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.

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.

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.

Prophylactic administration of HPA-1a-specific antibodies prevents fetal/neonatal alloimmune thrombocytopenia in mice.

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is a life-threatening bleeding disorder caused by maternal alloantibodies directed against paternally inherited human platelet alloantigens (HPAs) present on the surface of fetal and neonatal platelets. There are currently no approved therapies for the prevention of FNAIT. We report herein the ability of 2 human HPA-1a-specific therapeutic candidates, one a polyclonal, and the other a monoclonal antibody, to prevent alloimmunization in a novel preclinical mouse model of FNAIT. Both antibody preparations effected the rapid and complete elimination of HPA-1a+ platelets from circulation and prevented the development of HPA-1a alloantibodies. HPA-1a- female mice treated prophylactically with anti-HPA-1a antibody prior to exposure to HPA-1a+ platelets gave birth to HPA-1a+/- pups with significantly improved platelet counts and no bleeding symptoms. These preclinical data establish both the potential and threshold exposure targets for prophylactic treatment with HPA-1a-specific antibodies for the prevention of FNAIT in humans.

Prevention of Fetal/Neonatal Alloimmune Thrombocytopenia in Mice: Biochemical and Cell Biological Characterization of Isoforms of a Human Monoclonal Antibody.

Maternal alloantibodies toward paternally inherited Ags on fetal platelets can cause thrombocytopenia and bleeding complications in the fetus or neonate, referred to as fetal and neonatal alloimmune thrombocytopenia (FNAIT). This is most commonly caused by Abs against the human platelet Ag (HPA)-1a in Caucasians, and a prophylactic regimen to reduce the risk for alloimmunization to women at risk would be beneficial. We therefore aimed to examine the prophylactic potential of a fully human anti-HPA-1a IgG1 (mAb 26.4) with modified Fc region or altered N-glycan structures. The mAb 26.4 wild-type (WT) variants all showed efficient platelet clearance capacity and ability to mediate phagocytosis independent of their N-glycan structure, compared with an effector silent variant (26.4.AAAG), although the modified N-glycan variants showed differential binding to FcγRs measured in vitro. In an in vivo model, female mice were transfused with platelets from transgenic mice harboring an engineered integrin ß3 containing the HPA-1a epitope. When these preimmunized mice were bred with transgenic males, Abs against the introduced epitope induced thrombocytopenia in the offspring, mimicking FNAIT. Prophylactic administration of the mAb 26.4.WT, and to some extent the mAb 26.4.AAAG, prior to platelet transfusion resulted in reduced alloimmunization in challenged mice and normal platelet counts in neonates. The notion that the effector silent variant hampered alloimmunization demonstrates that rapid platelet clearance, as seen with mAb 26.4.WT, is not the sole mechanism in action. Our data thus successfully demonstrate efficient Ab-mediated immunosuppression and prevention of FNAIT by anti-HPA-1a monoclonal variants, providing support for potential use in humans.

New developments in fetal and neonatal alloimmune thrombocytopenia.

Fetal and neonatal alloimmune thrombocytopenia, the platelet equivalent of hemolytic disease of the fetus and newborn, can have devastating effects on both the fetus and neonate. Current management of fetal and neonatal alloimmune thrombocytopenia in a subsequent affected pregnancy involves antenatal administration of intravenous immune globulin and prednisone to the pregnant woman to prevent the development of severe fetal thrombocytopenia and secondary intracranial hemorrhage in utero. That therapy has proven to be highly effective but is associated with maternal side effects and is expensive. This commentary describes 4 advances that could substantially change the current approach to detecting and managing fetal and neonatal alloimmune thrombocytopenia in the near future. The first would be an introduction of a program to screen all antepartum patients in this country for pregnancies at risk of developing fetal and neonatal alloimmune thrombocytopenia. Strategies to implement this complex process have been described. A second advance is testing of cell-free fetal DNA obtained from maternal blood to noninvasively determine the fetal human platelet antigen 1 genotype. A third, in preliminary development, is creation of a prophylactic product that would be the platelet equivalent of Rh immune globulin (RhoGAM). Finally, a fourth major potential advance is the development of neonatal Fc receptor inhibitors to replace the current medical therapy administered to pregnant women with an affected fetus. Neonatal Fc receptor recycles plasma immunoglobulin G to increase its half-life and is the means by which immunoglobulin G crosses the placenta from the maternal to the fetal circulation. Blocking the neonatal Fc receptor is an ideal way to prevent maternal immunoglobulin G antibody from causing fetal and neonatal alloimmune thrombocytopenia in a fetus at risk of developing that disorder. The pertinent pathophysiology and rationale for each of these developments will be presented in addition to our thoughts relating to steps that must be taken and difficulties that each approach would face for them to be successfully implemented.

Fetal and Neonatal Alloimmune Thrombocytopenia-New Prospects for Fetal Risk Assessment of HPA-1a-Negative Pregnant Women.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare and potentially serious bleeding condition in the fetus/newborn. FNAIT is usually considered as the platelet counterpart of hemolytic disease of the fetus and newborn. In FNAIT, maternal alloantibodies against paternally inherited platelet antigens traverse the placenta and cause thrombocytopenia in the fetus/newborn. The most common and most serious cases of FNAIT among white people are caused by alloantibodies against the human platelet antigen 1a (HPA-1a), which is absent in 2.3% of women. Today, there is no screening for FNAIT, and for this reason, FNAIT is not suspected until an otherwise healthy child, born at term, presents with thrombocytopenia. Clinical management of subsequent pregnancies at risk of FNAIT is mostly based on the obstetric history. During the last 5 decades, hemolytic disease of the fetus and newborn caused by antibodies against RhD has successfully been prevented by administration of hyperimmune anti-D IgG drug products to RhD-negative women after delivery of an RhD-positive child. Similarly, a hyperimmune anti-HPA-1a IgG (NAITgam) is under development for the prevention of HPA-1a immunization and FNAIT. If NAITgam becomes licensed for FNAIT prophylaxis and national health authorities decide to include FNAIT screening in their antenatal health care programs, it will be necessary to improve today's tools for assessing the risk of FNAIT. Although the primary risk factor for HPA-1a immunization is platelet type HPA-1bb, not all HPA-1a-negative women develop anti-HPA-1a. The women who are HLA-DRB3:01:01 negative (72%) only rarely develop anti-HPA-1a, and for those few who become HPA-1a immunized, it is quite rare to have a child with severe thrombocytopenia. Determination of fetal HPA-1 type is important because 15% of HPA-1a-negative women will carry an HPA-1a-negative fetus and therefore not be at risk of FNAIT. The severity of FNAIT seems to be associated with the level of anti-HPA-1a. Hence, in Norway, for example, an Ab threshold of 3 IU/mL is used to distinguish between low- and high-risk pregnancies. The current review will discuss to what extent these analyses, as well as determination of subtypes of anti-HPA-1a (anti-ß3, anti-αIIbß3, and anti-αvß3) and Fc core fucosylation of anti-HPA-1a IgG, can be used as risk stratification tools.

Non-invasive risk-assessment and bleeding prophylaxis with IVIG in pregnant women with a history of fetal and neonatal alloimmune thrombocytopenia: management to minimize adverse events.

INTRODUCTION: In pregnant women with a history of fetal and neonatal alloimmune thrombocytopenia (FNAIT), prenatal intervention in subsequent pregnancies may be required to prevent fetal bleeding. Several invasive and non-invasive protocols have been published: amniocentesis for fetal genotyping, fetal blood sampling for the determination of fetal platelet count, intrauterine platelet transfusions, and weekly maternal i.v. immunoglobulin (IVIG) infusion with or without additional corticosteroid therapy. This is the first retrospective study that report the experience with a non-invasive protocol focused on side effects of maternal IVIG treatment and neonatal outcome. METHODS: Pregnant women with proven FNAIT in history and an antigen positive fetus were treated with IVIG (1 g/kg/bw) every week. To identify potential IVIG-related hemolytic reactions isoagglutinin titer of each IVIG lot and maternal blood count were controlled. IVIG-related side effects were prospectively documented and evaluated. Furthermore, ultrasound examination of the fetus was performed before starting IVIG administration and continued regularly during treatment. Outcome of the index and subsequent pregnancy was compared. Corresponding data of the newborns were analyzed simultaneously. RESULTS: IVIG was started at 20 weeks of gestation (median). Compared to the index pregnancy, platelet counts of the newborns were higher in all cases. No intracranial hemorrhage occurred (Index pregnancies: 1 case). Platelet counts were 187 × 109/l (median, range 22-239, 95% CI) and one newborn had mild bleeding. No severe hemolytic reaction was observed and side effects were moderate. CONCLUSION: Among pregnant women with FNAIT history, the use of non-invasive fetal risk determination and maternal IVIG resulted in favorite outcome of all newborns. Invasive diagnostic or therapeutic procedures in women with a history of FNAIT should be abandoned.

Strategies to develop a prophylaxis for the prevention of HPA-1a immunization and fetal and neonatal alloimmune thrombocytopenia.

Anti-HPA-1a-antibodies are the main cause of fetal and neonatal alloimmune thrombocytopenia (FNAIT) which may result in intracranial hemorrhage (ICH) and death among fetuses and newborns. Advances in understanding the pathogenesis of FNAIT and proof of concept for prophylaxis to prevent immunization suggest that development of hyperimmune anti-HPA-1a IgG aimed at preventing immunization against HPA-1a and FNAIT is feasible. Anti-HPA-1a IgG can be obtained either by isolating immunoglobulin from already-immunized women or by development of monoclonal anti-HPA-1a antibodies. Here we discuss recent advances that may lead to the development of a prenatal and postnatal prophylactic treatment for the prevention of HPA-1a-associated FNAIT and life-threatening FNAIT-induced complications.

Murine models for studying treatment, prevention and pathogenesis of FNAIT.

Maternal alloimmunization to paternally inherited antigens on fetal/neonatal platelets can cause fetal/neonatal alloimmune thrombocytopenia (FNAIT) after antibody-mediated removal of platelets from the fetal circulation. The complications vary from mild bleeding symptoms to severe intracranial hemorrhage and subsequent neurological impairment or death. Studies on in vivo mechanisms are challenging to measure directly in pregnant women, rendering murine models as valuable and attractive alternatives, despite some critical differences between mice and men affecting the translational value. Here we present and discuss, the different murine models that substantially have increased our knowledge and understanding of FNAIT pathogenesis - as well as pre-clinical evaluation of therapeutic and preventive strategies.

Prenatal Management of Pregnancies at Risk of Fetal Neonatal Alloimmune Thrombocytopenia (FNAIT): Scientific Impact Paper No. 61.

WHAT IS IT?: Fetal neonatal alloimmune thrombocytopenia (FNAIT), also known as neonatal alloimmune thrombocytopenia (NAIT) or fetomaternal alloimmune thrombocytopenia (FMAIT), is a rare condition which affects a baby's platelets. This can put them at risk of problems with bleeding, particularly into the brain. One baby per week in the UK may be seriously affected and milder forms can affect one in every 1000 births. HOW IS IT CAUSED?: Platelets are blood cells that are very important in helping blood to clot. All platelets have natural proteins on their surface called human platelet antigens (HPAs). In babies, half of these antigens are inherited from the mother and half from the father. During pregnancy, some of the baby's platelets can cross into the mother's bloodstream. In most cases, this does not cause a problem. But in cases of FNAIT, the mother's immune system does not recognise the baby's HPAs that were inherited from the father and develops antibodies, which can cross the placenta and attack the baby's platelets. These antibodies are called anti-HPAs, and the commonest antibody implicated is anti-HPA-1a, but there are other rarer antibody types. If this happens, the baby's platelets may be destroyed causing their platelet count to fall dangerously low. If the platelet count is very low there is a risk to the baby of bleeding into their brain before they are born. This is very rare but if it happens it can have serious effects on the baby's health. HOW IS IT INHERITED?: A baby inherits half of their HPAs from its mother and half from its father. Consequently, a baby may have different HPAs from its mother. As the condition is very rare, and even if the baby is at risk of the condition we have no way of knowing how severely they will be affected, routine screening is not currently recommended. WHAT CAN BE DONE?: FNAIT is usually diagnosed if a previous baby has had a low platelet count. The parents are offered blood tests and the condition can be confirmed or ruled out. There are many other causes of low platelets in babies, which may also need to be tested for. As the condition is so rare, expertise is limited to specialist centres and normally a haematologist and fetal medicine doctor will perform and interpret the tests together. Fortunately, there is an effective treatment for the vast majority of cases called immunoglobulin, or IVIg. This 'blood product' is given intravenously through a drip every week to women at risk of the condition. It may be started from as early as 16 weeks in the next pregnancy, until birth, which would be offered at around 36-37 weeks. Less common treatments that may be considered depending on individual circumstances include steroid tablets or injections, or giving platelet transfusions to the baby. WHAT DOES THIS PAPER TELL YOU?: This paper considers the latest evidence in relation to treatment options in the management of pregnancies at risk of FNAIT. Specifically, we discuss the role of screening, when IVIg should be started, what dose should be used, and what evidence there is for maternal steroids. We also consider in very rare selected cases, the use of fetal blood sampling and giving platelet transfusions to the baby before birth. Finally, we consider the approaches to blood testing mothers to tell if babies are at risk, which is offered in some countries, and development of new treatments to reduce the risk of FNAIT.

Noninvasive prenatal diagnosis by cell-free DNA screening for fetomaternal HPA-1a platelet incompatibility.

BACKGROUND: The development of new noninvasive approaches for the diagnosis of human platelet antigen (HPA)-1 fetomaternal incompatibility has become of great interest. These approaches allow determination of whether the fetus is incompatible or not with the mother and a decision on antenatal therapy to avoid fetal or neonatal alloimmune thrombocytopenia (FNAIT). The objective of this work was to perform rapid, noninvasive prenatal test for HPA-1ab fetal antigen detection after the detection of an HPA-1-homozygous mother by using plasma cell-free DNA (cfDNA). STUDY DESIGN AND METHODS: The HPA-1 genotypes of 142 pregnant women and 17 nonpregnant controls were retrospectively determined by high-resolution melting (HRM) polymerase chain reaction (PCR). Coamplification at lower denaturation temperature (COLD) HRM PCR was performed to determine the fetal genotype analyzing cfDNA from all HPA-1bb pregnant women. RESULTS: After the HRM analysis, the following genotypes were identified: HPA-1aa (71.13%), HPA-1bb (2.8%), and HPA-1ab (26.06%). Four HPA-1bb-homozygous pregnant women were carrying an incompatible fetus. Plasma samples from these mothers were analyzed by HRM COLD-PCR. Homozygous HPA-1bb pregnant women carrying an HPA-1ab-heterozygous fetus did not group with either the HPA-1ab or the HPA-1bb controls. Thus, COLD-PCR analysis allows the detection of HPA-1ab-heterozygous fetuses carried by homozygous mothers during first weeks of pregnancy. CONCLUSION: The fetal genotype from HPA-1bb-homozygous women was detected by a noninvasive prenatal test as soon as 12 weeks of gestation.

[Establishing a screening programme in Denmark for foetal and neonatal alloimmune thrombocytopenia].

Foetal and neonatal alloimmune thrombocytopenia (FNAIT) can cause cerebral haemorrhage in newborns. FNAIT occurs in women, who do not have the thrombocyte type human platelet antigen (HPA)-1a and are carrying an HPA-1a positive foetus. Maternal antibodies can cause thrombocytopenia in the foetus or newborn. Antenatal screening for FNAIT can easily be integrated in the already existing national screening programme for rhesus immunisation. Prophylactic treatment with immunoglobulines for pregnancies at risk can prevent neonatal complications. We argue, that the WHO criteria for a screening programme for FNAIT are met.

Successful management of a hydropic fetus with severe anemia and thrombocytopenia caused by anti-CD36 antibody.

Cases of CD36 deficiency are not rare in Asian populations, foetal and neonatal alloimmune thrombocytopenia (FNAIT) caused by anti-CD36 isoantibodies appears more frequent than other HPA alloantibodies. However, little is known about the treatment of anti-CD36 mediated FNAIT in this region. A Chinese male foetus, whose mother had a history of multiple intrauterine foetal demise and/or hydrops, was diagnosed with severe FNAIT at 27 weeks of gestational age. Immunological analysis revealed total absence of CD36 on platelets and monocytes from mother, caused by a 329-330delAC mutation of the CD36 gene. Anti-CD36 and anti-HLA class I antibodies were detected in the maternal serum, whereas only anti-CD36 isoantibodies were detectable in the foetal blood sample. Serial intrauterine transfusions with red blood cells (RBC) and platelets from a CD36null donor were performed to improve the severe anaemia and thrombocytopenia. The baby (2250 g; Apgar scores 10) was delivered vaginally at 32 weeks of gestation with normal haemoglobin (186 g/L) but low platelet count (48 × 109/L). After 2 days the platelet count rose to 121 × 109/L. This report suggests that intrauterine transfusions with compatible RBC and CD36null platelets are useful in preventing the deleterious clinical effects of anti-CD36-mediated severe FNAIT.

Fetal and neonatal alloimmune thrombocytopenia: evidence based antenatal and postnatal management strategies.

INTRODUCTION: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a relatively rare but potentially lethal disease, leading to severe bleeding complications in 1 in 11.000 newborns. It is the leading cause of thrombocytopenia in healthy term-born neonates. Areas covered: This review summarizes the antenatal as well as postnatal treatment, thus creating a complete overview of all possible management strategies for FNAIT. Expert commentary: The optimal antenatal therapy in order to prevent bleeding complications in pregnancies complicated by FNAIT is non-invasive treatment with weekly intravenous immunoglobulin (IVIG). Based on risk stratification, weekly doses of IVIG of 0.5 or 1.0g/kg should be administered started early in the second in high risk cases or at the end of the second trimester in low risk cases. The optimal postnatal treatment depends on the platelet count and the clinical condition of the newborn. Prompt administration of compatible platelet transfusion is the first treatment of choice in case of severe thrombocytopenia or active bleeding. In case matched platelets are not directly available, random platelets can also be administered initially to gain time until matched platelets are available. In case of persistent thrombocytopenia despite transfusions, IVIG 1.0-2.0g/kg can be administered.

Low-dose prednisone and immunoglobulin G treatment for woman at risk for neonatal alloimmune thrombocytopenia and T helper 1 immunity.

PROBLEM: Fetal and neonatal alloimmune thrombocytopenia is an alloimmune disorder resulting from platelet opsonization by maternal antibodies that destroy fetal platelets. As there is no antenatal screening or immunization to prevent sensitization, selection of high-risk population or the prevention of antenatal sensitization is significantly limited. METHOD OF STUDY: (i) A case report of ante- and postnatal management of a woman with paternal homozygosity for human platelet antigen-1(HPA) incompatibility. (ii) A retrospective case-control study of 11 confirmed FNAIT patients, 8 possible-FNAIT women, and 10 women with confirmed ITP. RESULT: Antenatal screening, prevention of maternal sensitization by serial monitoring and immunosuppression with prednisone and intravenous immunoglobulin G (IVIG) infusion resulted in two successful pregnancies without sensitization. CONCLUSION: Screening for couples at risk and prednisone and/or IVIG treatment is an option for women with paternal homozygosity for offending HPA antigen to prevent antenatal sensitization. HPA incompatibility is associated with increased Th1 immunity and NK cell cytotoxicity.

Association between Fetal Cerebral Ventriculomegaly and Platelet Alloimmunisation.

INTRODUCTION: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare condition that may lead to intracerebral haemorrhage (ICH) in the fetus or neonate. Platelet alloimmunisation causing FNAIT has been described in association with fetal cerebral ventriculomegaly (VM), presumably due to subclinical ICH. The objective of this study was to assess the association between fetal VM and platelet alloimmunisation. METHODS: This is a case series of pregnancies with fetal VM screened for platelet alloantibodies from 2003 to 2012. Cases of multiple pregnancies, structural anomalies, aneuploidies, or congenital infection were excluded. RESULTS: Of 45 pregnancies with fetal VM that were screened for platelet alloantibodies, 5 (11%) were positive. There was only one antenatal ICH, with confirmed fetal severe thrombocytopenia before termination of pregnancy. The other cases were treated with intravenous immunoglobulins without prior fetal blood sampling. No other case of neonatal thrombocytopenia was confirmed. CONCLUSIONS: The prevalence of platelet alloimmunisation was high in this series of fetal VM. Prospective large studies are needed to confirm the role of platelet alloimmunisation in fetal VM.

Anti-Human Platelet Antigen-1a Immunoglobulin G Preparation Intended to Prevent Fetal and Neonatal Alloimmune Thrombocytopenia.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a severe disease that is caused by maternal alloantibodies generated during pregnancy or at delivery as a result of incompatibility between maternal and fetal human platelet antigens (HPAs) inherited from the father. Antibody-mediated immune suppression using anti-HPA-1a immunoglobulins is thought to be able to prevent FNAIT caused by HPA-1a. A fractionation process to prepare anti-HPA-1a immunoglobulin (Ig) G (IgG) from human plasma was therefore developed. Anti-HPA-1a plasma was obtained from volunteer mothers who underwent alloimmunization against HPA-1a during a previous pregnancy. Plasma was cryoprecipitated and the supernatant treated with caprylic acid and solvent/detergent (S/D), purified by chromatography, nanofiltered, concentrated, and sterile-filtered. The anti-HPA-1a immunoglobulin fraction was characterized for purity and safety. PAK12 and quantitative monoclonal antibody immobilization of platelet antigen (MAIPA) assays were used to detect anti-HPA-1a IgG. Hepatitis C virus (HCV) removal during nanofiltration was assessed by spiking experiments, using cell culture-derived reporter HCV and luciferase analysis. The caprylic acid treatment precipitated non-Ig proteins yielding a 90% pure Ig supernatant. S-HyperCel chromatography of the S/D-treated supernatant followed by HyperCel STAR AX provided high IgG recovery (>80%) and purity (>99.5%), and efficient IgA and IgM removal. Concentrations of complement factors C3 and C4 were < 0.5 and < 0.4 mg/dL, respectively. The final IgG could be nanofiltered on Planova 20N under conditions removing more than 3 log HCV infectivity to baseline mock infection level, and concentrated to ca. 30 g/L. Proteolytic activity and thrombin generation were low in the final fraction. The Pak12 and MAIPA assays showed good recovery of anti-HPA-1a throughout the process. Clinical-grade HPA-1a IgG can be prepared using a process compliant with current quality requirements opening perspectives for the prevention of FNAIT.