ABSTRACT:
The development of high-level lamivudine resistance in clinical isolates is typically due to the rapid selection of M184V mutation in HIV-1 RT. Less frequently, 65R and codon 69 insertions confer modest lamivudine resistance. Analysis of over 4000 samples obtained for routine resistance testing revealed that 37% had the 184V mutation. However, we observed significant numbers of phenotypically lamivudine-resistant clinical samples that lacked this mutation, suggesting that 184V did not account for all lamivudine resistance.
These samples revealed common genotypic patterns including zidovudine resistance mutations (typically, 41L, 67N, 210W and 215Y) plus novel polymorphisms E44D and/or V118I. Seventy-one clinical samples with this pattern of genotypic mutations had a mean fold increase in IC50 of nine. In contrast, samples with 184V showed characteristically higher levels of lamivudine resistance in the Antivirogram phenotypic assay (mean increase of 73-fold in 83 samples). In a panel of site-directed mutant viruses, no sensitivity changes were seen with 44D and /or 118I in an otherwise wild-type background. However, in a background of zidovudine resistance mutations (including 41L, 67N, 210W, 215Y), E44D and/or V118I conferred five- to 15-fold resistance to lamivudine and did not restore zidovudine sensitivity. To determine if lamivudine or zidovudine therapy induced these changes we investigated the prevalence of 44D and 118I in different clinical sample populations.
In 171 therapy-naïve subjects, no 44D changes and only six 118I substitutions were seen. However, in over 1000 samples with 41L plus 215Y, 27% had 44D and 37% 118I. Examination of longitudinal samples from zidovudine and lamivudine treated patients confirmed that 44D and 118I can pre-exist before lamivudine therapy. Thus, it seems likely that 44D and 118I appear in a background of zidovudine resistance mutations which fortuitously also confer lamivudine resistance. It will be important to establish the significance of these polymorphisms for response to lamivudine therapy.
