Resistance-associated substitutions after sofosbuvir/velpatasvir/voxilaprevir triple therapy failure

Direct-acting antivirals (DAAs) resolve chronic HCV infection in >95% of patients, but a small percentage do not respond to DAA-based therapy. These may be difficult to treat because of resistance-associated substitutions (RAS) emerging after treatment failure. Triple therapy with sofosbuvir (SOF)/velpatasvir (VEL)/voxilaprevir (VOX) is the recommended retreatment after DAA-based failure. However, in rare cases, failure to triple therapy occurs, and there is little information characterizing the viruses that relapse. To determine the RAS profile after failing SOF/VEL/VOX, and seek suitable alternatives for retreatment, samples from 5 patients were analysed using MiSeq Illumina deep sequencing before and after triple therapy. All patients were men, aged 59–78 years, 2 HCV genotype (G) 1b and 3 G3a. The most prevalent NS3 substitutions after SOF/VEL/VOX failure were Y56F and A166T. Four patients had the NS5A RAS, Y93H, after triple failure, and Y93H was observed in both G1b patients before retreatment and after SOF/ledipasvir failure. In 2 G3a patients, Y93H appeared at triple failure, and on the other G3a, A30K persisted in 100% of viral genomes. Finally, G1b patients showed C316N in NS5B, associated with SOF failure, but G3a patients had no known NS5B substitutions. HCV RAS analysis identified the following substitutions present at higher rates after triple failure: Y56F in NS3 (G1b), A166T in NS3 (G3a), A30K or Y93H in NS5A, and C316N in NS5B (G1b). A RAS-based salvage treatment (SOF + glecaprevir/pibrentasvir + RBV) was successfully used in one G3a patient.