Novel mutations L228I and Y232H cause NNRTI resistance in combinational pattern.

The emergence of drug resistance mutations is increasing after the implementation of highly active antiretroviral therapy (HAART). To characterize two novel mutations L228I and Y232H in the primer grip of reverse transcriptase (RT) of HIV-1 CRF08_BC subtype, both mutant clones were constructed to determine their impacts on viral phenotypic susceptibility and replication capacity (RC). Results showed that the novel mutation, L228I, conferred low level resistance to ETR by itself. L228I in combination with Y188C displayed a high level of cross-resistance to both NVP and EFV. The co-presence of A139V and Y232H induced a moderate level of resistance to NVP and EFV. Mutations Y188C/L228I, A139V, Y232H and A139V/Y232H reduced more than 55% of viral RC compared with that of the wild type (WT) reference virus. Modeling study suggested that the co-presence of Y188C/L228I or A139V/Y232H might induce conformational changes to RT, which might result in reduced drug susceptibility and viral RC due to abolished hydrogen bonding or complex interaction with vicinal residues. Our results demonstrated that L228I and Y232H were novel accessory NNRTI-resistance related mutations and provided valuable information for clinicians to design more effective treatment to patients infected with HIV-1 subtype CRF08_BC.