Fetal and neonatal alloimmune thrombocytopenia (FNAITFetal and neonatal alloimmune thrombocytopenia A rare condition in which a mother’s immune system attacks fetal platelets, leading to dangerously low platelet levels before and/or after birth.) is a potentially life-threatening disease that occurs when maternal antibodies target platelet antigens inherited by the fetus from the father. These antibodies can cross the placenta and destroy fetal platelets, which can lead to severe thrombocytopeniaSevere thrombocytopenia A dangerously low platelet count, typically below 50,000 platelets per microliter and sometimes far lower in FNAIT. and bleeding, including intracranial hemorrhageBrain bleed Bleeding inside the fetal brain, also known as an intracranial hemorrhage. In FNAIT, it's often caused by severe thrombocytopenia and can lead to long-term disability or death. .
As scientists search for more targeted ways to prevent the complications associated with FNAIT, many are taking a closer look at a protein called the neonatal Fc receptorFc receptor A specialized transport protein. In FNAIT, it carries maternal antiplatelet IgG antibodies across the placenta into the fetus, which destroys the fetus's platelets. (FcRnFc receptor A specialized transport protein. In FNAIT, it carries maternal antiplatelet IgG antibodies across the placenta into the fetus, which destroys the fetus's platelets.).
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FcRn’s role in pregnancy
FcRn plays an important role in pregnancy. It helps transport immunoglobulin G (IgG) antibodies from the mother across the placenta to the fetus. Normally, this process provides the developing baby with maternal antibodies that can offer protection against infections during the first months of life.
In FNAIT, however, the same pathway can transport harmful antibodies. Once these antibodies reach the placenta and fetal circulation, they can contribute to platelet destruction.
Can targeting FcRn prevent FNAIT?
Researchers are investigating whether interfering with FcRn could reduce the amount of harmful maternal IgG reaching the fetus.
Research in animals suggests this strategy might work. Studies using mouse models of FNAIT have found that blocking FcRn can prevent the transfer of harmful antibodies and protect against the resulting disease.
Learn more about FNAIT treatment and care
Researchers are now exploring whether similar approaches could eventually be developed for humans. In 2024, the U.S. Food & Drug Administration granted Fast Track designation to the investigational drug nipocalimab, which blocks FcRn to stop harmful antibodies from crossing the placenta. It is now being studied in clinical trials at medical institutions around the world.
What researchers still need to understand
FcRn is also responsible for transferring beneficial maternal antibodies to the fetus, so blocking the pathway would need to be carefully controlled.
Researchers must therefore determine how effectively FcRn-targeted treatments can reduce harmful antibody transfer while preserving the protective functions of maternal IgG.
Looking forward
FcRn-targeted therapies are still an area of research, but the pathway offers a potential route for preventing FNAIT-related complications.
Continued research will be needed to determine whether FcRn-targeted approaches can safely and effectively reduce harmful antibody transfer.
