Mosaic vaccines elicit CD8+ T lymphocyte responses that confer enhanced immune coverage of diverse HIV strains in monkeys

Autologous HIV-specific T cell therapy targeting conserved epitopes is well-tolerated in six adults with HIV: an open-label, single-arm phase 1 study

Novel cellular therapies may enable HIV control or cure. HIV-specific T cells targeting conserved immunogenic protein regions of HIV Gag/Pol and the entirety of HIV Nef, termed HST-NEETs, eliminate HIV infected cells in vitro. Here we enroll seven participants in an open-label, single-arm phase 1 study (NCT03485963) to evaluate the safety (primary endpoint) of two autologous administrations of HST-NEET products without prescribed lymphodepletion. Adults with well-controlled HIV on anti-retroviral therapy are eligible. Six participants completed safety monitoring. No serious product-related toxicities are observed. Secondary endpoints are to assess expansion and persistence of HIV-reactive T cell clones, and changes to the HIV reservoir for each infused participant. HIV-specific T cell and HIV anti-Env antibody responses increase in two participants after infusion two. A trend towards decreasing levels of intact proviruses is observed in 2 participants. Three participants show persistence of HIV-reactive, product-associated T cell clones for ≥40 weeks post infusions. HST-NEETs infusions are well-tolerated. Future trials are needed to evaluate the efficacy of HST-NEETs in this population.

ALVAC-prime and monomeric gp120 protein boost induces distinct HIV-1 specific humoral and cellular responses compared with adenovirus-prime and trimeric gp140 protein boost

Although clade-specific and cross-clade mosaic prime-boost HIV-1 vaccine regimens were advanced to the HVTN 702 and HVTN 705 efficacy trials, neither regimen prevented HIV acquisition. The respective Phase 1/2a studies, HVTN 100 (NCT02404311) and HVTN 117/HPX2004 (NCT02788045), provided rich immunological data, including previously identified correlates of risk, for comparing immune responses elicited by these vaccine regimens over time. We analyzed antibody responses measured by binding antibody multiplex assay, and CD4+ and CD8+ T-cell responses measured by intracellular cytokine staining in per-protocol vaccinees in HVTN 100 (n=186) vs. HVTN 117/HPX2004 (n=99) after the months 6 and 12 vaccinations (months 6.5/7 and 12.5/13), and 6 months after the last vaccination (month 18). At month 12.5/13, both regimens induced similarly high IgG breadth against gp120, gp140, and V1V2 antigens, and similar IgG responses to gp70-BCaseA V1V2. IgG V1V2 responses were more durable in HVTN 117/HPX2004, with the largest difference in the gp70-BCaseA V1V2 IgG response rate at month 18 (17.8% in HVTN 100 vs 61.9% in HVTN 117/HPX2004, p<0.001). IgG3 responses to consensus Env antigens were higher and more durable in HVTN117/HPX2004; for example, IgG3 response rate to the consensus gp140 antigen was 65.9% in HVTN 117/HPX2004 vs 6.3% in HVTN 100 at month 18 (TMLE p<0.0001). At month 18, both regimens induced similar IgG3 responses to gp70-BCaseA V1V2 (3.2% in HVTN 100 vs 1.1% in HVTN 117/HPX2004). Polyfunctional CD4+ Env was significantly higher in HVTN 100, and polyfunctional CD4+ Gag was higher in HVTN 117/HPX2004. CD8+ T-cell responses were not seen in HVTN 100, while CD8+ T-cell response rates in HVTN 117/HPX2004 reached up to 42%. Despite the distinct immune responses induced by the two HIV vaccine regimens, the lack of demonstrated efficacy suggests that broader, higher magnitude, and possibly qualitatively different immune responses are needed for protection against HIV acquisition. Trial registration: ClinicalTrials.gov NCT02404311 and NCT02788045; South African National Clinical Trials Registry (DOH-27-0215-4796).

Diversifying T-cell responses: safeguarding against pandemic influenza with mosaic nucleoprotein

Pre-existing T-cell responses have been linked to reduced disease severity and better clinical outcomes during the 2009 influenza pandemic and the recent COVID-19 pandemic. We hypothesized that diversifying T-cell responses, particularly targeting conserved viral proteins such as the influenza A virus (IAV) nucleoprotein (NP), could protect against both epidemic and pandemic IAV strains. To test this, we created a mosaic nucleoprotein (MNP) by synthesizing a sequence that maximized the representation of 9-mer epitopes from 7422 NP sequences across human, swine, and avian IAVs. Notably, the MNP sequence showed high homology with the NP of the H5N1 strain affecting dairy cows in the ongoing outbreak. Mucosal immunization with the adjuvanted MNP vaccine induced robust CD8 and CD4 T-cell responses against both known immunodominant and in silico predicted subdominant epitopes. MNP-vaccinated mice challenged with epidemic H1N1 and H3N2 strains, which shared immunodominant CD8 and/or CD4 T-cell epitopes, showed a significant (~4 log) reduction in lung viral load. Importantly, MNP-vaccinated mice challenged with a pandemic H1N1 strain lacking shared immunodominant CD8 or CD4 epitopes exhibited a superior reduction in lung viral load, linked to T-cell responses targeting subdominant epitopes present in both the MNP and pandemic strain NP. These results suggest that a diversified T-cell response induced by the MNP vaccine could provide broad protection against severe disease from both current and emerging IAV strains.

IMPORTANCE

The World Health Organization (WHO) estimates that seasonal influenza causes 3-5 million cases of severe illness annually. The influenza virus frequently undergoes genetic changes through antigenic drift and antigenic shift, resulting in annual epidemics and occasional pandemics. Consequently, a major public health objective is to develop a universal influenza vaccine that offers broad protection against both current and pandemic influenza A strains. In this study, we designed a nucleoprotein (NP) antigen (termed mosaic NP) comprising antigenic regions found in thousands of influenza viruses, aiming to use it as a vaccine to induce broad anti-influenza T-cell responses. Our findings indicate that the mosaic NP vaccine provided significant protection against seasonal H1N1 and H3N2, as well as the pandemic H1N1 strain, demonstrating its effectiveness across various influenza subtypes. These findings suggest that the mosaic NP is a potential universal influenza vaccine antigen, capable of protecting against diverse strains of influenza viruses.

Developing T Cell Epitope-Based Vaccines Against Infection: Challenging but Worthwhile

T cell epitope-based vaccines are designed to elicit long-lived pathogen-specific memory T cells that can quickly activate protective effector functions in response to subsequent infections. These vaccines have the potential to provide sustained protection against mutated variants, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which are increasingly capable of evading neutralizing antibodies. Recent advancements in epitope discovery, T cell receptor analysis, and bioinformatics have enabled the precise selection of epitopes and the sophisticated design of epitope-based vaccines. This review outlines the development process for T cell epitope-based vaccines. We summarize the current progress in T cell epitope discovery technologies, highlighting the advantages and disadvantages of each method. We also examine advancements in the design and optimization of epitope-based vaccines, particularly through bioinformatics tools. Additionally, we discuss the challenges of validating the accurate processing and presentation of individual epitopes and establishing suitable rodent models to evaluate vaccine immunogenicity and protective efficacy.

Nanoparticles in Subunit Vaccines: Immunological Foundations, Categories, and Applications

Subunit vaccines, significant in next-generation vaccine development, offer precise targeting of immune responses by focusing on specific antigens. However, this precision often comes at the cost of eliciting strong and durable immunity, posing a great challenge to vaccine design. To address this limitation, recent advancements in nanoparticles (NPs) are utilized to enhance antigen delivery efficiency and boost vaccine efficacy. This review examines how the physicochemical properties of NPs influence various stages of the immune response during vaccine delivery and analyzes how different NP types contribute to immune activation and enhance vaccine performance. It then explores the unique characteristics and immune activation mechanisms of these NPs, along with their recent advancements, and highlights their application in subunit vaccines targeting infectious diseases and cancer. Finally, it discusses the challenges in NP-based vaccine development and proposes future directions for innovation in this promising field.

mRNA-based HIV-1 vaccines

SUMMARYThe success of the Severe Acute Respiratory Syndrome Coronavirus 2 mRNA vaccines to lessen/prevent severe COVID-19 opened new opportunities to develop RNA vaccines to fight other infectious agents. HIV-1 is a lentivirus that integrates into the host cell genome and persists for the lifetime of infected cells. Multiple mechanisms of immune evasion have posed significant obstacles to the development of an effective HIV-1 vaccine over the last four decades since the identification of HIV-1. Recently, attempts to address some of these challenges have led to multiple studies that manufactured, optimized, and tested, in different animal models, mRNA-based HIV-1 vaccines. Several clinical trials have also been initiated or are planned to start soon. Here, we review the current strategies applied to HIV-1 mRNA vaccines, discuss different targeting approaches, summarize the latest findings, and offer insights into the challenges and future of HIV-1 mRNA vaccines.

Influenza B Virus Vaccine Innovation through Computational Design

As respiratory pathogens, influenza B viruses (IBVs) cause a significant socioeconomic burden each year. Vaccine and antiviral development for influenza viruses has historically viewed IBVs as a secondary concern to influenza A viruses (IAVs) due to their lack of animal reservoirs compared to IAVs. However, prior to the global spread of SARS-CoV-2, the seasonal epidemics caused by IBVs were becoming less predictable and inducing more severe disease, especially in high-risk populations. Globally, researchers have begun to recognize the need for improved prevention strategies for IBVs as a primary concern. This review discusses what is known about IBV evolutionary patterns and the effect of the spread of SARS-CoV-2 on these patterns. We also analyze recent advancements in the development of novel vaccines tested against IBVs, highlighting the promise of computational vaccine design strategies when used to target both IBVs and IAVs and explain why these novel strategies can be employed to improve the effectiveness of IBV vaccines.

Increase in HIV reservoir and T cell immune response after CoronaVac vaccination in people living with HIV

Introduction

CoronaVac, an inactivated vaccine developed by Sinovac Life Sciences, has been widely used for protection against Coronavirus Disease 2019 (COVID-19). This study investigates its effect on the HIV reservoir and T cell repertoires in people living with HIV (PLWHs).

Methods

Blood samples were collected from fifteen PLWHs who were administered at least two doses of CoronaVac between April 2021 and February 2022. The levels of cell-associated HIV RNA (CA HIV RNA) and HIV DNA, as well as the T cell receptor (TCR) repertoire profiles, TCR clustering and TCRβ annotation, were studied.

Results

A significant increase was observed in CA HIV RNA at 2 weeks (431.5 ± 164.2 copies/106 cells, P = 0.039) and 12 weeks (330.2 ± 105.9 copies/106 cells, P = 0.019) after the second dose, when compared to the baseline (0 weeks) (73.6 ± 23.7 copies/106 cells). Various diversity indices of the TCRβ repertoire, including Shannon index, Pielou's evenness index, and Hvj Index, revealed a slight increase (P < 0.05) following CoronaVac vaccination. The proportion of overlapping TCRβ clonotypes increased from baseline (31.9 %) to 2 weeks (32.5 %) and 12 weeks (40.4 %) after the second dose. We also found that the breadth and depth of COVID-19-specific T cells increased from baseline (0.003 and 0.0035) to 12 weeks (0.0066 and 0.0058) post the second dose.

Conclusions

Our study demonstrated an initial increase in HIV reservoir and TCR repertoire diversity, as well as an expansion in the depth and breadth of COVID-19-specific T-cell clones among CoronaVac-vaccinated PLWHs. These findings provide important insights into the effects of COVID-19 vaccination in PLWHs.

Mosaic vaccine design targeting mutational spike protein of SAR-SCoV-2: An immunoinformatics approach

INTRODUCTION

Presently, the development of effective vaccines against SARS-CoV-2 is absolutely necessary, especially regarding the emergence of new variants that cause increasing morbidity and fatalities.

METHODS

In the present study we designed a mosaic vaccine targeting the mutational spike protein of COVID-19 using a bioinformatics approach. Various immunoinformatics tools were utilized to provide the highest potential for a mosaic vaccine that could activate immune responses against COVID-19.

RESULTS

The evaluation of the constructed vaccine revealed that it is antigenic and immunogenic as well as nonallergenic. The physicochemical properties also show promising characteristics, including being highly stable and hydrophilic. As expected, the vaccine shows strong interactions with several important receptors including angiotensin-converting enzyme 2 (ACE2), Toll-like receptor 3 (TLR3) and TLR8 by the lowest energy level, docking score and binding free energy. The vaccine binds to receptors via certain amino acids using various types of binding including salt bridges, hydrogen bonds, and other means. As shown in computationally derived models, the interactions promote activation of the immune response by eliciting the release of various cytokines, antibodies, memory B and T cells, as well as increasing of natural killer cell and dendrite cell counts.

CONCLUSION

Therefore, the novel designed mosaic vaccine could be considered as a potential vaccine candidate for immediate production to stem the continuing and tragic effects of the COVID-19 pandemic. However, several advanced experimental studies should be conducted to ensure and verify the effectivity and safety against SARS‑CoV‑2 in vivo.

Alternating Arenavirus Vector Immunization Generates Robust Polyfunctional Genotype Cross-Reactive Hepatitis B Virus-Specific CD8 T-Cell Responses and High Anti-Hepatitis B Surface Antigen Titers

Hepatitis B Virus (HBV) is a major driver of infectious disease mortality. Curative therapies are needed and ideally should induce CD8 T cell-mediated clearance of infected hepatocytes plus anti-hepatitis B surface antigen (HBsAg) antibodies (anti-HBs) to neutralize residual virus. We developed a novel therapeutic vaccine using non-replicating arenavirus vectors. Antigens were screened for genotype conservation and magnitude and genotype reactivity of T cell response, then cloned into Pichinde virus (PICV) vectors (recombinant PICV, GS-2829) and lymphocytic choriomeningitis virus (LCMV) vectors (replication-incompetent, GS-6779). Alternating immunizations with GS-2829 and GS-6779 induced high-magnitude HBV T cell responses, and high anti-HBs titers. Dose schedule optimization in macaques achieved strong polyfunctional CD8 T cell responses against core, HBsAg, and polymerase and high titer anti-HBs. In AAV-HBV mice, GS-2829 and GS-6779 were efficacious in animals with low pre-treatment serum HBsAg. Based on these results, GS-2829 and GS-6779 could become a central component of cure regimens.

Exploring HIV Vaccine Progress in the Pre-Clinical and Clinical Setting: From History to Future Prospects

The human immunodeficiency virus (HIV) continues to pose a significant global health challenge, with millions of people affected and new cases emerging each year. While various treatment and prevention methods exist, including antiretroviral therapy and non-vaccine approaches, developing an effective vaccine remains the most crucial and cost-effective solution to combating the HIV epidemic. Despite significant advancements in HIV research, the HIV vaccine field has faced numerous challenges, and only one clinical trial has demonstrated a modest level of efficacy. This review delves into the history of HIV vaccines and the current efforts in HIV prevention, emphasizing pre-clinical vaccine development using the non-human primate model (NHP) of HIV infection. NHP models offer valuable insights into potential preventive strategies for combating HIV, and they play a vital role in informing and guiding the development of novel vaccine candidates before they can proceed to human clinical trials.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Prospects of Cytomegalovirus-Specific T-Cell Receptors in Clinical Diagnosis and Therapy

Human cytomegalovirus (HCMV) is responsible for widespread infections worldwide. In immunocompetent individuals it is typically latent, while infection or reactivation in immunocompromised individuals can result in severe clinical symptoms or even death. Although there has been significant progress in the treatment and diagnosis of HCMV infection in recent years, numerous shortcomings and developmental limitations persist. There is an urgent need to develop innovative, safe, and effective treatments, as well as to explore early and timely diagnostic strategies for HCMV infection. Cell-mediated immune responses are the primary factor controlling HCMV infection and replication, but the protective role of humoral immune responses remains controversial. T-cells, key effector cells of the cellular immune system, are critical for clearing and preventing HCMV infection. The T-cell receptor (TCR) lies at the heart of T-cell immune responses, and its diversity enables the immune system to differentiate between self and non-self. Given the significant influence of cellular immunity on human health and the indispensable role of the TCR in T-cell immune responses, we posit that the impact of TCR on the development of novel diagnostic and prognostic methods, as well as on patient monitoring and management of clinical HCMV infection, will be far-reaching and profound. High-throughput and single-cell sequencing technologies have facilitated unprecedented quantitative detection of TCR diversity. With these current sequencing technologies, researchers have already obtained a vast number of TCR sequences. It is plausible that in the near future studies on TCR repertoires will be instrumental in assessing vaccine efficacy, immunotherapeutic strategies, and the early diagnosis of HCMV infection.

Cohort-Specific Peptide Reagents Broaden Depth and Breadth Estimates of the CD8 T Cell Response to HIV-1 Gag Potential T Cell Epitopes

An effective HIV vaccine will need to stimulate immune responses against the sequence diversity presented in circulating virus strains. In this study, we evaluate breadth and depth estimates of potential T-cell epitopes (PTEs) in transmitted founder virus sequence-derived cohort-specific peptide reagents against reagents representative of consensus and global sequences. CD8 T-cells from twenty-six HIV-1+ PBMC donor samples, obtained at 1-year post estimated date of infection, were evaluated. ELISpot assays compared responses to 15mer consensus (n = 121), multivalent-global (n = 320), and 10mer multivalent cohort-specific (n = 300) PTE peptides, all mapping to the Gag antigen. Responses to 38 consensus, 71 global, and 62 cohort-specific PTEs were confirmed, with sixty percent of common global and cohort-specific PTEs corresponding to consensus sequences. Both global and cohort-specific peptides exhibited broader epitope coverage compared to commonly used consensus reagents, with mean breadth estimates of 3.2 (global), 3.4 (cohort) and 2.2 (consensus) epitopes. Global or cohort peptides each identified unique epitope responses that would not be detected if these peptide pools were used alone. A peptide set designed around specific virologic and immunogenetic characteristics of a target cohort can expand the detection of CD8 T-cell responses to epitopes in circulating viruses, providing a novel way to better define the host response to HIV-1 with implications for vaccine development.

Trivalent mosaic or consensus HIV immunogens prime humoral and broader cellular immune responses in adults

BACKGROUNDMosaic and consensus HIV-1 immunogens provide two distinct approaches to elicit greater breadth of coverage against globally circulating HIV-1 and have shown improved immunologic breadth in nonhuman primate models.METHODSThis double-blind randomized trial enrolled 105 healthy HIV-uninfected adults who received 3 doses of either a trivalent global mosaic, a group M consensus (CON-S), or a natural clade B (Nat-B) gp160 env DNA vaccine followed by 2 doses of a heterologous modified vaccinia Ankara-vectored HIV-1 vaccine or placebo. We performed prespecified blinded immunogenicity analyses at day 70 and day 238 after the first immunization. T cell responses to vaccine antigens and 5 heterologous Env variants were fully mapped.RESULTSEnv-specific CD4+ T cell responses were induced in 71% of the mosaic vaccine recipients versus 48% of the CON-S recipients and 48% of the natural Env recipients. The mean number of T cell epitopes recognized was 2.5 (95% CI, 1.2-4.2) for mosaic recipients, 1.6 (95% CI, 0.82-2.6) for CON-S recipients, and 1.1 (95% CI, 0.62-1.71) for Nat-B recipients. Mean breadth was significantly greater in the mosaic group than in the Nat-B group using overall (P = 0.014), prime-matched (P = 0.002), heterologous (P = 0.046), and boost-matched (P = 0.009) measures. Overall T cell breadth was largely due to Env-specific CD4+ T cell responses.CONCLUSIONPriming with a mosaic antigen significantly increased the number of epitopes recognized by Env-specific T cells and enabled more, albeit still limited, cross-recognition of heterologous variants. Mosaic and consensus immunogens are promising approaches to address global diversity of HIV-1.TRIAL REGISTRATIONClinicalTrials.gov NCT02296541.FUNDINGUS NIH grants UM1 AI068614, UM1 AI068635, UM1 AI068618, UM1 AI069412, UL1 RR025758, P30 AI064518, UM1 AI100645, and UM1 AI144371, and Bill & Melinda Gates Foundation grant OPP52282.

Breast cancer vaccines: New insights into immunomodulatory and nano-therapeutic approaches

Breast cancer (BC) is known to be a highly heterogeneous disease that is clinically subdivided into four primary molecular subtypes, each having distinct morphology and clinical implications. These subtypes are principally defined by hormone receptors and other proteins involved (or not involved) in BC development. BC therapeutic vaccines [including peptide-based vaccines, protein-based vaccines, nucleic acid-based vaccines (DNA/RNA vaccines), bacterial/viral-based vaccines, and different immune cell-based vaccines] have emerged as an appealing class of cancer immunotherapeutics when used alone or combined with other immunotherapies. Employing the immune system to eliminate BC cells is a novel therapeutic modality. The benefit of active immunotherapies is that they develop protection against neoplastic tissue and readjust the immune system to an anti-tumor monitoring state. Such immunovaccines have not yet shown effectiveness for BC treatment in clinical trials. In recent years, nanomedicines have opened new windows to increase the effectiveness of vaccinations to treat BC. In this context, some nanoplatforms have been designed to efficiently deliver molecular, cellular, or subcellular vaccines to BC cells, increasing the efficacy and persistence of anti-tumor immunity while minimizing undesirable side effects. Immunostimulatory nano-adjuvants, liposomal-based vaccines, polymeric vaccines, virus-like particles, lipid/calcium/phosphate nanoparticles, chitosan-derived nanostructures, porous silicon microparticles, and selenium nanoparticles are among the newly designed nanostructures that have been used to facilitate antigen internalization and presentation by antigen-presenting cells, increase antigen stability, enhance vaccine antigenicity and remedial effectivity, promote antigen escape from the endosome, improve cytotoxic T lymphocyte responses, and produce humoral immune responses in BC cells. Here, we summarized the existing subtypes of BC and shed light on immunomodulatory and nano-therapeutic strategies for BC vaccination. Finally, we reviewed ongoing clinical trials on BC vaccination and highlighted near-term opportunities for moving forward.

Infectious RNA: Human Immunodeficiency Virus (HIV) Biology, Therapeutic Intervention, and the Quest for a Vaccine

Different mechanisms mediate the toxicity of RNA. Genomic retroviral mRNA hijacks infected host cell factors to enable virus replication. The viral genomic RNA of the human immunodeficiency virus (HIV) encompasses nine genes encoding in less than 10 kb all proteins needed for replication in susceptible host cells. To do so, the genomic RNA undergoes complex alternative splicing to facilitate the synthesis of the structural, accessory, and regulatory proteins. However, HIV strongly relies on the host cell machinery recruiting cellular factors to complete its replication cycle. Antiretroviral therapy (ART) targets different steps in the cycle, preventing disease progression to the acquired immunodeficiency syndrome (AIDS). The comprehension of the host immune system interaction with the virus has fostered the development of a variety of vaccine platforms. Despite encouraging provisional results in vaccine trials, no effective vaccine has been developed, yet. However, novel promising vaccine platforms are currently under investigation.

AZD1222/ChAdOx1 nCoV-19 vaccination induces a polyfunctional spike protein-specific TH1 response with a diverse TCR repertoire

AZD1222 (ChAdOx1 nCoV-19), a replication-deficient simian adenovirus–vectored vaccine, has demonstrated safety, efficacy, and immunogenicity against coronavirus disease 2019 in clinical trials and real-world studies. We characterized CD4+ and CD8+ T cell responses induced by AZD1222 vaccination in peripheral blood mononuclear cells from 296 unique vaccine recipients aged 18 to 85 years who enrolled in the phase 2/3 COV002 trial. Total spike protein–specific CD4+ T cell helper type 1 (TH1) and CD8+ T cell responses were increased in AZD1222-vaccinated adults of all ages after two doses of AZD1222. CD4+ TH2 responses after AZD1222 vaccination were not detected. Furthermore, AZD1222-specific TH1 and CD8+ T cells both displayed a high degree of polyfunctionality in all adult age groups. T cell receptor β (TCRβ) sequences from vaccinated participants mapped against TCR sequences known to react to SARS-CoV-2 revealed substantial breadth and depth across the SARS-CoV-2 spike protein for both AZD1222-induced CD4+ and CD8+ T cell responses. Overall, AZD1222 vaccination induced a polyfunctional TH1-dominated T cell response, with broad CD4+ and CD8+ T cell coverage across the SARS-CoV-2 spike protein.

Current approaches to HIV vaccine development: a narrative review

INTRODUCTION

The development of an effective vaccine to protect against HIV is a longstanding global health need complicated by challenges inherent to HIV biology and to the execution of vaccine efficacy testing in the context of evolving biomedical prevention interventions. This review describes lessons learnt from previous efficacy trials, highlights unanswered questions, and surveys new approaches in vaccine development addressing these gaps.

METHODS

We conducted a targeted peer-reviewed literature search of articles and conference abstracts from 1989 through 2021 for HIV vaccine studies and clinical trials. The US National Library of Medicine's Clinical Trials database was accessed to further identify clinical trials involving HIV vaccines. The content of the review was also informed by the authors' own experience and engagement with collaborators in HIV vaccine research.

DISCUSSION

The HIV vaccine field has successfully developed multiple vaccine platforms through advanced clinical studies; however, the modest efficacy signal of the RV144 Thai trial remains the only demonstration of HIV vaccine protection in humans. Current vaccine strategies include prime-boost strategies to improve elicitation of immune correlates derived from RV144, combination mosaic antigens, novel viral vectors, antigens designed to elicit broadly neutralizing antibody, new nucleic acid platforms and potent adjuvants to enhance immunogenicity across multiple classes of emerging vaccine candidates.

CONCLUSIONS

HIV vaccine developers have applied lessons learnt from previous successes and failures to innovative vaccine design approaches. These strategies have yielded novel mosaic antigen constructs now in efficacy testing, produced a diverse pipeline of early-stage immunogens and novel adjuvants, and advanced the field towards a globally effective HIV vaccine.

Where to Next? Research Directions after the First Hepatitis C Vaccine Efficacy Trial

Thirty years after its discovery, the hepatitis C virus (HCV) remains a leading cause of liver disease worldwide. Given that many countries continue to experience high rates of transmission despite the availability of potent antiviral therapies, an effective vaccine is seen as critical for the elimination of HCV. The recent failure of the first vaccine efficacy trial for the prevention of chronic HCV confirmed suspicions that this virus will be a challenging vaccine target. Here, we examine the published data from this first efficacy trial along with the earlier clinical and pre-clinical studies of the vaccine candidate and then discuss three key research directions expected to be important in ongoing and future HCV vaccine development. These include the following: 1. design of novel immunogens that generate immune responses to genetically diverse HCV genotypes and subtypes, 2. strategies to elicit broadly neutralizing antibodies against envelope glycoproteins in addition to cytotoxic and helper T cell responses, and 3. consideration of the unique immunological status of individuals most at risk for HCV infection, including those who inject drugs, in vaccine platform development and early immunogenicity trials.

The current and future role of nanovaccines in HIV-1 vaccine development

Introduction: An efficacious vaccine for HIV-1 has been sought for over 30 years to eliminate the virus from the human population. Many challenges have occurred in the attempt to produce a successful immunogen, mainly caused by the basic biology of the virus. Immunogens have been developed focusing on inducing one or more of the following types of immune responses; neutralizing antibodies, non-neutralizing antibodies, and T-cell mediated responses. One way to better present and develop an immunogen for HIV-1 is through the use of nanotechnology and nanoparticles.Areas covered: This article gives a basic overview of the HIV-1 vaccine field, as well as nanotechnology, specifically nanovaccines. It then covers the application of nanovaccines made from biological macromolecules to HIV-1 vaccine development for neutralizing antibodies, non-neutralizing antibodies, and T-cell-mediated responses.Expert opinion: Nanovaccines are an area that is ripe for further exploration in HIV-1 vaccine field. Not only are nanovaccines capable of carrying and presenting antigens in native-like conformations, but they have also repeatedly been shown to increase immunogenicity over recombinant antigens alone. Only through further research can the true role of nanovaccines in the development of an efficacious HIV-1 vaccine be established.

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.

Effect of epitope variant co-delivery on the depth of CD8 T cell responses induced by HIV-1 conserved mosaic vaccines

To stop the HIV-1 pandemic, vaccines must induce responses capable of controlling vast HIV-1 variants circulating in the population as well as those evolved in each individual following transmission. Numerous strategies have been proposed, of which the most promising include focusing responses on the vulnerable sites of HIV-1 displaying the least entropy among global isolates and using algorithms that maximize vaccine match to circulating HIV-1 variants by vaccine cocktails of optimized complementing sequences. In this study, we investigated CD8 T cell responses induced by a bi-valent mosaic of highly conserved HIVconsvX regions delivered by a combination of simian adenovirus ChAdOx1 and poxvirus MVA. We compared partially and fully mono- and bi-valent prime-boost regimens and their ability to elicit T cells recognizing natural epitope variants using an interferon-γ enzyme-linked immunospot (ELISPOT) assay. We used 11 well-defined CD8 T cell epitopes in two mouse haplotypes and, for each epitope, assessed recognition of the two vaccine forms together with the other most frequent epitope variants in the HIV-1 database. We conclude that for the magnitude and depth of epitope recognition, CD8 T cell responses benefitted in most comparisons from the combined bi-valent mosaic and envisage the main advantage of the bi-valent vaccine during its deployment to diverse populations.

Comprehensive epitope mapping using polyclonally expanded human CD8 T cells and a two-step ELISpot assay for testing large peptide libraries

The genetic diversity of circulating HIV-1 strains poses a major barrier to the design, development and evaluation of HIV-1 vaccines. The assessment of both vaccine- and natural infection-elicited T cell responses is commonly done with multivalent peptides that are designed to maximally capture the diversity of potential T cell epitopes (PTEs) observed in natural circulating sequences. However, depending on the sequence diversity of viral subtypes and number of the HIV immunogens under investigation, PTE estimates, including HLA-guided computational methods, can easily generate enormous peptide libraries. Evaluation of T cell epitope specificity using such extensive peptide libraries is usually limited by sample availability, even for high-throughput and robust epitope mapping techniques like ELISpot assays. Here we describe a novel, two-step protocol for in-vitro polyclonal expansion of CD8 T cells from a single vial of frozen PBMC, which facilitated the screening 441 HIV-1 Gag peptides for immune responses among 32 HIV-1 positive subjects and 40 HIV-1 negative subjects for peptide qualification. Using a pooled-peptide mapping strategy, epitopes were mapped in two sequential ELISpot assays; the first ELISpot screened 33 large peptide pools using CD8 T cells expanded for 7 days, while the second step tested pool-matrix peptides to identify individual peptides using CD8 T cells expanded for 10 days. This comprehensive epitope screening established the breadth and magnitude of HIV-1 Gag-specific CD8 T cells and further revealed the extent of immune responses to variable/polymorphic epitopes.

The diversity of HIV-1 fights against vaccine efficacy: how self-assembling protein nanoparticle technology may fight back

An efficacious HIV-1 vaccine has remained an elusive target for almost 40 years. The sheer diversity of the virus is one of the major roadblocks for vaccine development. HIV-1 frequently mutates and various strains predominate in different geographic regions, making the development of a globally applicable vaccine extremely difficult. Multiple approaches have been taken to overcome the issue of viral diversity, including sequence optimization, development of consensus and mosaic sequences and the use of different prime-boost approaches. To develop an efficacious vaccine, these approaches may need to be combined. One way to potentially synergize these approaches is to use a rationally designed protein nanoparticle that allows for the native-like presentation of antigens, such as the self-assembling protein nanoparticle.

Recombinant MVA-prime elicits neutralizing antibody responses by inducing antigen-specific B cells in the germinal center

The RV144 HIV-1 vaccine trial has been the only clinical trial to date that has shown any degree of efficacy and associated with the presence of vaccine-elicited HIV-1 envelope-specific binding antibody and CD4+ T-cell responses. This trial also showed that a vector-prime protein boost combined vaccine strategy was better than when used alone. Here we have studied three different priming vectors-plasmid DNA, recombinant MVA, and recombinant VSV, all encoding clade C transmitted/founder Env 1086 C gp140, for priming three groups of six non-human primates each, followed by a protein boost with adjuvanted 1086 C gp120 protein. Our data showed that MVA-priming favors the development of higher antibody binding titers and neutralizing activity compared with other vectors. Analyses of the draining lymph nodes revealed that MVA-prime induced increased germinal center reactivity characterized by higher frequencies of germinal center (PNAhi) B cells, higher frequencies of antigen-specific B-cell responses as well as an increased frequency of the highly differentiated (ICOShiCD150lo) Tfh-cell subset.

Non-synonymous Substitutions in HIV-1 GAG Are Frequent in Epitopes Outside the Functionally Conserved Regions and Associated With Subtype Differences

In 2019, 38 million people lived with HIV-1 infection resulting in 690,000 deaths. Over 50% of this infection and its associated deaths occurred in Sub-Saharan Africa. The West African region is a known hotspot of the HIV-1 epidemic. There is a need to develop an HIV-1 vaccine if the HIV epidemic would be effectively controlled. Few protective cytotoxic T Lymphocytes (CTL) epitopes within the HIV-1 GAG (HIV_gagconsv) have been previously identified to be functionally conserved among the HIV-1 M group. These epitopes are currently the focus of universal HIV-1 T cell-based vaccine studies. However, these epitopes' phenotypic and genetic properties have not been observed in natural settings for HIV-1 strains circulating in the West African region. This information is critical as the usefulness of universal HIV-1 vaccines in the West African region depends on these epitopes' occurrence in strains circulating in the area. This study describes non-synonymous substitutions within and without HIV_gagconsv genes isolated from 10 infected Nigerians at the early stages of HIV-1 infection. Furthermore, we analyzed these substitutions longitudinally in five infected individuals from the early stages of infection till after seroconversion. We identified three non-synonymous substitutions within HIV_gagconsv genes isolated from early HIV infected individuals. Fourteen and nineteen mutations outside the HIV_gagconsv were observed before and after seroconversion, respectively, while we found four mutations within the HIV_gagconsv. These substitutions include previously mapped CTL epitope immune escape mutants. CTL immune pressure likely leaves different footprints on HIV-1 GAG epitopes within and outside the HIV_gagconsv. This information is crucial for universal HIV-1 vaccine designs for use in the West African region.

Safety and immunogenicity of two heterologous HIV vaccine regimens in healthy, HIV-uninfected adults (TRAVERSE): a randomised, parallel-group, placebo-controlled, double-blind, phase 1/2a study

Background

Bioinformatically designed mosaic antigens increase the breadth of HIV vaccine-elicited immunity. This study compared the safety, tolerability, and immunogenicity of a newly developed, tetravalent Ad26 vaccine with the previously tested trivalent formulation.

Methods

This randomised, parallel-group, placebo-controlled, double-blind, phase 1/2a study (TRAVERSE) was done at 11 centres in the USA and one centre in Rwanda. Eligible participants were adults aged 18 to 50 years, who were HIV-uninfected, healthy at screening based on their medical history and a physical examination including laboratory assessment and vital sign measurements, and at low risk of HIV infection in the opinion of study staff, who applied a uniform definition of low-risk guidelines that was aligned across sites. Enrolled participants were randomly assigned at a 2:1 ratio to tetravalent and trivalent groups. Participants in tetravalent and trivalent groups were then further randomly assigned at a 5:1 ratio to adenovirus 26 (Ad26)-vectored vaccine and placebo subgroups. Randomisation was stratified by region (USA and Rwanda) and based on a computer-generated schedule using randomly permuted blocks prepared under the sponsor's supervision. We masked participants and investigators to treatment allocation throughout the study. On day 0, participants received a first injection of tetravalent vaccine (Ad26.Mos4.HIV or placebo) or trivalent vaccine (Ad26.Mos.HIV or placebo), and those injections were repeated 12 weeks later. At week 24, vaccine groups received a third dose of tetravalent or trivalent together with clade C gp140, and this was repeated at week 48, with placebos again administered to the placebo group. All study vaccines and placebo were administered by intramuscular injection in the deltoid muscle. We assessed adverse events in all participants who received at least one study injection (full analysis set) and Env-specific binding antibodies in all participants who received at least the first three vaccinations according to the protocol-specified vaccination schedule, had at least one measured post-dose blood sample collected, and were not diagnosed with HIV during the study (per-protocol set). This study is registered with Clinicaltrials.gov, NCT02788045.

Findings

Of 201 participants who were enrolled and randomly assigned, 198 received the first vaccination: 110 were in the tetravalent group, 55 in the trivalent group, and 33 in the placebo group. Overall, 185 (93%) completed two scheduled vaccinations per protocol, 180 (91%) completed three, and 164 (83%) completed four. Solicited, self-limiting local, systemic reactogenicity and unsolicited adverse events were similar in vaccine groups and higher than in placebo groups. All participants in the per-protocol set developed clade C Env binding antibodies after the second vaccination, with higher total IgG titres after the tetravalent vaccine than after the trivalent vaccine (10 413 EU/mL, 95% CI 7284–14 886 in the tetravalent group compared with 5494 EU/mL, 3759–8029 in the trivalent group). Titres further increased after the third and fourth vaccinations, persisting at least through week 72. Other immune responses were also higher with the tetravalent vaccine, including the magnitude and breadth of binding antibodies against a cross-clade panel of Env antigens, and the magnitude of IFNγ ELISPOT responses (median 521 SFU/10⁶ peripheral blood mononuclear cells [PBMCs] in the tetravalent group and median 282 SFU/10⁶ PBMCs in the trivalent group after the fourth vaccination) and Env-specific CD4+ T-cell response rates after the third and fourth vaccinations. No interference by pre-existing Ad26 immunity was identified.

Interpretation

The tetravalent vaccine regimen was generally safe, well-tolerated, and found to elicit higher immune responses than the trivalent regimen. Regimens that use this tetravalent vaccine component are being advanced into field trials to assess efficacy against HIV-1 infection.

Funding

National Institutes of Health, Henry M Jackson Foundation for Advancement of Military Medicine and the US Department of Defense, Ragon Institute of MGH, MIT, & Harvard, Bill & Melinda Gates Foundation, and Janssen Vaccines & Prevention.

Vaccine Advances against Venezuelan, Eastern, and Western Equine Encephalitis Viruses

Vaccinations are a crucial intervention in combating infectious diseases. The three neurotropic Alphaviruses, Eastern (EEEV), Venezuelan (VEEV), and Western (WEEV) equine encephalitis viruses, are pathogens of interest for animal health, public health, and biological defense. In both equines and humans, these viruses can cause febrile illness that may progress to encephalitis. Currently, there are no licensed treatments or vaccines available for these viruses in humans. Experimental vaccines have shown variable efficacy and may cause severe adverse effects. Here, we outline recent strategies used to generate vaccines against EEEV, VEEV, and WEEV with an emphasis on virus-vectored and plasmid DNA delivery. Despite candidate vaccines protecting against one of the three viruses, few studies have demonstrated an effective trivalent vaccine. We evaluated the potential of published vaccines to generate cross-reactive protective responses by comparing DNA vaccine sequences to a set of EEEV, VEEV, and WEEV genomes and determining the vaccine coverages of potential epitopes. Finally, we discuss future directions in the development of vaccines to combat EEEV, VEEV, and WEEV.

Boosting the Immune System for HIV Cure: A γδ T Cell Perspective

The major barrier to HIV cure is a population of long-lived cells that harbor latent but replication-competent virus, are not eliminated by antiretroviral therapy (ART), and remain indistinguishable from uninfected cells. However, ART does not cure HIV infection, side effects to treatment still occur, and the steady global rate of new infections makes finding a sustained ART-free HIV remission or cure for HIV-seropositive individuals urgently needed. Approaches aimed to cure HIV are mostly based on the "shock and kill" method that entails the use of a drug compound to reactivate latent virus paired together with strategies to boost or supplement the existing immune system to clear reactivated latently infected cells. Traditionally, these strategies have utilized CD8+ cytotoxic lymphocytes (CTL) but have been met with a number of challenges. Enhancing innate immune cell populations, such as γδ T cells, may provide an alternative route to HIV cure. γδ T cells possess anti-viral and cytotoxic capabilities that have been shown to directly inhibit HIV infection and specifically eliminate reactivated, latently infected cells in vitro. Most notably, their access to immune privileged anatomical sites and MHC-independent antigen recognition may circumvent many of the challenges facing CTL-based strategies. In this review, we discuss the role of γδ T cells in normal immunity and HIV infection as well as their current use in strategies to treat cancer. We present this information as means to speculate about the utilization of γδ T cells for HIV cure strategies and highlight some of the fundamental gaps in knowledge that require investigation.

Vaccines and Broadly Neutralizing Antibodies for HIV-1 Prevention

Development of improved approaches for HIV-1 prevention will likely be required for a durable end to the global AIDS pandemic. Recent advances in preclinical studies and early phase clinical trials offer renewed promise for immunologic strategies for blocking acquisition of HIV-1 infection. Clinical trials are currently underway to evaluate the efficacy of two vaccine candidates and a broadly neutralizing antibody (bNAb) to prevent HIV-1 infection in humans. However, the vast diversity of HIV-1 is a major challenge for both active and passive immunization. Here we review current immunologic strategies for HIV-1 prevention, with a focus on current and next-generation vaccines and bNAbs.

HIV-1 phylogenetics and vaccines

PURPOSE OF REVIEW

Although HIV-1 diversity is a critical barrier to HIV-1 vaccine development, implementing vaccine strategies that directly address HIV-1 genetic specificities has been challenging. Here, we discuss the intersection between HIV-1 phylogenetics and vaccine development.

RECENT FINDINGS

We describe the vaccine regimens that are currently tested in two vaccine efficacy trials and recent research highlighting HIV-1 genetic features that were associated with the development of broadly neutralizing antibodies.

SUMMARY

Compared with how widely HIV-1 diversity is recognized as a critical issue for vaccine research, relatively few genetically informed vaccine solutions have been compared, in part because the lack of correlates of protection against HIV-1 limits the ability to develop and test multiple vaccine candidates in a fully rational manner. Yet, recent findings have provided a better understanding of the viral features associated with the development of broad and potent neutralizing antibodies, offering new avenues for engineering vaccine candidates. Future research should also plan to address potential consequences associated with the rollout of an efficacious vaccine, including the possibility of vaccine resistance spreading in the population.

Mathematical model of broadly reactive plasma cell production

Strain-specific plasma cells are capable of producing neutralizing antibodies that are essential for clearance of challenging pathogens. These neutralizing antibodies also function as a main defense against disease establishment in a host. However, when a rapidly mutating pathogen infects a host, successful control of the invasion requires shifting the production of plasma cells from strain-specific to broadly reactive. In this study, we develop a mathematical model of germinal center dynamics and use it to predict the events that lead to improved breadth of the plasma cell response. We examine scenarios that lead to germinal centers that are composed of B-cells that come from a single strain-specific clone, a single broadly reactive clone or both clones. We find that the initial B-cell clonal composition, T-follicular helper cell signaling, increased rounds of productive somatic hypermutation, and B-cell selection strength are among the mechanisms differentiating between strain-specific and broadly reactive plasma cell production during infections. Understanding the contribution of these factors to emergence of breadth may assist in boosting broadly reactive plasma cells production.

T cell-based strategies for HIV-1 vaccines

Despite 30 years of effort, we do not have an effective HIV-1 vaccine. Over the past decade, the HIV-1 vaccine field has shifted emphasis toward antibody-based vaccine strategies, following a lack of efficacy in CD8+ T-cell-based vaccine trials. Several lines of evidence, however, suggest that improved CD8+ T-cell-directed strategies could benefit an HIV-1 vaccine. First, T-cell responses often correlate with good outcomes in non-human primate (NHP) challenge models. Second, subgroup studies of two no-efficacy human clinical vaccine trials found associations between CD8+ T-cell responses and protective effects. Finally, improved strategies can increase the breadth and potency of CD8+ T-cell responses, direct them toward preferred epitopes (that are highly conserved and/or associated with viral control), or both. Optimized CD8+ T-cell vaccine strategies are promising in both prophylactic and therapeutic settings. This commentary briefly outlines some encouraging findings from T-cell vaccine studies, and then directly compares key features of some T-cell vaccine candidates currently in the clinical pipeline.

Innovations in HIV-1 Vaccine Design

PURPOSE

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

METHODS

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

FINDINGS

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

IMPLICATIONS

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

Broad Protection of Pigs against Heterologous PRRSV Strains by a GP5-Mosaic DNA Vaccine Prime/GP5-Mosaic rVaccinia (VACV) Vaccine Boost

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) viruses are a major cause of disease and economic loss in pigs worldwide. High genetic diversity among PRRSV strains is problematic for successful disease control by vaccination. Mosaic DNA and vaccinia (VACV) vaccines were developed in order to improve protection against heterologous PRRSV strains.

METHODS

Piglets were primed and boosted with GP5-Mosaic DNA vaccine and recombinant GP5-Mosaic VACV (rGP5-Mosaic VACV), respectively. Pigs vaccinated with rGP5-WT (VR2332) DNA and rGP5-WT VACV, or empty vector DNA and empty VACV respectively, served as controls. Virus challenge was given to separate groups of vaccinated pigs with VR2332 or MN184C. Necropsies were performed 14 days after challenge.

RESULTS

Vaccination with the GP5-Mosaic-based vaccines resulted in cellular reactivity and higher levels of neutralizing antibodies to both VR2332 and MN184C PRRSV strains. In contrast, vaccination of animals with the GP5-WT vaccines induced responses only to VR2332. Furthermore, vaccination with the GP5-Mosaic based vaccines resulted in protection against challenge with two heterologous virus strains, as demonstrated by the significantly lower viral loads in serum, tissues, porcine alveolar macrophages (PAMs), and bronchoalveolar lavage (BAL) fluids, and less severe lung lesions after challenge with either MN184C or VR2332, which have only 85% identity. In contrast, significant protection by the GP5-WT based vaccines was only achieved against the VR2332 strain. Conclusions: GP5-Mosaic vaccines, using a DNA-prime/VACV boost regimen, conferred protection in pigs against heterologous viruses.

CD8+ T cells in HIV control, cure and prevention

HIV infection can be effectively treated by lifelong administration of combination antiretroviral therapy, but an effective vaccine will likely be required to end the HIV epidemic. Although the majority of current vaccine strategies focus on the induction of neutralizing antibodies, there is substantial evidence that cellular immunity mediated by CD8⁺ T cells can sustain long-term disease-free and transmission-free HIV control and may be harnessed to induce both therapeutic and preventive antiviral effects. In this Review, we discuss the increasing evidence derived from individuals who spontaneously control infection without antiretroviral therapy as well as preclinical immunization studies that provide a clear rationale for renewed efforts to develop a CD8⁺ T cell-based HIV vaccine in conjunction with B cell vaccine efforts. Further, we outline the remaining challenges in translating these findings into viable HIV prevention, treatment and cure strategies.

Recently, antibody-mediated control of HIV infection has received considerable attention. Here, the authors discuss the importance of CD8⁺ T cells in HIV infection and suggest that efforts to develop vaccines that target these cells in conjunction with B cells should be renewed.

Strategies for inducing effective neutralizing antibody responses against HIV-1

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

HLA-I Associated Adaptation Dampens CD8 T-Cell Responses in HIV Ad5-Vectored Vaccine Recipients

HLA-I-associated human immunodeficiency virus (HIV) adaptation is known to negatively affect disease progression and CD8 T-cell responses. We aimed to assess how HLA-I-associated adaptation affects HIV vaccine-induced CD8 T-cell responses in 2 past vaccine efficacy trials. We found that vaccine-encoded adapted epitopes were less immunogenic than vaccine-encoded nonadapted epitopes, and adapted epitope-specific responses were less polyfunctional than nonadapted epitope-specific responses. Along those lines, vaccine recipients with higher HLA-I adaptation to the Gag vaccine insert mounted less polyfunctional CD8 T-cell responses at the protein level. Breadth of response, which correlated with viral control in recipients who became infected, is also dampened by HLA-I adaptation. These findings suggest that HLA-I-associated adaptation is an important consideration for strategies aiming to induce robust CD8 T-cell responses.

Use of a Novel Enhanced DNA Vaccine Vector for Preclinical Virus Vaccine Investigation

DNA vaccines are stable, safe, and cost effective to produce and relatively quick and easy to manufacture. However, to date, DNA vaccines have shown relatively poor immunogenicity in humans despite promising preclinical results. Consequently, a number of different approaches have been investigated to improve the immunogenicity of DNA vaccines. These include the use of improved delivery methods, adjuvants, stronger promoters and enhancer elements to increase antigen expression, and codon optimization of the gene of interest. This review describes the creation and use of a DNA vaccine vector containing a porcine circovirus (PCV-1) enhancer element that significantly increases recombinant antigen expression and immunogenicity and allows for dose sparing. A 172 bp region containing the PCV-1 capsid protein promoter (Pcap) and a smaller element (PC; 70 bp) within this were found to be equally effective. DNA vaccines containing the Pcap region expressing various HIV-1 antigens were found to be highly immunogenic in mice, rabbits, and macaques at 4-10-fold lower doses than normally used and to be highly effective in heterologous prime-boost regimens. By lowering the amount of DNA used for immunization, safety concerns over injecting large amounts of DNA into humans can be overcome.

Prime-Boost Immunizations with DNA, Modified Vaccinia Virus Ankara, and Protein-Based Vaccines Elicit Robust HIV-1 Tier 2 Neutralizing Antibodies against the CAP256 Superinfecting Virus

A vaccine regimen that elicits broadly neutralizing antibodies (bNAbs) is a major goal in HIV-1 vaccine research. In this study, we assessed the immunogenicity of the CAP256 superinfecting viral envelope (CAP256 SU) protein delivered by modified vaccinia virus Ankara (MVA) and DNA vaccines in different prime-boost combinations followed by a soluble protein (P) boost. The envelope protein (Env) contained a flexible glycine linker and I559P mutation. Trimer-specific bNAbs PGT145, PG16, and CAP256 VRC26_08 efficiently bound to the membrane-bound CAP256 envelope expressed on the surface of cells transfected or infected with the DNA and MVA vaccines. The vaccines were tested in two different vaccination regimens in rabbits. Both regimens elicited autologous tier 2 neutralizing antibodies (NAbs) and high-titer binding antibodies to the matching CAP256 Env and CAP256 V1V2 loop scaffold. The immunogenicity of DNA and MVA vaccines expressing membrane-bound Env alone was compared to that of Env stabilized in a more native-like conformation on the surface of Gag virus-like particles (VLPs). The inclusion of Gag in the DNA and MVA vaccines resulted in earlier development of tier 2 NAbs for both vaccination regimens. In addition, a higher proportion of the rabbits primed with DNA and MVA vaccines that included Gag developed tier 2 NAbs than did those primed with vaccine expressing Env alone. Previously, these DNA and MVA vaccines expressing subtype C mosaic HIV-1 Gag were shown to elicit strong T cell responses in mice. Here we show that when the CAP256 SU envelope protein is included, these vaccines elicit autologous tier 2 NAbs.IMPORTANCE A vaccine is urgently needed to combat HIV-1, particularly in sub-Saharan Africa, which remains disproportionately affected by the AIDS pandemic and accounts for the majority of new infections and AIDS-related deaths. In this study, two different vaccination regimens were compared. Rabbits that received two DNA primes followed by two modified vaccinia virus Ankara (MVA) and two protein inoculations developed better immune responses than those that received two MVA and three protein inoculations. In addition, DNA and MVA vaccines that expressed mosaic Gag VLPs presenting a stabilized Env antigen elicited better responses than Env alone, which supports the inclusion of Gag VLPs in an HIV-1 vaccine.

HIV Vaccine Efficacy Trials: RV144 and Beyond

Despite progress in antiretroviral therapy, pre-exposure prophylaxis, microbicides, and other preventive strategies, a vaccine to prevent HIV-1 infection remains desperately needed. Development of an effective vaccine is challenged by several immunologic features of HIV-1 evidenced by the failure of five of the six HIV-1 candidate vaccine efficacy trials to date. This chapter reviews these efficacy trials with a focus on the Phase 3 RV144 trial in Thailand, the only HIV-1 vaccine efficacy trial to show a moderate protective effect of 31% with respect to placebo administration. Although modest, this protection has allowed for the study of potential immunologic correlates of protection to improve development of future HIV-1 pox-protein and other vaccine strategies. Trials in Thailand and South Africa have built upon the RV144 framework to provide additional immunologic insights which enable current and future efficacy testing of related vaccine candidates.

A PRRSV GP5-Mosaic vaccine: Protection of pigs from challenge and ex vivo detection of IFNγ responses against several genotype 2 strains

Porcine reproductive and respiratory syndrome virus (PRRSV), is a highly mutable RNA virus that affects swine worldwide and its control is very challenging due to its formidable heterogeneity in the field. In the present study, DNA vaccines constructed with PRRSV GP5-Mosaic sequences were complexed to cationic liposomes and administered to experimental pigs by intradermal and intramuscular injection, followed by three boosters 14, 28 and 42 days later. The GP5-Mosaic vaccine thus formulated was immunogenic and induced protection from challenge in vaccinated pigs comparable to that induced by a wild type (VR2332) GP5 DNA vaccine (GP5-WT). Periodic sampling of blood and testing of vaccine-induced responses followed. Interferon-γ (IFN-γ) mRNA expression by virus-stimulated peripheral blood mononuclear cells (PBMCs) of GP5-Mosaic-vaccinated pigs was significantly higher compared to pigs vaccinated with either GP5-WT or empty vector at 21, 35 and 48 days after vaccination. Cross-reactive cellular responses were also demonstrated in GP5-Mosaic vaccinated pigs after stimulation of PBMCs with divergent strains of PRRSV. Thus, significantly higher levels of IFN-γ mRNA were detected when PBMCs from GP5-Mosaic-vaccinated pigs were stimulated by four Genotype 2 strains (VR2332, NADC9, NADC30 and SDSU73), which have at least 10% difference in GP5 amino acid sequences, while such responses were recorded only upon VR2332 stimulation in GP5-WT-vaccinated pigs. In addition, the levels of virus-specific neutralizing antibodies were higher in GP5-Mosaic or GP5-WT vaccinated pigs than those in vector-control pigs. The experimental pigs vaccinated with either the GP5-Mosaic vaccine or the GP5-WT vaccine were partially protected from challenge with VR2332, as measured by significantly lower viral loads in sera and tissues and lower lung lesion scores than the vector control group. These data demonstrate that the GP5-Mosaic vaccine can induce cross-reactive cellular responses to diverse strains, neutralizing antibodies, and protection in pigs.

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.

A high throughput lentivirus sieving assay identifies neutralization resistant Envelope sequences and predicts in vivo sieving

An effective prophylactic vaccine against human immunodeficiency virus (HIV) will likely require a potent antibody response that can neutralize the virus at the mucosal portal of entry. The elicitation of potent broadly-neutralizing anti-sera will be an iterative process, optimizing candidates that only block a fraction of potential viral strains. This effect, termed "sieving", is evidence of a partially efficacious vaccine. Understanding the mechanisms of resistance of the breakthrough viruses is important for improving vaccines. We developed a high-throughput assay that can be used on vaccine-elicited antisera or monoclonal antibodies. Using the SIVsmE660 swarm stock and sera from a large NHP vaccine/challenge study, our in vitro sieving assay identified the same viral subspecies as in the animal study-those with a canonical C1 amino acid variants conferring global neutralization resistance to antibodies. Using a genetically divergent swarm stock, we identified five other amino acid variants that confer global resistance; the C1 mutations in this stock were not selected, also in agreement with in vivo challenge studies. Thus, the in vitro sieving assay can be used with genetically diverse challenge stocks to predict the coverage of a vaccine-elicited sera and possibly inform candidate vaccine development efforts.

Gag and env conserved element CE DNA vaccines elicit broad cytotoxic T cell responses targeting subdominant epitopes of HIV and SIV Able to recognize virus-infected cells in macaques

HIV sequence diversity and the propensity of eliciting immunodominant responses targeting inessential variable regions are hurdles in the development of an effective AIDS vaccine. We developed a DNA vaccine comprising conserved elements (CE) of SIV p27^Gag and HIV-1 Env and found that priming vaccination with CE DNA is critical to efficiently overcome the dominance imposed by Gag and Env variable regions. Here, we show that DNA vaccinated macaques receiving the CE prime/CE+full-length DNA co-delivery booster vaccine regimens developed broad, potent and durable cytotoxic T cell responses targeting conserved protein segments of SIV Gag and HIV Env. Gag CE-specific T cells showed robust anamnestic responses upon infection with SIV_mac239 which led to the identification of CE-specific cytotoxic lymphocytes able to recognize epitopes covering distinct CE on the surface of SIV infected cells in vivo. Though not controlling infection overall, we found an inverse correlation between Gag CE-specific CD8⁺ T cell responses and peak viremia. The T cell responses induced by the HIV Env CE immunogen were recalled in some animals upon SIV infection, leading to the identification of two cross-reactive epitopes between HIV and SIV Env based in sequence homology. These data demonstrate that a vaccine combining Gag and Env CE DNA subverted the normal immunodominance patterns, eliciting immune responses that included subdominant, highly conserved epitopes. These vaccine regimens augment cytotoxic T cell responses to highly conserved epitopes in the viral proteome and maximize response breadth. The vaccine-induced CE-specific T cells were expanded upon SIV infection, indicating that the predicted CE epitopes incorporated in the DNA vaccine are processed and exposed by infected cells in their natural context within the viral proteome.

DNA prime/MVTT boost regimen with HIV-1 mosaic Gag enhances the potency of antigen-specific immune responses

HIV-1 diversity and latent reservoir are the major challenges for the development of an effective AIDS vaccine. It is well indicated that Gag-specific CD8⁺ T cells serve as the dominant host immune surveillance for HIV-1 control, but it still remains a challenge for vaccine design to induce broader and stronger cytotoxic T cell immunity against the virus. Genetic variation of the HIV-1 gag gene across different clades is one of the reasons for the reduction of antigenic epitope coverage. Here, we report an immunization strategy with heterologous vaccines expressing a mosaic Gag antigen aimed to increase antigenic breadth against a wider spectrum of HIV-1 strains. Priming using a DNA vaccine via in vivo electroporation, followed by boosting with a live replication-competent modified vaccinia TianTan (MVTT) vectored vaccine, elicited greater and broader protective Gag-specific immune responses in mice. Compared to DNA or MVTT homologous immunization, the heterologous DNA/MVTT vaccination resulted in higher frequencies of broadly reactive, Gag-specific, polyfunctional, long-lived cytotoxic CD8⁺ T cells, as well as increased anti-Gag antibody titer. Importantly, the DNA/MVTT heterologous vaccination induced protection against EcoHIV and mesothelioma AB1-Gag challenges. In summary, the stronger protective Gag-specific immunity induced by the heterologous regimen using two safe vectors shows promise for further development to enhance anti-HIV-1 immunity. Our study has important implications for immunogen design and the development of an effective HIV-1 heterologous vaccination strategy.

DNA Vaccine-Induced Long-Lasting Cytotoxic T Cells Targeting Conserved Elements of Human Immunodeficiency Virus Gag Are Boosted Upon DNA or Recombinant Modified Vaccinia Ankara Vaccination

DNA-based vaccines able to induce efficient cytotoxic T-cell responses targeting conserved elements (CE) of human immunodeficiency virus type 1 (HIV-1) Gag have been developed. These CE were selected by stringent conservation, the ability to induce T-cell responses with broad human leukocyte antigen coverage, and the association between recognition of CE epitopes and viral control in HIV-infected individuals. Based on homology to HIV, a simian immunodeficiency virus p27^gag CE DNA vaccine has also been developed. This study reports on the durability of the CE-specific T-cell responses induced by HIV and simian immunodeficiency virus CE DNA-based prime/boost vaccine regimens in rhesus macaques, and shows that the initially primed CE-specific T-cell responses were efficiently boosted by a single CE DNA vaccination after the long rest period (up to 2 years). In another cohort of animals, the study shows that a single inoculation with non-replicating recombinant Modified Vaccinia Ankara (rMVA62B) also potently boosted CE-specific responses after around 1.5 years of rest. Both CE DNA and rMVA62B booster vaccinations increased the magnitude and cytotoxicity of the CE-specific responses while maintaining the breadth of CE recognition. Env produced by rMVA62B did not negatively interfere with the recall of the Gag CE responses. rMVA62B could be beneficial to further boosting the immune response to Gag in humans. Vaccine regimens that employ CE DNA as a priming immunogen hold promise for application in HIV prevention and therapy.