Decay of the HIV reservoir in patients receiving antiretroviral therapy for extended periods: implications for eradication of virus

Determinants of the establishment of human immunodeficiency virus type 1 latency

Recent research has emphasized the notion that human immunodeficiency virus type 1 (HIV-1) latency is controlled by a restrictive histone code at, or DNA methylation of, the integrated viral promoter (long terminal repeat [LTR]). The present concept of HIV-1 latency has essentially been patterned from the principles of cellular gene regulation. Here we introduce an experimental system that allows for the qualitative and quantitative kinetic study of latency establishment and maintenance at the population level. In this system, we find no evidence that HIV-1 latency establishment is the consequence of downregulation of initial active infection followed by the establishment of a restrictive histone code at the viral LTR. Latent infection was established following integration of the virus in the absence of viral gene expression (silent integration) and was a function of the NF-kappaB activation level in the host cell at the time of infection. In the absence of a role for epigenetic regulation, we demonstrate that transcriptional interference, a mechanism that has recently been suggested to add to the stabilization of HIV-1 latency, is the primary mechanism to govern latency maintenance. These findings provide direct experimental evidence that the high number of viral integration events (>90%) found in actively expressed genes of CD4(+) memory T cells from highly active antiretroviral therapy-suppressed patients represent indeed latent infection events and that transcriptional interference may be the primary mechanism to control HIV-1 latency in vivo. HIV-1 latency may thus not be governed by the principles of cellular gene regulation, and therapeutic strategies to deplete the pool of latently HIV-1-infected cells should be reconsidered.

The amplitudes of viral blips in HIV-1 infected patients treated with antiretroviral therapy are power-law distributed

We previously reported that in patients treated with highly active antiretroviral therapy (HAART) who achieve viral load (VL) suppression, low fluctuations of viral load over the threshold of detection (viral blips) more than 4 weeks apart occur at random, with a frequency that does not change with longer times of observation. The etiology of viral blips is currently unknown, but viral blip frequency inversely correlates with the decay of the latent reservoir, whose stability has been proposed as the major hurdle to HIV eradication. We show here that the distribution of viral blip amplitudes observed in a group of 272 patients successfully treated with highly active antiretroviral therapy appears to be power-law distributed. Such a distribution can be theoretically generated by randomly sampling the arrival of asynchronous and overlapping elementary pulses of viremia, with asymptotic exponential decay of kinetics, thus suggesting that the low fluctuations of viremia observed in patients during HAART treatment is, in part, a discrete phenomenon consistent with random activation of latently infected cells or release of virus and infected cells into the blood compartment from unknown sites of active viral replication.

Rapid CD4+ cell decrease after transient cART initiated during primary HIV infection (ANRS PRIMO and SEROCO cohorts)

OBJECTIVE

To modelize the rate of CD4 cell count decline and its determinants after cessation of combination antiretroviral therapy (cART) started during primary HIV infection (PHI) and compare it with never-treated patients.

METHODS

Kinetics of CD4 counts were analyzed on the square root scale by using a mixed-effects model in 170 patients who received cART during PHI from the Primary Infection (PRIMO) cohort and 123 never-treated patients from the Seroconverters (SEROCO) cohort.

RESULTS

After cART interruption in the PRIMO cohort, the CD4 cell count fell rapidly during the first 5 months and more slowly thereafter. The timing of treatment initiation had no influence on the rate of CD4 cell decline. In contrast, a larger increase in CD4 cell counts during cART was associated with a steeper decline and a larger loss of CD4 cells after treatment interruption. The mean CD4 cell loss 3 years postinterruption was 383 cells per microliter. In the SEROCO cohort, the CD4 T-cell decline was less steep (3-year CD4 loss 239 cells/microL). As a result, the mean CD4 cell counts were similar (416 cells/microL) 3 years after cART interruption (PRIMO) or after infection (SEROCO).

CONCLUSIONS

These data question the benefit of a limited course of cART even when initiated within 3 months after PHI diagnosis.

Transient antiretroviral therapy selecting for common HIV-1 mutations substantially accelerates the appearance of rare mutations

Background

Highly selective antiretroviral (ARV) regimens such as single dose nevirapine (NVP) used for prevention of mother to child transmission (PMTCT) in resource-limited settings produce transient increases in otherwise marginal subpopulations of cells infected by mutant genomes. The longer term implications for accumulation of further resistance mutations are not fully understood.

Methods

We develop a new strain-differentiated hybrid deterministic-stochastic population dynamic type model of healthy and infected cells. We explore how the transient increase in a population of cells transcribed with a common mutation (modelled deterministically), which occurs in response to a short course of monotherapy, has an impact on the risk of appearance of rarer, higher-order, therapy-defeating mutations (modelled stochastically).

Results

Scenarios with a transient of a magnitude and duration such as is known to occur under NVP monotherapy exhibit significantly accelerated viral evolution compared to no-treatment scenarios. We identify a possibly important new biological timescale; namely, the duration of persistence, after a seminal mutation, of a sub-population of cells bearing the new mutant gene, and we show how increased persistence leads to an increased probability that a rare mutant will be present at the moment at which a new treatment regimen is initiated.

Conclusion

Even transient increases in subpopulations of common mutants are associated with accelerated appearance of further rarer mutations. Experimental data on the persistence of small subpopulations of rare mutants, in unfavourable environments, should be sought, as this affects the risk of subverting later regimens.

Incidence and characterization of acute HIV-1 infection in a high-risk Thai population

OBJECTIVE

The objective of this study was to investigate the incidence, demographics, HIV subtype, and genotypic resistance of acute HIV infections in a high-risk Thai population.

METHODS

Between March 2006 and September 2007, 6426 stored samples at the Thai Red Cross Anonymous Clinic were screened for acute HIV infection by 2 methods: pooled nucleic acid testing (NAT) of fourth-generation enzyme immunoassay (EIA)-negative samples (n = 5402) and subsequent first-generation EIA testing of fourth-generation EIA-positive samples (n = 1024).

RESULTS

Eleven acute HIV-infected subjects were identified by pooled NAT (n = 7) and serial EIA (n = 4). Mean age was 28 years; 9 were male; and 60% were men who have sex with men. Median HIV RNA was 99,601 copies per milliliter (log10 viral load (VL) = 5.00). Eight samples could be genotyped: 6, CRF01_AE; 1, subtype B; and 1, CRF01_AE/B recombinant. No resistance to antiretroviral therapy was found. The HIV incidence per 100 person-years, calculated from the pooled, antibody-negative samples, was 2.7% (95% confidence interval, 2.2%-4.3%).

CONCLUSIONS

This is the first report of antibody-negative, NAT-positive, acute HIV infection in Thailand. The majority were men who have sex with men, which reflects the current epidemic in Thailand and justifies prevention programs aimed at this group. This high-risk population may be suitable for future studies on acute HIV infection, HIV treatment, vaccine, and prevention of onward transmission strategies.

Asymmetric division of activated latently infected cells may explain the decay kinetics of the HIV-1 latent reservoir and intermittent viral blips

Most HIV-infected patients when treated with combination antiretroviral therapy achieve viral loads that are below the current limit of detection of standard assays after a few months. Despite this, virus eradication from the host has not been achieved. Latent, replication-competent HIV-1 can generally be identified in resting memory CD4(+) T cells in patients with "undetectable" viral loads. Turnover of these cells is extremely slow but virus can be released from the latent reservoir quickly upon cessation of therapy. In addition, a number of patients experience transient episodes of viremia, or HIV-1 blips, even with suppression of the viral load to below the limit of detection for many years. The mechanisms underlying the slow decay of the latent reservoir and the occurrence of intermittent viral blips have not been fully elucidated. In this study, we address these two issues by developing a mathematical model that explores a hypothesis about latently infected cell activation. We propose that asymmetric division of latently infected cells upon sporadic antigen encounter may both replenish the latent reservoir and generate intermittent viral blips. Interestingly, we show that occasional replenishment of the latent reservoir induced by reactivation of latently infected cells may reconcile the differences between the divergent estimates of the half-life of the latent reservoir in the literature.

Supersensitive Viral Load Assay in Predicting CD4-Guided Treatment Failure

In HIV patients who discontinue highly active antiretroviral therapy (HAART), the degree of HIV RNA suppression at the time of treatment interruption may predict success of re-treatment after the interruption (STI). A case-control substudy of the Staccato trial in Thailand included CD4-guided STI subjects with HIV RNA > 50 copies /ml (virological failure cases, n=11) and HIV RNA < 50 copies/ml (controls, n=22) after 12-24 weeks of HAART re-treatment following a median of 2 STI cycles. Controls were matched for age, gender and pre-ART CD4 count. HIV RNA with 5 copies/ml detection limit was determined on pre-virological failure samples. HIV RNA increased in cases compared to controls with each successive STI cycle (p-trend across time-points 0.004). The last HIV RNA below 50 copies/ml was significantly higher among cases compared to controls (p=.004). Measuring HIV RNA below 50 copies/ml may be useful in predicting virological failure to STI.

Resting regulatory CD4 T cells: a site of HIV persistence in patients on long-term effective antiretroviral therapy

Background

In HIV-infected patients on long-term HAART, virus persistence in resting long-lived CD4 T cells is a major barrier to curing the infection. Cell quiescence, by favouring HIV latency, reduces the risk of recognition and cell destruction by cytotoxic lymphocytes. Several cell-activation-based approaches have been proposed to disrupt cell quiescence and then virus latency, but these approaches have not eradicated the virus. CD4⁺CD25⁺ regulatory T cells (Tregs) are a CD4⁺ T-cell subset with particular activation properties. We investigated the role of these cells in virus persistence in patients on long-term HAART.

Methodology/Principal Findings

We found evidence of infection of resting Tregs (HLADR⁻CD69⁻CD25^hiFoxP3⁺CD4⁺ T cells) purified from patients on prolonged HAART. HIV DNA harbouring cells appear more abundant in the Treg subset than in non-Tregs. The half-life of the Treg reservoir was estimated at 20 months. Since Tregs from patients on prolonged HAART showed hyporesponsiveness to cell activation and inhibition of HIV-specific cytotoxic T lymphocyte-related functions upon activation, therapeutics targeting cell quiescence to induce virus expression may not be appropriate for purging the Treg reservoir.

Conclusions

Our results identify Tregs as a particular compartment within the latent reservoir that may require a specific approach for its purging.

HIV-1 DNA for the measurement of the HIV reservoir is predictive of disease progression in seroconverters whatever the mode of result expression is

BACKGROUND

HIV-1 DNA levels, reported as copies/10(6) peripheral blood mononuclear cells (PBMC), are very predictive of disease progression in seroconverters, independently of CD4(+)T cell count and HIV-RNA. Previously, HIV-DNA levels have sometimes been reported by other means: copies/10(6) CD4(+)T cells, reflecting the proportion of infected cells; or copies/mL whole blood, reflecting the global blood reservoir size.

OBJECTIVES

We investigated if the predictive value over the natural course of the disease depends on how the results are reported.

STUDY DESIGN

Results reported as HIV-DNA copies/10(6) PBMC were converted to copies/10(6) CD4(+)T cells or to copies/mL whole blood for 422 seroconverters included in the French SEROCO cohort (ANRS).

RESULTS

The three methods for reporting HIV-DNA levels yielded different ranges, but these values were highly correlated. The level of HIV-DNA during the seroconversion period was strongly associated with disease progression in all three reporting methods.

CONCLUSIONS

This reinforces the value of HIV-DNA quantification in physiopathological and therapeutical studies, particularly in an era of research aimed at diminishing the HIV reservoir. Even if blood represents a small part of this reservoir, HIV-DNA in blood is a simple marker that provides an informative picture of the global reservoir and is strongly predictive of disease progression.

Beyond the end of exceptionalism: integrating HIV testing into routine medical care and HIV prevention

In September 2006, the US CDC issued new guidelines for HIV testing. These guidelines were designed not only to simplify and expand HIV testing but also to integrate testing into routine medical care in the USA. The nationwide implementation of these guidelines is currently facing several political and legal barriers. In this article, we examine the origins of current patient-driven and risk-based HIV testing in the USA and highlight shortcomings of this strategy. We then demonstrate how the changing HIV epidemic in the USA requires routine HIV screening at all points of contact in the medical system in order to control the HIV epidemic and how novel testing strategies could increase the yield of testing in these settings.