IgM-enriched human introvenous immunoglobulin strongly inhibits complement-dependent porcine cell cytotoxicity mediated by human xenoreactive antibodies

Multifaceted Tissue-Protective Functions of Polyvalent Immunoglobulin Preparations in Severe Infections-Interactions with Neutrophils, Complement, and Coagulation Pathways

Severe infections induce immune defense mechanisms and initial tissue damage, which produce an inflammatory neutrophil response. Upon dysregulation of these responses, inflammation, further tissue damage, and systemic spread of the pathogen may occur. Subsequent vascular inflammation and activation of coagulation processes may cause microvascular obstruction at sites distal to the primary site of infection. Low immunoglobulin (Ig) M and IgG levels have been detected in patients with severe infections like sCAP and sepsis, associated with increased severity and mortality. Based on Ig's modes of action, supplementation with polyvalent intravenous Ig preparations (standard IVIg or IgM/IgA-enriched Ig preparations) has long been discussed as a treatment option for severe infections. A prerequisite seems to be the timely administration of Ig preparations before excessive tissue damage has occurred and coagulopathy has developed. This review focuses on nonclinical and clinical studies that evaluated tissue-protective activities resulting from interactions of Igs with neutrophils, complement, and the coagulation system. The data indicate that coagulopathy, organ failure, and even death of patients can possibly be prevented by the timely combined interactions of (natural) IgM, IgA, and IgG with neutrophils and complement.

A new hope? Possibilities of therapeutic IgA antibodies in the treatment of inflammatory lung diseases

Inflammatory lung diseases represent a persistent burden for patients and the global healthcare system. The combination of high morbidity, (partially) high mortality and limited innovations in the last decades, have resulted in a great demand for new therapeutics. Are therapeutic IgA antibodies possibly a new hope in the treatment of inflammatory lung diseases? Current research increasingly unravels the elementary functions of IgA as protector against infections and as modulator of overwhelming inflammation. With a focus on IgA, this review describes the pathological alterations in mucosal immunity and how they contribute to chronic inflammation in the most common inflammatory lung diseases. The current knowledge of IgA functions in the circulation, and particularly in the respiratory mucosa, are summarized. The interplay between neutrophils and IgA seems to be key in control of inflammation. In addition, the hurdles and benefits of therapeutic IgA antibodies, as well as the currently known clinically used IgA preparations are described. The data highlighted here, together with upcoming research strategies aiming at circumventing the current pitfalls in IgA research may pave the way for this promising antibody class in the application of inflammatory lung diseases.

The first clinical pig heart transplant: Was IVIg or pig cytomegalovirus detrimental to the outcome?

The clinical course of the first patient to receive a gene-edited pig heart transplant was recently reported by the University of Maryland team. Although the pig heart functioned well for >40 days, serum anti-pig antibodies then increased, and the patient sadly died after 60 days. Because of his debilitated pre-transplant state, the patient never thrived despite excellent graft function for several weeks, and the cause of his demise continues to be uncertain. A few days before an increase in anti-pig antibodies was observed, the patient had received intravenous human immunoglobulin (IVIg), and whether this played a role in his cardiac deterioration has been discussed. Furthermore, mcfDNA testing indicated an increase in pig cytomegalovirus (CMV), and its possible role in the development of cardiac dysfunction has also been considered. On the basis of the limited data provided in the publication and on our previous investigations into whether IVIg contains anti-TKO pig antibodies and therefore might be deleterious to TKO pig organ xenografts, we suggest that the steady rise in anti-pig antibody titer was more consistent with the failure of the immunosuppressive regimen to prevent elicited anti-TKO pig antibody production, rather than from the passive transfusion of IVIg or the presence of pig CMV in the graft. Although the outcome of the Maryland experience was disappointing, valuable lessons were learned. Our attention was drawn to the potential risks of heart transplantation in a "deconditioned" patient, the administration of IVIg, the transmission of pig CMV, and of the difficulties in interpreting myocardial biopsy findings.

The Dual Role of a Polyvalent IgM/IgA-Enriched Immunoglobulin Preparation in Activating and Inhibiting the Complement System

Activation of the complement system is important for efficient clearance of a wide variety of pathogens via opsonophagocytosis, or by direct lysis via complement-dependent cytotoxicity (CDC). However, in severe infections dysregulation of the complement system contributes to hyperinflammation. The influence of the novel IgM/IgA-enriched immunoglobulin preparation trimodulin on the complement pathway was investigated in in vitro opsonophagocytosis, binding and CDC assays. Immunoglobulin levels before and after trimodulin treatment were placed in relation to complement assessments in humans. In vitro, trimodulin activates complement and induces opsonophagocytosis, but also interacts with opsonins C3b, C4b and anaphylatoxin C5a in a concentration-dependent manner. This was not observed for standard intravenous IgG preparation (IVIg). Accordingly, trimodulin, but not IVIg, inhibited the downstream CDC pathway and target cell lysis. If applied at a similar concentration range in healthy subjects, trimodulin treatment resulted in C3 and C4 consumption in a concentration-dependent manner, which was extended in patients with severe community-acquired pneumonia. Complement consumption is found to be dependent on underlying immunoglobulin levels, particularly IgM, pinpointing their regulative function in humans. IgM/IgA provide a balancing effect on the complement system. Trimodulin may enhance phagocytosis and opsonophagocytosis in patients with severe infections and prevent excessive pathogen lysis and release of harmful anaphylatoxins.

Approaches for Controlling Antibody-Mediated Allograft Rejection Through Targeting B Cells

Both acute and chronic antibody-mediated allograft rejection (AMR), which are directly mediated by B cells, remain difficult to treat. Long-lived plasma cells (LLPCs) in bone marrow (BM) play a crucial role in the production of the antibodies that induce AMR. However, LLPCs survive through a T cell-independent mechanism and resist conventional immunosuppressive therapy. Desensitization therapy is therefore performed, although it is accompanied by severe side effects and the pathological condition may be at an irreversible stage when these antibodies, which induce AMR development, are detected in the serum. In other words, AMR control requires the development of a diagnostic method that predicts its onset before LLPC differentiation and enables therapeutic intervention and the establishment of humoral immune monitoring methods providing more detailed information, including individual differences in the susceptibility to immunosuppressive agents and the pathological conditions. In this study, we reviewed recent studies related to the direct or indirect involvement of immunocompetent cells in the differentiation of naïve-B cells into LLPCs, the limitations of conventional methods, and the possible development of novel control methods in the context of AMR. This information will significantly contribute to the development of clinical applications for AMR and improve the prognosis of patients who undergo organ transplantation.

Effect of intravenous immunoglobulin (IVIg) on primate complement-dependent cytotoxicity of genetically engineered pig cells: relevance to clinical xenotransplantation

Triple-knockout (TKO) pigs may be ideal sources of organs for clinical xenotransplantation because many humans have no preformed antibody to TKO pig cells. Intravenous immunoglobulin (IVIg) is widely used for severe infection or the treatment/prevention of antibody-mediated rejection in allotransplantation. Anti-pig antibodies in IVIg could be harmful in clinical xenotransplantation. It is unknown whether anti-TKO pig antibodies are present in IVIg. The main aim of this study was to investigate in vitro whether IVIg contains anti-TKO pig antibodies with cytotoxic effect to pig cells. Undiluted pooled human serum (HS) and five different commercial preparations of IVIg were tested for IgM and IgG binding to red blood cells (RBCs) from wild-type (WT), α1,3-galactosyltransferase gene-knockout (GTKO), and TKO pigs by flow cytometry. Complement-dependent lysis of IVIg against these pig pRBCs was measured by hemolytic assay. Pooled HS and 4 of 5 IVIg commercial preparations contained anti-pig IgG that bound to WT and GTKO pRBCs, but not to TKO pRBCs. One preparation of IVIg contained antibodies that bound to TKO pRBCs, but there was no cytotoxicity of IVIg to TKO pRBCs. The results suggest that IVIg administration to human recipients of TKO pig grafts would be safe. However, the specific preparation of IVIg would need to be screened before its administration.

Influence of the serum levels of immunoglobulins on clinical outcomes in medical intensive-care patients

INTRODUCTION

Endogenous immunoglobulins (Igs) are of fundamental importance in the host defense after microbial infections. However, the therapeutic administration of intravenous IgG (IVIgG) has not yet been shown to improve clinical outcomes in patients suffering from sepsis, and in the case of IgM-containing preparations (IVIgGMA) the positive evidence is only weak. Recently published studies implicate that Ig levels on admission could have an impact on the patient's response to IVIg treatment and on outcomes of critically ill patients.

METHODS

In this noninterventional study, the serum levels of IgG, IgM, and IgA were determined in 340 medical patients on ICU admission, and clinical outcomes were prospectively recorded (ICU mortality, need for renal replacement therapy (RRT), need for mechanical ventilation, substitution of coagulation factors, and amount of red cell transfusions). Patients were prospectively grouped according to their main reason for ICU admission (sepsis, respiratory failure, cardiovascular diseases, acute renal failure, postoperative condition, state after cardiopulmonal resuscitation, gastrointestinal diseases, and others).

RESULTS AND DISCUSSION

There was no correlation between the Ig levels on admission and ICU mortality neither in the total cohort of medical ICU patients nor in any prespecified subgroup. However, in a logistic regression model that was adjusted for APACHE II score on admission, an increase in serum IgG was associated with a reduced need for mechanical ventilation in patients suffering from cardiovascular disease. On the other hand, in patients suffering from sepsis, an increased level of IgM was linked to an increased administration of coagulation factors.

CONCLUSION

Our data do not support the hypothesis that serum levels of immunoglobulins are linked to mortality in medical ICU patients.

Intravenous immunoglobulins--understanding properties and mechanisms

High-dose intravenous immunoglobulin (IVIg) preparations are used currently for the treatment of autoimmune or inflammatory diseases. Despite numerous studies demonstrating efficacy, the precise mode of action of IVIg remains unclear. Paradoxically, IgG can exert both pro- and anti-inflammatory activities, depending on its concentration. The proinflammatory activity of low-dose IVIg requires complement activation or binding of the Fc fragment of IgG to IgG-specific receptors (FcgammaR) on innate immune effector cells. In contrast, when administered in high concentrations, IVIg has anti-inflammatory properties. How this anti-inflammatory effect is mediated has not yet been elucidated fully, and several mutually non-exclusive mechanisms have been proposed. This paper represents the proceedings of a session entitled 'IVIg--Understanding properties and mechanisms' at the 6th International Immunoglobulin Symposium that was held in Interlaken on 26-28 March 2009. The presentations addressed how IgG may affect the cellular compartment, evidence for IVIg-mediated scavenging of complement fragments, the role of the dimeric fraction of IVIg, the anti-inflammatory properties of the minor fraction of sialylated IgG molecules, and the genetic organization and variation in FcgammaRs. These findings demonstrate the considerable progress that has been made in understanding the mechanisms of action of IVIgs, and may influence future perspectives in the field of Ig therapy.

Monoclonal anti-A antibody removal by synthetic A antigen immobilized on specific antibody filters

Removal of blood group anti-A and anti-B antibodies can prevent hyperacute organ rejection in ABO-incompatible transplantation. We are developing an extracorporeal-specific antibody filter (SAF) as an immunoadsorption device for direct removal of ABO blood group antibodies from whole blood, without the need for plasma separation and plasma exchange. A hollow fiber-based small scale SAF (mini-SAF) device was fabricated and synthetic A antigen, Atrisaccharide (Atri) conjugated to activated polyacrylic acid, was immobilized on the fiber lumen surface. Monoclonal antibody anti-A IgM were specifically removed up to 70% of initial antibodies using mini-SAF device. The monoclonal anti-A capture experiments on mini-SAF indicated that antibody removal relative to the initial concentration is independent of inlet concentration in the beginning; however, as the surface starts saturating with bound antibodies, removal becomes dependent on inlet concentration. No significant effect of flow rate on removal rate was observed. The radial diffusion and axial convection-based mathematical model developed for unsteady state antibody removal was in good agreement with the experimental data and showed that the antibody removal rate can be maximized by increasing the antibody-binding capacity of the SAF.

The efficacy of CD40 ligand blockade in discordant pig-to-rat islet xenotransplantation is correlated with an immunosuppressive effect of immunoglobulin

BACKGROUND

The authors' aim was to evaluate the efficacy of immunosuppression with monoclonal anti-CD40 ligand antibodies (aCD40L) or nonspecific polyclonal intravenous immunoglobulin (IVIG) in the pig-to-rat islet xenotransplantation model.

METHODS

Fetal porcine islet-like cell clusters were transplanted under the kidney capsule of nondiabetic rats. All antibodies were administered alone or in combination with cyclosporine A (CsA). In addition, some animals were administered antibodies plus tacrolimus (TAC) or sirolimus (SIR). Twelve days after transplantation, islet xenograft survival and rejection were evaluated using immunohistochemistry.

RESULTS

aCD40L plus CsA had a pronounced inhibitory effect on islet xenograft rejection for up to 12 days after transplantation. Unexpectedly, treatment with a monoclonal control antibody (anti-keyhole limpet hemocyanin [aKLH]) plus CsA had a similar inhibitory effect. Furthermore, a similar inhibition of islet xenograft rejection was observed also in animals administered IVIG plus CsA. Monotherapy with aCD40L, aKLH, IVIG, or CsA had no effect on the rejection process. Also, when aCD40L or aKLH was administered together with TAC, islet xenograft rejection was inhibited. There was no marked difference compared with rats treated with aCD40L or aKLH and CsA. Immunosuppression with aCD40L or aKLH in combination with SIR also inhibited pig-to-rat islet xenograft rejection, but the protective effect was not as pronounced.

CONCLUSIONS

Immunosuppression with high doses of antibodies, monoclonal or polyclonal, in combination with CsA or TAC inhibits pig-to-rat islet xenograft rejection. No specific effect of co-stimulatory blockade with aCD40L could be observed. Instead, the results indicate a nonspecific immunosuppressive effect of high doses of antibodies in this model.

ABO histo-blood group system-incompatible allografting

Most of the 29 blood group systems known today are not restricted to erythroid tissues hence their more recent identification as histo-blood group systems. Beyond the uncontested importance of the HLA system in human allograft survival, some of the histo-blood group systems might increasingly become recognised to play a role in graft-host interaction and peritransplant transfusion therapy. At least the ABO histo-blood group system has drawn a lot of interest since both, elective ABO-mismatch with living kidney donor/recipient pairs and infant heart recipients have been described as radical, but effective treatments of end-stage organ dysfunction. More recently, at least in part successful efforts to overcome unintentional ABO-mismatched lung and heart grafts spark interest in more precisely avoiding hyperacute transplant rejection due to complement-activating anti-A/B antibodies of the recipients. Such options as to prepare the recipient with plasma exchange and following him up with polyspecific intravenous immunoglobulins, monoclonal antibodies and targeted immunosuppression using mycophenolate, rabbit antithymocyte globulin and anti-CD20 antibody rituximab are bound to efficiently remove anti-A/B antibodies and apparently inhibit their resynthesis. The present contribution overviews recently acquired knowledge on the ABO histo blood group system and the role it plays in solid organ transplantation leant against a patient observed at our institution.

Immunoglobulin M-enriched intravenous immunoglobulin inhibits classical pathway complement activation, but not bactericidal activity of human serum

Acute or even hyperacute humoral graft rejection, mediated by classical pathway complement activation, occurs in allo- and xenotransplantation due to preformed anti-graft antibodies. Intravenous immunoglobulin (IVIg) preparations can prevent complement-mediated tissue injury and delay hyperacute xenograft rejection. It is known that IgM-enriched IVIg (IVIgM) has a higher capacity to block complement than IVIgG. Different IVIgs were therefore tested for specificity of complement inhibition and effect on anti-bacterial activity of human serum. IVIgM-I (Pentaglobin), 12% IgM), IVIgM-II (IgM-fraction of IVIgM-I, 60% IgM), and three different IVIgG (all >95% IgG) were used. The known complement inhibitor dextran sulfate was used as control. Hemolytic assays were performed to analyze pathway-specificity of complement inhibition. Effects of IVIg on complement deposition on pig cells and Escherichia coli were assessed by flow cytometry and cytotoxicity as well as bactericidal assays. Complement inhibition by IVIgM was specific for the classical pathway, with IC50 values of 0.8 mg/ml for IVIgM-II and 1.7 mg/ml for IVIgM-I in the CH50 assay. Only minimal inhibition of the lectin pathway was seen with IVIgM-II (IC50 15.5 mg/ml); no alternative pathway inhibition was observed. IVIgG did not inhibit complement in any hemolytic assay. Classical pathway complement inhibition by IVIgM was confirmed in an in vitro xenotransplantation model with PK15 cells. In contrast, IVIgM did not inhibit (mainly alternative pathway mediated) killing of E. coli by human serum. In conclusion, IgM-enriched IVIg is a specific inhibitor of the classical complement pathway, leaving the alternative pathway intact, which is an important natural anti-bacterial defense, especially for immunosuppressed patients.