The investigators aim at investigating the efficacy of grazoprevir/elbasvir ±ribavirin in HIV-positive MSM participating in the SHCS in a broader setting of coinfected MSM. The study pursues a comprehensive approach of a treat, counsel and cure strategy exploring the impact of such a strategy in a representative HIV/HCV-coinfected MSM population. This study is a nested project of the Swiss HIV Cohort Study entitled "The Swiss HCVree Trial".

The prevalence of hepatitis C virus (HCV) infection is increasing in HIV-positive men who have sex with men (MSM) participating in the Swiss HIV Cohort Study (SHCS). MSM with high-risk sexual behaviour are recognized to be the main drivers of the current HCV epidemic. However, in Switzerland treatment with the newest available direct acting agents (DAAs) is currently restricted to patients with a METAVIR fibrosis score ≥2 (i.e., patients with beginning or advanced liver fibrosis or cirrhosis) by the federal office of public health due to the tremendous costs of these DAAs. Within the study population (i.e. HIV-infected MSM with a replicating HCV-infection in Switzerland), about 90% of individuals have a METAVIR fibrosis score <2. As a consequence, HCV therapy with new DAAs is not covered by health insurances for the majority of this population. However, there is evidence that HCV treatment should not be delayed until the development of advanced liver disease. Treating HIV/HCV-coinfected individuals independently of their liver fibrosis score can prevent the development of liver related complications and the transmission of HCV infection.

The once daily oral combination regimen grazoprevir/elbasvir was approved by the Food and Drug Administration (FDA) in January 2016 for the treatment of genotype (GT) 1 and 4 HCV infection in mono- and HIV/HCV coinfected patients. In phase III clinical trial, a 12-week course of grazoprevir/elbasvir showed high efficacy with sustained virologic response (SVR) rates of ≥95%, and favourable tolerability. A 16 weeks treatment with grazoprevir/elbasvir in combination with weight-adjusted ribavirin is necessary in GT 1a infected patients with baseline resistance associated variants (RAV's) and GT 4 infected patients with a history of prior failure to HCV-treatment. Grazoprevir/elbasvir has only robust data from phase 2 and 3 clinical trials for GT 1, 4 HCV infections.

Of note, GT 1, 4 infections account for ~90% of HCV infections in the MSM population in the SHCS.

HCV reinfection remains a concern among MSM, who can be re-exposed to HCV through high-risk sexual behaviours after successful HCV treatment. A recent review shows evidence that behavioural interventions in high risk MSM have the potential to be effective at least in short term reduction of sexual risk behaviours.

To date the knowledge about the HCV-specific immune responses during DAA treatment is sparse. An effective adaptive cellular immunity is known to play a crucial role in spontaneous viral eradication after primary infection.

The investigators aim at investigating the efficacy of grazoprevir/elbasvir ±ribavirin in HIV-positive MSM participating in the SHCS in a broader setting of coinfected MSM. The study pursues a comprehensive approach of a treat, counsel and cure strategy exploring the impact of such a strategy in a representative HIV/HCV-coinfected MSM population. This study is a nested project of the Swiss HIV Cohort Study entitled "The Swiss HCVree Trial".

Inclusion Criteria:

• Informed consent documented by signature
• Participation in the SHCS
• Male individual ≥18 years old
• Homosexual or bisexual preference/transmission mode according to the SHCS entry state and/or in the opinion of the study physician.
• Replicating HCV infection (i.e., positive HCV-RNA-test).
• HCV GT 1 and/or 4 infection.

Exclusion Criteria:

• Contraindications to grazoprevir/elbasvir and ribavirin due to significant drug-drug interactions (DDI) (e.g., HIV protease inhibitors) according to the Liverpool drug-interaction data base.
• Contraindications to grazoprevir/elbasvir and ribavirin, e.g. known hypersensitivity or allergy to the class of drugs or the investigational product.
• Participant is under the age of legal consent, is mentally or legally incapacitated, has significant emotional problems at the time of pre-study screening visit or expected during the conduct of the study or has a history of a clinically significant psychiatric disorder which, in the opinion of the investigator, would interfere with the study procedures.
• Inability to follow the study procedures (e.g. language barriers, psychiatric disorders
• Known or suspected non-adherence to study-procedures.
• Currently participating or has participated in a study with an investigational compound within 30 days of signing informed consent and is not willing to refrain from participating in another such study during the course of this study.
• Enrolment of the investigator, his/her family members, employees and other dependent persons.
• Participant suffers from clinically significant concomitant diseases (for the detailed list of diseases we refer to the according section of this protocol).
• Participant has a history of malignancy ≤5 years prior to signing informed consent or is under evaluation for other active or suspected malignancy.
• Participant has a history of opportunistic infection in the preceding 6 months prior to screening.
• Participants with mixed HCV infection of genotype 1, 4 or 6 with genotype 2, 3 or 5.
• Participant is coinfected with HBV-DNA positive hepatitis B virus (of note, HBsAg positive individuals with suppressed HBV-DNA might be included).
• Participant has evidence of decompensated liver disease.
• Liver cirrhosis Child-Pugh Class B or C, or who have a Pugh-Turcotte (CPT) score >5,
• Participant has cirrhosis and liver imaging within 6 months of Day 1 showing evidence of hepatocellular carcinoma (HCC) or is under evaluation for HCC.
• Participant has clinically-relevant drug or alcohol abuse at the PI's discretion within 12 months of screening.
• Participant is a male whose female partner(s) is/are pregnant (this is a contraindication for ribavirin use)
• Participant has exclusionary laboratory values at the screening visit (for the table containing these laboratory values we refer to the according section of this protocol).