Cure research and viral reservoirs
Simon Collins, HIV i-Base
In addition to the prevention studies and the progress on pipeline drugs that made most headlines (see the previous issue of HTB), a third set of presentations through the meeting supported the IAS Conference Statement on the need for the cure. 
That “the Cure” might again re seen as an achievable goal for research was resuscitated in keynote lectures from NIAID lead Anthony Fauci several years ago and several medical networks, including the IAS, already hold annual meetings to coordinate different approaches. US public funding now requires cure research as a key work stream for HIV treatment networks.
Whilst the scientific challenge of curing HIV has been the consitent focus for many committed researchers, the renewed level of funding is clearly driven by the financial challenge of providing lifelong global treatment. Even when the generic costs are reduced to less than $100 per person per year, current treatment programmes need to more than double and then be sustained for coverage to meet the existing need. Perhaps increasing the resources for cure research is therefore perhaps also the most ethical way to be able to withdraw from responsibility for funding global treatment.
However, these sessions in Rome were mostly held in the smaller rooms, filled to capacity. They were also frustratingly insular with few being available as webcasts or slides to download, including the plenary session by IAS President Elect, Françoise Barré-Sinoussi. 
Neither the IAS pre-conference workshop (New concepts in HIV Immunopathogenesis, Treatment and Vaccine Strategies) nor the rapid summary report from that workshop in the main IAS conference by Nicolas Chomont was webcast. However, slides are available from some of the workshop sessions and for the summary by Chomont. [3, 4]
A satellite meeting cosponsored by amfAR and IAS also was not webcast, although the slide presentations can be downloaded.  This meeting focused on whether:
- viral replication persists on ART;
- eradication research can progress in animal models or is dependent on human studies;
- eradication is most likely to come from targeting the viral reservoir or more recent approaches using gene therapy.
Several other presentations at the conferences looked at strategies to selectively reactivate the reservoir of latently infected resting CD4 cells, either at the pre- or post-integration step. This challenge is highlighted by the pool being estimated to be less than one in a million resting cells for someone on stable treatment with undetectable viral load.
Some researchers believe that success in this goal might eradicate HIV, though this is dependent on whether current treatment suppresses replication sufficiently to halt viral evolution. This might turn out to be possible, as it has been the conclusion from several intensification studies that have shown no further reduction on low level viraemia after increasing the potency of a three drug combination with a fourth drug, including an integrase inhibitor.  An oral presentation from Brunetta and colleagues reported no impact on CD4 reservoirs in gut-associated lymphoid tissue obtained from sigmoid colon biopsies at 48 weeks of follow up following intensification with raltegravir. 
A case reported by Chun and colleagues in an article in AIDS last year perhaps also supports this view.  This paper described one person – “the Toronto patient” – who was enrolled and treated prior to seroconversion. Viral load was suppressed to <50 copies/mL on HAART for more than ten years, driving the pool of infected CD4 T cells down to less than one in 1.7 billion cells. Against advice, the person decided to stop treatment under research conditions. Viral rebound only occurred after 50 days with an increased to 1600 copies/mL followed by spontaneous suppression by day 95 back to undetectable. Subsequently, viral load steadily increased to approximately 8600 copies/mL on day 143 when treatment was restarted.
So one interpretation of this case could be to emphasise the difficulty of eradication – even with such an early, effective and sustained level of treatment. Another interpretation is that eradication might almost have been achieved. Perhaps another month, or year, or few years on treatment might have been sufficient to final exhaust the remaining pool on resting infected cells. This study is unlikely to be repeated.
Another more optimistic, but also unexplained, set of cases includes the 32 patients from the ANRS Visconti study reported at CROI this year. This group received antiretroviral therapy within ten weeks of seroconversion for a median of three years (1-7.5 years). Five of these people sustained virological control for a median of 6 years (range 4-10) after treatment discontinuation.  It is unclear why similar cohorts (Rosenberg, Walker et al.) have not had the same success.
However, over time, so long as treatment is maintained, the resting pool of infected cells might be able to be agitated to become active, most likely by using multiple approaches. This could reduce the time needed to eliminate this reservoir from decades down to years – with residual virus mopped up by antiretrovirals, allowing treatment to be stopped.
Importantly, research into activation of latently infected cells is already investigating a broad group of drugs that are already licensed. Studying HIV transcription at the molecular level is driving the understanding of differences between latent and productively infected CD4 cells including HDAC-1 and methylation sites in latent infection with the hope that these targets might switch cells away from latency.
A comprehensive review of potential molecules by Sharon Lewin and Christine Rouzioux in the 24 April edition of AIDS  was the basis of one of the presentations at the IAS cure workshop. 
These include histone deacetylase (HDAC) inhibitors (vorinostat, romidepsin, panabinostat, entinostat, belinostat, givinostat and at least nine others), a methylation inhibitor (5-azacytidine), cytokines (IL-7 – Eramune group, IL-15) and an antialcoholic (disulfiram). Immune modulators with similar potential incude antibotics (minocycline), antirheumatics (auranofin), anti-PD-1 (MDX-1106) and protein kinase C modulators (bryostatins and others). Many of these compounds are already being studied in HIV-positive people.
An oral presentation by Claire Vandergeeten from the Vaccine and Gene Therapy Institute reported results from in vitro studies that suggest that IL-15 therapy may be used as a strategy to deplete the latent HIV reservoir while IL-7 maintains the reservoir both in vitro and in patients on stable HAART. 
This research is important and exciting. Many of these compounds have been studied for several years and for other studies are ongoing. A combination therapy approach is therefore likely to have a greater chance of success, for example, valproic acid or vorinostat plus prostratin. 
However, other researchers believe that an as yet unidentified sanctuary site would prevent the latent reservoir from being a slowly diminishing pool that theoretically might wear itself out, with or without stimulation to do so. This includes Steven Deeks at UCSF who co-chairs the IAS working group on cure research and was heads a recent $4 million grant from the US NIH to develop a strategy to eradicate HIV. 
This raises the importance of finding out whether any compartments are actively replenishing the viral reservoir, currently untouched by the maximal suppression measured by plasma viral load.
If this is the case, then any strategy to activate latently infected cells would not be successful. In November 2010, Yuki and colleagues reported that ongoing replication (measured by unspliced HIV RNA in CD4 T cells) is present in higher levels in gut sites (duodenum, terminal illeum, right colon and rectum) compared to that in PBMCs in patients on HAART with viral load suppressed to <40 copies/mL. 
The same group then showed that intensification with raltegravir in this group of patients produced a reduction in levels of unspliced RNA in the terminal ileum and a trend towards reduced T cell activation in other gut sites. 
For these researchers, looking for the impact of intensification studies in plasma viral load is searching in the wrong place. If tissue compartments are a source of ongoing viral replication, the spillover pool found in plasma may have limited relevance. Other cellular sites distinct from CD4 T cells contributing to the latent cellular reservoir include macrophages, hematopoetic stem cells, naive T cells, astocytes, thymocytes and others.
Also, Maria Buzon and colleagues in Nature Medicine in 2010 reported increases in episomes following raltegravir intensification (shown by an increase in 2LTR in PMBCs) as evidence of de novo infection and reduced levels of activation. The extremely low level or replication is used to account for the non-development of resistance even over years. Also perhaps indicating that the chronic source for new virus drives a limited number of rounds of infection. 
Finally, in one of the few late breaker presentations with slides posted online, Hiroyu Hatano working with Deeks’ group at UCSF reported that viral persistence was consistently associated with markers of immune activation and dysfunction (including PD-1 expressing cells) rather than plasma viral load. These measures were particularly elevated in people on treatment with low CD4 counts despite treatment (less than 350 cells/mm3 compared to higher), suggesting that patients below this cut-off present a more difficult and sobering challenge to any approach to a cure.
More optimistically, Hatano noted that the preferential expression of PD-1 by latently infected cells supports targeting this molecule as a strategy for depleting HIV reservoirs. The AIDS Clinical Trials Group (ACTG) in the US is planning an exploratory trial of Merck’s experimental PD-1 inhibitor for this purpose. 
Unless stated otherwise, all references are to the abstracts and conference programme of the 6th IAS Conference on HIV Pathogenesis, Treatment and Prevention, 1720 July 2011, Rome.
- The Rome Statement for an HIV Cure: Major HIV/AIDS Stakeholders Call for HIV Cure Research to be Accelerated. International AIDS Society, July 2011.
- Barré-Sinoussi F. Discussing past and future accomplishments of HIV research. Abstract MOSS0103.
- Towards an HIV Cure: Insight into Residual Viral Replication, Establishment of Reservoirs and Understanding Mechanisms of Persistence. Conference workshop WEWS03.
- Chomont N. New concept in HIV: HIV immunopathogenesis, treatment and vaccine strategies – report back from pre-conference. Symposium WESY01.
- Controversies in HIV Cure Research. Joint IAS and amfAR workshop MOSA02.
- McMahon D et al. Short-course raltegravir intensification does not reduce persistent low-level viremia in patients with HIV-1 suppression during receipt of combination antiretroviral therapy. Clin Infect Dis. 2010 March 15; 50(6): 912-919.
- Kovacs C et al. Effect of intensification of long-term highly active antiretroviral therapy (HAART) with raltegravir on proviral HIV-1 DNA in gut associated lymphoid tissue (GALT): a randomized, placebo controlled trial. 6th IAS, Rome 2001. Oral abstract MOAA0103.
- Chun T-W et al. Rebound of plasma viremia following cessation of antiretroviral therapy despite profoundly low levels of HIV reservoir: implications for eradication. AIDS: 27 November 2010 – Volume 24 – Issue 18 – p 2803-2808.
- Saez-Cirion A et al. Long-term HIV-1 control after interruption of a treatment initiated at the time of primary infection is associated to low cell-associated HIV DNA levels: ANRS VISCONTI study. 18th CROI 2011, Abstract 515.
- Lewin SR, Rouzioux C. HIV cure and eradication: how will we get from the laboratory to effective clinical trials. AIDS: 24 April 2011 – Volume 25 – Issue 7 – p 885-897.
- Lewin S. Contribution of the immune system to HIV persistence. Workshop: Towards an HIV Cure: insight into residual viral replication, establishment of reservoirs and understanding mechanisms of persistence, July 2011, Rome.
- Vandergeeten C et al. Differential impact of IL-7 and IL-15 on HIV reservoir persistence. 6th IAS, Rome 2011. Oral abstract MOAA0101.
- Reuse S et al, Synergistic activation of HIV-1 expression by deacetylase inhibitors and prostratin: implications for treatment of latent infection. PLoS ONE 4(6): e6093.
- NIH supports new research strategy for finding a cure for HIV. (July 2011).
- Yukl SA et al. Differences in HIV burden and immune activation within the gut of HIV-positive patients receiving suppressive antiretroviral therapy. Journal of Infectious Diseases. Published online 12 October. 2010;202:000-000. DOI: 10.1086/656722.
- Yukl SA et al. Effect of raltegravir-containing intensification on HIV burden and T-cell activation in multiple gut sites of HIV-positive adults on suppressive antiretroviral therapy. AIDS. 2010 Oct 23;24(16):2451-60.