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)

Inclusion Criteria:

• Approximately 15 eligible participants and their offspring will be enrolled
• Each participant must meet all of the following criteria to be enrolled in the study:
• Female and greater than or equal to (>=)18 years of age
• Pregnant to an estimated gestational age of between 8 up to 14 weeks
• A previous pregnancy with a gestation that included at least one of the following prior to week 24 gestation:
• Severe fetal anemia, defined as hemoglobin less than or equal to (<=) 0.55 multiples of the median (MOM) for gestational age
• Fetal hydrops with peak systolic velocity MOM >=1.5
• Stillbirth with fetal or placental pathology indicative of hemolytic disease of the fetus and newborn (HDFN)
• Maternal alloantibody titers for anti-D of >=32, or anti-Kell titers >=4
• Free fetal deoxyribonucleic acid consistent with an antigen-positive fetus (blood sample taken from mother)
• Maternal evidence for Immunity to measles mumps, rubella, and varicella, as documented by serologies performed during Screening. If initial serologies are borderline or negative, they may be repeated at a second lab. Alternatively, vaccination records can be used to support evidence of immunity.
• Screening immunoglobulin G and albumin levels within the laboratory normal range for gestational age of pregnancy
• Willing to receive standard of care with intrauterine transfusion if clinically indicated
• Agree to receive recommended vaccinations per local standard of care for both mother and child throughout the course of the study
• It is recommended that patients are up-to-date on age-appropriate vaccinations prior to screening as per routine local medical guidelines. For study patients who received locally-approved (and including emergency use-authorized) Coronavirus Disease 2019 (COVID-19) vaccines recently prior to study entry, follow applicable local vaccine labelling, guidelines, and standard of care for pregnant women receiving immune-targeted therapy when determining an appropriate interval between vaccination and study enrollment

Exclusion Criteria:

• Currently pregnant with multiples (twins or more)
• Pre-eclampsia In current pregnancy or history of pre-eclampsia in a previous pregnancy
• Gestational hypertension in the current pregnancy
• Current unstable hypertension
• History of severe or recurrent pyelonephritis, 4 or more lower urinary tract infections in the past year or in a previous pregnancy
• History of genital herpes infection
• Active Infection at Screening or Baseline with Coxsackie, syphilis, cytomegalovirus, toxoplasmosis or herpes simplex 1 or 2, as evidenced by clinical signs and symptoms (evidence for prior Infection or exposure, but without clinical signs and symptoms of active infection is acceptable)
• Active infection with tuberculosis as evidenced by positive QuantiFERON-tuberculosis testing
• Requires treatment with corticosteroids or immunosuppression for disorders unrelated to the pregnancy (use of low-potency topical corticosteroids or intra-articular corticosteroids is permitted)
• Has received or is expected to receive any live virus or bacterial vaccine within 12 weeks prior to screening or has a known need to receive a live vaccine while receiving nipocalimab, or within 12 weeks after the last administration of nipocalimab in the study or has received Bacille Calmett-Guérin (BCG) vaccine within 1 year prior to the first administration of nipocalimab
• Currently receiving an antibody-based drug or an Fc-fusion protein drug
• Received plasmapheresis and/or intravenous immunoglobulin during the current pregnancy for treatment of HDFN
• COVID-19 infection: during the 6 weeks prior to baseline (regardless of vaccination status), have had any of: a) confirmed severe acute respiratory syndrome coronavirus(-2) (SARS-CoV-2) (COVID-19) infection (test positive), or; b) suspected SARS-CoV-2 infection (clinical features without documented test results), or; c) close contact with a person with known or suspected SARS-CoV-2 infection. Exception: may be included with a documented negative result for a validated SARSCoV-2 test: obtained at least 2 weeks after conditions a), b), c) above (timed from resolution of key clinical features if present, example fever, cough, dyspnea) and; with absence of all conditions a), b), c) above during the period between the negative test result and the baseline study visit