Hepatitis B virus rtCYE/rtCYEI mutations may contribute limited tenofovir resistance: Analysis of a large sample of Chinese patients

BACKGROUND Whether rtS106C+H126Y+D134E/rtS106C+H126Y+D134E+L269I (rtCYE/rtCYEI) mutations in the hepatitis B virus (HBV) reverse-transcriptase (RT) region are associated with tenofovir disoproxil fumarate (TDF) resistance is controversial. AIM To evaluate the presence of the rtCYE/rtCYEI mutations in a large cohort of Chinese patients with chronic HBV infection. METHODS A total of 28236 patients who underwent drug resistance testing at the Fifth Medical Center of Chinese PLA General Hospital from 2007 to 2019 were enrolled. All patients received nucleoside/nucleotide analogues (NAs) therapy, and serum samples were collected for sequence analysis of the HBV RT domain with mutation analysis. RESULTS The detection rates of a single mutation of rtS106C, rtH126Y, rtD134E, and rtL269I were 8.21%, 3.20%, 2.55% and 61.49% in 23718 genotype C patients, and 1.31%, 1.76%, 0.21%, and 92.33% in 4266 genotype B patients, respectively. The combined mutations of rtCYE/rtCYEI were only detected in 12 genotype C patients, accounting for 0.042% of all patients. These 12 patients had received NA treatments except TDF before testing. Among them, 6 patients had coexisting rtCYE/rtCYEI and lamivudine-resistance mutations, and 2 patients had coexisting rtCYE/rtCYEI and adefovir-resistance mutations. Compared with the wild-type (WT) strain, the replication capacity of rtCYE/rtCYEI mutants from representative patients decreased by 41.1%-71.8%, and TDF susceptibility reduced by less than 2-fold, but rtCYEI+rtA181V/N236T mutants exhibited a 6.2-/9.9-fold decrease in TDF susceptibility. Molecular modeling showed that rtCYE/rtCYEI mutants had a slight decrease in binding energy to TDF compared to the WT strain. In the clinic, emergence of the rtCYE/rtCYEI mutations was not specifically associated with TDF treatment. CONCLUSION HBV rtCYE/rtCYEI mutations have a limited effect on TDF susceptibility and are not sufficient to cause TDF resistance.