Factors associated with viral rebound in HIV-1-infected individuals enrolled in a therapeutic HIV-1 gag vaccine trial

Design of multivalent-epitope vaccine models directed toward the world's population against HIV-Gag polyprotein: Reverse vaccinology and immunoinformatics

Significant progress has been made in HIV-1 research; however, researchers have not yet achieved the objective of eradicating HIV-1 infection. Accordingly, in this study, eucaryotic and procaryotic in silico vaccines were developed for HIV-Gag polyproteins from 100 major HIV subtypes and CRFs using immunoinformatic techniques to simulate immune responses in mice and humans. The epitopes located in the conserved domains of the Gag polyprotein were evaluated for allergenicity, antigenicity, immunogenicity, toxicity, homology, topology, and IFN-γ induction. Adjuvants, linkers, CTLs, HTLs, and BCL epitopes were incorporated into the vaccine models. Strong binding affinities were detected between HLA/MHC alleles, TLR-2, TLR-3, TLR-4, TLR-7, and TLR-9, and vaccine models. Immunological simulation showed that innate and adaptive immune cells elicited active and consistent responses. The human vaccine model was matched with approximately 93.91% of the human population. The strong binding of the vaccine to MHC/HLA and TLR molecules was confirmed through molecular dynamic stimulation. Codon optimization ensured the successful translation of the designed constructs into human cells and E. coli hosts. We believe that the HIV-1 Gag vaccine formulated in our research can reduce the challenges faced in developing an HIV-1 vaccine. Nevertheless, experimental verification is necessary to confirm the effectiveness of these vaccines in these models.

An evidence map of randomised controlled trials evaluating genetic therapies

OBJECTIVES

Genetic therapies replace or inactivate disease-causing genes or introduce new or modified genes. These therapies have the potential to cure in a single application rather than treating symptoms through repeated administrations. This evidence map provides a broad overview of the genetic therapies that have been evaluated in randomised controlled trials (RCTs) for efficacy and safety.

ELIGIBILITY CRITERIA

Two independent reviewers screened publications using predetermined eligibility criteria. Study details and data on safety and efficacy were abstracted from included trials. Results were visualised in an evidence map.

INFORMATION SOURCES

We searched PubMed, EMBASE, Web of Science, ClinicalTrials.gov and grey literature to November 2018.

RISK OF BIAS

Only RCTs were included in this review to reduce the risk of selection bias in the evaluation of genetic therapy safety and efficacy.

INCLUDED STUDIES

We identified 119 RCTs evaluating genetic therapies for a variety of clinical conditions.

SYNTHESIS OF RESULTS

On average, samples included 107 participants (range: 1-1022), and were followed for 15 months (range: 0-124). Interventions using adenoviruses (40%) to treat cardiovascular diseases (29%) were the most common.

DESCRIPTION OF THE EFFECT

In RCTs reporting safety and efficacy outcomes, in the majority (60%) genetic therapies were associated with improved symptoms but in nearly half (45%) serious adverse event (SAEs) were also reported. Improvement was reported in trials treating cancer, cardiovascular, ocular and muscular diseases. However, only 19 trials reported symptom improvement for at least 1 year.

STRENGTHS AND LIMITATIONS OF EVIDENCE

This is the first comprehensive evidence map of RCTs evaluating the safety and efficacy of genetic therapies. Evidence for long-term effectiveness and safety is still sparse. This lack of evidence has implications for the use, ethics, pricing and logistics of genetic therapies.

INTERPRETATION

This evidence map provides a broad overview of research studies that allow strong evidence statements regarding the safety and efficacy of genetic therapies. Most interventions improve symptoms, but SAE are also common. More research is needed to evaluate genetic therapies with regard to the potential to cure diseases.

Antiretroviral Therapy Interruption (ATI) in HIV-1 Infected Patients Participating in Therapeutic Vaccine Trials: Surrogate Markers of Virological Response

A functional Human immunodeficiency Virus (HIV) cure has been proposed as an alternative to antiretroviral treatment for life, and therapeutic vaccines represent one of the most promising approaches. The goal of therapeutic vaccination is to augment virus-specific immune responses that have an impact on HIV viral load dynamics. To date, the agreed feature to evaluate the effects of these therapeutic interventions is analytical antiretroviral treatment interruption (ATI), at least until we find a reliable biomarker that can predict viral control. Different host, immunologic, and virologic markers have been proposed as predictors of viral control during ATI after therapeutic interventions. This review describes the relevance of ATI and the different surrogate markers of virological control assessed in HIV therapeutic vaccine clinical trials.

Modulation of immune responses using adjuvants to facilitate therapeutic vaccination

Therapeutic vaccination offers great promise as an intervention for a diversity of infectious and non-infectious conditions. Given that most chronic health conditions are thought to have an immune component, vaccination can at least in principle be proposed as a therapeutic strategy. Understanding the nature of protective immunity is of vital importance, and the progress made in recent years in defining the nature of pathological and protective immunity for a range of diseases has provided an impetus to devise strategies to promote such responses in a targeted manner. However, in many cases, limited progress has been made in clinical adoption of such approaches. This in part results from a lack of safe and effective vaccine adjuvants that can be used to promote protective immunity and/or reduce deleterious immune responses. Although somewhat simplistic, it is possible to divide therapeutic vaccine approaches into those targeting conditions where antibody responses can mediate protection and those where the principal focus is the promotion of effector and memory cellular immunity or the reduction of damaging cellular immune responses as in the case of autoimmune diseases. Clearly, in all cases of antigen-specific immunotherapy, the identification of protective antigens is a vital first step. There are many challenges to developing therapeutic vaccines beyond those associated with prophylactic diseases including the ongoing immune responses in patients, patient heterogeneity, and diversity in the type and stage of disease. If reproducible biomarkers can be defined, these could allow earlier diagnosis and intervention and likely increase therapeutic vaccine efficacy. Current immunomodulatory approaches related to adoptive cell transfers or passive antibody therapy are showing great promise, but these are outside the scope of this review which will focus on the potential for adjuvanted therapeutic active vaccination strategies.

Analytical Treatment Interruption after Short-Term Antiretroviral Therapy in a Postnatally Simian-Human Immunodeficiency Virus-Infected Infant Rhesus Macaque Model

To achieve long-term viral remission in human immunodeficiency virus (HIV)-infected children, novel strategies beyond early antiretroviral therapy (ART) will be necessary. Identifying clinical predictors of the time to viral rebound upon ART interruption will streamline the development of novel therapeutic strategies and accelerate their evaluation in clinical trials. However, identification of these biomarkers is logistically challenging in infants, due to sampling limitations and the potential risks of treatment interruption. To facilitate the identification of biomarkers predicting viral rebound, we have developed an infant rhesus macaque (RM) model of oral simian-human immunodeficiency virus (SHIV) SHIV.CH505.375H.dCT challenge and analytical treatment interruption (ATI) after short-term ART. We used this model to characterize SHIV replication kinetics and virus-specific immune responses during short-term ART or after ATI and demonstrated plasma viral rebound in 5 out of 6 (83%) infants. We observed a decline in humoral immune responses and partial dampening of systemic immune activation upon initiation of ART in these infants. Furthermore, we monitored SHIV replication and rebound kinetics in infant and adult RMs and found that both infants and adults demonstrated equally potent virus-specific humoral immune responses. Finally, we validated our models by confirming a well-established correlate of the time to viral rebound, namely, the pre-ART plasma viral load, as well as identified additional potential humoral immune correlates. Thus, this model of infant ART and viral rebound can be used and further optimized to define biomarkers of viral rebound following long-term ART as well as to preclinically assess novel therapies to achieve a pediatric HIV functional cure.IMPORTANCE Novel interventions that do not rely on daily adherence to ART are needed to achieve sustained viral remission for perinatally infected children, who currently rely on lifelong ART. Considering the risks and expense associated with ART interruption trials, the identification of biomarkers of viral rebound will prioritize promising therapeutic intervention strategies, including anti-HIV Env protein therapeutics. However, comprehensive studies to identify those biomarkers are logistically challenging in human infants, demanding the need for relevant nonhuman primate models of HIV rebound. In this study, we developed an infant RM model of oral infection with simian-human immunodeficiency virus expressing clade C HIV Env and short-term ART followed by ATI, longitudinally characterizing the immune responses to viral infection during ART and after ATI. Additionally, we compared this infant RM model to an analogous adult RM rebound model and identified virologic and immunologic correlates of the time to viral rebound after ATI.

Therapeutic vaccination for HIV: hopes and challenges

PURPOSE OF REVIEW

This review summarizes the recent landscape of HIV therapeutic vaccine research, emphasizing the results of randomized controlled trials that included analytical treatment interruption (ATI) to assess efficacy.

RECENT FINDINGS

Therapeutic vaccines for HIV are designed to re-educate the host immune response in HIV-infected individuals to better control viral replication in the absence of antiretroviral therapy. No therapeutic vaccine has yet to induce long-term HIV remission following ATI in a randomized controlled trial. This is likely because the vaccines have not elicited a broad enough immune response to suppress the diverse escape variants that emerge during viral rebound, and have not been used with effective agents to reduce the HIV reservoir. Recent studies in nonhuman primates using combination approaches are showing significant successes, with several candidates eliciting significant antiviral activity following ATI. Future studies pairing these vaccines with effective reservoir reduction hold great promise.

SUMMARY

Therapeutic vaccines aim to modulate the immune system of HIV-infected individuals to elicit sustained virologic control in the absence of antiretroviral therapy. Therapeutic vaccines that elicit broad immune responses have recently shown promise in randomized controlled trials and nonhuman primate studies.

Requirements for Empirical Immunogenicity Trials, Rather than Structure-Based Design, for Developing an Effective HIV Vaccine

The claim that it is possible to rationally design a structure-based HIV-1 vaccine is based on misconceptions regarding the nature of protein epitopes and of immunological specificity. Attempts to use reverse vaccinology to generate an HIV-1 vaccine on the basis of the structure of viral epitopes bound to monoclonal neutralizing antibodies have failed so far because it was not possible to extrapolate from an observed antigenic structure to the immunogenic structure required in a vaccine. Vaccine immunogenicity depends on numerous extrinsic factors such as the host immunoglobulin gene repertoire, the presence of various cellular and regulatory mechanisms in the immunized host and the process of antibody affinity maturation. All these factors played a role in the appearance of the neutralizing antibody used to select the epitope to be investigated as potential vaccine immunogen, but they cannot be expected to be present in identical form in the host to be vaccinated. It is possible to rationally design and optimize an epitope to fit one particular antibody molecule or to improve the paratope binding efficacy of a monoclonal antibody intended for passive immunotherapy. What is not possible is to rationally design an HIV-1 vaccine immunogen that will elicit a protective polyclonal antibody response of predetermined efficacy. An effective vaccine immunogen can only be discovered by investigating experimentally the immunogenicity of a candidate molecule and demonstrating its ability to induce a protective immune response. It cannot be discovered by determining which epitopes of an engineered antigen molecule are recognized by a neutralizing monoclonal antibody. This means that empirical immunogenicity trials rather than structural analyses of antigens offer the best hope of discovering an HIV-1 vaccine.

Perspectives for immunotherapy: which applications might achieve an HIV functional cure?

The major advances achieved in devising successful combined antiretroviral therapy (cART) have enabled the sustained control of HIV replication. However, this is associated with costly lifelong treatment, partial immune restoration, chronic inflammation and persistent viral reservoirs. In this context, new therapeutic strategies deserve investigation as adjuncts to cART so as to potentiate immune responses that are capable of completely containing HIV pathogenicity, particularly if cART is discontinued. This may seem a dauntingly high hurdle given the results to date. This review outlines the key research efforts that have recently resurrected immunotherapeutic options, and some of the approaches tested to date. These areas include promising cytokines or vaccine strategies, using different viral or non-viral vectors based on polyvalent “mosaic” antigens and highly conserved HIV envelope peptides, broadly neutralizing antibodies or new properties of antibodies to improve the control of immune system homeostasis. These novel immunotherapeutic strategies appear promising per se, or in combination with TLR-agonists in order to bypass the complexity of the interplay between immune activation, massive CD4⁺ T-cell loss and viral persistence.

Evaluation of the immunogenicity and impact on the latent HIV-1 reservoir of a conserved region vaccine, MVA.HIVconsv, in antiretroviral therapy-treated subjects

Introduction: Vaccines may be key components of a curative strategy for HIV-1. We investigated whether a novel immunogen, HIVconsv, designed to re-direct T cell responses to conserved viral epitopes, could impact the HIV-1 reservoir in chronic antiretroviral therapy (ART)-treated subjects when delivered by modified vaccinia virus Ankara (MVA).

Methods: Nineteen virologically suppressed individuals were randomized to receive vaccinations with MVA.HIVconsv (5.5 × 10⁷ plaque-forming units, pfu, n = 8; 2.2 × 10⁸ pfu, n = 7) or placebo (n = 4) at 0, 4 and 12 weeks. Magnitude, breadth and antiviral function of vaccine-induced T cells, cell-associated HIV-1 DNA in circulating CD4+ T cells and residual viremia in plasma were measured before and after vaccination.

Results: 90% of subjects completed the vaccine regimen; there were no serious vaccine-related adverse events. The magnitude of HIVconsv-specific IFN-γ-secreting T cells was not significantly boosted in vaccinees when compared with placebos in ex vivo Elispot assays, due to greater than expected variation in HIV-specific T cell responses in the latter during the observation period. Ex vivo CD8+ T cell viral inhibitory capacity was modest but significantly increased post-vaccination with MVA.HIVconsv at the higher dose (p = 0.004) and was positively correlated with the frequency of HIVconsv-specific CD8+ CD107+ IFN-α± T cells (r = 0.57, p = 0.01). Total HIV-1 DNA and residual viral load did not change significantly from baseline in any group.

Conclusions: Homologous prime-boost vaccination with MVA.HIVconsv was safe in HIV-positive ART-treated subjects but showed modest immunogenicity and did not significantly change the size of the viral reservoir. MVA.HIVconsv may be more effective when used in a heterologous prime-boost vaccination regimen and when combined with a latency-reversing agent.

Clinical Trials Registration NCT01024842

Virological and immunological outcome of treatment interruption in HIV-1-infected subjects vaccinated with MVA-B

The most relevant endpoint in therapeutic HIV vaccination is the assessment of time to viral rebound or duration of sustained control of low-level viremia upon cART treatment cessation. Structured treatment interruptions (STI) are however not without risk to the patient and reliable predictors of viral rebound/control after therapeutic HIV-1 vaccination are urgently needed to ensure patient safety and guide therapeutic vaccine development. Here, we integrated immunological and virological parameters together with viral rebound dynamics after STI in a phase I therapeutic vaccine trial of a polyvalent MVA-B vaccine candidate to define predictors of viral control. Clinical parameters, proviral DNA, host HLA genetics and measures of humoral and cellular immunity were evaluated. A sieve effect analysis was conducted comparing pre-treatment viral sequences to breakthrough viruses after STI. Our results show that a reduced proviral HIV-1 DNA at study entry was independently associated with two virological parameters, delayed HIV-1 RNA rebound (p = 0.029) and lower peak viremia after treatment cessation (p = 0.019). Reduced peak viremia was also positively correlated with a decreased number of HLA class I allele associated polymorphisms in Gag sequences in the rebounding virus population (p = 0.012). Our findings suggest that proviral DNA levels and the number of HLA-associated Gag polymorphisms may have an impact on the clinical outcome of STI. Incorporation of these parameters in future therapeutic vaccine trials may guide refined immunogen design and help conduct safer STI approaches.

Ad26/MVA therapeutic vaccination with TLR7 stimulation in SIV-infected rhesus monkeys

The development of immunologic interventions that can target the viral reservoir in HIV-1-infected individuals is a major goal of the HIV-1 cure field^1,2. However, little evidence exists that the viral reservoir can be sufficiently targeted to improve virologic control following discontinuation of antiretroviral therapy (ART). Here we show that Ad26/MVA^3,4 therapeutic vaccination with toll-like receptor 7 (TLR7) stimulation improves virologic control and delays viral rebound following ART discontinuation in SIV-infected rhesus monkeys that initiated ART during acute infection. Ad26/MVA therapeutic vaccination resulted in a dramatic increase in the magnitude and breadth of SIV-specific cellular immune responses in virologically suppressed, SIV-infected monkeys. TLR7 agonist administration led to innate immune stimulation and cellular immune activation. The combination of Ad26/MVA vaccination and TLR7 stimulation resulted in decreased levels of viral DNA in lymph nodes and peripheral blood, as well as improved virologic control and delayed viral rebound following ART discontinuation. Cellular immune breadth correlated inversely with setpoint viral loads and correlated directly with time to viral rebound. These data demonstrate the potential of therapeutic vaccination with innate immune stimulation as a strategy aimed at an HIV-1 functional cure.

Viremic control and viral coreceptor usage in two HIV-1-infected persons homozygous for CCR5 Δ32

OBJECTIVES

To determine viral and immune factors involved in transmission and control of HIV-1 infection in persons without functional CCR5.

DESIGN

Understanding transmission and control of HIV-1 in persons homozygous for CCR5(Δ32) is important given efforts to develop HIV-1 curative therapies aimed at modifying or disrupting CCR5 expression.

METHODS

We identified two HIV-infected CCR5(Δ32/Δ32) individuals among a cohort of patients with spontaneous control of HIV-1 infection without antiretroviral therapy and determined coreceptor usage of the infecting viruses. We assessed genetic evolution of full-length HIV-1 envelope sequences by single-genome analysis from one participant and his sexual partner, and explored HIV-1 immune responses and HIV-1 mutations following virologic escape and disease progression.

RESULTS

Both participants experienced viremia of less than 4000 RNA copies/ml with preserved CD4(+) T-cell counts off antiretroviral therapy for at least 3.3 and 4.6 years after diagnosis, respectively. One participant had phenotypic evidence of X4 virus, had no known favorable human leukocyte antigen alleles, and appeared to be infected by minority X4 virus from a pool that predominately used CCR5 for entry. The second participant had virus that was unable to use CXCR4 for entry in phenotypic assay but was able to engage alternative viral coreceptors (e.g., CXCR6) in vitro.

CONCLUSION

Our study demonstrates that individuals may be infected by minority X4 viruses from a population that predominately uses CCR5 for entry, and that viruses may bypass traditional HIV-1 coreceptors (CCR5 and CXCR4) completely by engaging alternative coreceptors to establish and propagate HIV-1 infection.

Safety and immunogenicity of a modified vaccinia Ankara-based HIV-1 vaccine (MVA-B) in HIV-1-infected patients alone or in combination with a drug to reactivate latent HIV-1

OBJECTIVES

The safety, immunogenicity, impact on the latent reservoir and rebound of viral load after therapeutic HIV-1 vaccination with recombinant modified vaccinia Ankara-based (MVA-B) HIV-1 vaccine expressing monomeric gp120 and the fused Gag-Pol-Nef polyprotein of clade B with or without a drug to reactivate latent HIV-1 (disulfiram) were assessed.

METHODS

HIV-1-infected patients were randomized to receive three injections of MVA-B (n = 20) or placebo (n = 10). Twelve patients (eight who received vaccine and four who were given placebo) received a fourth dose of MVA-B followed by 3 months of disulfiram. Combined ART (cART) was discontinued 8 weeks after the last dose of MVA-B. Clinical Trials.gov identifier: NCT01571466.

RESULTS

MVA-B was safe and well tolerated. A minor, but significant, increase in the T cell responses targeting vaccine inserts of Gag was observed [a median of 290, 403 and 435 spot-forming-cells/10(6) PBMCs at baseline, after two vaccinations and after three vaccinations, respectively; P = 0.02 and P = 0.04]. After interruption of cART, a modest delay in the rebound of the plasma viral load in participants receiving vaccine but not disulfiram was observed compared with placebo recipients (P = 0.01). The dynamics of the viral load rebound did not change in patients receiving MVA-B/disulfiram. No changes in the proviral reservoir were observed after disulfiram treatment.

CONCLUSIONS

MVA-B vaccination was a safe strategy to increase Gag-specific T cell responses in chronically HIV-1-infected individuals, but it did not have a major impact on the latent reservoir or the rebound of plasma viral load after interruption of cART when given alone or in combination with disulfiram.

Relationship of HIV reservoir characteristics with immune status and viral rebound kinetics in an HIV therapeutic vaccine study

OBJECTIVES

The objective of this study is to evaluate the impact of therapeutic HIV vaccination on the HIV reservoir and assess the relationship of the viral reservoir with HIV-specific immune status and viral rebound kinetics.

DESIGN

A retrospective analysis of ACTG A5197, a randomized, placebo-controlled trial of a therapeutic rAd5 HIV-1 gag vaccine.

METHODS

Participants received vaccine/placebo at weeks 0, 4 and 26 prior to a 16-week analytic treatment interruption (ATI) at week 38. Cell-associated HIV-1 RNA and DNA (CA-RNA and CA-DNA) and HIV-1 residual viremia were quantified at weeks 0, 8 and 38. HIV-specific CD4(+)/CD8(+) activity was assessed by an intracellular cytokine staining assay.

RESULTS

At study entry, CA-RNA and CA-DNA levels were correlated inversely with the numbers of HIV-specific CD4(+) interferon-γ producing cells (CA-RNA: r = -0.23, P = 0.03 and CA-DNA: r = -0.28, P < 0.01, N = 93). Therapeutic HIV vaccination induced HIV-specific CD4(+) activity, but did not significantly affect levels of CA-RNA or CA-DNA. Vaccine recipients with undetectable residual viremia at week 8 had higher frequencies of HIV-specific CD4(+) and CD8(+) interferon-γ producing cells (undetectable versus detectable residual viremia: 277 versus 161 CD4(+) cells/10(6) lymphocytes, P = 0.03 and 1326 versus 669 CD8(+) cells/10 lymphocytes, P = 0.04). Pre-ATI CA-RNA and CA-DNA were associated with post-ATI plasma HIV set point (CA-RNA: r = 0.51, P < 0.01 and CA-DNA: r = 0.47, P < 0.01).

CONCLUSION

Vaccine-induced T-cell responses were associated with a modest transient effect on residual viremia, but more potent immune responses and/or combination treatment with latency-reversing agents are needed to reduce the HIV reservoir. HIV reservoir measures may act as biomarkers of post-ATI viral rebound kinetics.

CLINICAL TRIALS REGISTRATION

NCT00080106.

Safety and efficacy of the peptide-based therapeutic vaccine for HIV-1, Vacc-4x: a phase 2 randomised, double-blind, placebo-controlled trial

BACKGROUND

Present combination antiretroviral therapy (cART) alone does not cure HIV infection and requires lifelong drug treatment. The potential role of HIV therapeutic vaccines as part of an HIV cure is under consideration. Our aim was to assess the efficacy, safety, and immunogenicity of Vacc-4x, a peptide-based HIV-1 therapeutic vaccine targeting conserved domains on p24(Gag), in adults infected with HIV-1.

METHODS

Between July, 2008, and June, 2010, we did a multinational double-blind, randomised, phase 2 study comparing Vacc-4x with placebo. Participants were adults infected with HIV-1 who were aged 18-55 years and virologically suppressed on cART (viral load <50 copies per mL) with CD4 cell counts of 400 × 10(6) cells per L or greater. The trial was done at 18 sites in Germany, Italy, Spain, the UK, and the USA. Participants were randomly assigned (2:1) to Vacc-4x or placebo. Group allocation was masked from participants and investigators. Four primary immunisations, weekly for 4 weeks, containing Vacc-4x (or placebo) were given intradermally after administration of adjuvant. Booster immunisations were given at weeks 16 and 18. At week 28, cART was interrupted for up to 24 weeks. The coprimary endpoints were cART resumption and changes in CD4 counts during treatment interruption. Analyses were by modified intention to treat: all participants who received one intervention. Furthermore, safety, viral load, and immunogenicity (as measured by ELISPOT and proliferation assays) were assessed. The 52 week follow-up period was completed in June, 2011. For the coprimary endpoints the proportion of participants who met the criteria for cART resumption was analysed with a logistic regression model with the treatment effect being assessed in a model including country as a covariate. This study is registered with ClinicalTrials.gov, number NCT00659789.

FINDINGS

174 individuals were screened; because of slow recruitment, enrolment stopped with 136 of a planned 345 participants and 93 were randomly assigned to receive Vacc-4x and 43 to receive placebo. There were no differences between the two groups for the primary efficacy endpoints in those participants who stopped cART at week 28. Of the participants who resumed cART, 30 (34%) were in the Vacc-4x group and 11 (29%) in the placebo group, and percentage changes in CD4 counts were not significant (mean treatment difference -5·71, 95% CI -13·01 to 1·59). However, a significant difference in viral load was noted for the Vacc-4x group both at week 48 (median 23,100 copies per mL Vacc-4x vs 71,800 copies per mL placebo; p=0·025) and week 52 (median 19,550 copies per mL vs 51,000 copies per mL; p=0·041). One serious adverse event, exacerbation of multiple sclerosis, was reported as possibly related to study treatment. Vacc-4x was immunogenic, inducing proliferative responses in both CD4 and CD8 T-cell populations.

INTERPRETATION

The proportion of participants resuming cART before end of study and change in CD4 counts during the treatment interruption showed no benefit of vaccination. Vacc-4x was safe, well tolerated, immunogenic, seemed to contribute to a viral-load setpoint reduction after cART interruption, and might be worth consideration in future HIV-cure investigative strategies.

FUNDING

Norwegian Research Council GLOBVAC Program and Bionor Pharma ASA.

Temporal association between incident tuberculosis and poor virological outcomes in a South African antiretroviral treatment service

Introduction:

The temporal relationship between incident tuberculosis (TB) and virological outcomes during antiretroviral therapy (ART) is poorly defined. This was studied in a cohort in Cape Town, South Africa.

Methods:

Data regarding TB diagnoses, ART regimens, and 4-monthly updated viral load (VL) and CD4 count measurements were extracted from a prospectively maintained database. Rates of virological breakthrough (VL > 1000 copies/mL) and failure (VL > 1000 copies/mL on serial measurements) following initial VL suppression were calculated. Poisson models were used to calculate incidence rate ratios (IRRs) and identify risk factors for these virological outcomes.

Results:

Incident TB was diagnosed in 391 (28.5%) of 1370 patients during a median of 5.2 years follow-up. Five hundred seventy-eight episodes of virological breakthrough and 231 episodes of virological failure occurred, giving rates of 10.0 episodes per 100 person-years and 4.0 episodes per 100 person-years, respectively. In multivariate analyses adjusted for baseline and time-updated risk factors, TB was an independent risk factor for adverse virological outcomes. These associations were strongly time dependent; the 6-month period following diagnosis of incident TB was associated with a substantially increased risk of virological breakthrough (IRR: 2.3, 95% confidence interval: 1.7 to 3.2) and failure (IRR: 2.6, 95% confidence interval: 1.6 to 4.3) compared with time without a TB diagnosis. Person-time preceding TB diagnosis or more than 6 months after a TB diagnosis was not associated with poor virological outcomes.

Conclusions:

Incident TB during ART was strongly associated with poor virological outcomes during the 6-month period following TB diagnosis. Although underlying mechanisms remain to be defined, patients with incident TB may benefit from virological monitoring and treatment adherence support.

Vaccine and immunotherapeutic interventions

PURPOSE OF REVIEW

As we enter the fourth decade in HIV epidemic, advances in understanding HIV pathogenesis and development of potent and safer antiretroviral drugs have been spectacular. More than 30 antiviral drugs have been registered and the impact of combination antiviral therapy on morbidity and mortality has been dramatic. However, despite long-term virus suppression, HIV invariably rebounds after interruption of therapy. Long-term antiviral therapy does not cure HIV infection nor does it induce restoration/development of virus-specific immune responses capable of controlling HIV replication. Therefore, development of immune-based interventions is needed to restore effective defenses that can lead to HIV functional cure and ultimately eradication.

RECENT FINDINGS

Therapeutic vaccination and immune interventions that generate de-novo or that boost preexisting HIV-specific T-cell responses are being investigated as a potential means to achieve a 'functional HIV cure'. One major hurdle in the quest of an HIV cure is control and elimination of the HIV latent reservoir. Several immune interventions that target the latent reservoir have been tried in recent years. In parallel, several therapeutic vaccination strategies have been developed and tested in early clinical studies. Recent encouraging studies show for the first time that vaccination can have an impact on HIV load.

SUMMARY

This review summarizes the main immune interventions evaluated over the last years. Ways to improve them, as well as challenges in monitoring/evaluating effects of such strategies, are being discussed. In addition, clinical efficacy and potential clinical benefits of immunotherapeutic interventions are particularly difficult to measure. This review highlights current assays used and their shortcoming.

Controlling the HIV/AIDS epidemic: current status and global challenges

This review provides an overview of the current status of the global HIV pandemic and strategies to bring it under control. It updates numerous preventive approaches including behavioral interventions, male circumcision (MC), pre- and post-exposure prophylaxis (PREP and PEP), vaccines, and microbicides. The manuscript summarizes current anti-retroviral treatment options, their impact in the western world, and difficulties faced by emerging and resource-limited nations in providing and maintaining appropriate treatment regimens. Current clinical and pre-clinical approaches toward a cure for HIV are described, including new drug compounds that target viral reservoirs and gene therapy approaches aimed at altering susceptibility to HIV infection. Recent progress in vaccine development is summarized, including novel approaches and new discoveries.

Therapeutic vaccines against HIV infection

Resistance to medication, adverse effects in the medium-to-long-term and cost all place important limitations on lifelong adherence to combined antiretroviral therapy (cART). In this context, new therapeutic alternatives to 'cART for life' in HIV-infected patients merit investigation. Some data suggest that strong T cell-mediated immunity to HIV can indeed limit virus replication and protect against CD4 depletion and disease progression. The combination of cART with immune therapy to restore and/or boost immune-specific responses to HIV has been proposed, the ultimate aim being to achieve a 'functional cure'. In this scenario, new, induced, HIV-specific immune responses would be able to control viral replication to undetectable levels, mimicking the situation of the minority of patients who control viral replication without treatment and do not progress to AIDS. Classical approaches such as whole inactivated virus or recombinant protein initially proved useful as therapeutic vaccines. Overall, however, the ability of these early vaccines to increase HIV-specific responses was very limited and study results were discouraging, as no consistent immunogenicity was demonstrated and there was no clear impact on viral load. Recent years have seen the development of new approaches based on more innovative vectors such as DNA, recombinant virus or dendritic cells. Most clinical trials of these new vectors have demonstrated their ability to induce HIV-specific immune responses, although they show very limited efficacy in terms of controlling viral replication. However, some preliminary results suggest that dendritic cell-based vaccines are the most promising candidates. To improve the effectiveness of these vaccines, a better understanding of the mechanisms of protection, virological control and immune deterioration is required; without this knowledge, an efficacious therapeutic vaccine will remain elusive.

Characteristics and outcomes of initial virologic suppressors during analytic treatment interruption in a therapeutic HIV-1 gag vaccine trial

BACKGROUND

In the placebo-controlled trial ACTG A5197, a trend favoring viral suppression was seen in the HIV-1-infected subjects who received a recombinant Ad5 HIV-1 gag vaccine.

OBJECTIVE

To identify individuals with initial viral suppression (plasma HIV-1 RNA set point <3.0 log(10) copies/ml) during the analytic treatment interruption (ATI) and evaluate the durability and correlates of virologic control and characteristics of HIV sequence evolution.

METHODS

HIV-1 gag and pol RNA were amplified and sequenced from plasma obtained during the ATI. Immune responses were measured by flow cytometric analysis and intracellular cytokine expression assays. Characteristics of those with and without initial viral suppression were compared using the Wilcoxon rank sum and Fisher's exact tests.

RESULTS

Eleven out of 104 participants (10.6%) were classified as initial virologic suppressors, nine of whom had received the vaccine. Initial virologic suppressors had significantly less CD4+ cell decline by ATI week 16 as compared to non-suppressors (median 7 CD4+ cell gain vs. 247 CD4+ cell loss, P = 0.04). However, of the ten initial virologic suppressors with a pVL at ATI week 49, only three maintained pVL <3.0 log(10) copies/ml. HIV-1 Gag-specific CD4+ interferon-γ responses were not associated with initial virologic suppression and no evidence of vaccine-driven HIV sequence evolution was detected. Participants with initial virologic suppression were found to have a lower percentage of CD4+ CTLA-4+ cells prior to treatment interruption, but a greater proportion of HIV-1 Gag-reactive CD4+ TNF-α+ cells expressing either CTLA-4 or PD-1.

CONCLUSIONS

Among individuals participating in a rAd5 therapeutic HIV-1 gag vaccine trial, initial viral suppression was found in a subset of patients, but this response was not sustained. The association between CTLA-4 and PD-1 expression on CD4+ T cells and virologic outcome warrants further study in trials of other therapeutic vaccines in development.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00080106.

Effect of therapeutic HIV recombinant poxvirus vaccines on the size of the resting CD4+ T-cell latent HIV reservoir

OBJECTIVES

Therapeutic HIV vaccinations may alter the size of the resting memory CD4 T-cell latent HIV reservoir as HIV establishes latency when memory responses are formed, including those toward HIV. Alternatively, latently infected CD4 T cells maybe killed, while exiting the reservoir upon activation.

METHODS

The effect of therapeutic immunization with modified vaccinia Ankara and Fowlpox-based HIV vaccines on the latent reservoir was examined in 19 young adults who were receiving effective antiretroviral therapy. Correlations between size of the reservoir [measured in infectious units per million (IUPM)] resting CD4 T cells and HIV-specific immune responses, including immune activation were examined. Decay of the reservoir was assessed using random-effects model.

RESULTS

A modest transient decrease in the size of the reservoir was observed at week 40 [mean -0.31 log(10) IUPM (95% confidence interval: -0.60 to -0.03; P = 0.03] following HIV vaccinations. The estimated half-life (T1/2) of the reservoir during the 40 weeks following vaccination was 9.8 months and statistically different from zero (P = 0.02), but 35.3 months and not different from zero (P = 0.21) over 72 weeks of study. Latent reservoir size at baseline was not correlated with HIV-specific CD4, CD8 responses or immune activation, but became correlated with CD4 IFNγ (r = 0.54, P = 0.02) and IL-2 responses at 6 weeks after immunization (r = 0.48, P = 0.04).

CONCLUSION

Therapeutic HIV vaccinations led to a transient increase in decay of latently infected CD4 T cells. Further studies of therapeutic HIV vaccines may provide important insights into facilitating decay of the latent reservoir.

Requirements for empirical immunogenicity trials, rather than structure-based design, for developing an effective HIV vaccine

The claim that it is possible to rationally design a structure-based HIV-1 vaccine is based on misconceptions regarding the nature of protein epitopes and of immunological specificity. Attempts to use reverse vaccinology to generate an HIV-1 vaccine on the basis of the structure of viral epitopes bound to monoclonal neutralizing antibodies have failed so far because it was not possible to extrapolate from an observed antigenic structure to the immunogenic structure required in a vaccine. Vaccine immunogenicity depends on numerous extrinsic factors such as the host immunoglobulin gene repertoire, the presence of various cellular and regulatory mechanisms in the immunized host and the process of antibody affinity maturation. All these factors played a role in the appearance of the neutralizing antibody used to select the epitope to be investigated as potential vaccine immunogen, but they cannot be expected to be present in identical form in the host to be vaccinated. It is possible to rationally design and optimize an epitope to fit one particular antibody molecule or to improve the paratope binding efficacy of a monoclonal antibody intended for passive immunotherapy. What is not possible is to rationally design an HIV-1 vaccine immunogen that will elicit a protective polyclonal antibody response of predetermined efficacy. An effective vaccine immunogen can only be discovered by investigating experimentally the immunogenicity of a candidate molecule and demonstrating its ability to induce a protective immune response. It cannot be discovered by determining which epitopes of an engineered antigen molecule are recognized by a neutralizing monoclonal antibody. This means that empirical immunogenicity trials rather than structural analyses of antigens offer the best hope of discovering an HIV-1 vaccine.