This study from JHEP Reports investigates the development of genetic variants in HEV during treatment with sofosbuvir (SOF) and ribavirin (RBV) in patients with chronic infection. By analyzing these variants’ emergence and their resistance to the combined drug therapy both in vivo and through cell culture evaluations, the research focuses on the virus’s intra-host evolutionary dynamics. These dynamics are important for assessing current treatment efficacy and guiding the development of more effective next-generation antiviral therapies.

Combination treatment successfully lowered viral load towards the quantification limit but did not achieve sustained virological response during treatment. Variants like A1343V and G1634R, associated with SOF or RBV, emerged, with A1343V, alone or with G1634R, showing SOF resistance in concomitant in vitro treatment.

“We closely monitored HEV ribonucleic acid (RNA) levels in stool and blood during concurrent treatment to ensure that, if clearance is possible, all virus is removed,” investigators wrote. “This may also be an important monitoring procedure, as HEV often remains longer in stool, possibly indicating residual viral reservoirs. Thus, stool sequencing may increase the detection window and increase the sensitivity for the detection of minor variants. Indeed, at the end of treatment, both patients were able to clear HEV in plasma but not in stool samples.”¹

The study involved 2 individuals with chronic HEV infection who had not responded to ribavirin therapy and subsequently received a combined treatment of sofosbuvir and ribavirin. To evaluate the treatment’s effectiveness, the investigators monitored liver enzyme levels and the presence of the virus in blood and fecal samples. They also examined the virus’s evolution using high-throughput sequencing targeted at the viral polymerase and evaluated the replication capability of resistance-associated variants using an HEV replicon system.

“As we have previously shown, highly diverse virus populations may already harbor resistance-associated variants at low frequency – such as the A1343V. RBV may thus promote virus heterogeneity which in turn promotes the emergence of variants,” investigators wrote. “However, it is interesting to note that viral relapse was weaker and delayed in these two patients, as indicated by viral loads near LOD throughout treatment, especially compared to SOF monotherapy, where viral relapse occurred between weeks 4 and 12 after treatment initiation.”¹

The study’s limitation was its 2-patient sample size. Viral relapse in these patients was weaker and delayed, maintaining viral loads near the limit of detection throughout treatment, in contrast to the quicker relapse observed in cases of SOF monotherapy, which typically occurred between weeks 4 and 12. The study found evidence that HEV relapse during SOF monotherapy is associated with a specific mutation, A1343V, in the HEV polymerase finger domain. This mutation was found in a separate cohort of 8 out of 9 patients at the consensus level and was associated with a fivefold reduction in SOF susceptibility in vitro.

Administering high doses of both medications can negate the edge provided by variants associated with resistance. Given the limited number of studies currently available, future research should explore the impact of combined treatments and dosage levels, alongside tracking the diversity of HEV.

Reference

Gömer A, Dinkelborg K, Klöhn M, Steinmann E, Maasoumy B et al. Dynamic evolution of the sofosbuvir-associated variant A1343V in hev-infected patients under concomitant sofosbuvir-ribavirin treatment. JHEP Reports. Published January 2, 2024. Accessed February 15, 2024. doi: https://doi.org/10.1016/j.jhepr.2023.100989