Engineered Antibodies May Prevent Placental Transfer of Biologic Drugs

Researchers at the University of Oslo and Oslo University Hospital have reported a method to engineer monoclonal antibodies so they no longer cross the placenta, a finding that could eventually reshape how we manage biologic therapies in women who are pregnant or planning pregnancy. Published in Science Immunology and led by Professor Jan Terje Andersen, the study targets the FcRn receptor — the cellular gateway that normally ferries maternal IgG to the fetus in the third trimester.

How the modification works

Most modern biologics are built on an IgG backbone because IgG has a long plasma half-life: FcRn recycles the antibody and keeps it in circulation for weeks, which is what allows the less frequent dosing schedules we rely on in chronic disease. That same FcRn pathway, however, is what carries IgG across the placenta late in pregnancy. According to the research team, the placenta is more selective than previously recognized, and their engineered antibodies exploit that selectivity. In preclinical work, the modified antibody appears to retain maternal efficacy while reaching the fetus at substantially lower levels. Postdoctoral researcher Jeannette Nilsen is first author of the paper, which has also been highlighted in Nature. Andersen serves as deputy director of PRIMA, a Centre of Excellence at UiO and Oslo University Hospital, and is part of AFIRE, an emerging-technologies initiative funded by the Norwegian Ministry of Education and Research.

Why it matters in clinical management

We encounter the trade-off this study addresses in real clinics: a woman whose rheumatoid arthritis, inflammatory bowel disease, lupus, or severe migraine is finally controlled on a biologic, who is now planning a pregnancy or has conceived. Stopping the drug risks a maternal flare that itself can threaten the pregnancy; continuing it risks fetal and neonatal exposure to an immunosuppressive agent. Antibody-based drugs are now used across chronic inflammatory disease, autoimmunity, and severe migraine, so the population affected is large and the quality-of-life stakes are real for both mother and child. If engineered antibodies preserve maternal benefit while sparing the fetus, the management pathway becomes far less of a forced compromise. For pediatric teams the implications are equally direct, because maternal IgG is what protects the newborn during the first weeks of life, and any modification has to be weighed against that natural transfer of immune protection to the infant.

What to watch next

The work is preclinical, and the team frames it as a new technological principle rather than an imminent therapy. We will be watching for independent replication, pharmacokinetic data in pregnant animal models, and eventually first-in-human studies that confirm the placenta-sparing effect holds in people. For now, this is a credible step: a mechanistic foothold that, if it translates, could change the calculus of biologic use in pregnancy and reduce a longstanding source of risk for the developing immune system of the fetus.