With a global focus on strategies to curb expansion of a fast-moving coronavirus pandemic, the question again has arisen:
Although many antiretroviral medications have been approved over the years, new strategies are under development that theoretically could deliver a knockout blow to HIV. Medical investigators are exploring the possibility of gene therapy as a potential HIV cure. Other teams are examining CAR T-cell therapy, a form of immunotherapy that has demonstrated effectiveness against certain forms of cancer.
Technically known as chimeric antigen receptor-modified T cell therapy, the method involves extracting T cells from a patient’s blood, followed by modifying them in a laboratory to recognize and destroy HIV-infected cells.
But there are other efforts still, and a new proof-of-concept trial might pave the way for further studies of an experimental immune-boosting compound, which has been tested in combination with coventional antiretroviral therapy, commonly known as ART. The experimental compound – vesatolimod – activates components of the innate and acquired immune systems to put additional pressure on HIV. Vesatolimod essentially marshals a diverse army of immune system fighters in its assault on the human immunodeficiency virus.
Currently, ART can impressively reduce viral loads to undetectable levels in the blood, a feat that some medical investigators call a functional cure. Antiretroviral therapy works by controlling the replication of HIV, and when replication is controlled, the viral load in the blood dramatically diminishes. But HIV can hide in the body, persisting in a stubborn latent state that’s impervious to ART. The virus can also rebound prolifically when patients stop taking ART.
Writing in Science Translational Medicine, medical investigators from Gilead Sciences, a pharmaceutical company in Foster City, Calif., and collaborators from leading research centers throughout the United States, describe their small Phase 1b clinical study of vesatolimod.
The experimental compound works by ramping up key members of the innate immune system: Interferon, proteins that “interfere” with viruses to block their replication; and natural killer cells, immune constituents whose name aptly describes their function. The compound also has a hand in T cell activation.
“Compared with placebo, vesatolimod was associated with an increase in interferon signaling and natural killer cell and T cell activation, and a decay in the frequency of cells harboring intact HIV genomes,” wrote Dr. Devi SenGupta of Gilead Sciences, lead author of the research. “Vesatolimod also induced a modest increase in the time to virus rebound after antiretroviral therapy was interrupted.”
Vesatolimod is described as a toll-like receptor 7 agonist, or more simply, a TLR7 agonist. Any agonist initiates a response from a protein receptor. In this case, vesatolimod initiates activity from toll-like receptor 7. Structural biologists have identified more than a dozen distinct toll-like receptors, which are most commonly found stippling the surfaces of macrophages and dendritic cells.
When a virus or other pathogenic invader infiltrates cells, toll-like receptors activate innate immune system responses. With an agonist, such as vesatolimod, scientists are targeting a specific toll-like receptor to do a specific job: Assault HIV.
Toll-like receptor agonists are considered a promising class of compounds because in addition to boosting interferon signaling and natural killer cell activity, these compounds as a group are potent dendritic cell activators. Dendritic cells are critical links between the innate and acquired immune systems. T cells, key members of the acquired immune system, have a ramped presence under the influence of the experimental compound.
It’s important to underscore: HIV infection is indelibly characterized by the deadly depletion of CD4+ T cells, which are targeted by the virus. While the experimental therapy is in no way capable of capable of boosting CD4+ T cells, it is being investigated for its potential to help eliminate the viral reservoir of HIV by amplifying the immune response.
More than 70 million people have been infected with HIV since the human immunodeficiency pandemic began in the early 1980s, and an estimated 35 million people have died of the infection over the past 40 years, according to UNAIDS, a joint United Nations effort involving 11 UN organizations aimed at combating HIV/AIDS.
UNAIDS estimates that more than 37 million people worldwide are living with HIV, and that ART has helped significantly reduce morbidity and mortality caused by the virus, transforming the infection into a chronic disease for people in many parts of the world.
Vesatolimod, meanwhile, isn’t the first toll-like receptor agonist to be used in a clinical study, others have been developed and are being explored in cancer treatment as potent adjuvants—boosters—in cancer vaccine therapy.
In the HIV research, SenGupta and colleagues focused on a unique group of patients known as “controllers.” These patients can stop taking their prescribed antiretroviral therapy but, remarkably, even when not on the life-saving medication, they are able to keep HIV replication somewhat under control.
Beyond the investigators’ focus on these unusual patients, the research team also wanted to determine how well vesatolimod augments treatment with ART. Hitting the virus with ART and vesatolimod is one way to deliver a one-two punch against HIV. Whether it’s a way to deliver a knock-out punch can be answered only through many, many more rounds of research, experts say.
Scientists initially developed vesatolimod to treat chronic hepatitis infections, but it was research beyond those initial studies that produced a eureka moment involving the experimental compound.
In animal studies vesatolimod substantially shrank the reservoir of an HIV-like virus – simian immunodeficiency virus – that infects monkeys. After that discovery, scientists began analyses to determine the compound’s efficacy as a treatment for HIV.
SenGupta and colleagues recruited 25 HIV “controllers” on ART, gave 17 of them vesatolimod – TLR7 – on a biweekly basis, and then halted ART. The remaining 8 received a placebo. Controllers treated with vesatolimod fared better than controllers treated who were given a placebo – but only modestly.
Those treated with vesatolimod showed an increase in active immune cells and a significant drop in HIV DNA. Their HIV rebounded a full week after the HIV rebound of the placebo group.
Stunningly, one participant didn’t experience an HIV rebound for 15 weeks after taking the oral experimental compound. The team is now calling for larger clinical trials to further evaluate vesatolimod.
SenGupta describes the current research as a proof-of-concept study and suggests that adding vesatolimod to antiretroviral therapy regimens could enhance therapeutic measures to control HIV infection. The experimental compound seems to increase signaling activity and interaction between key components of the innate immune system, according to the research.
“Inferred pathway analysis suggested increased dendritic cell and natural killer cell cross-talk and an increase in cytotoxicity potential after vesatolimod dosing,” SenGupta wrote. “Larger clinical studies will be necessary to assess the efficacy of vesatolimod-based combination therapies aimed at long-term control of HIV infection.”
For millions of HIV patients worldwide, antiretroviral therapy means taking medication daily – for life. More than 40 drugs have been approved over the years, and some, such the integrase inhibitors, Biktarvy and Duvato, are single-tablet medications. ART not only keeps HIV infections from developing into full-blown AIDS, but viral levels can be driven so low, they are undetectable by laboratory tests. Once viral levels are undetectable, HIV can no longer be sexually transmitted.
Yet, as impressive as that may seem, undetectable does not constitute a cure and some HIV patients – controllers in particular – wax and wane between periods of taking and not taking prescribed ART.
Also, antiretroviral therapy is not without its drawbacks. The medications can cause side effects that range from mild to formidable. For example, skin rashes and weight gain are possible side effects with some HIV medications. High cholesterol levels and heart and kidney problems are side are among the more serious side effects associated with others.
Still, antiretrovial therapy is considered one of modern medicine’s greatest triumphs because it grants HIV patients near-normal life expectancy. Researchers have therefore prioritized finding a cure for HIV that can either eliminate the virus or prevent it from rebounding after patients interrupt their daily regimen of ART.
Thus, the pursuit of a compound such as vesatolimod – TLR7 – and its ability to prompt an immune response against HIV. Future studies, the team hopes, may produce stronger results.
For now, the proof-of-concept research suggests scientists are moving in the right direction: “The TLR7 agonist vesatolimod induced a modest delay in viral rebound in HIV controllers after cessation of antiretroviral therapy,” SenGupta wrote.
Within days of infection, human immunodeficiency virus (HIV)–1 stably integrates into the host genome, establishing the latent HIV-1 reservoir [1–4]. This transcriptionally inactive viral reservoir is undetectable by the immune system and is not impacted by antiretroviral therapy (ART); with interruption of ART, HIV RNA rebounds to pretreatment levels [5, 6]. Despite the availability of highly efficacious ART, people living with HIV (PLWH) continue to suffer from low-level inflammation, immune activation, treatment side effects, and psychosocial stigma [7, 8]. A definitive therapeutic intervention able to eradicate or control HIV reservoirs and lead to long-term, ART-free remission is an ongoing medical need.
Vesatolimod is an orally administered agonist of toll-like receptor 7 (TLR7), which mediates both HIV-1 and immune cell activation in vitro . Vesatolimod induced transient viremia and decreased the amount of cell-associated simian immunodeficiency virus (SIV) DNA in ART-suppressed, chronically SIV–infected rhesus macaques .
Although in subsequent macaque studies treatment with TLR7 agonists did not induce detectable plasma viremia while on ART [11–14], the immune modulatory activity of TLR7 agonists, such as cytokine induction and cellular activation, has been consistently demonstrated across nonhuman primate (NHP) studies [10–13, 15]. Additionally, when combined with a therapeutic vaccine or monoclonal anti-HIV envelope antibody, TLR7 agonists induced viral remission in SIV or simian-human immunodeficiency virus (SHIV)-infected NHP, likely by enhancing antiviral immunity and/or reducing the reservoir [11, 12].
The administration of vesatolimod has been shown to be safe in healthy volunteers and in individuals infected with hepatitis B virus [16–19]. We now report the first data on the safety, virologic effects, pharmacokinetics, and immunologic activity of vesatolimod in PLWH receiving ART.
Study Design and Participants
This randomized, double-blind, multicenter, placebo-controlled, dose-escalation, Phase Ib trial was conducted at 7 outpatient centers in the United States. Participants were adults (aged ≥ 18 years) living with HIV-1 who had plasma HIV-1 RNA < 50 copies/mL for at least 12 months prior to screening while on stable ART, an estimated glomerular filtration rate ≥ 60 mL/minute, and no documented history of resistance to their current antiretroviral regimen (see Supplementary Material for full eligibility criteria).
The trial had 6 vesatolimod dose groups. All participants received vesatolimod or matching placebo orally every 2 weeks in clinic (while fasting), while continuing ART. For each cohort, 8 participants were randomly assigned to vesatolimod or placebo in a 6:2 ratio, receiving 1, 2, or 4 mg of the study drug every 2 weeks for 6 doses; 6 or 8 mg every 2 weeks for 10 doses; or 10 mg every 2 weeks for 3 doses, followed by 12 mg for 7 doses.
This trial was undertaken in accordance with the Declaration of Helsinki and was approved by central or site-specific review boards or ethics committees. All participants provided written informed consent.
Study visits were conducted at 1-, 2-, or 3-day intervals, depending on the dose cohort (see the Supplementary Material for the full visit schedule). Safety was assessed by physical examinations, laboratory tests, a 12-lead electrocardiogram, a review of concomitant drugs, and recording of adverse events, which were coded using the Medical Dictionary for Regulatory Activities (MedDRA, version 21.1). The relatedness of adverse events to blinded study treatment was determined by the investigator.
Virologic effects were assessed by plasma HIV-1 RNA concentration (Roche TaqMan 2.0, Roche Diagnostics, Rotkreuz, Switzerland) and single copy assay (SCA) . HIV-1 transcription and the HIV-1 reservoir were assessed by cell-associated HIV-1 RNA (CA-RNA) and DNA (CA-DNA) quantification, intact proviral DNA assays (IPDA), and inducible virus production assays (IVPA).
Pharmacokinetics were assessed following the first dose of treatment. The plasma concentration of vesatolimod was determined by high-performance liquid chromatography tandem mass spectroscopy.
Pharmacodynamics were assessed through biomarkers that measure the downstream effects of TLR7 stimulation. Serum levels of IP-10, IL-1RA, ITAC, and interferon alpha (IFN-α) were quantified using high-sensitivity Ciraplex assays (Aushon Biosystems, Billerica, MA). Messenger RNA levels of interferon-stimulated genes (ISGs; myxovirus resistance 1 (MX1), oligoadenylate synthetase 1 (OAS1), and ISG15) were measured using a quantitative polymerase chain reaction (Covance Genomics Laboratory, Redmond, WA). Quantification of cell populations and cell activation was assessed using flow cytometry (Covance CLS, Indianapolis, IN). HIV antigen–specific T-cell responses to Env, Gag, Nef, and Pol peptides were measured by enzyme-linked immune absorbent spot (Cellular Technology Ltd, Shaker Heights, OH). See the Supplementary Materials for additional information on laboratory assays.
The primary objectives of this trial were: (1) to assess the safety and tolerability of escalating, multiple doses of vesatolimod; and (2) to evaluate the virologic effect of vesatolimod. The virologic endpoint was the maximum change from baseline in plasma log10 HIV-1 RNA at any postdose time point up to 10 days after the final study drug administration.
The secondary objectives were to evaluate the (1) plasma pharmacokinetics of vesatolimod; (2) change from baseline in plasma log10 HIV-1 RNA at postbaseline visits; and (3) the proportion of participants with plasma HIV-1 RNA ≥ 50 copies/mL at any postdose time point.
The exploratory objectives were to evaluate the (1) changes in plasma viremia by SCA and CA-RNA from predose to 2 days postdose at Doses 1, 4, and 6 (for Cohorts 1 to 3) or at Dose 1, 5, and 10 (for Cohorts 4 to 7); and (2) changes in the HIV-1 reservoir, as assessed by changes in CA-DNA, intact proviral DNA by IPDA, or viral production by IVPA in samples taken before the first dose and at the end of the study.
Other endpoints included evaluating (1) changes, percentage changes, and fold changes from baseline in the levels of serum cytokines; (2) fold changes in messenger RNA for ISGs; and (3) changes and percentage changes from baseline in the frequency of activated T cells (CD38+HLA-DR+ CD4+ or CD8+ T cells, and CD69+ CD4+ or CD8+ T cells), the frequency of activated NK cells (CD69+ natural killer [NK] cells), and T-cell responses to HIV-1 peptides.
This study demonstrates that vesatolimod was well tolerated by PLWH up to the highest dose of 12 mg, with no discontinuations due to adverse events. Influenza-like symptoms consistent with innate immune cell activation occurred in a subset of participants, particularly at higher doses, but were mild to moderate in severity and resolved without treatment.
The adverse event profile in this study differed somewhat from that reported in people living without HIV, where higher frequencies of chills, pyrexia, and other adverse events occurred . Participants living without HIV also experienced transient, nongraded platelet decreases and lymphopenia, which were not seen in this study.
Plasma exposures were similar between the 2 populations. However, compared to individuals living without HIV, PLWH had less induction of IFN-α and proinflammatory cytokines, potentially explaining the observed differences in tolerability.
As in most NHP studies, we did not observe consistent evidence of viral expression in plasma or peripheral blood mononuclear cell (PBMC), nor any consistent effect of vesatolimod on the viral reservoir. Vesatolimod has been shown to modestly increase viral production from ex vivo PBMC isolated from ART-suppressed individuals, via a plasmacytoid dendritic cell–/IFN-α–dependent pathway .
Although initial NHP studies in chronically SIV-infected animals confirmed this effect , subsequent NHP studies [13, 21] did not replicate this finding; in the current study, vesatolimod did not induce plasma viremia. Only 1 treated participant had any detectable viral “blips” above 50 copies/mL.
This participant, a 54-year-old man in the 4 mg cohort, treated with abacavir, dolutegravir, and lamivudine, had HIV RNA >50 copies/mL on Day 47 after the fourth dose and on Days 64 and 67 after the fifth dose. Interestingly, this same individual also had a significantly higher CA-DNA level at baseline, suggesting that reactivation may be more readily measurable in individuals with a large HIV reservoir. However, more data are needed to confirm this observation.
Other agents aimed at inducing HIV latency reversal have had mixed results. The TLR9 agonist lefitolimod was associated with immune activation and transient plasma viremia in a small cohort of PLWH, although relatedness to the drug was not established due to the lack of a control group . Similarly, studies of histone deacetylase inhibitors such as romidepsin have inconsistently reported the induction of plasma viral blips [23, 24]. None of these trials have shown reductions in total HIV CA-DNA or quantitative viral outgrowth assay, suggesting that a combination of approaches will be needed to eliminate the reservoir.
Although we did not observe consistent viral transcription, immune modulatory activity of vesatolimod was clearly detected. The most sensitive indicator of the pharmacodynamic activity of vesatolimod was the expression of ISGs. These were detectable at doses lower than those required to induce IFN-α production in peripheral blood, consistent with previous reports of the “presystemic” activity of vesatolimod [10, 19].
These data support the idea that oral administration of vesatolimod can result in local exposure of TLR7-responsive cells (such as plasmacytoid dendritic cells) in the gut-associated lymphoid tissue, liver, and mesenteric lymph nodes, which in turn release IFN-α primarily in these compartments . Other cytokines/chemokines, such as IP-10, IL-1RA, and ITAC, were more readily measured in blood after vesatolimod dosing. IP-10 and ITAC promote the recruitment of activated lymphocytes to sites of inflammation and are associated with gut epithelial barrier dysfunction and persistent activation even during ART suppression .
NHP studies suggest that vesatolimod may enhance the efficacy of therapeutic vaccines and broadly neutralizing antibodies, even in the absence of peripheral viral reactivation . The mechanism leading to this effect is unknown, but it is plausible that vesatolimod-induced cellular activation may improve the efficacy of other agents. In the current study, vesatolimod increased the frequency of activated NK cells. A similar rise in activated CD4+ and CD8+ T cells was seen; however, HIV-specific T-cell responses did not appreciably increase. This is consistent with a NHP study reporting a lack of virus-specific T-cell responses in animals on ART .
Notably, in NHP, virus-specific T-cell responses increase when vesatolimod is dosed during the viral rebound phase. Although in vitro vesatolimod treatment of PBMCs from donors living with HIV can activate HIV-specific CD8+ T-cell responses , antigen exposure may be needed in addition to vesatolimod administration in order to prime virus-specific CD8+ T cells and enhance their responses in vivo.
Therapeutic T-cell vaccines may potentially accomplish a similar goal: in a study by Borducchi et al , a recombinant adenovirus serotype 26 (Ad26)/modified vaccinia ankara (MVA) SIV vaccine led to CD8-mediated postrebound viral control in a subset of animals only when combined with a TLR7 agonist. Ultimately, the role of vesatolimod in augmenting efficacy may depend on the partner agent. For example, the improved antiviral/reservoir-targeting activity of a broadly neutralizing antibody (PGT121) in SHIV infection could be linked to the vesatolimod-mediated upregulation of CD16 (FcyRIII) in myeloid cell populations [12, 13].
Interestingly, vesatolimod immunomodulatory effects were higher at 8 mg than at 10/12 mg, a phenomenon that was not observed in healthy volunteers . This may be due to the kinetics of immune activation, which peaks 12 hours after dosing and may not be fully captured at 24 hours. Alternatively, immune activation resulting from higher doses of vesatolimod, combined with the persistent immune activation of chronic HIV infection,  may trigger counterregulatory mechanisms, leading to immune response downregulation. Ultimately, more data are needed to determine the optimal immunomodulatory dose of vesatolimod in PLWH.
Limitations of this study include the small sizes of the treatment cohorts, limited plasma sampling time points, and lack of tissue sampling. The low enrollment of women limits the generalizability of the results, since TLR7 expression can differ based on gender . Heterogeneity of clinical characteristics (such as durations of HIV infection and ART suppression and time to ART initiation) may have also impacted the overall variability of responses to vesatolimod.
In conclusion, vesatolimod was safe and well tolerated in ART-suppressed PLWH. The immunomodulatory effects of vesatolimod, in combination with other agents, have the potential to play a role in a finite treatment strategy for HIV infection. Trials evaluating the efficacy of vesatolimod in combination with other agents in the context of antiretroviral analytical treatment interruption are ongoing.
reference link : https://academic.oup.com/cid/article/72/11/e815/5921029
More information: Devi SenGupta et al, The TLR7 agonist vesatolimod induced a modest delay in viral rebound in HIV controllers after cessation of antiretroviral therapy, Science Translational Medicine (2021). DOI: 10.1126/scitranslmed.abg3071