Low-level HIV replication versus latency: identifying the source of viral rebounds during treatment interruption

2 October 2009. Related: Basic science and immunology.

Richard Jefferys, TAG

In HIV research, there is a persistent and vigorous debate around the question of whether or not viral replication persists in the face of successful antiretroviral therapy. During a plenary session at the International AIDS Conference in Mexico City in August 2008, Bob Siliciano made a compelling argument that, in most cases, antiretroviral therapy completely shuts down virus production. [1]

Now, a paper in PNAS provides additional support for this view. [2]

Beda Joos and colleagues evaluated a staggering 1,753 genetic sequences from the envelope region of HIV, sampled over the course of a treatment interruption trial known as SSITT (Swiss-Spanish Intermittent Treatment Trial). The study design involved a series of two-week treatment breaks followed by a prolonged interruption (therapy was subsequently reinitiated according to the CD4 and viral load thresholds used in current treatment guidelines).

The researchers used the sequence data to plot the relationships between the different viruses, using a technique called phylogenetic analyses. For each study participant analysed, the sequences were used to define “the most recent common ancestor” (MRCA), which is an approximation of the ancestral virus sequence from which all the others derived. Viruses that appeared during treatment interruptions (TIs) were then compared to the MRCA, to see if the sequences suggested that there had been ongoing replication and evolution while the study participants were on ART. The results showed that the rebounding viruses during TI were actually more distant from the MRCA than the viruses detected when the participants first entered the study. The researchers conclude: “the striking lack of a temporal relationship between rebounding virus and pretreatment viruses strongly suggests that rebounding virus originates from reactivated, latently infected cells rather than from a cellular pool or compartment engaged in low-level replication.”

Source: TAG Basic Science web log (20.11.08)

http://tagbasicscienceproject.typepad.com

References

1. SilicianoR. HIV Persistence on Patients on HAART: Re-Evaluating Prospects for Eradication. Plenary lecture WEPL01. XVII International Siliciano R. XVII International HIV Persistence on Patients on HAART:: Evaluating Prospects for Eradication. Plenary lecture WEPL01. XVII International AIDS Conference, 3-8 August 2008, Mexico City.
   http://www.aids2008.org/Pag/PSession.aspx?s=33
2. Joos B et al. HIV rebounds from latently infected cells, rather than from continuing low-level replication. PNAS October 28, 2008 vol. 105 no. 43 16725-16730. Published online before print October 20, 2008, doi:: 10.1073/pnas.0804192105
   http://www.pnas.org/content/105/43/16725

Comment

Although this paper and the blog summary was published at the end of last year this is one of the most important, yet least appreciated, aspect of treatment, so data from another study is very helpful.

Although not reported in these studies, it also implies that HIV isn’t being seeded from CNS or genital compartments – ie for most people it may also be controlled in these sites.