Prospective Registry Investigating Maternal, Infant, and Lactation Outcomes in Anifrolumab Users (PRIMULA Lac) is a Post Marketing Requirements (PMR) study designed to fulfill the FDA post-marketing requirements. The study will collect data about the presence of anifrolumab in human breast milk and serum (maternal and infant) among lactating individuals who are receiving anifrolumab therapeutically via intravenous (IV) or subcutaneous (SC) administration and evaluate exposure and effects on the breastfed infant.

PRIMULA Lac is an open-label, open enrollment, post marketing study to assess concentrations of anifrolumab in breast milk and serum in lactating individuals who are receiving anifrolumab therapeutically via intravenous (IV) or subcutaneous (SC) administration, and to evaluate exposure on the breastfed infant. For participants with IV administration of anifrolumab, milk collection will occur at a series of 14 timepoints, 1 pre-dose (spot) and 13 post-dose: Day 1 [0-4 hours, 4-8 hours, 8-12 hours, 12-18 hours, 18-24 hours], Day 3 [48 hours, spot], Day 4 (spot), Day 6 (spot), Day 8 (spot), Day 12 (spot), Day 16 (spot), Day 22 (spot), and Day 29 (prior to next dose, spot). Maternal serum will be collected on Day 1 (pre-dose and 0-4 hours post-dose), Day 12, and approximately Day 29 (immediately preceding subsequent dose). Infant serum will be collected on approximately Day 30 following the next dose and after 24 hours of breast feeding. Total duration of participation for each participant with IV administration of anifrolumab will be approximately 1 month.

For participants with SC administration of anifrolumab, the total duration of participation will be approximately 9 days. For these participants, milk collection will occur at a series of 10 timepoints, 1 pre-dose (spot) and 9 post-dose: Day 1 [0-4 hours, 4-8 hours, 8-12 hours, 12-18 hours, 18-24 hours], Day 3 [48 hours, spot], Day 4 (spot), Day 6 (spot), Day 8 (prior to next dose, spot). Maternal serum will be collected on Day 1 (pre-dose and 0-4 hours postdose), and approximately Day 8 (immediately preceding subsequent dose). Infant serum will be collected approximately Day 9 following the next dose and after 24 hours of breastfeeding.

Maternal and infant adverse events (AEs) will be actively collected for the duration of participation in the study for IV and SC administration of anifrolumab.

This is a Post Marketing Requirements (PMR) study designed to fulfill the FDA post-marketing requirements.

Inclusion Criteria:

Maternal:

1. 18 years or older
2. Signed informed consent to participate
3. Diagnosis of moderate/severe SLE
4. Ongoing treatment with anifrolumab
5. Has reached or will reach steady state (~85 days postpartum, equivalent to at least 3 consecutive previous IV doses or at least 12 previous SC doses during the post-partum period) with anifrolumab by the time of study Day 1 (pre-dose milk collection)
6. 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)
7. 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
8. Plans to continue feeding infant breast milk at least throughout the duration of the study and is not weaning
9. 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
10. Agrees to use only lanolin nipple cream during the sampling period

Infant:

1. Gestational age at delivery ≥32 weeks
2. Birthweight > 10th percentile
3. Weight > 10th percentile at the time of enrollment

Exclusion Criteria:

Maternal:

1. Received any investigational compound or approved biologic or biosimilar within 30 days or 5 half-lives (whichever is longer) prior to enrollment in the study
2. Diagnosis of lupus nephritis in the last 12 months
3. History of breast implants, breast augmentation, or breast reduction surgery that significantly impacts breastfeeding or collection of milk from 1 or both breasts
4. History of malignancy in the last 10 years
5. History of mastectomy
6. Evidence of mastitis or any other significant active infection at Day 1 (pre-dose)

Infant:

1. Any abnormality noted or clinically significant medical condition, including cardiac, pulmonary, and liver disease, glucose instability, or active infection at the time of screening that, in the opinion of the investigator, may make implementation of the protocol or interpretation of the trial difficult or would put the infant participant at risk by participating in the study

Qualified researchers can request access to anonymized individual patient-level data from

AstraZeneca group of companies sponsored clinical trials via the request portal Vivli.org. All requests will be evaluated as per the AZ disclosure commitment:

https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure. Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA PhRMA Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the anonymized individual patient-level data via secure research environment Vivli.org. Signed Data Usage Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information.