A novel genotype encoding a single amino acid insertion and five other substitutions between residues 64 and 74 of the HIV-1 reverse transcriptase confers high-level cross-resistance to nucleoside reverse transcriptase inhibitors

We investigated HIV-1 reverse transcriptase (RT) polymorphisms of plasma is olates from 98 HIV-1-infected study subjects with >2 years of antiretrovira l therapy who were failing their current protease inhibitor (PI)-containing regimen. In 1 patient, we detected a virus with a heavily mutated beta 3-b eta 4 connecting loop of the HIV-1 RT fingers subdomain, consisting of a si ngle aspartate codon insertion between positions 69 and 70 and five additio nal variations: 64N, K65, K66, 67G, 68Y, T69, Ins D, 70R, W71, R72, K73, 74 I. Mutants with the recently described 2-aa insertions between codons 68 an d 70 of RT were detected in another 3 patients. Among the four isolates wit h the 1- or 2-aa insertions, the novel genotype was the most refractory to therapy and displayed the highest level of phenotypic resistance to nucleos ide reverse transcriptase inhibitors (NRTIs). Follow-up samples demonstrate d that the novel mutant represents a stable genetic rearrangement and that the amino acid insertions can coexist with nonnucleoside analogue reverse t ranscriptase inhibitors (NNRTI) mutations resulting in phenotypic resistanc e to both NRTIs and NNRTIs. An increasing number of HIV-1 isolates containi ng various insertions in the beta 3-beta 4 hairpin of the HIV-1 RT fingers subdomain appear to emerge after prolonged therapy with different NRTIs, an d these polymorphisms can confer multiple drug resistance against NRTIs.