September 20, 2018
In the aftermath of the 22nd International AIDS Conference (AIDS 2018), which took place in Amsterdam in July, there has been some reflecting on the challenges facing the HIV cure research field. The presentations that garnered the most news coverage described disappointing study results, but there were also nuggets of novelty and encouragement to be found amidst the sea of data on offer (see previous post for links to relevant conference sessions, many of which now have video and/or slides available).
The most widely reported findings came from a clinical trial in the UK known as RIVER (Research In Viral Eradication of HIV Reservoirs). Participants with primary HIV infection were randomized to receive a standard antiretroviral therapy (ART) combination plus the integrase inhibitor raltegravir or ART plus raltegravir along with a therapeutic HIV vaccine regimen and a short course of the HDAC inhibitor vorinostat (a candidate HIV latency-reversing agent). The primary purpose was to evaluate whether the vorinostat and vaccine combination -- a version of the proposed "kick & kill" approach to depleting the HIV reservoir -- had a significant effect on HIV reservoir measures compared to ART.
As described in detail in multiple online reports (e.g. see i-Base, AIDSMap, and the Imperial College website), the size of the HIV reservoir -- as assessed by both total HIV DNA and the viral outgrowth assay -- remained equivalent between the two arms. Presenter Sarah Fidler pointed out some possible caveats, such as the relatively short follow up time, but the data appear to rule out any significant effect by this particular kick & kill combination.
The researchers cited several potential explanations: the latency-reversing activity of vorinostat may be suboptimal, and there is uncertainty as to whether the HIV-specific T cell responses that were successfully induced by the vaccines were targeting parts of the virus most likely to be displayed by infected cells after latency reversal. As is emphasized in much of the coverage, the study itself should not be considered a failure because it provided a clear answer to the question it was designed to address. The interventions were also found to be safe and no participants withdrew.
The results echo a theme that has been sounding recently in HIV cure research: randomized controlled trials are required to rigorously evaluate the potential of candidate interventions, and positive results from single-arm exploratory trials (which tend to compare results to baseline values or historical controls) need to be interpreted with caution.
Studies published over the past year that have reached a similar conclusion include randomized controlled evaluations of a therapeutic vaccine combination and single doses of the candidate latency-reversing agent romidepsin.
The second piece of unwelcome news related to vedolizumab, an antibody that targets the α₄β₇ integrin, a protein involved in CD4 T cell trafficking to the gut that may also facilitate HIV entry into target cells. In 2016, an experiment in SIV-infected macaques generated excitement when administration of vedolizumab was associated with control of viral load after ART interruption. Human trials were initiated relatively quickly because vedolizumab is already FDA approved as treatment for ulcerative colitis and Crohn's disease.
During a talk at the conference on HIV remission, Anthony Fauci from the National Institute of Allergy and Infectious Diseases (NIAID) provided a glimpse at the data from the first of these trials, and sadly the results did not mirror the published macaque study. While it appeared that one or two participants displayed some evidence of viral load containment after an analytical treatment interruption (ATI), the majority did not.
Fauci suggested the variations in viral load levels were similar to those his group has observed in placebo recipients in prior trials, and were not indicative of any effect from vedolizumab. At least two other clinical trials involving the antibody are ongoing, so additional results will be forthcoming.
In a separate presentation, Michele DiMascio put another dent in the optimism that had surrounded vedolizumab by reporting that an attempt to repeat the original results obtained in SIV-infected macaques had failed. This time, there was no evidence of vedolizumab-induced SIV control. The reasons for the divergent outcomes are unclear, but may relate to the type of SIV used in the experiments, which has a mutation in the nef gene.
A number of presentations described novel approaches for targeting the HIV reservoir, highlighting the amount of work that is underway to try and improve upon the interventions tested to date.
Isa Munoz-Arias and colleagues from UCSF and Merck reported that a number of FDA-approved chemotherapeutic drugs have HIV latency-reversing activity in laboratory studies. In some cases the magnitude of the effect was demonstrated to be greater than the combination of bryostatin and romidepsin, which has previously been shown to be among the most potent latency-reversing strategies in vitro. The effects were not associated with significant T cell activation or CD4 T cell death (although it's important to note that this does not mean the drugs are without side effects -- those are described on their labels).
A total of 12 FDA-approved chemotherapies were found to reverse HIV latency via a variety of novel pathways, suggesting new avenues for exploration beyond the current candidates, which primarily comprise HDAC inhibitors. The details of the presentation can be found on Jules Levin's NATAP website (which often does more to make information public than conferences themselves), and it was also covered by Simon Collins for i-Base.
The research group of Wen Kang debuted data from a small, uncontrolled pilot study of the HDAC inhibitor chidamide, which is approved in China as a cancer therapy. Kang described evidence that the drug had stimulated production of HIV RNA in seven individuals on ART, and may have slightly reduced HIV DNA levels. However in the Q&A after the talk Sharon Lewin noted that the various possible markers of activity that were analyzed did not appear to necessarily correlate with each other. A larger randomized controlled trial that should provide more definitive results is now ongoing.
Tim Henrich from UCSF followed up on work published earlier this year in PLoS Pathogens identifying CD30 -- a cell surface molecule known for its association with lymphoma -- as preferentially expressed on HIV-infected CD4 T cells.
In the paper, the researchers describe an individual with HIV who exhibited undetectable viral RNA and DNA levels after receiving therapy for lymphoma including brentuximab vedotin, an anti-CD30 antibody-drug conjugate. Unfortunately the individual died after cancer recurrence so no further investigation was possible.
Henrich's conference abstract reports the identification of a second person with HIV who received brentuximab vedotin as part of treatment for lymphoma (now in remission). Three weeks after administration of the first dose, HIV RNA was reduced to undetectable from a previous level of 7,359 copies per million CD4 T cells (a greater than 3 log reduction). HIV DNA levels fell by 42%. The individual is now being followed longitudinally.
This research opens up the possibility of targeting CD30 as a means to deplete the HIV reservoir, and in addition to brentuximab vedotin there are also CD30-specific chimeric antigen receptor (CAR) T cells in development that are already being studied in clinical trials for cancer.
An interesting presentation by Sarah Joseph from the University of North Carolina at Chapel Hill outlined an effort to establish when viruses enter the latent reservoir. Using complex phylogenetic analyses (see the abstract for an example), Joseph uncovered evidence that in most individuals studied, the majority (~72%) of the replication-competent latent HIV reservoir was most closely related to viruses circulating in the year prior to ART initiation. In contrast, only 5% was derived from virus replicating during the first year of infection.
A paper published in the journal eLife in 2016, involving ten participants, reported similar results, although Joseph also pointed out that a much smaller study presented at the conference by Zabrina Brumme (subsequently published in PNAS) reached different conclusions, finding more diverse dates of establishment of the reservoir.
Joseph's data suggests that latently infected cells tend to be shorter-lived during untreated infection, with ART initiation triggering the formation of the bulk of the long-lived HIV reservoir. The implication for therapeutic strategies targeting the reservoir is that there might be a window of opportunity to intervene at the time ART is started (currently, almost all clinical trials involve testing candidate therapies in individuals after ART has suppressed viral load). This idea could potentially be explored in the SIV/macaque model.
Participants in the VISCONTI cohort represent the best known and most widely cited examples of post-treatment control of HIV replication. In 2013, when Asier Sáez-Cirión and colleagues published a detailed report in PLoS Pathogens, the cohort comprised 14 individuals. Updates have been fragmented since that time, occurring at various conferences, and as yet there have been no follow up publications as thorough as the original paper (at least that I'm aware of -- for the sake of disclosure I should note that I chided the investigators about this situation in a public comment to the PLoS Pathogens article in 2017).
At AIDS 2018, Laurent Hocqueloux and colleagues presented a poster on factors associated with loss of post-treatment controller status that included an update on the VISCONTI cohort. The study also offered results from analyses of inflammatory biomarkers, which I've not seen described previously.
A total of 24 post-treatment controllers have now been added to the VISCONTI cohort; all started ART during primary infection and then interrupted after a median of 3.5 years of treatment. During subsequent follow up (current median of 12 years), five (21%) have restarted ART, four due to increasing viral load and one as a result of a head and neck cancer diagnosis.
These five participants were among seven who experienced one or more viral load measurements above 400 copies/ml during monitoring; none of the 17 who remained below this viral load level restarted ART (a highly statistically significant difference). The fact that the individual who developed cancer was in the former group, despite not reinitiating ART based on viral load criteria, may raise concern that prior exposure to detectable HIV viremia was a risk factor for cancer development. Whether remaining on ART would have been associated with lower risk is an unanswerable question. This conundrum illustrates that firm conclusions about the clinical benefits of post-treatment control compared to continuous ART cannot be drawn until post-treatment control can be induced in sufficient numbers of people to allow a randomized comparison.
Overall, CD4 counts and CD4:CD8 ratios have remained stable in the cohort with medians not significantly different between the time of ART interruption and last follow up. Individual plots are not shown in the poster, however, so it's unclear if declines occurred in participants who experienced viral load increases.
Encouragingly, the majority of VISCONTI cohort members have maintained viral loads below 50 copies/ml, and levels of three inflammatory biomarkers -- IP-10, sCD163 and sCD14 -- were not significantly different between these post-treatment controllers and healthy HIV-negative individuals (see figure 6 in the poster).
In a separate oral presentation, Asier Sáez-Cirión showed evidence that certain immune response genes are associated with post-treatment control in the VISCONTI cohort, and may be mediating their effects -- at least partly -- through superior natural killer (NK) cell activity against HIV (unfortunately neither slides or video of this presentation are available on the conference website).
Lisa Chakrabarti described an investigation of potential mechanisms of HIV control in a different population: elite controllers participating in the ANRS CODEX cohort. The researchers focused on HIV Gag-specific CD4 T cell responses, and found that CCR5 expression was lower among elite controllers compared to a control group of people with HIV on ART.
The lower CCR5 expression by Gag-specific CD4 T cells was associated with reduced susceptibility to HIV infection, suggesting this may contribute to elite controller status. The results may offer support to efforts to protect virus-specific CD4 T cells from HIV infection using gene therapies that ablate CCR5 expression (or otherwise attempt to protect the cells from HIV entry), an approach being pursued by researchers at the defeatHIV collaboratory.
A controversial component of research working toward achieving post-treatment control of HIV is the use of ATIs. A systematic review of past studies involving ART interruptions could help shed light on the safest approaches to conducting ATIs in clinical trials, and Jillian Lau and colleagues from Alfred Hospital and Monash University in Melbourne, Australia delivered just such a review as a poster presentation at the conference. Their work is now in press at a journal and will hopefully be published soon.
As is always the case, an array of excellent reporting has become available online since the conference. See below for a selection.
AIDS 2018 HIV Cure Research Highlights -- Karine Dubé and Jeff Berry, Positively Aware
The Road Ahead for HIV Cure Research -- Benjamin Ryan, POZ Magazine, September 6, 2018
Cure Updates from AIDS 2018 -- hivcure.com.au/Doherty Institute
[Note from TheBodyPRO: This article was originally published by Treatment Action Group on Sept. 19, 2018. We have cross-posted it with their permission.]
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