Mechanisms of Intravenous Immunoglobulin Action in Immune Thrombocytopenic Purpura

Population Pharmacokinetics of Total Rabbit Anti-thymocyte Globulin in Non-obese Adult Patients Undergoing Hematopoietic Cell Transplantation for Hematologic Malignancy

BACKGROUND AND OBJECTIVES

Rabbit anti-thymocyte globulin (rATG), a therapeutic polyclonal antibody against human T cells, is commonly used in conditioning therapy prior to allogeneic hematopoietic cell transplantation (HCT). Previous studies successfully developed an individualized rATG dosing regimen based on "active" rATG population PK (popPK) analysis, while "total" rATG can be a more logistically favorable alternative for early HCT outcomes. We conducted a novel popPK analysis of total rATG.

METHODS

Total rATG concentration was measured in adult human-leukocyte antigen (HLA) mismatched HCT patients who received a low-dose rATG regimen (total 2.5-3 mg/kg) within 3 days prior to HCT. PopPK modeling and simulation was performed using nonlinear mixed effect modeling approach.

RESULTS

A total of 504 rATG concentrations were available from 105 non-obese patients with hematologic malignancy (median age 47 years) treated in Japan. The majority had acute leukemia or malignant lymphoma (94%). Total rATG PK was described by a two-compartment linear model. Influential covariate relations include ideal body weight [positively on both clearance (CL) and central volume of distribution], baseline serum albumin (negatively on CL), CD4+ T cell dose (positively on CL), and baseline serum IgG (positively on CL). Simulated covariate effects predicted that early total rATG exposures were affected by ideal body weight.

CONCLUSIONS

This novel popPK model described the PK of total rATG in the adult HCT patients who received a low-dose rATG conditioning regimen. This model can be used for model-informed precision dosing in the settings with minimal baseline rATG targets (T cells), and early clinical outcomes are of interest.

Alternatives for managing patients with newly diagnosed immune thrombocytopenia: a narrative review

INTRODUCTION

Primary immune thrombocytopenia (ITP) is an acquired bleeding disorder. Conventionally, first-line ITP therapy aims to obtain a rapid response and stop or decrease the risk of bleeding by increasing the platelet count. At this point, the duration of the response, the tolerability, and the long-term safety of pharmacologic interventions are considered less of a priority. Combination treatments that simultaneously address multiple disease mechanisms are an attractive strategy to increase efficacy in acute ITP therapy. In this review, we discuss the treatment of newly diagnosed ITP patients, emphasizing the use of new combinations to benefit from their synergy.

AREAS COVERED

This article summarizes conventional treatment, recent and novel combinations, and COVID-19 management recommendations of newly diagnosed ITP patients.

EXPERT OPINION

The key areas for improvement consider the long-term effects of conventional first-line therapy, reducing relapse rates, and extending responses to achieve long-term remission. Although corticosteroids remain first-line therapy, restricting their use to avoid toxicity and the increasing use of rituximab and TPO-RAs in the first three months after diagnosis open the landscape for future interventions in frontline therapy for ITP. First-line therapy intensification or synergistic drug combination offers a potential and realistic shift in future treatment guidelines.

Intravenous human immunoglobulin utilization patterns and cost analysis in a Malaysian tertiary referral hospital

Introduction

While intravenous human immunoglobulin therapy is potentially lifesaving for rare diseases, the significant costs associated with its usage warrant due attention. This study evaluated the costs and prescribing patterns of IVIg.

Methods

This was a retrospective analysis of medical records in a tertiary hospital. The evidence category IIA and below, as well as strength of recommendations level B and below were classified as lower evidence category and lower strength of recommendation, respectively. Patients’ demographic data, indications, dosing regimen, physician specialty were retrieved from medical records, while the cost was derived based on total prescribed doses.

Results

Out of 78 patients, more than half of the patients were prescribed with off-label IVIg based on MOHM Formulary (52, 66.7%), FDA indications (52, 66.7%) and EMA indications (46, 59.0%). 37 (47.4%) cases used IVIg for indications with lower evidence category and 52 (66.7%) cases with lower strength of recommendation. The total cost of IVIg use within the 2-year period was RM 695,426.36, with RM267,993.40 (38.5%) spent for indications with lower evidence category. Immunoglobulin use in rheumatology and neurology cases were associated with lower evidence category (p < 0.001).

Conclusions

A high proportion of off-label immunoglobulin use was observed. A timely update of prescribing policy, standardization of prescribing guidelines may promote appropriate immunoglobulin prescribing and justify expenses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40545-022-00430-2.

Splenectomy Outcomes in Relapsed or Refractory Immune Thrombocytopenia according to First-Line Intravenous Immunoglobulin Response

OBJECTIVES

Although splenectomy has long been second-line option for immune thrombocytopenia (ITP) patients, an indicator that reliably predicts the efficacy of splenectomy is still being explored. We investigated the treatment outcomes of splenectomy as a second-line therapy for relapsed/refractory ITP according to first-line intravenous immunoglobulin (IVIG) responses.

METHODS

Fifty-two adult patients treated with splenectomy as second-line therapy for ITP between 2009 and 2019 were included, and they were classified according to first-line IVIG responses (no response to IVIG: nonresponders; only transient IVIG response shorter than 4 weeks: poor responders; IVIG response for a longer period; stable responders). The efficacy of splenectomy was analyzed in the three subgroups.

RESULTS

Of the 52 patients, 10 were IVIG nonresponders, 34 were poor responders, and the remaining 8 were stable responders. Response to splenectomy was observed in 50.0% of IVIG nonresponders, 94.1% of poor responders, and 100% of stable responders (p = 0.0030). Among the 45 patients who responded to splenectomy, 51.1% relapsed subsequently, and a significantly lower relapse rate was noted in the stable IVIG responders (12.5%, p = 0.0220) than in nonresponders (60.0%) and poor responders (59.4%).

CONCLUSIONS

First-line IVIG response is indicated as a useful predictive factor for response to splenectomy.

Association between body mass index, dosing strategy, and efficacy of immune checkpoint inhibitors

Background

Increased body mass index (BMI) has been associated with improved response to immune checkpoint inhibitors (ICIs) in multiple cancer types. We evaluated associations between BMI, ICI dosing strategy, and clinical outcomes.

Methods

We abstracted clinical data on patients with cancer treated with ICI, including age, sex, cancer type, BMI, ICI type, dosing strategy (weight-based or fixed), radiographic response, overall survival (OS), and progression-free survival (PFS). We compared clinical outcomes between low-BMI and high-BMI populations using Kaplan-Meier curves, Cox regressions, and Pearson product-moment correlation coefficients.

Results

A total of 297 patients were enrolled, of whom 40% were women and 59% were overweight (BMI≥25). Of these, 204 (69%) received fixed and 93 (31%) received weight-based ICI dosing. In the overall cohort, overweight BMI was associated with improved PFS (HR 0.69; 95% CI 0.51 to 0.94; p=0.02) and had a trend toward improved OS (HR 0.77; 95% CI 0.57 to 1.04; p=0.08). For both endpoints, improved outcomes in the overweight population were limited to patients who received weight-based ICI dosing (PFS HR 0.53; p=0.04 for weight-based; vs HR 0.79; p=0.2 for fixed dosing) (OS HR 0.56; p=0.03 for weight-based; vs HR 0.89; p=0.54 for fixed dosing). In multivariable analysis, BMI was not associated with PFS or OS. However, the interaction of BMI≥25 and weight-based dosing had a trend toward association with PFS (HR 0.53; 95% CI 0.26 to 1.10; p=0.09) and was associated with OS (HR 0.50; 95% CI 0.25 to 0.99; p=0.05). Patients with BMI<25 tended to have better outcomes with fixed-dose compared with weight-based ICI, while patients with BMI≥25 tended to have better outcomes with weight-based ICI, although these differences did not achieve statistical significance. There was no association between radiographic response and BMI with fixed-dose ICI (p=0.97), but a near-significant trend with weight-based ICI (p=0.1). In subset analyses, the association between BMI, ICI dosing strategy, and clinical outcomes appeared limited to men.

Conclusions

The clinical benefit of ICI in high-BMI populations appears limited to individuals receiving weight-based ICI dosing. Further research into optimal ICI dosing strategies may be warranted.

In vivo blockade of mononuclear phagocyte system with solid nanoparticles: Efficiency and affecting factors

Smart nanomaterials, contrast nanoparticles and drug nanocarriers of advanced targeting architecture were designed for various biomedical applications. Most of such agents demonstrate poor pharmacokinetics in vivo due to rapid elimination from the bloodstream by cells of the mononuclear phagocyte system (MPS). One of the promising methods to prolong blood circulation of the nanoparticles without their modification is MPS blockade. The method temporarily decreases macrophage endocytosis in response to uptake of a low-toxic non-functional material. The effect of different factors on the efficiency of macrophage blockade in vivo induced by solid nanomaterials has been studied here. Those include: blocker nanoparticle size, ζ-potential, surface coating, dose, mice strain, presence of tumor or inflammation. We found that the blocker particle coating type had the strongest effect on MPS blockade efficiency, which allowed to prolong functional particle blood circulation half-life 18 times. The mechanisms capable of regulation of the MPS blockade have been demonstrated, which can promote application of this phenomenon in medicine for improving delivery of diagnostic and therapeutic nanomaterials.

Platelet Dysfunction Diseases and Conditions: Clinical Implications and Considerations

INTRODUCTION

Platelet diseases and dysfunction are taught early in medical school to all future physicians. Understanding of the coagulation cascade and hemostatic mechanisms has allowed for targeted pharmacological therapies that have been significantly impactful in clinical practice. Platelets are an early participant in hemostasis physiologically and under pathophysiological states.

METHODS

A review of literature involving platelet disfunction.

RESULTS

Various presentations of platelet diseases and dysfunction challenge clinicians and require a firm understanding of normal platelet function, drugs that mediate or modulate platelet effectiveness, and nonpharmacologic etiologies of platelet diseases and dysfunction with corresponding best practice treatment approaches.

CONCLUSION

This review summarizes normal and abnormal states associated with platelets and treatment strategies.

Relevance of the Materno-Fetal Interface for the Induction of Antigen-Specific Immune Tolerance

In humans, maternal IgGs are transferred to the fetus from the second trimester of pregnancy onwards. The transplacental delivery of maternal IgG is mediated by its binding to the neonatal Fc receptor (FcRn) after endocytosis by the syncytiotrophoblast. IgGs present in the maternal milk are also transferred to the newborn through the digestive epithelium upon binding to the FcRn. Importantly, the binding of IgGs to the FcRn is also responsible for the recycling of circulating IgGs that confers them with a long half-life. Maternally delivered IgG provides passive immunity to the newborn, for instance by conferring protective anti-flu or anti-pertussis toxin IgGs. It may, however, lead to the development of autoimmune manifestations when pathological autoantibodies from the mother cross the placenta and reach the circulation of the fetus. In recent years, strategies that exploit the transplacental delivery of antigen/IgG complexes or of Fc-fused proteins have been validated in mouse models of human diseases to impose antigen-specific tolerance, particularly in the case of Fc-fused factor VIII (FVIII) domains in hemophilia A mice or pre-pro-insulin (PPI) in the case of preclinical models of type 1 diabetes (T1D). The present review summarizes the mechanisms underlying the FcRn-mediated transcytosis of IgGs, the physiopathological relevance of this phenomenon, and the repercussion for drug delivery and shaping of the immune system during its ontogeny.

Understanding Fc Receptor Involvement in Inflammatory Diseases: From Mechanisms to New Therapeutic Tools

Fc receptors (FcRs) belong to the ITAM-associated receptor family. FcRs control the humoral and innate immunity which are essential for appropriate responses to infections and prevention of chronic inflammation or auto-immune diseases. Following their crosslinking by immune complexes, FcRs play various roles such as modulation of the immune response by released cytokines or of phagocytosis. Here, we review FcR involvement in pathologies leading notably to altered intracellular signaling with functionally relevant consequences to the host, and targeting of Fc receptors as therapeutic approaches. Special emphasis will be given to some FcRs, such as the FcαRI, the FcγRIIA and the FcγRIIIA, which behave like the ancient god Janus depending on the ITAM motif to inhibit or activate immune responses depending on their targeting by monomeric/dimeric immunoglobulins or by immune complexes. This ITAM duality has been recently defined as inhibitory or activating ITAM (ITAMi or ITAMa) which are controlled by Src family kinases. Involvement of various ITAM-bearing FcRs observed during infectious or autoimmune diseases is associated with allelic variants, changes in ligand binding ability responsible for host defense perturbation. During auto-immune diseases such as rheumatoid arthritis, lupus or immune thrombocytopenia, the autoantibodies and immune complexes lead to inflammation through FcR aggregation. We will discuss the role of FcRs in autoimmune diseases, and focus on novel approaches to target FcRs for resolution of antibody-mediated autoimmunity. We will finally also discuss the down-regulation of FcR functionality as a therapeutic approach for autoimmune diseases.

Efficacy and Safety of IQYMUNE®, a Ten Percent Intravenous Immunoglobulin in Adult Patients With Chronic, Primary Immune Thrombocytopenia

Background

Intravenous immunoglobulin (IVIG) IQYMUNE® is a highly purified 10% IVIG that was assessed using the new stringent definition of response described in the revised guideline on the clinical investigation of IVIG. The efficacy and the safety of IQYMUNE® were investigated in adult patients with chronic primary immune thrombocytopenia (ITP).

Methods

In this phase III multinational, multicentre, prospective, uncontrolled, open-label, single-arm study, adult patients with a baseline platelet count < 30 × 10⁹/L were treated with IVIG 10% at a dose of 2 g/kg body weight administered over 2 consecutive days. The primary endpoint was Response over the study period and was defined according to the recent and most stringent European Medicines Agency guidelines (platelet count ≥ 30 × 10⁹/L and a ≥ 2-fold increase from baseline, no new bleeding, and no concomitant treatment with drugs that affect platelet count and/or induce bleeding cessation).

Results

Thirty-eight patients were enrolled; 73 infusions were administered (38 on Day 1 and 35 on Day 2). Response was reached by 24 patients corresponding to 63.2% of patients in the full analysis set (95% CI: 46.0; 78.2) and 68.6% of patients in the per-protocol set (95% CI: 50.7; 83.1). The median time to Response was 1 day. The median duration of Response was 13.5 days. Reasons for non-response were failure to reach the required platelet count (n = 12), a new bleeding event (n = 1), and forbidden medication use (n = 1). Among the 23 patients with a baseline platelet count ≤ 20 × 10⁹/L, 19 patients (82.6%) achieved a platelet count ≥ 50 × 10⁹/L at least once before Day 5 (previous European Medicines Agency definition of response). Treatment was well tolerated even in patients with a high flow rate (≥ 6 mL/kg/h in 40% of patients). Headache (34.2%), pyrexia (15.8%), and creatinine renal clearance decrease, including one case of decrease in glomerular filtration rate (10.5%) were the most frequently reported drug-related adverse events.

Conclusions

Administration of IQYMUNE® for 2 consecutive days at a dose of 2 g/kg was safe and efficacious. These results support the treatment of adult patients with chronic ITP with IQYMUNE®.

Modulatory effect of intravenous immunoglobulin on Th17/Treg cell balance in women with unexplained recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is a growing problem worldwide. In a majority of cases, the cause remains unknown but there is increasing evidence that immunologic factors play an important role. Intravenous immunoglobulin (IVIg) therapy has been proposed to have immune modulatory effects and therefore been applicable for the treatment of patients with RSA. Although its efficacy is still controversial, several recent studies suggest that IVIg treatment may improve pregnancy outcomes. CD4⁺ T cells and their related cytokines play an important role in maternal-fetal immune regulation, and an imbalance of Th17/Treg cell ratio has been proposed as a cause for RSA. We review the scientific evidence supporting a modulatory effect of IVIg on Th17/Treg cell balance and discuss the potential mechanisms how IVIg might enhance Treg cells function. We propose that correction of Th17/Treg cell dysregulation could be one of the mechanisms that can explain the positive therapeutic effects of IVIg therapy. Consequently, selecting patients with abnormal Th17/Treg cell ratios could increase the success of IVIg therapy.

Understanding the in vivo fate of radioimmunoconjugates for nuclear imaging

Over the past 25 years, antibodies have emerged as extraordinarily promising vectors for the delivery of radionuclides to tumors for nuclear imaging. While radioimmunoconjugates often produce very high activity concentrations in target tissues, they also are frequently characterized by elevated activity concentrations in healthy organs as well. The root of this background uptake lies in the complex network of biological interactions between the radioimmunoconjugate and the subject. In this review, we seek to provide an overview of these interactions and thus paint a general picture of the in vivo fate of radioimmunoconjugates. To cover the entire story, we have divided our discussion into 2 parts. First, we will address the path of the entire radioimmunoconjugate as it travels through the body. And second, we will cover the fate of the radionuclide itself, as its course can diverge from the antibody under certain circumstances. Ultimately, our goal is to provide the nuclear imaging field with a resource covering these important-yet often underestimated-pathways.

Pharmacokinetics of Monoclonal Antibodies

Monoclonal antibodies (mAbs) have developed in the last two decades into the backbone of pharmacotherapeutic interventions in a variety of indications, with currently more than 40 mAbs approved by the US Food and Drug Administration, and several dozens more in clinical development. This tutorial will review major drug disposition processes relevant for mAbs, and will highlight product‐specific and patient‐specific factors that modulate their pharmacokinetic (PK) behavior and need to be considered for successful clinical therapy.

Immune Gamma Globulin Therapeutic Indications in Immune Deficiency and Autoimmunity

Immune gamma globulin (IgG) has a long history in the treatment of both primary immune deficiency and autoimmune disorders. Disease indications continue to expand and new-generation products increase the versatility of delivery. This review encompasses a historical perspective as well as current and future implications of human immune globulin for the treatment of immune-mediated illness.

Human IgGs induce synthesis and secretion of IgGs and neonatal Fc receptor in human umbilical vein endothelial cells

Human IgGs are increasingly used in the therapy of many different immune and inflammatory diseases, however their mechanism of action still remains unclear in most diseases. To gain insight into the mechanism by which IgGs might also exert their effects on endothelial cells, we tested human IgGs on human umbilical vein endothelial cells (HUVECs). IgGs induced a time-dependent increase in the synthesis and secretion of IgGs, together with a marked angiogenic-like transformation of HUVECs that was maximal after a 20-h incubation. IgGs stimulated IG gene transcription without affecting the process of gene rearrangement, already present in control HUVECs. The mechanism involved the activation of transcription factors with the increased expression of HSP90, HSP70 and inactive MMP-9 responsible for the phenotypic differentiation associated with the most intense IgG synthesis and secretion. However, even a short incubation with IgGs followed by recovery of cells was sufficient to trigger and sustain in time the synthesis and secretion of new IgGs, independently of the angiogenic-like transformation visible only when cells were continuously exposed to IgGs. Under the stimulus of IgGs, specific secretory pathways were also activated in HUVECs together with the expression of FcRn, which was always associated with IgGs of new synthesis, forming complexes that were also secreted. Our results disclose a so far unknown and unexpected mechanism of IgGs on HUVECs that behave as Ig-producing immune cells. Results might have relevance for the effects that IgGs also exert in vivo in physiological conditions.

A First-in-Human Study To Assess the Safety and Pharmacokinetics of Monoclonal Antibodies against Human Cytomegalovirus in Healthy Volunteers

Human cytomegalovirus (HCMV) can cause significant disease in immunocompromised patients and treatment options are limited by toxicities. CSJ148 is a combination of two anti-HCMV human monoclonal antibodies (LJP538 and LJP539) that bind to and inhibit the function of viral HCMV glycoprotein B (gB) and the pentameric complex, consisting of glycoproteins gH, gL, UL128, UL130, and UL131. Here, we evaluated the safety, tolerability, and pharmacokinetics of a single intravenous dose of LJP538 or LJP539 or their combination in healthy volunteers. Adverse events and laboratory abnormalities occurred sporadically with similar incidence between antibody and placebo groups and without any apparent relationship to dose. No subject who received antibody developed a hypersensitivity, infusion-related reaction or anti-drug antibodies. After intravenous administration, both LJP538 and LJP539 demonstrated typical human IgG1 pharmacokinetic properties, with slow clearances, limited volumes of distribution, and long terminal half-lives. The pharmacokinetic parameters were linear and dose proportional for both antibodies across the 50-fold range of doses evaluated in the study. There was no apparent impact on pharmacokinetics when the antibodies were administered alone or in combination. CSJ148 and the individual monoclonal antibodies were safe and well tolerated, with pharmacokinetics as expected for human immunoglobulin.

Targeting the Fc receptor in autoimmune disease

INTRODUCTION

The Fc receptors (FcRs) and their interactions with immunoglobulin and innate immune opsonins, such as C-reactive protein, are key players in humoral and cellular immune responses. As the effector mechanism for some therapeutic monoclonal antibodies, and often a contributor to the pathogenesis and progression of autoimmunity, FcRs are promising targets for treating autoimmune diseases.

AREAS COVERED

This review discusses the nature of different FcRs and the various mechanisms of their involvement in initiating and modulating immunocyte functions and their biological consequences. It describes a range of current strategies in targeting FcRs and manipulating their interaction with specific ligands, while presenting the pros and cons of these approaches. This review also discusses potential new strategies including regulation of FcR expression and receptor crosstalk.

EXPERT OPINION

FcRs are appealing targets in the treatment of inflammatory autoimmune diseases. However, there are still knowledge limitations and technical challenges, the most important being a better understanding of the individual roles of each of the FcRs and enhancement of the specificity in targeting particular cell types and specific FcRs.

Second-generation minimal physiologically-based pharmacokinetic model for monoclonal antibodies

Minimal physiologically-based pharmacokinetic (mPBPK) models provide a sensible modeling approach when fitting only plasma (or blood) data yielding physiologically-relevant PK parameters that may provide more practical value than parameters of mammillary models. We propose a second-generation mPBPK model specifically for monoclonal antibodies (mAb) by including (lumping) several essential components of mAb PK used in full PBPK models. These components include convection as the primary mechanism of antibody movement from plasma into tissues and return to plasma with interstitial fluid as the major extravascular distribution space. The model divides tissue spaces into two groups according to their vascular endothelial structure, leaky and tight, which consequently allows discernment of two types and general sites of distribution. This mPBPK model was applied to two mAbs in mice and ten mAbs with linear kinetics in humans. The model captured their plasma PK profiles well with predictions of concentrations in interstitial fluid for two types of tissues. Predictions of tissue concentrations for mAb 7E3 and 8C2 were consistent with actual measurements in mice, indicating the feasibility of this model in assessing extravascular distribution in the two categories of tissues. The vascular reflection coefficients (σ₁) of tight tissues (V(tight)) ranged 0.883-0.987 and coefficients (σ₂) for leaky tissues (V(leaky)) ranged 0.311 to 0.837. The plasma clearance (CL(p)) varied among the mAbs in humans from 0.0054 to 0.03 L/h. In addition, applying this model generates parameters for mAb transcapillary escape rates and assesses major sites of elimination. Four of ten mAbs exhibited better fitting statistics premised on elimination from interstitial fluid than from plasma. This approach allows comparisons of mAb PK when only plasma data are available, provides more realistic parameters and predictions than mammillary models, and may provide an intermediate step towards utilizing full PBPK models for mAbs.

Acute renal failure in a child with thrombocytopenic purpura caused by acute Epstein-Barr virus infection after treatment with anti-D immunoglobulin

Immune thrombocytopenia (ITP) in children is usually a benign, self-limiting disorder. An acute Epstein-Barr virus (EBV) infection usually causes atypical lymphocytosis and mild decrease in platelets. Severe thrombocytopenia is an extremely rare complication. Anti-D immunoglobulin has been used for treatment of ITP in Rh(D)-positive nonsplenectomized patients. Severe hemolysis and acute renal failure are extremely rare complications that may be aggravated by the presence of an acute EBV infection. It is believed that anti-D immunoglobulin triggers an unusual virus-induced immune response causing hemolysis. We present a 4-year-old girl with ITP caused by an acute EBV infection that developed acute kidney injury following treatment with anti-D immunoglobulin. The patient recovered completely from thrombocytopenia and renal dysfunction. Intravascular hemolysis and acute kidney injury are consistent with anti-D immunoglobulin mechanism of action. Pediatric patients treated with anti-D immunoglobulin for ITP should be closely monitored for signs and symptoms of hemolysis that may be aggravated by the presence of EBV infection leading to impaired renal function.

Use of intravenous immunoglobulin compared with standard therapy is associated with improved clinical outcomes in children with acute encephalitis syndrome complicated by myocarditis

Although an autoimmune mechanism has been postulated for acute encephalitis syndrome (AES) complicated by myocarditis, immunomodulatory treatment strategies are still under investigation. To study the role of intravenous immunoglobulin (IVIG) in AES complicated by myocarditis in children age 2-12 years. This nonrandomized study was conducted in a tertiary care teaching hospital from July 2008 to January 2010. A total of 83 consecutive children with AES complicated by myocarditis were enrolled. Diagnosis of myocarditis was based on clinical, electrocardiogram, and echocardiogram findings. Patients were allocated to the two groups based on the days of the week: Those presenting on Monday and Friday were allocated to IVIG treatment (group I), and those presenting on the other days of the week to standard care (group II). Group I (n = 26) patients received IVIG at a dose of 400 mg/kg/day for 5 days in addition to standard care. All baseline and outcome data were recorded prospectively in a prestructured performa. The primary outcomes were mortality and improvement of left-ventricular dysfunction. A total of 83 children were studied: 26 in group I and 57 in group II. The mean (SD) age of the enrolled children was 4.6 years (3.1). The baseline characteristics were comparable between the two groups. A viral etiology could be established in 14 children, with the 2 most common agents isolated being Coxackie virus and enterovirus. Mortality was lower in the IVIG group [n = 1 (3.8 %)] patients compared with the standard care group [n = 13 (22.8 %)] with a relative risk of 0.17 (95 % CI = 0.02, 1.22). The difference in mortality reached borderline significance (p = 0.05). At discharge, mean (SD) ejection fraction improved from 32.8 % (6.31 %) to 49.5 % (9.04 %) in group I patients, which was significantly greater than that of group II (p = 0.001). Use of IVIG seemed to have a beneficial effect in terms of improved clinical outcomes in children with AES complicated by myocarditis. Our findings need further validation before IVIG can be incorporated into the treatment protocol of these children.

Intravenous immunoglobulin does not increase FcγRIIB expression levels on monocytes in children with immune thrombocytopenia

Intravenous immunoglobulin (IVIG) produces a rapid and prolonged increase in the platelet counts of children with immune thrombocytopenia (ITP). The mechanism of IVIG efficacy in a murine model of ITP has been reported to operate through an IVIG-mediated increase in the expression of the inhibitory Fc receptor FcγRIIB(CD32B) on splenic macrophages. This investigation examined whether IVIG administration results in a similar increase in FcγRIIB expression on peripheral blood CD14(+) monocytes in 20 children with ITP. FcγRIIB expression on peripheral blood monocytes was measured by flow cytometry in ITP patients, before and after IVIG therapy, as well as in control subjects. Peripheral blood monocytes were labelled with fluorescent-specific antibodies. There were no significant differences in the absolute number of [corrected] CD14(+) CD32B(+) monocytes, and [corrected] the percentages of CD14(+) CD32B(+) cells in mononuclear cells or monocytes. [corrected]. We suggest that IVIG does not increase FcγRIIB expression in peripheral blood monocytes in children with ITP.

Pharmacokinetic models for FcRn-mediated IgG disposition

The objectives were to review available PK models for saturable FcRn-mediated IgG disposition, and to explore an alternative semimechanistic model. Most available empirical and mechanistic PK models assumed equal IgG concentrations in plasma and endosome in addition to other model-specific assumptions. These might have led to inappropriate parameter estimates and model interpretations. Some physiologically based PK (PBPK) models included FcRn-mediated IgG recycling. The nature of PBPK models requires borrowing parameter values from literature, and subtle differences in the assumptions may render dramatic changes in parameter estimates related to the IgG recycling kinetics. These models might have been unnecessarily complicated to address FcRn saturation and nonlinear IgG PK especially in the IVIG setting. A simple semimechanistic PK model (cutoff model) was developed that assumed a constant endogenous IgG production rate and a saturable FcRn-binding capacity. The FcRn-binding capacity was defined as MAX, and IgG concentrations exceeding MAX in endosome resulted in lysosomal degradation. The model parameters were estimated using simulated data from previously published models. The cutoff model adequately described the rat and mouse IgG PK data simulated from published models and allowed reasonable estimation of endogenous IgG turnover rates.

Monoclonal antibodies directed against human FcRn and their applications

The MHC class I-like Fc receptor (FcRn) is an intracellular trafficking Fc receptor that is uniquely responsible for the extended serum half-life of antibodies of the IgG subclass and their ability to transport across cellular barriers. By performing these functions, FcRn affects numerous facets of antibody biology and pathobiology. Its critical role in controlling IgG pharmacokinetics has been leveraged for the design of therapeutic antibodies and related biologics. FcRn also traffics serum albumin and is responsible for the enhanced pharmacokinetic properties of albumin-conjugated therapeutics. The understanding of FcRn and its therapeutic applications has been limited by a paucity of reliable serological reagents against human FcRn. Here, we describe the properties of a new panel of highly specific monoclonal antibodies (mAbs) directed against human FcRn with diverse epitope specificities. We show that this antibody panel can be used to study the tissue expression pattern of human FcRn, to selectively block IgG and serum albumin binding to human FcRn in vitro and to inhibit FcRn function in vivo. This mAb panel provides a powerful resource for probing the biology of human FcRn and for the evaluation of therapeutic FcRn blockade strategies.

A case of isoniazid-induced thrombocytopenia: recovery with immunoglobulin therapy

Treatment for a 51-year-old man with pulmonary tuberculosis was initiated with isoniazid, rifampicin, ethambutol, and pyrazinamide, and discontinued after 3 weeks because of skin rash and itchiness. Isoniazid monotherapy was restarted after 2 weeks. Two days later, the platelet count decreased from 150 to 4×10(3)/mm(3). Despite platelet transfusion and oral corticosteroid treatment, the platelet count did not recover. However, after a 2-day administration of intravenous immunoglobulin, the platelet count recovered to 209×10(3)/mm(3). This report describes a case of isoniazid-induced thrombocytopenia that was reversed with intravenous immunoglobulin, thus highlighting the efficacy of this treatment for this rare condition.

The neonatal Fc receptor (FcRn) is not required for IVIg or anti-CD44 monoclonal antibody–mediated amelioration of murine immune thrombocytopenia

To definitively determine whether the neonatal Fc receptor (FcRn) is required for the acute amelioration of immune thrombocytopenia (ITP) by IVIg, we used FcRn-deficient mice in a murine ITP model. Mice injected with antiplatelet antibody in the presence or absence of IVIg displayed no difference in platelet-associated IgG between FcRn deficient versus C57BL/6 mice. FcRn-deficient mice treated with high-dose (2 g/kg) IVIg or a low–dose (2 mg/kg) of an IVIg-mimetic CD44 antibody were, however, protected from thrombocytopenia to an equivalent extent as wild-type mice. To verify and substantiate the results found with FcRn-deficient mice, we used β2-microglobulin–deficient mice (which do not express functional FcRn) and found that IVIg or CD44 antibody also protected them from thrombocytopenia. These data suggest that for both high-dose IVIg as well as low-dose CD44 antibody treatment in an acute ITP model, FcRn expression is neither necessary nor required.

Enrichment of sialylated IgG by lectin fractionation does not enhance the efficacy of immunoglobulin G in a murine model of immune thrombocytopenia

Intravenous immunoglobulin G (IVIg) is widely used against a range of clinical symptoms. For its use in immune modulating therapies such as treatment of immune thrombocytopenic purpura high doses of IVIg are required. It has been suggested that only a fraction of IVIg causes this anti immune modulating effect. Recent studies indicated that this fraction is the Fc-sialylated IgG fraction. The aim of our study was to determine the efficacy of IVIg enriched for sialylated IgG (IVIg-SA (+)) in a murine model of passive immune thrombocytopenia (PIT). We enriched IVIg for sialylated IgG by Sambucus nigra agglutinin (SNA) lectin fractionation and determined the degree of sialylation. Analysis of IVIg-SA (+) using a lectin-based ELISA revealed that we enriched predominantly for Fab-sialylated IgG, whereas we did not find an increase in Fc-sialylated IgG. Mass spectrometric analysis confirmed that Fc sialylation did not change after SNA lectin fractionation. The efficacy of sialylated IgG was measured by administering IVIg or IVIg-SA (+) 24 hours prior to an injection of a rat anti-mouse platelet mAb. We found an 85% decrease in platelet count after injection of an anti-platelet mAb, which was reduced to a 70% decrease by injecting IVIg (p<0.01). In contrast, IVIg-SA (+) had no effect on the platelet count. Serum levels of IVIg and IVIg-SA (+) were similar, ruling out enhanced IgG clearance as a possible explanation. Our results indicate that SNA lectin fractionation is not a suitable method to enrich IVIg for Fc-sialylated IgG. The use of IVIg enriched for Fab-sialylated IgG abolishes the efficacy of IVIg in the murine PIT model.

Clinical ramifications of the MHC family Fc receptor FcRn

INTRODUCTION

Knowledge that antibodies of the IgG isotype have remarkably extended persistence in circulation and are able to pass through cell barriers has substantial implications. While it is well established that so-called neonatal Fc receptor, FcRn, acts throughout life to confer these unusual properties, its ramifications on clinical medicine and therapeutic uses are not broadly appreciated.

SCOPE

Here we discuss basic principles and gaps in understanding of FcRn, including its management of IgG antibodies and along with albumin, its impact on use and design of antibody-based therapeutics, and its genetics.

Pharmacokinetics and pharmacodynamics of monoclonal antibodies: concepts and lessons for drug development

Monoclonal antibodies (mAbs) have complex pharmacology; pharmacokinetics and pharmacodynamics depend on mAb structure and target antigen. mAbs targeting soluble antigens often exhibit linear pharmacokinetic behavior, whereas mAbs targeting cell surface antigens frequently exhibit nonlinear behavior due to receptor-mediated clearance. Where nonlinear kinetics exist, clearance can change due to receptor loss following repeated dosing and/or disease severity. mAb pharmacodynamics are often indirect, with delayed clinically relevant outcomes. This behavior provides challenges during clinical development; studies must be carefully planned to account for complexities specific to each agent. Selection of a starting dose for human studies can be difficult. Species differences in pharmacology need to be considered. Various metrics are available for scaling from animals to humans. Optimal dose selection should ensure uniform mAb exposure across all individuals. Traditional approaches such as flat dosing and variable dosing based upon body surface area or weight should be supported by pharmacokinetic and pharmacodynamic behavior, including target antigen and concurrent disease states. The use of loading doses or dose adjustments to improve clinical response is also a consideration. The evaluation of drug interactions requires innovative designs. Due to the pharmacokinetic properties of mAbs, interacting drugs may need to be administered for protracted periods. Consequently, population pharmacokinetic and pharmacodynamic model-based approaches are often implemented to evaluate mAb drug interactions.

Mechanisms of platelet recovery in ITP associated with therapy

Immune thrombocytopenia (ITP) is an autoimmune disease primarily characterized by increased clearance of auto-antibody-sensitized platelets by Fc-receptor-bearing macrophages in the spleen and liver. It has been classically accepted that antibody-mediated platelet destruction is Fc dependent. Recent studies, however, may also indicate the involvement of Fc-independent pathways of platelet destruction. Current treatment options work by immunosuppression (e.g., corticosteroids), immunomodulation (e.g., IVIg and anti-D), or removal of the platelet destruction site (splenectomy) in ITP. This review will discuss the mechanisms of action of these and other treatments for ITP.

Chapter 4: Multitasking by exploitation of intracellular transport functions the many faces of FcRn

The MHC Class I-related receptor, FcRn, transports antibodies of the immunoglobulin G (IgG) class within and across a diverse array of different cell types. Through this transport, FcRn serves multiple roles throughout adult life that extend well beyond its earlier defined function of transcytosing IgGs from mother to offspring. These roles include the maintenance of IgG levels and the delivery of antigen in the form of immune complexes to degradative compartments within cells. Recent studies have led to significant advances in knowledge of the intracellular trafficking of FcRn and (engineered) IgGs at both the molecular and cellular levels. The engineering of FcRn-IgG (or Fc) interactions to generate antibodies of increased longevity represents an area of active interest, particularly in the light of the expanding use of antibodies in therapy. The strict pH dependence of FcRn-IgG interactions, with binding at pH 6 that becomes essentially undetectable as near neutral pH is approached, is essential for efficient transport. The requirement for retention of low affinity at near neutral pH increases the complexity of engineering antibodies for increased half-life. Conversely, engineered IgGs that have gained significant binding for FcRn at this pH can be potent inhibitors of FcRn that lower endogenous IgG levels and have multiple potential uses as therapeutics. In addition, molecular studies of FcRn-IgG interactions indicate that mice have limitations as preclinical models for FcRn function, primarily due to cross-species differences in FcRn-binding specificity.

Monoclonal antibody pharmacokinetics and pharmacodynamics

More than 20 monoclonal antibodies have been approved as therapeutic drugs by the US Food and Drug Administration, and it is quite likely that the number of approved antibodies will double in the next 7-10 years. Antibody drugs show several desirable characteristics, including good solubility and stability, long persistence in the body, high selectivity and specificity, and low risk for bioconversion to toxic metabolites. However, many antibody drugs demonstrate attributes that complicate drug development, including very poor oral bioavailability, incomplete absorption following intramuscular or subcutaneous administration, nonlinear distribution, and nonlinear elimination. In addition, antibody administration often leads to an endogenous antibody response, which may alter the pharmacokinetics and efficacy of the therapeutic antibody. Antibodies have been developed for a wide range of disease conditions, with effects produced through a complex array of mechanisms. This article attempts to provide a brief overview of the main determinants of antibody pharmacokinetics and pharmacodynamics. Clinical Pharmacology & Therapeutics (2008); 84, 5, 548-558 doi:10.1038/clpt.2008.170.

Acute thrombocytopenia after liver transplant: role of platelet activation, thrombopoietin deficiency and response to high dose intravenous IgG treatment

BACKGROUND/AIMS

Thrombocytopenia is common after liver transplantation due to platelet sequestration secondary to hypersplenism. The aim of this study was to further investigate the causes of this condition, as well as the response of thrombocytopenia to high dose intravenous immunoglobulins.

METHODS

We retrospectively studied 73 patients who underwent liver transplantation. Out of these 73 patients, 27 had severe thrombocytopenia and were treated with high dose intravenous immunoglobulin. Additionally, we retrospectively studied 8 patients undergoing liver transplantation.

RESULTS

Our data suggest that splenomegaly is not the only factor responsible for thrombocytopenia after liver transplantion and two additional phenomena, namely, reduced platelet production due to reduced thrombopoietin levels and sustained platelets activation take part in the pathogenesis of this condition. The infusion of high dose immunoglobulins induced a safe, prompt, complete and persistent resolution of severe thrombocytopenia in more than 70% of patients.

CONCLUSIONS

Based on these findings, treatment with high dose intravenous immunoglobulins should be considered in the management of severe thrombocytopenia after liver transplant, although additional randomized trials are warranted.

Pharmacokinetic/pharmacodynamic modeling of IVIG effects in a murine model of immune thrombocytopenia

IVIG may achieve its beneficial effects in immune thrombocytopenia (ITP) patients via several mechanisms; however, little is known of the relative importance of various mechanisms associated with IVIG action in ITP. The purposes of this study were to develop a pharmacokinetic/pharmacodynamic (PK/PD) model relating an anti-platelet antibody, MWReg30, to platelet counts in a mouse model of sustained ITP, to use modeling to characterize effects of IVIG on MWReg30 elimination, and to use PK/PD modeling to assess the contribution of IVIG effects on MWReg30 disposition to the effects of IVIG on MWReg30-induced thrombocytopenia in mice. A pharmacokinetic model, based on the competitive occupancy of protective FcRn receptors, was used to characterize the effects of IVIG on MWReg30 pharmacokinetics. The relationships between MWReg30 plasma concentrations to MWReg30-induced thrombocytopenia, in the presence and absence of IVIG treatment, were characterized using an indirect response model. The pharmacokinetic model well-captured MWReg30 plasma concentration-time profiles, with and without administration of IVIG. The indirect response model accurately characterized the effects of IVIG on MWReg30-induced thrombocytopenia in mice. Using these models, it was estimated that 43 +/- 5% of overall effects of IVIG on MWReg30-induced thrombocytopenia in mice could be accounted for by the IVIG-mediated increases in MWReg30 clearance.

Antibody therapy (IVIG): evaluation of the use of genomics and proteomics for the study of immunomodulation therapeutics

BACKGROUND AND OBJECTIVES

Intravenous immunoglobulin (IVIG) is used for an increasingly diverse number of therapeutic applications as an immunomodulation drug. Although it has demonstrated therapeutic effectiveness, the mechanism of action of IVIG in these disorders is poorly understood; this lack of understanding complicates rational clinical application and reimbursement for 'off-label' use.

MATERIALS AND METHODS

Selected literature on the clinical use of IVIG as an immunomodulation drug is reviewed. We present a brief description of DNA microarray and protein microarray technology and the application of such technologies to the study of immune system cells. The several studies on the application of DNA microarray technology to study gene expression in response to IVIG are presented.

RESULTS

There is increasing data on the use of DNA microarray and protein microarray technology to study gene expression in immune system cells including T cells, B cells, macrophages, and leucocytes. There is less information on the effect of IVIG on gene expression in immune system cells. However, there is sufficient information available to suggest that this is a practical approach with the caveat that such work will require careful experimental design and clear definition of the normal population.

CONCLUSIONS

DNA and protein microarray assays can be used to (i) provide rational indications for the clinical use of IVIG, (ii) provide for specific analysis of raw material and end product IVIG in screening for content related to immunomodulation, and (iii) accelerate the development of next generation products which would be more focused and/or targeted therapeutics.

Limited effects of high-dose intravenous immunoglobulin (IVIG) treatment on molecular expression in muscle tissue of patients with inflammatory myopathies

OBJECTIVES

The study was conducted with the aim of achieving an improved understanding of the molecular mechanisms of high-dose intravenous immunoglobulin (IVIG) in inflammatory myopathies by investigating the effects on muscle function and immunological molecules in skeletal muscle of polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM) patients.

METHODS

Thirteen treatment-resistant patients, 6 PM, 4 DM, 2 IBM and 1 juvenile DM, were treated with 2 g/kg of IVIG, three times at monthly intervals. Functional Index in Myositis and serum creatinine kinase (CK) levels were determined, and muscle biopsies were performed before treatment and after the third IVIG infusion. Immunological molecules were also studied in biopsies taken 24-48 h after the first infusion.

RESULTS

Improved muscle function was observed in three patients (1 PM, 1 DM and 1 IBM) and CK levels decreased in five. T cells, macrophages, major histocompatibility complex (MHC) class I antigen on muscle fibres, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression and membranolytic attack complex (MAC) deposits on capillaries were present to an equal degree in biopsies before and after IVIG treatment. No correlation between the clinical response and molecular changes was found.

CONCLUSIONS

The clinical effects of high-dose IVIG on muscle function in patients with refractory inflammatory active myositis did not correspond to effects on any of the investigated molecules in our study. T cells, macrophages, phenotypical changes in muscle fibres and endothelial cell activation were still present after treatment. These observations question a role for IVIG as an immune-modulating therapy in patients with inflammatory myopathies.

The CD14+ CD16+ blood monocytes: their role in infection and inflammation

Blood monocyte subpopulations have been defined in man initially, and the two major types of monocytes are the CD14++ CD16- and the CD14+ CD16+ monocytes. These cells have been shown to exhibit distinct phenotype and function, and the CD14+ CD16+ were labeled proinflammatory based on higher expression of proinflammatory cytokines and higher potency in antigen presentation. The current review describes these properties, including the relationship to dendritic cells, and summarizes the host of publications about CD14+ CD16+ monocytes in inflammation and infectious disease in man, all of which suggest a crucial role of these cells in the disease processes. The review also covers the more recent description of homologues of these cells in other model species, which is expected to better define the role of monocyte subsets in disease.

Development and research in idiopathic thrombocytopenic purpura: an inflammatory and autoimmune disorder

Bleeding and isolated thrombocytopenia in idiopathic thrombocytopenic purpura (ITP) are phenomena of a transient or long-term disturbed immune response. Since 1980, ITP has become a model for targeted therapeutic immunomodulation with still unclear mechanisms of action. The systematic analysis of ITP aims to determine more clearly defined patient subgroups for targeted therapy and to explore the complex immune disturbances in this autoimmune disorder.

Kinetics of FcRn-mediated recycling of IgG and albumin in human: pathophysiology and therapeutic implications using a simplified mechanism-based model

The nonclassical MHC class-I molecule, FcRn, salvages both IgG and albumin from degradation. Here we introduce a mechanism-based kinetic model for human to quantify FcRn-mediated recycling of both ligands based on saturable kinetics and data from the literature using easily measurable plasma concentrations rather than unmeasurable endosomal concentrations. The FcRn-mediated fractional recycling rates of IgG and albumin were 142% and 44% of their fractional catabolic rates, respectively. Clearly, FcRn-mediated recycling is a major contributor to the high endogenous concentrations of these two important plasma proteins. While familial hypercatabolic hypoproteinemia is caused by complete FcRn deficiency, the hypercatabolic IgG deficiency of myotonic dystrophy could be explained, based on the kinetic analyses, by a normal number of FcRn with lowered affinity for IgG but normal affinity for albumin. A simulation study demonstrates that the plasma concentrations of IgG and albumin could be dynamically controlled by both FcRn-related and -unrelated parameters.

The role of intravenous immunoglobulin in the treatment of chronic heart failure

Chronic heart failure (HF), including both ischemic and idiopathic dilated cardiomyopathies, is accompanied by a dysregulated cytokine network characterized not only by a rise in inflammatory cytokines, but also by an inadequate elevation of anti-inflammatory mediators. This dysregulation has been implicated in the development and progression of chronic HF, and in the last decade, attempts have been made to modulate this persistent inflammation. Failure of anti-tumor necrosis factor therapy in HF has led to further interest in a more general immunomodulatory approach, directed against the inflammatory imbalance rather than one particular cytokine. Treatment with intravenous immunoglobulin (IVIg) may represent such a broad-based approach trying to restore the dysregulated cytokine network through various mechanisms such as Fc receptor blockade, neutralization of microbial antigens and superantigens and more direct anti-inflammatory effects on the cytokine network. However, although one randomized placebo-controlled study in patients with chronic HF showed that IVIg improved left ventricular ejection fraction, accompanied by anti-inflammatory net effects, IVIg had no effect in another placebo-controlled study examining the effect of this medication in recent-onset cardiomyopathy. So far, few patients have been included in clinical trials, and there is clearly a need for larger placebo-controlled mortality studies involving a diverse group of patients with regard to cause and severity of HF.