Retrovirus Reverse Transcriptases Containing a Modified YXDD Motif

The YXDD motif, where X is a variable amino acid, is highly conserved among various viral RNA-dependent DNA polymerases. Mutations in the YXDD motif can abolish enzymatic activity, alter the processivity and fidelity of enzymes and decrease virus infectivity. This review provides a summary of the significant documented studies on the YXDD motif of HIV-1, simian immunodeficiency virus, feline immunodeficiency virus and murine leukaemia virus and the impact of mutation that this motif has had on viral pathogenesis and drug treatment.

Trends in Prevalence of HIV-1 Drug Resistance in a Public Clinic in Maputo, Mozambique

Background

An observational study was conducted in Maputo, Mozambique, to investigate trends in prevalence of HIV drug resistance (HIVDR) in antiretroviral (ART) naïve subjects initiating highly active antiretroviral treatment (HAART).

Methodology/Principal Findings

To evaluate the pattern of drug resistance mutations (DRMs) found in adults on ART failing first-line HAART [patients with detectable viral load (VL)]. Untreated subjects [Group 1 (G1; n=99)] and 274 treated subjects with variable length of exposure to ARV´s [6–12 months, Group 2 (G2;n=93); 12-24 months, Group 3 (G3;n=81); >24 months (G4;n=100)] were enrolled. Virological and immunological failure (VF and IF) were measured based on viral load (VL) and T lymphocyte CD4+ cells (TCD4+) count and genotypic resistance was also performed. Major subtype found was C (untreated: n=66, 97,06%; treated: n=36, 91.7%). Maximum virological suppression was observed in G3, and significant differences intragroup were observed between VF and IF in G4 (p=0.022). Intergroup differences were observed between G3 and G4 for VF (p=0.023) and IF between G2 and G4 (p=0.0018). Viral suppression (<50 copies/ml) ranged from 84.9% to 90.1%, and concordant VL and DRM ranged from 25% to 57%. WHO cut-off for determining VF as given by 2010 guidelines (>5000 copies/ml) identified 50% of subjects carrying DRM compared to 100% when lower VL cut-off was used (<50 copies/ml). Length of exposure to ARVs was directly proportional to the complexity of DRM patterns. In Mozambique, VL suppression was achieved in 76% of individuals after 24 months on HAART. This is in agreement with WHO target for HIVDR prevention target (70%).

Conclusions

We demonstrated that the best way to determine therapeutic failure is VL compared to CD4 counts. The rationalized use of VL testing is needed to ensure timely detection of treatment failures preventing the occurrence of TDR and new infections.

Antiretroviral therapy response among HIV-2 infected patients: a systematic review

BACKGROUND

Few data are available on antiretroviral therapy (ART) response among HIV-2 infected patients. We conducted a systematic review on treatment outcomes among HIV-2 infected patients on ART, focusing on the immunological and virological responses in adults.

METHODS

Data were extracted from articles that were selected after screening of PubMed/MEDLINE up to November 2012 and abstracts of the 1996-2012 international conferences. Observational cohorts, clinical trials and program reports were eligible as long as they reported data on ART response (clinical, immunological or virological) among HIV-2 infected patients. The determinants investigated included patients' demographic characteristics, CD4 cell count at baseline and ART received.

RESULTS

Seventeen reports (involving 976 HIV-2 only and 454 HIV1&2 dually reactive patients) were included in the final review, and the analysis presented in this report are related to HIV-2 infected patients only. There was no randomized controlled trial and only two cohorts had enrolled more than 100 HIV-2 only infected patients. The median CD4 count at ART initiation was 165 cells/mm3, [IQR; 137-201] and the median age at ART initiation was 44 years (IQR: 42-48 years). Ten studies included 103 patients treated with three nucleoside reverse transcriptase inhibitors (NRTI). Protease inhibitor (PI) based regimens were reported by 16 studies. Before 2009, the most frequent PIs used were Nelfinavir and Indinavir, whereas it was Lopinavir/ritonavir thereafter. The immunological response at month-12 was reported in six studies and the mean CD4 cell count increase was +118 cells/μL (min-max: 45-200 cells/μL).

CONCLUSION

Overall, clinical and immuno-virologic outcomes in HIV-2 infected individuals treated with ART are suboptimal. There is a need of randomized controlled trials to improve the management and outcomes of people living with HIV-2 infection.

Salvage Therapy with Atazanavir/Ritonavir Combined to Tenofovir in HIV-Infected Patients with Multiple Treatment Failures: Randomized Anrs 107 Trial

Background

Ritonavir (RTV)-boosted atazanavir (ATV) and tenofovir disoproxil fumarate (TDF-DF) are promising in highly experienced patients because of their pharmacokinetic profile, activity, safety and resistance properties.

Methods

A 26-week study of the safety and efficacy of RTV-boosted ATV plus TDF-DF was conducted in 53 HIV-infected patients who were failing their current highly active antiretroviral therapy (HAART) regimen. Patients with history of failure to at least two protease inhibitors (PIs) and one non-nucleoside reverse transcriptase inhibitor (NNRTI) were randomized to either continue their current regimen (group 1) or replace the PI by ATV (300 mg once daily) boosted by RTV (100 mg; group 2) for 2 weeks. Then, all patients received the same combination of ATV, RTV and TDF-DF (300 mg) plus optimized NRTIs regimen.

Results

At baseline, median CD4+ T-cell count was 206/mm3, median viral load (VL) 5.0 log10/ml and median numbers of NRTI, NNRTI and PI resistance mutations were 7, 1 and 8, respectively. At week 2, median VL remained unchanged from baseline in group 2 as compared with group 1 (-0.1 vs -0.1 log10/ml). At week 26, a mild decrease in median VL from baseline of 0.2 log10/ml was observed, with 16 (31%) and 9 (17%) patients exhibiting a decrease in viral load of at least 0.5 and 1.0 log10/ml, respectively. Baseline phenotypic and genotypic resistance to ATV were the most predictive independent factors of virological response. The regimen was well tolerated.

Conclusion

In these very advanced patients failing highly HAART, the combination of boosted ATV plus TDF-DF yielded low antiretroviral activity.

Using a Database of HIV Patients Undergoing Genotypic Resistance Test after Haart Failure to Understand the Dynamics of M184V Mutation

Objective

M184V/I mutation is associated with high-level phenotypic resistance to lamivudine (3TC). The aim of the present analysis was to correlate the time of appearance/disappearance of M184V/I with duration of 3TC treatment.

Methods

Overall, 211 patients were selected from a database of HIV patients undergoing genotypic resistance test after virological failure of HAART regimens in two major reference centres in Rome between 1999 and 2001. At the time of genotyping, 120 of them (56.9%) were failing a 3TC-including HAART, while 91 (43.1%) received 3TC only in previous HAART. Duration of the current 3TC-containing regimen and the time from the end of last 3TC treatment to genotypic resistance test (GRT) were analysed.

Results

Among patients currently undergoing 3TC-containing HAART, the prevalence of M184V/I was 82.5% (78.3/4.2%, respectively) and significantly associated to current 3TC use at GRT. Prevalence of M184V/I was associated to longer history of 3TC (from 47.1% in patients treated with 3TC for <6 months, to 84.0% among those treated for 7–12 months; 100.0% of patients with >42 months of current 3TC carried M184V. At logistic regression analysis, the rate of increase of M184V/I in 3TC-failing patients was statistically significant (OR: 1.066 per month of current 3TC therapy, 95% CI: 1.020–1.114, P<0.01), suggesting a 6.6% monthly increase of probability of M184V/I. Among patients who interrupted 3TC, overall prevalence of M184V/I was 23.1%: proportion of patients carrying the M184V/I dropped from 83.3% among those who interrupted 3TC from ≤3 months, to 56.3, 20, 10.5 and 0% for those interrupting 3TC from 6, 12, 24 and ≥24 months, respectively. At logistic regression, the rate of disappearance of M184V/I was also statistically significant (OR: 0.883 per month, 95% CI: 0.804–0.970, P=0.01), indicating a 11.7% monthly decrease of probability of M184V/I after 3TC interruption.

Conclusions

Dynamics of appearance/disappearance of M184V/I mutation is rapid after 3TC failure/interruption, suggesting ease of development of such a mutation, but also suggesting a remarkable growth disadvantage for HIV. From the clinical perspective, recycling of drugs whose antiviral activity is affected by M184V mutation can be successful after appropriate drug wash-out, also in heavily pretreated patients.

Impact of Stavudine Phenotype and Thymidine Analogues Mutations on Viral Response to Stavudine plus Lamivudine in Altis 2 Anrs Trial

Objective

Stavudine-based antiretroviral combinations are less effective in zidovudine-experienced patients than in naive subjects and recently, mutations have been described to be associated to the use of both stavudine and zidovudine. In the ALTIS 2 trial, it was shown that a combination of stavudine and lamivudine is less effective in zidovudine-experienced patients than in naive patients. We conducted a retrospective genotypic and phenotypic resistance study (expressed as stavudine phenotypic index, calculated by dividing the inhibitory concentrations 50% [IC50] by the mean value of the sensitive viruses) to evaluate the factors associated with decrease in plasma HIV-1 RNA.

Design

Associations with continuous variables were studied using non-parametric Spearman correlation coefficients. Associations with categorical variables were studied using non-parametric Mann–Whitney tests. Multivariate stepwise regression analyses were used to determine independent prognostic factors of the virological response.

Results

At baseline, most of the subjects harboured zidovudine-associated mutations in plasma and peripheral blood mononuclear cells. Zidovudine and stavudine IC50 and IC90 were strongly associated with response. It appears that a cut-off of stavudine phenotypic index of 1.8-fold of IC50, much lower than the usually used value, could be clinically significant for response to stavudine. In the multivariate analysis, the stepwise model with the higher multiple correlation coefficient ( R2=0.742) included the presence of a 215 Y/F mutation, the number of previously used nucleoside analogues and a resistant stavudine phenotype.

Conclusion

These results argue for a phenotypic and genotypic cross resistance between stavudine and zidovudine. Modest increases of IC50 and IC90 for stavudine had an important impact on the virological response during the trial and plead for a new definition of the threshold value for stavudine phenotypic index.