Report and Commentary from the Fifth International Workshop on HIV Persistence During Therapy

As Savarino stresses in his video interview with Alain Lafeuillade, human trials are now required to ascertain if the macaque results can be translated to HIV.

Paul Luciw from UC Davis presented results of an experiment in which macaques infected with SHIV-RT had prostratin and valproic acid added to long-term ART (efavirenz, emtricitabine and tenofovir) prior to an interruption. Luciw showed evidence of reduced viral RNA and DNA in tissues but when treatment was interrupted there was no significant difference in viral load rebound compared to macaques treated with ART alone. Daria Hazuda from Merck has included several of Luciw's slides in her recent presentations on cure research so the main findings can be viewed online, however note that prostratin is only referenced as a "protein kinase C activator" and valproic acid as an "HDAC inhibitor". Hazuda's powerpoint can be downloaded online (bottom of the page, Luciw's data is on slides 21-25). Luciw also mentioned that he repeated the experiment adding raltegravir to the ART regimen and in that case there was no additional viral RNA and DNA reduction in tissues resulting from the anti-reservoir drugs, but he was running out of time and was unable to give any details.

Victor Garcia-Martinez, University of North Carolina, gave an overview of a model at the smaller end of the mammalian scale: mice. As recently reported in several papers, mice can be equipped with "humanized" immune systems in order to facilitate HIV infection and the preclinical study of viral latency. Although there are a number of limitations to the system, it is likely to be a useful addition to the options for screening approaches prior to embarking on more costly macaque experiments.

In the subsequent basic science segment of the agenda, Jonathan Karn from Case Western Reserve University gave a presentation suggesting that the way HIV gets repressed into latency in cells may be somewhat different from the way that cellular genes get shut down, which could be a cause for optimism in terms of developing better ways to selectively de-repress latent HIV. Jerome Zack (UCLA) introduced the audience to a type of cellular particle called a vault, which consist of three proteins and a piece of RNA. Vaults were discovered by UCLA scientist Leonard Rome, and Zack is working to adapt them into drug-delivery nanoparticles for the purposes of delivering anti-reservoir compounds into cells. Zack presented some preliminary evidence that vaults can be engineered to deliver potential latency activators prostratin and bryostatin, he is also working with Paul Wender at Stanford to develop better analogs of these drugs to use. The goal is to come up with some lead vault-delivered anti-latency compounds to test in the humanized mouse model.

Shifting topics to the virological aspects of HIV persistence, Sarah Palmer from the Karolinska Institute reported results of an intensive evaluation of viral genetics pre-ART and on long-term ART (up to >12 yrs) in 12 people (seven treated at acute infection, five during chronic infection) to look for evidence of viral evolution that would be indicative of ongoing replication. No evidence suggestive of HIV replication was found in various CD4 subsets and other cell types in blood, lymph tissue, bone marrow and gut. Palmer noted that no hematopoetic progenitor cells (HPCs) containing HIV DNA could be found; occasional positive signals from HPC samples turned out to be due to low-level contamination with CD4 cells (this finding was recently echoed in a paper from Bob Siliciano's group at Johns Hopkins).

Palmer drew attention to one case where a large amount of HIV DNA containing a huge deletion encompassing all of the protease gene was discovered. Since HIV can't replicate without protease, this demonstrates that the division of CD4 T cells carrying integrated, non-functional proviral HIV DNA can contribute to what may appear to be an HIV reservoir by some measures (but really isn't because the virus is defective). Mario Stevenson coined the term "junkyard DNA" for these non-functional proviruses, and it was quickly adopted at the workshop.