The role of Complement in Post-Transfusion Hemolysis and Hyperhemolysis Reaction

Study of the antigenic characteristics of red blood cells units and their sickle cell disease recipients and the G6PD activity of transfused red blood cells units

INTRODUCTION

Transfusion has a central place in the treatment of patients with sickle cell disease (SCD). Matching blood groups of red blood cell (RBC) units with the blood groups of the patient is essential to prevent alloimmunization and delayed hemolytic transfusion reaction. African ancestry donors have the best phenocompatibility with patients of the same origin, however their RBCs may present characteristic that can alter quality of the unit such as glucose-6-phosphate dehydrogenase (G6PD) deficiency. The objective is to analyze transfusion protocol, immunization rate and mismatch situations of SCD recipients and to evaluate the frequency of G6PD deficiency in RBCs units from African ancestry donors.

METHODS

Samples of units transfused to SCD patients were analyzed. Transfusion data were collected from institutional databases. The activity of G6PD was measured in the segment of the RBC units.

RESULTS

A total of 98 segments of units transfused to 37 SCD recipients in 41 transfusions episodes was collected. Among patients, 35.1% (n = 13) had no antibodies; 10.8% (n = 4) had antibodies against Fya/Fyb, Jka/Jkb, M/N, S/s; 21.6% (n = 8) against RH/K antigens. In all cases, the protocols were in line with the recommendations. G6PD deficiency was observed in 9 units, that were all collected from Afro-Caribbean donors.

CONCLUSION

The transfusion protocol is established to prevent immunological reactions due to disparities in blood group antigens between donors and SCD recipients. However, the units of African ancestry donors, which allowed the best compatibility, displayed a high rate of G6PD deficiency. The storage and recovery impact of this deficiency must be evaluated.

Eculizumab for management of hyperhemolysis syndrome in pediatric patients with sickle cell disease: A single-center case series

Chronic hemolytic anemia and vascular occlusion are hallmarks of sickle cell disease (SCD). Blood transfusions are critical for supportive and preventive management of SCD complications. Patients with SCD are at risk for hyperhemolysis syndrome (HHS), a subtype of delayed hemolytic transfusion reactions. HHS management includes intravenous immunoglobulin, corticosteroids, and avoidance of further transfusions. Not all patients respond to first-line agents. Eculizumab, which blocks terminal complement activation, has been proposed as second-line management of HHS. We describe two patients who received eculizumab for refractory HHS. In our experience, eculizumab is a safe and effective option for refractory pediatric HHS.

Expert consensus on the management of infusion-related reactions (IRRs) in patients with sickle cell disease (SCD) receiving crizanlizumab: a RAND/UCLA modified Delphi panel

Crizanlizumab, a monoclonal antibody against P-selectin, has been shown to reduce vaso-occlusive crises (VOCs) compared to placebo in patients ≥ 16 years with sickle cell disease (SCD). However, there have been rare reports of patients experiencing severe pain and subsequent complications within 24 hours of crizanlizumab infusions. These events are defined as infusion-related reactions (IRRs). Informed by current literature and clinical experience, a group of content experts developed clinical guidelines for the management of IRRs in patients with SCD. We used the RAND/University of California, Los Angeles (UCLA) modified Delphi panel method, a valid, reproducible technique for achieving consensus. We present our recommendations for managing IRRs, which depend on patient characteristics including: prior history of IRRs to other monoclonal antibodies or medications, changes to crizanlizumab infusion rate and patient monitoring, pain severity relative to patient's typical SCD crises, and severe allergic symptoms. These recommendations outline how to evaluate and manage IRRs in patients receiving crizanlizumab. Future research should validate this guidance using clinical data and identify patients at risk for these IRRs.

What is the role of complement in bystander hemolysis? Old concept, new insights

INTRODUCTION

Bystander hemolysis occurs when antigen-negative red blood cells (RBCs) are lysed by the complement system. Many clinical entities including passenger lymphocyte syndrome, hyperhemolysis following blood transfusion, and paroxysmal nocturnal hemoglobinuria are complicated by bystander hemolysis.

AREAS COVERED

The review provides data about the role of the complement system in the pathogenesis of bystander hemolysis. Moreover, future perspectives on the understanding and management of this syndrome are described.

EXPERT OPINION

Complement system can be activated via classical, alternative, and lectin pathways. Classical pathway activation is mediated by antigen-antibody (autoantibodies and alloantibodies against autologous RBCs, infectious agents) complexes. Alternative pathway initiation is triggered by heme, RBC microvesicles, and endothelial injury that is a result of intravascular hemolysis. Thus, C5b is formed, binds with C6-C9 compomers, and MAC (C5b-9) is formulated in bystander RBCs membranes, leading to cell lysis. Intravascular hemolysis, results in activation of the alternative pathway, establishing a vicious cycle between complement activation and bystander hemolysis. C5 inhibitors have been used effectively in patients with hyperhemolysis syndrome and other entities characterized by bystander hemolysis.

Cell-Penetrating and Enzyme-Responsive Peptides for Targeted Cancer Therapy: Role of Arginine Residue Length on Cell Penetration and In Vivo Systemic Toxicity

For the improved delivery of cancer therapeutics and imaging agents, the conjugation of cell-penetrating peptides (CPPs) increases the cellular uptake and water solubility of agents. Among the various CPPs, arginine-rich peptides have been the most widely used. Combining CPPs with enzyme-responsive peptides presents an innovative strategy to target specific intracellular enzymes in cancer cells and when combined with the appropriate click chemistry can enhance theranostic drug delivery through the formation of intracellular self-assembled nanostructures. However, one drawback of CPPs is their high positive charge which can cause nonspecific binding, leading to off-target accumulation and potential toxicity. Hence, balancing cell-specific penetration, toxicity, and biocompatibility is essential for future clinical efficacy. We synthesized six cancer-specific, legumain-responsive RnAANCK peptides containing one to six arginine residues, with legumain being an asparaginyl endopeptidase that is overexpressed in aggressive prostate tumors. When conjugated to Alexa Fluor 488, R1-R6AANCK peptides exhibited a concentration- and time-dependent cell penetration in prostate cancer cells, which was higher for peptides with higher R values, reaching a plateau after approximately 120 min. Highly aggressive DU145 prostate tumor cells, but not less aggressive LNCaP cells, self-assembled nanoparticles in the cytosol after the cleavage of the legumain-specific peptide. The in vivo biocompatibility was assessed in mice after the intravenous injection of R1-R6AANCK peptides, with concentrations ranging from 0.0125 to 0.4 mmol/kg. The higher arginine content in R4-6 peptides showed blood and urine indicators for the impairment of bone marrow, liver, and kidney function in a dose-dependent manner, with instant hemolysis and morbidity in extreme cases. These findings underscore the importance of designing peptides with the optimal arginine residue length for a proper balance of cell-specific penetration, toxicity, and in vivo biocompatibility.

A guide to complement biology, pathology and therapeutic opportunity

Complement has long been considered a key innate immune effector system that mediates host defence and tissue homeostasis. Yet, growing evidence has illuminated a broader involvement of complement in fundamental biological processes extending far beyond its traditional realm in innate immunity. Complement engages in intricate crosstalk with multiple pattern-recognition and signalling pathways both in the extracellular and intracellular space. Besides modulating host-pathogen interactions, this crosstalk guides early developmental processes and distinct cell trajectories, shaping tissue immunometabolic and regenerative programmes in different physiological systems. This Review provides a guide to the system-wide functions of complement. It highlights illustrative paradigm shifts that have reshaped our understanding of complement pathobiology, drawing examples from evolution, development of the central nervous system, tissue regeneration and cancer immunity. Despite its tight spatiotemporal regulation, complement activation can be derailed, fuelling inflammatory tissue pathology. The pervasive contribution of complement to disease pathophysiology has inspired a resurgence of complement therapeutics with major clinical developments, some of which have challenged long-held dogmas. We thus highlight major therapeutic concepts and milestones in clinical complement intervention.

Alloimmunization and hyperhemolysis in sickle cell disease

Alloimmunization against red blood cell antigens and delayed hemolytic transfusion reaction (DHTR) are major barriers to transfusion in sickle cell disease (SCD). In SCD, DHTR is a potentially life-threatening. Blood group polymorphism in SCD patients, who are of African ancestry and frequently exposed to antigens they do not carry; an inflammatory clinical state; and occasional transfusion in acute situations are risk factors for alloimmunization and DHTR. In patients at risk, the transfusion indication must be balanced against the risk of developing DHTR. However, when transfusion is absolutely necessary, protocols combining the prevention of exposure to immunogenic antigens with immunosuppressive treatments must be implemented, and patients should be carefully monitored during posttransfusion follow-up. This close monitoring makes it possible to diagnose hyperhemolysis as soon as possible; to avoid retransfusion, which can exacerbate hemolysis; and to administer specific treatments, such as anticomplement therapy, in severe cases. Finally, in patients with severe disease, hematopoietic stem cell transplantation may be indicated. However, transfusion is also required in this context, and its management is complex because these risks must be taken into account.

The ongoing challenge of RBC alloimmunization in the management of patients with sickle cell disease

RBC transfusion remains a cornerstone in the treatment of sickle cell disease (SCD). However, as with many interventions, transfusion of RBCs is not without risk. Allogeneic RBC exposure can result in the development of alloantibodies, which can make it difficult to find compatible RBCs for future transfusion and increases the likelihood of life-threatening complications. The development of RBC alloantibodies occurs when a patient's immune system produces alloantibodies against foreign alloantigens present on RBCs. Despite its longstanding recognition, RBC alloimmunization has increasingly become a challenge when caring for patients with SCD. The growing prominence of alloimmunization can be attributed to several factors, including expanded indications for transfusions, increased lifespan of patients with SCD, and inadequate approaches to prevent alloimmunization. Recognizing these challenges, recent observational studies and preclinical models have begun to elucidate the immune pathways that underpin RBC alloimmunization. These emerging data hold promise in paving the way for innovative prevention strategies, with the goal of increasing the safety and efficacy of RBC transfusion in patients with SCD who are most vulnerable to alloimmunization.

The Development and Consequences of Red Blood Cell Alloimmunization

While red blood cell (RBC) transfusion is the most common medical intervention in hospitalized patients, as with any therapeutic, it is not without risk. Allogeneic RBC exposure can result in recipient alloimmunization, which can limit the availability of compatible RBCs for future transfusions and increase the risk of transfusion complications. Despite these challenges and the discovery of RBC alloantigens more than a century ago, relatively little has historically been known regarding the immune factors that regulate RBC alloantibody formation. Through recent epidemiological approaches, in vitro-based translational studies, and newly developed preclinical models, the processes that govern RBC alloimmunization have emerged as more complex and intriguing than previously appreciated. Although common alloimmunization mechanisms exist, distinct immune pathways can be engaged, depending on the target alloantigen involved. Despite this complexity, key themes are beginning to emerge that may provide promising approaches to not only actively prevent but also possibly alleviate the most severe complications of RBC alloimmunization.

Long-term Use of Eculizumab for Prolonged Hemolysis Following a Delayed Hemolytic Transfusion Reaction in Pediatric Sickle Cell: A Case Report

Complement activation has been implicated in delayed hemolytic transfusion reaction (DHTR) in patients with sickle cell disease (SCD), and eculizumab has been reported as an effective treatment for patients with DHTR. Previously reported patients with SCD and DHTR responded well after a few doses of eculizumab. We report on the long-term use of eculizumab in a pediatric sickle cell patient with prolonged hemolysis of unknown etiology after a DHTR who had a slow and less sustained response. Long-term use of eculizumab in this young patient with SCD was successful with limited adverse effects.

Management of Hyperhemolysis in β-thalassemia With Multiple Immunosuppressives, Including Complement Blockade

Hyperhemolysis is a life-threatening condition of exaggerated hemolysis of red blood cells which occurs in patients receiving chronic transfusion therapy. We present a 19-year-old male with the β-thalassemia major with an episode of hyperhemolysis. Hemolysis was initially unresponsive to immunosuppression but responded after the addition of eculizumab. Several weeks after stabilization, hemolysis returned; which was also managed with immunosuppression and eculizumab. Hyperhemolysis presents significant challenges in β-thalassemia due to the underlying dysfunctional erythropoiesis and transfusion dependence. Aggressive immunosuppression combined with eculizumab successfully slowed the hemolysis and allowed for the resumption of transfusions.

Transfusion Reactions and Adverse Events

Blood transfusions are generally safe but can carry considerable risks. This review summarizes the different types of transfusion reactions and ways to diagnose and manage them. Symptoms are often overlapping and nonspecific. When a reaction is suspected, it is critical to stop the transfusion immediately and report the reaction to the blood bank, as this can affect the patient's outcome. New evidence-based algorithms of transfusion, newer blood screening methods and donor policies and deferrals, new laboratory testing, electronic verification systems, and improved hemovigilance lead to the avoidance of unnecessary transfusions and decrease the incidence of serious transfusion reactions.

Soluble Membrane Attack Complex: Biochemistry and Immunobiology

The soluble membrane attack complex (sMAC, a.k.a., sC5b-9 or TCC) is generated on activation of complement and contains the complement proteins C5b, C6, C7, C8, C9 together with the regulatory proteins clusterin and/or vitronectin. sMAC is a member of the MACPF/cholesterol-dependent-cytolysin superfamily of pore-forming molecules that insert into lipid bilayers and disrupt cellular integrity and function. sMAC is a unique complement activation macromolecule as it is comprised of several different subunits. To date no complement-mediated function has been identified for sMAC. sMAC is present in blood and other body fluids under homeostatic conditions and there is abundant evidence documenting changes in sMAC levels during infection, autoimmune disease and trauma. Despite decades of scientific interest in sMAC, the mechanisms regulating its formation in healthy individuals and its biological functions in both health and disease remain poorly understood. Here, we review the structural differences between sMAC and its membrane counterpart, MAC, and examine sMAC immunobiology with respect to its presence in body fluids in health and disease. Finally, we discuss the diagnostic potential of sMAC for diagnostic and prognostic applications and potential utility as a companion diagnostic.

Hyperhemolytic Transfusion Reaction in Non-Hemoglobinopathy Patients and Terminal Complement Pathway Activation: Case Series and Review of the Literature

Hyperhemolytic transfusion reaction (HHTR) is a severe, life-threatening hemolytic transfusion reaction where hemoglobin value after red blood cell (RBC) transfusion is lower than the pre-transfusion value. When HHTR occurs, mainly in patients with hemoglobinopathy, complement activation up to membrane attack complex (MAC) is strongly suspected. However, our knowledge of HHTR in patients without hemoglobinopathy is limited. In the present study, we retrospectively reviewed patients with the diagnosis of HHTR who were attended at our hospital between 2013 and 2016. We also performed a literature search to identify other reported cases of HHTR. Finally, the role of terminal complement pathway activation in the pathogenesis of HHTR was assessed by exposing endothelial cells in vitro to activated-patient plasma to analyze C5b-9 deposits by immunofluorescence. HHTR was diagnosed in 3 patients according to current criteria. Patients were treated with intravenous immunoglobulins (alone or in conjunction with rituximab and plasma exchange), and all of them recovered successfully. We retrieved from literature search 10 patients without hemoglobinopathy who developed HHTR. A marked increase of C5b-9 (MAC) deposition on endothelial cells (almost 2.5-fold increase versus control, P < .05) was observed with the plasma sample obtained from one of our patients. In conclusion, HHTR was a rare transfusion reaction that occurred in patients without hemoglobinopathy. We add more evidence that complement cascade activation up to MAC might play a role in the pathogenesis of HHTR.