1. LDV/SOF Failure Open-label W24 Chronic HCV infection Genotype 1 Failure to achieve SVR on LDV/SOF-containing regimen Compensated cirrhosis (liver biopsy or Fibrotest > 0.75 + APRI > 2) allowed No HBV or HIV co-infection  Objective –Primary endpoint : SVR 12 (HCV RNA < 15 IU/ml) by intention to treat, with 2-sided 95% CI, no statistical hypothesis LDV/SOF 90/400 x 1 qd SVR 12 N = 41  Design LDV/SOF Failure Study: LDV/SOF for retreatment of genotype 1 with prior failure to LDV/SOF Lawitz E. EASL 2015, Abs. O005

2. LDV/SOF Failure Study: LDV/SOF for retreatment of genotype 1 with prior failure to LDV/SOF N = 41 Mean age, years58 Female17% IL28B CC genotype7% HCV RNA log 10 IU/ml, mean6.2 Cirrhosis46% Genotype 1a83% Prior HCV treatment LDV/SOF + RBV LDV/SOF + GS-9669 80% 20% Prior HCV treatment duration 8 weeks Presence of NS5A RAVs 30 (73%) 19/30 (63%) Prior HCV treatment duration 12 weeks Presence of NS5A RAVs 11 (27%) 11/11 (100%) Lawitz E. EASL 2015, Abs. O005 LDV/SOF Failure Baseline characteristics

3. SVR 12 (HCV RNA < 15 IU/ml) 25 50 100 75 71 % 80 60 100 N41305 33 50 100 11 AllNoYes 68 46 7469 80 Q30R or M28T L31MY93H/NNoYes≥ 28W Cirrhosis 1 22191116301456 12W Prior treatment duration Baseline NS5A RAVs 100 None 11 Number of NS5A RAVs Type of single NS5A RAVs LDV/SOF Failure Study: LDV/SOF for retreatment of genotype 1 with prior failure to LDV/SOF Lawitz E. EASL 2015, Abs. O005 LDV/SOF Failure 0

4.  NS5B Resistance analysis –Baseline : No NS5B resistance associated (S282T) or treatment- emergent (L159F, V321A) variants were detected –At virologic failure : NS5B variants detected in 4 of 12 (33%) patients S282T (N = 2) L159F (N = 1) Double-mutant S282T + L159F (N = 1)  Adverse events –Serious adverse events : 3 –Discontinuation due to adverse event : 0 –Grade 3 adverse events : 3 (none related to study drug) –Adverse events in ≥ 10% of patients : headache, fatigue –Grade 3 laboratory abnormality : 2 LDV/SOF Failure Study: LDV/SOF for retreatment of genotype 1 with prior failure to LDV/SOF Lawitz E. EASL 2015, Abs. O005 LDV/SOF Failure

5. LDV/SOF Failure Study: LDV/SOF for retreatment of genotype 1 with prior failure to LDV/SOF  Summary –71% of patients who failed prior LDV/SOF-containing regimens achieved SVR 12 when retreated with LDV/SOF for 24 weeks –The presence of baseline NS5A RAV(s), which was more likely to develop with longer prior LDV/SOF treatment, was associated with virologic failure –Emergence of S282T was observed in 3 of 12 virologic failures Lawitz E. EASL 2015, Abs. O005 LDV/SOF Failure