TAG HIV Basic Science, Vaccines, and Cure Project Blog

By Richard Jefferys, Project Director at Treatment Action Group (TAG).

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  • Gene Therapy in HIV Cure Research: A Brief Year in Review

    The past year has seen a notable expansion of efforts to apply gene therapy approaches to HIV cure research, and several online events have highlighted progress in the field. In parallel, work is underway that aims to make gene therapies more affordable and accessible globally.

    Two papers published early in the year (one in the Journal of Clinical Investigation, the other a preprint in bioRxiv) reported that a small number of participants in trials of a gene therapy developed by Sangamo Therapeutics showed evidence of partial control of HIV viral load after antiretroviral therapy (ART) interruption. Importantly, the enhanced control of HIV replication was associated with improved HIV-specific immunity. These publications were highlighted by researcher Danny Douek in an excellent plenary presentation on HIV cure research at the virtual IAS 2021 conference in July.

    The Sangamo Therapeutics approach applies gene editing to CD4 T cells to prevent expression of the CCR5 co-receptor used by most HIV strains to enter cells. Large volumes of CD4 T cells are sampled from participants, gene edited in the laboratory, and then reinfused. The reported results suggest that strategies that protect CD4 T cells from HIV infection may also have the capacity to bolster HIV-specific immunity, particularly HIV-specific CD8 T cell responses (at least in some cases).

    This idea is being explored further by the biotech company American Gene Technologies, which is currently conducting a trial that focuses on genetic modification of HIV-specific CD4 T cells (rather than CD4 T cells in bulk). The goal is to protect the CD4 T cells that should be leading the immune response against HIV. The company has reported that initial infusions appear safe and preliminary results are anticipated next year.

    Sangamo Therapeutics aren’t pursuing commercial development of their candidate but are supporting a large trial in people with HIV that is ongoing in Cincinnati. Led by Rafick-Pierre Sekaly and Carl Fichtenbaum, the study will evaluate the factors associated with improved HIV-specific immunity and HIV reservoir reductions in greater detail.

    Another approach to enhancing HIV-specific immunity with gene therapy is to equip cells with receptors that are adept at recognizing the virus and triggering the killing of infected cells. T cells are sampled from the intended recipient, gene modified in the laboratory to give them what is known as a “chimeric antigen receptor” (CAR), and then reinfused. Several CAR T cell gene therapies are licensed for the treatment of cancers (in that setting, the CAR is designed to target the cancer).

    In August, a preliminary study from Bingfeng Liu and colleagues in China was published in the Journal of Clinical Investigation reporting that delivery of CAR T cells targeting HIV was associated with modest reductions in the viral reservoir. The intervention was not able to promote control of viral load after an analytical treatment interruption (ATI), but rebounding viruses showed evidence of mutations suggesting that the CAR T cells were exerting anti-HIV activity. The researchers are continuing to work on improving the potency of the CAR T cells and note in their paper the possibility of combining with gene therapies that protect CD4 T cells from HIV infection.

    Steve Deeks and colleagues at UCSF are working with the company Lentigen to study a duoCAR T cell gene therapy in people with HIV. The technology has shown promise in preclinical humanized mouse studies. A phase I/IIa clinical trial, which includes an ATI, is now recruiting.

    Scientists involved in founding Lentigen are also key players in a global initiative to bring gene therapies to resource-limited settings, starting with India and Uganda. The initiative is coordinated by a non-profit company, Caring Cross, and involves many partners. The ultimate goal is to make gene therapies accessible and affordable globally. Dr. Boro Dropulić of Caring Cross provided an overview of the effort at the virtual Pre-CROI Community HIV Cure Research Workshop in March of this year.  

    Gene therapies may also have the potential to target HIV directly, with several groups of researchers developing technologies that aim to remove the virus from persistently infected cells or disable it in ways that prevent viral load rebound when ART is interrupted.

    The most well publicized gene editing technology is CRISPR/Cas9. The laboratory of Kamel Khalili at Temple University in Philadelphia has published a series of preclinical studies indicating that CRISPR/Cas9 can excise (or otherwise disable) HIV from the latently infected cells that make up the persistent viral reservoir. The group has published evidence of variable reservoir reductions in a small number of macaques infected with SIV, the simian counterpart of HIV (TAG covered this study when it was presented at CROI in 2019).

    Excision Biotherapeutics, a company founded by Khalili to commercially develop the technology, recently announced a major milestone: The US Food and Drug Administration has authorized the first clinical trial in people with HIV. The CRISPR/Cas9 construct (named EBT-101) will be delivered using an adeno-associated virus (AAV) vector, which is a commonly used platform for gene therapies.

    Media coverage of the preclinical research results has been guilty of overhyping near term prospects (see entries to TAG’s Cure Research Media Monitor). Eradication of HIV is not considered likely due to the difficulty of reaching all the intact viruses in the body, but the hope is to reduce the amount of HIV to a level the immune system might be able to contain in the absence of ongoing ART.

    Safety will be carefully monitored as there are concerns about the potential for off-target edits to human genes. No such problems have been documented in extensive preclinical studies, but there are technological limitations to how extensively off-target edits can be analyzed. It will also be important to assess whether the Cas9 protein (which is derived from bacteria) is targeted by the human immune response. Encouragingly, a preliminary report on the use of CRISPR/Cas9 to treat a small number of people with transthyretin amyloidosis was published in August, describing evidence of safety and activity.

    On a webinar hosted by the European AIDS Treatment Group on October 26, Joachim Hauber presented plans for a clinical trial involving a different gene editing approach that directly targets HIV. The editing is accomplished by an enzyme from bacteria dubbed Broad Range Recombinase 1 (Brec1).

    The researchers intend to sample hematopoietic stem cells from people with HIV requiring stem cell infusions to treat diffuse large B cell lymphoma, then introduce Brec1 into the cells via a lentiviral vector. The stem cells will be reinfused with the goal of generating a population of cells equipped with Brec1 and able to fend off HIV infection. The estimated start date for the trial is the fourth quarter of 2022.

    Future studies involving direct delivery of Brec1 with AAV vectors are also under consideration. The EATG webinar recording isn’t posted yet, but Joachim Hauber discussed the work in a presentation at the IAS 2021 meeting which is available online.

    The vulnerability of CD4 T cells to HIV has led some scientists to believe that genetic modifications will be essential to cure strategies, so it’s encouraging to see gene therapy research now progressing on multiple fronts.  

    HIV Gene Therapy Meetings and Presentations in 2021

    Pre-CROI Community HIV Cure Research Workshop Session #2, March 5, 2021

    Overview of gene therapy in HIV cure research
    Christopher Peterson, PhD, Fred Hutch

    Anti-HIV duoCAR-T cells: Preclinical studies leading to a Phase I/IIa clinical trial and a model for affordable access of gene-modified cell therapy products
    Kim Antony-Gonda, PhD, MB ASCP
    Boro Dropulić, PhD, MBA

    Bringing safe, effective, and accessible curative interventions for HIV to all
    Joseph (Mike) McCune, MD, PhD, Head, HIV Frontiers, Global Health Innovative Technology Solutions

    IAS 2021 HIV Cure & Gene Therapy Forum, July 19-21, 2021

  • Imbokodo Trial Results Highlight Challenge of Developing an HIV Vaccine and Urgent Need for Access to Proven Prevention Tools

    At the end of August, disappointing results were released from Imbokodo, a phase IIb clinical trial evaluating the efficacy of an HIV vaccine candidate developed by the Janssen Pharmaceutical Companies of Johnson & Johnson. Among cisgender women recruited in five African countries, the vaccine regimen didn’t offer significant protection against acquisition of HIV infection. The outcome underscores the difficulty of inducing protective immunity against HIV compared to other pathogens, and highlights the importance of making effective biomedical prevention options—oral or injectable pre-exposure prophylaxis (PrEP) and the dapavirine ring—accessible to those in need, including women in the communities where Imbokodo took place. 

    The Imbokodo Trial

    The trial enrolled 2,637 cisgender women aged 18-35 years old in Malawi, Mozambique, South Africa, Zambia, and Zimbabwe. The vaccine comprised priming immunizations with adenovirus serotype 26 (Ad26) vectors encoding four different HIV “mosaic” antigens that include elements from multiple virus clades, followed by boosts combining the Ad26 vector with an HIV gp140 envelope protein (from a clade C virus) in alum adjuvant.

    HIV clades are groups of similar virus variants that primarily circulate in particular geographic regions across the globe (e.g. clade B is predominant in the Americas while clades A, C and D are most common on the African continent). A key idea behind the vaccine was to induce immune responses capable of targeting HIV from many clades.

    Behavioral risk factors for HIV acquisition were evenly distributed between the vaccine and placebo groups in the trial. Uptake of oral PrEP, which was made available to all participants, was low—only around 3% of participants displayed detectable tenofovir levels, and the proportion in each arm with levels considered likely to be effective was even lower at 0.2% in the placebo group and 0.4% in the vaccine group (this slight difference was not statistically significant).

    Trial Results

    The results were that 63 of 1,109 participants (5.68%) who received a placebo or dummy immunization acquired HIV over a two-year period, compared with 51 of 1,079 participants (4.73%) given the vaccine. There were 25% fewer HIV infections in the vaccine group compared to placebo, but the difference was not statistically significant—in other words, it may have resulted from chance (update: in a presentation at the AIDS 2022 conference, Avi Kenny revised these numbers to 65 vs 54 HIV acquisition events and disclosed that there was an error in the original analysis and the true efficacy estimate is 14%, with 95% confidence interval of -22% to 40%, rendering the following discussion related to a possible hint of efficacy redundant).

    Statisticians calculate a “confidence interval” (CI) that gives a range of possibilities for where the true result may lie and, in this case, it was anywhere from a 10% increase in the risk of HIV acquisition to a 49% reduction (-10% to 49%). For a result to be considered statistically significant, the lower end of the CI must be above zero.

    Some researchers have speculated that the apparent 25% difference between the vaccine and placebo arms might have reached statistical significance if the trial had been larger, but this is not certain.

    The hint of a slight reduction in HIV incidence among vaccine recipients cannot be considered formal evidence of vaccine-induced protection from infection. But it does allow researchers to explore whether there might be notable differences between vaccine recipients who acquired HIV and those who did not, such as particular types of vaccine-induced immune responses.

    Importantly, the vaccine regimen was found to be safe, with the typical reaction of mild local injection site pain and redness reported as more common among vaccine compared to placebo recipients.

    Implications for the HIV Vaccine Field

    The most immediate question for HIV vaccine research was whether another ongoing efficacy trial of the Johnson & Johnson vaccine should continue. Mosaico is studying a similar regimen in 3,600 cisgender men and transgender people who have sex with cisgender men and/or transgender people. After review by the trial’s Data Safety Monitoring Board (DSMB), it was recommended that Mosaico continue for several reasons: it includes a slightly different protein boost immunization (consisting of a mosaic rather than clade C gp140 protein), the prevalent HIV clade where the trial is taking place is different from Imbokodo (clade B versus clade C), and the route of exposure to HIV is also likely to be different (rectal versus vaginal).

    The potential for Mosaico to produce a better result is unclear. There may be some reason to hope that the larger sample size of the trial could lead to a similar degree of vaccine efficacy achieving statistical significance. But it would be surprising if the Mosaico results showed a level of efficacy sufficient to justify licensure (e.g. >50% reduction in risk of HIV acquisition).

    Perhaps the most optimistic possibility is that Mosaico, combined with prior results from Imbokodo and RV144 (an older vaccine trial in Thailand where a reduction in HIV incidence of around 30% crept above the threshold for statistical significance), could add to a body of evidence that current experimental vaccine approaches can offer a low level of protective efficacy. Work could then continue to try to figure out if there is any way of improving efficacy to reach the threshold considered necessary for licensure, or if it represents the ceiling for what these types of vaccine can achieve.

    The broad common thread between all experimental HIV vaccines tested to date is that, while there are many nuances to each regimen, they induce immune responses against the virus that are known as “non-neutralizing.” In the case of the Johnson & Johnson vaccine, these include T cell and antibody responses intended to mediate clearance of virus-infected cells. Induction of these responses was associated with protection against persistent infection in the SIV/macaque animal model.

    If researchers can’t figure out a way to enhance the efficacy of vaccines that induce non-neutralizing responses, the primary option that remains is solving the extremely difficult challenge of inducing broadly neutralizing antibodies (bNAbs) with HIV vaccines.

    Neutralizing antibodies are considered a critical component of the protective response created by many licensed vaccines (including recently developed COVID-19 vaccines). Stimulating the production of bNAbs against HIV is far more difficult than for most other pathogens, for a variety of reasons, including:

    • The virus’s outer envelope protein is cloaked in glycan (sugar) molecules that are difficult for antibodies to penetrate or attach to.
    • The mutation rate of the envelope protein is extremely high, with very few parts of the protein offering stable, conserved targets for antibodies.

    Despite these challenges, rare bNAbs with strong anti-HIV activity have been identified and characterized using new techniques that allow researchers to fish the B cells that produce them out of blood samples taken from people with HIV. The bNAbs are typically not able to benefit the individuals they were sampled from, likely due to being present at low levels in the face of high amounts of virus. But the bNAbs can be grown to high levels in the lab and are being tested as both preventive and therapeutic interventions, delivered via infusion or subcutaneous injection. They also provide a guide for the type of bNAb response an HIV vaccine would need to induce to be successful.

    In recent years, HIV vaccine constructs that aim to coax B cells down the first steps toward the long-term goal of bNAb production have begun to enter clinical trials. Results presented at the beginning of 2021 indicate that it’s possible to bolster the number of B cells that may represent a starting point for bNAb production (these results, while promising, were unfortunately widely misunderstood in the media).

    Researchers are now employing Moderna’s mRNA technology to test whether delivering specially engineered proteins into the body can enhance the numbers of B cells that may have the potential to produce bNAbs. The launch of these trials has generated considerable news coverage. But even if successful, additional vaccines will need to be designed to take the B cells further toward the goal of bNAb generation. An article in the UK’s Independent does a good job of conveying that this work is at an early stage.

    In addition to bNAbs, some researchers are exploring whether there might be novel types of immune responses—not yet induced by any vaccine candidates—that could offer some protection against HIV. The main hope is a strategy that employs a weakened form of cytomegalovirus (CMV) as a vaccine vector to deliver HIV components into the body. The vaccine has shown promise in the SIV/macaque model, consistently protecting around 50% of immunized animals. Protection is associated with induction of an unusual type of CD8 T cell response. Phase I clinical testing in humans is now underway.

    Implications for Access to Biomedical Prevention

    In the absence of an imminent HIV vaccine, the Imbokodo results underscore the urgent need to make existing biomedical HIV prevention interventions accessible to those who most stand to benefit from them. The cisgender African women who participated in the trial represent a critically important population, as is demonstrated by the high rate of HIV infections that occurred. Many biomedical HIV prevention trials have recruited large cohorts of dedicated volunteers from communities of African women, but the payoff in terms of accessible interventions has so far been minimal.

    This inequity must be addressed by scaling up availability of oral PrEP, and—when approved—the vaginal dapavirine ring and long-acting injectable PrEP. These points are emphasized in AVAC’s statement on the Imbokodo results and in a follow up interview with their regional stakeholder engagement advisor Nandisile Luthuli and executive director Mitchell Warren (conducted by Tim Murphy for the Body.com).

    Additional Resources

    AVAC Webinar: Imbokodo Vaccine Trial Results and Implications for the Field—A Global Discussion, September 9, 2021.

    Cohen J. Failed HIV vaccine trial marks another setback for the field. Science Insider, August 31, 2021.

    Herper M. Johnson & Johnson’s HIV vaccine fails first efficacy trial. STAT News, August 31, 2021.

    HIV Vaccine Trials Network (HVTN). Experimental Phase 2b HIV Vaccine Regimen Provides Insufficient Protection in Preventing HIV. August 31, 2021.

    Johnson & Johnson. Johnson & Johnson and Global Partners Announce Results from Phase 2b Imbokodo HIV Vaccine Clinical Trial in Young Women in Sub-Saharan Africa. August 31, 2021.

  • Explosion of Social Media Misinformation on First Trial of Germline Targeting HIV Vaccine Strategy

    A misunderstanding of the results of a recently presented phase I HIV vaccine study has prompted an outbreak of misinformation on social media. Several erroneous claims are being made, including:

    • That it was an mRNA vaccine – it was a specially engineered protein plus an adjuvant.
    • That it induced antibody responses against HIV in 97% of the trial participants – antibody responses were not measured in the study.
    • That the vaccine will be tested for efficacy – it won't be, it's only a first "priming" vaccine that will need to be followed by booster vaccines that haven't been designed yet.

    The study results were presented by William Schief at the recent R4P virtual conference and the primary sponsors of the work, the Scripps Research Institute and IAVI, both issued a press release back on February 3rd. The results do potentially represent good news, but unfortunately they don't mean that an efficacious HIV vaccine is imminent (as many viral social media posts have suggested).

    In reality, the research represents a highly technical effort to bolster the number of B cells that might eventually – with further encouragement by additional vaccines – have the capacity to produce antibodies capable of effectively inhibiting HIV (broadly neutralizing antibodies or bNAbs for short). Inducing bNAbs is the Holy Grail of HIV vaccine research. The approach under study is referred to as a germline targeting strategy (germline refers to B cell genes that may represent a starting point for bNAb generation). 

    Over the past decade or so, new technologies have allowed scientists to discover that some people with HIV slowly develop bNAbs against the virus. These bNAbs are typically present at too low a level in the body to benefit the individual, but it's possible for researchers to fish out the B cells that produce them. The genetic code within the B cell responsible for producing the bNAb can then be used as a template to manufacture large amounts of the antibody. This has allowed the initiation of clinical trials in which bNAbs are infused or injected subcutaneously both as potential HIV treatments and preventive interventions.

    The approach being taken by Schief and colleagues uses knowledge about how B cells shuffle their genetic code to produce progressively superior antibodies – a process called somatic hypermutation – to figure out how the process of bNAb production might be stimulated with a vaccine.

    The phase I trial that's caused the online hooplah was the first attempt to boost the number of a certain type of B cell in humans that could represent a starting point on the pathway toward bNAb production. Metaphorically, it's like trying to create a pool of B cell trainees that can then be further educated until they hopefully become capable of making bNAbs against HIV. The researchers used a specially designed protein named eOD-GT8 60mer administered with an adjuvant (AS01B) to immunize trial participants.

    The trial was a success in terms of reaching its goal. Almost all (35 of 36 or 97%) of the vaccine recipients displayed the desired type of B cell after immunization, whereas only five had detectable levels of the B cell prior to immunization. In some of the incorrect social media posts, this result has been misrepresented as showing that 97% of recipients showed antibody responses against HIV (antibody responses weren't measured).

    The next steps for this research will involve designing additional vaccines (which Schief refers to as "shepherding" and "polishing" vaccines) that aim to complete the education of the trainee B cells and thus prompt bNAb production. This is likely to be a lengthy process, and success isn't guaranteed.

    The mistaken claims on social media that the vaccine involved mRNA likely arose because the researchers plan to collaborate with Moderna to deliver the protein used in the study (and potentially other proteins) via mRNA in the future. Hopefully the use of mRNA can accelerate the evaluation of candidate proteins that are designed to coax B cells further down the pathway toward making bNAbs.

    Unfortunately it can't be assumed that simply applying mRNA technology to HIV vaccines would lead to similar efficacy to that seen with COVID-19 vaccines. HIV has evolved to be highly resistant to antibody responses, which is not the case for SARS-CoV-2. The reason bNAbs against HIV (and the B cells that make them) are rare is that the antibodies need to have unusual shapes to penetrate the cloak of sugar molecules that shrouds HIV's outer Envelope protein. But the fact that bNAbs can nevertheless arise gives hope that the work of Schief and colleagues will ultimately pay off.

  • New Insights into Elite Control of HIV and a Possible Case of Virus Clearance

    Several media outlets are reporting on a newly published study of elite controllers, a rare subset of people with HIV who suppress viral load to low or undetectable levels without treatment. A major impetus for the interest is a finding that one long-term elite controller, Loreen Willenberg, may have cleared all the intact HIV from her body. The study was published today in the journal Nature (paired with an open access commentary by Nicolas Chomont), and Apoorva Mandavilli covered the research in a story for the New York Times. Jon Cohen has authored an excellent explanatory article for Science. The study results offer potentially important clues about how HIV may be cured in some circumstances, but unfortunately do not directly help design interventions that might produce similar outcomes in the majority of people living with the virus (who are not elite controllers).

    The crux of the new paper is that elite controllers appear to preferentially deplete the HIV-infected cells from their bodies that contain virus capable of replicating, likely due to potent anti-HIV immune responses (particularly HIV-specific CD8 and CD4 T cells). The HIV-infected cells that are left behind preferentially harbor viral DNA in regions of the cell’s genetic code that are inactive, essentially entombing the virus and preventing its reemergence. In some cases, the HIV DNA is not intact, which also prevents further replication. For Loreen Willenberg, analyses of huge numbers of cells from both the blood and gut could not find any intact HIV, leading to the suggestion that all virus capable of replicating (referred to as replication-competent HIV) has been eliminated over time.

    In the New York Times article, scientist Steve Deeks notes that a somewhat similar phenomenon may occur in people with HIV on long term antiretroviral therapy (ART), raising the possibility that over a period of decades cells containing replication-competent virus might be eliminated. Deeks intends to investigate this scenario in people on very long-term ART. However, it’s important to note that the evidence is very thin—the most detailed paper indicating the phenomenon might be occurring involves only three individuals on ART. Furthermore, the Nature paper compares elite controllers with people on ART, finding that the entombment of HIV in cells is far more common in the former group than the latter. Given the significant uncertainty, people on long-term ART shouldn’t attempt to interrupt treatment outside of research studies.

    Another way researchers are attempting to translate the knowledge gleaned from elite controllers is by testing approaches that may be able to enhance immune responses against HIV. Examples include therapeutic vaccines, broadly neutralizing antibodies, toll-like receptor agonists and gene therapies (see TAG’s Research Toward a Cure clinical trials listing and 2020 Pipeline Report). Success to date has been limited, and part of the challenge may be that elite controllers tend to possess particular genetic traits associated with superior HIV-specific immunity.

    While the Nature paper was published today, the content was partially known to people who follow HIV research. Xu Yu described some of the data, including the case of Loreen Willenberg, at the IAS 2019 conference. Loreen was subsequently profiled in an article for Leapsmag by Bob Roehr. In a tour-de-force plenary talk on cure research at CROI 2020 earlier this year, Sharon Lewin highlighted the need to consider how much of the HIV reservoir that persists on ART is replication-competent and able to reemerge if treatment is interrupted. Lewin cited the work of the Nature paper’s lead author Chenyang Jiang, who also presented during the conference.

  • New HIV Remission Case Report at AIDS 2020

    Today, a presentation by Ricardo Diaz at the ongoing virtual International AIDS Conference (AIDS 2020) caused a major splash in the media by reporting that one out of 30 participants in a clinical trial conducted in Brazil has experienced a lack of viral load rebound for a little over a year (64.7 weeks) after interrupting antiretroviral therapy (ART).

    The trial was launched in 2015 and involved a complex design in which 30 participants with HIV were divided into six groups of five people each. One group continued on a standard ART regimen and served as controls, while the other five groups received the following additional interventions:

    • Group 2: Dolutegravir and the CCR5 inhibitor maraviroc (which has been reported to also exert HIV latency-reversing effects)
    • Group 3: Dolutegravir, maraviroc and nicotinamide (a water-soluble form of vitamin B3 that may have HIV latency-reversing activity)
    • Group 4: Dolutegravir, maraviroc and auranofin (an antiproliferative drug)
    • Group 5: Dolutegravir and a dendritic cell therapeutic vaccine
    • Group 6: Dolutegravir, a dendritic cell therapeutic vaccine, auranofin and nicotinamide

    Results from the trial have been presented on a number of previous occasions, including at AIDS 2018, CROI 2019, and the 2019 HIV Persistence Workshop (see abstract OP 8.6 in the abstract book and the report from NATAP toward the base of this page). Results from participants who received auranofin were also the subject of a published paper last year. Overall, declines in HIV DNA levels (a surrogate measure of the HIV reservoir) were found to be greatest among recipients of the multiple interventions in group six.

    The original study design did not include an analytical treatment interruption (ATI), but the protocol was later revised and 25 of the participants underwent an ATI approximately 2.5 years after the end of the 48-week study period (during which the interventions were administered).

    The presentation at last year's HIV Persistence Workshop reported that two participants in group six and one in group three displayed undetectable HIV viral loads after the ATI. However, after around 16 weeks the two people from group six showed evidence of viral load rebound and restarted ART.

    The remaining participant from group three was the subject of today's AIDS 2020 presentation. The individual was diagnosed with HIV infection in October 2012 and started ART two months later. According to an article by Jon Cohen in Science, they estimate the date of HIV acquisition to be around June 2012 (the last previous HIV negative test result was in 2010). Viral load at ART initiation was relatively low: 20,221 copies/mL.

    At the time of entry into the trial in September 2015, viral load was undetectable and the CD4 count 720. Two very low level transient viral load blips occurred while receiving the study interventions but otherwise undetectable levels have been maintained while on ART.

    HIV DNA was detectable in rectal tissue and blood samples at the end of the 48-week intervention period. Measurements of blood HIV DNA levels subsequently showed a decline during treatment with regular ART regimens, eventually becoming undetectable immediately prior to the ATI which was initiated in March 2019.

    After the ATI, viral load did not rebound and has remained undetectable ever since (the last available measurement at the time of the presentation was from June 22, 2020). Slides showing CD4 count and CD4:CD8 ratio over time indicated a notable decline shortly after the ATI, which is surprising given the apparent lack of viral load rebound in the blood, but no further longitudinal data on these measures was reported.

    HIV antibody levels evaluated by the Abbott ARCHITECT antigen/antibody combination assay have declined throughout follow up, with the exception of one possible slight increase immediately after the ATI. Results of a rapid HIV antibody test are now negative (in some media reports this has been mistakenly represented as indicating that no HIV antibodies are detectable, which is not accurate). 

    The case appears encouraging for HIV cure research, with the caveat that late rebounds in viral load have occurred in some previous examples of HIV remission. Importantly, it's unclear as yet whether the interventions received during the trial contributed to the outcome; the person may have started ART fairly soon after HIV acquisition and there have been other case reports of early-treated individuals containing viral load for variable periods after ART interruptions.

    Notably, of the other 29 study participants, nine received nicotinamide and 14 received dolutegravir and maraviroc. Although it's unclear whether all of these other participants were among those that underwent ATI, no additional examples of similarly prolonged absence of viral load rebound were observed. This appears to argue against a strong effect of these interventions. Additionally, HIV DNA levels continued to decline long after the cessation of the interventions in the participant who has not rebounded.

    Emphasizing the uncertainty about the role of the study drugs is important given that nicotinamide is available over-the-counter as a supplement. At the current time, there is no evidence to suggest that adding dolutegravir, maraviroc and nicotinamide to ART regimens would lead to similar outcomes in other people with HIV.

    Further analyses will hopefully shed light on how viral load rebound has so far been prevented, and whether the interventions contributed in some way. Information on HIV-specific T cell responses and the individual's HLA type could be particularly helpful. The Associated Press article on the research includes the welcome news that Diaz will receive support to conduct a larger 60-person trial, so more robust results should be forthcoming.

  • A Step Forward for AAV-Mediated Delivery of bNAbs

    Many years ago, Phil Johnson from the Children’s Hospital of Philadelphia began pursuing a novel workaround to overcome the challenge of inducing broadly neutralizing antibodies (bNAbs) against HIV. The idea borrows from gene therapy, using adeno-associated virus (AAV) as a vector to deliver the genetic code for a bNAb into the body. The aim is for the AAV to persist inside cells and act as a factory for churning out the bNAb into systemic circulation. As previously covered on the blog, promising results were obtained in macaques over a decade ago, but the first human trial (conducted in HIV-negative volunteers) did not achieve detectable levels of the bNAb PG9—likely due to the induction of anti-PG9 antibodies. At CROI 2020, Joseph P. Casazza from the Vaccine Research Center (VRC) at the National Institutes of Health presented evidence that the approach may yet have promise.

    Casazza described preliminary results from an ongoing trial of the bNAb VRC07 delivered via an AAV serotype 8 (AAV8) vector. The vector was designed by David Baltimore and Alejandro Balazs, and is different to the AAV serotype 1 vector used in the previous human trial. The study is recruiting people with HIV on ART with undetectable viral loads, and Casazza presented data from eight participants (six men and two women, with five African American and three Caucasian).

    Three escalating doses are being evaluated, and Casazza’s presentation included data from three recipients of the lowest dose, two recipients of the intermediate dose and three recipients of the highest dose. Follow up ranged from five months to a little over two years.

    In contrast to the prior trial with AAV1, the bNAb VRC07 became persistently detectable in a majority of participants (six out of eight). In most cases, a pattern was observed in which an initial peak in levels occurred 2-4 weeks after injection, followed by a decline and then a rebound toward steady state levels after around 14-16 weeks.

    Three participants developed anti-VRC07 antibodies, which has been the Achilles heel of the AAV-based delivery approach. In two of these individuals VRC07 levels became undetectable after the initial peak, and in the third the secondary peak was blunted. Casazza noted that anti-VRC07 antibodies did not appear to be the only factor influencing VRC07 levels, because one participant in the high dose group experienced a significant decline between weeks 22 and 40 which has yet to be explained.

    Adverse events were minimal, with mild pain and tenderness at the injection sites reported in the high dose group and one case of muscle pain in the intermediate dose group—all resolved within seven days.

    Casazza did not discuss the potential reasons for the greater success compared to the results achieved with AAV1-based delivery but, in addition to differences in the technical aspects of vector design, AAV8 is liver tropic and it’s been suggested that this is more likely to lead to immunological tolerance of the delivered bNAb.

    Notably, the maximum VRC07 concentration achieved was a little over one microgram/mL in the high dose group, which is low compared to the levels that are obtained by intravenous infusion of bNAbs. For example, levels of well over 50 micrograms/mL have been reported in studies involving i.v. administration of the bNAb VRC01. In a recent trial that administered a combination of the bNAbs 3BNC117 and 10-1074 and then interrupted antiretroviral therapy (ART), an undetectable viral load was maintained for as long as the concentration of both antibodies was above 10 micrograms/mL.

    Casazza’s results offer some hope that the use of AAV vectors to deliver bNAbs (or other therapeutic proteins) will turn out to be feasible. However, work remains to improve both the consistency and magnitude of bNAb production. In a preclinical macaque study in which an AAV8 vector was used to deliver VRC07, the addition of transient immune suppression with cyclosporine was able to increase average peak bNAb levels to ~40 micrograms/mL (compared to ~5 micrograms/mL without), however it’s unclear if this approach could be practically adapted for human use.

    Casazza and his colleagues at the VRC are not the only research group still pursuing the idea. Michael Farzan from the Scripps Institute gave a talk at CROI describing the latest results obtained with AAV-based delivery of eCD4-Ig, a protein that inhibits HIV replication by binding the virus envelope at sites that attach to CD4 and CCR5 receptors on CD4 T cells.

    In a therapeutic experiment involving six macaques infected with the SIV/HIV hybrid virus SHIV-AD08, eCD4-Ig delivered by AAV (two injections, the first using an AAV8 vector and the second using an AAV1 vector) was able to maintain viral load control to varying degrees after an ART interruption. At the most recent timepoint after 80-90 weeks off ART, five animals have viral loads ≤15 copies/mL and the sixth has a viral load of 25 copies/mL. Concentrations of eCD4-Ig ranged from 4.7 to 10.3 micrograms/mL, and Farzan explained that they hope to further refine delivery to achieve higher levels.

    The laboratory of Ron Desrosiers is also working on AAV delivery, focusing on payloads of combination bNAbs. Farzan cited the best known example of this work: the “Miami monkey,” a recipient of AAV-delivered 3BNC117 and 10-1074 that has exhibited prolonged containment of a SHIV AD8 challenge at such vanishingly low levels that the virus has been extremely challenging to even detect (at one point it was thought virus eradication may have occurred).

    On March 17th, Desrosiers and colleagues provided an update on another individual macaque that was originally part of a prevention study published in 2015. This animal has now maintained high levels (240-350 micrograms/mL) of the anti-SIV antibody 5L7 for over six years. The researchers are now working to create this type of response more reliably and they conclude:

    “If satisfactory delivery methods are found, it becomes possible to envision long-term control of viral replication in the absence of antiretroviral treatment by delivering a combination of antibodies in people, and long-lasting protection when this approach is used in a prophylactic setting.”

    It may still be a big “if,” but the data clearly justify efforts to solve the technological challenge.

  • Halting Start for Kick & Kill, CROI Previews New Approaches on the Horizon

    One of the most widely discussed and publicized ideas for targeting the HIV reservoir is “kick and kill” or “shock and kill.” The aim is to kick dormant, latent HIV into revealing itself so the cells that contain the virus are visible to the immune system; the kill aspect involves trying to enhance the immune response so it’s able to recognize and destroy these HIV-infected cells. The ultimate goal is to deplete the latent HIV reservoir that persists in people on antiretroviral therapy (ART).

    The RIVER trial, launched in the UK in December 2015, represents the first large, randomized controlled evaluation of the approach. Preliminary results were first reported at the AIDS 2018 conference in Amsterdam, and have now been described in detail in a paper in Lancet HIV. While the interventions were unable to reduce the HIV reservoir, the negative outcome still holds important lessons for the cure research field. New candidates for both the kick and the kill are in the research pipeline.

    RIVER recruited a total of 60 participants with primary HIV infection—all men—and randomized them to receive either a standard ART regimen plus the integrase inhibitor raltegravir or standard ART, raltegravir, a prime-boost therapeutic HIV vaccine combination and a short course of the HDAC inhibitor vorinostat (a latency-reversing agent reported to have some activity in prior trials). The vaccines consisted of chimpanzee adenovirus and modified Vaccinia Ankara strain virus vectors carrying HIV antigens designed to induce T cell immune responses focused on parts of the virus that mutate the least (conserved regions).

    The results showed that after 16-18 weeks there were no differences between the two groups in any measures of HIV persistence, including HIV DNA and the quantitative virus outgrowth assay (QVOA). A laboratory test assessing the ability of CD8 T cells to kill HIV-infected cells indicated that therapeutic vaccination helped maintain this capacity: killing activity declined from baseline in the ART only arm of the study but was maintained in the intervention arm. Vorinostat increased histone acetylation after dosing (the mechanism by which it can trigger the activity of latent HIV), however sensitive tests for low-level HIV RNA did not reveal any concomitant increases suggestive of HIV latency reversal.

    In discussing their findings, the authors posit a number of possible reasons why this particularly kick and kill combination did not prove effective. Fewer doses of vorinostat were used than in some prior trials, and the evidence of latency reversal that has been described (increases in HIV RNA associated with dosing) was obtained in people with chronic rather than primary HIV infection. Another possibility is that even if vorinostat did cause some latently infected cells to reveal themselves to the immune system by expressing HIV antigens, the HIV-specific CD8 T cells induced and/or maintained by therapeutic vaccination may not have been capable of recognizing these antigens. Presentation of the antigens to CD8 T cells could also be inhibited by the HIV Nef protein, which is known to have the capacity to interfere in this process.

    The researchers also acknowledge the argument that analytical treatment interruptions (ATIs) may be a better test of the effects of interventions than laboratory measures of the HIV reservoir, but at the time RIVER was designed ATIs were not in favor due to safety concerns, and they still believe that an ATI wouldn’t be justified in this case. They conclude that:

    “RIVER helps to set the standard for how future trials might be done because of the new insights gained with regard to trial design, the inclusion of community representation, the need for better interventions, the necessity for clarity regarding the most relevant measures of the reservoir, and probably the use of an analytical treatment interruption approach.”

    An example of a next generation kick and kill study was presented last week at CROI by Ole Schmeltz Søgaard. Known as ROADMAP, the trial compared romidepsin (an HDAC inhibitor that appears to have greater latency-reversing activity than vorinostat) to romidepsin plus the broadly neutralizing antibody (bNAb) 3BNC117 in people with chronic HIV infection on long-term ART. The bNAb was included in hopes of both promoting killing of HIV-infected cells via antibody-dependent cellular cytotoxicity (ADCC) and enhancing HIV-specific T cell immunity (as recently reported in a study of 3BNC117 combined with another bNAb, 10-1074).

    A total of 20 participants were enrolled (17 men and three women); 11 were randomized to receive 3BNC117 and romidepsin, nine to romidepsin. There were two cycles of romidepsin administration: at weeks 0, 1, 2 and weeks 8, 9, and 10. The 3BNC117 group received a single infusion of the bNAb two days prior to these cycles. After 24 weeks, participants underwent an ATI in order to evaluate time to viral load rebound (defined as two consecutive measures equal to or greater than 200 copies/mL). Two participants opted out of the ATI, while a third was excluded after stopping ART while receiving romidepsin.

    Søgaard reported that, disappointingly, there was no significant difference in time to viral load rebound between the two arms of the study: it took an average of 28 days in the romidepsin group compared to 17.5 days in the 3BNC117 plus romidepsin group. The slight difference in favor of the romidepsin group wasn’t statistically significant and Søgaard noted it was driven by one outlying participant who didn’t experience rebound until 12 weeks into the ATI.

    HIV DNA levels measured at the midpoint between the romidepsin cycles and immediately prior to the ATI showed no significant changes. HIV-specific CD8 T cell responses remained stable over the same period and weren’t enhanced by 3BNC117 administration or negatively affected by romidepsin.

    As was the case in the RIVER trial, Søgaard concluded that this particular combination was ineffective and that superior strategies are needed.

    At CROI, Sharon Lewin—a leading scientist in HIV cure research—delivered an impressive, comprehensive update on the field, providing reasons to hope that better results will be obtainable in the future.

    One key development is that the scientific understanding of HIV latency has improved significantly in recent years. The picture is now far more nuanced compared to when the HIV reservoir was first identified in the late 1990s.

    The first relatively new concept highlighted by Lewin is that not all latent HIV remains stably latent (inactive) in people on effective ART. The HIV DNA that’s integrated into the genomes of infected cells can be transcribed into HIV RNA (which in turn can make HIV proteins), either intermittently or possibly also continuously in some cases.

    A number of factors can affect the transcription of HIV DNA into HIV RNA, including the location of the infected cell. Lymph nodes, the gastrointestinal tract and the female genital tract are sites where HIV RNA is most frequently detected. Time of day also has an influence because proteins involved in the circadian cycle can activate HIV transcription, leading to fluctuations in HIV RNA levels.

    Lewin described this phenomenon as “reservoir activity” and it’s important to stress that it does not represent ongoing HIV replication—any new infectious HIV viruses that are produced would be blocked from infecting new cells by the presence of ART. Gaining an understanding of the processes involved in reservoir activity should help researchers develop better latency-reversing agents.

    Another aspect of HIV latency that is now coming into view is the importance of where exactly the virus lands when it integrates into the genome of a cell. As a loose analogy, if you think of the genome as a factory for producing all the proteins a cell needs to go about its business, HIV DNA tends to land in machinery that gets switched on regularly, which gives the virus opportunities to hijack that machinery to make more HIV RNA (and potentially more copies of infectious HIV).

    But HIV DNA can also land in the genomic equivalent of a darkened factory storage room nobody goes into—in that case, the virus may be trapped and unable to reactivate. Between these two extremes there are likely a range of possibilities, from HIV DNA being integrated in a spot where the transcription of HIV RNA is likely, to HIV DNA being integrated into a genomic dead end from which it can never emerge. Again, these new findings have implications for latency-reversing agents because they demonstrate that there’s a spectrum of reversibility that will need to be addressed.

    The potential importance of where latent HIV resides in a cell’s genome has been emphasized by recent studies of elite controllers (as presented at CROI by Chenyang Jiang), which suggest that their immune responses can clear the more active HIV reservoir, leaving behind only those cells containing HIV integrated in places from which it cannot reactivate—essentially, the intact HIV that remains in their bodies may be trapped, and unable to replicate or cause harm.

    A further wrinkle in the latency story is the ability of CD4 T cells containing integrated HIV to proliferate, duplicating the viral genes they contain along with the cell. As Lewin noted, it’s now recognized that a large proportion—typically around half—of the HIV reservoir in people on ART has been created by what is referred to as clonal proliferation of CD4 T cells. The proportion of the HIV reservoir generated by clonal proliferation can be identified because the viruses are genetically identical and integrated into exactly the same spot in the genome of CD4 T cells that contain them.

    The mechanisms driving the proliferation of latently infected CD4 T cells are still being elucidated but Lewin listed several possibilities:

    • Homeostatic proliferation: this is a normal part of the life of CD4 T cells that facilitates the survival of the cell and maintenance of overall CD4 T cell numbers. Evidence that it plays a role in maintaining the HIV reservoir was first published back in 2009.
    • Antigen-specific proliferation: the process by which CD4 T cells proliferate after recognizing a specific antigen (e.g. an antigen derived from HIV or other infectious agents such as CMV) and becoming activated to respond. Lewin cited several studies reporting new data on the importance of antigen-specific proliferation in HIV persistence (including two at CROI: Simonetti et al and Mendoza et al)
    • HIV integration site driven proliferation: in this scenario, it’s been proposed that HIV can influence the proliferation of CD4 T cells by integrating into certain places in a cell’s genome. At CROI, John Coffin described findings that may support this possibility, but only for a limited number of integration sites.

    There are published studies showing that latently infected CD4 T cell clones contribute to viral load rebound after ART interruption, and also that HIV reservoir activity in these cells can in some cases generate sufficient HIV RNA to be measurable by standard viral load tests (making it necessary for clinicians to be alert to the possibility of mistakenly attributing detectable HIV RNA in people on ART to treatment failure).

    The last but critical point made by Lewin about the HIV reservoir is the distinction between intact and defective HIV. It’s been known for some time that the vast majority of HIV DNA present in people on ART represents defective viruses that are incapable of replicating (although in some cases capable of generating viral proteins), but researchers have lacked the tools to easily distinguish replication-competent HIV.

    The recently developed intact provirus detection assay (IPDA) is an example of progress on this front. Lewin cited an encouraging new analysis by Gregory Laird and colleagues indicating that levels of intact HIV decline on ART, while the amount of defective HIV DNA remains relatively stable. Based on the case of the elite controller Loreen Willenberg, in whom no intact HIV can be detected, Lewin also suggested that perhaps a cure should be defined as the elimination of all intact virus (rather than the absence of any detectable HIV genetic material).

    Moving on to the future of kick and kill, Lewin selected some examples of advances that offer reasons for optimism. Earlier this year, results of an evaluation of the candidate latency-reversing agent AZD5582 were published in the journal Nature. The compound belongs to a class of drugs called SMAC mimetics, which appear to have considerably less potential to cause toxicity compared to the drugs studied to date. In studies in both HIV-infected humanized mice and SIV-infected macaques, potent induction of viral RNA expression was observed in blood and multiple tissues after dosing.

    Immunomodulatory compounds such as immune checkpoint inhibitors (e.g. anti-PD1 antibodies that are approved for cancer) and toll-like receptor (TLR) agonists may have the ability to both reverse HIV latency and enhance killing of infected cells. Concerns about serious immune-mediated side effects are currently limiting the use of the former, but might eventually be addressed by different formulations and dosing strategies. Two studies are testing TLR agonists in combination with dual bNAbs (one with the addition of therapeutic vaccination): TITAN and JAWS. Both trials involve ATIs. JAWS is taking place at the University of California San Francisco (UCSF) but was only due to start enrolling very recently (and is not yet registered in clinicaltrials.gov), so may well be delayed by the current COVID-19 emergency.

    The field of gene therapy is contributing another kill strategy: Chimeric Antigen Receptor (CAR) T cells, which are genetically modified to efficiently target virus-infected cells for destruction. Blake Rust presented results of a small CAR T cell experiment in SHIV-infected macaques at CROI, which showed some potential to control viral replication—one animal experienced an 89 day delay in viral load rebound after ATI, and two out of the four total animals displayed post-ATI suppression of viral load. Other research groups are also pursuing the idea.

    At the Pre-CROI Community HIV Cure Research Workshop—an event co-sponsored by TAG that was held via webinar this year—James Riley described the status of efforts to translate the CAR T cell approach for use in people with HIV. A pilot trial combining CAR T cells with CD4 T cells gene-modified to lack the CCR5 co-receptor is now underway the University of Pennsylvania.

    The lack of success observed to date with kick and kill may seem disheartening, but it does not necessarily spell doom—the ever-improving understanding of the biology of HIV latency combined with the expanding array of therapeutic candidates suggests the stubborn persistence of the HIV reservoir can yet be overcome.

  • CROI 2020: Updates on the London and Düsseldorf Patients, New Case of Infant Remission

    Important news has unfolded this week regarding possible additional cases of HIV cures and remission. Yesterday, the London Patient (LP) courageously publicly identified himself as Adam Castillejo in an excellent, thoughtful and empathetic article in the New York Times by Apoorva Mandivilli. While his name is now known, I’ll follow his preference to go by the acronym LP here. Following this story, a scientific update was published in Lancet HIV today (open access), timed to coincide with a poster presentation at the Conference on Retroviruses and Opportunistic Infections (CROI)—a conference that was due to occur in Boston this week, but is now ongoing in a virtual format due to concerns over coronavirus. The same poster session also featured new information on the similar case of the Düsseldorf patient, along with a report on an infant treated early with ART in whom treatment was subsequently interrupted without HIV rebound (which has echoes of the HIV remission described in the Mississippi baby in 2013).

    The Lancet HIV paper describes the latest results from extensive studies of LP. The embargo on the publication was lifted at 8:30am ET today, so there are a number of excellent online articles reporting in detail on the findings, including those by Simon Collins for HIV i-Base and Ben Ryan for POZ Magazine. Simon Collins was the first to ever report on LP, after noticing a reference made to the case by Ian Gabriel at a British HIV Association conference in October 2018. LP also released a statement which is quoted extensively in an article by Eagle Radio.

    LP has now been off antiretroviral therapy (ART) for 2.5 years and the major take home message from the science is that no evidence of intact, replication-competent HIV could be found in multiple samples of blood, cerebrospinal fluid, semen, gut and lymph nodes. Rare examples of extremely low-level positive signals for HIV DNA fragments were detected in memory CD4 T cells and samples from an axillary lymph node, but this represented a minority of samples from multiple replicates. It was not possible to sequence any HIV genes from these positive samples. The researchers suggest the results could be explained by detection of fragmentary, defective HIV DNA or false positives. Similarly rare low-level positive readings for HIV DNA and RNA were reported in some samples from Timothy Brown back in 2012. Antibody responses to HIV are waning, as was also observed in Brown.  

    The researchers collaborated with mathematical modeler Alison Hill to explore the probability that LP is cured of HIV. The modeling takes into account donor chimerism, which refers to the proportion of cells in LP that are from the stem cell donor (who was homozygous for the CCR5Δ32 mutation). The model's output indicated that if greater than 90% of the cells in LP are from the donor, then a lifelong HIV cure is almost certain. Measures of the peripheral blood showed that donor chimerism was approximately 99%, so even accounting for the possibility of lower levels in tissues, the paper concludes that a cure has probably been achieved. Nevertheless, viral load testing will continue twice a year for up to 60 months after ART was interrupted, then be switched to yearly for a further 60 months.

    As articulated in an accompanying commentary by Jennifer Zerbato and Sharon Lewin, certainty remains elusive when it comes to defining HIV cures. The most important factor is time. Much as confidence in Timothy Brown’s HIV cure has grown the longer he has gone without HIV rebound, the same will be true for LP. But as Zerbato and Lewin note: “We will need more than a handful of patients cured of HIV to really understand the duration of follow-up needed and the likelihood of an unexpected late rebound in virus replication.”

    In the poster session scheduled for 2:30-4:00pm ET at CROI today (for which the embargo has just lifted), Björn-Erik 0. Jensen provided the latest information on the Düsseldorf patient, who might represent a third individual cured of HIV after receipt of a stem cell transplant from a donor homozygous for the CCR5Δ32 mutation. Follow up is considerably shorter in this case, at just 15 months after ART interruption. Mirroring the findings in both LP and Timothy Brown, the researchers have detected traces of HIV DNA in some samples from lymph nodes and the gastrointestinal tract, but not found any evidence of replication-competent HIV. Antibody responses to HIV are declining.

    The same poster session also featured a report by Gloria Heresi from the University of Texas Health Science Center, describing a child experiencing apparent ongoing HIV remission for more three years after an ART interruption. The case closely parallels that of the Mississippi baby, who appeared to have possibly been cured by very early initiation of ART after birth but eventually rebounded after an interruption in treatment that lasted a little over 27 months.

    For reasons that are not explained, the mother was untreated at the time of the birth and had a viral load of 14,400 copies the day after delivery. ART regimens were initiated in the infant after 33 hours, but subsequently stopped by the mother at 13 months of age. Viral load has remained <20 copies/mL since that time and the HIV antibody test has been negative from 15 months of age onward (the child is now 4 years of age).

    While the mechanisms at work are unknown and further analyses and follow up will be needed, the case may indicate that early restriction of the HIV reservoir by ART can lead to longer periods of HIV remission than was seen in the Mississippi baby. This could be encouraging news for the IMPAACT P1115 trial, which is testing whether early initiation of treatment in HIV-exposed newborns can subsequently facilitate HIV remission, at least for some participants.  

  • HIV Vaccine Regimen Does Not Show Efficacy in the HVTN 702 Trial in South Africa

    On Monday February 3rd it was announced that HVTN 702, a large-scale HIV vaccine efficacy trial taking place in South Africa, had found no evidence of protection against HIV acquisition. The information emerged from a pre-planned review of interim results conducted by the trial’s Data Safety Monitoring Board (DSMB), which revealed roughly equal numbers of HIV infections among vaccine and placebo (dummy vaccine) recipients. There were no indications that the vaccine regimen had caused harm. Following the DSMB’s recommendation, immunizations have been stopped, and plans are being made to unblind participants (inform them whether they received active vaccine or placebo) and follow them for an additional 12 months to monitor for safety.

    The research was sponsored by the HIV Vaccine Trials Network (HVTN) and had hoped to build on marginal evidence of efficacy observed in RV144, a vaccine trial that took place in Thailand with results reported in 2009.

    Since the initial announcement, two webinars accessible to people in the USA have provided additional details on the HVTN 702 results and plans for follow up—the first was sponsored by the HVTN and Black AIDS Institute (BAI) and held on February 5th, the second was sponsored by AVAC and Advocacy for the Prevention of HIV and AIDS (APHA) and held on February 19th (a recording of this webinar is available).

    The HVTN 702 Results

    HVTN 702 recruited 5,407 sexually active, HIV-negative men and women aged between 18 and 35 years. On the HVTN/BAI webinar, principal investigator Glenda Gray explained that the DSMB’s interim analysis was based on 5,383 participants – 2,694 in the vaccine arm and 2,689 in the placebo arm. The median follow up time was 18 months. The DSMB analysis found that there had been 129 infections among vaccine recipients and 123 among those who received the placebo, indicating no effect on the risk of acquiring HIV in this population. Importantly, there was no possibility of the vaccine showing a significant effect on HIV acquisition if the trial had been allowed to continue until the original planned completion date, hence the DSMB recommendation to cease further immunizations.

    Gray noted that 77% of the total planned follow up between study entry and month 24 had been completed, and 62.1% of participants had reached month 18.5, two weeks after the final vaccination. Data on the incidence of HIV infection measured every three months showed that it was almost identical between vaccine and placebo arms at every timepoint.

    Gray also presented the incidence rates based on participant sex at birth and again the numbers were closely matched between vaccine and placebo. There were more women than men in the trial, so this analysis was based on 1886 female vaccine recipients, 1886 female placebo recipients, 808 male vaccine recipients and 803 male placebo recipients. At month 24, 114 HIV infections had occurred in females in the vaccine arm, 107 in females in the placebo arm, 14 in males in the vaccine arm and 14 in males in the placebo arm. HIV incidence was approximately four-fold higher in females, consistent with what is seen at the population level in South Africa.

    Gray made clear the disappointment felt by the HVTN 702 co-chairs (Gray, Linda-Gail Bekker, Fatima Laher and Mookho Malahleha) and everyone else involved in the trial, but also pointed to the DSMB’s commendations for the how the research was conducted and the high regard shown for the participants. The trial answered a critical question, albeit not in the way that had been hoped, and there are over 15,000 samples available that will facilitate efforts to understand why the vaccine regimen did not work.

    Discussing the possible implications of the results, Gray highlighted that one key difference with the RV144 trial in Thailand is the far greater rate of exposure to HIV among women—approximately 14 times higher in the South African versus Thai trial populations. Additionally, the failure of the specific vaccine regimen used in RV144 does not mean that other approaches under study are also doomed—Gray cited several ongoing trials, such as those of an HIV vaccine designed by Janssen, the PrepVacc study which is evaluating both pre-exposure prophylaxis (PrEP) and vaccination, the AMP protocols testing the efficacy of broadly neutralizing antibodies, and research into long-acting antiretrovirals for PrEP.

    Community Feedback and Next Steps

    On the AVAC/APHA webinar, Linda-Gail Bekker provided additional information on the follow up plans for HVTN 702. Participants are being invited to consent to being followed for a further 12 months to evaluate safety, and at their next visit will be informed as to whether they were in the vaccine or placebo arm of the trial. Bekker also explained that a journal article describing the results is in preparation, and the most likely forum for more detailed presentations on a range of issues related to the trial will be the R4P conference which takes place in Cape Town from October 11-15, 2020.

    Ntando Yola, co-founder of APHA, introduced several community representatives involved with the HVTN 702 sites in South Africa who discussed their perspectives on the trial and feedback from participants. As with those responsible for conducting the trial, disappointment was the overarching feeling but there was also recognition that the negative result was still very important. There have been some expressions of concern by participants about the slight numerical difference in the number of HIV infections between the vaccine and placebo arms of the trial (six more in the vaccine group) and communications have focused on explaining why this is not a significant difference or evidence that the vaccine was harmful.

    Questions have also arisen about the possibility of vaccine-induced seropositivity (VISP), provision of PrEP and the approach taken to participants who seroconverted. Linda-Gail Bekker addressed these issues, noting that to date very little VISP has been observed in HVTN 702. PrEP was made available to participants (and continues to be available), but uptake has been disappointingly low, mirroring the situation in South Africa outside of the trial. Bekker hopes that imminent PrEP promotion and demand creation initiatives from the Department of Health will help remedy this problem. Individuals who seroconverted during the trial were immediately referred for HIV treatment and are being followed.

    The Vaccine Regimen in HVTN 702 and Other Efficacy Trials

    On the topic of the specific HIV vaccine regimen used in HVTN 702, Mary Marovich, Director of the Vaccine Research Program at the Division of AIDS (National Institute of Allergy and Infectious Diseases, US National Institutes of Health) presented information on the types of scientific studies likely to be conducted to try to understand why it did not work. Marovich also addressed how the regimen is different from other HIV vaccines currently in efficacy trials.

    HVTN 702 tested a prime-boost regimen similar to—but not exactly the same as—that used in the Thai RV144 trial. A harmless canarypox virus vector (ALVAC) delivering selected HIV antigens (parts of the virus capable of inducing an immune response) was administered at months 0, 1, 3, 6, 12 and 18. The antigens were derived from HIV clade C, the predominant virus variant circulating in South Africa. The boost part of the regimen comprised two differing forms of the HIV gp120 envelope protein, both also derived from HIV clade C, delivered with the adjuvant MF59. The boost was administered at months 3, 6, 12 and 18.

    In RV144, the HIV antigens were derived from clades B and E (also known as CRF01_AE) and the immunizations were less frequent: ALVAC was given at months 0, 1, 3 and 6 and the gp120 protein boost at months 3 and 6. The gp120 protein boost was delivered with a different adjuvant, Alum.

    A preparatory study (HVTN 100) conducted in South Africa demonstrated that the vaccines used in HVTN 702 induced similar—in some cases superior—immune responses compared to those observed in RV144 participants. These results were published in Lancet HIV in 2018 with additional information on the effects of the 12-month booster presented earlier this week in PLoS Medicine.

    Marovich explained that samples from HVTN 702 will be studied to confirm that the vaccines induced robust immune responses, and to evaluate whether these responses were capable of recognizing the HIV strains that participants acquired during the trial. A particular focus will be placed on looking at the types of immune responses that appeared to correlate with reduced HIV risk in RV144 (sometimes described as “correlates of protection”).

    The two other large ongoing HIV vaccine efficacy trials are HVTN 705 (Imbokodo) and HVTN 706 (Mosaico). There are superficial similarities with HVTN 702 in that they both involve a prime-boost HIV vaccine regimen, but Marovich cited several key differences. The HIV antigens are, for the most part, not derived from a single virus clade but rather represent specially tailored mosaics made up of elements from multiple different clades—the goal is to develop vaccines capable of working globally, regardless of the locally prevalent HIV clade.

    The regimen also comprises a different viral vector, adenovirus serotype 26 (Ad26) and an HIV envelope protein boost containing gp140 rather than gp120. The adjuvant for the boost is Alum, as was used in RV144 but not HVTN 702. Additionally, in HVTN 705, the HIV envelope protein boost is from clade C HIV, whereas HVTN 706 is employing a “bivalent” boost containing both clade C and mosaic HIV gp140 proteins.

    Another important distinction is that the rationale for HVTN 705 and 706 does not primarily derive from a prior human HIV vaccine trial, but rather promising results in animal models involving exposure of macaques to SHIVs (hybrids of simian and human immunodeficiency viruses). However, researchers have reported that certain immune profiles induced by the vaccines mirror those associated with reduced risk of HIV infection in RV144.

    Revisiting RV144

    Arguably, a question that looms over the HVTN 702 results that was not discussed on either webinar is: was the RV144 result real, or a fluke? This has been a matter of some controversy in the scientific community, primarily because the statistical significance of the RV144 result was extremely borderline—the reported reduction in risk of HIV acquisition was 31.2%, with a wide 95% confidence interval of 1.1 to 52.1. If the lower bound of a confidence interval crosses 1, then the result is not statistically significant, emphasizing the fragility of the result. Statisticians have estimated that there is an approximately 22% possibility that the finding could have occurred by chance.

    Evidence advanced in support of the protection being real include an analysis of HIV incidence after the first year of RV144, which suggested that efficacy may have been as high as 60% at this timepoint, before vaccine-induced immune responses waned. But this analysis was not planned in advance (described as “post hoc”) and so may be unreliable.

    A range of potential immune correlates of protection against HIV have also been reported for RV144. In some cases, there is evidence that similar immune responses offered protection in animal models. Again, however, these results do not represent definitive proof that the vaccine regimen in RV144 was protective—for example, it can be unclear if an individual’s immune response to a vaccine reflects some aspect of their immune system that renders them less susceptible to HIV independent of vaccination. Vaccine research veteran Stanley Plotkin, in a commentary co-authored with Georgia Tomaras, emphasizes that:

    “To date, correlates of HIV-1 risk involving multiple immune responses have been identified for the RV144 HIV-1 vaccine efficacy trial. However, these are not yet accepted to be CoP [correlates of protection] since they have not been confirmed in another vaccine efficacy trial.”

    There have been lively debates in the scientific literature, with commentaries by Ron Desrosiers and Per Johan Klasse and John P. Moore raising questions about the veracity of the RV144 analyses. These commentaries have in turn have been criticized and at least partly rebutted in a paper by Susan Zolla-Pazner and Peter B. Gilbert, researchers heavily involved in generating the data related to potential correlates of protection.

    Importantly, there is very broad agreement—albeit not universal—that none of this uncertainty regarding RV144 undermines the rationale for conducting HVTN 702. The dismaying data from HVTN 702 confirming the high rates of HIV infection in South Africa, particularly in women, underscores that it was vital for researchers to follow up on the possibility of vaccine efficacy reported in RV144. But as the HIV vaccine field works to understand the results and learn from them, revisiting RV144 should not be off the table.

    Additional Reading

  • Conference Catch Up: HIV Cure Research

    A number of conferences and workshops related to HIV cure research have taken place over the past several months, many of which can be viewed or learned about online. Links and some brief reports from four events are provided below.

    Promising Approaches to HIV Remission and Cure

    HIV cure research was the chosen topic for the Harvard University Center for AIDS Research (CFAR) annual symposium, held on October 23rd. The organizers have created a YouTube playlist featuring all presentations and panel discussions from the event.  

    5th Conference on Cell & Gene Therapy for HIV Cure

    The only conference that specifically focuses on cell and gene therapy in HIV cure research was launched in 2014 under the auspices of the defeatHIV Collaboratory at the Fred Hutchinson Cancer Research Center in Seattle. The meeting has quickly become established as the key annual get together for this area of the cure research field. The 5th conference took place from August 22-23 in Seattle; the agenda is available on the event website and videos of presentations are now being added to the defeatHIV YouTube channel (a playlist is available for day 1).

    Fred Hutch News published two stories about the conference, the first highlighting the work of keynote speaker Dr. Robert Siliciano and the second covering presentations and a workshop focused on strategies to make gene therapies more affordable and globally accessible.

    The latter workshop was co-organized by the well-known HIV researcher Mike McCune, who is now leading the HIV Frontiers program at Global Health Innovative Technology Solutions, Bill & Melinda Gates Foundation. McCune recently co-authored a commentary in the journal EBioMedicine outlining how an accessible gene therapy might theoretically contribute to achieving an HIV cure.

    A significant step toward making the hope of accessible gene therapies a reality was announced by the Bill & Melinda Gates Foundation and the National Institutes of Health (NIH) on October 23rd. The two research behemoths have joined forces to launch an initiative that will invest at least $100 million over the next four years to develop affordable, gene-based cures for sickle cell disease (SCD) and HIV.

    In tandem with the Cell & Gene Therapy conference, defeatHIV’s indefatigable Community Engagement Project Manager Michael Louella organized a public event at the Seattle Library co-hosted by DeAunte' Damper, the LGBTQ Chair of the Seattle King County NAACP. Discussants included the researcher Carl June, gene therapy trial participants Matt Sharp and Matt Chappell, and defeatHIV Community Advisory Board members Tranisha Arzah and Manuel Venegas. Video is available on the Seattle Channel and the defeatHIV YouTube channel.

    Finding and Characterizing HIV Reservoirs

    A second example of collaboration between the Bill & Melinda Gates Foundation and the NIH in the area of cure research was a workshop on finding and characterizing HIV reservoirs, held July 30-31 on the NIH campus. Thanks to the wonders of the NIH videocast system, the entire meeting can be viewed online (see day 1 and day 2).

    Particularly recommended is a tour de force presentation by Robert Siliciano, one of the first researchers to identify the HIV reservoir. Siliciano highlighted the recent shift in understanding of how the HIV reservoir persists despite antiretroviral therapy (ART). Initially, there were suspicions that continuing low-level viral replication in tissues (sometimes referred to as “sanctuary sites”) was playing a role, but it has now become apparent that—in his words— “the vast majority of cells in the reservoir are not generated by direct infection but by proliferation of previously infected cells.”

    Siliciano also discussed a new assay developed in his laboratory that attempts to simplify the detection of the replication-competent HIV reservoir. In a study published in Nature earlier this year (now available free in PMC), Siliciano’s group described their approach to assessing the intactness of HIV DNA proviruses, which they’ve named the intact proviral DNA assay (IPDA).

    In the workshop presentation, Siliciano showed unpublished data from Gregory Laird indicating that the decay of the HIV reservoir in people on ART is the same (~44 months) when measured with the IPDA or the far more cumbersome and expensive quantitative virus outgrowth assay (QVOA). He noted, however, that the IPDA also revealed outliers around the average value – some study participants had precipitous declines in their HIV reservoir, while others showed increases (likely the result of proliferation of latently infected CD4 T cells).

    IAS HIV and HBV Cure Forum/IAS 2019

    In recent years, the International AIDS Society (IAS) has scheduled symposiums on HIV cure research immediately preceding their main annual conference (which alternates between the International AIDS Conference and the IAS Conference on HIV Science). The theme differs at each event, and in 2019 the focus was on parallels between the efforts to cure HIV and hepatitis B (HBV).

    A detailed report from the meeting was published on October 22nd in the open access Journal of Virus Eradication. Oral and poster abstracts are also available from the same journal. Slide presentations are posted on the IAS website for the event.

    Among the presentations:

    Maria Pino described research in the SIV/macaque model suggesting that the approved multiple sclerosis treatment fingolimod (trade name Gilenya) can cause retention of cytotoxic T cells in lymphoid tissue and reduce the reservoir of virus DNA in T follicular helper cells (some of the work was published in PLoS Pathogens on October 18th). A subset of macaques administered fingolimod at the time of ART initiation showed evidence of a delayed and lower magnitude viral load rebound after an analytical treatment interruption.

    There is considerable interest in the prospects for Gilead Sciences toll-like receptor 7 (TLR-7) agonist vesatolimod in HIV, due to encouraging results in macaques. Preliminary data from a phase I trial in people on ART were presented by Sharon Riddler from the University of Pittsburgh School of Medicine. The compound appeared safe and there was evidence of immune-stimulating activity at doses over 6mg. The ultimate aim is to study vesatolimod in combination with other interventions such as broadly neutralizing antibodies.

    One question that the trial didn’t address is whether responses to vesatolimod might be different in women compared to men. A decade ago the research group of Marcus Altfeld reported evidence of sex differences in responsiveness to TLR7 agonists, and female sex was associated with greater induction of interferon-stimulated gene expression in a previous trial of vesatolimod as a treatment for hepatitis B.

    Out of 48 participants in the dose-escalating HIV trial, only five were women, and three of the six dose groups included only men. It will be important for future studies to investigate whether sex influences the response to vesatolimod in people with HIV. An ongoing trial is evaluating vesatolimod in HIV controllers who have started ART, but demographic information on participants is not yet available.

    Sharon Lewin from the Doherty Institute in Australia described a new effort that is underway to develop a “target product profile” (TPP) for an HIV cure with particular focus on global accessibility, and the formation of a related “HIV Cure Acceleration for Africa” (HCAAP) working group. These plans grew out of a summit hosted by the IAS in partnership with the Annenberg Trust at Sunnylands.

    A presentation at the main IAS 2019 conference that drew attention was delivered by Xu Yu from Massachusetts General Hospital. Yu highlighted cases of extreme elite control of HIV that may represent clearance of all replication-competent viruses, focusing in particular on a long-term elite controller referred to as the “San Francisco patient.” Recently, an article in Leapsmag by Bob Roehr revealed the individual to be Loreen Willenberg, who is renowned among activists for her key role in promoting elite controller research via the Zephyr Foundation. Official IAS 2019 video of Yu’s presentation is not available, but a partial recording is posted to the defeatHIV Facebook page.

    Links to cure-related IAS 2019 sessions are appended below.

    Stem cell and genome editing for HIV cure (plenary session, presentation starts at 0:31:40)
    Paula Cannon, University of Southern California, United States

    New and old players in HIV replication

    HIV transcription: The sound of silence

    What is the cure, why do we need it and how do we get there?

    Keep control: Elite and post-treatment controllers

    Hide and seek: Reservoirs and strategies to target them

    Research by and for whom? Community engagement in research

    HIV remission and control trials

    50 shades of reservoirs

    Kill the enemy: CTL and NK cells

    Paediatric HIV infection: It's never too early

    Pathogenesis: And the band plays on

    Mission remission: Challenge accepted