Low-level K65R mutation in HIV-1 reverse transcriptase of treatment-experienced patients exposed to abacavir or didanosine

Switching to coformulated bictegravir, emtricitabine, and tenofovir alafenamide maintained viral suppression in adults with historical virological failures and K65N/R mutation

OBJECTIVES

Real-world experience with coformulated bictegravir, emtricitabine, and tenofovir alafenamide (BIC/FTC/TAF) is sparse as a switch regimen among people living with HIV (PLWH) having achieved viral suppression after previous virologic failures with the emergence of K65N/R.

METHODS

In this retrospective study, PLWH aged ≥20 years who had previous virologic failures with emergent K65N/R were included for switching to BIC/FTC/TAF after having achieved plasma HIV RNA load (PVL) <200 copies/ml for ≥3 months. PLWH were excluded if integrase inhibitor resistance-associated mutations were detected. The primary end point was losing virologic control (PVL >50 copies/ml) at week 48 using a modified US Food and Drug Administration snapshot algorithm.

RESULTS

A total of 72 PLWH with K65N/R who switched to BIC/FTC/TAF were identified. A total of 42 (59.7%) had concurrent M184V/I, and 9 (12.5%) had ≥1 thymidine analog mutations. The median duration of viral suppression was 4.7 years (interquartile range 2.3-5.8), and 97.2% (n = 70) had PVL <50 copies/ml before switching. After a median observation of 98.6 weeks (interquartile range 77.9-120.3), 94.4% (n = 68) continued BIC/FTC/TAF. At week 48, the rate of losing virologic control was 2.8% (2/72). M184V/I was not associated with viral rebound.

CONCLUSION

Despite the emergence of K65N/R +/- M184V/I after virologic failures, BIC/FTC/TAF could be an option for simplification after viral suppression.

The Effect of Treatment-Associated Mutations on HIV Replication and Transmission Cycles

HIV/AIDS mortality has been decreasing over the last decade. While promising, this decrease correlated directly with increased use of antiretroviral drugs. As a natural consequence of its high mutation rate, treatments provide selection pressure that promotes the natural selection of escape mutants. Individuals may acquire drug-naive strains, or those that have already mutated due to treatment. Even within a host, mutation affects HIV tropism, where initial infection begins with R5-tropic virus, but the clinical transition to AIDS correlates with mutations that lead to an X4-tropic switch. Furthermore, the high mutation rate of HIV has spelled failure for all attempts at an effective vaccine. Pre-exposure drugs are currently the most effective drug-based preventatives, but their effectiveness is also threatened by viral mutation. From attachment and entry to assembly and release, the steps in the replication cycle are also discussed to describe the drug mechanisms and mutations that arise due to those drugs. Revealing the patterns of HIV-1 mutations, their effects, and the coordinated attempt to understand and control them will lead to effective use of current preventative measures and treatment options, as well as the development of new ones.

HIV Drug Resistance Mutations (DRMs) Detected by Deep Sequencing in Virologic Failure Subjects on Therapy from Hunan Province, China

Objective

Determine HIV drug resistance mutations (DRMs) prevalence at low and high levels in ART-experienced patients experiencing virologic failure (VF).

Methods

29 subjects from 18 counties in Hunan Province that experienced VF were evaluated for the prevalence of DRMs (Stanford DRMs with an algorithm value ≥15, include low-, intermediate and high-level resistance) by both Sanger sequencing (SS) and deep sequencing (DS) to 1% frequency levels.

Results

DS was performed on samples from 29 ART-experienced subjects; the median viral load 4.95×10⁴ c/ml; 82.76% subtype CRF01_AE. 58 DRMs were detected by DS. 18 DRMs were detected by SS. Of the 58 mutations detected by DS, 40 were at levels <20% frequency (26 NNRTI, 12 NRTI and 2 PI) and the majority of these 95.00% (38/40) were not detected by standard genotyping. Of these 40 low-level DRMs, 16 (40%) were detected at frequency levels of 1–4% and 24 (60%) at levels of 5–19%. SS detected 15 of 17 (88.24%) DRMs at levels ≥ 20% that were detected by DS. The only variable associated with the detection of DRMs by DS was ART adherence (missed doses in the prior 7 days); all patients that reported missing a dose in the last 7 days had DRMs detected by DS.

Conclusions

DS of VF samples from treatment experienced subjects infected with primarily AE subtype frequently identified Stanford HIVdb NRTI and NNRTI resistance mutations with an algorithm value 15. Low frequency level resistant variants detected by DS were frequently missed by standard genotyping in VF specimens from antiretroviral-experienced subjects.

Low-frequency nevirapine (NVP)-resistant HIV-1 variants are not associated with failure of antiretroviral therapy in women without prior exposure to single-dose NVP

BACKGROUND

Low-frequency nevirapine (NVP)-resistant variants have been associated with virologic failure (VF) of initial NVP-based combination antiretroviral therapy (cART) in women with prior exposure to single-dose NVP (sdNVP). We investigated whether a similar association exists in women without prior sdNVP exposure.

METHODS

Pre-cART plasma was analyzed by allele-specific polymerase chain reaction to quantify NVP-resistant mutants in human immunodeficiency virus-infected African women without prior sdNVP who were starting first-line NVP-based cART in the OCTANE/A5208 trial 2. Associations between NVP-resistant mutants and VF or death were determined and compared with published results from women participating in the OCTANE/A5208 trial 1 who had taken sdNVP and initiated NVP-based cART.

RESULTS

Pre-cART NVP-resistant variants were detected in 18% (39/219) of women without prior sdNVP exposure, compared to 45% (51/114) with prior sdNVP exposure (P < .001). Among women without prior sdNVP exposure, 8 of 39 (21%) with NVP-resistant variants experienced VF or death vs 31 of 180 (17%) without such variants (P = .65); this compares with 21 of 51 (41%) vs 9 of 63 (14%) among women with prior exposure (P = .001).

CONCLUSIONS

The risk of VF on NVP-based cART from NVP-resistant variants differs between sdNVP-exposed and -unexposed women. This difference may be driven by drug-resistance mutations emerging after sdNVP exposure that are linked on the same viral genome.

CLINICAL TRIALS REGISTRATION

NCT00089505.

Allele-specific real-time PCR system for detection of subpopulations of genotype 1a and 1b hepatitis C NS5B Y448H mutant viruses in clinical samples

The Y448H mutation in NS5B has been selected by GS-9190 as well as several benzothiadiazine hepatitis C virus (HCV) polymerase inhibitors in vitro and in vivo. However, the level and the evolution kinetics of this resistance mutation prior to and during treatment are poorly understood. In this study, we developed an allele-specific real-time PCR (AS-PCR) assay capable of detecting Y448H when it was present at a level down to 0.5% within an HCV population of genotype 1a or 1b. No Y448H mutation was detected above the assay cutoff of 0.5% in genotype 1b-infected Con-1 replicons prior to in vitro treatment. However, the proportion of replicons with the Y448H mutation rapidly increased in a dose-dependent manner upon treatment with GS-9190. After 3 days of treatment, 1.2%, 6.8%, and >50% of the replicon population expressed Y448H with the use of GS-9190 at 1, 10, and 20 times its 50% effective concentration, respectively. In addition, plasma from 65 treatment-naïve HCV-infected patients (42 and 23 with genotype 1a and 1b, respectively) was tested for the presence of Y448H by AS-PCR and population sequencing. As expected, all patient samples were wild type at NS5B Y448 by population sequencing. AS-PCR results were obtained for 62/65 samples tested, with low levels of Y448H ranging from 0.5% to 3.0% detected in 5/62 (8%) treatment-naïve patient samples. These findings suggest the need for combination therapy with HCV-specific inhibitors to avoid viral rebound of preexisting mutant HCV.

Tenofovir (TDF)-selected or abacavir (ABC)-selected low-frequency HIV type 1 subpopulations during failure with persistent viremia as detected by ultradeep pyrosequencing

Detection of drug resistance is critical for determining antiretroviral treatment options. Ultradeep pyrosequencing (UDPS; 454 Life Sciences) is capable of detecting virus variant subpopulations with much greater sensitivity than population sequencing, which typically has a detection limit around 20%. UDPS of the HIV-1 reverse transcriptase (RT) (amino acids 56-120) was performed to detect the key mutations K65R and L74V associated with tenofovir and abacavir use. Plasma specimens from subjects with persistent rebound viremia following suppression on tenofovir (n = 8) or abacavir (n = 9)-based therapy were studied. Samples from a subject treated with zidovudine/lamivudine/efavirenz with a similar loss of virologic response served as a control. HIV-1 plasma RNA was ≥3.68 log(10) copies/ml at all time points sequenced. The median number of UDPS sequences analyzed/time point was 33,246. Among the eight tenofovir-treated subjects, three showed high-frequency (>20%) RT K65R at the time of failure, whereas one showed low-frequency (<20%) L74V; no low-frequency K65R was detected in these subjects. Among the nine abacavir-treated subjects, three showed low-frequency K65R; no L74V was detected in these patients. No K65R or L74V was detected in the samples from the control subject. At failure, other RT mutations were detected, including low-frequency NNRTI-resistant species detected at ≥1 time point in nine subjects; the key NNRTI mutation K103N, however, was always observed at >20% frequency. Although UDPS is useful in the detection of low-frequency subpopulations with transmitted resistance in antiviral-naive patients, it may have less utility in treatment-experienced patients with persistent viremia on therapy.

Low level of the K103N HIV-1 above a threshold is associated with virological failure in treatment-naive individuals undergoing efavirenz-containing therapy

BACKGROUND

Study GS-01-934 was a randomized open-label phase III study comparing efavirenz and tenofovir/emtricitabine to efavirenz and zidovudine/lamivudine in treatment-naive HIV-1-infected individuals. Through 144 weeks, 50 of 487 participants without baseline nonnucleoside reverse transcriptase inhibitor resistance by population sequencing (efavirenz/tenofovir/emtricitabine, n = 19; efavirenz/zidovudine/lamivudine, n = 31) experienced virologic failure (>400 copies/ml). Here, we analyzed whether the presence of low levels of K103N at baseline correlated with virologic failure.

METHODS

Available baseline plasma samples (n = 485) were amplified and tested for K103N using an allele-specific PCR (AS-PCR) assay with a lower detection cut-off of 0.5%.

RESULTS

Sixteen of 476 (3.4%) evaluable participants had low-level K103N at baseline by AS-PCR (0.8-15%). The abundance of the K103N subpopulation at baseline distinguished individuals with virologic failure from those who responded durably to efavirenz-containing therapy. Among six participants with at least 2000 K103N copies/ml before treatment, five experienced virologic failure, compared with only one virologic failure among 10 who had less than 2000 K103N copies/ml (P = 0.008). Multivariate logistic regression analysis showed that K103N viral load at least 2000 copies/ml increased the risk of virologic failure with an odds ratio of 47.4 (95% confidence interval 5.2-429.2, P = 0.0006).

CONCLUSION

The presence of K103N mutant virus in plasma above 2000 copies/ml prior to therapy in treatment-naive individuals correlated with increased risk of virologic failure of these efavirenz-containing triple-drug regimens.

A Leu to Ile but not Leu to Val change at HIV-1 reverse transcriptase codon 74 in the background of K65R mutation leads to an increased processivity of K65R+L74I enzyme and a replication competent virus

Background

The major hurdle in the treatment of Human Immunodeficiency virus type 1 (HIV-1) includes the development of drug resistance-associated mutations in the target regions of the virus. Since reverse transcriptase (RT) is essential for HIV-1 replication, several nucleoside analogues have been developed to target RT of the virus. Clinical studies have shown that mutations at RT codon 65 and 74 which are located in β3-β4 linkage group of finger sub-domain of RT are selected during treatment with several RT inhibitors, including didanosine, deoxycytidine, abacavir and tenofovir. Interestingly, the co-selection of K65R and L74V is rare in clinical settings. We have previously shown that K65R and L74V are incompatible and a R→K reversion occurs at codon 65 during replication of the virus. Analysis of the HIV resistance database has revealed that similar to K65R+L74V, the double mutant K65R+L74I is also rare. We sought to compare the impact of L→V versus L→I change at codon 74 in the background of K65R mutation, on the replication of doubly mutant viruses.

Methods

Proviral clones containing K65R, L74V, L74I, K65R+L74V and K65R+L74I RT mutations were created in pNL4-3 backbone and viruses were produced in 293T cells. Replication efficiencies of all the viruses were compared in peripheral blood mononuclear (PBM) cells in the absence of selection pressure. Replication capacity (RC) of mutant viruses in relation to wild type was calculated on the basis of antigen p24 production and RT activity, and paired analysis by student t-test was performed among RCs of doubly mutant viruses. Reversion at RT codons 65 and 74 was monitored during replication in PBM cells. In vitro processivity of mutant RTs was measured to analyze the impact of amino acid changes at RT codon 74.

Results

Replication kinetics plot showed that all of the mutant viruses were attenuated as compared to wild type (WT) virus. Although attenuated in comparison to WT virus and single point mutants K65R, L74V and L74I; the double mutant K65R+L74I replicated efficiently in comparison to K65R+L74V mutant. The increased replication capacity of K65R+L74I viruses in comparison to K65R+L74V viruses was significant at multiplicity of infection 0.01 (p = 0.0004). Direct sequencing and sequencing after population cloning showed a more pronounced reversion at codon 65 in viruses containing K65R+L74V mutations in comparison to viruses with K65R+L74I mutations. In vitro processivity assays showed increased processivity of RT containing K65R+L74I in comparison to K65R+L74V RT.

Conclusions

The improved replication kinetics of K65R+L74I virus in comparison to K65R+L74V viruses was due to an increase in the processivity of RT containing K65R+L74I mutations. These observations support the rationale behind structural functional analysis to understand the interactions among unique RT mutations that may emerge during the treatment with specific drug regimens.

New technology to detect low-level drug-resistant HIV variants

Genotypic assays to detect HIV drug resistance are recommended for use in the routine clinical care of HIV-infected persons. Genotypic resistance assays have demonstrated good clinical utility, instructing antiretroviral drug selection and improving therapy outcomes. However, a major limitation of clinically available genotypic assays is the inability to detect low-level drug-resistant variants that exist at low levels within the circulating viral population. Recent data from multiple groups have demonstrated that low-level resistant viral variants are clinically important as they can rapidly grow under drug selection pressure and lead to therapy failure. This article will discuss how ultra-deep sequencing and other new sensitive genotyping technologies can be used to detect low-level drug-resistant HIV variants. It will also address the biological and clinical questions facing the field of HIV genotyping: first, the need to better define the level of sensitivity required to detect drug-resistant variants; second, the effects different resistant variants have on treatment response, and; third, the requirement for genotypic assays to provide information on resistance mutation linkage. Finally, the limitations of the new sensitive genotyping methods will be discussed and how these limitations can lead to discordant results between the different technologies.

Analysis of low-frequency mutations associated with drug resistance to raltegravir before antiretroviral treatment

Raltegravir is highly efficacious in the treatment of HIV-1 infection. The prevalence and impact on virologic outcome of low-frequency resistant mutations among HIV-1-infected patients not previously treated with raltegravir have not been fully established. Samples from HIV treatment-experienced patients entering a clinical trial of raltegravir treatment were analyzed using a parallel allele-specific sequencing (PASS) assay that assessed six primary and six secondary integrase mutations. Patients who achieved and sustained virologic suppression (success patients, n = 36) and those who experienced virologic rebound (failure patients, n = 35) were compared. Patients who experienced treatment failure had twice as many raltegravir-associated resistance mutations prior to initiating treatment as those who achieved sustained virologic success, but the difference was not statistically significant. The frequency of nearly all detected resistance mutations was less than 1% of viral population, and the frequencies of mutations between the success and failure groups were similar. Expansion of pre-existing mutations (one primary and five secondary) was observed in 16 treatment failure patients in whom minority resistant mutations were detected at baseline, suggesting that they might play a role in the development of drug resistance. Two or more mutations were found in 13 patients (18.3%), but multiple mutations were not present in any single viral genome by linkage analysis. Our study demonstrates that low-frequency primary RAL-resistant mutations were uncommon, while minority secondary RAL-resistant mutations were more frequently detected in patients naïve to raltegravir. Additional studies in larger populations are warranted to fully understand the clinical implications of these mutations.

Minority variants of drug-resistant HIV

Minor drug-resistant variants exist in every patient infected with human immunodeficiency virus (HIV). Because these minority variants are usually present at very low levels, they cannot be detected and quantified using conventional genotypic and phenotypic tests. Recently, several assays have been developed to characterize these low-abundance drug-resistant variants in the large, genetically complex population that is present in every HIV-infected individual. The most important issue is what results generated by these assays can predict clinical or treatment outcomes and might guide the management of patients in clinical practice. Cutoff values for the detection of these low-abundance viral variants that predict an increased risk of treatment failure should be determined. These thresholds may be specific for each mutation and treatment regimen. In this review, we summarize the attributes and limitations of the currently available detection assays and review the existing information about both acquired and transmitted drug-resistant minority variants.

Prevalence and clinical significance of HIV drug resistance mutations by ultra-deep sequencing in antiretroviral-naïve subjects in the CASTLE study

BACKGROUND

CASTLE compared the efficacy of atazanavir/ritonavir with lopinavir/ritonavir, each in combination with tenofovir-emtricitabine in ARV-naïve subjects from 5 continents.

OBJECTIVES

Determine the baseline rate and clinical significance of TDR mutations using ultra-deep sequencing (UDS) in ARV-naïve subjects in CASTLE.

METHODS

A case control study was performed on baseline samples for all 53 subjects with virologic failures (VF) at Week 48 and 95 subjects with virologic successes (VS) randomly selected and matched by CD4 count and viral load. UDS was performed using 454 Life Sciences/Roche technology.

RESULTS

Of 148 samples, 141 had successful UDS (86 subtype B, 55 non-B subtypes). Overall, 30.5% of subjects had a TDR mutation at baseline; 15.6% only had TDR(s) at <20% of the viral population. There was no difference in the rate of TDRs by B (30.2%) or non-B subtypes (30.9%). VF (51) and VS (90) had similar rates of any TDRs (25.5% vs. 33.3%), NNRTI TDRs (11.1% vs.11.8%) and NRTI TDRs (24.4% vs. 25.5%). Of 9 (6.4%) subjects with M184V/I (7 at <20% levels), 6 experienced VF. 16 (11.3%) subjects had multiple TAMs, and 7 experienced VF. 3 (2.1%) subjects had both multiple TAMs+M184V, and all experienced VF. Of 14 (9.9%) subjects with PI TDRs (11 at <20% levels): only 1 experienced virologic failure. The majority of PI TDRs were found in isolation (e.g. 46I) at <20% levels, and had low resistance algorithm scores.

CONCLUSION

Among a representative sample of ARV-naïve subjects in CASTLE, TDR mutations were common (30.5%); B and non-B subtypes had similar rates of TDRs. Subjects with multiple PI TDRs were infrequent. Overall, TDRs did not affect virologic response for subjects on a boosted PI by week 48; however, a small subset of subjects with extensive NRTI backbone TDR patterns experienced virologic failure.

Development of a didanosine genotypic resistance interpretation system based on large derivation and validation datasets

OBJECTIVE

To assess the genotypic determinants of the virological response to didanosine (ddI) in HIV-infected patients.

METHODS

The Forum database on ddI was randomly divided into a derivation set (n = 1000) and a validation set (n = 453). Linear regression models and bootstrap sampling were used to select resistance mutations and to estimate their resistance scores. Linear regression models, accounted for the censoring of viral load measurements due to assay lower limits, of the week 8 reduction in viral load from baseline were adjusted for baseline viral load, the exact number of weeks between baseline and the week 8 viral load measurements, and the Stanford genotypic sensitivity score.

RESULTS

The ddI resistance mutations and their resistance scores based on the derivation set were as follows: M41L (score of 14), T69D (24), D123S (40), T139M (54), I180V (53), M184V (-12), V189I (55), Q207K (37), L210W (25), and T215Y (eight). The total score is obtained by adding the individual scores. Viruses with scores of 19 or less, 20-59, and 60 or more are considered sensitive, intermediate, and resistant, respectively. In the validation set, respectively, 58.7, 36.9, and 4.4% of viruses were predicted to be sensitive, intermediate, and resistant to ddI. The observed viral load reductions at week 8 were, respectively, 1.51 log10 copies/ml [interquartile range (IQR) 1.26-1.76] (P = 0.0001 versus resistant), 1.11 (0.94-1.30) (P = 0.0077 versus sensitive), and 0.46 (0.32-0.74) (P = 0.0079 versus intermediate).

CONCLUSION

We developed a genotypic resistance score for didanosine including four mutations never previously used.

Development of an allele-specific PCR for detection of the K65R resistance mutation in patients infected with subtype C human immunodeficiency virus type 1

The selection of drug-resistant variants of human immunodeficiency virus type 1 (HIV-1) is an impediment to the efficiency of antiretroviral (ARV) therapy. We have developed an allele-specific real-time PCR assay to explore the presence of K65R minority species among treated HIV-1 subtype B and C infections. Thirty HIV-1 subtype C- and 26 subtype B-infected patients lacking K65R as determined by conventional sequencing methods were studied, and viral minority species were found in four HIV-1 subtype C samples.

The K65R mutation in HIV-1 reverse transcriptase: genetic barriers, resistance profile and clinical implications

Resistance to antiviral therapy is the limiting factor in the successful management of HIV. In general, the K65R mutation is rarely selected (1.7-4%) with tenofovir disoproxil fumarate (TDF), abacavir (ABC), didanosine (ddI), and stavudine (d4T), as compared with the high incidence (>40%) of thymidine analog mutations associated with zidovudine and d4T. The high barrier to the development of K65R may reflect a combination of factors, including the high potency of K65R-selecting drugs, including recommended TDF/emtricitabine and ABC/lamivudine (ABC/3TC) combinations; the partial (low-intermediate level) profile of cross-resistance conferred by K65R to TDF, ABC and 3TC; the favorable viral fitness constraint imposed by K65R and the 3TC/emtricitabine-associated M184V mutations; the bidirectional antagonism between the K65R and thymidine analog mutation pathways; and unique RNA structural considerations in the region surrounding codon 65. Nevertheless, surprisingly high levels of treatment failures and K65R resistance may be associated with triple nucleoside analog regimens. The use of TDF + ABC, TDF + ddI and ABC + d4T in combination with 3TC or emtricitabine should be avoided. This selection of K65R may be reduced by the inclusion of zidovudine in two-four nucleoside reverse-transcriptase regimens. Clinical studies have demonstrated an increased frequency of K65R in association with suboptimal d4T and ddI regimens, as well as nevirapine and its resistance mutations Y181C and G190A. The potential for the development of the K65R mutation in subtype C is particularly problematic wherein a signature KKK nucleotide motif, at codons 64, 65 and 66 in reverse transcriptase, appear to lead to template pausing, facilitating the selection of K65R. Optimizing regimens may attenuate the emergence of K65R, leading to better long-term treatment management in different geographic settings. TDF-based regimens are the leading candidates for first- and second-line therapy, microbicides and chemoprophylaxis strategies.

Five-year follow up of genotypic resistance patterns in HIV-1 subtype C infected patients in Botswana after failure of thymidine analogue-based regimens

Objective

Our objective was to establish genotypic resistance profiles among the 4% of Batswana patients who experienced virologic failure while being followed within Botswana's National Antiretroviral Treatment Program between 2002 and 2007.

Methods

At the beginning of the national program in 2002, almost all patients received stavudine (d4T), together with didanosine (ddI), as part of their first nucleoside reverse transcriptase inhibitor (NRTI)-based regimen (Group 1). In contrast, the standard of care for all patients subsequently enrolled (2002-2007) included zidovudine/lamivudine (ZDV/3TC) (Group 2). Genotypes were analyzed in 26 patients from Group 1 and 37 patients from Group 2. Associations between mutations were determined using Pearson's correlation coefficient and Jaccard's coefficient of similarity.

Results

Seventy-eight percent of genotyped patients possessed mutations associated with protease inhibitor (PI) resistance while 87% and 90%, respectively, exhibited mutations associated with NRTIs and non-nucleoside reverse transcriptase inhibitors (NNRTIs). The most frequent PI mutations involving resistance to NFV were L90M (25.2%) and D30N (16.2%), but mutations at positions K45Q and D30N were often observed in tandem (P = 60.5, J = 50; p = 0.002; Group 2) alongside Q61E in 42.8% of patients who received ZDV/3TC. Both major patterns of thymidine analogue mutations, TAM 1 (48%) and TAM 2 (59%), were represented in patients from Group 1 and 2, although M184V was higher among individuals who had initially received ddI (61% versus 40.5%). In contrast, L74V was more frequent among individuals from Group 2 (16.2% versus 7.7%). Differences in regard to NNRTI mutations were also observed between Group 1 and Group 2 patients.

Conclusion

Despite a low rate of therapeutic failure (4%) among these patients, those who failed possessed high numbers of resistance mutations as well as novel resistance mutations and/or polymorphisms at sites within reverse transcriptase and protease.

Clinical management of HIV-1 resistance

Antiretroviral drug resistance is a fundamental survival strategy for the virus that stems from its vast capacity to generate diversity. With the recent availability of new ARV drugs and classes, it is now possible to prescribe fully active ART to most HIV-infected subjects and achieve viral suppression even in those with multidrug-resistant HIV. It is uncertain, however, if this scenario will endure. Given that ART must be given for life, and new compounds other than second-generation integrase inhibitors may not reach the clinic soon, all efforts must be done to avoid the development of resistance to the new agents. Here, we discuss relevant aspects for the clinical management of antiretroviral drug resistance, leaving detailed explanations of mechanisms and mutation patterns to other articles in this issue. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, vol. 85, issue 1, 2010.

Low-abundance drug-resistant viral variants in chronically HIV-infected, antiretroviral treatment-naive patients significantly impact treatment outcomes

BACKGROUND

Minor (i.e., <20% prevalence) drug-resistant human immunodeficiency virus (HIV) variants may go undetected, yet be clinically important.

OBJECTIVES

To compare the prevalence of drug-resistant variants detected with standard and ultra-deep sequencing (detection down to 1% prevalence) and to determine the impact of minor resistant variants on virologic failure (VF).

METHODS

The Flexible Initial Retrovirus Suppressive Therapies (FIRST) Study (N = 1397) compared 3 initial antiretroviral therapy (ART) strategies. A random subset (n = 491) had baseline testing for drug-resistance mutations performed by use of standard sequencing methods. Ultra-deep sequencing was performed on samples that had sufficient viral content (N = 264). Proportional hazards models were used to compare rates of VF for those who did and did not have mutations identified.

RESULTS

Mutations were detected by standard and ultra-deep sequencing (in 14% and 28% of participants, respectively; P < .001). Among individuals who initiated treatment with an ART regimen that combined nucleoside and nonnucleoside reverse-transcriptase inhibitors (hereafter, "NNRTI strategy"), all individuals who had an NNRTI-resistance mutation identified by ultra-deep sequencing experienced VF. When these individuals were compared with individuals who initiated treatment with the NNRTI strategy but who had no NNRTI-resistance mutations, the risk of VF was higher for those who had an NNRTI-resistance mutation detected by both methods (hazard ratio [HR], 12.40 [95% confidence interval {CI}, 3.41-45.10]) and those who had mutation(s) detected only with ultra-deep sequencing (HR, 2.50 [95% CI, 1.17-5.36]).

CONCLUSIONS

Ultra-deep sequencing identified a significantly larger proportion of HIV-infected, treatment-naive persons as harboring drug-resistant viral variants. Among participants who initiated treatment with the NNRTI strategy, the risk of VF was significantly greater for participants who had low- and high-prevalence NNRTI-resistant variants.

Advantages of predicted phenotypes and statistical learning models in inferring virological response to antiretroviral therapy from HIV genotype

Background

Inferring response to antiretroviral therapy from the viral genotype alone is challenging. The utility of an intermediate step of predicting in vitro drug susceptibility is currently controversial. Here, we provide a retrospective comparison of approaches using either genotype or predicted phenotypes alone, or in combination.

Methods

Treatment change episodes were extracted from two large databases from the USA (Stanford-California) and Europe (EuResistDB) comprising data from 6,706 and 13,811 patients, respectively. Response to antiretroviral treatment was dichotomized according to two definitions. Using the viral sequence and the treatment regimen as input, three expert algorithms (ANRS, Rega and HIVdb) were used to generate genotype-based encodings and VircoTYPE™ 4.0 (Virco BVBA, Mechelen, Belgium) was used to generate a predicted phenotype-based encoding. Single drug classifications were combined into a treatment score via simple summation and statistical learning using random forests. Classification performance was studied on Stanford- California data using cross-validation and, in addition, on the independent EuResistDB data.

Results

In all experiments, predicted phenotype was among the most sensitive approaches. Combining single drug classifications by statistical learning was significantly superior to unweighted summation ( P<2.2x10-16). Classification performance could be increased further by combining predicted phenotypes and expert encodings but not by combinations of expert encodings alone. These results were confirmed on an independent test set comprising data solely from EuResistDB.

Conclusions

This study demonstrates consistent performance advantages in utilizing predicted phenotype in most scenarios over methods based on genotype alone in inferring virological response. Moreover, all approaches under study benefit significantly from statistical learning for merging single drug classifications into treatment scores.

Minority quasispecies of drug-resistant HIV-1 that lead to early therapy failure in treatment-naive and -adherent patients

BACKGROUND

Early virological failure of antiretroviral therapy associated with the selection of drug-resistant human immunodeficiency virus type 1 in treatment-naive patients is very critical, because virological failure significantly increases the risk of subsequent failures. Therefore, we evaluated the possible role of minority quasispecies of drug-resistant human immunodeficiency virus type 1, which are undetectable at baseline by population sequencing, with regard to early virological failure.

METHODS

We studied 4 patients who experienced early virological failure of a first-line regimen of lamivudine, tenofovir, and either efavirenz or nevirapine and 18 control patients undergoing similar treatment without virological failure. The key mutations K65R, K103N, Y181C, M184V, and M184I in the reverse transcriptase were quantified by allele-specific real-time polymerase chain reaction performed on plasma samples before and during early virological treatment failure.

RESULTS

Before treatment, none of the viruses showed any evidence of drug resistance in the standard genotype analysis. Minority quasispecies with either the M184V mutation or the M184I mutation were detected in 3 of 18 control patients. In contrast, all 4 patients whose treatment was failing had harbored drug-resistant viruses at low frequencies before treatment, with a frequency range of 0.07%-2.0%. A range of 1-4 mutations was detected in viruses from each patient. Most of the minority quasispecies were rapidly selected and represented the major virus population within weeks after the patients started antiretroviral therapy. All 4 patients showed good adherence to treatment. Nonnucleoside reverse-transcriptase inhibitor plasma concentrations were in normal ranges for all 4 patients at 2 separate assessment times.

CONCLUSIONS

Minority quasispecies of drug-resistant viruses, detected at baseline, can rapidly outgrow and become the major virus population and subsequently lead to early therapy failure in treatment-naive patients who receive antiretroviral therapy regimens with a low genetic resistance barrier.

Prevalence, Genotypic Associations and Phenotypic Characterization of K65R, L74V and other HIV-1 RT Resistance Mutations in a Commercial Database

Background

Nucleoside reverse transcriptase inhibitor (NRTI)-associated mutations (NAMs) can affect response to treatment with NRTIs and might also result in HIV-1 with reduced replication capacity.

Methods

A large commercial HIV-1 database ( n=60,487) was analysed for the prevalence of NAMs, antiviral drug susceptibilities and viral replication capacity.

Results

Thymidine analogue mutations (TAMs) and M184V were the most commonly observed NAMs (>25%). L74V/I was detected in 11% of isolates. K65R was detected in 3.3% of isolates and its frequency remained stable from 2003 to 2006, similar to trends observed for other NAMs. TAMs were rarely observed in combination with K65R, but frequently associated with L74V/I. HIV-1 with K65R or L74V/I alone were fully susceptible to zidovudine and stavudine. K65R was associated with reduced susceptibility to tenofovir, didanosine, abacavir and lamivudine; L74V/I was associated with reduced susceptibility to abacavir and didanosine. The addition of M184V to either K65R or L74V/I improved susceptibility to tenofovir, zidovudine and stavudine, but reduced susceptibility to abacavir, didanosine and lamivudine. Other NAMs commonly associated with K65R were A62V, S68G and Y115F; their NRTI susceptibilities were similar to those of viruses containing K65R alone. The replication capacity for HIV-1 with M184V/I or K65R was significantly reduced compared with wild-type (median 68% and 72%, respectively; P<0.0001), whereas replication capacity for HIV-1 with L74V or TAMs was not significantly reduced (88% and 97%, respectively).

Conclusions

These results demonstrate a relative stability in the prevalence of HIV-1 clinical isolates with NAMs from 2003 to 2006. Differences between the genotypic patterns, phenotype and replication capacity associated with common NAMs are described.