A Phase 3, Open-label Study to Investigate the Efficacy and Safety of GS-7977 Plus Ribavirin in Chronic Genotype 1, 2 and 3 Hepatitis C Virus (HCV) and Human Immunodeficiency Virus (HIV) Co-infected Subjects

Inclusion Criteria:

Subjects must meet all of the following inclusion criteria to be eligible for participation in this study.

1. Willing and able to provide written informed consent
2. Male or female, age ≥ 18 years with chronic HCV and HIV-1 infection
3. HCV RNA > 1 x 104 IU/mL at Screening
4. Infection with HCV genotype 1, 2 or 3 as determined at Screening
5. HIV-1 infection confirmed with positive ELISA or Western blot at Screening
6. The subject's medical records must be sufficient to be categorized on IFN eligibility or prior treatment history with PEG/RBV.
7. Confirmation of chronic HCV infection
8. Ability to determine presence/absence of cirrhosis.

9. HIV antiretroviral therapy (ARV) criteria of one of the following:

   • ARV untreated with a CD4 T-cell count >500 cells/mm3
   • On a stable, protocol-approved, ARV for >8 weeks prior to Screening with a CD4 T-cell count >200 cells/mm3 and a documented undetectable plasma HIV-1 RNA level for ≥ 8 weeks preceding the Screening visit
10. Approved HIV antiretroviral medications based on drug interaction studies
11. Subject has not been treated with any investigational drug or device within 30 days of the Screening visit
12. Females if confirmed that she is not pregnant or nursing of non-childbearing potential or of childbearing potential but has a negative serum pregnancy test at screening and agrees to use protocol approved method of birth control from screening through 6 months after the last dose of RBV
13. Male subjects who agree to consistently and correctly use a condom while their female partner agrees to use protocol approved method of birth control from screening through 7 months after the last dose of RBV
14. Subject must be of generally good health as determined by the Investigator.
15. Liver imaging within 6 months of Baseline/Day 1 is required in cirrhotic patients only, to exclude hepatocellular carcinoma (HCC)

Exclusion Criteria:

Subjects who meet any of the following exclusion criteria are not to be enrolled in this study.

1. Non-genotype 1/2/3 or mixed genotype at Screening
2. Genotype 1 with prior treatment for HCV
3. Poor control with ARV regimen
4. Prior exposure to a direct-acting antiviral targeting the HCV NS5B polymerase
5. Chronic liver disease of a non-HCV etiology (e.g., hemochromatosis, Wilson's disease, α1 antitrypsin deficiency, cholangitis)
6. A new AIDS-defining condition diagnosed within 30 days prior to screening
7. Active, serious infection (other than HIV or HCV) requiring parenteral antibiotics, antivirals or antifungals within 30 days prior to Baseline
8. Infection with hepatitis B virus (HBV)
9. Contraindication to RBV therapy
10. Chronic use of systemically administered immunosuppressive agents (e.g., prednisone equivalent > 10 mg/day)
11. History of solid organ transplantation or malignancy diagnosed or treated within 5 years
12. Current or prior history of clinical hepatic decompensation or other significant gastrointestinal disorder