Q151M-mediated multinucleoside resistance: prevalence, risk factors, and response to salvage therapy

Risk factors and outcomes for the Q151M and T69 insertion HIV-1 resistance mutations in historic UK data

Background

The prevalence of HIV-1 resistance to antiretroviral therapies (ART) has declined in high-income countries over recent years, but drug resistance remains a substantial concern in many low and middle-income countries. The Q151M and T69 insertion (T69i) resistance mutations in the viral reverse transcriptase gene can reduce susceptibility to all nucleoside/tide analogue reverse transcriptase inhibitors, motivating the present study to investigate the risk factors and outcomes associated with these mutations.

Methods

We considered all data in the UK HIV Drug Resistance Database for blood samples obtained in the period 1997–2014. Where available, treatment history and patient outcomes were obtained through linkage to the UK Collaborative HIV Cohort study. A matched case–control approach was used to assess risk factors associated with the appearance of each of the mutations in ART-experienced patients, and survival analysis was used to investigate factors associated with viral suppression. A further analysis using matched controls was performed to investigate the impact of each mutation on survival.

Results

A total of 180 patients with Q151M mutation and 85 with T69i mutation were identified, almost entirely from before 2006. Occurrence of both the Q151M and T69i mutations was strongly associated with cumulative period of virological failure while on ART, and for Q151M there was a particular positive association with use of stavudine and negative association with use of boosted-protease inhibitors. Subsequent viral suppression was negatively associated with viral load at sequencing for both mutations, and for Q151M we found a negative association with didanosine use but a positive association with boosted-protease inhibitor use. The results obtained in these analyses were also consistent with potentially large associations with other drugs. Analyses were inconclusive regarding associations between the mutations and mortality, but mortality was high for patients with low CD4 at detection.

Conclusions

The Q151M and T69i resistance mutations are now very rare in the UK. Our results suggest that good outcomes are possible for people with these mutations. However, in this historic sample, viral load and CD4 at detection were important factors in determining prognosis.

Electronic supplementary material

The online version of this article (10.1186/s12981-018-0198-7) contains supplementary material, which is available to authorized users.

High fidelity simian immunodeficiency virus reverse transcriptase mutants have impaired replication in vitro and in vivo

The low fidelity of HIV replication facilitates immune and drug escape. Some reverse transcriptase (RT) inhibitor drug-resistance mutations increase RT fidelity in biochemical assays but their effect during viral replication is unclear. We investigated the effect of RT mutations K65R, Q151N and V148I on SIV replication and fidelity in vitro, along with SIV replication in pigtailed macaques. SIVmac239-K65R and SIVmac239-V148I viruses had reduced replication capacity compared to wild-type SIVmac239. Direct virus competition assays demonstrated a rank order of wild-type>K65R>V148I mutants in terms of viral fitness. In single round in vitro-replication assays, SIVmac239-K65R demonstrated significantly higher fidelity than wild-type, and rapidly reverted to wild-type following infection of macaques. In contrast, SIVmac239-Q151N was replication incompetent in vitro and in pigtailed macaques. Thus, we showed that RT mutants, and specifically the common K65R drug-resistance mutation, had impaired replication capacity and higher fidelity. These results have implications for the pathogenesis of drug-resistant HIV.

Increased risk of Q151M and K65R mutations in patients failing stavudine-containing first-line antiretroviral therapy in Cambodia

Background

Multi-nucleos(t)ide resistance (MNR) mutations including Q151M, K65R mutations, and insertion at codon 69 of HIV-1 reverse transcriptase coding region may confer resistance to all molecules of nucleos(t)ide reverse transcriptase inhibitors (NRTI). The presence of these mutations is an emerging problem compromising non-nucleoside reverse transcriptase inhibitors and protease inhibitors-based therapies. Furthermore, factors associated with selection of these mutations are still not well defined. The current study aimed to evaluate the frequency and to characterize factors associated with the occurrence of multi-nucleos(t)ide resistance mutations among HIV-1 infected patients failing recommended first-line antiretroviral regimens in Cambodia.

Methodology/Principal Finding

This is a retrospective analysis of HIV-1 drug resistance genotyping of 520 HIV-1 infected patients in virological failure (viral load > 250 copies/mL) while on first-line antiretroviral therapy in Cambodia with at least one reverse transcriptase inhibitor resistance associated mutation. Among these 520 patients, a total of 66 subjects (66/520, 12.7%) presented ≥1 MNR mutation, including Q151M, K65R, and Insert69 for 59 (11.3%), 29 (5.6%), and 2 (0.4%) patients, respectively. In multivariate analysis, both Q151M (p = 0.039) and K65R (p = 0.029) mutations were independently associated with current stavudine- compared to zidovudine-use.

Conclusion

Such selection of mutations by stavudine drastically limits the choice of antiretroviral molecules available for second-line therapy in resource-limited settings. This finding supports the World Health Organization’s recommendation for stavudine phase-out.

High-levels of acquired drug resistance in adult patients failing first-line antiretroviral therapy in a rural HIV treatment programme in KwaZulu-Natal, South Africa

Objective

To determine the frequency and patterns of acquired antiretroviral drug resistance in a rural primary health care programme in South Africa.

Design

Cross-sectional study nested within HIV treatment programme.

Methods

Adult (≥18 years) HIV-infected individuals initially treated with a first-line stavudine- or zidovudine-based antiretroviral therapy (ART) regimen and with evidence of virological failure (one viral load >1000 copies/ml) were enrolled from 17 rural primary health care clinics. Genotypic resistance testing was performed using the in-house SATuRN/Life Technologies system. Sequences were analysed and genotypic susceptibility scores (GSS) for standard second-line regimens were calculated using the Stanford HIVDB 6.0.5 algorithms.

Results

A total of 222 adults were successfully genotyped for HIV drug resistance between December 2010 and March 2012. The most common regimens at time of genotype were stavudine, lamivudine and efavirenz (51%); and stavudine, lamivudine and nevirapine (24%). Median duration of ART was 42 months (interquartile range (IQR) 32–53) and median duration of antiretroviral failure was 27 months (IQR 17–40). One hundred and ninety one (86%) had at least one drug resistance mutation. For 34 individuals (15%), the GSS for the standard second-line regimen was <2, suggesting a significantly compromised regimen. In univariate analysis, individuals with a prior nucleoside reverse-transcriptase inhibitor (NRTI) substitution were more likely to have a GSS <2 than those on the same NRTIs throughout (odds ratio (OR) 5.70, 95% confidence interval (CI) 2.60–12.49).

Conclusions

There are high levels of drug resistance in adults with failure of first-line antiretroviral therapy in this rural primary health care programme. Standard second-line regimens could potentially have had reduced efficacy in about one in seven adults involved.

Polymorphic mutations associated with the emergence of the multinucleoside/tide resistance mutations 69 insertion and Q151M

BACKGROUND

We hypothesized that polymorphic mutations exist that are associated with the emergence of the multinucleoside resistance mutations (MNR), 69 insertion and Q151M.

METHODS

The Swiss HIV Cohort Study was screened, and the frequencies of polymorphic mutations in HIV-1 (subtype B) were compared between patients detected with the 69 insertion (n = 17), Q151M (n = 29), ≥2 thymidine analogue mutations (TAM) 1 (n = 400) or ≥2 TAM 2 (n = 249). Logistic regressions adjusted for the antiretroviral treatment history were performed to analyze the association of the polymorphic mutations with MNR.

RESULTS

The 69 insertion and TAM 1 were strongly associated and occurred in 94.1% (16 of 17) together. The 69 insertion seemed to emerge as a consequence of the TAM 1 pathway (median years until detection: 6.8 compared with 4.4 for ≥2 TAM 1, P Wilcoxon = 0.009). Frequencies of 8 polymorphic mutations (K43E, V60I, S68G, S162C, T165I, I202V, R211K, F214L) were significantly different between groups. Logistic regression showed that F214L and V60I were associated with the emergence of Q151M/TAM 2 opposed to 69 insertion/TAM 1. S68G, T165I, and I202V were associated with Q151M instead of TAM 2.

CONCLUSIONS

Besides antiretroviral therapy, polymorphic mutations may contribute to the emergence of specific MNR mutations.

Predictors for the emergence of the 2 multi-nucleoside/nucleotide resistance mutations 69 insertion and Q151M and their impact on clinical outcome in the Swiss HIV cohort study

The 69 insertion and Q151M mutations are multi-nucleoside/nucleotide resistance mutations (MNR). The prevalence among 4078 antiretroviral therapy (ART)-experienced individuals was <1.3%. Combined ART fully prevented MNR in subtype B infections. Case-control studies were performed to identify risk factors. Control subjects were patients with ≥ 3 thymidine-analogue mutations. The 69 insertion study (27 control subjects, 14 case patients) identified didanosine exposure as a risk (odds ratio, 5.0 per year; P = .019), whereas the Q151M study (which included 44 control subjects and 25 case patients) detected no associations. Following detection, individuals with Q151M tended to have lower suppression rates and higher mortality rates, relative to control subjects. Additional studies are needed to verify these findings in non-subtype B infections.

Resistance pathways of human immunodeficiency virus type 1 against the combination of zidovudine and lamivudine

A better understanding of human immunodeficiency virus type 1 drug-resistance evolution under the selective pressure of combination treatment is important for the design of long-term effective treatment strategies. We applied Bayesian network learning to sequences from patients treated with the reverse transcriptase inhibitor combination of zidovudine (AZT) and lamivudine (3TC) to identify the role of many treatment-selected mutations in the development of resistance. Based on the Bayesian network structure, an in vivo fitness landscape was built, reflecting the necessary selective pressure under treatment, to evolve naive sequences to sequences obtained from patients treated with the combination. This landscape, combined with an evolutionary model, was used to predict resistance evolution in longitudinal sequence pairs. In our analysis, mutations 41L, 70R, 184V and 215F/Y were identified as major resistance mutations to the combination of AZT and 3TC, as they were associated directly with treatment experience. The network also suggested a possible role in resistance development for a number of novel mutations. Estimated fitness, using the landscape, correlated significantly with in vitro resistance phenotype in genotype-phenotype pairs (R(2)=0.70). Variation in predicted evolution under selective pressure correlated significantly with observed in vivo evolution during AZT plus 3CT treatment. In conclusion, we confirmed current knowledge on resistance development to the combination of AZT and 3CT, but additional novel mutations were identified. Moreover, a model to predict resistance evolution during AZT and 3CT treatment has been built and validated.

Implementation of raltegravir in routine clinical practice: selection criteria for choosing this drug, virologic response rates, and characteristics of failures

BACKGROUND

Raltegravir (RAL) achieved remarkable virologic suppression rates in randomized-clinical trials, but today efficacy data and factors for treatment failures in a routine clinical care setting are limited.

METHODS

First, factors associated with a switch to RAL were identified with a logistic regression including patients from the Swiss HIV Cohort Study with a history of 3 class failure (n = 423). Second, predictors for virologic outcome were identified in an intent-to-treat analysis including all patients who received RAL. Last observation carried forward imputation was used to determine week 24 response rate (HIV-1 RNA >or= 50 copies/mL).

RESULTS

The predominant factor associated with a switch to RAL in patients with suppressed baseline RNA was a regimen containing enfuvirtide [odds ratio 41.9 (95% confidence interval: 11.6-151.6)]. Efficacy analysis showed an overall response rate of 80.9% (152/188), whereas 71.8% (84/117) and 95.8% (68/71) showed viral suppression when stratified for detectable and undetectable RNA at baseline, respectively. Overall CD4 cell counts increased significantly by 42 cells/microL (P < 0.001). Characteristics of failures were a genotypic sensitivity score of the background regimen <or=1, very low RAL plasma concentrations, poor adherence, and high viral load at baseline.

CONCLUSIONS

Virologic suppression rates in our routine clinical care setting were promising and comparable with data from previously published randomized-controlled trials.

Clinical and genotypic findings in HIV-infected patients with the K65R mutation failing first-line antiretroviral therapy in Nigeria

INTRODUCTION

The HIV-1 epidemic in African countries is largely due to non-B HIV-1 subtypes. Patterns and frequency of antiretroviral drug resistance mutations observed in these countries may differ from those in the developed world, where HIV-1 subtype B predominates.

METHODS

HIV-1 subtype and drug resistance mutations were assayed among Nigerian patients with treatment failure on first-line therapy (plasma HIV RNA >1000 copies/mL). Sequence analysis of the reverse transcriptase and protease gene revealed drug resistance mutations and HIV-1 viral subtype. Specific patterns of mutations and clinical characteristics are described in patients with the K65R mutation.

RESULTS

Since 2005, 338 patients were evaluated. The most prevalent subtypes were CRF02_AG [152 of 338 (44.9%)] and G [128 of 338 (37.9%)]. Three hundred seven of 338 (90.8%) patients had previously received stavudine and/or zidovudine + lamivudine + efavirenz or nevirapine; 41 of 338 (12.1%) had received tenofovir (TDF). The most common nucleoside reverse transcriptase inhibitor mutations observed were M184V (301, 89.1%) and K70R (91, 26.9%). The K65R mutation was present in 37 of 338 patients (10.9%). The Q151M (P < 0.05), K219R, and T69del (P < 0.01) mutations were more common in patients with K65R who had not received TDF.

CONCLUSIONS

The K65R mutation is increasingly recognized and is a challenging finding among patients with non-B HIV subtypes, whether or not they have been exposed to TDF.

Effect of suppressing HIV viremia on the HIV progression of patients undergoing a genotype resistance test after treatment failure

BACKGROUND

Treatment guidelines for multi-experienced HIV patients have recently evolved from aiming to preserve immunity to achieving virological success, largely due to the availability of new antiretroviral drugs and drug classes. To assess the role of viral suppression on clinical progression following a genotypic resistance test (GRT), we have examined a database on patients failing to respond to combined antiretroviral therapy (cART).

METHODS

Patients undergoing a GRT after failure to respond to cART between January 1999 and May 2006 were followed up to December 2006. Time-to-death or a new AIDS event/death were considered to be analysis end-points. Viral suppression (< 50 copies/ml [c/ml]) after GRT, a time-dependent covariate, was tested as predictor of disease progression.

RESULTS

Overall, 1,389 patients were included in this observational study. After the GRT, patients were followed up to 72 months (median 28 months, IQ range 13-51 months). During the follow-up, 124 patients (9%) died, and 86 (6%) experienced a new AIDS event. 774 patients (56%) achieved < 50 c/ml HIV-RNA. The results of an adjusted Cox model showed that undetectable HIV-RNA after the GRT was significantly associated with a lower risk of death (hazard ration [HR] 0.46, 95% confidence interval [CI] 0.27-0.76) and AIDS/death (HR 0.43, 95% CI 0.28-0.65). The adjusted hazard ratios suggested a twofold risk reduction. A threefold risk reduction of death related to achieved undetectable viral load was found in patients with resistance to more than one drug class and with CDC-C diagnosis; a fourfold reduction was found in patients with < 200 CD4+/mm(3).

CONCLUSIONS

Maximal viral suppression has a large impact on HIV progression, particularly in heavily pre-treated individuals. Our findings support the latest treatment guidelines, which have rapidly evolved from an initial lack of indication to suggestions, and finally to strong recommendations for achieving the goal of suppressing viremia.

Changes in darunavir/r resistance score after previous failure to tipranavir/r in HIV-1-infected multidrug-resistant patients

OBJECTIVES

To evaluate changes in resistance to tipranavir/r (TPV/r) and darunavir/r (DRV/r) in patients who had failed a TPV/r-including regimen.

METHODS

HIV genotypes obtained both at baseline and at tipranavir/r failure (TPVF) were analyzed in 47 HIV-infected patients failing a TPV/r-including regimen. Genotypes were evaluated through the Stanford mutation score: patients were ranked for TPV/r and DRV/r resistance as susceptible (class 1), potential low-level (class 2), low-level (class 3), intermediate-level (class 4), and high-level resistance (class 5). Values are expressed as median (interquartile range) or as frequency (%).

RESULTS

Forty-seven patients were eligible. At baseline (tipranavir initiation), the scoring for TPV/r was: class 3 = 4 (8.5%); class 4 = 31 (66%); and class 5 = 12 (25.5%). Corresponding scores for DRV/r were: class 2 = 1 (2%), class 3 = 12 (25.5%), class 4 = 32 (68%), and class 5 = 2 (4.5%). At TPVF, a shift toward a higher TPV/r scoring class was seen in 16 (34.1%) patients (P = 0.001), whereas a shift toward a higher DRV/r scoring class was observed in 9 (19.2%) patients (P = 0.2381). After TPVF, 25/47 patients (53%) were treated with a DRV/r-containing regimen. After 24 weeks (on-treatment analysis), the median HIV RNA decrease was 3.04 (2.13-3.45) log10 copies per milliliter in DRV/r group versus -0.04 (-0.44; 0.50) log10 copies per milliliter in patients not treated with a DRV/r-containing regimen (P < 0.0001); CD4 increase was 126 (70-169) cells per cubic millimeter in DRV/r group versus -42 (-121; 42) (P < 0.0001).

DISCUSSION

Treatment with TPV/r did not significantly increase the resistance score to DRV/r and did not preclude the efficacy of subsequent treatment with DRV/r.

Emergence of human immunodeficiency virus type 1 variants containing the Q151M complex in children receiving long-term antiretroviral chemotherapy

We examined 28 children with HIV-1 infection who were not responding to existing antiviral regimens and were enrolled into clinical trials conducted at the National Cancer Institute to receive salvage therapy. In 3 of the 28 patients (10.7%), the Q151M complex amino acid substitutions were identified. The three patients had received nucleoside reverse transcriptase inhibitor (NRTI) monotherapy and/or combination regimens with multiple NRTIs for 4.3-8.6 years prior to the study. Recombinant infectious clones generated by incorporating the RT-encoding region of HIV-1 isolated from patients' plasma samples were highly resistant to zidovudine, didanosine and stavudine, while they were moderately resistant to lamivudine and tenofovir disoproxil fumarate (TDF). TDF-containing regimens reduced HIV-1 viremia in two of the three children carrying the Q151M complex. These data suggest that the Q151M could be prevalent in pediatric patients with long-term NRTI monotherapy and/or dual NRTI regimens and that HAART regimens containing TDF may be meritorious in such patients.

Minority memory genomes can influence the evolution of HIV-1 quasispecies in vivo

One of the consequences of viral quasispecies dynamics is the presence, in the mutant spectrum, of minority memory genomes that reflect those variants that were dominant at an earlier phase of the same evolutionary lineage. Replicative and cellular (or anatomical) contributions to quasispecies memory were previously defined during intrahost evolution of human immunodeficiency virus type 1 (HIV-1) [Briones, C., Domingo, E., Molina-París, C., 2003. Memory in retroviral quasispecies: experimental evidence and theoretical model for human immunodeficiency virus. J. Mol. Biol. 331, 213-229.]. However, the effects of replicative memory regarding virus evolution in vivo have not been investigated. Here we document that a multidrug-resistant (MDR) HIV-1, present at memory level, determined the ensuing evolution of the virus in an infected patient. Nucleotide sequencing and detailed phylogenetic analyses of sequential viral populations and individual molecular clones evidenced that the progeny of a minority MDR genome during a treatment interruption contributed the dominant genomes when an antiretroviral treatment was restored. An extension of a mathematical model of establishment and maintenance of memory, based on quasispecies theory, supports the experimental data. Therefore a replicative memory subpopulation, not detectable in a consensus nucleotide sequence, affected decisively subsequent states of viral evolution in vivo.

Drug-Class-Wide Resistance to Antiretrovirals in HIV-Infected Patients Failing Therapy: Prevalence, Risk Factors and Virological Outcome

Background

Drug-class-wide resistance (DCWR) to anti-retrovirals substantially reduces treatment options.

Methods

A database of 602 patients failing highly active antiretroviral therapy (HAART) undergoing genotypic resistance test (GRT) was analysed. DCWR was defined according to the International AIDS Society consensus. A multiple logistic regression model was built to define factors significantly associated with DCWR and to assess virological response to salvage regimens.

Results

NRTI DCWR was observed in 28.5% of 592 NRTI-exposed patients, NNRTI DCWR in 57.7% of 284 NNRTI exposed patients, PI DCWR in 19.9% of 412 PI exposed patients, and three-class resistance in 21.4% of 112 three-class-exposed patients. The prevalence of NRTI and PI DCWR increased significantly by year of exposure to the same class from 8.9% (<1 year) to 35.3% (>4 years) and from 1.2% (<1 year) to 34.8% (>4 years), respectively ( P<0.001, for trend). The risk of developing NRTI and PI DCWR increased by 25% (95% confidence interval [CI]: 1.6%–51.3%) and by 53% (20.5%–94.3%) for each year of treatment, and by 17% (95% CI: 5.6%–29.3%) and by 32% (17.7%–50.3%) for each previous failing NRTI- and PI-containing regimen, respectively. NRTI DCWR due to at least four nucleoside analogues mutations (NAMs) increased by year of NRTI exposure from 8.9% (<1 year) to 32.6% (>4 years; P<0.001, for trend). After adjustment for confounding factors, the probability of achieving plasma viral load <500 copies/ml was significantly reduced in patients with NRTI (OR: 0.750; 95% CI: 0.574–0.979), NNRTI (OR: 0.746; 95% CI: 0.572–0.975), PI (OR: 0.655; 95% CI: 0.456–0.941), three-class (OR: 0.220; 95% CI: 0.082–0.593) resistance.

Conclusions

The probability of developing NRTI and PI DCWR increased with length of class exposure and with the number of previously failing regimens. By contrast, high levels of NNRTI DCWR were observed within 1 year in NNRTI-failing patients, with a steady prevalence over time. The increase in prevalence with time of NRTI DCWR was due to the accumulation of NAMs. DCWR to NRTIs, NNRTIs, PIs or all the three together was associated with an increased probability of virological failure to subsequent HAART regimens.

Clinical and genotypic correlates of mutation K65R in HIV-infected patients failing regimens not including tenofovir

The mutation RT-K65R confers resistance to tenofovir (TDF). Although its prevalence is increasing with the use of this drug, clinical and genotypic correlates of K65R occurrence have yet to be fully identified. Clinical, virological and immunological and genotypic data of patients naïve for TDF who failed HAART regimens and underwent genotypic resistance test (GRT) during 1999-2003 were collected in a database and analyzed retrospectively. Out of 1392 GRT performed for 771 patients, 12 TDF-naïve patients had the K65R mutation with an overall prevalence of 1.6%. Previous AIDS, the use of abacavir, and treatment with efavirenz at GRT were independently associated with a greater risk of expressing K65R, while patients with longer exposure to lamivudine were less likely to present the mutation. Among genotypic correlates, the presence of M184V and NAMs seems to be protective for the emergence of K65R, while a strong positive correlation was found with the Q151M complex mutation. Moreover, the L100I mutation was independently associated with a higher probability of presenting K65R. The selection of mutation K65R in patients failing without TDF is rare. However, exposure to abacavir and/or efavirenz, presence of Q151M and/or L100I, and prior AIDS may favor the selection of this mutation. Conversely, long 3TC exposure, and the presence of M184V or NAMs seem to be protective.

Multiple drug class-wide resistance associated with poorer survival after treatment failure in a cohort of HIV-infected patients

OBJECTIVE

To evaluate the effect of drug class-wide resistance (CWR) on survival in HIV-infected individuals who underwent genotypic resistance test after antiretroviral failure.

DESIGN

Observational, longitudinal cohort study.

METHODS

HIV-infected individuals experiencing treatment failure were enrolled at first genotypic resistance test. End-points were death for any cause, AIDS-related death and AIDS-defining event/death. CWR was defined according to the International AIDS Society consensus. Survival analysis was performed with Cox's model.

RESULTS

Among 623 patients enrolled and followed for a median of 19 months (interquartile range, 12-29), Kaplan-Meier analyses for end-points at 48 months in patients with no CWR, one CWR, two CWR or three CWR were 8.9, 11.7, 13.4 and 27.1%, respectively, for death; 6.1, 9.9, 13.4 and 21.5%, respectively, for AIDS-related death; and 16.0, 17.7, 19.3 and 35.9%, respectively, for new AIDS event/death. In a multivariate Cox's model, higher HIV RNA level, previous AIDS and detection of three CWR (hazard ratio, 5.34; 95% confidence interval, 1.76-16.24) were all significantly associated with increased risk of death, while higher CD4 cell count and use of a new boosted protease inhibitor drug after identifying genotypic resistance were associated with reduced risk. Detection of three CWR was also significantly associated with higher risk of AIDS-related death and new AIDS event/death.

CONCLUSIONS

Even in the late era of highly effective antiretroviral treatments, detection of CWR, particularly if extended to all three drug classes is related to poorer clinical outcome and represents a risk-marker of disease progression and death.

CD8 epitope escape and reversion in acute HCV infection

In the setting of acute hepatitis C virus (HCV) infection, robust HCV-specific CD8+ cytotoxic T lymphocyte (CTL) responses are associated with initial control of viremia. Despite these responses, 70-80% of individuals develop persistent infection. Although viral escape from CD8 responses has been illustrated in the chimpanzee model of HCV infection, the effect of CD8 selection pressure on viral evolution and containment in acute HCV infection in humans remains unclear. Here, we examined viral evolution in an immunodominant human histocompatibility leukocyte antigen (HLA)-B8-restricted NS3 epitope in subjects with acute HCV infection. Development of mutations within the epitope coincided with loss of strong ex vivo tetramer and interferon gamma enzyme-linked immunospot responses, and endogenous expression of variant NS3 sequences suggested that the selected mutations altered processing and presentation of the variant epitope. Analysis of NS3 sequences from 30 additional chronic HCV-infected subjects revealed a strong association between sequence variation within this region and expression of HLA-B8, supporting reproducible allele-specific selection pressures at the population level. Interestingly, transmission of an HLA-B8-associated escape mutation to an HLA-B8 negative subject resulted in rapid reversion of the mutation. Together, these data indicate that viral escape from CD8+ T cell responses occurs during human HCV infection and that acute immune selection pressure is of sufficient magnitude to influence HCV evolution.

A pathophysiological approach to antiretroviral therapy

A discussion of the pathophysiology of HIV infection is important not only to understand both routine and novel therapeutic approaches, but also to appreciate the challenges of long-term control and viral eradication. This article will first briefly review certain pathophysiologic principles of HIV infection that have particular therapeutic implications, and then discuss general tenets of antiretroviral therapy, followed by new developments in the field.