Safety and Efficacy Study of OMS721 in Patients With Atypical Hemolytic Uremic Syndrome

This is a Phase 3, multicenter study of OMS721 in adults and adolescents with atypical
hemolytic uremic syndrome (aHUS). The uncontrolled, open-label study will evaluate the effect
of OMS721 in subjects with plasma therapy-resistant aHUS and plasma therapy-responsive aHUS.
This study has four periods: Screening, Treatment Induction, Treatment Maintenance, and
Follow-up. Approximate enrollment is 80 subjects. An interim analysis will be performed after
40 subjects have completed 26 weeks of treatment for potential registration.

Inclusion Criteria:

- Competent to provide informed consent, or if a minor, have at least one parent or
legal guardian to provide informed consent with written assent from the subject.

- Are at least 12 years old at screening (Visit 1).

- Have a clinically diagnosis of primary atypical hemolytic uremic syndrome (aHUS), with
ADAMTS13 activity greater than 5% in plasma.

- Plasma therapy-resistant aHUS patients must have a screening platelet count less than
150,000/uL, evidence of microangiopathic hemolysis, and serum creatinine greater than
upper limit of normal.

- Plasma therapy-responsive aHUS patients must have documented history of requiring
plasma therapy to prevent aHUS exacerbation and received plasma therapy at least once
every 2 weeks at an unchanged frequency for at least 8 weeks before first dose of
OMS721.

Exclusion Criteria:

- Have STEC-HUS, a direct positive Coombs test, history of hematopoietic stem cell
transplant, and/or HUS from an identified drug.

- History of vitamin B12 deficiency-related HUS, systemic lupus erythematosus, and/or
antiphospholipid syndrome.

- Active cancer or history of cancer (except non-melanoma skin cancers) within 5 years
of screening.

- Have been on hemodialysis or peritoneal dialysis for greater than or equal to 12
weeks.

- Have an active systemic bacterial or fungal infection requiring systemic antimicrobial
therapy (prophylactic antimicrobial therapy administered as standard of care is
allowed).

- Baseline resting heart rate less than 45 beats per minute or greater than 115 beats
per minute.

- Baseline QTcF greater than 470 milliseconds.

- Have malignant hypertension (diastolic blood pressure [BP] greater than 120 mm Hg with
bilateral hemorrhages or "cotton-wool" exudates on funduscopic examination).

- Have a poor prognosis with a life expectancy of less than three months in the opinion
of the Investigator.

- Are pregnant or lactating.

- Have received treatment with an investigational drug or device within four weeks prior
to screening.

- Have abnormal liver function tests defined as ALT or AST > five times ULN.

- Have HIV infection.

- History of cirrhosis of the liver.

- Have previously completed treatment in an OMS721study.