BACKGROUND:Antenatal treatment with nipocalimab, a neonatal Fc receptor (FcRn) blocker, delayed or prevented fetal anemia, as compared with a historical benchmark, in a phase 2 study of early-onset severe hemolytic disease of the fetus and newborn (HDFN). We report on the fetal and neonatal pharmacokinetics of nipocalimab and infant immunity through 96 weeks after birth. METHODS:The UNITY study was a single-group, open-label study assessing pregnant individuals at high risk of early-onset severe HDFN treated with weekly intravenous nipocalimab (30 or 45 mg/kg) from 14 to 35 weeks' gestation, unless discontinued for safety-related stopping criteria or intrauterine transfusion initiation. Pharmacokinetics were assessed in maternal, fetal, and infant blood and colostrum or breast milk; FcRn receptor occupancy and immunoglobulin G (IgG) were measured in neonatal and maternal blood; and infant IgG and safety were monitored through 96 weeks after birth. RESULTS:Safety analysis included 12 live-born infants from 13 pregnancies (one fetal loss occurred following intrauterine transfusion complications). Nipocalimab concentrations were maintained in maternal participants at pharmacologically active concentrations (greater than 10 μg/ml) during the weekly dosing intervals, but were observed at low concentrations (10 μg/ml or less) in one of four fetal cordocenteses (0.04 μg/ml), one of 11 cord blood samples (0.7 μg/ml), three of seven colostrum samples (less than 4 μg/ml), and two of nine breast milk samples (less than 2 μg/ml). Low infant IgG at birth (cord blood median, 175 mg/dl; range, 92-941) reached levels consistent with a physiologic nadir by 24 weeks after birth (median, 273 mg/dl; range, 153-429) and recovered to normal range (with one exception) between 16 and 96 weeks (median, 762 mg/dl; range, 407-925). Infectious adverse events were primarily mild to moderate and typical for early childhood. Protective titers to age-appropriate vaccinations (diphtheria and tetanus) were observed in six of seven infants at or before 96 weeks. CONCLUSIONS:In this cohort of 12 live-born infants, antenatal treatment with nipocalimab resulted in low levels of detectable drug in fetal, neonatal, and infant samples. Treatment was associated with low IgG levels at birth; however, unusual or unexpected childhood illnesses or impaired vaccine responses were not observed. (Funded by Johnson & Johnson; ClinicalTrials.gov number, NCT03842189.).

OBJECTIVES:To describe haemolytic disease outcomes, growth, neurodevelopment and health-related quality of life (HRQoL) through 24 months of life in infants exposed to nipocalimab in pregnancies at high risk of early-onset severe haemolytic disease of the fetus and newborn (EOS-HDFN). DESIGN:A multicentre, open-label, single-arm trial. SETTING:Centres with expertise in HDFN management. PATIENTS:Pregnant individuals with previous EOS-HDFN and maternal anti-D titres ≥32 or anti-K titres ≥4. INTERVENTIONS:Weekly nipocalimab (30 and/or 45 mg/kg) from 14 to 35 gestational weeks. MAIN OUTCOME MEASURES:Infants' cord-blood alloantibody titres at birth, HDFN management, growth through 6 months, neurodevelopment (caregiver-reported Ages and Stages Questionnaire, third edition (ASQ-3)) and HRQoL assessments through 24 months of life. RESULTS:Of 13 pregnancies, 12 resulted in live births; one fetal loss occurred due to intrauterine transfusion (IUT) complications. A single simple transfusion was administered in one of seven infants delivered after a maternal nipocalimab course without IUTs, where cord blood alloantibody titres were <8. Multiple transfusions (one to seven simple transfusions/infant; one exchange transfusion) were administered to five infants delivered after early nipocalimab discontinuation and IUTs, with cord-blood alloantibody titres ranging from 512 to 32 768. No unusual growth patterns were observed through 6 months. No neurodevelopmental delays were identified through 24 months of life, with mean ASQ-3 domain scores within normal ranges. HRQoL outcomes were positive across physical, emotional, social and cognitive functioning. CONCLUSIONS:Maternal nipocalimab in pregnancies at high risk of EOS-HDFN may reduce adverse neonatal outcomes correlating with low cord-blood alloantibody titres, without affecting growth through 6 months, neurodevelopment or HRQoL through 24 months of life. TRIAL REGISTRATION NUMBER:NCT03842189.

Background:In fetal and neonatal alloimmune thrombocytopenia (FNAIT), maternal antibodies react with alloantigen expressed on fetal platelets, leading to their clearance via antibody-dependent phagocytosis. In Caucasians, most FNAIT cases are caused by anti-HPA-1a antibodies. In contrast, anti-HLA class I antibodies are rarely found in FNAIT, but are frequently implicated in cases of platelet transfusion refractoriness (PTR). This phenomenon leads to ongoing debate regarding the role of anti-HLA class I antibodies in FNAIT. In this study, we investigated the platelet clearance mediated by anti-HLA class I antibodies in whole blood both in vitro and in vivo. Methods:Clearance of opsonized platelet was analyzed by platelet phagocytosis assay and by antibody administration to Balb/c female mice. Results:To mimic FNAIT conditions, whole blood was pretreated with anti-HLA antibodies before the phagocytosis of anti-HPA-1a antibody-opsonized platelets. Compared to untreated whole blood, anti-HLA-ABC and anti-HLA-DR IgG antibodies inhibited the phagocytosis of anti-HPA-1a-antibody-opsonized platelets. Similar results were obtained with purified monocytes, indicating that anti-HLA-ABC antibodies bound to monocytes can interfere with antibody-mediated platelet phagocytosis. Furthermore, the administration of anti-MHC-I antibodies to mice led to a significant decrease in the platelet count within 24 h. However, anti-αIIbβ3 antibody administration resulted in significantly higher platelet clearance over different time points. Analysis of antibody-bound platelets showed the presence of anti-αIIbβ3 antibodies on the platelet surface, but not on monocytes. In contrast, anti-MHC-I antibodies were found on both platelets and monocytes. Interestingly, monocytes exhibited higher levels of anti-MHC-I binding than platelets (87.0% vs. 25.5%), most likely because platelets express significantly fewer HLA class I antigens than monocytes, as indicated by our flow cytometric analysis of whole blood. Conclusions:These results indicated that anti-MHC-I antibodies preferentially bind to monocytes rather than platelets in whole blood and can be cleared by monocytes via endocytosis. Furthermore, we found that the presence of anti-HLA class I antibodies did not significantly influence platelet clearance induced by anti-αIIbβ3 antibodies. The question of whether these observations can explain the controversial opinions regarding the relative roles of anti-HLA class I and anti-αIIbβ3 antibodies in FNAIT requires further assessment in a murine model of FNAIT.

ZusammenfassungDie fetale und neonatale Alloimmunthrombozytopenie (FNAIT) wird durch mütterliche Antikörper hervorgerufen, die gegen ein vom Vater ererbtes Blutgruppenmerkmal an fetalen Thrombozyten gerichtet sind. Während Teil 1 des Beitrags Ausgabe die Ätiologie, die Pathogenese und die Diagnostik der FNAIT thematisiert hatte, widmet sich dieser 2. Teil der Risikostratifizierung und Behandlung 1.

(Abstracted from N Engl J Med 2024;391:526–537) Severe hemolytic disease of the fetus and newborn (HDFN) is the result of a transplacental transfer of maternal IgG alloantibodies, which can cause fetal anemia. Early-onset severe HDFN occurs at ≤24 weeks of gestation.

Background: It is widely accepted that autoantibodies directed against platelet glycoproteins (GPs) are a major pathophysiological mechanism in immune thrombocytopenia, but little clinical data are available demonstrating an association between platelet antibodies and platelet counts. Objectives: We hypothesized that if platelet antibodies are clinically relevant, the number of targeted GPs and antibody concentration should be associated with the extent of thrombocytopenia. Methods: Platelet antibodies were identified in a direct GP-specific test that detects antibodies against GPIIb/IIIa and GPIb/IX. Using laboratory data from 12 335 thrombocytopenic patients with and without GP-specific platelet antibodies, we conducted a large retrospective cohort study. Results: We identified 1469 adults with GP-specific platelet antibodies in our database with complete entries. Compared with 10 866 adults without antibodies, patients with antibodies had significantly lower median platelet counts (54 G/L [IQR, 29-89] vs 85 G/L [IQR, 52-123], P < .0001). Patients with antibodies against 2 GPs had significantly lower platelet counts than patients with antibodies against 1 GP (47 G/L [IQR, 26-81] vs 62 G/L [IQR, 32-99], P < .0001 for GPIIb/IIIa and 58 G/L [IQR, 32-99], P = .0004 for GPIb/IX). Increasing antibody levels correlated with decreasing platelet counts for anti-GPIIb/IIIa (R-2 = .69; rho -0.84) and anti-GPIb/IX (R-2 = .57; rho -0.6). Conclusion: The presence of autoantibodies against GPIIb/IIIa or GPIb/IX is associated with lower platelet counts. More GPs targeted by autoantibodies and increasing antibody levels predict lower platelet counts. Platelet antibodies appear to be of clinical relevance.

Background: Antibodies of the mother, which are directed against paternal antigens on platelets of the child, can lead to the destruction of the fetal blood cells in the circulation after diaplacental passage. The clinical picture of fetal-neonatal alloimmune thrombocytopenia (FNAIT) is characterized by bleeding, of which intracranial bleeding is particularly feared. Our understanding of the pathophysiology of FNAIT and its targeted prophylaxis and therapy has improved significantly in recent years. Summary: FNAIT by anti-HPA-1a is the best studied. How exactly the mother is immunized is not known for certain, but, in clinically apparent cases, immunization usually occurs in the first pregnancy of an HLA-DRB3*01:01-positive, HPA-1a-negative woman. There is no convincing basis for assigning immunization against HPA-5b and against HLA class I any significance in the development of fetal thrombocytopenia. Newborns of mothers with anti-HPA-1a present a broad clinical picture ranging from isolated, clinically unremarkable thrombocytopenia to intracranial hemorrhage (ICH; in approx. 1–10% of cases). ICH usually occurs intrauterine (before week 28). There are indications that, in addition to the fetal platelets, the placenta can also be affected by anti-HPA-1a. As there are no screening programmes, the index diagnosis of FNAIT is random. It is made by serological and genetic laboratory tests. Predicting outcome in a subsequent pregnancy is problematic if the child is antigen-positive. Key Messages: With a first-born child with severe thrombocytopenia, the probability of a recurrence of severe thrombocytopenia is around 70%. Without ICH, the probability of ICH in the subsequent pregnancy is low but not zero, and with ICH the recurrence rate is high. There is no established laboratory diagnostic method to predict the severity of thrombocytopenia or the occurrence of ICH. Prophylaxis with immunoglobulins (IVIgs) is considered effective. Pharmaceutics that block placental transport are currently undergoing clinical trials and may replace IVIgs in the future. Intrauterine platelet transfusions should no longer be performed. For the mature, thrombocytopenic newborn without internal hemorrhage, a platelet transfusion is advisable for platelet counts <25 g/L.

The transport of maternal IgG antibodies into the fetal circulation provides the offspring with passive humoral immunity. The transplacental transport of IgG antibodies takes place in a complex process in which the neonatal receptor for the crystallizable fragment of IgG molecules (fragment cristallizable receptor neonatal, FcRn) is essentially involved. FcRn is ubiquitously expressed in the adult organism, regulates IgG and albumin homeostasis as well as innate and adaptive immunity against IgG immune complexes and is thus involved in the defense against infectious diseases and anti-tumor immunity. Therapeutic FcRn antagonists inhibit the recycling of IgG molecules and lead to a reduction in IgG serum levels. In the context of pregnancy, therapeutic FcRn antagonists inhibit transplacental IgG transport. This review is intended to present the status of the potential use of FcRn antagonists in immunohematological diseases caused by autoantibodies and in diseases of the fetus and newborn caused by maternal alloantibodies.

CD177 is a glycosyl phosphatidyl inositol (GPI)-linked, neutrophil-specific glycoprotein that in 3–5% of normal individuals is absent from all neutrophils. The molecular mechanism behind the absence of CD177 has not been unravelled completely. Here, we analyse the impact of the recently described CD177 c.1291G>A variant on CD177 expression. Recombinant CD177 c.1291G>A was expressed in HEK293F cells and its expression on the cell surface, inside the cell, and in the culture supernatant was investigated. The CD177 c.1291G>A protein was characterised serologically and its interaction with proteinase 3 (PR3) was demonstrated by confocal laser scanning microscopy. Our experiments show that CD177 c.1291G>A does not interfere with CD177 protein biosynthesis but affects the membrane expression of CD177, leading to very low copy numbers of the protein on the cellular surface. The mutation does not interfere with the ability of the protein to bind PR3 or human polyclonal antibodies against wild-type CD177. Carriers of the c.1291G>A allele are supposed to be phenotyped as CD177-negative, but the protein is present in soluble form. The presence of CD177 c.1291A leads to the production of an unstable CD177 protein and an apparent “CD177-null” phenotype.

Background In early-onset severe hemolytic disease of the fetus and newborn (HDFN), transplacental transfer of maternal antierythrocyte IgG alloantibodies causes fetal anemia that leads to the use of high-risk intrauterine transfusions in order to avoid fetal hydrops and fetal death. Nipocalimab, an anti-neonatal Fc receptor blocker, inhibits transplacental IgG transfer and lowers maternal IgG levels.Methods In an international, open-label, single-group, phase 2 study, we assessed treatment with intravenous nipocalimab (30 or 45 mg per kilogram of body weight per week) administered from 14 to 35 weeks' gestation in participants with pregnancies at high risk for recurrent early-onset severe HDFN. The primary end point was live birth at 32 weeks' gestation or later without intrauterine transfusions as assessed against a historical benchmark (0%; clinically meaningful difference, 10%).Results Live birth at 32 weeks' gestation or later without intrauterine transfusions occurred in 7 of 13 pregnancies (54%; 95% confidence interval, 25 to 81) in the study. No cases of fetal hydrops occurred, and 6 participants (46%) did not receive any antenatal or neonatal transfusions. Six fetuses received an intrauterine transfusion: five fetuses at 24 weeks' gestation or later and one fetus before fetal loss at 22 weeks and 5 days' gestation. Live birth occurred in 12 pregnancies. The median gestational age at delivery was 36 weeks and 4 days. Of the 12 live-born infants, 1 received one exchange transfusion and one simple transfusion and 5 received only simple transfusions. Treatment-related decreases in the alloantibody titer and IgG level were observed in maternal samples and cord blood. No unusual maternal or pediatric infections were observed. Serious adverse events were consistent with HDFN, pregnancy, or prematurity.Conclusions Nipocalimab treatment delayed or prevented fetal anemia or intrauterine transfusions, as compared with the historical benchmark, in pregnancies at high risk for early-onset severe HDFN. (Funded by Janssen Research and Development; UNITY ClinicalTrials.gov number, NCT03842189.) In a trial involving 13 pregnancies at high risk for early-onset severe hemolytic disease of the fetus and newborn, nipocalimab increased the percentage with live birth at 32 weeks' gestation or later without intrauterine transfusions.

Zusammenfassung Durch den Transport von mütterlichen IgG-Antikörpern in die Zirkulation des Fetus erhalten die Nachkommen den humoralen „Nestschutz“ bzw. die mütterliche „Leihimmunität“. Der transplazentare Transport von IgG-Antikörpern erfolgt in einem komplexen Prozess, an dem der neonatale Rezeptor für das kristallisierbare Fragment von IgG-Molekülen (Fragment cristallizable receptor neonatal, FcRn) essenziell beteiligt ist. FcRn ist im adulten Organismus ubiquitär exprimiert, reguliert die IgG- und Albumin-Homöostase, sowie die angeborene und adaptive Immunität gegen IgG-Immunkomplexe und ist damit an der Abwehr infektiöser Erkrankungen und der Anti-Tumor-Immunität beteiligt. Therapeutische FcRn-Antagonisten blockieren das Recycling von IgG-Molekülen und führen zu einer Absenkung der IgG-Serumspiegel. Im Rahmen einer Schwangerschaft blockieren therapeutische FcRn-Antagonisten den transplazentaren IgG-Transport. Die vorliegende Übersichtsarbeit soll den aktuellen Stand der potenziellen Anwendung von FcRn-Antagonisten bei immunhämatologischen Erkrankungen durch Autoantikörper sowie im Rahmen von Erkrankungen des Fetus und Neugeborenen durch mütterliche Alloantikörper darstellen.

Einleitung und Fragestellung Einige Studien konnten zeigen, dass die Entwicklung eines AVB III° in weniger als 24 Stunden nach einem völlig normalen PR-Intervall erfolgen kann. Wöchentliche Dopplerkontrollen sind für die meisten schwangeren Frauen mit anti-Ro/anti-La-Antikörpern nicht nötig, für betroffene Feten jedoch zu selten. Hier könnte das Homemonitoring eine zielführende Überwachungsmöglichkeit sein. Um die Machbarkeit dieser Maßnahme zu evaluieren, haben wir eine prospektive Studie initiiert.

Zusammenfassung In der vorliegenden Übersichtsarbeit diskutieren wir, wie iatrogene Blutverluste durch immunhämatologische Untersuchungen bei Früh- und Reifgeborenen minimiert werden können. Die Hauptursache für die Transfusion von Erythrozytenkonzentraten (EK) sind dabei iatrogene Blutverluste durch diagnostische Blutentnahmen. In einer Beobachtungsstudie betrug der iatrogene Blutverlust bei Frühgeborenen in den ersten 28 Lebenstagen im Median 24,2 mL/kg im Vergleich zum transfundierten EK-Volumen von 30 mL/kg im selben Zeitraum 1. Die Reduktion von diagnostischen Blutentnahmen stellt somit eine effiziente Maßnahme zur Reduzierung von EK-Transfusionen bei Frühgeborenen dar. Rationale und bedarfsadaptierte immunhämatologische Untersuchungen können den Blutverlust reduzieren, Transfusionen vermeiden und die entstehenden Kosten senken. Ferner stellen wir dar, wie durch differenzierte Auswahl von Blutkomponenten das Auftreten unerwünschter Ereignisse bei der Transfusion von Neugeborenen verhindert werden kann und regen an, restriktivere Indikationsstellungen zur Transfusion insbesondere in der Frühgeborenenmedizin zu diskutieren.

Pemphigus vulgaris (PV) is an autoimmune blistering disorder of the skin and/or mucous membranes caused by IgG autoantibodies that predominantly target two transmembrane desmosomal cadherins: desmoglein (DSG)1 and DSG3. DSG-specific T cells play a central role in PV pathogenesis because they provide help to autoreactive B cells for autoantibody production. In this study, we characterized DSG3-specific peripheral T cells in a cohort of 52 patients with PV and 41 healthy controls with regard to cytokine profile and epitope specificity. By ELISpot analysis, type 2 T cells reactive with the DSG3 ectodomain were significantly increased in patients with PV compared with those in healthy controls. By dextramer analysis, CD4 thorn T cells specific for an epitope within the extracellular domain of DSG3, DSG3(206-220), were found at significantly higher frequencies in patients with PV than in HLA-matched healthy controls. T-cell recognition of two distinct DSG3 epitopes, that is, DSG3(206-220) and DSG3(378-392), correlated significantly, suggesting a synergistic effect in B-cell help. Immunization of HLADRB1*04:02-transgenic mice with PV with the same set of DSG3 peptides induced pathogenic DSG3-specific IgG antibodies, which induced loss of keratinocyte adhesion in vitro. Thus, DSG3 peptide-specific T cells are of particular interest as surrogate markers of disease activity and potential therapeutic targets in PV.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare condition in which maternal alloantibodies to fetal platelets cause fetal thrombocytopenia that may lead to intracranial hemorrhage (ICH). Off-label intravenous immunoglobulin (IVIg) has for 30 years been the standard of care for pregnant women who previously have had a child with FNAIT. The efficacy of this treatment has never been tested in a placebo-controlled clinical trial. Although IVIg treatment may improve the neonatal outcome in women who previously have had a child with FNAIT-associated ICH, the question is whether IVIg is necessary for all immunized pregnant women at risk of having a child with FNAIT. The results from some recent publications suggest that antenatal IVIg treatment is not necessary for women who are (1) HPA-1a-immunized and HLA-DRB3*01:01-negative, (2) HPA-1a-immunized with a previous child with FNAIT but without ICH or (3) HPA-5b-immunized. If IVIg is not used for these categories of pregnant women, the amount of IVIg used in pregnant women with platelet antibodies would be reduced to less than ¼ of today's use. This is important because IVIg is a scarce resource, and the collection of plasma for the treatment of one pregnant woman is not only extremely expensive but also requires tremendous donor efforts.

In the present review, we discuss how iatrogenic blood loss through immunohematologic testing can be minimized in preterm and mature infants. In this context, the main cause of red blood cell (RBC) concentrate transfusion is iatrogenic blood loss due to diagnostic blood sampling. In an observational study, the median iatrogenic blood loss in preterm infants during the first 28 days of life was 24.2 mL/kg compared with the transfused RBC volume of 30 mL/kg during the same period 1 . Thus, reduction of diagnostic blood sampling is an efficient measure to reduce RBC concentrate transfusions in preterm infants. Evidence-based immunohematologic testing can reduce blood loss, avoid transfusions, and reduce the costs incurred. Furthermore, we present how the occurrence of adverse events in neonatal transfusion can be prevented by evidence-based selection of blood components and suggest discussing more restrictive indications for transfusion, especially in premature infants.

Background The relevance of IgM antibodies in autoimmune mediated hemocytopenias remains a matter of debate. For autoimmune neutropenia, conflicting results were published. This study was performed as part of the Giessen Neutropenia Registry, which prospectively included children with suspected autoimmune neutropenia. Methods Children with suspected autoimmune neutropenia were prospectively enrolled and data central to their suspected diagnosis were collected over 3 years. Sera were tested for the presence of autoantibodies against neutrophils by granulocyte immunofluorescence test (GIFT) and granulocyte agglutination test (GAT). The presence of IgG and IgM antibodies was assessed in a subgroup of patients with positive initial GIFT in whom spontaneous remission of their neutropenia was documented. Results A total of 406 children were included in the study. A remission was reported for 114 patients during the study period. Of those, 96 children (84%) had an initial positive GIFT. Their median age at diagnosis was 11 months (7-17.5), and their mean neutrophil count was 293 (±267)/µL, ranging from 0 to 975. In total 75/96 (78%) of children had at least one documented infection at diagnosis. In 29/96 (30%), a bone marrow aspirate was available. At the documented time point of remission, children were 27 months (18-41) old. In the initial sample send for diagnosis, IgG antibodies against neutrophils were detected in 94/96 children (98%), and IgM antibodies were detected in 2/96 (2%). We did not observe children with autoantibodies of both Ig classes. Conclusion To our knowledge, this is the first study to demonstrate the contribution of IgG or IgM antibodies in a well-defined clinical cohort with a typical course including, spontaneous disease remission. IgG antibodies were present in 98%. Only very rarely, IgM antibodies can be detected. We conclude that in general, screening for IgG autoantibodies is appropriate as a first diagnostic step. In cases with strong clinical suspicion but negative GIFT with anti-IgG, anti-IgM testing may be considered.