Safety and Efficacy Study of OMS721 in Patients With Thrombotic Microangiopathies

This is a Phase 2, uncontrolled, three-stage, dose-escalation cohort study in subjects with
three forms of TMA: atypical hemolytic uremic syndrome (aHUS), thrombotic thrombocytopenia
(TTP), and hematopoietic stem cell transplant -associated TMA (HSCT-associated TMA). In the
first stage, OMS721 will be administered to escalating dose cohorts of three subjects per
cohort to identify the optimal dosing regimen. In the second stage, the dose selected in the
first stage will be administered to expanded cohorts of 40 subjects per cohort with distinct
etiologies (aHUS alone in one cohort and TTP or HSCT-TMA in the other cohort). Subjects
completing the second stage may be eligible for continued treatment in the third stage if the
investigator believes the subject is at risk for relapse of TMA, the subject tolerated OMS721
treatment, and the subject has no conditions that increase the risk of OMS721 treatment.

Inclusion Criteria:

1. Are at least age 18 at screening (Visit 1)

2. Have a diagnosis of primary aHUS, persistent HSCT-associated TMA or TTP

3. No clinically apparent alternative explanation for thrombocytopenia and anemia

Exclusion Criteria:

1. Had eculizumab therapy within three months prior to screening

2. Have STEC-HUS

3. Have a positive direct Coombs test

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