‣ Maternal:

• 18 years or older

• Signed informed consent to participate

• Diagnosis of moderate/severe SLE

• Ongoing treatment with anifrolumab

• Has reached or will reach steady state (\

‣ 85 days postpartum, at least 3 consecutive previous doses during the post-partum period) with anifrolumab by the time of study Day 1 (pre-dose milk collection)1

• Established lactation in the index post-partum period (breastfeeding or pumping for at least 4 weeks at time of Day 1 visit to ensure mature milk production)

• Willing to breastfeed or pump regularly during the study period to maintain milk supply and exclusively pump breast milk for the 24-hour period of breast milk collection on Day 1 post IV dose.

• Plans to continue feeding infant breast milk at least throughout the duration of the study and is not weaning

• Must be exclusively breast milk-feeding their infant (or if not exclusively breast milk-feeding, not providing more than 1 supplemental bottle of formula per day) at the time of enrollment and throughout the study period

⁃ Agrees to use only lanolin nipple cream during the sampling period

‣ Infant:

• Gestational age at delivery ≥32 weeks

• Birthweight \> 10th percentile

• Weight \> 10th percentile at the time of enrollment