Development of replication-competent viral vectors for HIV vaccine delivery

The Coming of Age of Nucleic Acid Vaccines during COVID-19

In the 21st century, several emergent viruses have posed a global threat. Each pathogen has emphasized the value of rapid and scalable vaccine development programs. The ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has made the importance of such efforts especially clear. New biotechnological advances in vaccinology allow for recent advances that provide only the nucleic acid building blocks of an antigen, eliminating many safety concerns. During the COVID-19 pandemic, these DNA and RNA vaccines have facilitated the development and deployment of vaccines at an unprecedented pace. This success was attributable at least in part to broader shifts in scientific research relative to prior epidemics: the genome of SARS-CoV-2 was available as early as January 2020, facilitating global efforts in the development of DNA and RNA vaccines within 2 weeks of the international community becoming aware of the new viral threat. Additionally, these technologies that were previously only theoretical are not only safe but also highly efficacious. Although historically a slow process, the rapid development of vaccines during the COVID-19 crisis reveals a major shift in vaccine technologies. Here, we provide historical context for the emergence of these paradigm-shifting vaccines. We describe several DNA and RNA vaccines in terms of their efficacy, safety, and approval status. We also discuss patterns in worldwide distribution. The advances made since early 2020 provide an exceptional illustration of how rapidly vaccine development technology has advanced in the last 2 decades in particular and suggest a new era in vaccines against emerging pathogens. IMPORTANCE The SARS-CoV-2 pandemic has caused untold damage globally, presenting unusual demands on but also unique opportunities for vaccine development. The development, production, and distribution of vaccines are imperative to saving lives, preventing severe illness, and reducing the economic and social burdens caused by the COVID-19 pandemic. Although vaccine technologies that provide the DNA or RNA sequence of an antigen had never previously been approved for use in humans, they have played a major role in the management of SARS-CoV-2. In this review, we discuss the history of these vaccines and how they have been applied to SARS-CoV-2. Additionally, given that the evolution of new SARS-CoV-2 variants continues to present a significant challenge in 2022, these vaccines remain an important and evolving tool in the biomedical response to the pandemic.

Nano-vaccines for gene delivery against HIV-1 infection

INTRODUCTION

Over the last four decades, human immunodeficiency virus type 1 (HIV-1) infection has been a major public health concern. It is acknowledged that an effective vaccine remains the best hope for eliminating the HIV-1 pandemic. The prophylaxis of HIV-1 infection remains a central theme because of the absence of an available HIV-1 vaccine. The incapability of conventional delivery strategies to induce potent immunity is a crucial task to overcome and ultimately lead to a major obstacle in HIV-1 vaccine research.

AREAS COVERED

The literature search was conducted in the following databases: PubMed, Web of Science, and Embase. Nano-platforms based vaccines have proven prophylaxis of various diseases for effectively activating the immune system. Nano-vaccines, including non-viral and viral vectored nano-vaccines, are in a position to improve the effectiveness of HIV-1 antigen delivery and enhance the innate and adaptive immune responses against HIV-1. Compared to traditional vaccination strategies, genetic immunization can elicit a long-term immune response to provide protective immunity for HIV-1 prevention.

EXPERT OPINION

The research progress on nano-vaccines for gene delivery against HIV-1 was discussed. The vaccine strategies based on nano-platforms that are being applied to stimulate effective HIV-1-specific cellular and humoral immune responses were particularly emphasized.

The Coming of Age of Nucleic Acid Vaccines during COVID-19

In the 21st century, several emergent viruses have posed a global threat. Each pathogen has emphasized the value of rapid and scalable vaccine development programs. The ongoing SARS-CoV-2 pandemic has made the importance of such efforts especially clear. New biotechnological advances in vaccinology allow for recent advances that provide only the nucleic acid building blocks of an antigen, eliminating many safety concerns. During the COVID-19 pandemic, these DNA and RNA vaccines have facilitated the development and deployment of vaccines at an unprecedented pace. This success was attributable at least in part to broader shifts in scientific research relative to prior epidemics; the genome of SARS-CoV-2 was available as early as January 2020, facilitating global efforts in the development of DNA and RNA vaccines within two weeks of the international community becoming aware of the new viral threat. Additionally, these technologies that were previously only theoretical are not only safe but also highly efficacious. Although historically a slow process, the rapid development of vaccines during the COVID-19 crisis reveals a major shift in vaccine technologies. Here, we provide historical context for the emergence of these paradigm-shifting vaccines. We describe several DNA and RNA vaccines and in terms of their efficacy, safety, and approval status. We also discuss patterns in worldwide distribution. The advances made since early 2020 provide an exceptional illustration of how rapidly vaccine development technology has advanced in the last two decades in particular and suggest a new era in vaccines against emerging pathogens.

Applications of self-replicating RNA

Self-replicating RNA viral vectors have been engineered for both prophylactic and therapeutic applications. Mainly the areas of infectious diseases and cancer have been targeted. Both positive and negative strand RNA viruses have been utilized including alphaviruses, flaviviruses, measles viruses and rhabdoviruses. The high-level of RNA amplification has provided efficient expression of viral surface proteins and tumor antigens. Immunization studies in animal models have elicit robust neutralizing antibody responses. In the context of infectious diseases, immunization with self-replicating RNA viral vectors has provided protection against challenges with lethal doses of pathogens in animal models. Similarly, immunization with vectors expressing tumor antigens has resulted in tumor regression and eradication and protection against tumor challenges in animal models. The transient nature and non-integration of viral RNA into the host genome are ideal features for vaccine development. Moreover, self-replicating RNA viral vectors show great flexibility as they can be applied as recombinant viral particles, RNA replicons or DNA replicon plasmids. Several clinical trials have been conducted especially in the area of cancer immunotherapy.

Targeting memory T cell metabolism to improve immunity

Vaccination affords protection from disease by activating pathogen-specific immune cells and facilitating the development of persistent immunologic memory toward the vaccine-specific pathogen. Current vaccine regimens are often based on the efficiency of the acute immune response, and not necessarily on the generation of memory cells, in part because the mechanisms underlying the development of efficient immune memory remain incompletely understood. This Review describes recent advances in defining memory T cell metabolism and how metabolism of these cells might be altered in patients affected by mitochondrial diseases or metabolic syndrome, who show higher susceptibility to recurrent infections and higher rates of vaccine failure. It discusses how this new understanding could add to the way we think about immunologic memory, vaccine development, and cancer immunotherapy.

Strategies for successful designing of immunocontraceptive vaccines and recent updates in vaccine development against sexually transmitted infections - A Review

Background

Objective

Methods

Results

Conclusion

Mucosal Priming with a Recombinant Influenza A Virus-Vectored Vaccine Elicits T-Cell and Antibody Responses to HIV-1 in Mice

Recombinant influenza A viral (IAV) vectors are potential to stimulate systemic and mucosal immunity, but the packaging capacity is limited and only one or a few epitopes can be carried. Here, we report the generation of a replication-competent IAV vector that carries a full-length HIV-1 p24 gene linked to the 5'-terminal coding region of the neuraminidase segment via a protease cleavage sequence (IAV-p24). IAV-p24 was successfully rescued and stably propagated, and P24 protein was efficiently expressed in infected mammalian cells. In BALB/c mice, IAV-p24 showed attenuated pathogenicity compared to that of the parental A/PR/8/34 (H1N1) virus. An intranasal inoculation with IAV-p24 elicited moderate HIV-specific cell-mediated immune (CMI) responses in the airway and vaginal tracts and in the spleen, and an intranasal boost with a replication-incompetent adenovirus type 2 vector expressing the HIV-1 gag gene (Ad2-gag) greatly improved these responses. Importantly, compared to an Ad2-gag prime plus IAV-p24 boost regimen, the IAV-p24 prime plus Ad2-gag boost regimen had a greater efficacy in eliciting HIV-specific CMI responses. P24-specific CD8⁺ T cells and antibodies were robustly provoked both systemically and in mucosal sites and showed long-term durability, revealing that IAV-p24 may be used as a mucosa-targeted priming vaccine. Our results illustrate that IAV-p24 is able to prime systemic and mucosal immunity against HIV-1 and warrants further evaluation in nonhuman primates.IMPORTANCE An effective HIV-1 vaccine remains elusive despite nearly 40 years of research. CD8⁺ T cells and protective antibodies may both be desirable for preventing HIV-1 infection in susceptible mucosal sites. Recombinant influenza A virus (IAV) vector has the potential to stimulate these immune responses, but the packaging capacity is extremely limited. Here, we describe a replication-competent IAV vector expressing the HIV-1 p24 gene (IAV-p24). Unlike most other IAV vectors that carried one or several antigenic epitopes, IAV-p24 stably expressed the full-length P24 protein, which contains multiple epitopes and is highly conserved among all known HIV-1 sequences. Compared to the parental A/PR/8/34 (H1N1) virus, IAV-p24 showed an attenuated pathogenicity in BALB/c mice. When combined with an adenovirus vector expressing the HIV-1 gag gene, IAV-p24 was able to prime P24-specific systemic and mucosal immune responses. IAV-p24 as an alternative priming vaccine against HIV-1 warrants further evaluation in nonhuman primates.

Emerging concepts in the science of vaccine adjuvants

Adjuvants are vaccine components that enhance the magnitude, breadth and durability of the immune response. Following its introduction in the 1920s, alum remained the only adjuvant licensed for human use for the next 70 years. Since the 1990s, a further five adjuvants have been included in licensed vaccines, but the molecular mechanisms by which these adjuvants work remain only partially understood. However, a revolution in our understanding of the activation of the innate immune system through pattern recognition receptors (PRRs) is improving the mechanistic understanding of adjuvants, and recent conceptual advances highlight the notion that tissue damage, different forms of cell death, and metabolic and nutrient sensors can all modulate the innate immune system to activate adaptive immunity. Furthermore, recent advances in the use of systems biology to probe the molecular networks driving immune response to vaccines ('systems vaccinology') are revealing mechanistic insights and providing a new paradigm for the vaccine discovery and development process. Here, we review the 'known knowns' and 'known unknowns' of adjuvants, discuss these emerging concepts and highlight how our expanding knowledge about innate immunity and systems vaccinology are revitalizing the science and development of novel adjuvants for use in vaccines against COVID-19 and future pandemics.

The immunological impact of adenovirus early genes on vaccine-induced responses in mice and nonhuman primates

Adenovirus (Ad) is being explored for use in the prevention and treatment of a variety of infectious diseases and cancers. Ad with a deletion in early region 3 (ΔE3) provokes a stronger immune response than Ad with deletions in early regions 1 and E3 (ΔE1/ΔE3). The ΔE1/ΔE3 Ads are more popular because they can carry a larger transgene and because of the deleted E1 (E1A and E1B), are perceived safer for clinical use. Ad with a deletion in E1B55K (ΔE1B55K) has been in phase III clinical trials for use in cancer therapy in the US and has been approved for use in head and neck tumor therapy in China, demonstrating that Ad containing E1A are safe for clinical use. We have shown previously that ΔE1B55K Ad, even while promoting lower levels of an inserted transgene, promoted similar levels of transgene-specific immune responses as a ΔE3 Ad. Products of the Ad early region 4 (E4) limit the ability of cells to mount an innate immune response. Using this knowledge, we deleted the Ad E4 open reading frames 1-4 (E4orf1-4) from the ΔE1B55K Ad. Here, we show that innate cytokine network genes are elevated in the ΔE4 Ad-infected cells beyond that of ΔE3 Ad-infected cells. Further, in immunized mice the IgG2a subclass was favored as was the IgG1 subclass in immunized nonhuman primates. Thus, Ad E4 impacts immune responses in cells, in immunized mice, and immunized nonhuman primates. These Ad may offer advantages that are beneficial for clinical use.Importance: Adenovirus (Ad) is being explored for use in the prevention and treatment of a variety of infectious diseases and cancers. Here we provide evidence in cells, mice, and nonhuman primates supporting the notion that Ad early gene-products limit specific immune responses. Ad constructed with deletions in early genes and expressing HIV envelope protein was shown to induce greater HIV-specific cellular immune responses and higher titer antibodies compared to the parental Ad with the early genes. In addition to eliciting enhanced immunity, the deleted Ad possesses more space for insertion of additional or larger transgenes needed for targeting other infectious agents or cancers.

Platforms Exploited for SARS-CoV-2 Vaccine Development

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the only zoonotic-origin coronavirus (CoV) that has reached the pandemic stage. The virus uses its spike (S) glycoprotein to attach to the host cells and initiate a cascade of events that leads to infection. It has sternly affected public health, economy, education, and social behavior around the world. Several scientific and medical communities have mounted concerted efforts to limit this pandemic and the subsequent wave of viral spread by developing preventative and potential vaccines. So far, no medicine or vaccine has been approved to prevent or treat coronavirus disease 2019 (COVID-19). This review describes the latest advances in the development of SARS-CoV-2 vaccines for humans, mainly focusing on the lead candidates in clinical trials. Moreover, we seek to provide both the advantages and the disadvantages of the leading platforms used in current vaccine development, based on past vaccine delivery efforts for non-SARS CoV-2 infections. We also highlight the population groups who should receive a vaccine against COVID-19 in a timely manner to eradicate the pandemic rapidly.

Development of vaccines against the sexually transmitted infections gonorrhoea, syphilis, Chlamydia, herpes simplex virus, human immunodeficiency virus and Zika virus

The success in preventing hepatitis B virus and human papillomavirus infections by means of vaccination paves the way for the development of other vaccines to prevent sexually transmitted infections (STIs) such as gonorrhoea, syphilis, chlamydia, herpes simplex virus, human immunodeficiency virus and Zika virus. The current status of vaccine development for these infections will be explored in this review.

The general principles for success include the need for prevention of latency, persistence and repeat infections. A reduction in transmission of STIs would reduce the global burden of disease. Therapeutic activity of vaccines against STIs would be advantageous over preventative activity alone, and prevention of congenital and neonatal infections would be an added benefit. There would be an added value in the prevention of long-term consequences of STIs. It may be possible to re-purpose ‘old’ vaccines for new indications. One of the major challenges is the determination of the target populations for STI vaccination.

[Vaccine of the future]

La vaccination représente une des avancées majeures dans le domaine de la santé. Les premiers vaccins ont été produits sur un concept assez empirique reposant sur la stratégie des « 3 i » : isolement, inactivation, injection. Plus récemment sont apparus les vaccins protéiques. Cependant l’émergence de nouveaux pathogènes, l’inefficacité des stratégies vaccinales actuelles pour protéger contre certaines infections, la nécessité de pouvoir développer rapidement et à bas coût de revient des vaccins ont conduit à développer de nouveaux types de vaccins. C’est dans ce contexte que se sont développés des vaccins basés sur l’utilisation des séquences codantes d’acides nucléiques des antigènes d’intérêt (vecteurs viraux, vaccins ADN, vaccins ARN) visant à améliorer l’efficacité des vaccins actuellement disponibles et à proposer des plateformes génériques potentiellement utilisables contre un grand nombre de pathogènes différents. Outre l’utilisation de ces nouveaux vaccins, les recherches vaccinales en cours bénéficient d’évolutions technologiques visant à délivrer de manière optimale les vaccins, en ciblant par exemple les cellules dendritiques, et de mieux caractériser les antigènes d’intérêt via notamment l’utilisation de la vaccinologie inverse.

Mucosal Vaccine Approaches for Prevention of HIV and SIV Transmission

Optimal protective immunity to HIV will likely require that plasma cells, memory B cells and memory T cells be stationed in mucosal tissues at portals of viral entry. Mucosal vaccine administration is more effective than parenteral vaccine delivery for this purpose. The challenge has been to achieve efficient vaccine uptake at mucosal surfaces, and to identify safe and effective adjuvants, especially for mucosally administered HIV envelope protein immunogens. Here, we discuss strategies used to deliver potential HIV vaccine candidates in the intestine, respiratory tract, and male and female genital tract of humans and nonhuman primates. We also review mucosal adjuvants, including Toll-like receptor agonists, which may adjuvant both mucosal humoral and cellular immune responses to HIV protein immunogens.

Lessons for general vaccinology research from attempts to develop an HIV vaccine

In the past when large investments have been made in tackling narrow scientific challenges, the enormous expansion in our knowledge in one small area has had a spill-over effect on research and treatment of other diseases. The large investment in HIV vaccine development in recent years has the potential for such an effect on vaccine development for other diseases. HIV vaccine developers have experienced repeated failure using the standard approaches to vaccine development. This has forced them to consider immune responses in greater depth and detail. It has led to a recognition of the importance of epitopic specificity in both antibody and T cell responses. Also, it has led to an understanding of the importance of affinity maturation in antibody responses and the quality of T cell responses in T cell-mediated immunity. It has advanced the development of many novel vaccine vectors and vehicles that are now available for use in other vaccines. Further, it has focused attention on the impact of research funding mechanisms and community engagement on vaccine development. These developments and considerations have implications for vaccinology more generally. Some suggestions are made for investigators working on other "hard-to-develop" vaccines.

Replication-Competent NYVAC-KC Yields Improved Immunogenicity to HIV-1 Antigens in Rhesus Macaques Compared to Nonreplicating NYVAC

As part of the continuing effort to develop an effective HIV vaccine, we generated a poxviral vaccine vector (previously described) designed to improve on the results of the RV144 phase III clinical trial. The construct, NYVAC-KC, is a replication-competent, attenuated recombinant of the vaccinia virus strain NYVAC. NYVAC is a vector that has been used in many previous clinical studies but is replication deficient. Here, we report a side-by-side comparison of replication-restricted NYVAC and replication-competent NYVAC-KC in a nonhuman primate study, which utilized a prime-boost regimen similar to that of RV144. NYVAC-C and NYVAC-C-KC express the HIV-1 antigens gp140, and Gag/Gag-Pol-Nef-derived virus-like particles (VLPs) from clade C and were used as the prime, with recombinant virus plus envelope protein used as the boost. In nearly every T and B cell immune assay against HIV-1, including neutralization and antibody binding, NYVAC-C-KC induced a greater immune response than NYVAC-C, indicating that replication competence in a poxvirus may improve upon the modestly successful regimen used in the RV144 clinical trial.IMPORTANCE Though the RV144 phase III clinical trial showed promise that an effective vaccine against HIV-1 is possible, a successful vaccine will require improvement over the vaccine candidate (ALVAC) used in the RV144 study. With that goal in mind, we have tested in nonhuman primates an attenuated but replication-competent vector, NYVAC-KC, in direct comparison to its parental vector, NYVAC, which is replication restricted in human cells, similar to the ALVAC vector used in RV144. We have utilized a prime-boost regimen for administration of the vaccine candidate that is similar to the one used in the RV144 study. The results of this study indicate that a replication-competent poxvirus vector may improve upon the effectiveness of the RV144 clinical trial vaccine candidate.

Defining the interval for monitoring potential adverse events following immunization (AEFIs) after receipt of live viral vectored vaccines

Live viral vectors that express heterologous antigens of the target pathogen are being investigated in the development of novel vaccines against serious infectious agents like HIV and Ebola. As some live recombinant vectored vaccines may be replication-competent, a key challenge is defining the length of time for monitoring potential adverse events following immunization (AEFI) in clinical trials and epidemiologic studies. This time period must be chosen with care and based on considerations of pre-clinical and clinical trials data, biological plausibility and practical feasibility. The available options include: (1) adapting from the current relevant regulatory guidelines; (2) convening a panel of experts to review the evidence from a systematic literature search to narrow down a list of likely potential or known AEFI and establish the optimal risk window(s); and (3) conducting "near real-time" prospective monitoring for unknown clustering's of AEFI in validated large linked vaccine safety databases using Rapid Cycle Analysis for pre-specified adverse events of special interest (AESI) and Treescan to identify previously unsuspected outcomes. The risk window established by any of these options could be used along with (4) establishing a registry of clinically validated pre-specified AESI to include in case-control studies. Depending on the infrastructure, human resources and databases available in different countries, the appropriate option or combination of options can be determined by regulatory agencies and investigators.

First-in-human randomized controlled trial of an oral, replicating adenovirus 26 vector vaccine for HIV-1

BACKGROUND

Live, attenuated viral vectors that express HIV-1 antigens are being investigated as an approach to generating durable immune responses against HIV-1 in humans. We recently developed a replication-competent, highly attenuated Ad26 vector that expresses mosaic HIV-1 Env (rcAd26.MOS1.HIV-Env, "rcAd26"). Here we present the results of a first-in-human, placebo-controlled clinical trial to test the safety, immunogenicity and mucosal shedding of rcAd26 given orally.

METHODS

Healthy adults were randomly assigned to receive a single oral dose of vaccine or placebo at 5:1 ratio in a dosage escalation of 10^8 to 10^11 rcAd26 VP (nominal doses) at University of Rochester Medical Center, Rochester, NY, USA. Participants were isolated and monitored for reactogenicity for 10 days post-vaccination, and adverse events were recorded up to day 112. Rectal and oropharyngeal secretions were evaluated for shedding of the vaccine. Humoral and cellular immune responses were measured. Household contacts were monitored for secondary vaccine transmission.

RESULTS

We enrolled 22 participants and 11 household contacts between February 7 and June 24, 2015. 18 participants received one dose of HIV-1 vaccine and 4 participants received placebo. The vaccine caused only mild to moderate adverse events. No vaccine-related SAEs were observed. No infectious rcAd26 viral particles were detected in rectal or oropharyngeal secretions from any participant. Env-specific ELISA and ELISPOT responses were undetectable. No household contacts developed vaccine-induced HIV-1 seropositivity or vaccine-associated illness.

CONCLUSIONS

The highly attenuated rcAd26.MOS1.HIV-Env vaccine was well tolerated up to 10^11 VP in healthy, HIV-1-uninfected adults, though the single dose was poorly immunogenic suggesting the replicative capacity of the vector was too attenuated. There was no evidence of shedding of infectious virus or secondary vaccine transmission following the isolation period. These data suggest the use of less attenuated viral vectors in future studies of live, oral HIV-1 vaccines.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02366013.

Development of an epitope-based HIV-1 vaccine strategy from HIV-1 lipopeptide to dendritic-based vaccines

INTRODUCTION

Development of a safe, effective and globally affordable Human Immunodeficiency Virus strain 1 (HIV-1) vaccine offers the best hope for future control of the HIV-1 pandemic. However, with the exception of the recent RV144 trial, which elicited a modest level of protection against infection, no vaccine candidate has shown efficacy in preventing HIV-1 infection or in controlling virus replication in humans. There is also a great need for a successful immunotherapeutic vaccine since combination antiretroviral therapy (cART) does not eliminate the reservoir of HIV-infected cells. But to date, no vaccine candidate has proven to significantly alter the natural history of an individual with HIV-1 infection. Areas covered: For over 25 years, the ANRS (France Recherche Nord&Sud Sida-HIV hépatites) has been committed to an original program combining basic science and clinical research developing an epitope-based vaccine strategy to induce a multiepitopic cellular response against HIV-1. This review describes the evolution of concepts, based on strategies using HIV-1 lipopeptides towards the use of dendritic cell (DC) manipulation. Expert commentary: Understanding the crucial role of DCs in immune responses allowed moving from the non-specific administration of HIV-1 sequences with lipopeptides to DC-based vaccines. These DC-targeting strategies should improve HIV-1 vaccine efficacy.

Induction of Genotype Cross-Reactive, Hepatitis C Virus-Specific, Cell-Mediated Immunity in DNA-Vaccinated Mice

A universal hepatitis C virus (HCV) vaccine should elicit multiantigenic, multigenotypic responses, which are more likely to protect against challenge with the range of genotypes and subtypes circulating in the community. A vaccine cocktail and vaccines encoding consensus HCV sequences are attractive approaches to achieve this goal. Consequently, in a series of mouse vaccination studies, we compared the immunogenicity of a DNA vaccine encoding a consensus HCV nonstructural 5B (NS5B) protein to that of a cocktail of DNA plasmids encoding the genotype 1b (Gt1b) and Gt3a NS5B proteins. To complement this study, we assessed responses to a multiantigenic cocktail regimen by comparing a DNA vaccine cocktail encoding Gt1b and Gt3a NS3, NS4, and NS5B proteins to a single-genotype NS3/4/5B DNA vaccine. To thoroughly evaluate in vivo cytotoxic T lymphocyte (CTL) and T helper (Th) cell responses against Gt1b and Gt3a HCV peptide-pulsed target cells, we exploited a novel fluorescent-target array (FTA). FTA and enzyme-linked immunosorbent spot (ELISpot) analyses collectively indicated that the cocktail regimens elicited higher responses to Gt1b and Gt3a NS5B proteins than those with the consensus vaccine, while the multiantigenic DNA cocktail significantly increased the responses to NS3 and NS5B compared to those elicited by the single-genotype vaccines. Thus, a DNA cocktail vaccination regimen is more effective than a consensus vaccine or a monovalent vaccine at increasing the breadth of multigenotypic T cell responses, which has implications for the development of vaccines for communities where multiple HCV genotypes circulate.IMPORTANCE Despite the development of highly effective direct-acting antivirals (DAA), infections with hepatitis C virus (HCV) continue, particularly in countries where the supply of DAA is limited. Furthermore, patients who eliminate the virus as a result of DAA therapy can still be reinfected. Thus, a vaccine for HCV is urgently required, but the heterogeneity of HCV strains makes the development of a universal vaccine difficult. To address this, we developed a novel cytolytic DNA vaccine which elicits robust cell-mediated immunity (CMI) to the nonstructural (NS) proteins in vaccinated animals. We compared the immune responses against genotypes 1 and 3 that were elicited by a consensus DNA vaccine or a DNA vaccine cocktail and showed that the cocktail induced higher levels of CMI to the NS proteins of both genotypes. This study suggests that a universal HCV vaccine can most readily be achieved by use of a DNA vaccine cocktail.

Novel Concepts for HIV Vaccine Vector Design

The unprecedented challenges of developing effective vaccines against intracellular pathogens such as HIV, malaria, and tuberculosis have resulted in more rational approaches to vaccine development. Apart from the recent advances in the design and selection of improved epitopes and adjuvants, there are also ongoing efforts to optimize delivery platforms.

The unprecedented challenges of developing effective vaccines against intracellular pathogens such as HIV, malaria, and tuberculosis have resulted in more rational approaches to vaccine development. Apart from the recent advances in the design and selection of improved epitopes and adjuvants, there are also ongoing efforts to optimize delivery platforms. Viral vectors are the best-characterized delivery tools because of their intrinsic adjuvant capability, unique cellular tropism, and ability to trigger robust adaptive immune responses. However, a known limitation of viral vectors is preexisting immunity, and ongoing efforts are aimed at developing novel vector platforms with lower seroprevalence. It is also becoming increasingly clear that different vectors, even those derived from phylogenetically similar viruses, can elicit substantially distinct immune responses, in terms of quantity, quality, and location, which can ultimately affect immune protection. This review provides a summary of the status of viral vector development for HIV vaccines, with a particular focus on novel viral vectors and the types of adaptive immune responses that they induce.

Development of a recombinant yellow fever vector expressing a HIV clade C founder envelope gp120

Development of a HIV-1 vaccine is a major global priority. The yellow fever virus (YFV) attenuated vaccine 17D is among the most effective of currently used vaccines. However, the stability of the YFV17D vector when carrying non-flavivirus genes has been problematic. We have constructed and expressed HIV-1 Env in YFV17D with either single transmembrane (STM) or double transmembrane (DTM) YFV E protein domains for the development of anti-HIV antibodies. Here we describe modifications of the YFV17D vector such that HIV-1 Env gp120 is expressed in up to 5 passages in Vero cells. Immunization with recombinant YFV17D vector prime followed by HIV-1 CH505 TF gp120 protein boosts were able to induce neutralizing antibodies for a HIV-1 tier 1 isolate in mice. This modified YFV vector may be a starting point for constructing HIV-1 vaccine candidate priming vectors.

Lessons from HIV-1 vaccine efficacy trials

PURPOSE OF REVIEW

Only four HIV-1 vaccine concepts have been tested in six efficacy trials with no product licensed to date. Several scientific and programmatic lessons can be learned from these studies generating new hypotheses and guiding future steps.

RECENT FINDINGS

RV144 [ALVAC-HIV (canarypox vector) and AIDSVAX B/E (bivalent gp120 HIV-1 subtype B and CRF01_AE)] remains the only efficacy trial that demonstrated a modest vaccine efficacy, which led to the identification of immune correlates of risk. Progress on subtype-specific, ALVAC (canarypox vector) and gp120 vaccine prime-boost approaches has been slow, but we are finally close to the launch of an efficacy study in Africa in 2016. The quest of a globally effective HIV-1 vaccine has led to the development of new approaches. Efficacy studies of combinations of Adenovirus type 26 (Ad26)/Modified Vaccinia Ankara (MVA)/gp140 vaccines with mosaic designs will enter efficacy studies mid-2017 and cytomegalovirus (CMV)-vectored vaccines begin Phase I studies at the same time. Future HIV-1 vaccine efficacy trials face practical challenges as effective nonvaccine prevention programs are projected to decrease HIV-1 incidence.

SUMMARY

An HIV-1 vaccine is urgently needed. Increased industry involvement, mobilization of resources, expansion of a robust pipeline of new concepts, and robust preclinical challenge studies will be essential to accelerate efficacy testing of next generation HIV-1 vaccine candidates.

Novel approaches in preclinical HIV vaccine research

PURPOSE OF REVIEW

The purpose is to review recent novel approaches in HIV vaccine research and development being undertaken in the preclinical and early clinical space, as well as related and novel nonvaccine approaches such as genetic delivery of broadly neutralizing antibodies for protection from HIV infection and AIDS.

RECENT FINDINGS

We review novel HIV envelope immunogen design, including native trimer and germline targeting approaches as well as genetic delivery of broadly neutralizing antibodies and replicating vector vaccinesSUMMARY: Despite 30+ years of research and development, and billions of dollars spent, a well tolerated and effective HIV vaccine remains a public health priority for any chance of ending the AIDS pandemic. It has become very clear that significant investments in novel technologies, innovation, and multidisciplinary science will be necessary to accelerate progress.

Profiling the neutralizing antibody response in chronically HIV-1 CRF07_BC-infected intravenous drug users naïve to antiretroviral therapy

Characterizing neutralizing antibody (NAb) responses in individuals infected with diverse HIV-1 strains is necessary to reveal the novel targets for regional preventive and therapeutic strategies development. We evaluated the prevalence, breadth, and potency of NAb responses in 98 CRF07_BC-infected individuals using a large, multi-subtype panel of 30 tier 2-3 Env-pseudotyped viruses. Furthermore, we compared the neutralization pattern of CRF07_BC-infected people with that of subtype B’-infected individuals in China. Of the 98 plasma samples tested, 18% neutralized more than 80% of viruses in the panel, and 53% neutralized more than 50%, suggesting the presence of broadly NAbs in these individuals. A preferential intra-subtype neutralization of CRF07_BC was found. Notably, CRF07_BC-infected individuals generated higher neutralization titers against intra-subtype viruses than subtype B’-infected individuals with longer infection length. However, subtype B’-infected individuals mounted broader neutralization responses against inter-subtype viruses than CRF07_BC infection with shorter infection time, indicating the transition from narrow autologous to broad heterologous neutralization over time. Neutralization activity of the top six plasmas from each cohort was attributable to IgG fraction, and half of them developed CD4 binding site antibody reactivity. Heatmap analysis identified three statistically robust clusters of plasmas that offer valuable resources for further in-depth virological and immunological study.

Live virus vaccines based on a vesicular stomatitis virus (VSV) backbone: Standardized template with key considerations for a risk/benefit assessment

The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to evaluate the safety of live, recombinant viral vaccines incorporating genes from heterologous viral and other microbial pathogens in their genome (so-called "chimeric virus vaccines"). Many such viral vector vaccines are now at various stages of clinical evaluation. Here, we introduce an attenuated form of recombinant vesicular stomatitis virus (rVSV) as a potential chimeric virus vaccine for HIV-1, with implications for use as a vaccine vector for other pathogens. The rVSV/HIV-1 vaccine vector was attenuated by combining two major genome modifications. These modifications acted synergistically to greatly enhance vector attenuation and the resulting rVSV vector demonstrated safety in sensitive mouse and non-human primate neurovirulence models. This vector expressing HIV-1 gag protein has completed evaluation in two Phase I clinical trials. In one trial the rVSV/HIV-1 vector was administered in a homologous two-dose regimen, and in a second trial with pDNA in a heterologous prime boost regimen. No serious adverse events were reported nor was vector detected in blood, urine or saliva post vaccination in either trial. Gag specific immune responses were induced in both trials with highest frequency T cell responses detected in the prime boost regimen. The rVSV/HIV-1 vector also demonstrated safety in an ongoing Phase I trial in HIV-1 positive participants. Additionally, clinical trial material has been produced with the rVSV vector expressing HIV-1 env, and Phase I clinical evaluation will initiate in the beginning of 2016. In this paper, we use a standardized template describing key characteristics of the novel rVSV vaccine vectors, in comparison to wild type VSV. The template facilitates scientific discourse among key stakeholders by increasing transparency and comparability of information. The Brighton Collaboration V3SWG template may also be useful as a guide to the evaluation of other recombinant viral vector vaccines.

Promise and problems associated with the use of recombinant AAV for the delivery of anti-HIV antibodies

Attempts to elicit antibodies with potent neutralizing activity against a broad range of human immunodeficiency virus (HIV) isolates have so far proven unsuccessful. Long-term delivery of monoclonal antibodies (mAbs) with such activity is a creative alternative that circumvents the need for an immune response and has the potential for creating a long-lasting sterilizing barrier against HIV. This approach is made possible by an incredible array of potent broadly neutralizing antibodies (bnAbs) that have been identified over the last several years. Recombinant adeno-associated virus (rAAV) vectors are ideally suited for long-term delivery for a variety of reasons. The only products made from rAAV are derived from the transgenes that are put into it; as long as those products are not viewed as foreign, expression from muscle tissue may continue for decades. Thus, use of rAAV to achieve long-term delivery of anti-HIV mAbs with potent neutralizing activity against a broad range of HIV-1 isolates is emerging as a promising concept for the prevention or treatment of HIV-1 infection in humans. Experiments in mice and monkeys that have demonstrated protective efficacy against AIDS virus infection have raised hopes for the promise of this approach. However, all published experiments in monkeys have encountered unwanted immune responses to the AAV-delivered antibody, and these immune responses appear to limit the levels of delivered antibody that can be achieved. In this review, we highlight the promise of rAAV-mediated antibody delivery for the prevention or treatment of HIV infection in humans, but we also discuss the obstacles that will need to be understood and solved in order for the promise of this approach to be realized.

HIV-1 prophylactic vaccines: state of the art

The quest for an effective HIV-1 vaccine began early in the course of the HIV pandemic. Over time, the paradigm has evolved from B cell- towards T cell-based vaccines. Results from initial Phase II/III trials have been disappointing; however, while modest, the unexpected results of the Phase II/III RV144 trial in Thailand have re-energised the field. Indeed a clear correlation was demonstrated in this trial between protection and immunological biomarkers, namely non-neutralising antibodies against the V1V2 region. Recent data obtained from cohorts of recently HIV-1-infected individuals have enabled exploration of the role of neutralising antibodies and their potential use in HIV-1 prevention. Results from non-human primate models using a cytomegalovirus vector have also shown the potential for a prophylactic HIV vaccine to induce effective T cell responses. Finally, the development of new vaccine vectors and trial strategies has also allowed progress in the field. Therefore, HIV-1 vaccine research remains a dynamic field that has also been stimulated by the recent positive results of pre-exposure prophylaxis strategies with antiretrovirals.

Prospects for a Globally Effective HIV-1 Vaccine

A globally effective vaccine strategy must cope with the broad genetic diversity of HIV and contend with multiple transmission modalities. Understanding correlates of protection and the role of diversity in limiting protective vaccines with those correlates is key. RV144 was the first HIV-1 vaccine trial to demonstrate efficacy against HIV-1 infection. A correlates analysis comparing vaccine-induced immune responses in vaccinated-infected and vaccinated-uninfected volunteers suggested that IgG specific for the V1V2 region of gp120 was associated with reduced risk of HIV-1 infection and that plasma Env IgA was directly correlated with infection risk. RV144 and recent non-human primate (NHP) challenge studies suggest that Env is essential and perhaps sufficient to induce protective antibody responses against mucosally acquired HIV-1. Whether RV144 immune correlates can apply to different HIV vaccines, to populations with different modes and intensity of transmission, or to divergent HIV-1 subtypes remains unknown. Newer prime-boost mosaic and conserved sequence immunization strategies aiming at inducing immune responses of greater breadth and depth as well as the development of immunogens inducing broadly neutralizing antibodies should be actively pursued. Efficacy trials are now planned in heterosexual populations in southern Africa and men who have sex with men in Thailand. Although NHP challenge studies may guide vaccine development, human efficacy trials remain key to answer the critical questions leading to the development of a global HIV-1 vaccine for licensure.

Multiple Approaches for Increasing the Immunogenicity of an Epitope-Based Anti-HIV Vaccine

The development of a highly effective vaccine against the human immunodeficiency virus (HIV) will likely be based on rational vaccine design, since traditional vaccine approaches have failed so far. In recent years, an understanding of what type of immune response is protective against infection and/or disease facilitated vaccine design. T cell-based vaccines against HIV have the goal of limiting both transmission and disease progression by inducing broad and functionally relevant T cell responses. In this context, CD4(+) T cells play a direct cytotoxic role and are also important for the generation and maintenance of functional CD8(+) T and B cell responses. The use of MHC-binding algorithms has allowed the identification of novel CD4(+) T cell epitopes that could be used in vaccine design, the so-called epitope-driven vaccine design. Epitope-based vaccines have the ability to focus the immune response on highly antigenic, conserved epitopes that are fully recognized by the target population. We have recently mapped a set of conserved multiple HLA-DR-binding HIV-1 CD4 epitopes and observed interferon (IFN)-γ-producing CD4(+) T cells when we tested these peptides in peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals. We then designed multiepitopic DNA vaccines that induced broad and polyfunctional T cell responses in immunized mice. In this review we will focus on alternative strategies to increase the immunogenicity of an epitope-based vaccine against HIV infection.

Attenuation of Replication-Competent Adenovirus Serotype 26 Vaccines by Vectorization

Replication-competent adenovirus (rcAd)-based vaccine vectors may theoretically provide immunological advantages over replication-incompetent Ad vectors, but they also raise additional potential clinical and regulatory issues. We produced replication-competent Ad serotype 26 (rcAd26) vectors by adding the E1 region back into a replication-incompetent Ad26 vector backbone with the E3 or E3/E4 regions deleted. We assessed the effect of vectorization on the replicative capacity of the rcAd26 vaccines. Attenuation occurred in a stepwise fashion, with E3 deletion, E4 deletion, and human immunodeficiency virus type 1 (HIV-1) envelope (Env) gene insertion all contributing to reduced replicative capacity compared to that with the wild-type Ad26 vector. The rcAd26 vector with E3 and E4 deleted and containing the Env transgene exhibited 2.7- to 4.4-log-lower replicative capacity than that of the wild-type Ad26 in vitro. This rcAd26 vector is currently being evaluated in a phase 1 clinical trial. Attenuation as a result of vectorization and transgene insertion has implications for the clinical development of replication-competent vaccine vectors.

Prospects for a globally effective HIV-1 vaccine

A globally effective vaccine strategy must cope with the broad genetic diversity of HIV and contend with multiple transmission modalities. Understanding correlates of protection and the role of diversity in limiting protective vaccines with those correlates is key. RV144 was the first HIV-1 vaccine trial to demonstrate efficacy against HIV-1 infection. A correlates analysis compared vaccine-induced immune responses in vaccinated-infected and vaccinated-uninfected volunteers suggested that IgG specific for the V1V2 region of gp120 was associated with reduced risk of HIV-1 infection and that plasma Env IgA was directly correlated with infection risk. RV144 and recent NHP challenge studies suggest that Env is essential and perhaps sufficient to induce protective antibody responses against mucosally acquired HIV-1. Whether RV144 immune correlates can apply to different HIV vaccines, to populations with different modes and intensity of transmission, or to divergent HIV-1 subtypes remains unknown. Newer prime-boost mosaic and conserved sequence immunization strategies aiming at inducing immune responses of greater breadth and depth as well as the development of immunogens inducing broadly neutralizing antibodies should be actively pursued. Efficacy trials are now planned in heterosexual populations in southern Africa and MSM in Thailand. Although NHP challenge studies may guide vaccine development, human efficacy trials remain key to answer the critical questions leading to the development of a global HIV-1 vaccine for licensure.

A Multiantigenic DNA Vaccine That Induces Broad Hepatitis C Virus-Specific T-Cell Responses in Mice

There are 3 to 4 million new hepatitis C virus (HCV) infections annually around the world, but no vaccine is available. Robust T-cell mediated responses are necessary for effective clearance of the virus, and DNA vaccines result in a cell-mediated bias. Adjuvants are often required for effective vaccination, but during natural lytic viral infections damage-associated molecular patterns (DAMPs) are released, which act as natural adjuvants. Hence, a vaccine that induces cell necrosis and releases DAMPs will result in cell-mediated immunity (CMI), similar to that resulting from natural lytic viral infection. We have generated a DNA vaccine with the ability to elicit strong CMI against the HCV nonstructural (NS) proteins (3, 4A, 4B, and 5B) by encoding a cytolytic protein, perforin (PRF), and the antigens on a single plasmid. We examined the efficacy of the vaccines in C57BL/6 mice, as determined by gamma interferon enzyme-linked immunosorbent spot assay, cell proliferation studies, and intracellular cytokine production. Initially, we showed that encoding the NS4A protein in a vaccine which encoded only NS3 reduced the immunogenicity of NS3, whereas including PRF increased NS3 immunogenicity. In contrast, the inclusion of NS4A increased the immunogenicity of the NS3, NS4B, andNS5B proteins, when encoded in a DNA vaccine that also encoded PRF. Finally, vaccines that also encoded PRF elicited similar levels of CMI against each protein after vaccination with DNA encoding NS3, NS4A, NS4B, and NS5B compared to mice vaccinated with DNA encoding only NS3 or NS4B/5B. Thus, we have developed a promising "multiantigen" vaccine that elicits robust CMI.

IMPORTANCE

Since their development, vaccines have reduced the global burden of disease. One strategy for vaccine development is to use commercially viable DNA technology, which has the potential to generate robust immune responses. Hepatitis C virus causes chronic liver infection and is a leading cause of liver cancer. To date, no vaccine is currently available, and treatment is costly and often results in side effects, limiting the number of patients who are treated. Despite recent advances in treatment, prevention remains the key to efficient control and elimination of this virus. Here, we describe a novel DNA vaccine against hepatitis C virus that is capable of inducing robust cell-mediated immune responses in mice and is a promising vaccine candidate for humans.

Canine distemper virus neutralization activity is low in human serum and it is sensitive to an amino acid substitution in the hemagglutinin protein

Serum was analyzed from 146 healthy adult volunteers in eastern Africa to evaluate measles virus (MV) and canine distemper virus (CDV) neutralizing antibody (nAb) prevalence and potency. MV plaque reduction neutralization test (PRNT) results indicated that all sera were positive for MV nAbs. Furthermore, the 50% neutralizing dose (ND50) for the majority of sera corresponded to antibody titers induced by MV vaccination. CDV nAbs titers were low and generally were detected in sera with high MV nAb titers. A mutant CDV was generated that was less sensitive to neutralization by human serum. The mutant virus genome had 10 nucleotide substitutions, which coded for single amino acid substitutions in the fusion (F) and hemagglutinin (H) glycoproteins and two substitutions in the large polymerase (L) protein. The H substitution occurred in a conserved region involved in receptor interactions among morbilliviruses, implying that this region is a target for cross-reactive neutralizing antibodies.

New prospects for a preventive HIV-1 vaccine

The immune correlates of risk analysis and recent non-human primate (NHP) challenge studies have generated hypotheses that suggest HIV-1 envelope may be essential and, perhaps, sufficient to induce protective antibody responses against HIV-1 acquisition at the mucosal entry. New prime-boost mosaic and conserved-sequence, together with replicating vector immunisation strategies aiming at inducing immune responses or greater breadth, as well as the development of immunogens inducing broadly neutralising antibodies and mucosal responses, should be actively pursued and tested in humans. Whether the immune correlates of risk identified in RV144 can be extended to other vaccines, other populations, or different modes and intensity of transmission, and against increasing HIV-1 genetic diversity, remains to be demonstrated. Although NHP challenge studies may guide vaccine development, human efficacy trials remain key for answering the critical questions leading to the development of a global HIV-1 vaccine for licensure.

Live virus vaccines based on a yellow fever vaccine backbone: standardized template with key considerations for a risk/benefit assessment

The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to evaluate the safety of live, recombinant viral vaccines incorporating genes from heterologous viruses inserted into the backbone of another virus (so-called "chimeric virus vaccines"). Many viral vector vaccines are in advanced clinical trials. The first such vaccine to be approved for marketing (to date in Australia, Thailand, Malaysia, and the Philippines) is a vaccine against the flavivirus, Japanese encephalitis (JE), which employs a licensed vaccine (yellow fever 17D) as a vector. In this vaccine, two envelope proteins (prM-E) of YF 17D virus were exchanged for the corresponding genes of JE virus, with additional attenuating mutations incorporated into the JE gene inserts. Similar vaccines have been constructed by inserting prM-E genes of dengue and West Nile into YF 17D virus and are in late stage clinical studies. The dengue vaccine is, however, more complex in that it requires a mixture of four live vectors each expressing one of the four dengue serotypes. This vaccine has been evaluated in multiple clinical trials. No significant safety concerns have been found. The Phase 3 trials met their endpoints in terms of overall reduction of confirmed dengue fever, and, most importantly a significant reduction in severe dengue and hospitalization due to dengue. However, based on results that have been published so far, efficacy in preventing serotype 2 infection is less than that for the other three serotypes. In the development of these chimeric vaccines, an important series of comparative studies of safety and efficacy were made using the parental YF 17D vaccine virus as a benchmark. In this paper, we use a standardized template describing the key characteristics of the novel flavivirus vaccine vectors, in comparison to the parental YF 17D vaccine. The template facilitates scientific discourse among key stakeholders by increasing the transparency and comparability of information. The Brighton Collaboration V3SWG template may also be useful as a guide to the evaluation of other recombinant viral vector vaccines.

Architectural insight into inovirus-associated vectors (IAVs) and development of IAV-based vaccines inducing humoral and cellular responses: implications in HIV-1 vaccines

Inovirus-associated vectors (IAVs) are engineered, non-lytic, filamentous bacteriophages that are assembled primarily from thousands of copies of the major coat protein gp8 and just five copies of each of the four minor coat proteins gp3, gp6, gp7 and gp9. Inovirus display studies have shown that the architecture of inoviruses makes all coat proteins of the inoviral particle accessible to the outside. This particular feature of IAVs allows foreign antigenic peptides to be displayed on the outer surface of the virion fused to its coat proteins and for more than two decades has been exploited in many applications including antibody or peptide display libraries, drug design, and vaccine development against infectious and non-infectious diseases. As vaccine carriers, IAVs have been shown to elicit both a cellular and humoral response against various pathogens through the display of antibody epitopes on their coat proteins. Despite their high immunogenicity, the goal of developing an effective vaccine against HIV-1 has not yet materialized. One possible limitation of previous efforts was the use of broadly neutralizing antibodies, which exhibited autoreactivity properties. In the past five years, however, new, more potent broadly neutralizing antibodies that do not exhibit autoreactivity properties have been isolated from HIV-1 infected individuals, suggesting that vaccination strategies aimed at producing such broadly neutralizing antibodies may confer protection against infection. The utilization of these new, broadly neutralizing antibodies in combination with the architectural traits of IAVs have driven the current developments in the design of an inovirus-based vaccine against HIV-1. This article reviews the applications of IAVs in vaccine development, with particular emphasis on the design of inoviral-based vaccines against HIV-1.

Development of a duplex real-time RT-qPCR assay to monitor genome replication, gene expression and gene insert stability during in vivo replication of a prototype live attenuated canine distemper virus vector encoding SIV gag

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The duplex assay monitored replication, tissue distribution, and mRNA expression.

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The duplex assay monitored insert genetic stability during in vivo replication.

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Primary site of CDV replication in ferrets was abdominal cavity lymphoid tissue.

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CDV gRNA or mRNA was undetectable in brain tissue.

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Specific primers were used in the RT step to distinguish gRNA from mRNA.

Advancement of new vaccines based on live viral vectors requires sensitive assays to analyze in vivo replication, gene expression and genetic stability. In this study, attenuated canine distemper virus (CDV) was used as a vaccine delivery vector and duplex 2-step quantitative real-time RT-PCR (RT-qPCR) assays specific for genomic RNA (gRNA) or mRNA have been developed that concurrently quantify coding sequences for the CDV nucleocapsid protein (N) and a foreign vaccine antigen (SIV Gag). These amplicons, which had detection limits of about 10 copies per PCR reaction, were used to show that abdominal cavity lymphoid tissues were a primary site of CDV vector replication in infected ferrets, and importantly, CDV gRNA or mRNA was undetectable in brain tissue. In addition, the gRNA duplex assay was adapted for monitoring foreign gene insert genetic stability during in vivo replication by analyzing the ratio of CDV N and SIV gag genomic RNA copies over the course of vector infection. This measurement was found to be a sensitive probe for assessing the in vivo genetic stability of the foreign gene insert.

The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG)

Recombinant viral vectors provide an effective means for heterologous antigen expression in vivo and thus represent promising platforms for developing novel vaccines against human pathogens from Ebola to tuberculosis. An increasing number of candidate viral vector vaccines are entering human clinical trials. The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to improve our ability to anticipate potential safety issues and meaningfully assess or interpret safety data, thereby facilitating greater public acceptance when licensed.

A novel, live-attenuated vesicular stomatitis virus vector displaying conformationally intact, functional HIV-1 envelope trimers that elicits potent cellular and humoral responses in mice

Though vaccination with live-attenuated SIV provides the greatest protection from progressive disease caused by SIV challenge in rhesus macaques, attenuated HIV presents safety concerns as a vaccine; therefore, live viral vectors carrying HIV immunogens must be considered. We have designed a replication-competent vesicular stomatitis virus (VSV) displaying immunogenic HIV-1 Env trimers and attenuating quantities of the native surface glycoprotein (G). The clade B Env immunogen is an Env-VSV G hybrid (EnvG) in which the transmembrane and cytoplasmic tail regions are derived from G. Relocation of the G gene to the 5'terminus of the genome and insertion of EnvG into the natural G position induced a ∼1 log reduction in surface G, significant growth attenuation compared to wild-type, and incorporation of abundant EnvG. Western blot analysis indicated that ∼75% of incorporated EnvG was a mature proteolytically processed form. Flow cytometry showed that surface EnvG bound various conformationally- and trimer-specific antibodies (Abs), and in-vitro growth assays on CD4+CCR5+ cells demonstrated EnvG functionality. Neither intranasal (IN) or intramuscular (IM) administration in mice induced any observable pathology and all regimens tested generated potent Env-specific ELISA titers of 10(4)-10(5), with an IM VSV prime/IN VSV boost regimen eliciting the highest binding and neutralizing Ab titers. Significant quantities of Env-specific CD4+ T cells were also detected, which were augmented as much as 70-fold by priming with IM electroporated plasmids encoding EnvG and IL-12. These data suggest that our novel vector can achieve balanced safety and immunogenicity and should be considered as an HIV vaccine platform.

Mechanisms of HIV protein degradation into epitopes: implications for vaccine design

The degradation of HIV-derived proteins into epitopes displayed by MHC-I or MHC-II are the first events leading to the priming of HIV-specific immune responses and to the recognition of infected cells. Despite a wealth of information about peptidases involved in protein degradation, our knowledge of epitope presentation during HIV infection remains limited. Here we review current data on HIV protein degradation linking epitope production and immunodominance, viral evolution and impaired epitope presentation. We propose that an in-depth understanding of HIV antigen processing and presentation in relevant primary cells could be exploited to identify signatures leading to efficient or inefficient epitope presentation in HIV proteomes, and to improve the design of immunogens eliciting immune responses efficiently recognizing all infected cells.

HIV vaccines: a brief overview

The scope of the article is to review the different approaches that have been used for HIV vaccines. The review is based on articles retrieved by PubMed and clinical trials from 1990 up to date. The article discusses virus complexity, protective and non-protective immune responses against the virus, and the most important approaches for HIV vaccine development.

Clonotypic composition of the CD4+ T cell response to a vectored retroviral antigen is determined by its speed

The mechanisms whereby different vaccines may expand distinct Ag-specific T cell clonotypes or induce disparate degrees of protection are incompletely understood. We found that several delivery modes of a model retroviral Ag, including natural infection, preferentially expanded initially rare high-avidity CD4(+) T cell clonotypes, known to mediate protection. In contrast, the same Ag vectored by human adenovirus serotype 5 induced clonotypic expansion irrespective of avidity, eliciting a predominantly low-avidity response. Nonselective clonotypic expansion was caused by relatively weak adenovirus serotype 5-vectored Ag presentation and was reproduced by replication-attenuated retroviral vaccines. Mechanistically, the potency of Ag presentation determined the speed and, consequently, completion of the CD4(+) T cell response. Whereas faster completion retained the initial advantage of high-avidity clonotypes, slower completion permitted uninhibited accumulation of low-avidity clonotypes. These results highlighted the importance of Ag presentation patterns in determining the clonotypic composition of vaccine-induced T cell responses and ultimately the efficacy of vaccination.

Vaccines that stimulate T cell immunity to HIV-1: the next step

The search for a vaccine against human immunodeficiency virus type 1 (HIV-1) has many hurdles to overcome. Ideally, the stimulation of both broadly neutralizing antibodies and cell-mediated immune responses remains the best option, but no candidate in clinical trials at present has elicited such antibodies, and efficacy trials have not demonstrated any benefit for vaccines designed to stimulate immune responses of CD8(+) T cells. Findings obtained with the simian immunodeficiency virus (SIV) monkey model have provided new evidence that stimulating effective CD8(+) T cell immunity could provide protection, and in this Perspective we explore the path forward for optimizing such responses in humans.

HIV-1 vaccines: challenges and new perspectives

The development of a safe and effective preventive HIV-1 vaccine remains a public health priority. Despite scientific difficulties and disappointing results, HIV-1 vaccine clinical development has, for the first time, established proof-of-concept efficacy against HIV-1 acquisition and identified vaccine-associated immune correlates of risk. The correlate of risk analysis showed that IgG antibodies against the gp120 V2 loop correlated with decreased risk of HIV infection, while Env-specific IgA directly correlated with increased risk. The development of vaccine strategies such as improved envelope proteins formulated with potent adjuvants and DNA and vectors expressing mosaics, or conserved sequences, capable of eliciting greater breadth and depth of potentially relevant immune responses including neutralizing and non-neutralizing antibodies, CD4+ and CD8+ cell-mediated immune responses, mucosal immune responses, and immunological memory, is now proceeding quickly. Additional human efficacy trials combined with other prevention modalities along with sustained funding and international collaboration remain key to bring an HIV-1 vaccine to licensure.

Conserved immunogens in prime-boost strategies for the next-generation HIV-1 vaccines

INTRODUCTION

Effective vaccines are the best solution for stopping the spread of HIV/AIDS and other infectious diseases. Their development and in-depth understanding of pathogen-host interactions rely on technological advances.

AREAS COVERED

Rational vaccine development can be effectively approached by conceptual separation of, on one hand, design of immunogens from improving their presentation to the immune system and, on the other, induction of antibodies from induction of killer CD8(+) T cells. The biggest roadblock for many vaccines is the pathogens' variability. This is best tackled by focusing both antibodies and T cells on the functionally most conserved regions of proteins common to many variants, including escape mutants. For vectored vaccines, these 'universal' subunit immunogens are most efficiently delivered using heterologous prime-boost regimens, which can be further optimised by adjuvantation and route of delivery.

EXPERT OPINION

Development of vaccines against human diseases has many features in common. Acceleration of vaccine discovery depends on basic research and new technologies. Novel strategies should be safely, but rapidly tested in humans. While out-of-the-box thinking is important, vaccine success largely depends on incremental advances best achieved through small, systematic, iterative clinical studies. Failures are inevitable, but the end rewards are huge. The future will be exciting.