New findings from a Phase II study indicate that antenatal treatment with the FcRn blocker nipocalimab resulted in low fetal drug exposure and transient reductions in infant IgG levels at birth, without evidence of impaired immune recovery or vaccine response through nearly two years of follow-up.
Antenatal treatment with nipocalimab did not appear to adversely affect infant immune development through 96 weeks after birth, according to new data published in The New England Journal of Medicine.1
The analysis builds on Phase II data showing the neonatal Fc receptor (FcRn) blocker could delay or prevent fetal anemia in pregnancies at high risk for early-onset severe hemolytic disease of the fetus and newborn (HDFN).
The open-label UNITY study (NCT03842189) evaluated weekly intravenous nipocalimab administered between 14 and 35 weeks’ gestation in pregnant individuals with a history placing them at high risk for severe HDFN. While maternal drug concentrations remained at pharmacologically active levels, investigators reported minimal transfer of nipocalimab to fetal, neonatal, and infant compartments, including cord blood and breast milk.2
“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,” the study authors concluded. “Treatment was associated with low IgG levels at birth; however, unusual or unexpected childhood illnesses or impaired vaccine responses were not observed.”
The findings add mechanistic and safety context to the growing clinical profile of nipocalimab, an investigational monoclonal antibody designed to selectively reduce pathogenic IgG by blocking FcRn-mediated recycling. Beyond HDFN, the therapy has shown promise across multiple autoantibody-driven conditions.
Earlier this year, Johnson & Johnson reported positive Phase IIb
At 24 weeks, JASMINE met its primary endpoint of percentage of patients achieving Systemic Lupus Erythematosus Responder Index (SRI-4) compared with placebo.
In April 2025, the FDA approved nipocalimab, marketed as IMAAVY, for generalized myasthenia gravis (gMG) based on Phase III Vivacity-MG3 (NCT04951622) data demonstrating clinically meaningful improvements in activities of daily living.
In Vivacity-MG3, patients who received nipocalimab plus standard of care (SOC) saw an improvement of 4.70 points in activities of daily living (MG-ADL) score over 24 weeks—significantly higher than the 3.25-point increase demonstrated by placebo plus SOC.
In a press release from the time of the approval, Nicholas J. Silvestri, MD, professor of neurology at University of Buffalo, said: “The clinical results we’ve seen with IMAAVY represent a significant milestone in the treatment of gMG. Patients experienced substantial symptom relief and lasting disease control that translated into better daily function and did not fade over 24 weeks in the pivotal Vivacity-MG3 study. Having a treatment that delivers this level of durable symptom stability is a meaningful step forward for managing a complex and unpredictable disease like gMG, and to have it in both AChR+ and MuSK+ adults and pediatric patients 12 years and older brings an additional FcRn treatment to a broader range of patients.”
1. de Winter, D., et al. Infant Immunity after Maternal Nipocalimab in Severe Hemolytic Disease of the Fetus and Newborn. NEJM Evid 2026;5(2). DOI: 10.1056/EVIDoa2500097. Accessed January 30, 2026.
2. A Study to Evaluate the Safety, Efficacy, Pharmacokinetics and Pharmacodynamics of M281 Administered to Pregnant Women at High Risk for Early Onset Severe Hemolytic Disease of the Fetus and Newborn (HDFN). ClinicalTrials.gov. Updated January 28, 2026. Accessed January 30, 2026.
3. Nipocalimab Delivers Positive Phase IIb Results in JASMINE SLE Trial. Applied Clinical Trials. January 6, 2026. Accessed January 30, 2026.
