Subtype-specific differences in the development of accessory mutations associated with high-level resistance to HIV-1 nucleoside reverse transcriptase inhibitors.

To identify accessory mutations associated with high-level resistance to reverse transcriptase (RT) inhibitors in HIV-1 subtypes B and C. Changes relative to the wild-type for codons 1400 of RT were analysed from treatment-experienced patients infected with subtypes B (5464 patients) and C (1920 patients). Positions associated with the accumulation of mutations conferring resistance to thymidine analogues and to non-nucleoside RT inhibitors (NNRTIs) were identified. A subtype-specific single-replication cycle drug susceptibility assay was used to determine whether some of the mutations affected drug susceptibility or viral infectivity. In subtype B, mutations at 31 and 26 positions were associated with the accumulation of thymidine analogue mutations (TAMs) and NNRTI mutations, respectively; in subtype C, 18 and 13 positions were identified, respectively. Amino acid changes at the following positions were differentially associated with (i) the accumulation of 04 TAMs in subtypes B and C (away from consensus): 43 (27.0 B versus 2.5 C); 118 (36.4 B versus 16.2 C); 135 (12.5 B versus 28.0 C); and 326 (2.6 towards consensus in B versus 7.6 away in C) and (ii) the accumulation of 03 NNRTI mutations (away from consensus): 43 (10.2 B versus 0.5 C); and 68 (5.2 B versus 10.3 C). Codon changes K43E, E44D and V118I were found to have no effect on susceptibility to three NRTIs with or without TAMs in either subtype; however, some accessory mutations had subtype-specific effects on viral infectivity. Differences between subtypes B and C were observed in the development and effect of accessory mutations associated with high-level resistance to RT inhibitors.