Severe neonatal thrombocytopenia due to anti-HPA-4b alloantibodies: Third report described in a Caucasian mother.

BACKGROUND: Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT) results from maternal platelet alloimmunization against paternal antigens inherited by the fetus, most often due to the Human Platelet Antigen (HPA)-1 system in Caucasians. We investigated in 2023, a 30-year-old Caucasian woman Gravida 2 Para 1 who gave birth at 35 weeks of gestation to a male (body weight 2210 g) without signs of bleeding. A severe thrombocytopenia (platelet count at 3 G/L) was discovered incidentally a few hours after delivery in the context of the management of a respiratory distress. The newborn recovered after one platelet concentrate transfusion and normalized his platelet count at Day 5. STUDY DESIGN AND METHODS: FNAIT investigation was performed according to guideline recommendations. Platelet genotyping was carried out by multiplex PCR. Maternal serological investigation included Monoclonal Antibody-specific Immobilization of Platelet Antigens method (MAIPA) and Luminex technology. RESULTS: Parental and newborn genotyping pointed out an HPA-4 incompatibility between the mother and the newborn and the father. Serological investigation revealed an anti-HPA-4b alloantibody confirming the diagnosis of neonatal alloimmune thrombocytopenia. CONCLUSION: We described the third case of anti-HPA-4b alloantibody discovered in a Caucasian mother. This case strengthens the need for reference laboratory to genotype a panel of HPA alleles reflecting local genetic population diversity and for crossmatch of maternal serum with fresh paternal platelets in clinical suspected cases of neonatal alloimmune thrombocytopenia.

Association of the human platelet antigens polymorphisms with platelet count in patients with COVID-19.

Polymorphism in human platelet antigen (HPA)-1 and HPA-3 (GPIIb/IIIa), HPA-2 (GPIb/IX), HPA-4 (GPIIIa), HPA-5 (GPIa/IIa), & HPA-15 (CD109) was investigated in 86 COVID-19-infected patients with thrombocytopenia (Group A) and 136 COVID-19-infected patients without thrombocytopenia (Group B). HPA genotyping was done by the sequence-specific primers PCR method. Lower HPA-3a and higher HPA-3b (P = 0.028) allele frequencies were seen in Group A than in Group B, and homozygosity for HPA 3b (P = 0.038) alleles was more prevalent in Group A than in Group B. The allele and genotype distributions of the other HPA polymorphic variants were similar between the two groups. Univariate analysis identified the CCGGGC (P = 0.016) combined genotype to be negatively associated & the TCGGGC (P = 0.003) and CCGGGC (P = 0.003) to be positively associated with thrombocytopenia. The frequency of anti-HPA-1a and anti-HPA-3a antibodies was significantly higher in all patients compared to other anti-HPAs antibodies (P < 0.05). These results highlight the role of HPAs in the thrombocytopenia of COVID-19 infected patients. This is the first evidence demonstrating the differential association of the six common HPA gene variants and specific HPA genotype combinations with thrombocytopenia in COVID-19-infected patients.

An optimized procedure for Luminex-based human platelet antigen-specific antibody screening and identification (PakLx assay) with a cost-effective approach and improved sensitivity.

BACKGROUND AND OBJECTIVES: Detection of anti-platelet antibodies is required for the diagnosis of foetal/neonatal alloimmune thrombocytopaenia. The most commonly used methods for anti-platelet antibody detection are the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) and the Luminex bead assay (PakLx). However, for economic reasons, the use of the PakLx assay is limited. MATERIALS AND METHODS: In the present study, we evaluated the performance of an optimized protocol based on a half-volume of PakLx reagents. We compared two alternative procedures: one with a half-volume of all components including patient samples, and another based on a half-volume of reagents but a standard volume of patient sample. RESULTS: Our results obtained with a panel of 67 samples demonstrate improved sensitivity when using a standard sample volume. CONCLUSION: In the event of an inconclusive result with this optimized protocol (e.g., incomplete panel of positive Luminex beads), we recommend testing the sample with an alternative protocol (e.g., MAIPA or the original PakLx protocol).

The Impact of Human Platelet Antigen Allele on Antiplatelet Antibodies and Cryoglobulins in Patients with Primary Immune Thrombocytopenia and Hepatitis C Virus-Associated Immune Thrombocytopenia.

Background And Objectives: Human platelet antigens (HPAs) are alloantigens associated with antiplatelet alloantibodies and the risk of immune thrombocytopenia (ITP). However, few studies have investigated associations among HPAs, antiplatelet autoantibodies, and cryoglobulins. Methods: We enrolled 43 patients with primary ITP, 47 with hepatitis C virus-associated ITP (HCV-ITP), 21 with hepatitis B virus-associated ITP (HBV-ITP), 25 controls with HCV, and 1013 normal controls. We analyzed HPA allele frequencies, including HPA1-6 and 15, antiplatelet antibodies binding to platelet glycoprotein (GP) IIb/IIIa, Ia/IIa, Ib/IX, IV, human leukocyte antigen class I, cryoglobulin IgG/A/M, and their associations with thrombocytopenia. Results: In the ITP cohort, HPA2ab, rather than HPA2aa, predicted a low platelet count. HPA2b was associated with the risk of developing ITP. HPA15b was correlated with multiple antiplatelet antibodies. In HCV-ITP patients, HPA3b was correlated with anti-GPIIb/IIIa antibodies. HCV-ITP patients with anti-GPIIb/IIIa antibodies had a higher positive rate of cryoglobulin IgG and IgA compared with those without anti-GPIIb/IIIa antibodies. Overlapping detection was also found among other antiplatelet antibodies and cryoglobulins. Like the antiplatelet antibodies, cryoglobulins were associated with clinical thrombocytopenia, implying their close relationship. Finally, we extracted cryoglobulins to confirm the exhibition of cryoglobulin-like antiplatelet antibodies. In contrast, in primary ITP patients, HPA3b was correlated with cryoglobulin IgG/A/M rather than anti-GPIIb/IIIa antibodies. Conclusion: HPA alleles were associated with antiplatelet autoantibodies and had different impacts in primary ITP and HCV-ITP patients. HCV-ITP was considered to be a symptom of mixed cryoglobulinemia in HCV patients. The pathophysiology may differ between these two groups.

Frequency of Human Platelet Antigens -1 to -5 and -15 in Turkmen Blood Donors.

Background: Due to the presence of platelet antigen polymorphisms, human platelet membrane glycoproteins can be identified as an alloantigen or autoantigen. The aim of this study was to determine the frequencies of human platelet antigens (HPAs)-1 to-5 and-15 in Turkmen blood donors and establish a panel of accredited HPAs negative donors as well as an HPA-typed platelet donor registry. Materials and Methods: HPA-1 to-5 and-15 typing was performed by the polymerase chain reaction-sequence-specific primer techniques on 80 unrelated Turkmen donors who were referred to Aq-Qala Blood Transfusion Center in Golestan Province from September 2018 to October 2019. Results: The frequencies of HPA phenotypes were determined as follows: HPA-1aa: 92.5%, HPA-1ab: 7.5%, HPA-2aa: 77.5%, HPA-2ab: 20.0%, HPA-2bb: 2.5%, HPA-3aa: 75.3%, HPA-3ab: 50%, HPA-3bb: 11.2%, HPA-4aa: 100%, HPA-5aa: 78.5%, HPA-5ab: 21.5%, HPA-15aa: 41.2%, HPA-15ab: 56.2% and HPA-15bb: 17.5%. Conclusion: Determining the genotype of HPAs that play an important role in platelet refractory can improve the management of alloimmunization due to the incompatibility of HPAs between the recipients and donors. Therefore, the registration process for national platelet donors can help patients accelerate and improve the quality of transfused platelets.

An HPA-1a-positive platelet-depleting agent for prevention of fetal and neonatal alloimmune thrombocytopenia: a randomized, single-blind, placebo-controlled, single-center, phase 1/2 proof-of-concept study.

BACKGROUND: Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is a rare and potentially life-threatening bleeding disorder of the fetus/newborn. Antibodies against human platelet antigen 1a (HPA-1a) are associated with the most frequent FNAIT cases. There are no approved therapies for FNAIT prevention or treatment. RLYB211 is a polyclonal HPA-1a hyperimmune IgG being developed to prevent FNAIT. OBJECTIVES: To investigate whether a single dose of anti-HPA-1a (1000 IU) could markedly accelerate the elimination of HPA-1ab platelets transfused into healthy, HPA-1a-negative participants as compared with placebo. METHODS: This randomized, single-blind, placebo-controlled, single-center, phase 1/2 proof-of-concept study (EudraCT: 2019-003459-12) included HPA-1a- and HLA-A2-negative healthy men. Cohort 1 received intravenous RLYB211 or placebo 1 hour after transfusion of HPA-1ab platelets. Cohort 1B received RLYB211 or placebo, followed by platelet transfusion 1 week later. Primary endpoint was the half-life of transfused platelets in circulation after administration of RLYB211 or placebo, determined by flow cytometry. Proof of concept was ≥90% reduction of half-life relative to placebo. RESULTS: Twelve participants were allocated to cohort 1 or 1B and randomized to receive RLYB211 (n = 9) or placebo (n = 3). RLYB211 markedly accelerated the elimination of HPA-1ab platelets in all participants vs placebo. In cohort 1B, this effect was observed 7 days after RLYB211 administration. Two treatment-emergent adverse events were possibly related to treatment, both in RLYB211-treated participants. No participants developed HPA-1a antibodies at 12 or 24 weeks. CONCLUSION: These data support the hypothesis that anti-HPA-1a could be used as prophylaxis in women at risk of having an FNAIT-affected pregnancy.

Fetal and neonatal alloimmune thrombocytopenia: Current pathophysiological insights and perspectives for future diagnostics and treatment.

FNAIT is a pregnancy-associated condition caused by maternal alloantibodies against paternally-inherited platelet antigens, most frequently HPA-1a on integrin ß3. The clinical effects range from no symptoms to fatal intracranial hemorrhage, but underlying pathophysiological determinants are poorly understood. Accumulating evidence suggests that differential antibody-Fc-glycosylation, activation of complement/effector cells, and integrin function-blocking effects contribute to clinical outcome. Furthermore, some antibodies preferentially bind platelet integrin αIIbß3, but others bind αvß3 on endothelial cells and trophoblasts. Defects in endothelial cells and angiogenesis may therefore contribute to severe anti-HPA-1a associated FNAIT. Moreover, anti-HPA-1a antibodies may cause placental damage, leading to intrauterine growth restriction. We discuss current insights into diversity and actions of HPA-1a antibodies, gathered from clinical studies, in vitro studies, and mouse models. Assessment of all factors determining severity and progression of anti-HPA-1a-associated FNAIT may importantly improve risk stratification and potentially reveal novel treatment strategies, both for FNAIT and other immunohematological disorders.

[Genotyping and its applications, a look to the future]. / Genotipificación y sus aplicaciones, una mirada hacia el futuro.

The detection of the most significant erythrocyte antigens present in each one of the individuals is fundamental when carrying out a transfusion or a transplant. Detection to date is performed by conventional serological methods through the antigen-antibody reaction. But several drawbacks may arise depending on the pathology under study, limiting the availability of blood components. Molecular methods such as genotyping is a tool that complements sensitivity and specificity and has come to revolutionize immunohematology in the blood bank, allowing not only the detection of erythrocyte antigens but also platelet antigens. These methodologies are applicable in patients and in large-scale donors, starting from the allelic variants present in each of the genes that code for the antigens of clinical interest, using microarray systems or systems based on particles labeled with specific probes or their variants that allow an analysis from the immunohematological point of view.

La detección de los antígenos eritrocitarios más significativos presentes en cada uno de los individuos es fundamental cuando se lleva a cabo una transfusión o un trasplante. La detección a la fecha se realiza mediante métodos serológicos convencionales a través de la reacción de antígeno-anticuerpo. Pero se pueden presentar varios inconvenientes dependiendo de la patología en estudio, lo cual limita la disponibilidad de los hemocomponentes. Los métodos moleculares, como la genotipificación, son una herramienta que complementa la sensibilidad y especificidad y que han venido a revolucionar la inmunohematología en el banco de sangre, lo cual permite no solo la detención de antígenos eritrocitarios sino también la de antígenos plaquetarios. Estas metodologías son aplicables en pacientes y en donantes a gran escala, partiendo de las variantes alélicas presentes en cada uno de los genes que codifican para los antígenos de interés clínico, utilizando los sistemas de microarreglos o los sistemas basados en partículas marcadas con sondas específicas o sus variantes que permiten un análisis desde el punto de vista inmunohematológico.

Study on the extensibility of platelet donor gene database in Shaanxi / 中国输血杂志

【Objective】 To analyze the commonality and characteristics between voluntary blood donors and hematopoietic stem cell donors in this region, and explore the potential for integration and development between China Marrow Donors Program (CMDP) and voluntary blood donors, especially platelet donor databases, so as to improve recruitment success rate and inventory rate. 【Methods】 The database modeling and comparison methods were used to screen and stratify the matching and integration degree between the voluntary blood donors in recent 10 years and the marrow donors in the Shaanxi Branch of CMDP. The frequencies of HLA-A,-B alleles, HPA alleles and haplotypes were calculated with Arlequin 3. 5. 2. 2 software, and the matching probability of different platelet donor reserve pools was conducted according to the phenotypic frequencies. 【Results】 Among the voluntary donors with known HLA genotypes in this region, according to their blood donation behavior,the active blood donors excavated were divided into the first, second, third and fourth echelons of platelet donor reserve pools, with 696, 2 752, 9 092 and 12 028 donors, respectively. The first echelon had the highest proportion of 10-50 times of platelet donations and 10-20 times of whole blood donations, with 13.65% and 26.01%, respectively. The second echelon had 10-20 times of whole blood donations and 10-50 times of platelet donations, accounted for 15.04% and 1.38%, respectively, which were significantly different from other echelons' blood donation characteristics (P<0.05). With a database size of the existing platelet donor bank adding the first and second echelons (n=4 955), there was a 69.02% probability of matching at least one donor with matching HLA-A-B phenotype. When considering the matching ABO and HPA phenotypes, the probability of finding at least one donor with fully matching HLA, HPA and ABO isotype (type B as an example) was 48. 73%. 【Conclusion】 The three groups of whole blood donation, apheresis platelet donation and marrow donation in Xi'an area have a large cross-distribution. Compared with expanding the storage capacity from scratch, the active blood donors in CMDP database are the largest back-up force of platelet donors. While expanding the effective storage capacity, it can minimize the cost of building platelet donor bank and the demand for resources.

ABO Incompatibility between the Mother and Fetus Does Not Protect against Anti-Human Platelet Antigen-1a Immunization by Pregnancy.

(1) Background: ABO blood group incompatibility between the mother and fetus protects against anti-D immunization by pregnancy. The possible role of ABO incompatibility in protecting against anti-human platelet antigen-1a immunization is unclear. (2) Methods: This study retrospectively screened 817 families (mother-father-neonate trios) of suspected fetal and neonatal alloimmune thrombocytopenia for inclusion. ABO genotypes were determined in 118 mother-child pairs with confirmed alloimmune thrombocytopenia due to anti-HPA-1a antibodies, and 522 mother-child pairs served as the control group. The expression of blood group antigen A on platelets was determined in 199 consecutive newborns by flow cytometry and compared with adult controls. (3) Results: ABO incompatibility between mother and fetus did not protect against anti-human platelet antigen-1a immunization by pregnancy. ABO blood groups of mothers and/or fetuses were not associated with the severity of fetal and neonatal alloimmune thrombocytopenia. The expression pattern of blood group A antigens on the platelets of newborns mirrored that of adults, albeit on a lower level. Blood group A antigen was detected on a subpopulation of neonatal platelets, and some newborns revealed high platelet expression of A determinants on all platelets (type II high-expressers). (4) Conclusion: The lack of a protective effect of ABO incompatibility between mother and fetus against anti-human platelet antigen-1a immunization by pregnancy may indicate that fetal platelets are not the cellular source by which the mother is immunized.

Antenatal intravenous immunoglobulins in pregnancies at risk of fetal and neonatal alloimmune thrombocytopenia: comparison of neonatal outcome in treated and nontreated pregnancies.

BACKGROUND: Maternal alloantibodies to human platelet antigen-1a can cause severe intracranial hemorrhage in a fetus or newborn. Although never evaluated in placebo-controlled clinical trials, most Western countries use off-label weekly administration of high-dosage intravenous immunoglobulin in all pregnant women with an obstetrical history of fetal and neonatal alloimmune thrombocytopenia. In Norway, antenatal intravenous immunoglobulin is only recommended in pregnancies wherein a previous child had intracranial hemorrhage (high-risk) and is generally not given in other human platelet antigen-1a alloimmunized pregnancies (low-risk). OBJECTIVE: To compare the frequency of anti-human platelet antigen-1a-induced intracranial hemorrhage in pregnancies at risk treated with intravenous immunoglobulin vs pregnancies not receiving this treatment as a part of a different management program. STUDY DESIGN: This was a retrospective comparative study where the neonatal outcomes of 71 untreated human platelet antigen-1a-alloimmunized pregnancies in Norway during a 20-year period was compared with 403 intravenous-immunoglobulin-treated pregnancies identified through a recent systematic review. We stratified analyses on the basis of whether the mothers belonged to high- or low-risk pregnancies. Therefore, only women who previously had a child with fetal and neonatal alloimmune thrombocytopenia were included. RESULTS: Two neonates with brain bleeds were identified from 313 treated low-risk pregnancies (0.6%; 95% confidence interval, 0.2-2.3). There were no neonates born with intracranial hemorrhage of 64 nontreated, low-risk mothers (0.0%; 95% confidence interval, 0.0-5.7). Thus, no significant difference was observed in the neonatal outcome between immunoglobulin-treated and untreated low-risk pregnancies. Among high-risk mothers, 5 of 90 neonates from treated pregnancies were diagnosed with intracranial hemorrhage (5.6%; 95% confidence interval, 2.4-12.4) compared with 2 of 7 neonates from nontreated pregnancies (29%; 95% confidence interval, 8.2-64.1; P=.08). CONCLUSION: The most reliable data hitherto for the evaluation of intravenous immunoglobulins treatment in low-risk pregnancies is shown herein. We did not find evidence that omitting antenatal intravenous immunoglobulin treatment in low-risk pregnancies increases the risk of neonatal intracranial hemorrhage.

The polymorphism of HPA-1-6w, HPA-15 and HPA-32bw-35bw in platelet donors from Deyang, Sichuan / 中国输血杂志

【Objective】 To explore the polymorphism of HPA-1-6w, HPA-15 and 32bw-35bw in platelet donors in Deyang, Sichuan, and estimate whether to include the detection of 32bw-35bw in the platelet bank. 【Methods】 Polymerase chain reaction with sequenced based typing (PCR-SBT) was used to sequence the HPA-1-6w, HPA-15 and 32bw-35bw loci of 205 platelet donors in Deyang. Allele frequencies were calculated by the direct counting method. The frequencies of HPA-1-6 and 15 alleles in northern and southern Chinese, Japanese and Australian population were compared, and those HPA loci and HPA-32bw-35bw were searched in the Chinese Millionome Database (CMDB) and genomAD to obtain the polymorphism data. Then the Chi-square test was performed with the data of this study through GraphPad Prism 9 software. 【Results】 The allele frequencies of HPA-1b, 2b, 3b, 5b, 6bw and HPA-15b were 0.005(2/410), 0.037(15/410), 0.471(193/410), 0.020(8/410), 0.010(4/410) and 0.461(189/410), respectively, b allele of HPA-32bw-35bw and HPA-4 was not detected. Statistical significance was observed between the HPA-1b allele frequency of this study and northern Chinese, Australian population and genomAD global population sample (P< 0.05, 0.005 vs 0.014 vs 0.145 vs 0.122). The frequency of HPA-2b alleles in this study, Japanese population and genomAD global population samples was 0.037 vs 0.120 vs 0.100, with statistical difference(P<0.05). Comparison of HPA-5b and HPA-6bw allele frequencies with those of genomAD global population showed a statistical difference (P<0.05, 0.020 vs 0.089 and 0.010 vs 0.000 008, respectively). 【Conclusion】 The polymorphisms of HPA-1-6w and HPA-15 of donors in Deyang has characteristics of the southern Chinese. The frequencies of HPA-32bw-35bw were extremely low, which could be excluded from the platelet bank in Deyang.

The capacity evaluation and utilization strategy of the platelet donor database with known HLA/HPA genotype in Shaanxi / 中国输血杂志

【Objective】 To evaluate the appropriate optimal capacity and matching probability of the platelet donor database with known HLA/HPA genotype in Shaanxi aera, and provide data support for subsequent construction, maintenance and application of the local platelet donor database. 【Methods】 A total of 11 755 individuals from the Shaanxi Branch of China Marrow Donor Program, 401 and 249 unrelated random platelet donors in Shaanxi aera were enrolled to the population study of HLA-A, -B polymorphisms, HPA genotyping and CD36 antigen expression, respectively. The frequencies of HLA-A, -B alleles, HPA alleles and haplotypes were calculated with Arlequin 3. 5. 2. 2 software; matching probability and capacity evaluation of platelet donor database was conducted according to the phenotypic frequencies. 【Results】 The population genetic and phenotypic polymorphisms data of HLA-A, -B and HPA1-6, 10, 15, 21 in Shaanxi aera were obtained. The frequency of CD36 type Ⅰ or Ⅱ deficiency was 0.40%(1/249). According to the subsequent calculating and deriving, with a database size of 194 donors, the patient having approximate 95% probability could achieve matching of HPA1-6, 10, 15, 21 genotype. With a database size of 1500 donors, there is a 95% probability of matching at least one donor with HLA-A-B phenotype frequency >0.002 or haplotype frequency >0.001; meanwhile, the probability of matching a cross-reactive group donor should be 44.95%-97.57%. Based on database size of 8 856 and 15 033, the probabilities of matching HLA-A, -B phenotype were about 80% and 90%, respectively. 【Conclusion】 The differences in the distribution of HLA/HPA polymorphism in different regions make the establishment mode and optimal capacity of platelet donor database different. It is necessary to apply a variety of platelet matching transfusion strategies to expand the range of donor selection, thereby effectively reducing the database construction cost and resource requirements.

Analysis and prospect of platelet compatible transfusion / 中国输血杂志

Platelet compatible transfusion can effectively solve the immune mediated platelet transfusion refractoriness (PTR), save platelet resources and improve blood safety. This paper comments and prospects the compatibility modes of HLA, HPA and CD36, HLA antibody titer, antigen immunogenicity and the development of platelet compatible transfusion. The pattern of HLA compatible platelets involves the matching in the alleles, antigens and epitopes levels, respectively, as well as avoidance donor specificity antibody (DSA) method. While setting the mean fluorescence intensity (MFI) threshold of avoidance DSA needs to be explored when using the DSA prediction method. Allele specific HLA antibodies can be found in the patients with PTR. Therefore, the patients and donors should be genotyped for HLA-A, -B loci at high-resolution level in order to avoid allele specific HLA antibodies. The immunogenicity of various antigens or epitopes at HLA-A and -B loci are different. Selecting donor platelets with low antigen expression or low immunogenicity may be a way of HLA compatible platelets. As the probability and type of HPA antibody production are different in the various populations, the approaching of compatibility HPA involves allele matching and avoidance DSA. As to CD36, the compatibility mode mainly refers to avoidance DSA, which means blood donors with CD36 antigen type Ⅰdeficiency are preferentially selected, and then those with CD36 antigen type Ⅱ deficiency. In the future, more attention should be paid to the scale up of database capacity and update of the information construction. The time waiting for compatible platelets transfusion in clinical could be significantly shortened if the requiring and matching are only conducted within the inventory and candidate platelets.

Clinical characteristics of human platelet antigen (HPA)-1a and HPA-5b alloimmunised pregnancies and the association between platelet HPA-5b antibodies and symptomatic fetal neonatal alloimmune thrombocytopenia.

Fetal neonatal alloimmune thrombocytopenia (FNAIT) is caused by maternal alloantibodies directed against the human platelet antigens (mostly HPA-1a or HPA-5b) of the (unborn) child and can lead to severe bleeding. Anti-HPA-1a-mediated FNAIT shows a severe clinical outcome more often than anti-HPA-5b-mediated FNAIT. Given the relatively high prevalence of anti-HPA-5b in pregnant women, the detection of anti-HPA-5b in FNAIT-suspected cases may in some cases be an incidental finding. Therefore we investigated the frequency of anti-HPA-5b-associated severe bleeding in FNAIT. We performed a retrospective nationwide cohort study in cases with clinical suspicion of FNAIT. HPA antibody screening was performed using monoclonal antibody-specific immobilisation of platelet antigens. Parents and neonates were typed for the cognate antigen. Clinical data were collected by a structured questionnaire. In 1 864 suspected FNAIT cases, 161 cases (8·6%) had anti-HPA-1a and 60 (3·2%) had anti-HPA-5b. The proportion of cases with severe bleeding did not differ between the cases with anti-HPA-1a (14/129; 11%) and anti-HPA-5b (4/40; 10%). In multigravida pregnant women with a FNAIT-suspected child, 100% (81/81) of anti-HPA-1a cases and 79% (38/48) of anti-HPA-5b cases were HPA-incompatible, whereas 86% and 52% respectively were expected, based on the HPA allele distribution. We conclude that anti-HPA-5b can be associated with severe neonatal bleeding symptoms. A prospective study is needed for true assessment of the natural history of anti-HPA-5b mediated FNAIT.

[Management of high-risk pregnancies in a context of maternal antiplatelet alloimmunization: Expert opinion of the French-speaking working group]. / Prise en charge des grossesses à risque dans un contexte d'incompatibilité fœto-maternelle plaquettaire et/ou d'allo-immunisation : avis du groupe d'experts du GFHT (Groupe français d'études sur l'hémostase et la thrombose).

INTRODUCTION: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a potentially devastating disease, seen in 1/800-1000 neonates. FNAIT is the most common cause of early-onset isolated severe neonatal thrombocytopenia in maternity wards. A working group on fetomaternal platelet alloimmunization was created in 2017, under the auspices on the French Group of Thrombosis and Hemostasis (GFHT). OBJECTIVES: The objective was to survey clinical practices for management of high-risk pregnancies in a context of suspected or confirmed FNAIT. METHODS: Recommendations published by the ICTMG were translated in French, and discussed (Fetal and neonatal alloimmune thrombocytopenia: recommendations for evidence-based practice, an international approach. British J of Haematology, 2019, 185, 549-562). RESULTS: The study involved centers from France, Switzerland and Belgium: Angers, Besançon, Bordeaux, Brest, Créteil/Clamart, Genève, Grenoble, Liège, Lille, Lyon, Marseille, Nantes, Nîmes, Paris (hôpitaux Necker, Robert Debré et Trousseau), Poitiers, Rennes, Saint-Etienne, Strasbourg, Toulouse, Tours. CONCLUSIONS: Expert opinion was validated on September 23, 2020 (consensus≥90%).

Platelet alloimmunization is associated with low grade chronic histiocytic intervillositis - A new link to a rare placental lesion?

INTRODUCTION: Maternal alloimmunization against human platelet antigen (HPA)-1a has been implied to mediate both reduced birth weight and chronic placental inflammation. Fetal growth restriction is associated with different types of chronic inflammation in the placenta, mainly chronic histiocytic intervillositis and chronic villitis. The aim of this prospective study was to do a systematic examination of placentas from HPA-1a alloimmunized pregnancies, with focus on the histopathological and immunohistochemical diagnosis of variants of chronic inflammation. MATERIAL AND METHODS: In a Polish-Norwegian study, 48 placentas were examined. The histopathology of placentas from 27 HPA-1a immunized women was compared with 21 placentas from non-immunized HPA-1a negative women (controls). In the group of alloimmunized women, ten received antenatal intravenous immunoglobulin G (IVIg). Tissue sections from formalin fixed paraffin embedded placental tissue were stained with hematoxylin and eosin and microscopically examined with focus on various types of chronic placental inflammations. RESULTS: Chronic histiocytic intervillositis was observed in 40.7% of placentas from HPA-1a alloimmunized pregnancies, compared to none in the control group (p = 0.001). Chronic villitis of unknown etiology was more frequently found in the alloimmunized group, however this difference was not statistically significant. Maternal administration of IVIg did not seem to protect against chronic inflammatory lesions. DISCUSSION: Placentas with detectable maternal anti-HPA-1a antibodies are associated with highly increased risk of low-grade chronic histiocytic intervillositis.

Down syndrome with neonatal alloimmune thrombocytopenia due to anti-HLA A31 and B61 antibodies.

Neonatal alloimmune thrombocytopenia (NAIT) arises from fetomaternal platelet incompatibility that results in transplacental passage of maternal antibodies mostly against fetal human platelet antigens (HPA), whereas NAIT due to anti-human leukocyte antigen (HLA) antibodies is extremely rare. Here, we report a case of Down syndrome (DS) with NAIT that was attributed to HLA antibodies. A boy with DS was delivered at 36 weeks' gestation. His platelet count declined to 13.0 × 109/L, suggestive of NAIT rather than other conditions, including transient abnormal myelopoiesis. Random platelet concentrates and intravenous immunoglobulin administration resolved the thrombocytopenia without clinical complications. Immunoserological investigations detected anti-HLA, but no anti-HPA antibodies in samples from the patient and the mother. HLA typing and cross-matching indicated that anti-HLA antibodies to paternal HLA A31 and B61, which had probably been induced during a prior pregnancy, led to NAIT in this case. Although it is a rare condition, healthcare providers should consider NAIT due to HLA antibodies and be vigilant for subsequent cases in DS.

Minor impact of patient alloantibodies against human platelet antigen (HPA)-15 in the effectiveness of platelet transfusion: A pilot study.

BACKGROUND: Alloantibodies against human platelet antigen (HPA)-15 are sometimes detected in patients with platelet transfusion refractoriness (PTR); however, little is known about their impact on PTR. STUDY DESIGN AND METHODS: Two patients who possessed HPA-15 alloantibodies (Patient 1, anti-HPA-15b; Patient 2, anti-HPA-15a) and human leukocyte antigen (HLA) antibodies were enrolled. The efficacy of HPA-15-compatible vs -incompatible platelet transfusion was compared by focusing on ABO- and HLA-matched transfusions on the basis of the 24-hour corrected count increment (CCI-24 hours) for platelets. The titers of HPA-15 antibodies in the patients' sera were also monitored. RESULTS: The patients received 71 and 12 ABO-compatible, HLA-matched platelet transfusions, respectively, during the monitoring periods. Among these transfusions, CCI-24 hours could be calculated in 27 and 10 transfusions, respectively, and the HPA-15 genotype of the donors was determined. There were no significant differences in the CCI-24 hours between the HPA-15 compatible and incompatible transfusions in both patients (P = .30 and .56, respectively, Mann-Whitney U test). There was no significant change in the HPA-15b antibody titer in Patient 1 during the monitoring period, while the HPA-15a antibody level in Patient 2 was undetectable at the end of the monitoring period, although the titer was low at the beginning. CONCLUSION: The efficacy of HPA-15-incompatible platelet transfusions was not necessarily inferior to that of HPA-15 compatible ones. Although the case number was limited, our results suggest that HPA-15 antibodies do not have a significant impact on the effects of platelet transfusion.