The Efficacy and Safety of SerpinPC in Participants with Severe Hemophilia a or Moderately Severe to Severe Hemophilia B

Inclusion Criteria:

1. Male participants ≥12 and ≤65 years of age at the time of informed consent.Enrollment of adolescents (aged ≥12 to <18 years) will be deferred until at least 12adult participants from each SerpinPC treatment regimen have completed at least 12weeks of dosing in Part 1 and safety of SerpinPC has been assessed

2. Capable of providing written informed consent (adolescent assent andparental/guardian/legal representative consent when appropriate) for participationand having the opportunity to discuss the study with the investigator or delegate

3. Historically documented severe HemA (defined as factor VIII less than (<) 0.01international unit (IU)/milliliter(mL) [<1%]), with or without inhibitors, ormoderately severe to severe HemB (defined as factor IX ≤0.02 IU/mL [≤2%]), withoutinhibitors high titer inhibitor (high titer inhibitor defined as ≥5

4. Participant is currently included in a prophylaxis program. Fulfillment of thiscriterion will be based on investigator's judgment of adequate prophylaxis regimenOR participant is undergoing an on-demand treatment regimen and must have hadgreater than or equal to (≥) 6 documented acute bleeding episodes (spontaneous ortraumatic) that required treatment during the 6 months before screening.Irrespective of the treatment program that the participant is currently undergoing,they must be willing to remain in the same program for the duration of theprospective observational period

5. Participants who are currently in a prophylaxis program must be willing to stopprophylaxis (including episodic prophylaxis for sporting events) before the firstdose of SerpinPC

6. For Part 1: At least 12 weeks of prospective documentation of bleeding episodes inthe AP-0105 non-interventional study before SerpinPC dosing, or willing to completea 12-week observational period (at minimum) in AP-0102

7. For Part 2: At least 24 weeks of prospective documentation of bleeding episodes inthe AP-0105 non-interventional study before SerpinPC dosing or willing to complete a 24-week observational period (at minimum) in AP-0102

8. No bleeding in the 7 days before baseline (the prospective observation period can beextended by 10 days if there is an ongoing active bleed)

9. D-dimer of less than or equal to (≤) 750 micrograms(μg)/Liter(L). In cases wherethere is a resolving bleed, the exclusion threshold is ≤1750 milligrams(mg)/L atScreening and Pre-dosing visits

10. Adequate hematologic function, defined as a platelet count of ≥100,000/microliters(μL) (≥100 × 109/L) and hemoglobin level of ≥10grams(g)/deciliter(dL) (≥100 g/L or ≥6.206 millimols(mmol)/L) at Screening andPre-dosing visits

11. Adequate hepatic function, defined as a total bilirubin level of ≤1.5*upper limit ofnormal (ULN) (excluding Gilbert syndrome) and aspartate aminotransferase and/oralanine aminotransferase of ≤3 × ULN at Screening and Pre-dosing visits; no clinicalsigns or known laboratory or radiographic evidence consistent with cirrhosis of theliver

12. Adequate renal function, defined as a serum creatinine level of ≤2.0*ULN atScreening and Pre-dosing visits

13. Able to use a diary to document bleeding events and medication usage

14. Sexually active participants with a partner who could become pregnant should agreeto use effective contraception for the duration of the study effective contraceptivemeasures include condom with or without spermicide, a combination of male condomwith either cap, diaphragm, or sponge with spermicide (double barrier methods),vasectomy, partner using stable contraceptive measures (combined [estrogen andprogestogen-containing] hormonal contraception or progestogen-only hormonalcontraception initiated 2 or more menstrual cycles prior to screening, intrauterinedevice [IUD], intrauterine hormone-releasing system [IUS], bilateral tuballigation), and/or sexual abstinence.

Exclusion Criteria:

1. Known severe thrombophilia (defined as antithrombin deficiency and/or protein Sdeficiency and or protein C deficiency).

2. Participant with previous factor VIII or factor IX inhibitor who responded to immunetolerance induction and remains on prophylactic factor concentrate

3. Previous deep vein thrombosis, pulmonary embolism, myocardial infarction, or stroke

4. History of intolerance to SC injections

5. Uncontrolled hypertension (systolic blood pressure >160 millimeter of mercury (mmHg); diastolic blood pressure >100 mm Hg)

6. Weight >150 kg OR body mass index >40 Kilograms(kg)/meter square (m2)

7. Has active cancer and/or requires therapy for cancer, except for basal cellcarcinoma

8. Participation in another clinical trial (except for AP-0105) during the 30 daysbefore Screening

9. Use of emicizumab in the 24 weeks before Baseline (Day 0)

10. Prior, ongoing, or planned treatment with gene therapy for hemophilia

11. Any major medical, psychological, or psychiatric condition that could cause theparticipant to be unsuitable for the study or could interfere with theinterpretation of the study results

12. History of or other evidence of recent alcohol or drug abuse as determined by theinvestigator (in the 12 months before Screening)

13. Known human immunodeficiency virus (HIV) infection with CD4 count (or T-cell count)of <200 cells/μL within 24 weeks before Screening and Pre-dosing visits.Participants with HIV infection who have CD4 >200 and meet all other criteria areeligible

14. Current or planned treatment with anticoagulant or antiplatelet drugs

15. Is planning to donate/bank sperm during SerpinPC treatment AND within 30 days oflast dose of SerpinPC

16. Any other significant conditions or comorbidities that, in the opinion of theinvestigator, would make the participant unsuitable for enrollment or couldinterfere with participation in or completion of the study