What's with the boys? Lower birth weight in boys from HPA-1a alloimmunized pregnancies - New insights from a large prospective screening study in Poland.

Fetomaternal incompatibility in human platelet antigens (HPAs) can cause maternal alloimmunization, which in turn may lead to thrombocytopenia with or without intracranial hemorrhage (ICH) in the fetus or newborn. Retrospective studies suggest that boys from alloimmunized mothers may have higher risk of ICH and lower birth weight than girls. The objective of this study was to assess how maternal HPA-1a alloimmunization, sex of the neonate and birth weight relates in a large prospective cohort. Through a national screening study in Poland (PREVFNAIT) involving HPA-1 typing of 24,259 pregnant women during 2013-2017, 606 HPA-1a negative pregnant women and their offspring were identified and included. Various multivariate models were used to assess if and how maternal HPA-1a alloimmunization status was associated with birth weight and risk of having a small for gestational age (SGA) neonate, and if and how sex of the neonate mattered. Most immunized pregnancies had male fetuses (69 %). Women carrying a male fetus had increased likelihood of having an SGA newborn if they were HPA-1a alloimmunized compared to non-immunized mothers. Increasing maternal anti-HPA-1a antibody levels were significantly associated with reduced birth weight and SGA risk among male-fetus pregnancies, but not if the fetus was female. In conclusion, anti-HPA-1a antibodies in a male fetus pregnancy is associated with increased risk of SGA and lower birth weight, especially if the antibody level is high. Sex of the fetus may therefore be considered as a new clinical predictor of more severe FNAIT neonatal outcome.

Cellular surface plasmon resonance-based detection of anti-HPA-1a antibody glycosylation in fetal and neonatal alloimmune thrombocytopenia.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) can occur due to maternal IgG antibodies targeting platelet antigens, causing life-threatening bleeding in the neonate. However, the disease manifests itself in only a fraction of pregnancies, most commonly with anti-HPA-1a antibodies. We found that in particular, the core fucosylation in the IgG-Fc tail is highly variable in anti-HPA-1a IgG, which strongly influences the binding to leukocyte IgG-Fc receptors IIIa/b (FcγRIIIa/b). Currently, gold-standard IgG-glycoanalytics rely on complicated methods (e.g., mass spectrometry (MS)) that are not suited for diagnostic purposes. Our aim was to provide a simplified method to quantify the biological activity of IgG antibodies targeting cells. We developed a cellular surface plasmon resonance imaging (cSPRi) technique based on FcγRIII-binding to IgG-opsonized cells and compared the results with MS. The strength of platelet binding to FcγR was monitored under flow using both WT FcγRIIIa (sensitive to Fc glycosylation status) and mutant FcγRIIIa-N162A (insensitive to Fc glycosylation status). The quality of the anti-HPA-1a glycosylation was monitored as the ratio of binding signals from the WT versus FcγRIIIa-N162A, using glycoengineered recombinant anti-platelet HPA-1a as a standard. The method was validated with 143 plasma samples with anti-HPA-1a antibodies analyzed by MS with known clinical outcomes and tested for validation of the method. The ratio of patient signal from the WT versus FcγRIIIa-N162A correlated with the fucosylation of the HPA-1a antibodies measured by MS (r=-0.52). Significantly, FNAIT disease severity based on Buchanan bleeding score was similarly discriminated against by MS and cSPRi. In conclusion, the use of IgG receptors, in this case, FcγRIIIa, on SPR chips can yield quantitative and qualitative information on platelet-bound anti-HPA-1a antibodies. Using opsonized cells in this manner circumvents the need for purification of specific antibodies and laborious MS analysis to obtain qualitative antibody traits such as IgG fucosylation, for which no clinical test is currently available.

Research Progress in Neonatal Alloimmune Thrombocytopenia: A Narrative Review.

Background: Neonatal alloimmune thrombocytopenia (NAIT) is an immune disorder characterized by maternal antibodies that destroy fetal platelets, leading to thrombocytopenia. The prevalence of NAIT is approximately 0.05% to 0.15%. Fetal and neonatal severe thrombocytopenia represents the most common form of the disease, primarily occurring in firstborn children. It poses a greater risk and harm to the fetus and newborn. Neonatal intracranial hemorrhage is a severe complication of NAIT, resulting in irreversible damage to cranial nerves and potential neonatal death. Objective: This study aims to assess the current advancements in the pathogenesis, clinical characteristics, laboratory evaluation, and therapeutic interventions for neonatal alloimmune thrombocytopenia. Methods: This narrative review explores neonatal alloimmune thrombocytopenia through a thorough literature review. The study encompasses the pathogenesis, clinical features, laboratory examination, and treatment options associated with this condition. Results: The results of this study highlight that despite the extremely low incidence of NAIT, it carries a high risk. Currently, there is no timely and effective prevention method available. However, using HPA-1a as a screening item for prenatal prevention shows the potential to reduce the mortality rate of NAIT fetuses. Further research is required to evaluate its accuracy and specificity. Conclusions: The findings of this review emphasize the need for further research to develop effective prevention methods. The use of HPA-1a as a screening tool holds promise but requires additional investigation. Enhancing clinical understanding of NAIT will contribute to improved management and outcomes for affected infants.

Children Newly Diagnosed with Fetal and Neonatal Alloimmune Thrombocytopenia: Neurodevelopmental Outcome at School Age.

OBJECTIVE: To evaluate the neurodevelopmental outcome at school age in children newly diagnosed with fetal and neonatal alloimmune thrombocytopenia (FNAIT). STUDY DESIGN: This observational cohort study included children diagnosed with FNAIT between 2002 and 2014. Children were invited for cognitive and neurological testing. Behavioral questionnaires and school performance results were obtained. A composite outcome of neurodevelopmental impairment (NDI) was used, defined, and subdivided into mild-to-moderate and severe NDI. Primary outcome was severe NDI, defined as IQ <70, cerebral palsy with Gross Motor Functioning Classification System level ≥ III, or severe visual/hearing impairment. Mild-to-moderate NDI was defined as IQ 70-85, minor neurological dysfunction or cerebral palsy with Gross Motor Functioning Classification System level ≤ II, or mild visual/hearing impairment. RESULTS: In total, 44 children were included at a median age of 12 years (range: 6-17 years). Neuroimaging at diagnosis was available in 82% (36/44) of children. High-grade intracranial hemorrhage (ICH) was detected in 14% (5/36). Severe NDI was detected in 7% (3/44); two children had high-grade ICH, and one had low-grade ICH and perinatal asphyxia. Mild-to-moderate NDI was detected in 25% (11/44); one child had high-grade ICH, and eight children were without ICH, yet for two children, neuroimaging was not performed. Adverse outcome (perinatal death or NDI) was 39% (19/49). Four children (9%) attended special needs education, three of whom had severe NDI and one had mild-to-moderate NDI. Total behavioral problems within the clinical range were reported in 12%, which is comparable with 10% in the general Dutch population. CONCLUSION: Children who are newly diagnosed with FNAIT are at increased risk for long-term neurodevelopmental problems, even those without ICH. TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov (Identifier: NCT04529382).

How I diagnose and treat neonatal thrombocytopenia.

Neonatal thrombocytopenia, defined as the presence of a circulating platelet count <150 × 109/L, is a common abnormality in babies admitted to neonatal intensive care units. Thrombocytopenia that is typically mild and self-limiting often accompanies neonatal stress in scenarios such as premature delivery or intrauterine growth restriction. However, the differential diagnosis of neonatal thrombocytopenia is wide and includes potentially life-threatening disorders, such as bacterial sepsis, viral infection, and necrotizing enterocolitis. Distinguishing these causes of thrombocytopenia from entities such as genetic thrombocytopenia and fetal and neonatal alloimmune thrombocytopenia is critical for the accurate quantitation of significant adverse events, such as intracranial bleeding, and for the selection of treatments, such as platelet transfusion. In this review, we focus on common differential diagnoses of neonatal thrombocytopenia and highlight how the landscape of diagnosis and management is changing with recent advances in genomic technology and the completion of pivotal clinical trials of platelet transfusion practice. Increasing evidence highlights the need for judicious and restrictive use of platelet transfusions in neonates.

FNAIT pathogenesis determined by serial analysis of three subsequent pregnancies of a woman with severe fetal and neonatal alloimmune thrombocytopenia (FNAIT) with anti-HPA-4b and anti-HPA-5b alloantibodies in the first sibling.

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused by anti-HPA alloantibody, and anti-HPA-4b is the most common cause in Japanese. Anti-HPA-5b is frequently detected in pregnant women, but it is still controversial whether anti-HPA-5b causes severe FNAIT. CASE PRESENTATION: A Japanese woman with anti-HPA-4b and anti-HPA-5b alloantibodies delivered a baby with severe FNAIT who was both HPA-4b and HPA-5b incompatible. We carefully monitored the patient's following three pregnancies (the second and the fourth siblings were HPA-4b incompatible and HPA-5b compatible; the third sibling was both HPA-4b and HPA-5b compatible). FNAIT was not observed in all three siblings, although a modest decrease in cord blood platelet count was observed in the HPA-4b incompatible siblings compared to the HPA-4b compatible sibling. Serial monitoring of anti-HPA titer showed that anti-HPA-4b markedly decreased in late pregnancy and recovered after delivery of the HPA-4b incompatible siblings, but these decreases were not observed during the mother's pregnancy with the HPA-4b compatible sibling. In contrast, anti-HPA-5b remained at a high titer during pregnancy with all three siblings. CONCLUSION: Our data indicate that dynamic changes of anti-HPA-4b occur during pregnancy and strongly suggest that anti-HPA-5b was mainly responsible for severe FNAIT in this case.

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.

New Horizons in Fetal and Neonatal Alloimmune Thrombocytopenia.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a common cause of severe thrombocytopenia in newborns. Intracranial bleeding may lead to severe neurological sequelae and mortality. Current management of pregnancies at risk is suboptimal. Prenatal FNAIT diagnosis commonly requires invasive procedures and therapy is associated with a high treatment burden. The present review explores advances in the field and their potential contribution to modification of the diagnostic and therapeutic landscape. Topics addressed include the role of noninvasive prenatal testing using fetal cell free DNA, insights into novel and prospective therapeutic options achieved through the development of murine models of FNAIT as well as the forecast for the progress in pregnancy risk stratification through advancement in the investigation of biological characteristics of alloantibodies and their association with the risk of fetal bleeding.

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.

Postnatal treatment for children with fetal and neonatal alloimmune thrombocytopenia: a multicentre, retrospective, cohort study.

BACKGROUND: Children affected by fetal and neonatal alloimmune thrombocytopenia (FNAIT) are at risk of severe intracranial haemorrhage. Management in the postnatal period is based on sparse evidence. We aimed to describe the contemporary management and outcomes of patients with FNAIT in high-income countries. METHODS: In this multicentre, retrospective, cohort study, we set up a web-based registry for the collection of deidentified data on the management and course of neonates with FNAIT. Eight centres from seven countries (Australia, Norway, Slovenia, Spain, Sweden, the Netherlands, and the USA) participated. Eligibility criteria comprised neonates with FNAIT being liveborn between Jan 1, 2010, and Jan 1, 2020; anti-human platelet antigen (HPA) alloantibodies in maternal serum; confirmed maternal and fetal HPA incompatibility; and bleeding detected at antenatal ultrasound, neonatal thrombocytopenia (<150 × 109 platelets per L), or both in the current or previous pregnancy. Clinical data were retrieved from local medical records of the first neonatal admission and entered in the registry. The key outcome was the type of postnatal treatment given to neonates with FNAIT. Other outcomes were daily median platelet counts in the first week of life, median platelet count increment after first unmatched versus first matched transfusions, and the proportion of neonates with mild or severe bleeding. FINDINGS: 408 liveborn neonates with FNAIT were entered into the FNAIT registry, of whom 389 from Australia (n=74), Norway (n=56), Slovenia (n=19), Spain (n=55), Sweden (n=31), the Netherlands (n=138), and the USA (n=16) were included in our analyses. The median follow-up was 5 days (IQR 2-9). More neonates were male (241 [64%] of 379) than female (138 [36%]). Severe thrombocytopenia (platelet count <50 × 109 platelets per L) was reported in 283 (74%) of 380 neonates, and extreme thrombocytopenia (<10 × 109 platelets per L) was reported in 92 (24%) neonates. Postnatal platelet count nadir was higher in the no-treatment group than in all other groups. 163 (42%) of 389 neonates with FNAIT received no postnatal treatment. 207 (53%) neonates received platelet transfusions, which were either HPA-unmatched (88 [43%] of 207), HPA-matched (84 [41%]), or a combination of both (35 [17%]). The proportion of neonates who received HPA-matched platelet transfusions varied between countries, ranging from 0% (Slovenia) to 63% (35 of 56 neonates; Norway). Postnatal intravenous immunoglobulin treatment was given to 110 (28%) of 389 neonates (alone [n=19] or in combination with platelet transfusions [n=91]), with the proportion receiving it ranging from 12% (17 of 138 neonates; the Netherlands) to 63% (ten of 16 neonates; the USA) across countries. The median platelet increment was 59 × 109 platelets per L (IQR 35-94) after HPA-unmatched platelet transfusions and 98 × 109 platelets per L (67-134) after HPA-matched platelet transfusions (p<0·0001). Severe bleeding was diagnosed in 23 (6%) of 389 liveborn neonates, with one having a severe pulmonary haemorrhage and 22 having severe intracranial haemorrhages. Mild bleeding was diagnosed in 186 (48%) neonates. INTERPRETATION: Postnatal management of FNAIT varies greatly between international centres, highlighting the absence of consensus on optimal treatments. Our data suggest that HPA-matched transfusions lead to a larger median platelet count increment than HPA-unmatched transfusions, but whether HPA matching is also associated with a reduced risk of bleeding remains unknown. FUNDING: Sanquin.

[Serological Diagnosis and Clinical Data Analysis of Neonatal Alloimmune Thrombocytopenia].

OBJECTIVE: To investigate the pathogenesis and clinical diagnosis of fetal/neonatal alloimmune thrombocytopenia (FNAIT) and analyze the laboratory test results and clinical data related to the disease, so as to provide reference for clinical treatment and improvement of prognosis. METHODS: The clinical data of six neonatal patients with FNAIT in the Neonatology Department of our hospital from March 2017 to September 2020 were retrospectively analyzed, which included laboratory diagnosis, clinical symptoms, treatment, and prognosis. RESULTS: Among six patients, two cases occurred in the first pregnancy and four cases in the second pregnancy. The platelet count of six cases were decreased at admission or during hospitalization and maternal and neonatal serum autoimmune platelet antibody tests were positive. Five cases were accompanied by different degrees of skin and facial bleeding spots or petechiae and ecchymosis, intracranial hemorrhage. Four cases were treated with immunoglobulin and/or steroid hormone therapy (one of them received cross-matched platelets transfusion), while the symptoms of the other two cases improved spontaneously. Five cases recovered and were discharged from the hospital, while one case had not recovered but the family members requested to be discharged forwardly. Four cases were hospitalized within two weeks, but two cases were hospitalized for more than two weeks due to other diseases or factors (e.g., neonatal sepsis, neonatal enteritis, congenital heart disease, neonatal asphyxia, etc.). CONCLUSION: FNAIT is characterized by decreased platelet count, with or without bleeding symptoms, and may occur in the first and following pregnancy. FNAIT can recover spontaneously or have a good prognosis after treatment. However, the complication with other diseases or factors may affect the prognosis.