The cause and pathogenesis of hemolytic transfusion reactions in sickle-cell disease

Harnessing the potential of red blood cells in immunotherapy

Red blood cell (RBC) transfusion represents one of the earliest and most widespread forms of cellular therapy. While the primary purpose of RBC transfusions is to enhance the oxygen-carrying capacity of the recipient, RBCs also possess unique properties that make them attractive vehicles for inducing antigen-specific immune tolerance. Preclinical studies have demonstrated that RBC transfusion alone, in the absence of inflammatory stimuli, often fails to elicit detectable alloantibody formation against model RBC antigens. Several studies also suggest that RBC transfusion without inflammation may not only fail to generate a detectable alloantibody response but can also induce a state of antigen-specific non-responsiveness, a phenomenon potentially influenced by the density of the corresponding RBC alloantigen. The unique properties of RBCs, including their inability to divide and their stable surface antigen expression, make them attractive platforms for displaying exogenous antigens with the goal of leveraging their ability to induce antigen-specific non-responsiveness. This could facilitate antigen presentation to the host's immune system without triggering innate immune activation, potentially enabling the induction of antigen-specific tolerance for therapeutic applications in autoimmune disorders, preventing immune responses against protein therapeutics, or reducing alloreactivity in the setting of transfusion and transplantation.

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.

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.

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.

Impact of HLA-G +3142C>G on the development of antibodies to blood group systems other than the Rh and Kell among sensitized patients with sickle cell disease

BACKGROUND

Patients' inflammatory history is an important factor underlying red blood cell (RBC) alloimmunization, which is a frequent transfusion complication among individuals with sickle cell disease (SCD). HLA-G has been associated with different inflammatory and auto - immune diseases. Our goal was to verify whether the HLA-G + 3142 C>G and 14-bp Ins/Del variations are associated with RBC antibody development among SCD patients.

METHODS

This was a single-center case-control study. SCD patients were randomly selected for the study and divided into two groups: 'Alloimmunized' and 'Nonalloimmunized' depending on the presence of irregular antibodies. The 'Alloimmunized'group was further divided into two subgroups according to the presence of only antibodies against the Rh and Kell blood group systems or the existence of antibodies to antigens of the other blood group systems.

RESULTS

A total of 213 patients were included in the study (110 alloimmunized and 103 non-alloimmunized). The 'Alloimmunized' and 'Non-alloimmunized' groups did not differ statistically regarding the HLA-G + 14 bp Ins/Del ( p = 0.494) and + 3142 C>G ( p = 0.334). Individuals who had only antibodies against the Rh and Kell antigens had a frequency of HLA-G + 3142GG genotype almost twice as high compared to the groupwith antibodies against less immunogenic antigens ( p = 0.043).

CONCLUSIONS

The genotype frequency of HLA-G + 3142 C>G differs among alloimmunized SCD patients, depending on the presence of antibodies against low immunogenic RBC antigens. This highlights a possible role played by the HLA-G molecule in the RBC alloimmunization process.

Indications for transfusion in the management of sickle cell disease

The transfusion of red blood cells (RBCs) is a crucial treatment for sickle cell disease (SCD). While often beneficial, the frequent use of transfusions is associated with numerous complications. Transfusions should be offered with specific guidelines in mind. Here we present updates to the indications for transfusion of RBCs in SCD. We review recent publications and include expert perspectives from hematology and transfusion medicine. For some clinical indications, such as ischemic stroke, the role of transfusion has been well studied and can be applied almost universally. For many other clinical scenarios, the use of transfusion therapy has less conclusive data and therefore must be tailored to individual needs. We highlight the roles of RBC transfusions in preventing or mitigating neurological disease, in reducing perioperative complications, in managing acute chest syndrome, and in optimizing pregnancy outcomes in SCD. We further highlight various transfusion techniques and when each might be considered. Potential complications of transfusion are also briefly discussed.

Novel concepts in red blood cell clearance

PURPOSE OF REVIEW

Red blood cell (RBC) clearance has been studied for decades in many different pathologies, which has revealed different routes of RBC degradation, depending on the situation. This review summarizes the latest mechanistic insights on RBC clearance in different contexts; during homeostatic removal, immune-mediated destruction, and systemic inflammation.

RECENT FINDINGS

Besides the recognition of a variety of potential 'eat me' signals on RBCs, recent evidence suggests that normal RBC degradation is driven by the increase of the adhesive properties of RBCs, mediating the retention in the spleen and leading to RBC hemolysis. Furthermore, immune-mediated degradation of RBCs seems to be fine-tuned by the balance between the density of the antigens expressed on RBCs and the presence of 'don't eat me' signals. Moreover, besides RBC clearance by macrophages, neutrophils seem to play a much more prominent role in immune-mediated RBC removal than anticipated. Lastly, RBC clearance during systemic inflammation appears to be driven by a combination of extreme macrophage activity in response to proinflammatory cytokines as well as direct damage of RBC by the inflammation or inflammatory agent.

SUMMARY

Recent studies on RBC clearance have expanded our knowledge on their destruction in different contexts.

Hyperhaemolytic transfusion reaction in two β-thalassaemia major patients: The role of eculizumab

WHAT IS KNOWN AND OBJECTIVE

Hyperhaemolytic transfusion reactions are rare life-threatening events predominantly affecting patients with haemoglobinopathies. We report two cases in β-thalassaemia major patients on chronic transfusion therapy and highlight the role of eculizumab in its management.

CASE SUMMARY

Patient 1 presented with intravascular haemolysis on day 7 (D7) post-transfusion and responded to treatment with corticosteroids and intravenous immunoglobulin. However, patient 2 presented with severe symptomatic anaemia (D4 post-transfusion) unresponsive to the aforementioned measures. Eculizumab administration led to resolution of the hyperhaemolysis.

WHAT IS NEW AND CONCLUSION

We report the successful management of hyperhaemolysis with eculizumab in a β-thalassemia major patient.

The Role of α1-Microglobulin (A1M) in Erythropoiesis and Erythrocyte Homeostasis-Therapeutic Opportunities in Hemolytic Conditions

α₁-microglobulin (A1M) is a small protein present in vertebrates including humans. It has several physiologically relevant properties, including binding of heme and radicals as well as enzymatic reduction, that are used in the protection of cells and tissue. Research has revealed that A1M can ameliorate heme and ROS-induced injuries in cell cultures, organs, explants and animal models. Recently, it was shown that A1M could reduce hemolysis in vitro, observed with several different types of insults and sources of RBCs. In addition, in a recently published study, it was observed that mice lacking A1M (A1M-KO) developed a macrocytic anemia phenotype. Altogether, this suggests that A1M may have a role in RBC development, stability and turnover. This opens up the possibility of utilizing A1M for therapeutic purposes in pathological conditions involving erythropoietic and hemolytic abnormalities. Here, we provide an overview of A1M and its potential therapeutic effect in the context of the following erythropoietic and hemolytic conditions: Diamond-Blackfan anemia (DBA), 5q-minus myelodysplastic syndrome (5q-MDS), blood transfusions (including storage), intraventricular hemorrhage (IVH), preeclampsia (PE) and atherosclerosis.