The evolution of HIV-1 reverse transcriptase in route to acquisition of Q151M multi-drug resistance is complex and involves mutations in multiple domains

Abstract

Background: The Q151M multi-drug resistance (MDR) pathway in HIV-1 reverse transcriptase (RT) confers reduced susceptibility to all nucleoside reverse transcriptase inhibitors (NRTIs) excluding tenofovir (TDF). This pathway emerges after long term failure of therapy, and is increasingly observed in the resource poor world, where antiretroviral therapy is rarely accompanied by intensive virological monitoring. In this study we examined the genotypic, phenotypic and fitness correlates associated with the development of Q151M MDR in the absence of viral load monitoring.

Results: Single-genome sequencing (SGS) of full-length RT was carried out on sequential samples from an HIV-infected individual enrolled in ART rollout. The emergence of Q151M MDR occurred in the order A62V, V75I, and finally Q151M on the same genome at 4, 17 and 37 months after initiation of therapy, respectively. This was accompanied by a parallel cumulative acquisition of mutations at 20 other codon positions; seven of which were located in the connection subdomain. We established that fourteen of these mutations are also observed in Q151M-containing sequences submitted to the Stanford University HIV database. Phenotypic drug susceptibility testing demonstrated that the Q151M-containing RT had reduced susceptibility to all NRTIs except for TDF. RT domain-swapping of patient and wild-type RTs showed that patient-derived connection subdomains were not associated with reduced NRTI susceptibility. However, the virus expressing patient-derived Q151M RT at 37 months demonstrated ~44% replicative capacity of that at 4 months. This was further reduced to ~22% when the Q151M-containing DNA pol domain was expressed with wild-type C-terminal domain, but was then fully compensated by coexpression of the coevolved connection subdomain.

Conclusions: We demonstrate a complex interplay between drug susceptibility and replicative fitness in the acquisition Q151M MDR with serious implications for second-line regimen options. The acquisition of the Q151M pathway occurred sequentially over a long period of failing NRTI therapy, and was associated with mutations in multiple RT domains.

Figure 1

Clinical profile of patient P66. Longitudinal viral load, CD4% and ART regimen data for patient P66 during a 3-year follow up period starting from initiation of cART.

Figure 2

ML phylogenetic analysis of single genome sequences. Branch lengths were estimated using the GTR model of substitution and are drawn in scale with the bar at the bottom representing 0.008 nucleotide substitutions per site. The colour of each tip branch represents the time after initiation of therapy when the sample from which the single-genome originates was collected as shown in the legend in each figure. (A) Phylogenetic tree of 70 single genomes generated from 3 sequential samples from patient P66 infected with subtype C HIV-1 virus. (B) Same as (A) but with the following 12 RT drug resistance codons removed from the aligned single-genome sequences to determine the effect of drug resistance mutations on viral evolution: 62, 69, 75, 90, 138, 151, 181, 184, 210, 221, 230 and 348. The trees were rooted using the subtype C reference sequence MJ4.

Figure 3

NRTI susceptibilities and replicative capacity associated with RT domains of patient P66. (A) Schematic representation of full-length and chimeras of subtype C wild-type and patient-derived RT gag-pol expressing vectors used for drug susceptibility and replicative capacity testing. The positions of the restriction sites used for cloning of patient-derived PR-RT fragments (ApaI and ClaI) and for RT domain swapping (HpaI and SpeI) are indicated above the vector. The origins of the RT domains are shown as different coloured boxes: black, wild-type virus; dark gray, patient-derived RT at 4 months; light gray, patient-derived RT at 17 months; and white, patient-derived RT at 37 months. The names of the vectors are indicated on the right with a number representing the month when the sample was collected followed by the patient-derived domain(s) being expressed. Mutations present in each domain are shown on the full-length RT constructs as follows: inside the box, NRTI-associated resistance mutations; above the box, NNRTI-associated resistance mutations; and below the box, other mutations. Pol, DNA pol domain; Cn, Connection subdomain; Rh, RNase H domain. (B) Susceptibility to d4T exhibited by patient-derived full-length RTs and RT domains. (C) Susceptibility to second-line NRTI ABC exhibited by patient-derived full-length RTs. (D) Susceptibility to second-line NRTI ddI exhibited by patient-derived full-length RTs. (E) Susceptibility to TDF exhibited by patient-derived full-length RTs. (F) Replicative capacities relative to virus expressing full-length patient-derived RT from 4-months after initiation of therapy, set at 100%, are shown for each virus. The error bars represent standard error of the mean of three or more independent experiments.