Medical and economic implications of strategies to prevent alloimmunization in sickle cell disease

Longitudinal outcomes of chronically transfused adults with sickle cell disease and a history of childhood stroke

BACKGROUND

Many children with sickle cell disease (SCD) who suffer a stroke receive chronic transfusion therapy (CTT) indefinitely; however, their adulthood neurologic outcomes have not been reported. Understanding these outcomes is critical to inform decisions regarding curative therapy in childhood.

STUDY DESIGN AND METHODS

In this retrospective study, we described a cohort of adults with SCD and a history of childhood stroke who received care at a single center and compared their outcomes with matched subjects without childhood stroke using chi2 and Mann-Whitney U tests.

RESULTS

Of 42 subjects with childhood stroke, all received CTT for secondary stroke prophylaxis. Five (11%) developed recurrent stroke. The rate of stroke was similar in subjects with and without childhood stroke (0.7 vs. 1.1 per 100 person·years, p = .63). Both cohorts exhibited evidence of iron overload (median ferritin 2227 vs. 1409 ng/dL, p = .10) and alloimmunization (45% vs. 45%, p = 1.0), despite receiving care in a comprehensive SCD program.

DISCUSSION

For adults with SCD who had a childhood stroke, our results suggest CTT returns the risk of stroke to that of age-matched stroke naïve patients with SCD.

First investigation of RH gene polymorphism in patients with sickle cell disease and associated blood donors in Cameroon, Central Africa

BACKGROUND

Although genetic polymorphism of the RH blood group system is well known in sub-Saharan Africa, national/regional specificities still remain to be described precisely. For the first time in Cameroon, Central Africa, and in order to better characterize the molecular basis driving RH phenotype variability, as well as to identify the main antigens that may be potentially responsible for alloimmunization, we sought 1) to study the RH genes in a cohort of 109 patients with sickle cell disease; 2) to study the same genes in the corresponding donors whose red blood cells (RBCs) were transfused to the patients (108 donors in 98 patients); 3) to predict RH phenotype on the basis of the molecular data and compare the results with serologic testing; and 4) to identify retrospectively patients at risk for alloimmunization.

MATERIALS AND METHODS

In order to generate an exhaustive dataset, the RH genes of all patient and donor samples were systematically investigated 1) by quantitative multiplex PCR of short fluorescent fragments (QMPSF) for characterization of RHD gene zygosity and potential structural variants (SVs), and 2) by Sanger sequencing for identification of single nucleotide variants (SNVs). Subsequent to molecular analysis, the genotypes and RH phenotype were deduced and predicted, respectively, from reference databases.

RESULTS

In a total of 217 Cameroonian individuals, as many as 24 and up to 22 variant alleles were identified in the RHD and RHCE genes, respectively, in addition to the reference alleles. Interestingly, 65 patients with SCD (66.3%) were assumed to be exposed to one or more undesirable RH antigen(s) with varying degrees of clinical relevance.

DISCUSSION

Beyond the comprehensive report of the nature and distribution of RH variant alleles in a subset of Cameroonian patients treated by transfusion therapy, this work highlights the need for an extensive review of current practice, including routine serologic typing procedures, preferably in the near future.

Chronic automated red cell exchange therapy for sickle cell disease

BACKGROUND

The data to support chronic automated red cell exchange (RCE) in sickle cell disease (SCD) outside of stroke prevention, is limited, especially in adults.

STUDY DESIGN AND METHODS

A retrospective analysis was conducted of patients with SCD who were referred for chronic RCE at our institution over a 10-year period. Data that were evaluated included patient demographics, referral indications, and procedural details (e.g., vascular access, adverse events, etc.). In a subanalysis, the number of annual acute care encounters during 3 years of chronic RCE was compared with that in the year preceding the first RCE.

RESULTS

A total of 164 patients were referred for chronic RCE: median age was 28 years (interquartile range [IQR] = 22-36) at referral and 60% were female. Seventy (42.6%) were naïve to chronic transfusion (simple or RCE) prior to referral. The leading indications for referral were refractory pain (73/164, 44.5%) and iron overload (57/164, 34.7%). A total of 5090 procedures occurred during the study period (median = 19, IQR = 5-45). Of the 138 patients who had central vascular access, 8 (6%) and 16 (12%) had ≥1 central-line-related thrombosis and/or infection, respectively. Of those who were not RBC alloimmunized at initiation of RCE, 12/105 (11.4%) developed new antibodies during chronic RCE. In those 30 patients who were adherent to therapy for 3 years, there was no significant difference in acute care encounters following initiation of RCE.

CONCLUSION

Prospective clinical trials are needed to determine which patients are most likely to benefit from chronic RCE and refine selection accordingly.

Transfusing children with sickle cell disease using blood group genotyping when the pool of Black donors is limited

BACKGROUND

Red blood cell transfusion is an effective treatment for patients with sickle cell disease (SCD). Alloimmunization can occur after a single transfusion, limiting further usage of blood transfusion. It is recommended to match for the ABO, D, C, E, and K antigens to reduce risks of alloimmunization. However, availability of compatible blood units can be challenging for blood providers with a limited number of Black donors.

STUDY DESIGN AND METHODS

A prospective cohort of 205 pediatric patients with SCD was genotyped for the RH and FY genes. Transfusion and alloimmunization history were collected. Our capacity to find RhCE-matched donors was evaluated using a database of genotyped donors.

RESULTS

Nearly 9.8% of patients carried a partial D variant and 5.9% were D-. Only 45.9% of RHCE alleles were normal, with the majority of variants affecting the RH5 (e) antigen. We found an alloimmunization prevalence of 20.7% and a Rh alloimmunization prevalence of 7.1%. Since Black donors represented only 1.40% of all blood donors in our province, D- Caucasian donors were mostly used to provide phenotype matched products. Compatible blood for patients with rare Rh variants was found only in Black donors. A donor with compatible RhCE could be identified for all patients.

CONCLUSION

Although Rh-compatible donors were identified, blood units might not be available when needed and/or the extended phenotype or ABO group might not match the patient. A greater effort has to be made for the recruitment of Black donors to accommodate patients with SCD.

Decreasing alloimmunization-specific mortality in sickle cell disease in the United States: Cost-effectiveness of a shared transfusion resource

Red blood cell alloimmunization and consequent delayed hemolytic transfusion reaction (DHTR) incidence and mortality in patients with sickle cell disease (SCD) are high. A shared transfusion resource has decreased both in other countries, while in the United States cost concerns persist. We conducted a Markov cohort simulation of a birth cohort of alloimmunized patients with SCD to estimate lifetime DHTR incidence, DHTR-specific mortality, quality-adjusted life expectancy (QALE), and costs with the implementation of a shared transfusion resource to identify antibody history versus without (i.e., status quo). We conducted our analysis using a lifetime analytic time horizon and from a United States health system perspective. Implementation of shared transfusion resource projects to decrease cumulative DHTR-specific mortality by 26% for alloimmunized patients with SCD in the United States, relative to the status quo. For an average patient population of 32 000, this intervention would generate a discounted increment of 4000 QALYs at an incremental discounted cost of $0.3 billion, resulting in an incremental cost-effectiveness ratio of $75 600/QALY [95% credible interval $70 200-81 400/QALY]. The results are most sensitive to the baseline lifetime medical expenditure of patients with SCD. Alloantibody data exchange is cost-effective in 100% of 10 000 Monte Carlo simulations. The resource would theoretically need a minimum patient population of 1819 patients or cost no more than $5.29 million annually to be cost-effective. By reducing DHTR-specific mortality, a shared transfusion resource in the United States projects to be a life-saving and cost-effective intervention for patients with SCD in the United States.

Euvolemic automated transfusion to treat severe anemia in sickle cell disease patients at risk of circulatory overload

BACKGROUND

Red blood cell (RBC) transfusion remains a major treatment for sickle cell disease (SCD). Patients with SCD have a high prevalence of renal impairment and cardiorespiratory disease, conferring risk of transfusion-associated circulatory overload (TACO).

STUDY DESIGN AND METHODS

We describe an approach, titled euvolemic automated transfusion (EAT), to transfuse SCD patients with severe anemia who are at risk of TACO. In EAT, plasmapheresis is performed using donor RBCs, rather than albumin or plasma, as replacement fluid. Euvolemia is maintained. A retrospective analysis was conducted of patients with SCD who underwent EAT at our institution over a 10-year period, to evaluate the efficacy and safety of EAT.

RESULTS

Eleven SCD patients underwent 109 EAT procedures (1-59 procedures per patient). The median age was 42 years (IQR = [30-49]) and 82% (n = 9) were female. Most (82%; n = 9) patients had severe chronic kidney disease and 55% (n = 6) had heart failure. One (9%) patient had a history of life-threatening TACO. Mean pre- and post-procedure Hct values were 19.8% (SD ± 1.6%) and 29.1% (SD ± 1.4%), respectively. The average Hct increment was 3.2% per RBC unit. Only two EAT-related complications were recorded during the 109 procedures: central line-associated infection and citrate toxicity (muscle cramping). EAT used an average of two RBC units less than that projected for standard automated RBC exchange.

CONCLUSION

Our findings suggest that EAT is safe and effective to treat patients with SCD and severe anemia, who are at risk for TACO. EAT requires fewer RBC units compared to automated RBC exchange.

Hemoglobin S target of <50% as compared to 30% in chronic red cell exchange for secondary stroke prevention in sickle cell disease

BACKGROUND

Sickle cell disease (SCD) patients with a history of stroke are encouraged to receive chronic red blood cell exchange (RBCx) for stroke prevention. The American Society of Hematology guideline published in 2020 recommends an HbS target of <30%. However, this approach necessitates more frequent RBCx and more RBC units. UT Southwestern has devised a chronic exchange protocol that elevates the HbS target to <50% in patients with a low risk of stroke.

STUDY DESIGN

This retrospective chart review study reviewed the medical records of patients receiving chronic RBCx with a target of HbS <50% over the past 10-year period to assess the safety of maintaining higher HbS targets in SCD patients with a low risk of cerebrovascular accidents (CVA).

RESULTS

Among 49 SCD patients in the chronic RBCx program for secondary stroke prevention, 33 patients were maintained on an HbS target of <50% (average measured: 35.4%) for the duration of RBCx program enrollment (median 93.0 months, 95% CI, 83-99). Stroke or transient ischemic attack (TIA) clearly attributable to changing target HbS had not been identified among the 33 study subjects. Seven patients experienced conversion between the HbS targets of <50% and <30% HbS target. Significant reductions were observed in the frequency of RBCx and usage of blood volume in four of them.

CONCLUSION

The findings suggest that liberalizing the HbS target could confer clinical flexibility without increasing the risk of CVA in a selective population. Further studies to fully evaluate the potential benefits of this approach are indicated.

Screening for new red blood cell alloantibodies after transfusion in patients with sickle cell disease

BACKGROUND

Patients with sickle cell disease (SCD) are frequent recipients of red blood cell (RBC) transfusions and are at risk for RBC alloimmunization. RBC alloimmunization is diagnosed by identifying RBC alloantibodies as part of pre-transfusion testing, but this testing fails to detect alloantibodies that have evanesced. It may be beneficial to screen for new RBC alloantibody development after transfusion before possible antibody evanescence.

STUDY DESIGN AND METHODS

Our institution started a new initiative for episodically transfused patients with SCD to obtain at least one antibody screen 2-6 months after transfusion as part of their clinical care. A database was created to prospectively track all transfused patients for 1 year and their post-transfusion antibody screen results. Patients received prophylactically CEK-matched RBC units.

RESULTS

During the study year, 138 patients with SCD received a total of 242 RBC transfusions. Patients with a history of an RBC alloantibody (n = 13, 9.4%) had previously received more RBC units than non alloimmunized patients (median 11 vs. 2 RBC units, p = .0002). A total of 337 post-transfusion antibody screens were obtained in 127 patients (92.0%) with 110 patients (79.7%) having at least one antibody screen 2-6 months post-transfusion. With this prospective testing, two new RBC alloantibodies (anti-C and -M) were identified in two patients.

CONCLUSION

It is feasible to test for new RBC alloantibody development in most episodically transfused patients with SCD as part of their routine care. The yield of this screening appears low with CEK matching, but it could still provide important information for individual patients.

The Rh blood group system and its role in alloimmunization rate among sickle cell disease and sickle thalassemia patients in Iran

INTRODUCTION

The alloimmunization following blood transfusion can be life-threatening. The Rh alloantibodies are one of the most common causes contributing to alloimmunization. This study aimed to evaluate the rate and causes of alloimmunization and to determine the Rh phenotypes and genotypes among sickle cell disease (SCD) and sickle thalassemia (Sβ).

MATERIALS AND METHODS

Our study included 104 SCD and Sβ patients referring to Baghaei 2 Hospital of Ahvaz in 2019 using a non-random simple sampling method. The blood samples were collected for Rh phenotypes, alloantibody screening and identification, and molecular tests. The SSP-PCR and RFLP methods with the Pst 1 enzyme were used.

RESULTS

The alloimmunization rate was 9.6% and 13.2% based on immunohematological tests and medical records, respectively. The main alloantibodies (90%) were anti-Rh, and 40% of the patients had multiple alloantibodies. A significant correlation was found between gender and alloimmunization. The phenotypes of DCce (37.5%), DCcEe (24%), Dce (20.2%), and dce (5.8%) and genotypes of R1r (25%), R1R2 (20.2%), R1R1 (18.3%), and R1R0 (10.6%) were the most prevalent. The R1R2 was a frequent genotype in Sβ.

CONCLUSION

R0r' and R1R0 genotypes were limited to our population in Iran. Due to the differences in RH genotypes between our population and others, the blood transfusion from other ethnicities increased our total alloimmunization rate.

Hemolysis inhibits humoral B-cell responses and modulates alloimmunization risk in patients with sickle cell disease

Red blood cell alloimmunization remains a barrier for safe and effective transfusions in sickle cell disease (SCD), but the associated risk factors remain largely unknown. Intravascular hemolysis, a hallmark of SCD, results in the release of heme with potent immunomodulatory activity, although its effect on SCD humoral response, specifically alloimmunization, remains unclear. Here, we found that cell-free heme suppresses human B-cell plasmablast and plasma cell differentiation by inhibiting the DOCK8/STAT3 signaling pathway, which is critical for B-cell activation, as well as by upregulating heme oxygenase 1 (HO-1) through its enzymatic byproducts, carbon monoxide and biliverdin. Whereas nonalloimmunized SCD B cells were inhibited by exogenous heme, B cells from the alloimmunized group were nonresponsive to heme inhibition and readily differentiated into plasma cells. Consistent with a differential B-cell response to hemolysis, we found elevated B-cell basal levels of DOCK8 and higher HO-1-mediated inhibition of activated B cells in nonalloimmunized compared with alloimmunized SCD patients. To overcome the alloimmunized B-cell heme insensitivity, we screened several heme-binding molecules and identified quinine as a potent inhibitor of B-cell activity, reversing the resistance to heme suppression in alloimmunized patients. B-cell inhibition by quinine occurred only in the presence of heme and through HO-1 induction. Altogether, these data suggest that hemolysis can dampen the humoral B-cell response and that B-cell heme responsiveness maybe a determinant of alloimmunization risk in SCD. By restoring B-cell heme sensitivity, quinine may have therapeutic potential to prevent and inhibit alloimmunization in SCD patients.

Risk factors for hemolytic transfusion reactions resulting from ABO and minor red cell antigen incompatibility: From mislabeled samples to stem cell transplant and sickle cell disease

Advances in laboratory testing, pathogen reduction and donor qualification have dramatically reduced the risk of acquiring an infection from a blood transfusion. Despite this progress, the most feared complication of transfusion - a hemolytic reaction due to incompatibility between donor and recipient - remains, with essentially no recent progress in the prevention or recognition of this rare but frequently lethal complication. Herein, the role that compatibility testing and transfusion practice play in the occurrence of acute hemolysis are described, with a special emphasis on clinical scenarios confer an increased risk of a severe hemolytic reaction in response to red blood cell or platelet transfusion. In addition, the signs and symptoms of a severe hemolytic reaction are summarized, along with the initial approach to clinical management.

Red cell alloimmunization: A 2020 update

Management of maternal red cell alloimmunization has been revolutionized over the last 60 years. Advances in the prevention, screening, diagnosis, and treatment of alloimmune-induced fetal anemia make this condition an exemplar for contemporary practice in fetal therapy. Since survival is now an expectation, attention has turned to optimization of long-term outcomes following an alloimmunized pregnancy. In this review, the current management of red cell alloimmunization is described. Current research and future directions are discussed with particular emphasis on later life outcomes after alloimmune fetal anemia.

Transfusion Medicine Equations Made Internet Accessible

Multiple mathematical equations inform the practice of transfusion medicine. These equations apply to a wide range of topics: dosage of blood products, calculation of fluid volumes, and even specific treatment decisions (e.g. corrected count increment for determination of platelet refractoriness). The calculation of these equations can be complicated, prone to error, and time-consuming. A trusted source is needed to accurately perform these calculations 24 hours a day without error and without monetary cost. We sought to build internet-enabled calculators relevant to the practice of transfusion medicine. We partnered with MDCalc, an online host of medical calculators with 1 million monthly users in 196 countries, to design and host the calculators. The calculators guide users in the application of transfusion medicine equations by providing indications for use, inputs for the equations variables, error-checking, warnings for bad inputs, and interpretive guidance of the result. The following calculators were built: blood volume, corrected count increment (CCI), plasma dosage, cryoprecipitated antihemophilic factor dosage, approximate number of units for compatibility testing, maternal-fetal hemorrhage Rh(D) immune globulin dosage, intrauterine RBC transfusion dosage, neonatal polycythemia partial exchange, theoretical removal of a substance by plasmapheresis, sickle cell RBC exchange volume, peripheral blood stem cell collection, and a calculator relevant to donor lymphocyte infusion. Clinicians can now utilize this reputable and highly visible online source to access these common transfusion medicine equations at any time with an internet-enabled device (https://www.mdcalc.com/search?filter=transfusion+medicine).

Red blood cell storage lesion: causes and potential clinical consequences

Red blood cells (RBCs) are a specialised organ that enabled the evolution of multicellular organisms by supplying a sufficient quantity of oxygen to cells that cannot obtain oxygen directly from ambient air via diffusion, thereby fueling oxidative phosphorylation for highly efficient energy production. RBCs have evolved to optimally serve this purpose by packing high concentrations of haemoglobin in their cytosol and shedding nuclei and other organelles. During their circulatory lifetimes in humans of approximately 120 days, RBCs are poised to transport oxygen by metabolic/redox enzymes until they accumulate damage and are promptly removed by the reticuloendothelial system. These elaborate evolutionary adaptions, however, are no longer effective when RBCs are removed from the circulation and stored hypothermically in blood banks, where they develop storage-induced damages ("storage lesions") that accumulate over the shelf life of stored RBCs. This review attempts to provide a comprehensive view of the literature on the subject of RBC storage lesions and their purported clinical consequences by incorporating the recent exponential growth in available data obtained from "omics" technologies in addition to that published in more traditional literature. To summarise this vast amount of information, the subject is organised in figures with four panels: i) root causes; ii) RBC storage lesions; iii) physiological effects; and iv) reported outcomes. The driving forces for the development of the storage lesions can be roughly classified into two root causes: i) metabolite accumulation/depletion, the target of various interventions (additive solutions) developed since the inception of blood banking; and ii) oxidative damages, which have been reported for decades but not addressed systemically until recently. Downstream physiological consequences of these storage lesions, derived mainly by in vitro studies, are described, and further potential links to clinical consequences are discussed. Interventions to postpone the onset and mitigate the extent of the storage lesion development are briefly reviewed. In addition, we briefly discuss the results from recent randomised controlled trials on the age of stored blood and clinical outcomes of transfusion.

A Conceptual Framework for Optimizing Blood Matching Strategies: Balancing Patient Complications Against Total Costs Incurred

Alloimmunization is currently the most frequent adverse blood transfusion event. Whilst completely matched donor blood would nullify the alloimmunization risk, this is practically infeasible. Current matching strategies therefore aim at matching a limited number of blood groups only, and have evolved over time by systematically including matching strategies for those blood groups for which (serious) alloimmunization complications most frequently occurred. An optimal matching strategy for controlling the risk of alloimmunization however, would balance alloimmunization complications and costs within the entire blood supply chain, whilst fulfilling all practical requirements and limitations. In this article the outline of an integrated blood management model is described and various potential challenges and prospects foreseen with the development of such a model are discussed.

Red Blood Cell Alloimmunization in the Pregnant Patient

Alloimmunization to red blood cell (RBC) antigens represents a challenge for physicians caring for women of child bearing potential. Exposure to non-self RBC antigens may occur during transfusion or pregnancy leading to the development of antibodies. If a subsequent fetus bears that antigen, maternal antibodies may attack the fetal red blood cells causing red cell destruction and clinically significant hemolytic disease of the fetus and newborn (HDFN). In the most severe cases, HDFN may result in intrauterine fetal demise due to high output cardiac failure, effusions and ascites, known as "hydrops fetalis". This article reviews strategies for management and prevention of RBC alloimmunization in women of child bearing potential.