Overview of STEP and Phambili trial results: two phase IIb test-of-concept studies investigating the efficacy of MRK adenovirus type 5 gag/pol/nef subtype B HIV vaccine. Curr Opin HIV AIDS. 2010;5:357-361. [PMID: 20978374 DOI: 10.1097/coh.0b013e32833d2d2b]

Human Immunodeficiency Virus Vaccine: Promise and Challenges

Development of a safe and effective human immunodeficiency virus (HIV) vaccine is a persistent challenge despite decades of research. Previous strategies utilizing protein subunit and viral vector vaccines were safe but not protective. Current strategies seek to induce broadly neutralizing antibodies, with multiple early phase trials in progress seeking to achieve this through sequential vaccination, mRNA, or updated viral-vectored vaccines. A safe and effective vaccine is critical to ending the HIV epidemic.

Arenavirus-Based Vectors Generate Robust SIV Immunity in Non-Human Primates

Arenavirus-based vectors are being investigated as therapeutic vaccine candidates with the potential to elicit robust CD8 T-cell responses. We compared the immunogenicity of replicating (artPICV and artLCMV) and non-replicating (rPICV and rLCMV) arenavirus-based vectors expressing simian immunodeficiency virus (SIV) Gag and Envelope (Env) immunogens in treatment-naïve non-human primates. Heterologous regimens with non-replicating and replicating vectors elicited more robust SIV IFN-γ responses than a homologous regimen, and replicating vectors elicited significantly higher cellular immunogenicity than non-replicating vectors. The heterologous regimen elicited high anti-Env antibody titers when administered intravenously, with replicating vectors inducing significantly higher titers than non-replicating vectors. Intramuscular immunization resulted in more durable antibody responses than intravenous immunization for both vector platforms, with no difference between the replicating and non-replicating vectors. Overall, both replicating and non-replicating arenavirus vectors generated robust T- and B-cell-mediated immunity to SIV antigens in treatment-naïve non-human primates, supporting further evaluation of these vectors in a clinical setting for HIV therapy.

The Immune System-A Double-Edged Sword for Adenovirus-Based Therapies

Pathogenic adenovirus (Ad) infections are widespread but typically mild and transient, except in the immunocompromised. As vectors for gene therapy, vaccine, and oncology applications, Ad-based platforms offer advantages, including ease of genetic manipulation, scale of production, and well-established safety profiles, making them attractive tools for therapeutic development. However, the immune system often poses a significant challenge that must be overcome for adenovirus-based therapies to be truly efficacious. Both pre-existing anti-Ad immunity in the population as well as the rapid development of an immune response against engineered adenoviral vectors can have detrimental effects on the downstream impact of an adenovirus-based therapeutic. This review focuses on the different challenges posed, including pre-existing natural immunity and anti-vector immunity induced by a therapeutic, in the context of innate and adaptive immune responses. We summarise different approaches developed with the aim of tackling these problems, as well as their outcomes and potential future applications.

Making a Monkey out of Human Immunodeficiency Virus/Simian Immunodeficiency Virus Pathogenesis: Immune Cell Depletion Experiments as a Tool to Understand the Immune Correlates of Protection and Pathogenicity in HIV Infection

Understanding the underlying mechanisms of HIV pathogenesis is critical for designing successful HIV vaccines and cure strategies. However, achieving this goal is complicated by the virus's direct interactions with immune cells, the induction of persistent reservoirs in the immune system cells, and multiple strategies developed by the virus for immune evasion. Meanwhile, HIV and SIV infections induce a pandysfunction of the immune cell populations, making it difficult to untangle the various concurrent mechanisms of HIV pathogenesis. Over the years, one of the most successful approaches for dissecting the immune correlates of protection in HIV/SIV infection has been the in vivo depletion of various immune cell populations and assessment of the impact of these depletions on the outcome of infection in non-human primate models. Here, we present a detailed analysis of the strategies and results of manipulating SIV pathogenesis through in vivo depletions of key immune cells populations. Although each of these methods has its limitations, they have all contributed to our understanding of key pathogenic pathways in HIV/SIV infection.

Construction of cytomegalovirus promoter-driven gene expression system in Laodelphax striatellus

The small brown planthopper (SBPH, Laodelphax striatellus) is a significant rice pest, responsible for transmitting rice stripe virus (RSV) in a persistent and propagative manner. RSV is one of the most detrimental rice viruses, causing rice stripe disease, which results in considerable loss of rice grain yield. While RNA interference and gene knockout techniques have enabled gene downregulation in SBPH, no system currently exists for the overexpression of endogenous or exogenous genes. Consequently, the development of a protein expression system for SBPH is imperative to serve as a technical foundation for pest control and gene function investigations. This study aimed to construct an expression vector using the promoter of the constitutive-expressed tubulin gene of SBPH, and promoter of human cytomegalovirus (CMV). Fluorescence experiments demonstrated that both tubulin and CMV promoter could drive green fluorescent protein (GFP) expression in SBPH, and could also facilitate the expression of a nucleocapsid protein (NP) -GFP fusion protein containing viral NP with comparable efficiency. Through expression vector optimization, we have identified that the 3 tandem CMV promoters display a significantly higher promoter activity compared with both the 2 tandem CMV promoters and the single CMV promoter. In addition, the incorporation of Star polycation nanoparticles significantly enhanced the expression efficiency in SBPH. These results provide a promising technical platform for investigating gene functions in SBPH.

The Question of HIV Vaccine: Why Is a Solution Not Yet Available?

Ever since its discovery, human immunodeficiency virus type 1 (HIV-1) infection has remained a significant public health concern. The number of HIV-1 seropositive individuals currently stands at 40.1 million, yet definitive treatment for the virus is still unavailable on the market. Vaccination has proven to be a potent tool in combating infectious diseases, as evidenced by its success against other pathogens. However, despite ongoing efforts and research, the unique viral characteristics have prevented the development of an effective anti-HIV-1 vaccine. In this review, we aim to provide an historical overview of the various approaches attempted to create an effective anti-HIV-1 vaccine. Our objective is to explore the reasons why specific methods have failed to induce a protective immune response and to analyze the different modalities of immunogen presentation. This trial is registered with NCT05414786, NCT05471076, NCT04224701, and NCT01937455.

Advances of Recombinant Adenoviral Vectors in Preclinical and Clinical Applications

Adenoviruses (Ad) have the potential to induce severe infections in vulnerable patient groups. Therefore, understanding Ad biology and antiviral processes is important to comprehend the signaling cascades during an infection and to initiate appropriate diagnostic and therapeutic interventions. In addition, Ad vector-based vaccines have revealed significant potential in generating robust immune protection and recombinant Ad vectors facilitate efficient gene transfer to treat genetic diseases and are used as oncolytic viruses to treat cancer. Continuous improvements in gene delivery capacity, coupled with advancements in production methods, have enabled widespread application in cancer therapy, vaccine development, and gene therapy on a large scale. This review provides a comprehensive overview of the virus biology, and several aspects of recombinant Ad vectors, as well as the development of Ad vector, are discussed. Moreover, we focus on those Ads that were used in preclinical and clinical applications including regenerative medicine, vaccine development, genome engineering, treatment of genetic diseases, and virotherapy in tumor treatment.

High-Throughput Screening for the Prevalence of Neutralizing Antibodies against Human Adenovirus Serotype 5

Adenoviral vectors based on the human adenovirus species C serotype 5 (HAdV-C5) are commonly used for vector-based gene therapies and vaccines. In the preclinical stages of development, their safety and efficacy are often validated in suitable animal models. However, pre-existing neutralizing antibodies may severely influence study outcomes. Here, we generated a new HAdV-C5-based reporter vector and established a high-throughput screening assay for the multivalent detection of HAdV-C5-neutralizing antibodies in serum. We screened the sera of rhesus macaques at different primate centers, and of rabbits, horses, cats, and dogs, showing that HAdV-C5-neutralizing antibodies can be found in all species, albeit at different frequencies. Our results emphasize the need to prescreen model animals in HAdV-C5-based studies.

Seroprevalence of human adenovirus type 5 neutralizing antibodies in the Philippines

Human adenovirus (HAdV), particularly the HAdV type 5 (HAdV-5), has been extensively utilized in the development of vector vaccines due to its high immunogenicity, good safety profile, and ease of propagation. However, one of the main challenges in its use is the presence of pre-existing immunity among vaccine recipients. Pre-existing neutralizing antibodies (NAbs) can prevent the uptake of HAdV-5 vectors and reduce vaccine efficacy. Hence, this study investigated the seroprevalence of NAbs against HAdV-5 in urban and rural regions of the Philippines. Luciferase-based neutralization assay was performed on 391 plasma/serum samples. Out of these samples, 346 or 88.5% were positive for HAdV-5 NAbs, and the majority of them (56.8%) had high titers against the virus. Among the regions included in this study, Bicol (Region V) had the highest seroprevalence rate (94.1%). Our findings show that a significant number of adults in the Philippines have pre-existing immunity against HAdV-5. This supports the recommendation that vaccination programs in the country should consider implementing vaccination techniques, such as a prime-boost regimen or addition of booster doses, to address the potential negative effects of pre-existing HAdV-5 immunity in the efficacy of adenoviral vector-based vaccines.

Generating and measuring effective vaccine-elicited HIV-specific CD8 + T cell responses

PURPOSE OF REVIEW

There is growing consensus that eliciting CD8 + T cells in addition to antibodies may be required for an effective HIV vaccine for both prevention and cure. Here, we review key qualities of vaccine-elicited CD8 + T cells as well as major CD8 + T cell-based delivery platforms used in recent HIV vaccine clinical trials.

RECENT FINDINGS

Much progress has been made in improving HIV immunogen design and delivery platforms to optimize CD8 + T cell responses. With regards to viral vectors, recent trials have tested newer chimp and human adenovirus vectors as well as a CMV vector. DNA vaccine immunogenicity has been increased by delivering the vaccines by electroporation and together with adjuvants as well as administering them as part of a heterologous regimen. In preclinical models, self-amplifying RNA vaccines can generate durable tissue-based CD8 + T cells. While it may be beneficial for HIV vaccines to recapitulate the functional and phenotypic features of HIV-specific CD8 + T cells isolated from elite controllers, most of these features are not routinely measured in HIV vaccine clinical trials.

SUMMARY

Identifying a vaccine capable of generating durable T cell responses that target mutationally vulnerable epitopes and that can rapidly intercept infecting or rebounding virus remains a challenge for HIV. Comprehensive assessment of HIV vaccine-elicited CD8 + T cells, as well as comparisons between different vaccine platforms, will be critical to advance our understanding of how to design better CD8 + T cell-based vaccines for HIV.

HIV-1 Transmission Cluster in Injection Drug Users in Nairobi City, Kenya

Background

While there is a striking increase in the prevalence of HIV in injection drug users, information on envelope-gene subtypes and transmission clusters in injection drug users is scarce.

Method

In a cross-sectional study, 247 injection drug users were recruited via out-rich method. Deoxyribonucleic acid was extracted from dry blood spot samples, amplified by Polymerase Chain Reaction and sequenced. Subtyping was performed using COntext-based Modeling for Expeditious Typing (COMET) and Recombinant Identification Program (RIP) tools. Phylogenetic diversity and Transmission clusters were identified using MEGA version 6.0 and TreeLink, respectively.

Results

Overall, 42 (17.0%) injection drug users were sero-positive for HIV-1. Of the 37 samples successfully sequenced, 29 (78.4%) sequences were identified as A1, 6 (16.2%) as AG while 1 (2.7%) as A1/G/AE and A1/C recombinants. The HIV subtypes formed clusters with little genetic diversity.

Conclusion

The high HIV prevalence was associated with transmission clusters and diversity in subtypes indicating ongoing local transmission. Therefore, there is need for comprehensive HIV care tailored to this population.

The Effect of Treatment-Associated Mutations on HIV Replication and Transmission Cycles

HIV/AIDS mortality has been decreasing over the last decade. While promising, this decrease correlated directly with increased use of antiretroviral drugs. As a natural consequence of its high mutation rate, treatments provide selection pressure that promotes the natural selection of escape mutants. Individuals may acquire drug-naive strains, or those that have already mutated due to treatment. Even within a host, mutation affects HIV tropism, where initial infection begins with R5-tropic virus, but the clinical transition to AIDS correlates with mutations that lead to an X4-tropic switch. Furthermore, the high mutation rate of HIV has spelled failure for all attempts at an effective vaccine. Pre-exposure drugs are currently the most effective drug-based preventatives, but their effectiveness is also threatened by viral mutation. From attachment and entry to assembly and release, the steps in the replication cycle are also discussed to describe the drug mechanisms and mutations that arise due to those drugs. Revealing the patterns of HIV-1 mutations, their effects, and the coordinated attempt to understand and control them will lead to effective use of current preventative measures and treatment options, as well as the development of new ones.

The use of viral vectors in vaccine development

Vaccines represent the single most cost-efficient and equitable way to combat and eradicate infectious diseases. While traditional licensed vaccines consist of either inactivated/attenuated versions of the entire pathogen or subunits of it, most novel experimental vaccines against emerging infectious diseases employ nucleic acids to produce the antigen of interest directly in vivo. These include DNA plasmid vaccines, mRNA vaccines, and recombinant viral vectors. The advantages of using nucleic acid vaccines include their ability to induce durable immune responses, high vaccine stability, and ease of large-scale manufacturing. In this review, we present an overview of pre-clinical and clinical data on recombinant viral vector vaccines and discuss the advantages and limitations of the different viral vector platforms.

The repeated setbacks of HIV vaccine development laid the groundwork for SARS-CoV-2 vaccines

The decades-long effort to produce a workable HIV vaccine has hardly been a waste of public and private resources. To the contrary, the scientific know-how acquired along the way has served as the critical foundation for the development of vaccines against the novel, pandemic SARS-CoV-2 virus. We retell the real-world story of HIV vaccine research - with all its false leads and missteps - in a way that sheds light on the current state of the art of antiviral vaccines. We find that HIV-related R&D had more than a general spillover effect. In fact, the repeated failures of phase 2 and 3 clinical trials of HIV vaccine candidates have served as a critical stimulus to the development of successful vaccine technologies today. We rebut the counterargument that HIV vaccine development has been no more than a blind alley, and that recently developed vaccines against COVID-19 are really descendants of successful vaccines against Ebola, MERS, and SARS. These successful vaccines likewise owe much to the vicissitudes of HIV vaccine development. We then discuss how the failures of HIV vaccine development have taught us how adapt SARS-CoV-2 vaccines to immune escape from emerging variants. Finally, we inquire whether recent advances in the development of vaccines against SARS-CoV-2 might in turn further the development of an HIV vaccine - what we describe as a reverse spillover effect.

Adenovirus vector-based vaccine for infectious diseases

Replication-incompetent adenovirus (Ad) vectors have been widely used as gene delivery vehicles in both gene therapy studies and basic studies for gene function analysis due to their highly advantageous properties, which include high transduction efficiencies, relatively large capacities for transgenes, and high titer production. In addition, Ad vectors induce moderate levels of innate immunity and have relatively high thermostability, making them very attractive as potential vaccine vectors. Accordingly, it is anticipated that Ad vectors will be used in vaccines for the prevention of infectious diseases, including Ebola virus disease and acquired immune deficiency syndrome (AIDS). Much attention is currently focused on the potential use of an Ad vector vaccine for coronavirus disease 2019 (COVID-19). In this review, we describe the basic properties of an Ad vector, Ad vector-induced innate immunity and immune responses to Ad vector-produced transgene products. Development of novel Ad vectors which can overcome the drawbacks of conventional Ad vector vaccines and clinical application of Ad vector vaccines to several infectious diseases are also discussed.

So Pathogenic or So What?-A Brief Overview of SIV Pathogenesis with an Emphasis on Cure Research

HIV infection requires lifelong antiretroviral therapy (ART) to control disease progression. Although ART has greatly extended the life expectancy of persons living with HIV (PWH), PWH nonetheless suffer from an increase in AIDS-related and non-AIDS related comorbidities resulting from HIV pathogenesis. Thus, an HIV cure is imperative to improve the quality of life of PWH. In this review, we discuss the origins of various SIV strains utilized in cure and comorbidity research as well as their respective animal species used. We briefly detail the life cycle of HIV and describe the pathogenesis of HIV/SIV and the integral role of chronic immune activation and inflammation on disease progression and comorbidities, with comparisons between pathogenic infections and nonpathogenic infections that occur in natural hosts of SIVs. We further discuss the various HIV cure strategies being explored with an emphasis on immunological therapies and "shock and kill".

Current Status of HIV-1 Vaccines

HIV-1 infection and its progression to AIDS remains a significant global health challenge, particularly for low-income countries. Developing a vaccine to prevent HIV-1 infections has proven to be immensely challenging with complex biological acquisition and infection, unforeseen clinical trial disappointments, and funding issues. This paper discusses important landmarks of progress in HIV-1 vaccine development, various vaccine strategies, and clinical trials.

Preventive HIV Vaccines-Leveraging on Lessons from the Past to Pave the Way Forward

Almost four decades on, since the 1980’s, with hundreds of HIV vaccine candidates tested in both non-human primates and humans, and several HIV vaccines trials later, an efficacious HIV vaccine continues to evade us. The enormous worldwide genetic diversity of HIV, combined with HIV’s inherent recombination and high mutation rates, has hampered the development of an effective vaccine. Despite the advent of antiretrovirals as pre-exposure prophylaxis and preventative treatment, which have shown to be effective, HIV infections continue to proliferate, highlighting the great need for a vaccine. Here, we provide a brief history for the HIV vaccine field, with the most recent disappointments and advancements. We also provide an update on current passive immunity trials, testing proof of the concept of the most clinically advanced broadly neutralizing monoclonal antibodies for HIV prevention. Finally, we include mucosal immunity, the importance of vaccine-elicited immune responses and the challenges thereof in the most vulnerable environment–the female genital tract and the rectal surfaces of the gastrointestinal tract for heterosexual and men who have sex with men transmissions, respectively.

New insights into pathogenesis point to HIV-1 Tat as a key vaccine target

Despite over 30 years of enormous effort and progress in the field, no preventative and/or therapeutic vaccines against human immunodeficiency virus (HIV) are available. Here, we briefly summarize the vaccine strategies and vaccine candidates that in recent years advanced to efficacy trials with mostly unsatisfactory results. Next, we discuss a novel and somewhat contrarian approach based on biological and epidemiological evidence, which led us to choose the HIV protein Tat for the development of preventive and therapeutic HIV vaccines. Toward this goal, we review here the role of Tat in the virus life cycle as well as experimental and epidemiological evidence supporting its key role in the natural history of HIV infection and comorbidities. We then discuss the preclinical and clinical development of a Tat therapeutic vaccine, which, by improving the functionality and homeostasis of the immune system and by reducing the viral reservoir in virologically suppressed vaccinees, helps to establish key determinants for intensification of combination antiretroviral therapy (cART) and a functional cure. Future developments and potential applications of the Tat therapeutic vaccine are also discussed, as well as the rationale for its use in preventative strategies. We hope this contribution will lead to a reconsideration of the current paradigms for the development of HIV/AIDS vaccines, with a focus on targeting of viral proteins with key roles in HIV pathogenesis.

Evolving pharmacovigilance requirements with novel vaccines and vaccine components

This paper explores the pipeline of new and upcoming vaccines as it relates to monitoring their safety. Compared with most currently available vaccines, that are constituted of live attenuated organisms or inactive products, future vaccines will also be based on new technologies. Several products that include such technologies are either already licensed or at an advanced stage of clinical development. Those include viral vectors, genetically attenuated live organisms, nucleic acid vaccines, novel adjuvants, increased number of antigens present in a single vaccine, novel mode of vaccine administration and thermostabilisation. The Global Advisory Committee on Vaccine Safety (GACVS) monitors novel vaccines, from the time they become available for large scale use. GACVS maintains their safety profile as evidence emerges from post-licensure surveillance and observational studies. Vaccines and vaccine formulations produced with novel technologies will have different safety profiles that will require adapting pharmacovigilance approaches. For example, GACVS now considers viral vector templates developed on the model proposed by Brighton Collaboration. The characteristics of those novel products will also have implications for the risk management plans (RMPs). Questions related to the duration of active monitoring for genetic material, presence of adventitious agents more easily detected with enhanced biological screening, or physiological mechanisms of novel adjuvants are all considerations that will belong to the preparation of RMPs. In addition to assessing those novel products and advising experts, GACVS will also consider how to more broadly communicate about risk assessment, so vaccine users can also benefit from the committee’s advice.

Innate immune signatures to a partially-efficacious HIV vaccine predict correlates of HIV-1 infection risk

The pox-protein regimen tested in the RV144 trial is the only vaccine strategy demonstrated to prevent HIV-1 infection. Subsequent analyses identified antibody and cellular immune responses as correlates of risk (CoRs) for HIV infection. Early predictors of these CoRs could provide insight into vaccine-induced protection and guide efforts to enhance vaccine efficacy. Using specimens from a phase 1b trial of the RV144 regimen in HIV-1-uninfected South Africans (HVTN 097), we profiled innate responses to the first ALVAC-HIV immunization. PBMC transcriptional responses peaked 1 day post-vaccination. Type I and II interferon signaling pathways were activated, as were innate pathways critical for adaptive immune priming. We then identified two innate immune transcriptional signatures strongly associated with adaptive immune CoR after completion of the 4-dose regimen. Day 1 signatures were positively associated with antibody-dependent cellular cytotoxicity and phagocytosis activity at Month 6.5. Conversely, a signature present on Days 3 and 7 was inversely associated with Env-specific CD4+ T cell responses at Months 6.5 and 12; rapid resolution of this signature was associated with higher Env-specific CD4+ T-cell responses. These are the first-reported early immune biomarkers of vaccine-induced responses associated with HIV-1 acquisition risk in humans and suggest hypotheses to improve HIV-1 vaccine regimens.

The innate immune response is the body’s initial defense against pathogens and is linked to and shapes the subsequent adaptive immune response, which can confer long-lasting protection. For a vaccine with partial efficacy, such as the RV144 HIV vaccine regimen, identifying early innate responses that are linked with adaptive responses—particularly those for which evidence has accumulated that they might be important for protection—could help a more efficacious version be developed. In the HVTN 097 study, the RV144 prime-boost (ALVAC-HIV and AIDSVAX B/E) vaccine regimen was given to South African participants. We characterized the innate response to the first dose of ALVAC-HIV in these participants and identified gene expression signatures present within the first few days that were associated with antibody and T-cell responses to the full vaccine regimen measured up to 1 year later. As these antibody and T-cell responses have previously been implicated in protection, our findings suggest ways of refining the RV144 regimen and also have broader applications to vaccine development.

Adenoviral Vectors as Vaccines for Emerging Avian Influenza Viruses

It is evident that the emergence of infectious diseases, which have the potential for spillover from animal reservoirs, pose an ongoing threat to global health. Zoonotic transmission events have increased in frequency in recent decades due to changes in human behavior, including increased international travel, the wildlife trade, deforestation, and the intensification of farming practices to meet demand for meat consumption. Influenza A viruses (IAV) possess a number of features which make them a pandemic threat and a major concern for human health. Their segmented genome and error-prone process of replication can lead to the emergence of novel reassortant viruses, for which the human population are immunologically naïve. In addition, the ability for IAVs to infect aquatic birds and domestic animals, as well as humans, increases the likelihood for reassortment and the subsequent emergence of novel viruses. Sporadic spillover events in the past few decades have resulted in human infections with highly pathogenic avian influenza (HPAI) viruses, with high mortality. The application of conventional vaccine platforms used for the prevention of seasonal influenza viruses, such as inactivated influenza vaccines (IIVs) or live-attenuated influenza vaccines (LAIVs), in the development of vaccines for HPAI viruses is fraught with challenges. These issues are associated with manufacturing under enhanced biosafety containment, and difficulties in propagating HPAI viruses in embryonated eggs, due to their propensity for lethality in eggs. Overcoming manufacturing hurdles through the use of safer backbones, such as low pathogenicity avian influenza viruses (LPAI), can also be a challenge if incompatible with master strain viruses. Non-replicating adenoviral (Ad) vectors offer a number of advantages for the development of vaccines against HPAI viruses. Their genome is stable and permits the insertion of HPAI virus antigens (Ag), which are expressed in vivo following vaccination. Therefore, their manufacture does not require enhanced biosafety facilities or procedures and is egg-independent. Importantly, Ad vaccines have an exemplary safety and immunogenicity profile in numerous human clinical trials, and can be thermostabilized for stockpiling and pandemic preparedness. This review will discuss the status of Ad-based vaccines designed to protect against avian influenza viruses with pandemic potential.

Polyfunctional Fc Dependent Activity of Antibodies to Native Trimeric Envelope in HIV Elite Controllers

Antibody dependent (AD) functions such as AD cellular cytotoxicity (ADCC) were associated with lower viral load (VL) in untreated HIV progressors and protection from HIV infection in the modestly protective RV144 HIV vaccine trial. Target cells used to measure ADCC, AD complement deposition (ADCD), and AD cellular trogocytosis (ADCT) have been either HIV envelope (Env) gp120-coated CEM.NKr.CCR5 cells or HIV infected cell cultures. In HIV infected cell cultures, uninfected bystander cells take up gp120 shed from infected cells. Both gp120-coated and gp120+ bystander cells expose CD4 induced (CD4i) epitopes, which are normally hidden in native trimeric Env expressed by genuinely HIV infected cells since Nef and Vpu downmodulate cell surface CD4. Antibody dependent assays using either of these target cells probe for CD4i Abs that are abundant in HIV⁺ plasma but that do not recognize HIV-infected cells. Here, we examined ADCC, ADCD, and ADCT functions using a target cell line, sorted HIV-infected cell line cells, whose HIV infection frequency nears 100% and that expresses HIV Env in a native trimeric closed conformation. Using sorted HIV-infected cells (siCEM) as targets, we probed the binding and AD functions of anti-gp120/Env Abs in plasma from HIV-infected untreated progressor (UTP, n = 18) and treated (TP, n = 24) subjects, compared to that in Elite controllers (EC, n = 37) and Viral Controllers (VC, n = 16), which are rare subsets of HIV-infected individuals who maintain undetectable or low VL, respectively, without treatment. Gp120-coated beads were used to measure AD cellular phagocytosis. Equivalent concentrations of input IgG in plasma from UTPs, ECs, and VCs supported higher levels of all AD functions tested than plasma from TPs. When AD activities were normalized to the concentration of anti-gp120/Env-specific Abs, between-group differences largely disappeared. This finding suggests that the anti-gp120/Env Abs concentrations and not their potency determined AD functional levels in these assays. Elite controllers did differ from the other groups by having AD functions that were highly polyfunctional and highly correlated with each other. PCR measurement of HIV reservoir size showed that ADCC activity was higher in ECs and VCs with a reservoir size below the limit of detection compared to those having a measurable HIV reservoir size.

So much at stake: Ethical tradeoffs in accelerating SARSCoV-2 vaccine development

BACKGROUND

A sense of urgency exists to develop vaccines against SARS CoV-2, responsible for numerous global cases and deaths, as well as widespread social and economic disruption. Multiple approaches have been proposed to speed up vaccine development, including accelerated randomized controlled trials (RCT), controlled human challenge trials (CHI), and wide distribution through an emergency use authorization after collecting initial data. There is a need to examine how best to accelerate vaccine development in the setting of a pandemic, without compromising ethical and scientific norms.

METHODS

Trade-offs in scientific and social value between generating reliable evidence about safety and efficacy while promoting rapid vaccine availability are examined along five ethically relevant dimensions: (1) confidence in and generalizability of data, (2) feasibility, (3) speed and cost, (4) participant risks, and (5) social risks.

RESULTS

Accelerated individually randomized RCTs permit expeditious evaluation of vaccine candidates using established methods, expertise, and infrastructure. RCTs are more likely than other approaches to be feasible, increase speed and reduce cost, and generate reliable data about safety and efficacy without significantly increasing risks to participants or undermining societal trust.

CONCLUSION

Ethical analysis suggests that accelerated RCTs are the best approach to accelerating vaccine development in a pandemic, and more likely than other approaches to enhance social value without compromising ethics or science. RCTs can expeditiously collect rigorous data about vaccine safety and efficacy. Innovative and flexible designs and implementation strategies to respond to shifting incidence and test vaccine candidates in parallel or sequentially would add value, as will coordinated data sharing across vaccine trials. CHI studies may be an important complementary strategy when more is known. Widely disseminating a vaccine candidate without efficacy data will not serve the public health nor achieve the goal of identifying safe and effective SARS Co-V-2 vaccines.

High-Capacity Adenoviral Vectors: Expanding the Scope of Gene Therapy

The adaptation of adenoviruses as gene delivery tools has resulted in the development of high-capacity adenoviral vectors (HC-AdVs), also known, helper-dependent or "gutless". Compared with earlier generations (E1/E3-deleted vectors), HC-AdVs retain relevant features such as genetic stability, remarkable efficacy of in vivo transduction, and production at high titers. More importantly, the lack of viral coding sequences in the genomes of HC-AdVs extends the cloning capacity up to 37 Kb, and allows long-term episomal persistence of transgenes in non-dividing cells. These properties open a wide repertoire of therapeutic opportunities in the fields of gene supplementation and gene correction, which have been explored at the preclinical level over the past two decades. During this time, production methods have been optimized to obtain the yield, purity, and reliability required for clinical implementation. Better understanding of inflammatory responses and the implementation of methods to control them have increased the safety of these vectors. We will review the most significant achievements that are turning an interesting research tool into a sound vector platform, which could contribute to overcome current limitations in the gene therapy field.

A single lentivector DNA based immunization contains a late heterologous SIVmac251 mucosal challenge infection

Variety of conventional vaccine strategies tested against HIV-1 have failed to induce protection against HIV acquisition or durable control of viremia. Therefore, innovative strategies that can induce long lasting protective immunity against HIV chronic infection are needed. Recently, we developed an integration-defective HIV lentiDNA vaccine that undergoes a single cycle of replication in target cells in which most viral antigens are produced. A single immunization with such lentiDNA induced long-lasting T-cell and modest antibody responses in cynomolgus macaques. Here eighteen months after this single immunization, all animals were subjected to repeated low dose intra-rectal challenges with a heterologous pathogenic SIVmac251 isolate. Although the viral set point in SIVmac-infected cynomolgus is commonly lower than that seen in Indian rhesus macaques, the vaccinated group of macaques displayed a two log reduction of peak of viremia followed by a progressive and sustained control of virus replication relative to control animals. This antiviral control correlated with antigen-specific CD4+ and CD8+ T cells with high capacity of recall responses comprising effector and central memory T cells but also memory T cell precursors. This is the first description of SIV control in NHP model infected at 18 months following a single immunization with a non-integrative single cycle lentiDNA HIV vaccine. While not delivering sterilizing immunity, our single immunization strategy with a single-cycle lentivector DNA vaccine appears to provide an interesting and safe vaccine platform that warrants further exploration.

Innovations in HIV-1 Vaccine Design

PURPOSE

The field of HIV-1 vaccinology has evolved during the last 30 years from the first viral vector HIV gene insert constructs to vaccination regimens using a myriad of strategies. These strategies now include germline-targeting, lineage-based, and structure-guided immunogen design. This narrative review outlines the historical context of HIV vaccinology and subsequently highlights the scientific discoveries during the last 6 years that promise to propel the field forward.

METHODS

We conducted a search of 2 electronic databases, PubMed and EMBASE, for experimental studies that involved new HIV immunogen designs between 2013 and 2019. During the title and abstract reviews, publications were excluded if they were written in language other than English and/or were a letter to the editor, a commentary, or a conference-only presentation. We then used ClinicalTrials.gov to identify completed and ongoing clinical trials using these strategies.

FINDINGS

The HIV vaccinology field has undergone periods of significant growth during the last 3 decades. Findings elucidated in preclinical studies have revealed the importance of the interaction between the cellular and humoral immune system. As a result, several new rationally designed vaccine strategies have been developed and explored in the last 6 years, including native-like envelope trimers, nanoparticle, and mRNA vaccine design strategies among others. Several of these strategies have shown enough promise in animal models to progress toward first-in-human Phase I clinical trials.

IMPLICATIONS

Rapid developments in preclinical and early-phase clinical studies suggest that a tolerable and effective HIV vaccine may be on the horizon.

Myeloid Cell-Mediated Trained Innate Immunity in Mucosal AIDS Vaccine Development

Trained innate immunity has recently emerged as a novel concept of innate immune cells, such as myeloid cells, exhibiting immune memory, and nonspecific heterologous immunity to protect against infections. The memory and specificity are mediated by epigenetic, metabolic, and functional reprogramming of the myeloid cells and myeloid progenitors (and/or NK cells) in the bone marrow and peripheral tissues such as gut and lung mucosa. A variety of agents, such as BCG, viruses, and their components, as well as TLR agonists, and cytokines have been shown to be involved in the induction of trained immunity. Since these agents have been widely used in AIDS vaccine development as antigen delivery vectors or adjuvants, myeloid cell mediated trained immunity might also play an important role in protecting against mucosal AIDS virus transmission or in control of virus replication in the major gut mucosal reservoir. Here we review the trained innate immunity induced by these vectors/adjuvants that have been used in AIDS vaccine studies and discuss their role in mucosal vaccine efficacy and possible utilization in AIDS vaccine development. Delineating the protective effect of the trained innate immunity mediated by myeloid cells will guide the design of novel AIDS vaccines.

Effect of HIV Envelope Vaccination on the Subsequent Antibody Response to HIV Infection

Analysis of breakthrough HIV-1 infections could elucidate whether prior vaccination primes relevant immune responses. Here, we measured HIV-specific antibody responses in 14 South African volunteers who acquired HIV infection after participating in phase 1/2 trials of envelope-containing immunogens. Serum samples were collected annually following HIV-1 infection from participants in trials HVTN 073 (subtype C, DNA/MVA, phase 1 trial, n = 1), HVTN 086 (subtype C, DNA/MVA/gp140 protein, phase 1 trial, n = 2), and HVTN 204 (multisubtype, DNA/adenovirus serotype 5 [Ad5], phase 2 trial, n = 7) and 4 placebo recipients. Binding and neutralizing antibody responses to Env proteins and peptides were determined pre- and post-HIV infection using an enzyme-linked immunosorbent assay and the TZM-bl cell neutralization assay, respectively. HIV-infected South African individuals served as unvaccinated controls. Binding antibodies to gp41, V3, V2, the membrane-proximal external region (MPER), and the CD4 binding site were detected from the first year of HIV-1 subtype C infection, and the levels were similar in vaccinated and placebo recipients. Neutralizing antibody responses against tier 1A viruses were detected in all participants, with the highest titers being to a subtype C virus, MW965.26. No responses were observed just prior to infection, indicating that vaccine-primed HIV-specific antibodies had waned. Sporadic neutralization activity against tier 2 isolates was observed after 2 to 3 years of HIV infection, but these responses were similar in the vaccinated and placebo groups as well as the unvaccinated controls. Our data suggest that prior vaccination with these immunogens did not alter the antibody responses to HIV-1 infection, nor did it accelerate the development of HIV neutralization breadth.IMPORTANCE There is a wealth of information on HIV-specific vaccine-induced immune responses among HIV-uninfected participants; however, data on immune responses among participants who acquire HIV after vaccination are limited. Here we show that HIV-specific binding antibody responses in individuals with breakthrough HIV infections were not affected by prior vaccination with HIV envelope-containing immunogens. We also found that these vectored vaccines did not prime tier 2 virus-neutralizing antibody responses, which are thought to be required for prevention against HIV acquisition, or accelerate the development of neutralization breadth. Although this study is limited, such studies can provide insights into whether vaccine-elicited antibody responses are boosted by HIV infection to acquire broader neutralizing activity, which may help to identify antigens relevant to the design of more effective vaccines.

Strategies for inducing effective neutralizing antibody responses against HIV-1

Introduction: Despite intensive research efforts, there is still no effective prophylactic vaccine available against HIV-1. Currently, substantial efforts are devoted to the development of vaccines aimed at inducing broadly neutralizing antibodies (bNAbs), which are capable of neutralizing most HIV-1 strains. All bNAbs target the HIV-1 envelope glycoprotein (Env), but Env immunizations usually only induce neutralizing antibodies (NAbs) against the sequence-matched virus and not against other strains.Areas covered: We describe the different strategies that have been explored to improve the breadth and potency of anti-HIV-1 NAb responses. The discussed strategies include the application of engineered Env immunogens, optimization of (bNAb) epitopes, different cocktail and sequential vaccination strategies, nanoparticles and nucleic acid-based vaccines.Expert opinion: A combination of the strategies described in this review and future approaches are probably needed to develop an effective HIV-1 vaccine that can induce broad, potent and long-lasting NAb responses.

Perception of potential harm and benefits of HIV vaccine trial participation: A qualitative study from urban Tanzania

BACKGROUND

The development of an effective preventive HIV vaccine is the best-known option to halt incident HIV infections. Participants in HIV vaccine trials may possess expectations shaped by existing socio-cultural contexts that are important to understand to allow for improved trial design. Here, we describe post-phase I/II HIV vaccine trial perceptions within participating communities in Dar es Salaam, Tanzania.

MATERIALS AND METHODS

This descriptive qualitative study was conducted in May 2016. We conducted eight focus group discussions, each consisting of 5 to 12 participants. Four groups comprised of the past phase I/II HIV vaccine trial participants and four groups involved those who did not participate. We used a thematic analysis approach.

RESULTS

Ongoing concerns existed among non-vaccine trial participants who believed that those who participated in HIV vaccine trials were infected with HIV. Limited post-HIV vaccine trial result dissemination, the pre-existing negative beliefs about vaccines, and experiences from other previous medical experiments fueled these concerns. The participants anticipated that broader dissemination of facts regarding HIV vaccine trials using media, former volunteers, and flyers would reduce the reported concerns. In contrast, some participants embraced the benefits gained through participating in HIV vaccine trials. HIV vaccine trial participants appreciated trial interventions, such as health status check-ups, knowledge acquisition, and facilitation of access to medical services. They envisioned mutual benefits in the form of community protection and capacity building among the local scientists.

CONCLUSIONS

The future conduct of HIV vaccine trials in Tanzania requires wider community dissemination of information and post-trial feedback to alleviate concerns among the participating communities. Interventions such as medical services may represent essential incentives to the HIV vaccine trial volunteers. In future HIV vaccine trials, it is crucial to boost individual and perceived mutual benefits.

Aiming for protective T-cell responses: a focus on the first generation conserved-region HIVconsv vaccines in preventive and therapeutic clinical trials

Introduction: Despite life-saving antiretroviral drugs, an effective HIV-1 vaccine is the best solution and likely a necessary component of any strategy for halting the AIDS epidemic. The currently prevailing aim is to pursue antibody-mediated vaccine protection. With ample evidence for the ability of T cells to control HIV-1 replication, their protective potential should be also harnessed by vaccination. The challenge is to elicit not just any, but protective T cells.Areas covered: This article reviews the clinical experience with the first-generation conserved-region immunogen HIVconsv delivered by combinations of plasmid DNA, simian adenovirus, and poxvirus MVA. The aim of our strategy is to induce strong and broad T cells targeting functionally important parts of HIV-1 proteins common to global variants. These vaccines were tested in eight phase 1/2 preventive and therapeutic clinical trials in Europe and Africa, and induced high frequencies of broadly specific CD8⁺ T cells capable of in vitro inhibition of four major HIV-1 clades A, B, C and D, and in combination with latency-reactivating agent provided a signal of drug-free virological control in early treated patients.Expert opinion: A number of critical T-cell traits have to come together at the same time to achieve control over HIV-1.

Therapeutic Vaccination Refocuses T-cell Responses Towards Conserved Regions of HIV-1 in Early Treated Individuals (BCN 01 study)

BACKGROUND

Strong and broad antiviral T-cell responses targeting vulnerable sites of HIV-1 will likely be a critical component for any effective cure strategy.

METHODS

BCN01 trial was a phase I, open-label, non-randomized, multicenter study in HIV-1-positive individuals diagnosed and treated during early HIV-1 infection to evaluate two vaccination regimen arms, which differed in the time (8 versus 24 week) between the ChAdV63.HIVconsv prime and MVA.HIVconsv boost vaccinations. The primary outcome was safety. Secondary endpoints included frequencies of vaccine-induced IFN-γ⁺ CD8⁺ T cells, in vitro virus-inhibitory capacity, plasma HIV-1 RNA and total CD4⁺ T-cells associated HIV-1 DNA. (NCT01712425).

FINDINGS

No differences in safety, peak magnitude or durability of vaccine-induced responses were observed between long and short interval vaccination arms. Grade 1/2 local and systemic post-vaccination events occurred in 22/24 individuals and resolved within 3 days. Weak responses to conserved HIV-1 regions were detected in 50% of the individuals before cART initiation, representing median of less than 10% of their total HIV-1-specific T cells. All participants significantly elevated these subdominant T-cell responses, which after MVA.HIVconsv peaked at median (range) of 938 (73-6,805) IFN-γ SFU/10⁶ PBMC, representing on average 58% of their total anti-HIV-1 T cells. The decay in the size of the HIV-1 reservoir was consistent with the first year of early cART initiation in both arms.

INTERPRETATION

Heterologous prime-boost vaccination with ChAdV63-MVA/HIVconsv was well-tolerated and refocused pre-cART T-cell responses towards more protective epitopes, in which immune escape is frequently associated with reduced HIV-1 replicative fitness and which are common to most global HIV-1 variants.

FUNDING

HIVACAT Catalan research program for an HIV vaccine and Fundació Gloria Soler. Vaccine manufacture was jointly funded by the Medical Research Council (MRC) UK and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreements (G0701669.

RESEARCH IN CONTEXT

Evidence Before this Study: T cells play an important role in the control of HIV infection and may be particularly useful for HIV-1 cure by killing cells with reactivated HIV-1. Evidence is emerging that not all T-cell responses are protective and mainly only those targeting conserved regions of HIV-1 proteins are effective, but typically immunologically subdominant, while those recognizing hypervariable, easy-to-escape immunodominant 'decoys' do not control viremia and do not protect from a loss of CD4 T cells. We pioneered a vaccine strategy focusing T-cell responses on the most conserved regions of the HIV-1 proteome using an immunogen designated HIVconsv. T cells elicited by the HIVconsv vaccines in HIV-uninfected UK and Kenyan adults inhibited in vitro replication of HIV-1 isolates from 4 major global clades A, B, C and D.Added Value of this Study: The present study demonstrated the concept that epitopes subdominant in natural infection, when taken out of the context of the whole HIV-1 proteome and presented to the immune system by a potent simian adenovirus prime-poxvirus MVA boost regimen, can induce strong responses in patients on antiretroviral treatment and efficiently refocus HIV-1-specific T-cells to the protective epitopes delivered by the vaccine.Implications of all the Available Evidence: Nearly all HIV-1 vaccine strategies currently emphasize induction of broadly neutralizing Abs. The HIVconsv vaccine is one of a very few approaches focussing exclusively on elicitation of T cells and, therefore, can complement antibody induction for better prevention and cure. Given the cross-clade reach on the HIVconsv immunogen design, if efficient, the HIVconsv vaccines could be deployed globally. Effective vaccines will likely be a necessary component in combination with other available preventive measures for halting the HIV-1/AIDS epidemic.

Susceptibility to SIV Infection After Adenoviral Vaccination in a Low Dose Rhesus Macaque Challenge Model

Background:

Vaccination with the Merck human adenovirus serotype-5 (HAdV-5) vectored HIV-1 subtype B gag/pol/nef vaccine was unexpectedly associated with enhanced susceptibility to HIV-1 infection in uncircumcised HAdV-5 seropositive men. It has been hypothesized that vaccination may have resulted in activated CD4+ T lymphocytes trafficking to mucosal sites thereby increasing targets for HIV infection. We have previously shown that AdV-vector vacci-nation in rhesus macaques resulted in an increase in the frequency of activated mucosal CD4+ T cells. However, whether this increase in activation is sufficient to increase susceptibility to HIV/SIV infection is unclear.

Methods:

To examine this scenario, we developed a preliminary, proof-of-concept vaccination-challenge model in order to examine vaccine-induced SIV susceptibility in rhesus macaques. Rhesus macaques (n = 10/group) were vaccinated with a simian AdV-7 (SAdV-7)-vector encoding an irrelevant insert (SARS spike) and challenged 5 weeks post-prime in an escalating dosing regimen starting with sub-infectious doses (1:10,000 or 2TCID₅₀) of SIVmac251.

Results:

In contrast to our previous study, the SAdV-7 vaccine regimen did not induce detectable mucosal CD4+ T cell activation at the time points assessed in animals obtained from a different vendor and housed in a different facility. Within the power of the study, we did not observe significantly increased SIV acquisition in SAdV-7-vaccinated (5/10) versus placebo-vaccinated (3/10) macaques after repeated low-dose intra-rectal SIVmac251 challenge (P < 0.2).

Conclusions:

These results lay groundwork for future experiments to assess vaccine-induced SIV susceptibility in rhesus macaques. Further larger-scale studies are necessary to confirm the AdV-vector vaccination associated trend towards increased SIV/HIV acquisition and clarify associated mechanisms.

Live attenuated varicella-zoster virus vaccine does not induce HIV target cell activation

BACKGROUND

Varicella-zoster virus (VZV) is under consideration as a promising recombinant viral vector to deliver foreign antigens including HIV. However, new vectors have come under increased scrutiny, since trials with adenovirus serotype 5-vectored (Ad5-vectored) HIV vaccine demonstrated increased HIV risk in individuals with pre-immunity to the vector that was thought to be associated with mucosal immune activation (IA). Therefore, given the prospect of developing an HIV/VZV chimeric vaccine, it is particularly important to define the impact of VZV vaccination on IA.

METHODS

Healthy VZV-seropositive Kenyan women (n = 44) were immunized with high-dose live attenuated VZV vaccine, and we assessed the expression on CD4+ T cells isolated from blood, cervix, and rectum of IA markers including CD38 and HLA-DR and of markers of cell migration and tissue retention, as well as the concentration of genital and intestinal cytokines. A delayed-start group (n = 22) was used to control for natural variations in these parameters.

RESULTS

Although immunogenic, VZV vaccination did not result in significant difference in the frequency of cervical activated (HLA-DR+CD38+) CD4+ T cells (median 1.61%, IQR 0.93%-2.76%) at 12 weeks after vaccination when compared with baseline (median 1.58%, IQR 0.75%-3.04%), the primary outcome for this study. VZV vaccination also had no measurable effect on any of the IA parameters at 4, 8, and 12 weeks after vaccination.

CONCLUSION

This study provides the first evidence to our knowledge about the effects of VZV vaccination on human mucosal IA status and supports further evaluation of VZV as a potential vector for an HIV vaccine.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02514018.

FUNDING

Primary support from the Canadian Institutes for Health Research (CIHR). For other sources, see Acknowledgments.

Single-cycle adenovirus vectors in the current vaccine landscape

INTRODUCTION

Traditional inactivated and protein vaccines generate strong antibodies, but struggle to generate T cell responses. Attenuated pathogen vaccines generate both, but risk causing the disease they aim to prevent. Newer gene-based vaccines drive both responses and avoid the risk of infection. While these replication-defective (RD) vaccines work well in small animals, they can be weak in humans because they do not replicate antigen genes like more potent replication-competent (RC) vaccines. RC vaccines generate substantially stronger immune responses, but also risk causing their own infections. To circumvent these problems, we developed single-cycle adenovirus (SC-Ad) vectors that amplify vaccine genes, but that avoid the risk of infection. This review will discuss these vectors and their prospects for use as vaccines.

AREAS COVERED

This review provides a background of different types of vaccines. The benefits of gene-based vaccines and their ability to replicate antigen genes are described. Adenovirus vectors are discussed and compared to other vaccine types. Replication-defective, single-cycle, and replication-competent Ad vaccines are compared.

EXPERT COMMENTARY

The potential utility of these vaccines are discussed when used against infectious diseases and as cancer vaccines. We propose a move away from replication-defective vaccines towards more robust replication-competent or single-cycle vaccines.

Immunoglobulin G1 Allotype Influences Antibody Subclass Distribution in Response to HIV gp140 Vaccination

Antibody subclasses exhibit extensive polymorphisms (allotypes) that could potentially impact the quality of HIV-vaccine induced B cell responses. Allotypes of immunoglobulin (Ig) G1, the most abundant serum antibody, have been shown to display altered functional properties in regard to serum half-life, Fc-receptor binding and FcRn-mediated mucosal transcytosis. To investigate the potential link between allotypic IgG1-variants and vaccine-generated humoral responses in a cohort of 14 HIV vaccine recipients, we developed a novel protocol for rapid IgG1-allotyping. We combined PCR and ELISA assays in a dual approach to determine the IgG1 allotype identity (G1m3 and/or G1m1) of trial participants, using human plasma and RNA isolated from PBMC. The IgG1-allotype distribution of our participants mirrored previously reported results for caucasoid populations. We observed elevated levels of HIV gp140-specific IgG1 and decreased IgG2 levels associated with the G1m1-allele, in contrast to G1m3 carriers. These data suggest that vaccinees homozygous for G1m1 are predisposed to develop elevated Ag-specific IgG1:IgG2 ratios compared to G1m3-carriers. This elevated IgG1:IgG2 ratio was further associated with higher FcγR-dimer engagement, a surrogate for potential antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) function. Although preliminary, these results suggest that IgG1 allotype may have a significant impact on IgG subclass distribution in response to vaccination and associated Fc-mediated effector functions. These results have important implications for ongoing HIV vaccine efficacy studies predicated on engagement of FcγR-mediated cellular functions including ADCC and ADCP, and warrant further investigation. Our novel allotyping protocol provides new tools to determine the potential impact of IgG1 allotypes on vaccine efficacy.

HIV As Trojan Exosome: Immunological Paradox Explained?

The HIV pandemic is still a major global challenge, despite the widespread availability of antiretroviral drugs. An effective vaccine would be the ideal approach to bringing the pandemic to an end. However, developing an effective HIV vaccine has proven to be an elusive goal. Three major human HIV vaccine trials revealed a strong trend toward greater risk of infection among vaccine recipients versus controls. A similar observation was made in a macaque SIV vaccine study. The mechanism explaining this phenomenon is not known. Here, a model is presented that may explain the troubling results of vaccine studies and an immunological paradox of HIV pathogenesis: preferential infection of HIV-specific T cells. The central hypothesis of this perspective is that as “Trojan exosomes” HIV particles can directly activate HIV-specific T cells enhancing their susceptibility to infection. Understanding the biology of HIV as an exosome may provide insights that enable novel approaches to vaccine development.

Complex immune correlates of protection in HIV-1 vaccine efficacy trials

Development of an efficacious HIV-1 vaccine is a major priority for improving human health worldwide. Vaccine-mediated protection against human pathogens can be achieved through elicitation of protective innate, humoral, and cellular responses. Identification of specific immune responses responsible for pathogen protection enables vaccine development and provides insights into host defenses against pathogens and the immunological mechanisms that most effectively fight infection. Defining immunological correlates of transmission risk in preclinical and clinical HIV-1 vaccine trials has moved the HIV-1 vaccine development field forward and directed new candidate vaccine development. Immune correlate studies are providing novel hypotheses about immunological mechanisms that may be responsible for preventing HIV-1 acquisition. Recent results from HIV-1 immune correlates work has demonstrated that there are multiple types of immune responses that together, comprise an immune correlate-thus implicating polyfunctional immune control of HIV-1 transmission. An in depth understanding of these complex immunological mechanisms of protection against HIV-1 will accelerate the development of an efficacious HIV-1 vaccine.

Increased humoral immunity by DNA vaccination using an α-tocopherol-based adjuvant

DNA vaccines induce broad immunity, which involves both humoral and strong cellular immunity, and can be rapidly designed for novel or evolving pathogens such as influenza. However, the humoral immunogenicity in humans and higher animals has been suboptimal compared with that of traditional vaccine approaches. We tested whether the emulsion-based and α-tocopherol containing adjuvant Diluvac Forte® has the ability to enhance the immunogenicity of a naked DNA vaccine (i.e., plasmid DNA). As a model vaccine, we used plasmids encoding both a surface-exposed viral glycoprotein (hemagglutinin) and an internal non-glycosylated nucleoprotein in the Th1/Th2 balanced CB6F1 mouse model. The naked DNA (50 µg) was premixed at a 1:1 volume/volume ratio with Diluvac Forte®, an emulsion containing different concentrations of α-tocopherol, the emulsion alone or endotoxin-free phosphate-buffered saline (PBS). The animals received 2 intracutaneous immunizations spaced 3 weeks apart. When combined with Diluvac Forte® or the emulsion containing α-tocopherol, the DNA vaccine induced a more potent and balanced immunoglobulin G (IgG)1 and IgG2c response, and both IgG subclass responses were significantly enhanced by the adjuvant. The DNA vaccine also induced CD4+ and CD8+ vaccine-specific T cells; however, the adjuvant did not exert a significant impact. We concluded that the emulsion-based adjuvant Diluvac Forte® enhanced the immunogenicity of a naked DNA vaccine encoding influenza proteins and that the adjuvant constituent α-tocopherol plays an important role in this immunogenicity. This induction of a potent and balanced humoral response without impairment of cellular immunity constitutes an important advancement toward effective DNA vaccines.

Adenovirus-Mediated Gene Delivery: Potential Applications for Gene and Cell-Based Therapies in the New Era of Personalized Medicine

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology, it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies. Despite numerous setbacks, efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases. It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies. There has been a long-lasting interest in using viral vectors, especially adenoviral vectors, to deliver therapeutic genes for the past two decades. Among all currently available viral vectors, adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types. The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development. In fact, among over 2,000 gene therapy clinical trials approved worldwide since 1989, a significant portion of the trials have utilized adenoviral vectors. This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors, including adenoviral biology, approaches to engineering adenoviral vectors, and their applications in clinical and pre-clinical studies with an emphasis in the areas of cancer treatment, vaccination and regenerative medicine. Current challenges and future directions regarding the use of adenoviral vectors are also discussed. It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

Assessment of Anti-HIV-1 Antibodies in Oral and Nasal Compartments of Volunteers From 3 Different Populations

In this study, we assessed the feasibility of collecting standardized nasal and salivary samples at centers in Nairobi (Kenya), Kigali (Rwanda), and London (United Kingdom) using different collection devices and media (synthetic absorptive matrices versus flocked swabs, and Salimetrics oral swabs versus whole oral fluid collection). We detected anti-Gag (p24) and envelope (gp140) antibodies in both nasal fluid and salivary collections from all HIV-infected individuals, and cross-reactive anti-p24 antibodies were detected in 10% of HIV-uninfected individuals enrolled at one site. Collections from the nasal turbinates were comparable with samples collected deeper in the nasopharyngeal tract, and the yield of anti-p24 IgA in the whole oral fluid samples was higher than in samples collected from the parotid gland. We noted a trend toward reduced levels of anti-HIV antibody in the volunteers receiving anti-retroviral therapy. Levels of antibodies were stable over multiple collection visits. Overall, this study shows that nasal and salivary samples can be collected in a standardized manner over repeated visits in both low- and high-resource settings. These methods may be used in support for future HIV vaccine clinical trials.

Covalent decoration of adenovirus vector capsids with the carbohydrate epitope αGal does not improve vector immunogenicity, but allows to study the in vivo fate of adenovirus immunocomplexes

Adenovirus-based vectors are promising tools for genetic vaccination. However, several obstacles have to be overcome prior to a routine clinical application of adenovirus-based vectors as efficacious vectored vaccines. The linear trisaccharide epitope αGal (alpha-Gal) with the carbohydrate sequence galactose-α-1,3-galactosyl-β-1,4-N-acetylglucosamine has been described as a potent adjuvant for recombinant or attenuated vaccines. Humans and α-1,3-galactosyltransferase knockout mice do not express this epitope. Upon exposure of α-1,3-galactosyltransferase-deficient organisms to αGal in the environment, large amounts of circulating anti-Gal antibodies are produced consistently. Immunocomplexes formed between recombinant αGal-decorated vaccines and anti-Gal antibodies exhibit superior immunogenicity. We studied the effects of the trisaccharide epitope on CD8 T cell responses that are directed specifically to vector-encoded transgenic antigens. For that, covalently αGal-decorated adenovirus vectors were delivered to anti-Gal α-1,3-galactosyltransferase knockout mice. We generated replication-defective, E1-deleted adenovirus type 5 vectors that were decorated with αGal at the hexon hypervariable regions 1 or 5, at fiber knob, or at penton base. Surprisingly, none of the adenovirus immunocomplexes being formed from αGal-decorated adenovirus vectors and anti-Gal immunoglobulins improved the frequencies of CD8 T cell responses against the transgenic antigen ovalbumin. Humoral immunity directed to the adenovirus vector was neither increased. However, our data indicated that decoration of Ad vectors with the αGal epitope is a powerful tool to analyze the fate of adenovirus immunocomplexes in vivo.

Targeting Glycans of HIV Envelope Glycoproteins for Vaccine Design

The surface of the envelope spike of the human immunodeficiency virus (HIV) is covered with a dense array of glycans, which is sufficient to impede the host antibody response while maintaining a window for receptor recognition. The glycan density significantly exceeds that typically observed on self glycoproteins and is sufficiently high to disrupt the maturation process of glycans, from oligomannose- to complex-type glycosylation, that normally occurs during glycoprotein transit through the secretory system. It is notable that this generates a degree of homogeneity not seen in the highly mutated protein moiety. The conserved, close glycan packing and divergences from default glycan processing give a window for immune recognition. Encouragingly, in a subset of individuals, broadly neutralizing antibodies (bNAbs) have been isolated that recognize these features and are protective in passive-transfer models. Here, we review the recent advances in our understanding of the glycan shield of HIV and outline the strategies that are being pursued to elicit glycan-binding bNAbs by vaccination.

Replicating Single-Cycle Adenovirus Vectors Generate Amplified Influenza Vaccine Responses

Head-to-head comparisons of conventional influenza vaccines with adenovirus (Ad) gene-based vaccines demonstrated that these viral vectors can mediate more potent protection against influenza virus infection in animal models. In most cases, Ad vaccines are engineered to be replication-defective (RD-Ad) vectors. In contrast, replication-competent Ad (RC-Ad) vaccines are markedly more potent but risk causing adenovirus diseases in vaccine recipients and health care workers. To harness antigen gene replication but avoid production of infectious virions, we developed "single-cycle" adenovirus (SC-Ad) vectors. Previous work demonstrated that SC-Ads amplify transgene expression 100-fold and produce markedly stronger and more persistent immune responses than RD-Ad vectors in Syrian hamsters and rhesus macaques. To test them as potential vaccines, we engineered RD and SC versions of adenovirus serotype 6 (Ad6) to express the hemagglutinin (HA) gene from influenza A/PR/8/34 virus. We show here that it takes approximately 33 times less SC-Ad6 than RD-Ad6 to produce equal amounts of HA antigen in vitro SC-Ad produced markedly higher HA binding and hemagglutination inhibition (HAI) titers than RD-Ad in Syrian hamsters. SC-Ad-vaccinated cotton rats had markedly lower influenza titers than RD-Ad-vaccinated animals after challenge with influenza A/PR/8/34 virus. These data suggest that SC-Ads may be more potent vaccine platforms than conventional RD-Ad vectors and may have utility as "needle-free" mucosal vaccines.

IMPORTANCE

Most adenovirus vaccines that are being tested are replication-defective adenoviruses (RD-Ads). This work describes testing newer single-cycle adenovirus (SC-Ad) vectors that replicate transgenes to amplify protein production and immune responses. We show that SC-Ads generate markedly more influenza virus hemagglutinin protein and require substantially less vector to generate the same immune responses as RD-Ad vectors. SC-Ads therefore hold promise to be more potent vectors and vaccines than current RD-Ad vectors.