Viral fitness: relation to drug resistance mutations and mechanisms involved: nucleoside reverse transcriptase inhibitor mutations

Viral fitness: history and relevance for viral pathogenesis and antiviral interventions

The quasispecies dynamics of viral populations (continuous generation of variant genomes and competition among them) has as one of its frequent consequences variations in overall multiplication capacity, a major component of viral fitness. This parameter has multiple implications for viral pathogenesis and viral disease control, some of them unveiled thanks to deep sequencing of viral populations. Darwinian fitness is an old concept whose quantification dates back to the early developments of population genetics. It was later applied to viruses (mainly to RNA viruses) to quantify relative multiplication capacities of individual mutant clones or complex populations. The present article reviews the fitness concept and its relevance for the understanding of the adaptive dynamics of viruses in constant and changing environments. Many studies have addressed the fitness cost of escape mutations (to antibodies, cytotoxic T cells or inhibitors) as an influence on the efficacy of antiviral interventions. Here, we summarize the evidence that the basal fitness level can be a determinant of inhibitor resistance.

Preexposure prophylaxis-selected drug resistance decays rapidly after drug cessation

OBJECTIVE

Resistance to emtricitabine plus tenofovir disoproxil fumarate (FTC/TDF) or TDF alone used as preexposure prophylaxis (PrEP) has been detected in individuals who initiated PrEP during unrecognized acute HIV infection and, rarely, in PrEP breakthrough infections. PrEP-selected resistance could alter future treatment options, and therefore we sought to determine how long resistance persisted after PrEP cessation.

METHODS

The Partners PrEP Study was a randomized placebo-controlled trial of FTC/TDF or TDF as PrEP for HIV prevention. We previously reported that PrEP-related mutations (K65R, K70E or M184IV) were detected by 454 sequencing following seroconversion in nine individuals who acquired HIV during the Partners PrEP Study. In the current study, we used 454 sequencing to detect and quantify PrEP-related mutations in HIV RNA-positive plasma samples prior to seroconversion, as well as in plasma from 6, 12, and 24 months after PrEP cessation from these nine individuals.

RESULTS

HIV RNA-positive, antibody-negative samples were available prior to seroconversion for four of nine individuals with resistance detected at seroconversion. In all four cases, K65R, K70E and M184IV were not detected prior to seroconversion, suggesting PrEP-related resistance was selected and not transmitted. All PrEP-selected mutations were no longer detectable by 6 months after PrEP cessation and remained undetectable at 12 and 24 months in the absence of antiretroviral therapy.

CONCLUSION

Using highly sensitive assays, PrEP-selected resistance in plasma decays below detection by 6 months following drug cessation and remains undetectable for at least 24 months. Even high levels of resistance mutations during acute infection decay rapidly in the absence of ongoing PrEP exposure.

HIV-1 resistance to maraviroc conferred by a CD4 binding site mutation in the envelope glycoprotein gp120

Maraviroc (MVC) is a CCR5 antagonist that inhibits HIV-1 entry by binding to the coreceptor and inducing structural alterations in the extracellular loops. In this study, we isolated MVC-resistant variants from an HIV-1 primary isolate that arose after 21 weeks of tissue culture passage in the presence of inhibitor. gp120 sequences from passage control and MVC-resistant cultures were cloned into NL4-3 via yeast-based recombination followed by sequencing and drug susceptibility testing. Using 140 clones, three mutations were linked to MVC resistance, but none appeared in the V3 loop as was the case with previous HIV-1 strains resistant to CCR5 antagonists. Rather, resistance was dependent upon a single mutation in the C4 region of gp120. Chimeric clones bearing this N425K mutation replicated at high MVC concentrations and displayed significant shifts in 50% inhibitory concentrations (IC(50)s), characteristic of resistance to all other antiretroviral drugs but not typical of MVC resistance. Previous reports on MVC resistance describe an ability to use a drug-bound form of the receptor, leading to reduction in maximal drug inhibition. In contrast, our structural models on K425 gp120 suggest that this resistant mutation impacts CD4 interactions and highlights a novel pathway for MVC resistance.

High prevalence of X4/DM-tropic variants in children and adolescents infected with HIV-1 by vertical transmission

BACKGROUND

We studied HIV coreceptor tropism in vertically HIV-infected children and adolescents with the objective of predicting the proportion of children and adolescents that could be treated with CCR5 (R5) antagonists.

METHODS

One hundred eighteen multidrug-resistant pediatric patients (36 children and 82 adolescents) were enrolled in a cross-sectional study. Viral tropism was assessed using the new phenotypic HIV-1 tropism coreceptor assay information and Trofile.

RESULTS

Of 118 antiretroviral-experienced HIV-infected children and adolescents, 49 (57.0%) had dual-tropic and 20 (23.3%) had X4-tropic viruses by tropism coreceptor assay information testing. Only 17 (19.7%) showed R5-tropic variants. HIV-1 coreceptor usage was not detectable in 32 of 118 (27%) patients. Among 24 children and 62 adolescents with tropism coreceptor assay information results, 17 (70.8%) children and 51 (82.2%) adolescents showed viruses with dual-tropic or X4-tropic variants. Additionally, Trofile (ES) was performed in 42 of 118 patients with HIV-1 RNA > 1000 copies/mL. No patient showed X4-tropic variants; dual-tropic viruses were observed in 12 (28.6%) patients. In 6 (14.3%) patients, HIV tropism could not be determined. X4-tropic variants were more common in children (P = 0.031). CD4 T cell percentage was significantly lower in children (P = 0.011) and adolescents (P = 0.027) with R5-tropic viruses than in those with X4-tropic viruses.

CONCLUSIONS

The presence of X4-tropic variants in more than 80% of our cohort of antiretroviral-experienced children and adolescents with vertical HIV-1 infection indicates a very limited role for CCR5 antagonists as part of salvage regimens for highly treatment-experienced vertically HIV-1-infected patients with extensive antiretroviral drug resistance and limited treatment options.

The association between primary antiretroviral resistance and HAART virologic failure in a developing set

Santos is a Brazilian port city with high HIV incidence, high primary antiretroviral resistance levels, high HIV-1 BF recombinants prevalence, and high rates of antiretroviral virologic failure. We evaluated factors related to virologic failure after 48 weeks of HAART in this population. We compared demographic and HIV profiles among 43 individuals with virologic failure (group 1) and 37 with virologic success (group 2) after 48 weeks of HAART initiation. The overall primary antiretroviral resistance prevalence was 31.2%; 46.5% in group 1 and 13.5% in group 2 (p < 0.005). Nine patients from group 1 and seven from group 2 were infected by F or BF strains. Fifteen individuals presented with NRTI mutations, 13 with NNRTI mutations, three with PI mutations, and five with NRTI and NNRTI mutations. No significant differences were observed in baseline viral load, CD4, clade assignment, antiretrovirals used, or demographics among groups or patients harboring resistant versus wild-type viruses. In this region, there was a high prevalence of antiretroviral resistance among long standing infected patients whose disease had progressed. This finding supports the concept that resistance testing prior to ART initiation is cost effective. The association between primary antiretroviral resistance and virologic failure may suggest that primary resistance greatly impairs antiretroviral activity.