A novel association between high red blood cell alloimmunization rates and hereditary hemorrhagic telangiectasia

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.

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.

A curious case of delayed hemolytic transfusion reaction with evanescent antibodies in a patient with hereditary hemorrhagic telangiectasia

BACKGROUND

Delayed hemolytic reactions are potential complications of incompatible transfusions and are usually associated with the identification of a new antibody on serologic studies, following a second immunization event. However, in rare cases, the antibody investigation remains negative even if the clinical presentation would lead one to suspect otherwise.

CASE REPORT

A 44-year-old woman with hereditary hemorrhagic telangiectasia presented to the emergency department with hematuria and low back pain after she had received three units of RBCs 2 weeks earlier. Hematology and biochemistry results were consistent with delayed hemolytic transfusion reaction, but surprisingly, serologic antibody investigations were negative. It was only when her plasma was tested with enzyme (ficin)-treated panel cells that anti-e was finally detected, with a 3+ reaction with all homozygous e+ cells. No reaction was seen with heterozygous e+ cells. Four months later, an anti-K was also detected on standard panels, while the anti-e remained detectable only with ficin-treated panel cells. Three years later, both antibodies had vanished and remained undetectable. The weakness of anti-e reaction, combined with the quick evanescence of both antibodies led to the suspicion of a potential underlying immunodeficiency disorder, which was confirmed by low immunoglobulin levels on two occasions.

CONCLUSION

To our knowledge, this is the first case of immunodeficiency disorder diagnosed after the identification of evanescent antibody reactions. This case also outlines the importance of a good clinical history that should lead to further investigations when a hemolytic transfusion reaction is suspected.

Delayed haemolytic and serologic transfusion reactions: pathophysiology, treatment and prevention

PURPOSE OF REVIEW

The aim of this study was to summarize the basic epidemiology, pathophysiology and management of delayed serologic and delayed haemolytic transfusion reactions (DHTRs), as well as recent developments in our understanding of these adverse events.

RECENT FINDINGS

Several studies have identified risk factors for DHTRs, including high alloantibody evanescence rates among both general patient groups and those with sickle cell disease (SCD). Antibody detection is also hampered by the phenomenon of transfusion record fragmentation. There have also been enhancements in understanding of what may contribute to the more severe, hyperhaemolytic nature of DHTRs in SCD, including data regarding 'suicidal red blood cell death' and immune dysregulation amongst transfusion recipients with SCD. With growing recognition and study of hyperhaemolytic DHTRs, there have been improvements in management strategies for this entity, including a multitude of reports on using novel immunosuppressive agents for preventing or treating such reactions.

SUMMARY

Delayed serologic and haemolytic reactions remain important and highly relevant transfusion-associated adverse events. Future directions include further unravelling the basic mechanisms, which underlie DHTRs and developing evidence-based approaches for treating these reactions. Implementing practical preventive strategies is also a priority.