGS

Although blockade of TNF/lymphotoxin by etanercept has been shown to have an impact on memory B cells, recent studies of inhibiting the TNF family members BAFF/BlyS or simultaneously blocking BAFF/BlyS and APRIL in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) clearly demonstrated biologic activity, including reductions of immunoglobulin levels. However, clear evidence of clinical activity by any of the compounds interfering with BAFF/BLys or APRIL has not yet been shown.

SUMMARY

Although anticytokine therapies mainly blocking signaling pathways of innate immunity, that is TNF-alpha, have shown efficacy in the treatment of arthritides and have partial effects on memory B cells, current studies evaluate effects on adaptive immunity by blocking BAFF/BlyS and/or APRIL which indirectly act on B and plasma cells.

Common variable immunodeficiency

Common variable immunodeficiency is the most prevalent clinically significant antibody deficiency at all ages. The disorder is defined principally by characteristic infection susceptibility with hypogammaglobulinemia and impaired-specific antibody response. Several recent large registry-based studies have defined distinct phenotypic subtypes. Several studies have also correlated specific immunologic markers with these phenotypes. The biochemical or genetic abnormality in the majority of patients remains unknown. Recently, several molecular genetic lesions have been defined. Among these, mutations of inducible costimulator, and CD19, appear to be disease causing by themselves. These account for about 1% of cases. Other mutations or polymorphisms, such as in the human homolog of Escherichia coli MutS 5 (MSH5), and transmembrane activator and calcium mobilizing ligand interactor, seem to be disease associated in 5-10% of patients, but may require additional immunologic abnormalities for full expression of the phenotype, as unaffected heterozygotes have also been described.