Control of viremia and prevention of clinical AIDS in rhesus monkeys by cytokine-augmented DNA vaccination

Local delivery of cell surface-targeted immunocytokines programs systemic antitumor immunity

Systemically administered cytokines are potent immunotherapeutics but can cause severe dose-limiting toxicities. To overcome this challenge, cytokines have been engineered for intratumoral retention after local delivery. However, despite inducing regression of treated lesions, tumor-localized cytokines often elicit only modest responses at distal untreated tumors. In the present study, we report a localized cytokine therapy that safely elicits systemic antitumor immunity by targeting the ubiquitous leukocyte receptor CD45. CD45-targeted immunocytokines have lower internalization rates relative to wild-type counterparts, leading to sustained downstream cis and trans signaling between lymphocytes. A single intratumoral dose of αCD45-interleukin (IL)-12 followed by a single dose of αCD45-IL-15 eradicated treated tumors and untreated distal lesions in multiple syngeneic mouse tumor models without toxicity. Mechanistically, CD45-targeted cytokines reprogrammed tumor-specific CD8+ T cells in the tumor-draining lymph nodes to have an antiviral transcriptional signature. CD45 anchoring represents a broad platform for protein retention by host immune cells for use in immunotherapy.

Local delivery of cell surface-targeted immunocytokines programs systemic anti-tumor immunity

Cytokine therapies are potent immunotherapy agents but exhibit severe dose-limiting toxicities. One strategy to overcome this involves engineering cytokines for intratumoral retention following local delivery. Here, we develop a localized cytokine therapy that elicits profound anti-tumor immunity by engineered targeting to the ubiquitous leukocyte receptor CD45. We designed CD45-targeted immunocytokines (αCD45-Cyt) that, upon injection, decorated the surface of leukocytes in the tumor and tumor-draining lymph node (TDLN) without systemic exposure. αCD45-Cyt therapy eradicated both directly treated tumors and untreated distal lesions in multiple syngeneic mouse tumor models. Mechanistically, αCD45-Cyt triggered prolonged pSTAT signaling and reprogrammed tumor-specific CD8+ T cells in the TDLN to exhibit an anti-viral transcriptional signature. CD45 anchoring represents a broad platform for protein retention by host immune cells for use in immunotherapy.

Spatiotemporally programming cytokine immunotherapies through protein engineering

Cytokines have long been considered promising cancer immunotherapy agents due to their endogenous role in activating and proliferating lymphocytes. However, since the initial FDA approvals of Interleukin-2 (IL-2) and Interferon-ɑ (IFNɑ) for oncology over 30 years ago, cytokines have achieved little success in the clinic due to narrow therapeutic windows and dose-limiting toxicities. This is attributable to the discrepancy between the localized, regulated manner in which cytokines are deployed endogenously versus the systemic, untargeted administration used to date in most exogenous cytokine therapies. Furthermore, cytokines' ability to stimulate multiple cell types, often with paradoxical effects, may present significant challenges for their translation into effective therapies. Recently, protein engineering has emerged as a tool to address the shortcomings of first-generation cytokine therapies. In this perspective, we contextualize cytokine engineering strategies such as partial agonism, conditional activation and intratumoral retention through the lens of spatiotemporal regulation. By controlling the time, place, specificity, and duration of cytokine signaling, protein engineering can allow exogenous cytokine therapies to more closely approach their endogenous exposure profile, ultimately moving us closer to unlocking their full therapeutic potential.

Cytokines and their role as immunotherapeutics and vaccine Adjuvants: The emerging concepts

Cytokines are a protein family comprising interleukins, lymphokines, chemokines, monokines and interferons. They are significant constituents of the immune system, and they act in accordance with specific cytokine inhibiting compounds and receptors for the regulation of immune responses. Cytokine studies have resulted in the establishment of newer therapies which are being utilized for the treatment of several malignant diseases. The advancement of these therapies has occurred from two distinct strategies. The first strategy involves administrating the recombinant and purified cytokines, and the second strategy involves administrating the therapeutics which inhibits harmful effects of endogenous and overexpressed cytokines. Colony stimulating factors and interferons are two exemplary therapeutics of cytokines. An important effect of cytokine receptor antagonist is that they can serve as anti-inflammatory agents by altering the treatments of inflammation disorder, therefore inhibiting the effects of tumour necrosis factor. In this article, we have highlighted the research behind the establishment of cytokines as therapeutics and vaccine adjuvants, their role of immunotolerance, and their limitations.

Co-Anchoring of Engineered Immunogen and Immunostimulatory Cytokines to Alum Promotes Enhanced-Humoral Immunity

Protein antigens are often combined with aluminum hydroxide (alum), the most commonly used adjuvant in licensed vaccines; yet the immunogenicity of alum-adjuvanted vaccines leaves much room for improvement. Here, the authors demonstrate a strategy for codelivering an immunostimulatory cytokine, the interleukin IL-21, with an engineered outer domain (eOD) human immunodeficiency virus gp120 Env immunogen eOD, bound together to alum to bolster the humoral immune response. In this approach, the immunogen and cytokine are co-anchored to alum particles via a short phosphoserine (pSer) peptide linker, promoting stable binding to alum and sustained bioavailability following injection. pSer-modified eOD and IL-21 promote enhanced lymphatic drainage and lead to accumulation of the vaccine in B cell follicles in the draining lymph nodes. This in turn promotes enhanced T follicular helper cell priming and robust germinal center responses as well as increased antigen-specific serum IgG titers. This is a general strategy for codelivery of immunostimulatory cytokine with immunogens providing a facile approach to modulate T cell priming and GC reactions toward enhanced protective immunity using the most common clinical vaccine adjuvant.

Development of synthetic antigen vaccines for COVID-19

The current pandemic called COVID-19 caused by the SARS-CoV-2 virus brought the need for the search for fast alternatives to both control and fight the SARS-CoV-2 infection. Therefore, a race for a vaccine against COVID-19 took place, and some vaccines have been approved for emergency use in several countries in a record time. Ongoing prophylactic research has sought faster, safer, and precise alternatives by redirecting knowledge of other vaccines, and/or the development of new strategies using available tools, mainly in the areas of genomics and bioinformatics. The current review highlights the development of synthetic antigen vaccines, focusing on the usage of bioinformatics tools for the selection and construction of antigens on the different vaccine constructions under development, as well as strategies to optimize vaccines for COVID-19.

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.

Advances in simian--human immunodeficiency viruses for nonhuman primate studies of HIV prevention and cure

PURPOSE OF REVIEW

Simian--human immunodeficiency viruses (SHIVs), chimeric viruses that encode HIV-1 Env within an SIV backbone, are key reagents for nonhuman primate studies of antibody-based vaccines, broadly neutralizing antibodies (bnAbs), and other Env-targeting reagents. Here, we discuss the provenance and characteristics of currently relevant SHIVs, novel technical advances, recent discoveries enabled by SHIV challenge studies, and the continued development of SHIVs for persistence and cure experiments.

RECENT FINDINGS

SHIV SF162P3, SHIV AD8EO, and transmitter/founder SHIVs with Env375 mutations are now common reagents in nonhuman primate studies, with increased use and validation establishing their properties and potential applications. Genetic barcoding of SIV and SHIV, which allows tracing of individual lineages and elucidation of viral kinetics from transmission through latency has expanded the experimental capacity of SHIV models. SHIV challenge studies have determined the neutralizing antibody titers that correlate with protection for passive and active immunization and enabled complementary human and nonhuman primate studies of vaccine development. SHIV models of latency continue to evolve, aided by descriptions of SHIV persistence on ART and the proviral landscape.

SUMMARY

Recent advances and more thorough characterization of SHIVs allow for expanded applications and greater confidence in experimental results.

Sustained viremia suppression by SHIVSF162P3CN-recalled effector-memory CD8+ T cells after PD1-based vaccination

HIV-1 functional cure requires sustained viral suppression without antiretroviral therapy. While effector-memory CD8⁺ T lymphocytes are essential for viremia control, few vaccines elicit such cellular immunity that could be potently recalled upon viral infection. Here, we investigated a program death-1 (PD1)-based vaccine by fusion of simian immunodeficiency virus capsid antigen to soluble PD1. Homologous vaccinations suppressed setpoint viremia to undetectable levels in vaccinated macaques following a high-dose intravenous challenge by the pathogenic SHIV_SF162P3CN. Poly-functional effector-memory CD8⁺ T cells were not only induced after vaccination, but were also recalled upon viral challenge for viremia control as determined by CD8 depletion. Vaccine-induced effector memory CD8⁺ subsets displayed high cytotoxicity-related genes by single-cell analysis. Vaccinees with sustained viremia suppression for over two years responded to boost vaccination without viral rebound. These results demonstrated that PD1-based vaccine-induced effector-memory CD8⁺ T cells were recalled by AIDS virus infection, providing a potential immunotherapy for functional cure.

HIV-1/AIDS remains a major global pandemic although treatment regimen has improved. Identifying efficacious vaccines and therapeutics to achieve long-term viral control with very low/undetectable plasma viral loads in the absence of antiretroviral therapy, a status known as functional cure, would be highly beneficial. We previously demonstrated that antigens fused to a soluble program death-1 (PD1) domain could effectively bind and be cross-presented by dendritic cells that constitutively expressed PD1 ligands. When applied in the form of DNA vaccination, this antigen-targeting strategy was highly immunogenic in mice. Here, we investigated the efficacy of the PD1-based DNA vaccine approach against pathogenic simian-human immunodeficiency virus challenge in rhesus monkeys. Our results showed that homologous PD1-based DNA vaccinations induced highly functional effector-memory CD8⁺ T cells carrying a unique cytotoxicity gene expression profile. These T cells actively supressed viremia in monkeys and were re-activated via boost vaccination at 2 years after viral challenge without viral rebound. In summary, our study demonstrates the potential application of PD1-based DNA vaccination to control AIDS virus infection.

Ebola-GP DNA Prime rAd5-GP Boost: Influence of Prime Frequency and Prime/Boost Time Interval on the Immune Response in Non-human Primates

Heterologous prime-boost immunization regimens are a common strategy for many vaccines. DNA prime rAd5-GP boost immunization has been demonstrated to protect non-human primates against a lethal challenge of Ebola virus, a pathogen that causes fatal hemorrhagic disease in humans. This protection correlates with antibody responses and is also associated with IFNγ⁺ TNFα⁺ double positive CD8⁺ T-cells. In this study, we compared single DNA vs. multiple DNA prime immunizations, and short vs. long time intervals between the DNA prime and the rAd5 boost to evaluate the impact of these different prime-boost strategies on vaccine-induced humoral and cellular responses in non-human primates. We demonstrated that DNA/rAd5 prime-boost strategies can be tailored to induce either CD4⁺ T-cell or CD8⁺ T-cell dominant responses while maintaining a high magnitude antibody response. Additionally, a single DNA prime immunization generated a stable memory response that could be boosted by rAd5 3 years later. These results suggest DNA/rAd5 prime-boost provides a flexible platform that can be fine-tuned to generate desirable T-cell memory responses.

Development and evaluation of a rapid and cost-efficient NGS-based MHC class I genotyping method for macaques by using a prevalent short-read sequencer

Rhesus macaque is one of the most widely used primate model animals for immunological research of infectious diseases including human immunodeficiency virus (HIV) infection. It is well known that major histocompatibility complex (MHC) class I genotypes affect the susceptibility and disease progression to simian immunodeficiency virus (SIV) in rhesus macaques, which is resembling to HIV in humans. It is required to convincingly determine the MHC genotypes in the immunological investigations, that is why several next-generation sequencing (NGS)-based methods have been established. In general, NGS-based genotyping methods using short amplicons are not often applied to MHC because of increasing number of alleles and inevitable ambiguity in allele detection, although there is an advantage of short read sequencing systems that are commonly used today. In this study, we developed a new high-throughput NGS-based genotyping method for MHC class I alleles in rhesus macaques and cynomolgus macaques. By using our method, 95% and 100% of alleles identified by PCR cloning-based method were detected in rhesus macaques and cynomolgus macaques, respectively, which were highly correlated with their expression levels. It was noted that the simulation of new-allele detection step using artificial alleles differing by a few nucleotide sequences from a known allele could be identified with high accuracy and that we could detect a real novel allele from a rhesus macaque sample. These findings supported that our method could be adapted for primate animal models such as macaques to reduce the cost and labor of previous NGS-based MHC genotyping.

Simian-Human Immunodeficiency Virus SHIV.C.CH505 Persistence in ART-Suppressed Infant Macaques Is Characterized by Elevated SHIV RNA in the Gut and a High Abundance of Intact SHIV DNA in Naive CD4+ T Cells

Mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1) continues to cause new pediatric cases of infection through breastfeeding, a setting where it is not always possible to initiate early antiretroviral therapy (ART). Without novel interventions that do not rely on daily ART, HIV-1-infected children face lifelong medications to control infection. A detailed analysis of virus persistence following breast milk transmission of HIV-1 and ART has not been performed. Here, we used infant rhesus macaques orally infected with simian/human immunodeficiency virus (SHIV) (SHIV.C.CH505) to identify cellular and anatomical sites of virus persistence under ART. Viral DNA was detected at similar levels in blood and tissue CD4+ T cells after a year on ART, with virus in blood and lymphoid organs confirmed to be replication competent. Viral RNA/DNA ratios were elevated in rectal CD4+ T cells compared to those of other sites (P ≤ 0.0001), suggesting that the gastrointestinal tract is an active site of virus transcription during ART-mediated suppression of viremia. SHIV.C.CH505 DNA was detected in multiple CD4+ T cell subsets, including cells with a naive phenotype (CD45RA+ CCR7+ CD95-). While the frequency of naive cells harboring intact provirus was lower than in memory cells, the high abundance of naive cells in the infant CD4+ T cell pool made them a substantial source of persistent viral DNA (approximately 50% of the total CD4+ T cell reservoir), with an estimated 1:2 ratio of intact provirus to total viral DNA. This viral reservoir profile broadens our understanding of virus persistence in a relevant infant macaque model and provides insight into targets for cure-directed approaches in the pediatric population.IMPORTANCE Uncovering the sanctuaries of the long-lived HIV-1 reservoir is crucial to develop cure strategies. Pediatric immunity is distinct from that of adults, which may alter where the reservoir is established in infancy. Thus, it is important to utilize pediatric models to inform cure-directed approaches for HIV-1-infected children. We used an infant rhesus macaque model of HIV-1 infection via breastfeeding to identify key sites of viral persistence under antiretroviral therapy (ART). The gastrointestinal tract was found to be a site for low-level viral transcription during ART. We also show that naive CD4+ T cells harbored intact provirus and were a major contributor to blood and lymphoid reservoir size. This is particularly striking, as memory CD4+ T cells are generally regarded as the main source of latent HIV/simian immunodeficiency virus (SIV) infection of adult humans and rhesus macaques. Our findings highlight unique features of reservoir composition in pediatric infection that should be considered for eradication efforts.

T cell-inducing vaccine durably prevents mucosal SHIV infection even with lower neutralizing antibody titers

Recent efforts toward an HIV vaccine focus on inducing broadly neutralizing antibodies, but eliciting both neutralizing antibodies (nAbs) and cellular responses may be superior. Here, we immunized macaques with an HIV envelope trimer, either alone to induce nAbs, or together with a heterologous viral vector regimen to elicit nAbs and cellular immunity, including CD8+ tissue-resident memory T cells. After ten vaginal challenges with autologous virus, protection was observed in both vaccine groups at 53.3% and 66.7%, respectively. A nAb titer >300 was generally associated with protection but in the heterologous viral vector + nAb group, titers <300 were sufficient. In this group, protection was durable as the animals resisted six more challenges 5 months later. Antigen stimulation of T cells in ex vivo vaginal tissue cultures triggered antiviral responses in myeloid and CD4+ T cells. We propose that cellular immune responses reduce the threshold of nAbs required to confer superior and durable protection.

Interleukin-2 (IL-2) of flounder (Paralichthys olivaceus) as immune adjuvant enhance the immune effects of E. tarda subunit vaccine OmpV against Edwardsiellosis

In our previous study, we cloned and explored the biological functions of flounder (Paralichthys olivaceus) interleukin-2 (poIL-2), and showed that poIL-2 might have adjuvant potential for fish vaccines. In this study, the adjuvant effects of recombinant and molecular forms of poIL-2 (rIL-2 and pcIL-2) were comparatively analyzed and evaluated in flounder from several aspects by co-vaccination with the recombinant E. tarda OmpV (rOmpV). The results showed that co-vaccination with rOmpV plus rIL-2 or pcIL-2 resulted in a relative percent survival of 71% and 57% respectively, which was significantly higher than the control groups, rOmpV plus rHis (40%) or pcN3 (36%). Immunological analysis showed that: (1) the levels of specific serum antibodies and sIg + lymphocytes in head kidney, spleen and peripheral blood induced by rOmpV plus rIL-2 or pcIL-2 were significantly higher than that in the two control groups; (2) Compared to the two control groups, CD4-1, CD4-2, CD8α, CD8β, MHCIα, MHCIIα, IgM and IFN-γ mRNA levels were also significantly induced by rOmpV plus rIL-2 or pcIL-2; (3) the rOmpV plus rIL-2 could induce higher levels of sIg + lymphocytes, specific serum antibodies and the expressions of all investigated genes than rOmpV plus pcIL-2. These results demonstrated that co-vaccination with rOmpV with rIL-2 or pcIL-2 could induce stronger humoral and cellular immune responses, and evoked higher immune protective efficacy against E. tarda infection, suggesting that poIL-2 could be served as a promising candidate adjuvant and have a potential application in the control of flounder diseases.

Deletion of Vaccinia Virus A40R Gene Improves the Immunogenicity of the HIV-1 Vaccine Candidate MVA-B

Development of a safe and efficacious vaccine against the HIV/AIDS pandemic remains a major scientific goal. We previously described an HIV/AIDS vaccine based on the modified vaccinia virus Ankara (MVA) expressing HIV-1 gp120 and Gag-Pol-Nef (GPN) of clade B (termed MVA-B), which showed moderate immunogenicity in phase I prophylactic and therapeutic clinical trials. Here, to improve the immunogenicity of MVA-B, we generated a novel recombinant virus, MVA-B ΔA40R, by deleting in the MVA-B genome the vaccinia virus (VACV) A40R gene, which encodes a protein with unknown immune function. The innate immune responses triggered by MVA-B ΔA40R in infected human macrophages, in comparison to parental MVA-B, revealed an increase in the mRNA expression levels of interferon (IFN)-β, IFN-induced genes, and chemokines. Compared to priming with DNA-B (a mixture of DNA-gp120 plus DNA-GPN) and boosting with MVA-B, mice immunized with a DNA-B/MVA-B ΔA40R regimen induced higher magnitude of adaptive and memory HIV-1-specific CD4+ and CD8+ T-cell immune responses that were highly polyfunctional, mainly directed against Env. and of an effector memory phenotype, together with enhanced levels of antibodies against HIV-1 gp120. Reintroduction of the A40R gene into the MVA-B ΔA40R genome (virus termed MVA-B ΔA40R-rev) promoted in infected cells high mRNA and protein A40 levels, with A40 protein localized in the cell membrane. MVA-B ΔA40R-rev significantly reduced mRNA levels of IFN-β and of several other innate immune-related genes in infected human macrophages. In immunized mice, MVA-B ΔA40R-rev reduced the magnitude of the HIV-1-specific CD4+ and CD8+ T cell responses compared to MVA-B ΔA40R. These results revealed an immunosuppressive role of the A40 protein, findings relevant for the optimization of poxvirus vectors as vaccines.

Genetic Adjuvants in Replicating Single-Cycle Adenovirus Vectors Amplify Systemic and Mucosal Immune Responses against HIV-1 Envelope

Most infections occur at mucosal surfaces. Providing a barrier of protection at these surfaces may be a useful strategy to combat the earliest events in infection when there are relatively few pathogens to address. The majority of vaccines are delivered systemically by the intramuscular (IM) route. While IM vaccination can drive mucosal immune responses, mucosal immunization at intranasal (IN) or oral sites can lead to better immune responses at mucosal sites of viral entry. In macaques, IN immunization with replicating single-cycle adenovirus (SC-Ads) and protein boosts generated favorable mucosal immune responses. However, there was an apparent "distance effect" in generating mucosal immune responses. IN immunization generated antibodies against HIV envelope (env) nearby in the saliva, but weaker responses in samples collected from the distant vaginal samples. To improve on this, we tested here if SC-Ads expressing genetic adjuvants could be used to amplify antibody responses in distant vaginal samples when they are codelivered with SC-Ads expressing clade C HIV env immunogen. SC-Ads env 1157 was coadministered with SC-Ads expressing 4-1BBL, granulocyte macrophage colony-stimulating factor (GMCSF), IL-21, or Clostridoides difficile (C. diff.) toxin fragments by IN or IM routes. These data show that vaginal antibody responses were markedly amplified after a single immunization by the IN or IM routes, with SC-Ad expressing HIV env if this vaccine is complemented with SC-Ads expressing genetic adjuvants. Furthermore, the site and combination of adjuvants appear to "tune" these antibody responses towards an IgA or IgG isotype bias. Boosting these priming SC-Ad responses with another SC-Ad or with SOSIP native-like env proteins markedly amplifies env antibody levels in vaginal washes. Together, this data may be useful in informing the choice of route of delivery adenovirus and peptide vaccines against HIV-1.

An MVA Vector Expressing HIV-1 Envelope under the Control of a Potent Vaccinia Virus Promoter as a Promising Strategy in HIV/AIDS Vaccine Design

Highly attenuated poxviral vectors, such as modified vaccinia virus ankara (MVA), are promising vaccine candidates against several infectious diseases. One of the approaches developed to enhance the immunogenicity of poxvirus vectors is increasing the promoter strength and accelerating during infection production levels of heterologous antigens. Here, we have generated and characterized the biology and immunogenicity of an optimized MVA-based vaccine candidate against HIV/AIDS expressing HIV-1 clade B gp120 protein under the control of a novel synthetic late/early optimized (LEO) promoter (LEO160 promoter; with a spacer length of 160 nucleotides), termed MVA-LEO160-gp120. In infected cells, MVA-LEO160-gp120 significantly increased the expression levels of HIV-1 gp120 mRNA and protein, compared to the clinical vaccine MVA-B vector expressing HIV-1 gp120 under the control of the commonly used synthetic early/late promoter. When mice were immunized with a heterologous DNA-prime/MVA-boost protocol, the immunization group DNA-gp120/MVA-LEO160-gp120 induced an enhancement in the magnitude of gp120-specific CD4⁺ and CD8⁺ T-cell responses, compared to DNA-gp120/MVA-B; with most of the responses being mediated by the CD8⁺ T-cell compartment, with a T effector memory phenotype. DNA-gp120/MVA-LEO160-gp120 also elicited a trend to a higher magnitude of gp120-specific CD4⁺ T follicular helper cells, and modest enhanced levels of antibodies against HIV-1 gp120. These findings revealed that this new optimized vaccinia virus promoter could be considered a promising strategy in HIV/AIDS vaccine design, confirming the importance of early expression of heterologous antigen and its impact on the antigen-specific immunogenicity elicited by poxvirus-based vectors.

Reduction of peak viremia by an integration-defective SIV proviral DNA vaccine in rhesus macaques

An integrase-defective SIV (idSIV) vaccine delivered by a DNA prime and viral particle boost approach can suppress viral loads (VLs) during the acute infection stage after intravenous SIVmac239 challenge. This study investigated how idSIV DNA and viral particle immunization alone contributed to the suppression of VLs in Chinese rhesus macaques after SIV challenge. Two macaques were immunized with idSIV DNA five times and two macaques were immunized with idSIV viral particles three times. Cellular and humoral immune responses were measured in the vaccinated macaques after immunization. The VLs and CD4⁺ T cell counts were monitored for 28 weeks after the intravenous SIVmac239 challenge. The SIV-specific T cell responses were only detected in the DNA-vaccinated macaques. However, binding and neutralizing antibodies against autologous and heterologous viruses were moderately better in macaques immunized with viral particles than in macaques immunized with DNA. After the challenge, the mean peak viremia in the DNA group was 2.3 logs lower than that in the control group, while they were similar between the viral particle immunization and control groups. Similar CD4⁺ T cell counts were observed among all groups. These results suggest that idSIV DNA immunization alone reduces VLs during acute infection after SIV challenge in macaques and may serve as a key component in combination with other immunogens as prophylactic vaccines.

Defining Kinetic Properties of HIV-Specific CD8⁺ T-Cell Responses in Acute Infection

Multiple lines of evidence indicate that CD8 + T cells are important in the control of HIV-1 (HIV) replication. However, CD8 + T cells induced by natural infection cannot eliminate the virus or reduce viral loads to acceptably low levels in most infected individuals. Understanding the basic quantitative features of CD8 + T-cell responses induced during HIV infection may therefore inform us about the limits that HIV vaccines, which aim to induce protective CD8 + T-cell responses, must exceed. Using previously published experimental data from a cohort of HIV-infected individuals with sampling times from acute to chronic infection we defined the quantitative properties of CD8 + T-cell responses to the whole HIV proteome. In contrast with a commonly held view, we found that the relative number of HIV-specific CD8 + T-cell responses (response breadth) changed little over the course of infection (first 400 days post-infection), with moderate but statistically significant changes occurring only during the first 35 symptomatic days. This challenges the idea that a change in the T-cell response breadth over time is responsible for the slow speed of viral escape from CD8 + T cells in the chronic infection. The breadth of HIV-specific CD8 + T-cell responses was not correlated with the average viral load for our small cohort of patients. Metrics of relative immunodominance of HIV-specific CD8 + T-cell responses such as Shannon entropy or the Evenness index were also not significantly correlated with the average viral load. Our mathematical-model-driven analysis suggested extremely slow expansion kinetics for the majority of HIV-specific CD8 + T-cell responses and the presence of intra- and interclonal competition between multiple CD8 + T-cell responses; such competition may limit the magnitude of CD8 + T-cell responses, specific to different epitopes, and the overall number of T-cell responses induced by vaccination. Further understanding of mechanisms underlying interactions between the virus and virus-specific CD8 + T-cell response will be instrumental in determining which T-cell-based vaccines will induce T-cell responses providing durable protection against HIV infection.

Induction of neutralizing antibodies against tier 2 human immunodeficiency virus 1 in rhesus macaques infected with tier 1B simian/human immunodeficiency virus

We previously developed CCR5-tropic neutralization-resistant simian/human immunodeficiency virus (SHIV) strains and a rhesus macaque model of infection with these SHIVs. We induced the production of neutralizing antibodies (nAbs) against HIV-1 by infecting rhesus macaques with different neutralization-resistant SHIV strains. First, SHIV-MK1 (MK1) (neutralization susceptible, tier 1B) with CCR5 tropism was generated from SHIV-KS661 using CXCR4 as the main co-receptor. nAbs against parental-lineage and heterologous tier 2 viruses were induced by tier 1B virus (MK1) infection of the rhesus macaque MM482. We analyzed viral resistance to neutralization over time in MM482 and observed that the infecting virus mutated from tier 1B to tier 2 at 36 weeks postinfection (wpi). In addition, an analysis of mutations showed that N169D, K187E, S190N, S239, T459N (T459D at 91 wpi), and V842A mutations were present after 36 wpi. This led to the appearance of neutralization-resistant viral clones. In addition, MK1 was passaged in three rhesus macaques to generate neutralization-resistant SHIV-MK38 (MK38) (tier 2). We evaluated nAb production by rhesus macaques infected with SHIV-MK38 #818 (#818) (tier 2), a molecular clone of MK38. Neutralization of the parental lineage was induced earlier than in macaques infected with tier 1B virus, and neutralization activity against heterologous tier 2 virus was beginning to develop. Therefore, CCR5-tropic neutralization-resistant SHIV-infected rhesus macaques may be useful models of anti-HIV-1 nAb production and will facilitate the development of a vaccine that elicits nAbs against HIV-1.

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.

Accelerating HIV vaccine development using non-human primate models

INTRODUCTION

The search for a preventative HIV vaccine is ongoing after three decades of research. Contributions of non-human primate (NHP) models to this research are irrefutable, however interpreting data obtained for translation to humans has been problematic. As knowledge concerning NHP models has accumulated, their utility and value in assessing immunogenicity and efficacy of novel vaccines have become apparent. NHP models have become a critical component of vaccine design.

AREAS COVERED

Beginning with early vaccine studies, we trace the development and evolution of NHP models concurrent with changes in HIV vaccine concepts and in response to their ability to predict clinical trial efficacy. The value of NHP studies in guiding vaccine design is highlighted along with their importance in opening new areas of investigation and facilitating movement of promising approaches into the clinic.

EXPERT COMMENTARY

Due to their close relatedness to humans, NHPs are an excellent choice for immunogenicity studies. The ability of NHP models to predict clinical efficacy has improved with the introduction of low-dose challenge viruses and recognition of confounding variables in study outcomes. Use of NHP models has opened new research areas with outstanding potential for generating vaccine efficacy against HIV and other infectious agents.

Cytokine-Mediated Tissue Injury in Non-human Primate Models of Viral Infections

Viral infections trigger robust secretion of interferons and other antiviral cytokines by infected and bystander cells, which in turn can tune the immune response and may lead to viral clearance or immune suppression. However, aberrant or unrestricted cytokine responses can damage host tissues, leading to organ dysfunction, and even death. To understand the cytokine milieu and immune responses in infected host tissues, non-human primate (NHP) models have emerged as important tools. NHP have been used for decades to study human infections and have played significant roles in the development of vaccines, drug therapies and other immune treatment modalities, aided by an ability to control disease parameters, and unrestricted tissue access. In addition to the genetic and physiological similarities with humans, NHP have conserved immunologic properties with over 90% amino acid similarity for most cytokines. For example, human-like symptomology and acute respiratory syndrome is found in cynomolgus macaques infected with highly pathogenic avian influenza virus, antibody enhanced dengue disease is common in neotropical primates, and in NHP models of viral hepatitis cytokine-induced inflammation induces severe liver damage, fibrosis, and hepatocellular carcinoma recapitulates human disease. To regulate inflammation, anti-cytokine therapy studies in NHP are underway and will provide important insights for future human interventions. This review will provide a comprehensive outline of the cytokine-mediated exacerbation of disease and tissue damage in NHP models of viral infections and therapeutic strategies that can aid in prevention/treatment of the disease syndromes.

Willingness to participate in HIV research at the end of life (EOL)

INTRODUCTION

Animal models have been vital for scientific discovery but have limitations, especially in infectious disease research. It is essential to develop a means to study these diseases in human models. We hypothesized that altruistic people would willingly participate in research near the end-of-life (EOL), for the benefit of science and to provide one last gift to society.

METHODOLOGY

Two surveys were administered to 377 self-reported HIV-negative and 96 HIV-positive individuals. Hypothetical questions assessed their willingness to participate in altruistic research in the last 6 months of life, which might result in a shortened lifespan or physical discomforts. The self-reported HIV-negative group was also asked about willingness to be exposed to infectious pathogens for the sake of research.

RESULTS

Almost all responders expressed willingness to participate in research at the EOL, regardless of HIV-status. The majority of participants were willing to endure physical discomfort for the sake of research. 'Blood draws' was identified as the most tolerable physical discomfort (>70% in both groups). In both groups, >60% were willing to shorten their lifespans for the sake of research. A third of the self-reported HIV-negative group expressed willingness to be exposed to at least one infectious agent to participate in EOL research.

CONCLUSIONS

Our exploratory study demonstrates that people would welcome the opportunity to participate in altruistic research near the EOL. Such research could greatly impact the way infectious disease research is conducted. This study is limited however by its hypothetical nature. Further research is necessary to confirm this interest in those with terminal illness before any further clinical research effort at the EOL can be performed.

Designing optimal HIV-vaccine T-cell responses

PURPOSE OF REVIEW

T cells can efficaciously control HIV replication, and it has been hypothesized that inducing those responses before exposure occurs may prevent HIV infection. However, conventional attempts to generate protective CD8 T-cell responses against HIV have generally failed. Based on current knowledge from chronic HIV infection and previous vaccine trials, this review details optimal CD8 and CD4 T-cell response design that may confer protection from HIV infection.

RECENT FINDINGS

The failure of two vaccines geared toward inducing T-cell response (STEP trial and HVTN505/Phambili) as well as the modest protection of the RV144 that mainly demonstrated nonneutralizing antibodies to be a correlate of protection have rattled the idea that a pure T-cell-based vaccine may induce protection. Moreover, in the recent years, CD4 T cells, and in particular the T follicular helper cell subset, received attention as a critical component for T-cell-inducing and antibody-inducing vaccines.

SUMMARY

It is apparent that all vaccines depend for their efficacy on a cellular component either to directly kill virally infected cells or to provide important helper signals for the development of efficacious B-cell responses. Recent vaccine trials have had a major impact on the field and are guiding new approaches for HIV vaccine design.

Dynamics of SIV-specific CXCR5+ CD8 T cells during chronic SIV infection

A significant challenge to HIV eradication is the elimination of viral reservoirs in germinal center (GC) T follicular helper (Tfh) cells. However, GCs are considered to be immune privileged for antiviral CD8 T cells. Here, we show a population of simian immunodeficiency virus (SIV)-specific CD8 T cells express CXCR5 (C-X-C chemokine receptor type 5, a chemokine receptor required for homing to GCs) and expand in lymph nodes (LNs) following pathogenic SIV infection in a cohort of vaccinated macaques. This expansion was greater in animals that exhibited superior control of SIV. The CXCR5+ SIV-specific CD8 T cells demonstrated enhanced polyfunctionality, restricted expansion of antigen-pulsed Tfh cells in vitro, and possessed a unique gene expression pattern related to Tfh and Th2 cells. The increase in CXCR5+ CD8 T cells was associated with the presence of higher frequencies of SIV-specific CD8 T cells in the GC. Following TCR-driven stimulation in vitro, CXCR5+ but not CXCR5- CD8 T cells generated both CXCR5+ as well as CXCR5- cells. However, the addition of TGF-β to CXCR5- CD8 T cells induced a population of CXCR5+ CD8 T cells, suggesting that this cytokine may be important in modulating these CXCR5+ CD8 T cells in vivo. Thus, CXCR5+ CD8 T cells represent a unique subset of antiviral CD8 T cells that expand in LNs during chronic SIV infection and may play a significant role in the control of pathogenic SIV infection.

Can research at the end of life be a useful tool to advance HIV cure?

Despite extensive investigations, we still do not fully understand the dynamics of the total body HIV reservoir and how sub-reservoirs in various compartments relate to one another. Studies using macaque models are enlightening but eradication strategies will still need to be tested in humans. To take the next steps in understanding and eradicating HIV reservoirs throughout the body, we propose to develop a “peri-mortem translational research model” of HIV-infected individuals (called ‘The Last Gift’), which is similar to existing models in cancer research. In this model, altruistic, motivated HIV-infected individuals with advanced non-AIDS related diseases and with six months or less to live will participate in HIV cure research and donate their full body after they die. Engaging this population provides a unique opportunity to compare the HIV reservoir before and after death across multiple anatomic compartments in relation to antiretroviral therapy use and other relevant clinical factors. Furthermore, people living with HIV/AIDS at the end of their lives may be willing to participate to cure interventions and accept greater risks for research participation. A broad, frank, and pragmatic discussion about performing HIV cure research near the end of life is necessary.

Recursion-based depletion of human immunodeficiency virus-specific naive CD4(+) T cells may facilitate persistent viral replication and chronic viraemia leading to acquired immunodeficiency syndrome

Although antiretroviral therapy has made human immunodeficiency virus (HIV) infection a controllable disease, it is still unclear how viral replication persists in untreated patients and causes CD4(+) T-cell depletion leading to acquired immunodeficiency syndrome (AIDS) in several years. Theorists tried to explain it with the diversity threshold theory in which accumulated mutations in the HIV genome make the virus so diverse that the immune system will no longer be able to recognize all the variants and fail to control the viraemia. Although the theory could apply to a number of cases, macaque AIDS models using simian immunodeficiency virus (SIV) have shown that failed viral control at the set point is not always associated with T-cell escape mutations. Moreover, even monkeys without a protective major histocompatibility complex (MHC) allele can contain replication of a super infected SIV following immunization with a live-attenuated SIV vaccine, while those animals are not capable of fighting primary SIV infection. Here we propose a recursion-based virus-specific naive CD4(+) T-cell depletion hypothesis through thinking on what may happen in individuals experiencing primary immunodeficiency virus infection. This could explain the mechanism for impairment of virus-specific immune response in the course of HIV infection.

Functional differences in hepatitis C virus nonstructural (NS) 3/4A- and 5A-specific T cell responses

The hepatitis C virus nonstructural (NS) 3/4A and NS5A proteins are major targets for the new direct-acting antiviral compounds. Both viral proteins have been suggested as modulators of the response to the host cell. We have shown that NS3/4A- and NS5A-specific T cell receptors confer different effector functions, and that killing of NS3/4A-expressing hepatocytes is highly dependent on IFN-γ. We here characterize the functional differences in the T cell responses to NS3/4A and NS5A. NS3/4A- and NS5A-specific T cells could be induced at various frequencies in wild-type-, NS3/4A-, and NS5A-transgenic mice. Priming of NS5A-specific T cells required a high DNA dose, and was unlike NS3/4A dependent on both CD4⁺ and CD8⁺ T cells, but less influenced by CD25⁺/GITR⁺ regulatory T cells. The presence of IL-12 greatly improved specific CD8⁺ T cell priming by NS3/4A but not by NS5A, suggesting a less dependence of IFN-γ for NS5A. This notion was supported by the observation that NS5A-specific T cells could eliminate NS5A-expressing hepatocytes also in the absence of IFN-γ-receptor-2. This supports that NS3/4A- and NS5A-specific T cells become activated and eliminate antigen expressing, or infected hepatocytes, by distinct mechanisms, and that NS5A-specific T cells show an overall less dependence of IFN-γ.

Interleukin-21 administration leads to enhanced antigen-specific T cell responses and natural killer cells in HIV-1 vaccinated mice

Interleukin-21 (IL-21), which belongs to IL-2 γ chain receptor cytokine family, is as an important regulator of immune responses. In this study, we developed a novel strategy for immunizing mice with a DNA/vaccinia/protein vaccine in the presence or absence of mouse IL-21 (mIL-21) to evaluate whether mIL-21 could enhance immune responses. Our results demonstrated that co-immunization with mIL-21 did not increase significantly the capacity of vaccine induced antibodies to bind to HIV-1 GP140. An effect of mIL-21 in adjusting the efficacy of HIV-1 vaccine through enhancing Th1 type immune response was however observed. The frequencies of HIV-1-specific cytokine-producing CD4+ T and CD4+ TEM cells, especially multifunctional T cell responses, were significantly increased by co-administrating with mIL-21. A significant increase was also observed in the frequency of NK cells in mIL-21 adjuvant groups. Taken together, combination of mIL-21 with HIV-1 vaccines led to distinct enhancement of NK cells and T cell immune responses associated with immune protection.

Molecular mechanisms for enhanced DNA vaccine immunogenicity

In the two decades since their initial discovery, DNA vaccines technologies have come a long way. Unfortunately, when applied to human subjects inadequate immunogenicity is still the biggest challenge for practical DNA vaccine use. Many different strategies have been tested in preclinical models to address this problem, including novel plasmid vectors and codon optimization to enhance antigen expression, new gene transfection systems or electroporation to increase delivery efficiency, protein or live virus vector boosting regimens to maximise immune stimulation, and formulation of DNA vaccines with traditional or molecular adjuvants. Better understanding of the mechanisms of action of DNA vaccines has also enabled better use of the intrinsic host response to DNA to improve vaccine immunogenicity. This review summarizes recent advances in DNA vaccine technologies and related intracellular events and how these might impact on future directions of DNA vaccine development.

Development of a Sendai virus vector-based AIDS vaccine inducing T cell responses

Virus-specific CD8(+) T-cell responses play a major role in the control of HIV replication, and induction of HIV-specific T-cell responses is an important strategy for AIDS vaccine development. Optimization of the delivery system and immunogen would be the key for the development of an effective T cell-based AIDS vaccine. Heterologous prime-boost vaccine regimens using multiple viral vectors are a promising protocol for efficient induction of HIV-specific T-cell responses, and the development of a variety of potent viral vectors have been attempted. This review describes the current progress of the development of T cell-based AIDS vaccines using viral vectors, focusing on Sendai virus vectors, whose phase I clinical trials have been performed.

HIV Vaccine: Recent Advances, Current Roadblocks, and Future Directions

HIV/AIDS is a leading cause of mortality and morbidity worldwide. In spite of successful interventions and treatment protocols, an HIV vaccine would be the ultimate prevention and control strategy. Ever since identification of HIV/AIDS, there have been meticulous efforts for vaccine development. The specific aim of this paper is to review recent vaccine efficacy trials and associated advancements and discuss the current challenges and future directions. Recombinant DNA technologies greatly facilitated development of many viral products which were later incorporated into vectors for effective vaccines. Over the years, a number of scientific approaches have gained popularity and include the induction of neutralizing antibodies in late 1980s, induction of CD8 T cell in early 1990s, and combination approaches currently. Scientists have hypothesized that stimulation of right sequences of somatic hypermutations could induce broadly reactive neutralizing antibodies (bnAbs) capable of effective neutralization and viral elimination. Studies have shown that a number of host and viral factors affect these processes. Similarly, eliciting specific CD8 T cells immune responses through DNA vaccines hold future promises. In summary, future studies should focus on the continuous fight between host immune responses and ever-evasive viral factors for effective vaccines.

HIV-1 Coreceptor CXCR4 Antagonists Promote Clonal Expansion of Viral Epitope-Specific CD8+ T Cells During Acute SIV Infection in Rhesus Monkeys In Vivo

BACKGROUND

The underlying molecular mechanisms and the kinetics of T cell receptor (TCR) repertoire selection during administration of CXCR4 or CCR5 inhibitors in infection of AIDS viruses in vivo have remained largely unexplored. Viral epitope-specific CD8(+) T lymphocytes play a dominant role in the control of HIV and simian immunodeficiency virus (SIV). We hypothesized that blockade of CXCR4 or CCR5 might influence the clonal expansion of epitope-specific CD8(+) T cells, contributing to antiviral immune responses in vivo.

METHODS

We measured frequencies of the dominant epitope p11C-specific CD8(+) T cells and analyzed the TCR repertoire of those cells in SIV-infected rhesus monkeys treated by CXCR4 or CCR5 inhibitors and vMIP-II, which binds multiple chemokine receptors.

RESULTS

A significantly increase in the levels of epitope-specific CD8(+) T cells was observed after blockade of CXCR4 or CCR5 compared with untreated control groups. Those CD8(+) T cells exhibited selected usage of TCR Vβ families and complementarity-determining region 3 (CDR3) segments. The clonal expansion of distinct Vβ populations could efficiently inhibit SIV replication in vitro, and CXCR4 inhibitor induced more expansion of epitope-specific CD8(+) T cells than CCR5 antagonist (P < 0.01), whereas vMIP-II treatment showed the most marked augmentation of p11C-specific CD8(+) T cells.

CONCLUSIONS

Antagonists of HIV coreceptors, particularly CXCR4, play an important role in the clonal expansion of SIV epitope-specific CD8(+) T cells in vivo, thus inhibitors of chemokine receptors such as CXCR4 or CCR5 may contribute to the ability of epitope-specific CD8(+) T cells to inhibit SIV or HIV infection.

A Phase I Double Blind, Placebo-Controlled, Randomized Study of the Safety and Immunogenicity of Electroporated HIV DNA with or without Interleukin 12 in Prime-Boost Combinations with an Ad35 HIV Vaccine in Healthy HIV-Seronegative African Adults

BACKGROUND

Strategies to enhance the immunogenicity of DNA vaccines in humans include i) co-administration of molecular adjuvants, ii) intramuscular administration followed by in vivo electroporation (IM/EP) and/or iii) boosting with a different vaccine. Combining these strategies provided protection of macaques challenged with SIV; this clinical trial was designed to mimic the vaccine regimen in the SIV study.

METHODS

Seventy five healthy, HIV-seronegative adults were enrolled into a phase 1, randomized, double-blind, placebo-controlled trial. Multi-antigenic HIV (HIVMAG) plasmid DNA (pDNA) vaccine alone or co-administered with pDNA encoding human Interleukin 12 (IL-12) (GENEVAX IL-12) given by IM/EP using the TriGrid Delivery System was tested in different prime-boost regimens with recombinant Ad35 HIV vaccine given IM.

RESULTS

All local reactions but one were mild or moderate. Systemic reactions and unsolicited adverse events including laboratory abnormalities did not differ between vaccine and placebo recipients. No serious adverse events (SAEs) were reported. T cell and antibody response rates after HIVMAG (x3) prime-Ad35 (x1) boost were independent of IL-12, while the magnitude of interferon gamma (IFN-γ) ELISPOT responses was highest after HIVMAG (x3) without IL-12. The quality and phenotype of T cell responses shown by intracellular cytokine staining (ICS) were similar between groups. Inhibition of HIV replication by autologous T cells was demonstrated after HIVMAG (x3) prime and was boosted after Ad35. HIV specific antibodies were detected only after Ad35 boost, although there was a priming effect with 3 doses of HIVMAG with or without IL-12. No anti-IL-12 antibodies were detected.

CONCLUSION

The vaccines were safe, well tolerated and moderately immunogenic. Repeated administration IM/EP was well accepted. An adjuvant effect of co-administered plasmid IL-12 was not detected.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01496989.

Functional Heterogeneity and Antimycobacterial Effects of Mouse Mucosal-Associated Invariant T Cells Specific for Riboflavin Metabolites

Mucosal-associated invariant T (MAIT) cells have a semi-invariant TCR Vα-chain, and their optimal development is dependent upon commensal flora and expression of the nonpolymorphic MHC class I-like molecule MR1. MAIT cells are activated in an MR1-restricted manner by diverse strains of bacteria and yeast, suggesting a widely shared Ag. Recently, human and mouse MR1 were found to bind bacterial riboflavin metabolites (ribityllumazine [RL] Ags) capable of activating MAIT cells. In this study, we used MR1/RL tetramers to study MR1 dependency, subset heterogeneity, and protective effector functions important for tuberculosis immunity. Although tetramer(+) cells were detected in both MR1(+/+) and MR1(-/-) TCR Vα19i-transgenic (Tg) mice, MR1 expression resulted in significantly increased tetramer(+) cells coexpressing TCR Vβ6/8, NK1.1, CD44, and CD69 that displayed more robust in vitro responses to IL-12 plus IL-18 and RL Ag, indicating that MR1 is necessary for the optimal development of the classic murine MAIT cell memory/effector subset. In addition, tetramer(+) MAIT cells expressing CD4, CD8, or neither developing in MR1(+/+) Vα19i-Tg mice had disparate cytokine profiles in response to RL Ag. Therefore, murine MAIT cells are considerably more heterogeneous than previously thought. Most notably, after mycobacterial pulmonary infection, heterogeneous subsets of tetramer(+) Vα19i-Tg MAIT cells expressing CXCR3 and α4β1 were recruited into the lungs and afforded early protection. In addition, Vα19iCα(-/-)MR(+/+) mice were significantly better protected than were Vα19iCα(-/-)MR1(-/-), wild-type, and MR1(-/-) non-Tg mice. Overall, we demonstrate considerable functional diversity of MAIT cell responses, as well as that MR1-restricted MAIT cells are important for tuberculosis protective immunity.

HIV-1 vaccines based on replication-competent Tiantan vaccinia protected Chinese rhesus macaques from simian HIV infection

OBJECTIVE

To assess the efficacy of HIV vaccines constructed from replication-competent Tiantan vaccinia virus (rTV) alone or combined with DNA in protecting Chinese rhesus macaques from homologous Simian/Human Immunodeficiency Virus (SHIV)-CN97001 challenge.

METHODS

The nef, gag, pol, and gp140 genes from strain CRF07_BC HIV-1 CN54 were selected to construct an HIV vaccine using the rTV or rTV/DNA vaccine. After vaccination, the vaccine and control groups were intravenously challenged with SHIV-CN97001 (32 MID50). HIV-specific antibodies and neutralizing antibodies, gp70 V1V2 binding antibodies, and cytotoxic T-lymphocyte responses were measured prospectively after vaccination with an ELISA, a virus infectivity assay in TZM-bl cells, and ELISPOT assays, respectively. Viral RNA was quantified after challenge with real-time reverse transcriptase-PCR (RT-PCR), and protection efficacy was determined with an analysis of CD8 lymphocyte depletion in vivo.

RESULTS

Both rTV and DNA/rTV vaccine groups developed strong cellular and humoral responses against HIV-1 CN54 antigens, including Gag and Env, and also developed significant and persistent anti-Env antibodies and neutralizing antibodies after immunization. Both the rTV and DNA/rTV groups were significantly protected against SHIV-CN97001 or displayed lower viremia than the controls. After CD8 lymphocyte depletion, no viremia was detectable in the vaccinated monkeys, but rebounded rapidly in the control animals. Protection against infection correlated with vaccine-elicited neutralizing antibodies specific for homologous HIV-1 viruses.

CONCLUSION

An rTV-based HIV-1 vaccine, with or without a DNA primer, provided protection from SHIV challenge in a macaque model. Replication-competent Tiantan vaccinia is a promising vector and should enable advances in HIV-1 vaccine development.

Infection of monkeys by simian-human immunodeficiency viruses with transmitted/founder clade C HIV-1 envelopes

Simian-human immunodeficiency viruses (SHIVs) that mirror natural transmitted/founder (T/F) viruses in man are needed for evaluation of HIV-1 vaccine candidates in nonhuman primates. Currently available SHIVs contain HIV-1 env genes from chronically-infected individuals and do not reflect the characteristics of biologically relevant HIV-1 strains that mediate human transmission. We chose to develop clade C SHIVs, as clade C is the major infecting subtype of HIV-1 in the world. We constructed 10 clade C SHIVs expressing Env proteins from T/F viruses. Three of these ten clade C SHIVs (SHIV KB9 C3, SHIV KB9 C4 and SHIV KB9 C5) replicated in naïve rhesus monkeys. These three SHIVs are mucosally transmissible and are neutralized by sCD4 and several HIV-1 broadly neutralizing antibodies. However, like natural T/F viruses, they exhibit low Env reactivity and a Tier 2 neutralization sensitivity. Of note, none of the clade C T/F SHIVs elicited detectable autologous neutralizing antibodies in the infected monkeys, even though antibodies that neutralized a heterologous Tier 1 HIV-1 were generated. Challenge with these three new clade C SHIVs will provide biologically relevant tests for vaccine protection in rhesus macaques.

The role of chance in primate lentiviral infectivity: from protomer to host organism

Infection is best described as a stochastic process. Whether a host becomes infected upon exposure has a strong random element. The same applies to cells exposed to virions. In this review, we show how the mathematical formalism for stochastic processes has been used to describe and understand the infection by the Human and Simian Immunodeficiency Virus on different levels. We survey quantitative studies on the establishment of infection in the host (the organismal level) and on the infection of target cells (the cellular and molecular level). We then discuss how a synthesis of the approaches across these levels could give rise to a predictive framework for assessing the efficacy of microbicides and vaccines.

A critical analysis of the cynomolgus macaque, Macaca fascicularis, as a model to test HIV-1/SIV vaccine efficacy

The use of a number of non-rhesus macaque species, but especially cynomolgus macaques as a model for HIV-1 vaccine development has increased in recent years. Cynomolgus macaques have been used in the United Kingdom, Europe, Canada and Australia as a model for HIV vaccine development for many years. Unlike rhesus macaques, cynomolgus macaques infected with SIV show a pattern of disease pathogenesis that more closely resembles that of human HIV-1 infection, exhibiting lower peak and set-point viral loads and slower progression to disease with more typical AIDS defining illnesses. Several advances have been made recently in the use of the cynomolgus macaque SIV challenge model that allow the demonstration of vaccine efficacy using attenuated viruses and vectors that are both viral and non-viral in origin. This review aims to probe the details of various vaccination trials carried out in cynomolgus macaques in the context of our modern understanding of the highly diverse immunogenetics of this species with a view to understanding the species-specific immune correlates of protection and the efficacy of vectors that have been used to design vaccines.

Human immunodeficiency virus vaccines

Although some success was achieved in recent years in HIV prevention, an effective vaccine remains the means with the most potential of curtailing HIV-1 infections worldwide. Despite multiple failed attempts, a recent HIV vaccine regimen demonstrated modest protection from infection. Although the protective efficacy in this trial was not sufficient to warrant licensure, it spurred renewed optimism in the field and has provided valuable insights for improving future vaccine designs. This review summarizes the pertinent details of vaccine development and discusses ways the field is moving forward to develop a vaccine to prevent HIV infection and disease progression.

Challenges in HIV Vaccine Research for Treatment and Prevention

Many attempts have been made or are ongoing for HIV prevention and HIV cure. Many successes are in the list, particularly for HIV drugs, recently proposed also for prevention. However, no eradication of infection has been achieved so far with any drug. Further, a residual immune dysregulation associated to chronic immune activation and incomplete restoration of B and T cell subsets, together with HIV DNA persistence in reservoirs, are still unmet needs of the highly active antiretroviral therapy, causing novel “non-AIDS related” diseases that account for a higher risk of death even in virologically suppressed patients. These “ART unmet needs” represent a problem, which is expected to increase by ART roll out. Further, in countries such as South Africa, where six millions of individuals are infected, ART appears unable to contain the epidemics. Regretfully, all the attempts at developing a preventative vaccine have been largely disappointing. However, recent therapeutic immunization strategies have opened new avenues for HIV treatment, which might be exploitable also for preventative vaccine approaches. For example, immunization strategies aimed at targeting key viral products responsible of virus transmission, activation, and maintenance of virus reservoirs may intensify drug efficacy and lead to a functional cure providing new perspectives also for prevention and future virus eradication strategies. However, this approach imposes new challenges to the scientific community, vaccine developers, and regulatory bodies, such as the identification of novel immunological and virological biomarkers to assess efficacy end-points, taking advantage from the natural history of infection and exploiting lessons from former trials. This review will focus first on recent advancement of therapeutic strategies, then on the progresses made in preventative approaches, discussing concepts, and problems for the way ahead for the development of vaccines for HIV treatment and prevention.

Microdevices for examining immunological responses of single cells to HIV

More than 60 million people in the world have been diagnosed with HIV infections since the virus was recognized as the causative agent of AIDS in the 1980s. Even though more than half of the infected patients have died, effective disease treatment and prevention measures have not been established. ART (antiretroviral therapy) is the only proven HIV treatment that sustains the suppression of patient viraemia. Current routine approaches to treat HIV infections are targeted at developing vaccines that will induce humoral or cell memory immune responses. However, developing an effective vaccine has been challenging because the HIV mutates rapidly, which allows the virus to evade immune surveillances established against the previous strain. In addition, the virus is able to quickly establish a reservoir and treatment is difficult because of the general lack of knowledge about HIV immune response mechanisms. This review introduces common disease symptoms and the progression of HIV infection with a brief summary of the current treatment approaches. Different cellular immune responses against HIV are also discussed, with emphasis on a nanotechnology research that has focused on probing T-cell response to HIV infection. Furthermore, we discuss recent noteworthy nanotechnology updates on T-cell response screening that is focused on HIV infection. Finally, we review potential future treatment strategies based on the correlations between T-cell response and HIV infection.

Recent progress in HIV vaccines inducing mucosal immune responses

In spite of several attempts over many years at developing a HIV vaccine based on classical strategies, none has convincingly succeeded to date. As HIV is transmitted primarily by the mucosal route, particularly through sexual intercourse, understanding antiviral immunity at mucosal sites is of major importance. An ideal vaccine should elicit HIV-specific antibodies and mucosal CD8⁺ cytotoxic T-lymphocyte (CTL) as a first line of defense at a very early stage of HIV infection, before the virus can disseminate into the secondary lymphoid organs in mucosal and systemic tissues. A primary focus of HIV preventive vaccine research is therefore the induction of protective immune responses in these crucial early stages of HIV infection. Numerous approaches are being studied in the field, including building upon the recent RV144 clinical trial. In this article, we will review current strategies and briefly discuss the use of adjuvants in designing HIV vaccines that induce mucosal immune responses.

Intranasal DNA Vaccine for Protection against Respiratory Infectious Diseases: The Delivery Perspectives

Intranasal delivery of DNA vaccines has become a popular research area recently. It offers some distinguished advantages over parenteral and other routes of vaccine administration. Nasal mucosa as site of vaccine administration can stimulate respiratory mucosal immunity by interacting with the nasopharyngeal-associated lymphoid tissues (NALT). Different kinds of DNA vaccines are investigated to provide protection against respiratory infectious diseases including tuberculosis, coronavirus, influenza and respiratory syncytial virus (RSV) etc. DNA vaccines have several attractive development potential, such as producing cross-protection towards different virus subtypes, enabling the possibility of mass manufacture in a relatively short time and a better safety profile. The biggest obstacle to DNA vaccines is low immunogenicity. One of the approaches to enhance the efficacy of DNA vaccine is to improve DNA delivery efficiency. This review provides insight on the development of intranasal DNA vaccine for respiratory infections, with special attention paid to the strategies to improve the delivery of DNA vaccines using non-viral delivery agents.

DNA vaccination by intradermal electroporation induces long-lasting immune responses in rhesus macaques

BACKGROUND

A desirable HIV vaccine should induce protective long-lasting humoral and cellular immune responses.

METHODS

Macaques were immunized by env DNA, selected from a panel of recently transmitted SIVmac251 Env using intradermal electroporation as vaccine delivery method and magnitude, breadth and longevity of humoral and cellular immune responses.

RESULTS

The macaques developed high, long-lasting humoral immune responses with neutralizing capacity against homologous and heterologous Env. The avidity of the antibody responses was also preserved over 1-year follow-up. Analysis of cellular immune responses demonstrated induction of Env-specific memory T cells harboring granzyme B, albeit their overall levels were low. Similar to the humoral responses, the cellular immunity was persistent over the ~1-year follow-up.

CONCLUSION

These data show that vaccination by this intradermal DNA delivery regimen is able to induce potent and durable immune responses in macaques.

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.

DNA/MVA Vaccines for HIV/AIDS

Since the initial proof-of-concept studies examining the ability of antigen-encoded plasmid DNA to serve as an immunogen, DNA vaccines have evolved as a clinically safe and effective platform for priming HIV-specific cellular and humoral responses in heterologous "prime-boost" vaccination regimens. Direct injection of plasmid DNA into the muscle induces T- and B-cell responses against foreign antigens. However, the insufficient magnitude of this response has led to the development of approaches for enhancing the immunogenicity of DNA vaccines. The last two decades have seen significant progress in the DNA-based vaccine platform with optimized plasmid constructs, improved delivery methods, such as electroporation, the use of molecular adjuvants and novel strategies combining DNA with viral vectors and subunit proteins. These innovations are paving the way for the clinical application of DNA-based HIV vaccines. Here, we review preclinical studies on the DNA-prime/modified vaccinia Ankara (MVA)-boost vaccine modality for HIV. There is a great deal of interest in enhancing the immunogenicity of DNA by engineering DNA vaccines to co-express immune modulatory adjuvants. Some of these adjuvants have demonstrated encouraging results in preclinical and clinical studies, and these data will be examined, as well.