Fetal and neonatal alloimmune thrombocytopenia (FNAIT) occurs when an alloimmunized pregnant mother produces antibodies against her fetus’s blood platelets. Without early diagnosis and effective treatment, complications of FNAIT can be life-threatening.
An innovative new treatment, called an FcRn inhibitor, has recently shown promising results in targeting maternal antibodies. FcRn inhibitors are a class of drugs that target and block the neonatal Fc receptor.
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but serious condition that affects 0.1% of pregnancies in which a pregnant mother’s immune system produces antibodies against the platelets of her fetus. This occurs when a fetus inherits platelet antigens from the father that are not compatible with the mother, typically involving a protein called human platelet antigen (HPA). The mother’s immune system recognizes the fetal platelets as foreign, attacking and destroying them, leading to low platelet levels (thrombocytopenia) in the fetus or newborn.
What is an FcRn inhibitor?
In FNAIT, the maternal antibodies are immunoglobulin (IgG) antibodies. These antibodies bind to Fc receptors (FcRn) to cross the placenta and progressively destroy the fetal platelets.
As a result, the fetus’s platelet count drops and the blood loses its capacity to clot, leading to uncontrollable bleeding and hemorrhage. Severe complications include bleeding in the lungs, eyes, gastrointestinal tract and most severely, the brain, causing long-term neurological damage or fetal death.
An FcRn inhibitor prevents IgG antibodies from binding to the FcRn, blocking their access to the fetus via the placenta.
What is nipocalimab?
Nipocalimab is a fully human IgG monoclonal antibody designed to selectively block FcRns. A phase 3 clinical trial is currently testing the efficacy and safety of nipocalimab for use in pregnancies at risk of FNAIT.
What are the potential benefits of nipocalimab in FNAIT pregnancies?
If nipocalimab successfully stops IgG antibodies from attaching to the FcRn and crossing the placenta, the fetus’s blood platelets will be protected. This will avoid the risk of thrombocytopenia and its associated complications such as intracranial hemorrhage (ICH).
Nipocalimab may be shown to be more effective than intravenous immunoglobulin (IVIG) and corticosteroids, with fewer side effects.
As a targeted therapy, nipocalimab is a precise treatment that selectively blocks FcRns.
Is nipocalimab available for use in FNAIT pregnancies?
No, nipocalimab is still being evaluated for use in FNAIT pregnancies and is not yet available. Early results of the phase 3 trial are promising but the trial needs to reach its objectives in order to assess its efficacy and safety in treating FNAIT.
A phase 2 trial showed efficacy in preventing or delaying fetal anemia in hemolytic disease of the fetus and newborn (HDFN). Studies are also underway to test the use of nipocalimab in other auto-antibody diseases, such as Sjörgen’s disease.
If you are planning a pregnancy and you’ve already experienced an FNAIT-affected pregnancy, ask your doctor to keep you informed on the progress of the nipocalimab study. It is called the FREESIA-3 trial.
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