Sponsor decision to terminate program.

The primary objective of this study is to assess the safety and tolerability of ALXN1820 SC (subcutaneous) in participants with SCD (Sickle Cell Disease).

Inclusion Criteria:

• Confirmed diagnosis of SCD (HbSS, or HbSβ0-thalassemia).
• Body weight ≥ 40 kg (inclusive) at Screening.
• Must follow protocol-specified contraception guidance while on treatment and for up to 6 months after last dose.
• Hemoglobin between 5.5 and 10 g/dL at Screening
• Have had 1 to 10 VOCs in the past 12 months.
• Patients receiving hydroxyurea must have been on a stable dose for ≥ 3 months prior to providing informed consent, with no anticipated need for dose adjustment during the study.
• Patients will be vaccinated with MCV4 and serogroup B meningococcal vaccinations at least 14 days before dosing, if not already vaccinated within 3 years before the first dose.
• Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae vaccination are up to date according to current national/local vaccination guidelines for patients with SCD.

Exclusion Criteria:

• Planned initiation, termination, or dose alteration of hydroxyurea during the study.
• Receiving Voxelotor (OXBRYTA) or crizanlizumab (ADAKVEO) within 60 days of providing informed consent.
• Receiving treatment with recombinant human erythropoetins (eg, epoetin alfa).
• Treated with complement inhibitors within 6 months prior to the first dose.
• Patients who are on chronic transfusion or receive a transfusion within 60 days of first dose.
• Any significant disease or disorder which, in the opinion of the Investigator, may put the participant at risk.
• Hepatitis B (positive hepatitis surface antigen [HBsAg] or positive core antibody (anti-HBc) with negative surface antibody [anti-HBs]) or hepatitis C viral infection (hepatitis C virus [HCV] antibody positive, except for patients with documented successful treatment and documented sustained virologic response) at Screening.
• Active systemic bacterial, viral, or fungal infection within 14 days prior to dosing.
• Participation (ie, last protocol-required study visit) in a clinical study within 90 days or 5 half-lives of the investigational agent, whichever is longer, before initiation of dosing on Day 1.
• Participation in more than 1 clinical study of a monoclonal antibody (mAb), or participation in a clinical study of a mAb within the 6 months or 5 half-lives of the mAb, whichever is longer, prior to Screening, during which the participant was exposed to the active study drug.
• Severe renal impairment (estimated glomerular filtration rate [eGFR] < 30 mL/min/1.73 m2 ) or on chronic dialysis.
• History of allergy or hypersensitivity to excipients of ALXN1820 (eg, polysorbate 80).
• History of complement deficiency.
• History of N meningitidis, S pneumoniae, or H influenzae infection.
• History of malignancy with the exception of a nonmelanoma skin cancer or carcinoma in situ of the cervix that has been treated with no evidence of recurrence within 5 years.
• Participants who are pregnant or breastfeeding.

Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.

Per Sponsor decision, the study was terminated. Only 2 participants were enrolled. Due to concerns regarding participant confidentiality, no data are reported.

Per Sponsor decision, the study was terminated. Only 2 participants were enrolled. Due to concerns regarding participant confidentiality, no data are reported.

Per Sponsor decision, the study was terminated. Only 2 participants were enrolled. Due to concerns regarding participant confidentiality, no data are reported.

Per Sponsor decision, the study was terminated. Only 2 participants were enrolled. Due to concerns regarding participant confidentiality, no data are reported.