Frequency Of Alloimmunization Research Articles

Neonatal and Obstetrical Outcomes of Pregnancies Complicated by Alloimmunization.

Despite advances in the prevention of rhesus (Rh)(D) alloimmunization, alloantibodies to Rh(D) and non-Rh(D) red blood cell antigens continue to be detected in ∼4% of US pregnancies and can result in hemolytic disease of the fetus and newborn (HDFN). Recent reports on HDFN lack granularity and are unable to provide antibody-specific outcomes. The objective of this study was to calculate the frequency of alloimmunization in our large hospital system and summarize the outcomes based on antibody specificity, titer, and other clinical factors. We identified all births in a 6-year period after a positive red blood cell antibody screen result during pregnancy and summarized their characteristics and outcomes. A total of 707 neonates were born after a positive maternal antibody screen result (3.0/1000 live births). In 31 (4%), the positive screen result was due to rhesus immune globulin alone. Of the 676 neonates exposed to alloantibodies, the direct antibody test (DAT) result was positive, showing antigen-positivity and evidence of HDFN in 37% of those tested. Neonatal disease was most severe with DAT-positive anti-Rh antibodies (c, C, D, e, E). All neonatal red blood cell transfusions (15) and exchange transfusions (6) were due to anti-Rh alloimmunization. No neonates born to mothers with anti-M, anti-S, anti-Duffy, anti-Kidd A, or anti-Lewis required NICU admission for hyperbilirubinemia or transfusion. Alloimmunization to Rh-group antibodies continues to cause a majority of the severe HDFN cases in our hospital system. In neonates born to alloimmunized mothers, a positive DAT result revealing antigen-positivity is the best predictor of anemia and hyperbilirubinemia.

Analysis of risk factors for red blood cell alloimmunization and its incidence in hemoglobinopathy patients at a tertiary care center in Odisha, Eastern India

Abstract BACKGROUND: Sickle cell disease (SCD) and thalassemia are common hemoglobinopathies in Eastern India. Regular blood transfusion in these patients leads to alloimmunization. Finding compatible red blood cell units remain a challenge in these patients delaying the transfusion support. AIMS: This study aims to estimate the frequency of alloimmunization and predicts the associated risk factors. METHODOLOGY: A retrospective study was conducted for 2 years. Data were retrieved from the immunohematology work-up record. The Chi-square statistics determined the risk factors associated with alloimmunization. Multivariate regression analysis was used to identify independent risk factors of alloimmunization, adjusting the confounders. A P < 0.05 was considered as statistically significant. RESULTS: Forty-seven patients out of 132 developed antibodies. Of these, 41 presented with only alloantibodies, three patients had only autoantibodies, and the rest 3 had both autoantibodies and alloantibodies. Most commonly observed alloantibodies were against Rh, Kidd, Duffy, and S antigens. SCD appeared a significant risk factor for the development of alloimmunization in the Chi-square test (P = 0.003). However, multivariate analysis revealed only age of more than 2 years at the first transfusion, and up to ten transfusions are independent risk factors of alloimmunization (P < 0.05). CONCLUSION: We found a high incidence of alloimmunization in multitransfused hemoglobinopathies patients in this region. This study also shows the first transfusion at an age of more than 2 years and up to 10 transfusions are independent predictors of alloimmunization.

Red blood cell alloimmunization in blood transfusion-dependent β thalassemia major patients in Sana’a City-Yemen

The development of erythrocyte alloantibodies complicates transfusion therapy in β thalassemia major patients. These antibodies increase the need for blood and intensify transfusion complications. Data on erythrocyte alloimmunization is scarce in Yemeni thalassemia patients. We studied the frequency of alloimmunization in multitransfused β-thalassemia major patients and investigated risk factors that affect antibody formation. Blood samples were taken from 100 β thalassemia major patients who received multitransfused leukodepleted packed red-blood cells. Antibody screening and identification were performed by indirect antiglobulin test using the gel column technique. All patients were tested for autoantibodies using autocontrol and direct antiglobulin test. No adsorption test was done as no autoantibodies were detected in any patient. In our study of 100 β-thalassemia patients, 50 were male and 50 were female with ages ranging from 1 to 30 years. Alloantibodies were present in 6% of patients, while no autoantibodies were detected. Of the 17 alloantibodies identified, the majority were directed against Kell (41.2%) and Rh (29.4%) blood groups. Alloimmunization was significantly associated with age group and sex (p = 0.013, p = 0.030), respectively in β thalassemia major patients. The development of alloantibodies was not significantly associated with duration, total number of transfusions and splenectomy (P = 0.445, P = 0.125, P = 0.647). No autoantibodies found in patients with β thalassemia major. The study found low rates of erythrocyte alloimmunization in multitransfused β-thalassemia major patients, but significant alloantibodies were produced primarily from Kell and Rh blood groups, suggesting the need for providing phenotypically matched cells for selective antigens to improve transfusion efficiency.

Characterization of pediatric transfusion-dependent thalassemia patients in a large academic center.

Transfusion-dependent thalassemia patients are at high risk of transfusion-related complications. Yet, there is scanty data on the frequency of transfusion reactions, particularity alloimmunization among pediatric transfusion-dependent thalassemia patients. In addition, there is no consensus on the prophylactic antigen matching for prevention of alloimmunization or the extent of antigen matching for alloimmunized thalassemia patients. We conducted a retrospective study to assess the frequency and specificity of alloimmunization among pediatric transfusion-dependent thalassemia patients receiving ABO, RhD, and K-matched red blood cell units. In addition, we studied the association between patients' characteristics and alloimmunization. The clinical and transfusion records of transfusion-dependent thalassemia patients followed up at our institution between July 2018 and June 2022 were reviewed. Ninety-two transfusion-dependent thalassemia patients having mean age of 13.37 years (SD, 5.56) were included in our study. Eight patients (9%) had developed clinically significant alloantibodies; six patients (6%) developed alloantibody against E antigen while two patients (2%) developed more than one alloantibody. Of alloimmunized patients, five patients had received transfusion outside Canada. Patients' sex, age, having a genotype variant, total number, and duration of transfusion received were not associated with the risk of alloimmunization. The transfusion-recipient's diagnosis of β-thalassemia, having developed autoantibody, and history of receiving transfusion outside Canada were associated with alloimmunization. Blood matching for ABO, RhD, and K antigens resulted in, although not eliminated, lower frequency of alloimmunization than that previously reported among pediatric thalassemia patients. Extending matching to include Rh antigens could further reduce the rate of alloimmunization.

Red Blood Cell Alloimmunization and Its Associated Factors among Chronic Liver Disease Patients in a Teaching Hospital in Northeastern Malaysia

Red blood cell (RBC) alloimmunization is an important complication of blood transfusion. Variations in the frequency of alloimmunization have been noted among different patient populations. We aimed to determine the prevalence of RBC alloimmunization and associated factors among chronic liver disease (CLD) patients in our center. This is a case-control study involving 441 patients with CLD who were being treated at Hospital Universiti Sains Malaysia and subjected to pre-transfusion testing from April 2012 until April 2022. Clinical and laboratory data were retrieved and statistically analyzed. A total of 441 CLD patients were included in our study, with the majority being elderly, with the mean age of patients 57.9 (SD ± 12.1) years old, male (65.1%) and Malays (92.1%). The most common causes of CLD in our center are viral hepatitis (62.1%) and metabolic liver disease (25.4%). Twenty-four patients were reported to have RBC alloimmunization, resulting in an overall prevalence of 5.4%. Higher rates of alloimmunization were seen in females (7.1%) and patients with autoimmune hepatitis (11.1%). Most patients developed a single alloantibody (83.3%). The most common alloantibody identified belonged to the Rh blood group, anti-E (35.7%) and anti-c (14.3%), followed by the MNS blood group, anti-Mia (17.9%). There was no significant factor association of RBC alloimmunization among CLD patients identified. Our center has a low prevalence of RBC alloimmunization among CLD patients. However, the majority of them developed clinically significant RBC alloantibodies, mostly from the Rh blood group. Therefore, phenotype matching for Rh blood groups should be provided for CLD patients requiring blood transfusions in our center to prevent RBC alloimmunization.

A comparison of serological phenotyping and molecular genotyping for Kell, Kidd, and Duffy antigens in multi-transfused thalassemia patients.

In multi-transfused thalassemia patients, serological phenotyping fails to test patient's actual blood group antigen profile due to the presence of donor red blood cell (RBC) in the circulation. This limitation of serological tests can be overcome by genotype determination using the polymerase chain reaction (PCR)-based methods. The aim of this study is to compare the serological phenotyping of Kell, Kidd, and Duffy blood group systems with molecular genotyping in the normal blood donors and multi-transfused thalassaemia patients. Blood samples from 100 normal blood donors and 50 thalassemia patients were tested using standard serological techniques and PCR-based methods for Kell (K/k), Kidd (Jka/Jkb), and Duffy (Fya/Fyb) blood group systems. The results were compared for concordance. Genotyping and phenotyping results were 100% concordant for normal blood donors whereas those for thalassemia patients showed 24% discordance. The frequency of alloimmunization in thalassemia patients was 8%. The results of genotyping were used to provide Kell, Kidd, and Duffy matched blood for transfusion therapy to thalassemia patients. The actual antigen profile in multitransfused thalassaemia patients can be reliably determined using genotyping. This would benefit in providing better antigen matched transfusion therapy to such patients hence reducing the rate of alloimmunization.

Red cell alloimmunization in pregnancy: a study from a premier tertiary care centre of Western India.

The study was conducted to determine the frequency of alloimmunization to various blood group antibodies in pregnant women, and the risk of hemolytic disease in the fetus and newborn. All antenatal women, irrespective of the period of gestation or obstetric history, were included, whereas those taking anti-D immune-prophylaxis or with a history of blood transfusion were excluded. Antibody screening and identification were performed using a Bio-Rad ID microtyping system. Of 2,084 antenatal females, 1,765 were D-antigen positive and 319 D-antigen negative. Sixty-five (3.119%) women alloimmunized. Out of 54 (2.591%) who had sensitized to D-antigen, 11 (0.527%) also sensitized to other antibodies. These 11 alloantibodies identified included: anti-M (n=6; 9.23%), anti-C (n=1; 3.076%), anti-E (n=1; 1.538%), anti-e (n=1; 1.538%), anti-Lewis (a) (n=1; 1.538%), and unspecified antibodies (n=1; 1.538%). Multiple antibodies were seen in four patients that combined: anti-D and anti-C (n=2; 3.076%), anti-e and anti-c (n=1; 1.538%), and anti-D and anti-G (n=1; 1.538%). The rate of alloimmunization in D-antigen-negative women was high. Apart from this, the alloimmunization rate in women with bad obstetric history was very high, at 8.1%. In developing countries such as India, universal antenatal antibody screening, though desirable, may not be justified at present, as the cost and infrastructure required would be immense because of the lower alloimmunization rates in RhD antigen-positive women. However, it is necessary to impose properly formulated protocols to screen pregnant women with bad obstetric history.

Alloimmunization and Autoimmunization in Multi-Transfused Thalassemic Patients: A Single Center Study

Aim: To determine frequency of alloimmunization and autoimmunization among the patient of thalassemia with history of multiple blood transfusions. Methods: This study was conducted by consecutive sampling in six months duration from September 2020 to August 2021 at the department of Hematology and blood Transfusion Medicine, of University of Child Health Sciences, The Children's Hospital Lahore. Any patient with a positive Direct antiglobulin test (DAT) was labeled as auto-immunized and a positive indirect antiglobulin test (IAT) was labeled as alloimmunized. Results: Total 90 cases were enrolled with 62% male and 38% females with a mean age 6.04 + 3.3 years (range of age: 7 months to 14 years). Antibody screening and auto-antibodies were positive in 4.4% (n= 4) cases each, and allo-antibodies in 6.7% (n=6) cases (anti-E in 2, anti-C in 2, anti-K and anti-e in 1 each). Among all these patients of beta thalassemia, spleen was enlarged in 71% cases; around half of these were <5 years old. Around 96% had first transfusion <2 years. The frequency of patients positive on DAT, IAT and on anti-body screening was significantly related to the frequency of blood transfusion Practical Implications: Autoantibodies produce a positive direct antiglobulin test (DAT), resulting in hyperhemolysis of red cells in thalassemic patients, which exacerbates the existing alloantibodies factor in children who have received several blood transfusions. The gap between transfusions will be shortened. Routinely, greater emphasis is placed on the identification of allo-antibodies, but auto-antibodies should also be evaluated so that this phenomena may be better understood and handled. This study was conducted to examine the link between a greater transfusion demand and the existence of auto or allo antibodies in Thalassemia patients. I Conclusion: We found Alloimmunization and autoimmunization together not very uncommon in transfusion dependent patients of Thalassemia. The frequency of transfusions is affected in co-existing states. Extended matching, as well as early diagnosis and control of Auto and allo-antibodies both can improve the efficacy of blood transfusion. Keywords: Autoantibodies, IAT, DAT, Coomb’s test, Thalassemia, Allo-immunization

O-07: TRANSFUSION PRACTICE, POST-TRANSFUSION COMPLICATIONS AND RISK FACTORS IN SICKLE CELL DISEASE IN SENEGAL

Purpose: Blood transfusion is an indispensable therapy in sickle cell disease, despite its multiple and often harmful complications. The objective of this study was to evaluate the complications of alloimmunization, infection and iron overload secondary to blood transfusion in sickle cell disease patients. Materials and methods: This was a six-month cross-sectional case-control study conducted in the Clinical Hematology Department of Dakar (Senegal) on 253 patients followed for major sickle cell disease (153 polytransfused and 100 non-transfused patients). Transfusion practice (modalities, indications), post-transfusion complications (alloimmunization, iron overload, infections) and risk factors (sociodemographic, clinical, biological) for the occurrence of these complications were evaluated. Results: The median age of the patients was 28.5 years (5-59). The sex ratio (M/F) was 0.86. Homozygous sickle cell disease was more frequent (95.3%). The median follow-up time was 9.1 years (2-26). Simple transfusion was performed in 142 patients, exchange transfusion in 29 patients; 22 patients were on a transfusion program. The indications for transfusion were dominated by acute anemia (57.06%) and prolonged CVO (14%). Red blood cell concentrates were administered in 143 patients (93.46%). The median number of units of blood received per patient was 10 units (2 - 48). The frequency of alloimmunization was 16% and the most frequent alloantibodies were anti-rhesus (34.19%) and anti-Kell (23.67%). The prevalence of hepatitis C in transfused subjects was 1.33% and 1% in non-transfused subjects (p=0.64). The prevalence of HBV was 2% in transfused patients and 3% in non-transfused patients (p=0.45). HIV antibodies were not found in either the transfused or the non-transfused patients. Twelve patients (7.84%) had post-transfusion iron overload (ferritin level >1000 ng/ml). The higher the transfusion, the higher the ferritin level (strong positive correlation, r = 0.8). The number of packed red blood cells transfused was the only risk factor for alloimmunization (p=0.03) and post-transfusion iron overload (p=0.023). The frequency of blood transfusion was not related to the transmission of infectious. Conclusion: The management of sickle cell disease often requires blood transfusion to correct anemia or prevent certain complications. Despite the progress made in transfusion safety, this therapy still remains a risk for the recipient. The authors do not declare any conflict of interest

Detection of alloimmunization in Glanzmann Thrombasthenia and Bernard-Soulier Syndrome: Data from a Brazilian Center

IntroductionThe Glanzmann Thrombasthenia (GT) and Bernard-Soulier Syndrome (BSS) are rare hereditary disorders of platelet function. Their treatment often requires platelet transfusion, which can lead to the development of alloantibodies. ObjectiveIn this study, we aim to develop a strategy for alloantibody detection and to describe the frequency of alloimmunization in a patient population from a single center in southeastern Brazil. MethodsSamples from patients with GT or BSS were tested using the Platelet Immunofluorescence Test (PIFT). If a positive result was obtained, a confirmatory step using the Monoclonal Antibody Immobilization of Platelet Antigens (MAIPA) and Luminex bead-based platelet assay (PAKLx) was executed. Main results: Among 11 patients with GT, we detected the presence of alloantibodies in 5 using PIFT, with confirmation through MAIPA and PAKLx in 2 (1 anti-HLA and 1 anti-HPA), resulting in a frequency of 18.1%. Among 4 patients with BSS, PIFT was positive in 3, with confirmation by MAIPA and PAKLx in 1 (anti-HLA), showing a frequency of 25%. The two patients with anti-HLA antibodies exhibited a panel reactive antibody (PRA-HLA) testing greater than 97%. ConclusionOur study highlights the importance of identifying platelet alloimmunization in this patient population. The proposed algorithm for platelet alloantibodies detection allows resource optimization.

Antenatal antibody screening irrespective of RH status at a tertiary care hospital: A prospective study

Maternal alloimmunization is still the leading cause of fetal anemia and is responsible for neonatal mortality and morbidity in developing countries. Evidence-based guidelines are essential for implementing antenatal alloantibodies screening in developing countries like India which will help to formulate recommendations and reduce adverse outcomes of Hemolytic disease of fetus and new born. To determine the frequency of alloimmunization among in Antenatal women during routine antenatal visits irrespective of Rh status. The prospective study carried out in a tertiary care hospital has enrolled 1000 antenatal women (500 each of Rh-positive and Rh-negative women) attending antenatal clinics and admitted for institutional deliveries, were screened for red cell alloimmunization and association between alloimmunization rate in antenatal women with variables was carried out to determine the clinical significance. Among 1000 antenatal women enrolled and screened 33 (3.3%) antenatal women were found to be alloimmunized. The prevalence of alloimmunization among Rh-negative women is 5.4% (27/500). While the prevalence of alloimmunization among Rh-positive women is 1.2% (6/500). Majority of the alloimmunized cases were multigravida. 75.7% (25/33) antibodies identified in our study were anti-D antibodies and 24.24% (8/33) were non anti-D antibodies. Successful implementation of Antenatal antibody screening program requires a coordinated Team approach between the Transfusion medicine, Obstetrics, Radiology and Pediatrics departments. Early screening irrespective of Rh status and effective utilization of RhIg prophylaxis in Rh negative antenatal women is the only solution to reduce fetal, neonatal morbidity and mortality due to alloimmunization.

Red cell alloimunization and autoantibodies in transfusion dependent thalassemia patients of Jammu region

Background: Thalassemia is one of the most common genetic disorder of hemoglobin synthesis in Jammu region. Although RBC transfusion is life saving for these patients, it may be associated with some complications like RBC alloimmunization. Thus, alloimmunization against red blood cell antigens increases the need for transfusion and can significantly complicate transfusion therapy. Therefore, screening for unexpected antibodies should be a part of all pretransfusion testing, with antibody identification in the event of a positive result. The aim of the study was to determine the frequency of alloimmunization and autoimmunization and the most common alloantibodies involved.Methods:This was a descriptive study involving a total of 146 thalassemic patients in the age range of 2-32 years receiving regular blood transfusions, registered at SMGS blood bank, Jammu. Antibodies screening, antibody identification, and cross matching was done on all patient samples included in the study, during the period between November 2014 and October 2015.Results: At the start of the study, 8 patients who tested positive for alloantibodies 3 patients had more than one antibody subtype. Anti-E was the commonest antibody found in 4 (50%) patients. Similarly, at the end of study, antibody screening and then identification revealed presence of antibodies in 10 patients. Only 1 patient had more than one antibody subtype. Anti E was again the commonest antibody found in 5 (50%) patients. Conclusions:The most common alloantibodies identified were anti Rh system antibodies (anti-E and anti-D) followed by Kell antibodies. In order to reduce alloimmunization, a policy for performing extended red cell phenotyping of these patients is essential and at least antigen E and Kell negative blood should be provided for transfusion to these patients.

Frequency of Allo-Immunization in Sickle Cell Disease: Case of the Patients at the Laquintinie Hospital in Douala-Cameroon

<i>Background:</i> Allo-immunization is an immune response to foreign antigens after exposure to genetically different cells or tissues. Allo-immunized patients with sickle cell disease (SCD) appear to experience worse survival compared to non allo-immunized patients. Therefore, to contribute to the management of patients living with SCD and improve the blood transfusion process, we aimed to determine the frequency of allo-immunization in SCD’s patients. To realize this study, we carry out a cross sectional study in one Hospital of Douala-Cameroon. <i>Method: </i>Plasma was prepared from collected blood sample, electrophoresis was done and depending on the migration on the gel; the type of electrophoresis was determine. Blood group ABO/Rh was done. After electrophoresis, depending on the result obtained those that was not homozygote (SS) and heterozygote sickle cell anemia (AS) was discarded. The check for irregular agglutinins was done using the indirect Coombs test. Clinical and biological characteristics of the different participants were studied and analyzed using a Statview statistical software. <i>Result:</i> We obtained 104 sickle cell patient, out of these we had 55% of positive RAI, with an average transfusion of 7.35. Also 83 patients were homozygote sickle cell anemia for a mean age of 15.75 years old (ranging from 1 to 52 years). The result obtained shows that the number of blood transfusion for homozygote sickle cell patient increases with age and that homozygote sickle cell patient received more blood transfusion than heterozygote patient. It can also be said that allo-immunization in these patients originate from the multiple blood transfusion received that were not fully compatible and that it affects more children (from 1 – 15), they accounted for about 53.85% of the total population. Our result obtained implies that in the future, sickle cell patient will have difficulty in finding compatible blood for treatment and is a real problem since transfusion is the major standard of care for patient suffering from sickle cell anemia in Cameroon. The absence of treatment may lead to the death of the patient. To help reduced allo-immunization, extended compatibility test in all the red blood cell system and routinely screening for the presence of irregulars agglutinins may reduce the frequency of allo-immunization.

Alloimmunisation in polytransfused patients with non-phenotyped red blood cells at the University Hospital Souro Sanou of Bobo Dioulasso (Burkina Faso)

Introductionau Burkina Faso, la transfusion sanguine est réalisée en respectant uniquement la compatibilité ABO et RHD entre le donneur et le receveur. Une telle pratique comporte des risques d'allo-immunisation, pouvant engendrer des complications cliniques surtout chez les polytransfusés. L´objectif est de déterminer la prevalence et les facteurs associés à l´allo-immunisation chez les patients polytransfusés avec des concentrés de globules rouges non phénotypés au Centre Hospitalier Universitaire Souro Sanou.Méthodesnous avons réalisé une étude transversale chez des patients polytransfusés dans les services cliniques du Centre Hospitalier Universitaire Souro Sanou sur une période de 3 mois (Mars à Mai 2019). Chez chacun des 141 patients inclus, 5 ml de sang total ont été prélevés dans un tube Éthylènediaminetétraacétique (EDTA) pour la recherche des anticorps irréguliers. La recherche des anticorps irréguliers a été réalisée par la technique de Coombs indirect en gel filtration.Résultatsau total, la fréquence de l´allo-immunisation obtenue est de 5,67%. La majorité des anticorps identifiés appartenaient aux systèmes Rhésus et Kell. Nous n´avons pas trouvés de liaison statistiquement significative entre l´âge, le sexe, les antécédents pathologiques, le nombre de poches transfusés et la positivité de la recherche des anticorps irréguliers (p = 0.37, p= 0,75, p = 0.96).Conclusionnous avons trouvé que le risque d´allo-immunisation est majeur. Des mesures supplémentaires doivent être prises pour renforcer la sécurité immunologique des transfusions sanguines au Burkina Faso. Nous proposons qu´au Burkina Faso, la réalisation du test de compatibilité à l´anti-globuline soit systématique chez les patients présentant un grand risque d´immunisation.

Transfusion requirements and alloimmunization to red blood cell antigens in orthotopic liver transplantation.

Orthotopic liver transplantation (OLT) has been associated with high blood transfusion requirements. We evaluated the transfusion needs and frequency of alloimmunization to RBC antigens among OLT recipients pre- and post-transplantation. We reviewed the medical records of patients who underwent a first OLT between January 2007 and June 2017. Transfusions given only during the perioperative period, defined by 1week before OLT until 2 weeks following OLT, were included in this study. Records were reviewed in June 2019 for updated antibody testing results. A total of 970 patients underwent OLT during the study period. The median age of patients was 57 years; 608(62.7%) were male. During the perioperative period, transfused patients received an average of 10.7 (±10.7) RBC units, 15.6 (±16.2) thawed plasma units and 4.1 (±4.3) platelet units. At the time of OLT, a total of 101 clinically significant RBC alloantibodies were documented in 58(5.98%) patients. Fifty-three of these antibodies were directed against Rh blood group antigens. Twenty-two (37.9%) patients had more than one alloantibody. Patients with alloimmunization before OLT (N=58) received perioperatively comparable number of RBCs to non-alloimmunized patients (10.5 ± 10.6 vs. 9.6 ± 10.7; p=0.52). There was no significant difference in perioperative or intraoperative RBC transfusion between patients with one alloantibody and those with multiple alloantibodies. Only 16 patients (16/737; 2.17%) developed new alloantibodies at a median of 61 days after OLT. The overall alloimmunization rate was 9.8% (72/737), and female patients were more likely to be alloimmunized. Blood transfusion requirements in OLT remain high. However, the rate of RBC alloimmunization was not higher than the general patient population.

Altered type 1 interferon responses in alloimmunized and nonalloimmunized patients with sickle cell disease.

Patients with sickle cell disease (SCD) have a high prevalence of RBC alloimmunization. However, underlying mechanisms are poorly understood. Given that proinflammatory type 1 interferons (IFNα/β) and interferon stimulated genes (ISGs) promote alloimmunization in mice, we hypothesized that IFNα/β may contribute to the increased frequency of alloimmunization in patients with SCD. To investigate this, expression of ISGs in blood leukocytes and peripheral blood mononuclear cells (PBMCs) of previously transfused SCD patients with or without alloimmunization and race‐matched healthy controls were quantified, and IFNα/β gene scores were calculated. IFNα/β gene scores of SCD leukocytes and plasma cytokines were elevated, compared to controls (gene score, p < 0.01). Upon stimulation with IFNβ, isolated PBMCs from patients with SCD had elevated ISGs and IFNα/β gene scores (p < 0.05), compared to stimulated PBMCs from controls. However, IFNβ‐stimulated and unstimulated ISG expression did not significantly differ between alloimmunized and non‐alloimmunized patients. These findings indicate that patients with SCD express an IFNα/β gene signature, and larger studies are needed to fully determine its role in alloimmunization. Further, illustration of altered IFNα/β responses in SCD has potential implications for IFNα/β‐mediated viral immunity, responses to IFNα/β‐based therapies, and other sequelae of SCD.

The Role of Platelets in the Induction of Alloimmunization after Platelet Transfusion

Background Platelet (PLT) transfusion can elicit alloimmune responses leading to alloantibody formation. These alloantibodies can opsonize PLTs which causes rapid clearance of transfused PLTs and thereby render the transfusion ineffective. Contaminating WBCs in PLT concentrates are important for the induction of this alloimmunization which is evident from the fact that leukoreduction of platelet concentrates significantly reduced the frequency of alloimmunization. Despite universal leukoreduction, however, a residual risk remains. Currently, it is unknown if this is due to the residual WBCs (<1*106 / transfusion) in PLT concentrates or if PLTs themselves can also induce primary HLA-alloimmunization. Furthermore, it is not known which factors increase or reduce the likelihood of alloimmunization. Therefore, the aim of our study was, first, to determine the involvement of PLTs in the induction of alloimmunization, and second, to investigate whether storage of PLT concentrates might be a risk factor for alloimmunization.Methods To determine if PLTs are phagocytosed and presented by antigen presenting cells, monocyte derived dendritic cells (moDCs) were incubated at 37°C with allogeneic PLTs. After incubation, moDCs were either fixed and analysed for phagocytosis of PLTs using z-stacks obtained with confocal microscopy, or moDCs were lysed and HLA-DR was immunoprecipitated from this lysate. Thereafter, HLA-DR presented peptides were eluted and measured using mass spectrometry. Furthermore, HLADRB3*01:01+ moDCs were incubated with either HPA1a+ or HPA1b+ PLTs and later exposed for 24 hours to HPA1a-specific HLADRB3*01:01+ CD4 T cells after which production of IFNy by T cells was determined using ELISA. To investigate if storage may be a potential risk factor for alloimmunization, moDCs were incubated with freshly isolated PLTs or PLTs stored 7 days under blood bank conditions. Finally, in some experiments, freshly isolated PLTs were activated using thrombin-receptor agonistic peptide, treated with calcimycin A23187 to induce apoptosis, or incubated with either purified phosphatidylserine (PS) or phosphatidylcholine (PC). Subsequently, phagocytosis of these PLTs by moDCs was quantified using imaging flow cytometry.Results Confocal microscopy clearly showed that PLTs are phagocytosed by moDCs. Mass spectrometry analyses showed presentation of peptides derived from proteins exclusively expressed in PLT by HLA class II of moDCs. In addition, moDCs induced a significant HPA1a+ specific CD4 T cells response (measured as IFNy production) after incubation with HPA1a+ PLTs, which was not observed after incubation with HPA1b+ PLTs. PLTs obtained from stored PLT concentrates were significantly more phagocytosed compared to fresh PLTs. This might be caused by increased presence of apoptotic platelets in stored PLT concentrate, as phagocytosis of apoptotic platelets was significantly increased compared to activated or unstimulated PLTs. This increased phagocytosis was partially caused by PLT surface expression of PS. Furthermore, apoptotic PLTs also induced a stronger CD4 T cell response.Discussion Our studies clearly show that peptides of phagocytosed PLTs are presented by DCs, resulting in a platelet-specific CD4 T cell response. This implicates that not only WBCs, but also PLTs themselves can induce alloimmunization after PLT transfusion. As a result, factors that increase phagocytosis of PLTs could also increase the risk of alloimmunization after PLT transfusion. In this respect, PLTs stored for 7 days showed increased phagocytosis as compared to fresh PLTs. This increase is at least partly due surface expressed PS caused by storage-induced apoptosis and resulted in a stronger platelet-specific CD4 T cell responses compared to DCs incubated with untreated fresh PLTs. Although these in vitro experiments only partly represent the complex processes that are involved in an immune response in vivo , these data suggest that storage of PLT concentrates may be associated with increased alloimmunization. DisclosuresNo relevant conflicts of interest to declare.

Transfusion-induced platelet antibodies and regulatory T cells in multiply transfused patients.

BackgroundPlatelet transfusion refractoriness (PTR) remains a difficult problem in patients requiring long‐term platelet supportive care. However, there are little data on the frequency of platelet antibodies in multiply transfused Chinese patients. Moreover, the relationship between peripheral regulatory T cells (Tregs) and PTR remains unclear.MethodsWe retrospectively studied the frequency of alloimmunization against platelet antigens in patients receiving multiple transfusions between 2013 and 2017. Monoclonal antibody solid‐phase platelet antibody test (MASPAT) kits were used to screen for platelet antibodies before each platelet transfusion. Peripheral Tregs and CD4+CD25+CD127− T cells were detected by flow cytometry, while transforming growth factor‐beta (TGF‐β) and interleukin (IL)‐17 cytokines were detected by enzyme‐linked immunosorbent assay.ResultsA total of 399 patients who met the inclusion criteria were enrolled for the analysis of platelet antibodies and refractoriness. Among these patients, 10 (2.5%) were positive for platelet antibodies before transfusion and 47 (11.8%) became antibody‐positive during the study period. The number of alloimmunized patients was significantly higher in patients with hematological disease as compared with other disease groups (p < 0.05). Refractoriness and alloimmunization occurred in 77 (19.3%) and 22 (28.6%) patients, respectively. There were no significant differences in CD4+, CD8+, and CD4+CD25+CD127− T cell numbers and plasma levels of TGF‐β1 and IL‐17 between patients with PTR and the control group.ConclusionsRefractoriness was common in patients undergoing multiple platelet transfusions (19.3%), with alloimmunization observed in 28.6% of patients. However, Tregs in peripheral blood may not play a key role in PTR.

Alloimmunization in Egyptian children with sickle cell disease

Background Although transfusion is a cornerstone in the treatment of sickle cell disease (SCD), the subsequent erythrocyte alloimmunization creates a significant challenge in their management.Aim The aim was to measure the frequency of the occurrence of the alloimmune markers in SCD and to investigate its predicators.Patients and methods This cross-sectional study recruited 50 children and young adults with SCD. All patients were subjected to detailed medical history and thorough clinical examination. Laboratory investigations included complete blood count, markers of hemolysis, and serum ferritin. The D, C, c, E, e, M, NJKa, and JKb antigens were typed using monoclonal antisera. Fya, Fyb, Jka, Jkb, S, s, and anti-Lua antigens were typed by commercially prepared polyclonal antihuman sera. Antibody screening was performed using ortho screening panel.Results Sickle SS was the most common type of SCD, representing more than half of the recruited patients. The frequency of antibody positive screening among SCD was 16%. Higher frequency of alloimmunization was recorded in those with SB+ than those SS and SB0. Patients with SCD who had alloimmunization were significantly older when they received their first blood transfusion and had lower transfusion index (P=0.037) than those with negative antibodies screening (P=0.013). There were no significant differences between patients with alloimmunization and those without regarding age, sex, transfusion frequency, and SCD comorbidities; painful crisis (P=0.117), stroke (P=0.398), acute chest syndrome (ACS) (P=0.363).Conclusion Alloimmunization in patients with SCD has important clinical significance, especially those who require regular blood transfusion. Consequently early recognition and management of alloimunization is necessary.

In utero exposure to alloantigens primes alloimmunization to platelet transfusion in mice.

Platelet transfusions remain a mainstay of treatment for many patients with thrombocytopenia, but can lead to alloantibodies to Human Leukocyte Antigens (anti-HLA) resulting in inadequate responses to subsequent platelet transfusions (refractoriness), as well as complicate transplantation. Despite substantial decreases in alloimmunization with the implementation of leukoreduction, a significant percentage of patients still become alloimmunized following platelet transfusions. It remains unclear why some patients make anti-HLA antibodies, but others do not make anti-HLA antibodies even with chronic transfusion. Antecedent pregnancy correlates with risk of alloimmunization due to platelet transfusion in humans - however, isolation of pregnancy as a single variable is not possible in human populations. A tractable murine model of pregnancy and transfusion was engineered by breeding C57BL/6 (H-2b ) dames with BALB/c (H-2d ) sires. After pregnancy, female mice were transfused with leukoreduced platelets from F1 (H-2b/d ) donors that expressed the same paternal major histocompatibility complex (MHC) H-2d alloantigens as the sires. Control groups allowed isolation of pregnancy or transfusion alone as independent variables. Alloimmunization was determined by testing serum for antibodies to H-2d MHC alloantigens. No alloantibodies were detected after pregnancy alone, or in response to transfusion of platelets alone; however, significant levels of alloantibodies were detected when pregnancy was followed by transfusion. These findings isolate antecedent pregnancy as a causal contribution to increased frequencies of alloimmunization by subsequent platelet transfusion in mice and provide a platform for ongoing mechanistic investigation.