Study terminated due to business and strategic decision

The primary objective of this study is to obtain prospective baseline documentation of annualized bleeding rates (ABRs) and treatment under standard-of-care (SOC) therapy among participants with hemophilia A or B. Participants in the study may be eligible to enroll in future planned interventional studies to be conducted by Sponsor.

Inclusion Criteria:

1. Male participants greater than or equal to (>=) 12 and less than or equal to (<=) 65 years of age
2. Who are capable of providing written informed consent (adolescent assent and parental/guardian consent when appropriate) for participation after reading the information and consent form and having the opportunity to discuss the study with the Investigator or their designee
3. With historically documented severe HemA (defined as factor VIII [FVIII] less than (<) 0.01 International Units per milliliter (IU/mL) [<1 percent {%}]), with or without inhibitors, or moderately severe to severe HemB (defined as factor IX [FIX] <=0.02 IU/mL [<=2%]) without inhibitors. Participants must be currently included in a prophylactic treatment program or if undergoing an on-demand treatment regimen must have had >=6 documented acute bleeding episodes (spontaneous or traumatic) that required coagulation factor infusion during the 6 months before enrollment OR: Historically documented HemB (defined as FIX <=0.05 IU/mL [<=5%]) with inhibitors with a historical or ongoing high titer inhibitor [>=5 Bethesda Units/mL] based on medical records or laboratory reports) and an ABR of >=6 in the 6 months before enrollment
4. Who are able to use a diary to document bleeding events and associated treatment

Exclusion Criteria:

1. With known thrombophilia
2. With body weight greater than (>)150 kilogram (kg) or body mass index >40
3. With known current inadequate hematologic function (eg, platelet count <100,000 per microliter [/mcL] and/or hemoglobin level <10 grams per deciliter [g/dL], <100 g/L), hepatic function (that is, total bilirubin >1.5*upper limit of normal [ULN] [excluding Gilbert syndrome], aspartate transferase and/or alanine aminotransferase levels >3*ULN; clinical signs or known laboratory or radiographic evidence consistent with cirrhosis of the liver) or renal function (that is, serum creatinine >2*ULN; based on medical records or available laboratory reports)
4. With previous deep vein thrombosis and pulmonary embolism, myocardial infarction, or stroke
5. With history of intolerance to subcutaneous injections
6. With known current uncontrolled hypertension (systolic blood pressure >160 millimeter of mercury (mm Hg); diastolic blood pressure >100 mm Hg; based on medical records)
7. With active cancer or requires therapy for cancer, except for basal cell carcinoma
8. With concurrent participation in an interventional clinical trial
9. With current or planned use of emicizumab
10. With prior, ongoing, or planned treatment with gene therapy for hemophilia
11. With history of or other evidence of recent alcohol or drug abuse as determined by the Investigator or their designee (in the 12 months before enrollment)
12. With known Human Immunodeficiency Virus (HIV) infection with CD4 count (or T-cell count) of <200 cells/mcL within 24 weeks before enrollment
13. With current or planned treatment with anticoagulant or antiplatelet drugs
14. With any other significant conditions or comorbidities that, in the opinion of the Investigator or their designee, would make the participant unsuitable for enrollment

Participants with severe HemA with or without inhibitors, or moderately severe to severe HemB without inhibitors or HemB with inhibitors treated with SOC on-demand or prophylactic hemophilia therapy.

There is no plan to share IPD due to the Sponsor's strategic and data-driven decision to discontinue the global clinical development of SerpinPC.