Cure research at IAS 2014: TILDA measures the reservoir and romidepsin wakes it up
Simon Collins, HIV i-Base
Cure-related research was one of the leading medical and scientific issues at AIDS 2014, adding new pieces to a puzzle that leading researchers believe is likely to take at least a decade to solve.
Other researchers are more cautious about the timeline for a cure, given the overly optimistic predictions for a vaccine. Françoise Barré-Sinoussi, co-chair for the conference and Nobel laureate for discovering HIV, chose her reply carefully when asked when we could expect this: “We cannot answer this and we shouldn’t give dates, unlike vaccine predictions in the past – first two years, then every ten years – and we still don’t have one after 32 years. There is plenty of evidence saying we can make progress, but we can’t say when.”  This caution is important given that many of the 200 leading researchers attending a two-day cure workshop prior to the main conference, believe that an HIV vaccine itself may be an essential component of an eventual cure. 
Professor Steven Deeks, co-chair of the International AIDS Society group co-ordinating global responses to the search for a cure, emphasised the new scientific focus. “It is clear that international community is engaged – researchers, funders and community – but (with a few notable exceptions) – industry is still missing. And we need them to develop new drugs”. 
For those who have access, HIV treatment is remarkably effective – normalising life expectancy and linked to few side effects – especially if someone is diagnosed early after infection. Successful treatment sets a high safety bar for a cure. Within a few months of treatment, levels of HIV in blood become undetectable using routine monitoring tests. Residual HIV largely survives in a small reservoir of immune cells that contain HIV but that then enter a dormant or resting as a natural part of their cellular lifecycle, which leaves them out of reach of current HIV meds that only target active immune cells.
Key scientific issues for Deeks include finding out exactly where in the body the reservoir cells reside, noting that a “a single cell in a single reservoir” missed by treatment could have caused the recent report of viral load rebound in the Mississippi baby, who started HIV treatment within 30 hours of birth, and who was hoped to be cured after having remained off-treatment for 27 months.  “We need to measure size of reservoir for people on treatment who have very low levels of HIV viral load. We need to develop bigger and better studies to advance the agenda.”
Deborah Persaud from Johns Hopkins University reported that after restarting treatment in this child, CD4% increased from 28% back to 42% and the child is responding well. Although the viral rebound results are disappointing, especially for the child who is now back on treatment, this remains the only case of such a long period off treatment in a child without detectable viral load. The rebound confirms that that she was initially infected – some questioned this – and that the effects were due to treatment rather than PEP, providing a rationale for early therapy in trials.
In an overview lecture on cure and vaccine research, Dr Anthony Fauci, head of the US National Institute of Allergy and Infectious Diseases (NIAID) since 1984, highlighted the Mississippi baby as an optimistic case of prolonged virological remission that was just not sustained. “Given the lack of antibody response, we need to know what maintained that suppression for so long and what triggered the rebound?” For a future cure to be effective in a global context, he noted that it “needs to be simple, safe and generally applicable”. 
Fauci remains optimistic for a vaccine, following recent discovery of broadly neutralising antibodies and new research into B-cell lineage vaccine design. However, the classic approach to making a vaccine is to mimic human immune responses. With HIV, although the body generates neutralising antibodies, this is commonly only after six months and not sufficient to control infection: too little, too late. Also, broadly neutralising antibodies only develop in 20% of people after about two years and they are not able to protect against HIV reinfection.
Another part of the cure puzzle was reported in a research letter published on 21 July in the journal Nature, which looked at early SIV infection in macaques. This letter suggests that the reservoir seems to be established before HIV is detectable in blood, probably in the lymph nodes where the virus initially establishes infection, and that treatment within three days is not early enough to produce a cure. [6, 7]
The authors tracked viral responses to treatment in 20 monkeys in which combination treatment (with dolutegravir, tenofovir and emtricitabine) was started at 3, 7, 10 and 14 days after infection (four in each group, plus four control animals who received no treatment). HIV viral load was only prevented from becoming detectable in blood in the group treated after three days, but when drugs were stopped six months later, viral load promptly rebounded. Although ART has dramatic benefits, in this group it did not lead to HIV eradication, emphasising the importance of other strategies.
Ole Søgaard from Aarhus University Hospital, Denmark presented the most promising cure research at the conference as a late-breaker oral abstract on Tuesday afternoon. The study investigators used a cancer drug called romidepsin to awaken latent HIV – a first step toward targeting latently infected cells for elimination. 
Romidepsin is an HDAC inhibitor that in test tube studies has previously been shown to activate latent HIV. Treatment with romidepsin for 14 days in a group of five men and one woman who had previously been on ART for an average of nine years (who could therefore be expected to have a small reservoir) resulted in significant release of viral particles that were easily detectable with viral load tests. But, no reduction was seen in the reservoir of latently infected cells. These results are seen as a promising step to show that latent HIV can be activated but just not sufficiently to cause the death of latently infected cells and reduce the reservoir. Other more potent interventions might be more successful, but this study is an important proof of principal that sleeping cells can be targeted by treatment. Commenting on these results Deeks noted: “this is the first data to show we can find hidden virus and shock it out of hiding. With research driving viral load even lower so that only a tiny immune response could work”.
The IAS had previously identified developing assays to measure the size of the reservoir as a key scientific priority. So, another highlight was a presentation at the Towards a Cure symposium by Nicholas Chomont from the Vaccine & Gene Therapy Institute of Florida on a new nested PCR-based test called TILDA (Tat/Rev Induced Limiting Dilution Assay). This new test is able to measure the size of the reservoir of latently infected CD4 T cells. More importantly, this is rapid (taking less than two days), sensitive (to 1.4 cells/million), affordable (around $300), and only requires a 10 mL sample of whole blood. Previously, reservoir measurements have been limited to expensive and complex specialised labs. These results also highlighted that the reservoir may be larger than previously assumed (median 24 cells/million), with 90% of cells with inducible virus being latently infected in people on ART (compared to 75% of cells in people who are treatment-naive). TILDA is also able to differentiate between people who started ART during primary compared to chronic infection. 
Although designed as an approach to reduce the latent reservoir, the 14-day study using the HDAC inhibitor vorinostat in 20 people on stable ART reported potentially negative immunological changes including an increase in T-regs. TILDA showed no change in inducible virus from the latent reservoir following vorinostat. 
Other cases tentatively suggest that early treatment might generate an immune response in a minority of people who are able to start within the first months of infection that could possibly enable significant periods without treatment. Both Barré-Sinoussi and Fauci referenced the 14 people followed in the Visconti cohort.  Following treatment for 2-3 years, some of these people have since remained off treatment for over ten years, although different results have been reported in a similar US cohort.
Several attempts to replicate the functional cure reported for the Berlin patient following stem cell transplant form a donor with CCR5 delta-32 deletion have so far been unsuccessful. Two cases of allogenic transplantation that were initially reported as successful, notably reported viral rebound. [12, 13]
At AIDS 2014, two further cases were reported in Australian patients after HLA matched allogeneic bone marrow transplantation with reduced intensity conditioning. One patient was treated in 2010 for non-Hodgkin lymphoma and the other in 2011 for acute myeloid leukaemia respectively. Only one patient received a transplant from a CCR5 delta32 heterozygote (so lower CCR5 levels but not CCR5-negative) and the other received a transplant from a donor without the mutation. HIV RNA and DNA are no longer detectable in peripheral blood and CD4 T cell responses to HIV-1 antigen are dramatically reduced in both cases. Crucially, while HIV remains undetectable, both people remain on treatment, so reports that these people are cured are not only premature but also incorrect. 
A case study reported undetectable viral load and reduced CD4 HIV responses from a patient in Argentina who has been off treatment for more than seven years, though no intervention was involved. 
An oral presentation for another interesting case of possible HIV clearance from an HIV positive long-term non-progressor, who was infected 33 years ago through transfusion and has been off treatment with no detectable viral load, perhaps due to infection with a poorly replication competent virus. 
The final test of any cure research involves asking people to stop treatment in order to see what happens. But, treatment interruptions continue to be controversial and a community discussion paper was published during the conference that outlines safer research approaches. This document is currently posted online for another month for comments. 
Thanks to Richard Jefferys for editorial comment.
Unless stated otherwise, references are to the 20th International AIDS Conference, 20-25 July 2014, Melbourne.
- Barré-Sinoussi F. 20th IAS conference, 20-25 July 2014. Press conference, 21 July 2014.
Youtube video of press conference.
- IAS Towards a Cure Symposium. 19-20 July 2014.
- Deeks S. 20th IAS conference, 20-25 July 2014. Press conference, 21 July 2014.
Youtube video of press conference.
- NIH press statement. “Mississippi baby” now has detectable HIV, researchers find (10 July 2014).
- Fauci AS. Critical challenges in HIV discovery: cure and vaccine. 20th IAS conference, 20-25 July 2014. Special session: The future of science in the HIV response. 2MOSS01.
- Whitney JB et al. Rapid seeding of the viral reservoir prior to SIV viraemia in rhesus monkeys. Letter: Nature, 20 July 2014. DOI: 10.1038/nature13594.
- Deng K and Siliciano RF. HIV: Early treatment may not be early enough. Commentary: Nature (20 July 2014). DOI:10.1038/nature13647.
- Søgaard OS et al. The HDAC inhibitor romidepsin is safe and effectively reverses HIV-1 latency in vivo as measured by standard clinical assays. Late breaker oral abstract TUAA0106LB.
- Chomont N et al. A novel assay that precisely measures the size of the latent HIV reservoir reveals that ART-naive individuals harbour a large pool of latently infected CD4+ T cells. IAS Towards a Cure Symposium. 19-20 July 2014.
- Wightman F et al. Multidose vorinostat in HIV-infected individuals on effective ART leads to an increase in regulatory T cells but no change in inducible virus or HIV-specific T cells. Late breaker poster abstract LBPE07.
- Sáez-Cirión A et al. Post-treatment HIV-1 controllers with a long-term virological remission after the interruption of early initiated antiretroviral therapy ANRS VISCONTI Study. PLoS Pathogens, 14 March 2013. DOI: 10.1371/journal.ppat.1003211.
- Jefferys R. HIV rebounds in Boston stem cell transplant recipients. TAG basic science Blog. (06 December 2013).
- Henrich TJ. HIV-1 rebound following allogenic stem cell transplantation and treatment interruption. 21st CROI. 3-6 March 2014, Boston. Oral late breaker 144LB.
- Koelsch KK et al.Allogeneic bone marrow transplantation in two HIV-1 infected patients shows no detectable HIV-1 RNA or DNA, and a profound reduction in HIV-1 antibodies. 20th IAS conference, 20-25 July 2014. Late breaker poster abstract LBPE21.
- Urueña A et al. Functional cure and seroreversion after advanced HIV disease following 7-years of antiretroviral treatment interruption. 20th IAS conference, 20-25 July 2014. Poster abstract MOPE016.
- Zaunders J et al. Possible clearance of transfusion-acquired nef-deleted attenuated HIV-1 infection by a long-term non-progressor with CCR5 Delta32 heterozygous and HLA-B57/DR13 genotype. 20th IAS conference, 20-25 July 2014.Oral abstract TUAA0105.
- Collins S, Evans D, Jefferys R. Community recommendations for clinical research involving antiretroviral treatment interruptions. Published online for comment. (22 July 2014).