Deletion of the vaccinia virus N2L gene encoding an inhibitor of IRF3 improves the immunogenicity of modified vaccinia virus Ankara expressing HIV-1 antigens

Rendezvous with Vaccinia Virus in the Post-smallpox Era: R&D Advances

Smallpox was eradicated in less than 200 years after Edward Jenner's practice of cowpox variolation in 1796. The forty-three years of us living free of smallpox, beginning in 1979, never truly separated us from poxviruses. The recent outbreak of monkeypox in May 2022 might well warn us of the necessity of keeping up both the scientific research and public awareness of poxviruses. One of them in particular, the vaccinia virus (VACV), has been extensively studied as a vector given its broad host range, extraordinary thermal stability, and exceptional immunogenicity. Unceasing fundamental biological research on VACV provides us with a better understanding of its genetic elements, involvement in cellular signaling pathways, and modulation of host immune responses. This enables the rational design of safer and more efficacious next-generation vectors. To address the new technological advancement within the past decade in VACV research, this review covers the studies of viral immunomodulatory genes, modifications in commonly used vectors, novel mechanisms for rapid generation and purification of recombinant virus, and several other innovative approaches to studying its biology.

Highly attenuated poxvirus-based vaccines against emerging viral diseases

Although one member of the poxvirus family, variola virus, has caused one of the most devastating human infections worldwide, smallpox, the knowledge gained over the last 30 years on the molecular, virological and immunological mechanisms of these viruses has allowed the use of members of this family as vectors for the generation of recombinant vaccines against numerous pathogens. In this review, we cover different aspects of the history and biology of poxviruses with emphasis on their application as vaccines, from first- to fourth-generation, against smallpox, monkeypox, emerging viral diseases highlighted by the World Health Organization (COVID-19, Crimean-Congo haemorrhagic fever, Ebola and Marburg virus diseases, Lassa fever, Middle East respiratory syndrome and severe acute respiratory syndrome, Nipah and other henipaviral diseases, Rift Valley fever and Zika), as well as against one of the most concerning prevalent virus, the Human Immunodeficiency Virus, the causative agent of AcquiredImmunodeficiency Syndrome. We discuss the implications in human health of the 2022 monkeypox epidemic affecting many countries, and the rapid prophylactic and therapeutic measures adopted to control virus dissemination within the human population. We also describe the preclinical and clinical evaluation of the Modified Vaccinia virus Ankara and New York vaccinia virus poxviral strains expressing heterologous antigens from the viral diseases listed above. Finally, we report different approaches to improve the immunogenicity and efficacy of poxvirus-based vaccine candidates, such as deletion of immunomodulatory genes, insertion of host-range genes and enhanced transcription of foreign genes through modified viral promoters. Some future prospects are also highlighted.

An MVA-based vector expressing cell-free ISG15 increases IFN-I production and improves HIV-1-specific CD8 T cell immune responses

The human immunodeficiency virus (HIV), responsible of the Acquired Immune Deficiency Syndrome (AIDS), continues to be a major global public health issue with any cure or vaccine available. The Interferon-stimulated gene 15 (ISG15) encodes a ubiquitin-like protein that is induced by interferons and plays a critical role in the immune response. ISG15 is a modifier protein that covalently binds to its targets via a reversible bond, a process known as ISGylation, which is the best-characterized activity of this protein to date. However, ISG15 can also interact with intracellular proteins via non-covalent binding or act as a cytokine in the extracellular space after secretion. In previous studies we proved the adjuvant effect of ISG15 when delivered by a DNA-vector in heterologous prime-boost combination with a Modified Vaccinia virus Ankara (MVA)-based recombinant virus expressing HIV-1 antigens Env/Gag-Pol-Nef (MVA-B). Here we extended these results evaluating the adjuvant effect of ISG15 when expressed by an MVA vector. For this, we generated and characterized two novel MVA recombinants expressing different forms of ISG15, the wild-type ISG15GG (able to perform ISGylation) or the mutated ISG15AA (unable to perform ISGylation). In mice immunized with the heterologous DNA prime/MVA boost regimen, the expression of the mutant ISG15AA from MVA-Δ3-ISG15AA vector in combination with MVA-B induced an increase in the magnitude and quality of HIV-1-specific CD8 T cells as well as in the levels of IFN-I released, providing a better immunostimulatory activity than the wild-type ISG15GG. Our results confirm the importance of ISG15 as an immune adjuvant in the vaccine field and highlights its role as a potential relevant component in HIV-1 immunization protocols.

Poxviruses and the immune system: Implications for monkeypox virus

Poxviruses (PXVs) are mostly known for the variola virus, being the cause of smallpox; however, re-emerging PXVs have also shown a great capacity to develop outbreaks of pox-like infections in humans. The situation is alarming; PXV outbreaks have been involving both endemic and non-endemic areas in recent decades. Stopped smallpox vaccination is a reason offered mainly for this changing epidemiology that implies the protective role of immunity in the pathology of PXV infections. The immune system recognizes PXVs and elicits responses, but PXVs can antagonize these responses. Here, we briefly review the immunology of PXV infections, with emphasis on the role of pattern-recognition receptors, macrophages, and natural killer cells in the early response to PXV infections and PXVs’ strategies influencing these responses, as well as taking a glance at other immune cells, which discussion over them mainly occurs in association with PXV immunization rather than PXV infection. Throughout the review, numerous evasion mechanisms are highlighted, which might have implications for designing specific immunotherapies for PXV in the future.

The combined vaccination protocol of DNA/MVA expressing Zika virus structural proteins as efficient inducer of T and B cell immune responses

Zika virus (ZIKV) is a mosquito-borne pathogen with public health importance due to the high risk of its mosquito vector dissemination and the severe neurological and teratogenic sequelae associated with infection. Vaccines with broad immune specificity and control against this re-emerging virus are needed. Here, we described that mice immunized with a priming dose of a DNA plasmid mammalian expression vector encoding ZIKV prM-E antigens (DNA-ZIKV) followed by a booster dose of a modified vaccinia virus Ankara (MVA) vector expressing the same prM-E ZIKV antigens (MVA-ZIKV) induced broad, polyfunctional and long-lasting ZIKV-specific CD4⁺ and CD8⁺ T-cell immune responses, with high levels of CD4⁺ T follicular helper cells, together with the induction of neutralizing antibodies. All those immune parameters were significantly stronger in the heterologous DNA-ZIKV/MVA-ZIKV immunization group compared to the homologous prime/boost immunizations regimens. Collectively, these results provided an optimized immunization protocol able to induce high levels of ZIKV-specific T-cell responses, as well as neutralizing antibodies and reinforce the combined use of DNA-based vectors and MVA-ZIKV as promising prophylactic vaccination schedule against ZIKV.

Activation of interferon regulatory factor 3 by replication-competent vaccinia viruses improves antitumor efficacy mediated by T cell responses

Recently, oncolytic vaccinia viruses (VACVs) have shown their potential to provide for clinically effective cancer treatments. The reason for this clinical usefulness is not only the direct destruction of infected cancer cells but also activation of immune responses directed against tumor antigens. For eliciting a robust antitumor immunity, a dominant T helper 1 (Th1) cell differentiation of the response is preferred, and such polarization can be achieved by activating the Toll-like receptor 3 (TLR3)-interferon regulatory factor 3 (IRF3) signaling pathway. However, current VACVs used as oncolytic viruses to date still encode several immune evasion proteins involved in the inhibition of this signaling pathway. By inactivating genes of selected regulatory virus proteins, we aimed for a candidate virus with increased potency to activate cellular antitumor immunity but at the same time with a fully maintained replicative capacity in cancer cells. The removal of up to three key genes (C10L, N2L, and C6L) from VACV did not reduce the strength of viral replication, both in vitro and in vivo, but resulted in the rescue of IRF3 phosphorylation upon infection of cancer cells. In syngeneic mouse tumor models, this activation translated to enhanced cytotoxic T lymphocyte (CTL) responses directed against tumor-associated antigens and neo-epitopes and improved antitumor activity.

MVAΔ008 viral vector encoding the model protein OVA induces improved immune response against the heterologous antigen and equal levels of protection in a mice tumor model than the conventional MVA

Modified vaccinia Ankara virus (MVA) is extensively used as a vaccine vector. We have previously observed that MVAΔ008, an MVA lacking the gene that codes for interleukin-18 binding protein, significantly increases CD8+ and CD4+ T-cell responses to vaccinia virus (VACV) epitopes and recombinant HIV antigens. However, the efficacy of this vector against pathogens or tumor cells remains unclear. Thus, the aim of this study was to evaluate the cellular immune response and the protection induced by recombinant MVAs encoding the model antigen ovalbumin (OVA). We used the MO5 melanoma tumor model (OVA-expressing tumor) as an approach for evaluating the vector-induced efficacy. Our results show that MVAΔ008-OVA (optimized vector) induced higher in vivo specific cytotoxicity and ex vivo T-cell IFN-γ responses against OVA than the conventional MVA vector. Importantly, the recombinant vectors were capable of controlling MO5 tumor growth. Indeed, the administration of MVAΔ008-OVA or MVA-OVA in prophylactic and therapeutic schemes provided total protection and longer survival of mice, respectively. Overall, our results demonstrate the improved immunogenicity and the protective capacity of MVAΔ008 against a heterologous model antigen. These findings suggest that MVAΔ008 constitutes an excellent candidate for vaccine development against pathogens or cancer therapy.

COVID-19 vaccine candidates based on modified vaccinia virus Ankara expressing the SARS-CoV-2 spike induce robust T- and B-cell immune responses and full efficacy in mice

Vaccines against SARS-CoV-2, the causative agent of the COVID-19 pandemic, are urgently needed. We developed two COVID-19 vaccines based on modified vaccinia virus Ankara (MVA) vectors expressing the entire SARS-CoV-2 spike (S) protein (MVA-CoV2-S); their immunogenicity was evaluated in mice using DNA/MVA or MVA/MVA prime/boost immunizations. Both vaccines induced robust, broad and polyfunctional S-specific CD4+ (mainly Th1) and CD8+ T-cell responses, with a T effector memory phenotype. DNA/MVA immunizations elicited higher T-cell responses. All vaccine regimens triggered high titers of IgG antibodies specific for the S, as well as for the receptor-binding domain; the predominance of the IgG2c isotype was indicative of Th1 immunity. Notably, serum samples from vaccinated mice neutralized SARS-CoV-2 in cell cultures, and those from MVA/MVA immunizations showed a higher neutralizing capacity. Remarkably, one or two doses of MVA-CoV2-S protect humanized K18-hACE2 mice from a lethal dose of SARS-CoV-2. In addition, two doses of MVA-CoV2-S confer full inhibition of virus replication in the lungs. These results demonstrate the robust immunogenicity and full efficacy of MVA-based COVID-19 vaccines in animal models and support its translation to the clinic.IMPORTANCE The continuous dissemination of the novel emerging SARS-CoV-2 virus, with more than 78 million infected cases worldwide and higher than 1,700,000 deaths as of December 23, 2020, highlights the urgent need for the development of novel vaccines against COVID-19. With this aim, we have developed novel vaccine candidates based on the poxvirus modified vaccinia virus Ankara (MVA) strain expressing the full-length SARS-CoV-2 spike (S) protein, and we have evaluated their immunogenicity in mice using DNA/MVA or MVA/MVA prime/boost immunization protocols. The results showed the induction of a potent S-specific T-cell response and high titers of neutralizing antibodies. Remarkably, humanized K18-hACE2 mice immunized with one or two doses of the MVA-based vaccine were 100% protected from SARS-CoV-2 lethality. Moreover, two doses of the vaccine prevented virus replication in lungs. Our findings prove the robust immunogenicity and efficacy of MVA-based COVID-19 vaccines in animal models and support its translation to the clinic.

Injection site vaccinology of a recombinant vaccinia-based vector reveals diverse innate immune signatures

Poxvirus systems have been extensively used as vaccine vectors. Herein a RNA-Seq analysis of intramuscular injection sites provided detailed insights into host innate immune responses, as well as expression of vector and recombinant immunogen genes, after vaccination with a new multiplication defective, vaccinia-based vector, Sementis Copenhagen Vector. Chikungunya and Zika virus immunogen mRNA and protein expression was associated with necrosing skeletal muscle cells surrounded by mixed cellular infiltrates. The multiple adjuvant signatures at 12 hours post-vaccination were dominated by TLR3, 4 and 9, STING, MAVS, PKR and the inflammasome. Th1 cytokine signatures were dominated by IFNγ, TNF and IL1β, and chemokine signatures by CCL5 and CXCL12. Multiple signatures associated with dendritic cell stimulation were evident. By day seven, vaccine transcripts were absent, and cell death, neutrophil, macrophage and inflammation annotations had abated. No compelling arthritis signatures were identified. Such injection site vaccinology approaches should inform refinements in poxvirus-based vector design.

Poxvirus vector systems have been widely developed for vaccine applications. Despite considerable progress, so far only one recombinant poxvirus vectored vaccine has to date been licensed for human use, with ongoing efforts seeking to enhance immunogenicity whilst minimizing reactogenicity. The latter two characteristics are often determined by early post-vaccination events at the injection site. We therefore undertook an injection site vaccinology approach to analyzing gene expression at the vaccination site after intramuscular inoculation with a recombinant, multiplication defective, vaccinia-based vaccine. This provided detailed insights into inter alia expression of vector-encoded immunoregulatory genes, as well as host innate and adaptive immune responses. We propose that such injection site vaccinology can inform rational vaccine vector design, and we discuss how the information and approach elucidated herein might be used to improve immunogenicity and limit reactogenicity of poxvirus-based vaccine vector systems.

Enhancement of HIV-1 Env-Specific CD8 T Cell Responses Using Interferon-Stimulated Gene 15 as an Immune Adjuvant

Induction of the endogenous innate immune system by interferon (IFN) triggers the expression of many proteins that serve like alarm bells in the body, activating an immune response. After a viral infection, one of the genes activated by IFN induction is the IFN-stimulated gene 15 (ISG15), which encodes a ubiquitin-like protein that undergoes a reversible posttranslational modification (ISGylation). ISG15 protein can also act unconjugated, intracellularly and secreted, acting as a cytokine. Although ISG15 has an essential role in host defense responses to microbial infection, its role as an immunomodulator in the vaccine field remains to be defined. In this investigation, we showed that ISG15 exerts an immunomodulatory role in human immunodeficiency virus (HIV) vaccines. In mice, after priming with a DNA-ISG15 vector mixed with a DNA expressing HIV-1 gp120 (DNA-gp120), followed by a booster with a modified vaccinia virus Ankara (MVA) vector expressing HIV-1 antigens, both wild-type ISG15-conjugated (ISG15-wt) and mutant unconjugated (ISG15-mut) proteins act as immune adjuvants by increasing the magnitude and quality of HIV-1-specific CD8 T cells, with ISG15-wt providing better immunostimulatory activity than ISG15-mut. The HIV-1 Env-specific CD8 T cell responses showed a predominant T effector memory (TEM) phenotype in all groups. Moreover, the amount of DNA-gp120 used to immunize mice could be reduced 5-fold after mixing with DNA-ISG15 without affecting the potency and the quality of the HIV-1 Env-specific immune responses. Our study clearly highlights the potential use of the IFN-induced ISG15 protein as immune adjuvant to enhance immune responses to HIV antigens, suggesting that this molecule might be exploitable for prophylactic and therapeutic vaccine approaches against pathogens.IMPORTANCE Our study described the potential role of ISG15 as an immunomodulatory molecule in the optimization of HIV/AIDS vaccine candidates. Using a DNA prime-MVA boost immunization protocol, our results indicated an increase in the potency and the quality of the HIV-1 Env-specific CD8 T cell response. These results highlight the adjuvant potency of ISG15 to elicit improved viral antigen presentation to the immune system, resulting in an enhanced HIV-1 vaccine immune response. The DNA-ISG15 vector could find applicability in the vaccine field in combination with other nucleic acid-based vector vaccines.

Vaccinia Virus Activation and Antagonism of Cytosolic DNA Sensing

Cells express multiple molecules aimed at detecting incoming virus and infection. Recognition of virus infection leads to the production of cytokines, chemokines and restriction factors that limit virus replication and activate an adaptive immune response offering long-term protection. Recognition of cytosolic DNA has become a central immune sensing mechanism involved in infection, autoinflammation, and cancer immunotherapy. Vaccinia virus (VACV) is the prototypic member of the family Poxviridae and the vaccine used to eradicate smallpox. VACV harbors enormous potential as a vaccine vector and several attenuated strains are currently being developed against infectious diseases. In addition, VACV has emerged as a popular oncolytic agent due to its cytotoxic capacity even in hypoxic environments. As a poxvirus, VACV is an unusual virus that replicates its large DNA genome exclusively in the cytoplasm of infected cells. Despite producing large amounts of cytosolic DNA, VACV efficiently suppresses the subsequent innate immune response by deploying an arsenal of proteins with capacity to disable host antiviral signaling, some of which specifically target cytosolic DNA sensing pathways. Some of these strategies are conserved amongst orthopoxviruses, whereas others are seemingly unique to VACV. In this review we provide an overview of the VACV replicative cycle and discuss the recent advances on our understanding of how VACV induces and antagonizes innate immune activation via cytosolic DNA sensing pathways. The implications of these findings in the rational design of vaccines and oncolytics based on VACV are also discussed.

Antiviral therapy for the sexually transmitted viruses: recent updates on vaccine development

INTRODUCTION

The sexually transmitted infections (STIs) caused by viruses including human T cell leukemia virus type-1 (HTLV-1), human immunodeficiency virus-1 (HIV-1), human simplex virus-2 (HSV-2), hepatitis C virus (HCV), hepatitis B virus (HBV), and human papillomavirus (HPV) are major public health issues. These infections can cause cancer or result in long-term health problems. Due to high prevalence of STIs, a safe and effective vaccine is required to overcome these fatal viruses.

AREAS COVERED

This review includes a comprehensive overview of the literatures relevant to vaccine development against the sexually transmitted viruses (STVs) using PubMed and Sciencedirect electronic search engines. Herein, we discuss the efforts directed toward development of effective vaccines using different laboratory animal models including mice, guinea pig or non-human primates in preclinical trials, and human in clinical trials with different phases.

EXPERT OPINION

There is no effective FDA approved vaccine against the sexually transmitted viruses (STVs) except for HBV and HPV as prophylactic vaccines. Many attempts are underway to develop vaccines against these viruses. There are several approaches for improving prophylactic or therapeutic vaccines such as heterologous prime/boost immunization, delivery system, administration route, adjuvants, etc. In this line, further studies can be helpful for understanding the immunobiology of STVs in human. Moreover, development of more relevant animal models is a worthy goal to induce effective immune responses in humans.

A Zigzag but Upward Way to Develop an HIV-1 Vaccine

After decades of its epidemic, the human immunodeficiency virus type 1 (HIV-1) is still rampant worldwide. An effective vaccine is considered to be the ultimate strategy to control and prevent the spread of HIV-1. To date, hundreds of clinical trials for HIV-1 vaccines have been tested. However, there is no HIV-1 vaccine available yet, mostly because the immune correlates of protection against HIV-1 infection are not fully understood. Currently, a variety of recombinant viruses-vectored HIV-1 vaccine candidates are extensively studied as promising strategies to elicit the appropriate immune response to control HIV-1 infection. In this review, we summarize the current findings on the immunological parameters to predict the protective efficacy of HIV-1 vaccines, and highlight the latest advances on HIV-1 vaccines based on viral vectors.

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.

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.

Recent advances on HIV DNA vaccines development: Stepwise improvements to clinical trials

According to WHO (World Health Organization) reports, more than 770,000 people died from HIV and almost 1.7 million people becoming newly infected in the worldwide in 2018. Therefore, many attempts should be done to produce a forceful vaccine to control the AIDS. DNA-based vaccines have been investigated for HIV vaccination by researches during the recent 20 years. The DNA vaccines are novel approach for induction of both type of immune responses (cellular and humoral) in the host cells and have many advantages including high stability, fast and easy of fabrication and absence of severe side effects when compared with other vaccination methods. Recent studies have been focused on vaccine design, immune responses and on the use of adjuvants as a promising strategy for increased level of responses, delivery approaches by viral and non-viral methods and vector design for different antigens of HIV virus. In this review, we outlined the aforementioned advances on HIV DNA vaccines. Then we described the future trends in clinical trials as a strong strategy even in healthy volunteers and the potential developments in control and prevention of HIV.

Optimized Mucosal Modified Vaccinia Virus Ankara Prime/Soluble gp120 Boost HIV Vaccination Regimen Induces Antibody Responses Similar to Those of an Intramuscular Regimen

The benefits of mucosal vaccines over injected vaccines are difficult to ascertain, since mucosally administered vaccines often induce serum antibody responses of lower magnitude than those induced by injected vaccines. This study aimed to determine if mucosal vaccination using a modified vaccinia virus Ankara expressing human immunodeficiency virus type 1 (HIV-1) gp120 (MVAgp120) prime and a HIV-1 gp120 protein boost could be optimized to induce serum antibody responses similar to those induced by an intramuscularly (i.m.) administered MVAgp120 prime/gp120 boost to allow comparison of an i.m. immunization regimen to a mucosal vaccination regimen for the ability to protect against a low-dose rectal simian-human immunodeficiency virus (SHIV) challenge. A 3-fold higher antigen dose was required for intranasal (i.n.) immunization with gp120 to induce serum anti-gp120 IgG responses not significantly different than those induced by i.m. immunization. gp120 fused to the adenovirus type 2 fiber binding domain (gp120-Ad2F), a mucosal targeting ligand, exhibited enhanced i.n. immunogenicity compared to gp120. MVAgp120 was more immunogenic after i.n. delivery than after gastric or rectal delivery. Using these optimized vaccines, an i.n. MVAgp120 prime/combined i.m. (gp120) and i.n. (gp120-Ad2F) boost regimen (i.n./i.m.-plus-i.n.) induced serum anti-gp120 antibody titers similar to those induced by the intramuscular prime/boost regimen (i.m./i.m.) in rabbits and nonhuman primates. Despite the induction of similar systemic anti-HIV-1 antibody responses, neither the i.m./i.m. nor the i.n./i.m.-plus-i.n. regimen protected against a repeated low-dose rectal SHIV challenge. These results demonstrate that immunization regimens utilizing the i.n. route are able to induce serum antigen-specific antibody responses similar to those induced by systemic immunization.IMPORTANCE Mucosal vaccination is proposed as a method of immunization able to induce protection against mucosal pathogens that is superior to protection provided by parenteral immunization. However, mucosal vaccination often induces serum antigen-specific immune responses of lower magnitude than those induced by parenteral immunization, making the comparison of mucosal and parenteral immunization difficult. We identified vaccine parameters that allowed an immunization regimen consisting of an i.n. prime followed by boosters administered by both i.n. and i.m. routes to induce serum antibody responses similar to those induced by i.m. prime/boost vaccination. Additional studies are needed to determine the potential benefit of mucosal immunization for HIV-1 and other mucosally transmitted pathogens.

Novel Modified Vaccinia Virus Ankara Vector Expressing Anti-apoptotic Gene B13R Delays Apoptosis and Enhances Humoral Responses

Modified vaccinia virus Ankara (MVA), an attenuated poxvirus, has been developed as a potential vaccine vector for use against cancer and multiple infectious diseases, including human immunodeficiency virus (HIV). MVA is highly immunogenic and elicits strong cellular and humoral responses in preclinical models and humans. However, there is potential to further enhance the immunogenicity of MVA, as MVA-infected cells undergo rapid apoptosis, leading to faster clearance of recombinant antigens and potentially blunting a greater response. Here, we generated MVA-B13R by replacing the fragmented 181R/182R genes of MVA with a functional anti-apoptotic gene, B13R, and confirmed its anti-apoptotic function against chemically induced apoptosis in vitro In addition, MVA-B13R showed a significant delay in induction of apoptosis in muscle cells derived from mice and humans, as well as in plasmacytoid dendritic cells (pDCs) and CD141+ DCs from rhesus macaques, compared to the induction of apoptosis in MVA-infected cells. MVA-B13R expressing simian immunodeficiency virus (SIV) Gag and Pol and HIV envelope (SHIV) (MVA-B13R/SHIV) produced higher levels of envelope in the supernatants than MVA/SHIV-infected DF-1 cells in vitro Immunization of BALB/c mice showed induction of higher levels of envelope-specific antibody-secreting cells and memory B cells, higher IgG antibody titers, and better persistence of antibody titers with MVA-B13R/SHIV than with MVA/SHIV. Gene set enrichment analysis of draining lymph node cells from day 1 after immunization showed negative enrichment for interferon responses in MVA-B13R/SHIV-immunized mice compared to the responses in MVA/SHIV-immunized mice. Taken together, these results demonstrate that restoring B13R functionality in MVA significantly delays MVA-induced apoptosis in muscle and antigen-presenting cells in vitro and augments vaccine-induced humoral immunity in mice.IMPORTANCE MVA is an attractive viral vector for vaccine development due to its safety and immunogenicity in multiple species and humans even under conditions of immunodeficiency. Here, to further improve the immunogenicity of MVA, we developed a novel vector, MVA-B13R, by replacing the fragmented anti-apoptotic genes 181R/182R with a functional version derived from vaccinia virus, B13R Our results show that MVA-B13R significantly delays apoptosis in antigen-presenting cells and muscle cells in vitro and augments vaccine-induced humoral immunity in mice, leading to the development of a novel vector for vaccine development against infectious diseases and cancer.

A Vaccine Based on a Modified Vaccinia Virus Ankara Vector Expressing Zika Virus Structural Proteins Controls Zika Virus Replication in Mice

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that affects humans and can cause severe neurological complications, including Guillain-Barré syndrome and microcephaly. Since 2007 there have been three large outbreaks; the last and larger spread in the Americas in 2015. Actually, ZIKV is circulating in the Americas, Southeast Asia, and the Pacific Islands, and represents a potential pandemic threat. Given the rapid ZIKV dissemination and the severe neurological and teratogenic sequelae associated with ZIKV infection, the development of a safe and efficacious vaccine is critical. In this study, we have developed and characterized the immunogenicity and efficacy of a novel ZIKV vaccine based on the highly attenuated poxvirus vector modified vaccinia virus Ankara (MVA) expressing the ZIKV prM and E structural genes (termed MVA-ZIKV). MVA-ZIKV expressed efficiently the ZIKV structural proteins, assembled in virus-like particles (VLPs) and was genetically stable upon nine passages in cell culture. Immunization of mice with MVA-ZIKV elicited antibodies that were able to neutralize ZIKV and induced potent and polyfunctional ZIKV-specific CD8⁺ T cell responses that were mainly of an effector memory phenotype. Moreover, a single dose of MVA-ZIKV reduced significantly the viremia in susceptible immunocompromised mice challenged with live ZIKV. These findings support the use of MVA-ZIKV as a potential vaccine against ZIKV.

The 135 Gene of Goatpox Virus Encodes an Inhibitor of NF-κB and Apoptosis and May Serve as an Improved Insertion Site To Generate Vectored Live Vaccine

Goatpox virus (GTPV) is an important member of the Capripoxvirus genus of the Poxviridae Capripoxviruses have large and complex DNA genomes encoding many unknown proteins that may contribute to virulence. We identified that the 135 open reading frame of GTPV is an early gene that encodes an ∼18-kDa protein that is nonessential for viral replication in cells. This protein functioned as an inhibitor of NF-κB activation and apoptosis and is similar to the N1L protein of vaccinia virus. In the natural host, sheep, deletion of the 135 gene from the GTPV live vaccine strain AV41 resulted in less attenuation than that induced by deletion of the tk gene, a well-defined nonessential gene in the poxvirus genome. Using the 135 gene as the insertion site, a recombinant AV41 strain expressing hemagglutinin of peste des petits ruminants virus (PPRV) was generated and elicited stronger neutralization antibody responses than those obtained using the traditional tk gene as the insertion site. These results suggest that the 135 gene of GTPV encodes an immunomodulatory protein to suppress host innate immunity and may serve as an optimized insertion site to generate capripoxvirus-vectored live dual vaccines.IMPORTANCE Capripoxviruses are etiological agents of important diseases in sheep, goats, and cattle. There are rare reports about viral protein function related to capripoxviruses. In the present study, we found that the 135 protein of GTPV plays an important role in inhibition of innate immunity and apoptosis in host cells. Use of the 135 gene as the insertion site to generate a vectored vaccine resulted in stronger adaptive immune responses than those obtained using the tk locus as the insertion site. As capripoxviruses are promising virus-vectored vaccines against many important diseases in small ruminants and cattle, the 135 gene may serve as an improved insertion site to generate recombinant capripoxvirus-vectored live dual vaccines.

Removal of the C6 Vaccinia Virus Interferon-β Inhibitor in the Hepatitis C Vaccine Candidate MVA-HCV Elicited in Mice High Immunogenicity in Spite of Reduced Host Gene Expression

Hepatitis C virus (HCV) represents a major global health problem for which a vaccine is not available. Modified vaccinia virus Ankara (MVA)-HCV is a unique HCV vaccine candidate based in the modified vaccinia virus Ankara (MVA) vector expressing the nearly full-length genome of HCV genotype 1a that elicits CD8⁺ T-cell responses in mice. With the aim to improve the immune response of MVA-HCV and because of the importance of interferon (IFN) in HCV infection, we deleted in MVA-HCV the vaccinia virus (VACV) C6L gene, encoding an inhibitor of IFN-β that prevents activation of the interferon regulatory factors 3 and 7 (IRF3 and IRF7). The resulting vaccine candidate (MVA-HCV ΔC6L) expresses all HCV antigens and deletion of C6L had no effect on viral growth in permissive chicken cells. In human monocyte-derived dendritic cells, infection with MVA-HCV ΔC6L triggered severe down-regulation of IFN-β, IFN-β-induced genes, and cytokines in a manner similar to MVA-HCV, as defined by real-time polymerase chain reaction (PCR) and microarray analysis. In infected mice, both vectors had a similar profile of recruited immune cells and induced comparable levels of adaptive and memory HCV-specific CD8⁺ T-cells, mainly against p7 + NS2 and NS3 HCV proteins, with a T cell effector memory (TEM) phenotype. Furthermore, antibodies against E2 were also induced. Overall, our findings showed that while these vectors had a profound inhibitory effect on gene expression of the host, they strongly elicited CD8⁺ T cell and humoral responses against HCV antigens and to the virus vector. These observations add support to the consideration of these vectors as potential vaccine candidates against HCV.

Modulating Vaccinia Virus Immunomodulators to Improve Immunological Memory

The increasing frequency of monkeypox virus infections, new outbreaks of other zoonotic orthopoxviruses and concern about the re-emergence of smallpox have prompted research into developing antiviral drugs and better vaccines against these viruses. This article considers the genetic engineering of vaccinia virus (VACV) to enhance vaccine immunogenicity and safety. The virulence, immunogenicity and protective efficacy of VACV strains engineered to lack specific immunomodulatory or host range proteins are described. The ultimate goal is to develop safer and more immunogenic VACV vaccines that induce long-lasting immunological memory.

Characterizing the effects of insertion of a 5.2 kb region of a VACV genome, which contains known immune evasion genes, on MVA immunogenicity

Modified Vaccinia virus Ankara (MVA) is an attenuated Vaccinia virus (VACV) that is a popular vaccine vector candidate against many different pathogens. Its replication-restricted nature makes it a safe vaccine. However, higher doses or multiple boosts of MVA are necessary to elicit an immune response similar to wild-type VACV. Multiple strategies have been used to create modified MVA viruses that remain safe, but have increased immunogenicity. For example, one common strategy is to delete MVA immunomodulatory proteins in hopes of increasing the host immune response. Here, we take the opposite approach and examine, for the first time, how re-introduction of a 5.2 kb region of VACV DNA (that codes for multiple immunomodulatory proteins) into MVA alters viral immunogenicity. Since antigen presenting cells (APCs) are critical connectors between the innate and adaptive immune system, we examined the effect of MVA/5.2 kb infection in these cells in vitro. MVA/5.2 kb infection decreased virus-induced apoptosis and virus-induced NF-κB activation. MVA.5.2 kb infection decreased TNF production. However, MVA/5.2 kb infection did not alter APC maturation or IL-6 and IL-8 production in vitro. We further explored MVA/5.2 kb immunogenicity in vivo. VACV-specific CD8⁺ T cells were decreased after in vivo infection with MVA/5.2 kb versus MVA, suggesting that the MVA/5.2 kb construct is less immunogenic than MVA. These results demonstrate the limitations of in vitro studies for predicting the effects of genetic manipulation of MVA on immunogenicity. Although MVA/5.2 kb did not enhance MVA's immunogenicity, this study examined an unexplored strategy for optimizing MVA, and the insight gained from these results can help direct how to modify MVA in the future.

Hazard Characterization of Modified Vaccinia Virus Ankara Vector: What Are the Knowledge Gaps?

Modified vaccinia virus Ankara (MVA) is the vector of choice for human and veterinary applications due to its strong safety profile and immunogenicity in vivo. The use of MVA and MVA-vectored vaccines against human and animal diseases must comply with regulatory requirements as they pertain to environmental risk assessment, particularly the characterization of potential adverse effects to humans, animals and the environment. MVA and recombinant MVA are widely believed to pose low or negligible risk to ecosystem health. However, key aspects of MVA biology require further research in order to provide data needed to evaluate the potential risks that may occur due to the use of MVA and MVA-vectored vaccines. The purpose of this paper is to identify knowledge gaps in the biology of MVA and recombinant MVA that are of relevance to its hazard characterization and discuss ongoing and future experiments aimed at providing data necessary to fill in the knowledge gaps. In addition, we presented arguments for the inclusion of uncertainty analysis and experimental investigation of verifiable worst-case scenarios in the environmental risk assessment of MVA and recombinant MVA. These will contribute to improved risk assessment of MVA and recombinant MVA vaccines.

Immunogenicity and efficacy of DNA/MVA HIV vaccines in rhesus macaque models

INTRODUCTION

Despite 30 years of research on HIV, a vaccine to prevent infection and limit disease progression remains elusive. The RV144 trial showed moderate, but significant protection in humans and highlighted the contribution of antibody responses directed against HIV envelope as an important immune correlate for protection. Efforts to further build upon the progress include the use of a heterologous prime-boost regimen using DNA as the priming agent and the attenuated vaccinia virus, Modified Vaccinia Ankara (MVA), as a boosting vector for generating protective HIV-specific immunity. Areas covered: In this review, we summarize the immunogenicity of DNA/MVA vaccines in non-human primate models and describe the efficacy seen in SIV infection models. We discuss immunological correlates of protection determined by these studies and potential approaches for improving the protective immunity. Additionally, we describe the current progress of DNA/MVA vaccines in human trials. Expert commentary: Efforts over the past decade have provided the opportunity to better understand the dynamics of vaccine-induced immune responses and immune correlates of protection against HIV. Based on what we have learned, we outline multiple areas where the field will likely focus on in the next five years.

Distinct Roles of Vaccinia Virus NF-κB Inhibitor Proteins A52, B15, and K7 in the Immune Response

Poxviruses use a complex strategy to escape immune control, by expressing immunomodulatory proteins that could limit their use as vaccine vectors. To test the role of poxvirus NF-κB pathway inhibitors A52, B15, and K7 in immunity, we deleted their genes in an NYVAC (New York vaccinia virus) strain that expresses HIV-1 clade C antigens. After infection of mice, ablation of the A52R, B15R, and K7R genes increased dendritic cell, natural killer cell, and neutrophil migration as well as chemokine/cytokine expression. Revertant viruses with these genes confirmed their role in inhibiting the innate immune system. To different extents, enhanced innate immune responses correlated with increased HIV Pol- and Gag-specific polyfunctional CD8 T cell and HIV Env-specific IgG responses induced by single-, double-, and triple-deletion mutants. These poxvirus proteins thus influence innate and adaptive cell-mediated and humoral immunity, and their ablation offers alternatives for design of vaccine vectors that regulate immune responses distinctly.IMPORTANCE Poxvirus vectors are used in clinical trials as candidate vaccines for several pathogens, yet how these vectors influence the immune system is unknown. We developed distinct poxvirus vectors that express heterologous antigens but lack different inhibitors of the central host-cell signaling pathway. Using mice, we studied the capacity of these viruses to induce innate and adaptive immune responses and showed that these vectors can distinctly regulate the magnitude and quality of these responses. These findings provide important insights into the mechanism of poxvirus-induced immune response and alternative strategies for vaccine vector design.

HIV/AIDS Vaccine Candidates Based on Replication-Competent Recombinant Poxvirus NYVAC-C-KC Expressing Trimeric gp140 and Gag-Derived Virus-Like Particles or Lacking the Viral Molecule B19 That Inhibits Type I Interferon Activate Relevant HIV-1-Specific B and T Cell Immune Functions in Nonhuman Primates

The nonreplicating attenuated poxvirus vector NYVAC expressing clade C(CN54) HIV-1 Env(gp120) and Gag-Pol-Nef antigens (NYVAC-C) showed limited immunogenicity in phase I clinical trials. To enhance the capacity of the NYVAC vector to trigger broad humoral responses and a more balanced activation of CD4⁺ and CD8⁺ T cells, here we compared the HIV-1-specific immunogenicity elicited in nonhuman primates immunized with two replicating NYVAC vectors that have been modified by the insertion of the K1L and C7L vaccinia virus host range genes and express the clade C(ZM96) trimeric HIV-1 gp140 protein or a Gag(ZM96)-Pol-Nef(CN54) polyprotein as Gag-derived virus-like particles (termed NYVAC-C-KC). Additionally, one NYVAC-C-KC vector was generated by deleting the viral gene B19R, an inhibitor of the type I interferon response (NYVAC-C-KC-ΔB19R). An immunization protocol mimicking that of the RV144 phase III clinical trial was used. Two groups of macaques received two doses of the corresponding NYVAC-C-KC vectors (weeks 0 and 4) and booster doses with NYVAC-C-KC vectors plus the clade C HIV-1 gp120 protein (weeks 12 and 24). The two replicating NYVAC-C-KC vectors induced enhanced and similar HIV-1-specific CD4⁺ and CD8⁺ T cell responses, similar levels of binding IgG antibodies, low levels of IgA antibodies, and high levels of antibody-dependent cellular cytotoxicity responses and HIV-1-neutralizing antibodies. Small differences within the NYVAC-C-KC-ΔB19R group were seen in the magnitude of CD4⁺ and CD8⁺ T cells, the induction of some cytokines, and the neutralization of some HIV-1 isolates. Thus, replication-competent NYVAC-C-KC vectors acquired relevant immunological properties as vaccine candidates against HIV/AIDS, and the viral B19 molecule exerts some control of immune functions.IMPORTANCE It is of special importance to find a safe and effective HIV/AIDS vaccine that can induce strong and broad T cell and humoral immune responses correlating with HIV-1 protection. Here we developed novel replicating poxvirus NYVAC-based HIV/AIDS vaccine candidates expressing clade C HIV-1 antigens, with one of them lacking the vaccinia virus B19 protein, an inhibitor of the type I interferon response. Immunization of nonhuman primates with these novel NYVAC-C-KC vectors and the protein component gp120 elicited high levels of T cell and humoral immune responses, with the vector containing a deletion in B19R inducing a trend toward a higher magnitude of CD4⁺ and CD8⁺ T cell responses and neutralization of some HIV-1 strains. These poxvirus vectors could be considered HIV/AIDS vaccine candidates based on their activation of potential immune correlates of protection.

Modified Vaccinia Virus Ankara: History, Value in Basic Research, and Current Perspectives for Vaccine Development

Safety tested Modified Vaccinia virus Ankara (MVA) is licensed as third-generation vaccine against smallpox and serves as a potent vector system for development of new candidate vaccines against infectious diseases and cancer. Historically, MVA was developed by serial tissue culture passage in primary chicken cells of vaccinia virus strain Ankara, and clinically used to avoid the undesirable side effects of conventional smallpox vaccination. Adapted to growth in avian cells MVA lost the ability to replicate in mammalian hosts and lacks many of the genes orthopoxviruses use to conquer their host (cell) environment. As a biologically well-characterized mutant virus, MVA facilitates fundamental research to elucidate the functions of poxvirus host-interaction factors. As extremely safe viral vectors MVA vaccines have been found immunogenic and protective in various preclinical infection models. Multiple recombinant MVA currently undergo clinical testing for vaccination against human immunodeficiency viruses, Mycobacterium tuberculosis or Plasmodium falciparum. The versatility of the MVA vector vaccine platform is readily demonstrated by the swift development of experimental vaccines for immunization against emerging infections such as the Middle East Respiratory Syndrome. Recent advances include promising results from the clinical testing of recombinant MVA-producing antigens of highly pathogenic avian influenza virus H5N1 or Ebola virus. This review summarizes our current knowledge about MVA as a unique strain of vaccinia virus, and discusses the prospects of exploiting this virus as research tool in poxvirus biology or as safe viral vector vaccine to challenge existing and future bottlenecks in vaccinology.

Deletion of A44L, A46R and C12L Vaccinia Virus Genes from the MVA Genome Improved the Vector Immunogenicity by Modifying the Innate Immune Response Generating Enhanced and Optimized Specific T-Cell Responses

MVA is an attenuated vector that still retains immunomodulatory genes. We have previously reported its optimization after deleting the C12L gene, coding for the IL-18 binding-protein. Here, we analyzed the immunogenicity of MVA vectors harboring the simultaneous deletion of A44L, related to steroid synthesis and A46R, a TLR-signaling inhibitor (MVAΔA44L-A46R); or also including a deletion of C12L (MVAΔC12L/ΔA44L-A46R). The absence of biological activities of the deleted genes in the MVA vectors was demonstrated. Adaptive T-cell responses against VACV epitopes, evaluated in spleen and draining lymph-nodes of C57Bl/6 mice at acute/memory phases, were of higher magnitude in those animals that received deleted MVAs compared to MVAwt. MVAΔC12L/ΔA44L-A46R generated cellular specific memory responses of higher quality characterized by bifunctionality (CD107a/b⁺/IFN-γ⁺) and proliferation capacity. Deletion of selected genes from MVA generated innate immune responses with higher levels of determining cytokines related to T-cell response generation, such as IL-12, IFN-γ, as well as IL-1β and IFN-β. This study describes for the first time that simultaneous deletion of the A44L, A46R and C12L genes from MVA improved its immunogenicity by enhancing the host adaptive and innate immune responses, suggesting that this approach comprises an appropriate strategy to increase the MVA vaccine potential.

Use of functional genomics to understand replication deficient poxvirus-host interactions

High-throughput genomics technologies are currently being used to study a wide variety of viral infections, providing insight into which cellular genes and pathways are regulated after infection, and how these changes are related, or not, to efficient elimination of the pathogen. This article will focus on how gene expression studies of infections with non-replicative poxviruses currently used as vaccine vectors provide a global perspective of the molecular events associated with the viral infection in human cells. These high-throughput genomics approaches have the potential to lead to the identification of specific new properties of the viral vector or novel cellular targets that may aid in the development of more effective pox-derived vaccines and antivirals.

Balance between activation and regulation of HIV-specific CD8+ T-cell response after modified vaccinia Ankara B therapeutic vaccination

BACKGROUND

The causes of HIV-vaccines failure are poorly understood. Therapeutic vaccination with modified vaccinia Ankara (MVA)-B in HIV-1-infected individuals did not control the virus upon analytical treatment interruption (ATI). We investigated whether the functional characteristics of HIV-specific CD8 T-cell responses stimulated by this vaccine, and the level of exhaustion of these cells might explain these results.

METHODS

Twenty-one HIV-1 chronically infected patients on combination antiretroviral therapy, included in the therapeutic vaccine trial RISVAC03, were studied: 13 immunized and eight controls. Functional characteristics, cytotoxic potential and exhaustion of HIV-specific CD8 T cells, were evaluated by polychromatic flow cytometry. Differences between groups were tested using nonparametric tests.

RESULTS

MVA-B vaccine induced an increase in HIV-specific CD8 T-cell response, but also increased their levels of exhaustion. At week 18 (following three immunizations) the level of response increased with respect to baseline (P = 0.02). A significant increase at weeks 18 and 24 (ATI) in granzyme B content was also observed. Interestingly, an increase in expression of exhaustion markers was found at weeks 18 (P = 0.006) and 24 (P = 0.01). However, there was no significant change in the functional profile of vaccine-induced CD8 cells. At week 36, in parallel to the rebound of plasma viremia after 12 weeks ATI, a significant increase in the level of CD8 response, in granzyme B content and in exhaustion markers expression, was observed in both groups.

CONCLUSION

We show that therapeutic vaccination with MVA-B tilts the balance between activation and regulation of the response of HIV-specific CD8 T cells towards regulation, which impacts on the viral rebound after ATI.

Enhancing poxvirus vectors vaccine immunogenicity

Attenuated recombinant poxvirus vectors expressing heterologous antigens from pathogens are currently at various stages in clinical trials with the aim to establish their efficacy. This is because these vectors have shown excellent safety profiles, significant immunogenicity against foreign expressed antigens and are able to induce protective immune responses. In view of the limited efficacy triggered by some poxvirus strains used in clinical trials (i.e, ALVAC in the RV144 phase III clinical trial for HIV), and of the restrictive replication capacity of the highly attenuated vectors like MVA and NYVAC, there is a consensus that further improvements of these vectors should be pursuit. In this review we considered several strategies that are currently being implemented, as well as new approaches, to improve the immunogenicity of the poxvirus vectors. This includes heterologous prime/boost protocols, use of co-stimulatory molecules, deletion of viral immunomodulatory genes still present in the poxvirus genome, enhancing virus promoter strength, enhancing vector replication capacity, optimizing expression of foreign heterologous sequences, and the combined use of adjuvants. An optimized poxvirus vector triggering long-lasting immunity with a high protective efficacy against a selective disease should be sought.

A Chimeric HIV-1 gp120 Fused with Vaccinia Virus 14K (A27) Protein as an HIV Immunogen

In the HIV vaccine field, there is a need to produce highly immunogenic forms of the Env protein with the capacity to trigger broad B and T-cell responses. Here, we report the generation and characterization of a chimeric HIV-1 gp120 protein (termed gp120-14K) by fusing gp120 from clade B with the vaccinia virus (VACV) 14K oligomeric protein (derived from A27L gene). Stable CHO cell lines expressing HIV-1 gp120-14K protein were generated and the protein purified was characterized by size exclusion chromatography, electron microscopy and binding to anti-Env antibodies. These approaches indicate that gp120-14K protein is oligomeric and reacts with a wide spectrum of HIV-1 neutralizing antibodies. Furthermore, in human monocyte-derived dendritic cells (moDCs), gp120-14K protein upregulates the levels of several proinflammatory cytokines and chemokines associated with Th1 innate immune responses (IL-1β, IFN-γ, IL-6, IL-8, IL-12, RANTES). Moreover, we showed in a murine model, that a heterologous prime/boost immunization protocol consisting of a DNA prime with a plasmid expressing gp120-14K protein followed by a boost with MVA-B [a recombinant modified vaccinia virus Ankara (MVA) expressing HIV-1 gp120, Gag, Pol and Nef antigens from clade B], generates stronger, more polyfunctional, and greater effector memory HIV-1-specific CD4⁺ and CD8⁺ T-cell immune responses, than immunization with DNA-gp120/MVA-B. The DNA/MVA protocol was superior to immunization with the combination of protein/MVA and the latter was superior to a prime/boost of MVA/MVA or protein/protein. In addition, these immunization protocols enhanced antibody responses against gp120 of the class IgG2a and IgG3, together favoring a Th1 humoral immune response. These results demonstrate that fusing HIV-1 gp120 with VACV 14K forms an oligomeric protein which is highly antigenic as it activates a Th1 innate immune response in human moDCs, and in vaccinated mice triggers polyfunctional HIV-1-specific adaptive and memory T-cell immune responses, as well as humoral responses. This novel HIV-1 gp120-14K immunogen might be considered as an HIV vaccine candidate for broad T and B-cell immune responses.

Deletion of Fifteen Open Reading Frames from Modified Vaccinia Virus Ankara Fails to Improve Immunogenicity

Modified vaccinia virus Ankara (MVA) is a highly attenuated strain of vaccinia virus, which has been used as a recombinant vaccine vector in many vaccine development programmes. The loss of many immunosuppressive and host-range genes resulted in a safe and immunogenic vaccine vector. However it still retains some immunomodulatory genes that may reduce MVA immunogenicity. Earlier reports demonstrated that the deletion of the A41L, B15R, C6L, or C12L open reading frames (ORFs) enhanced cellular immune responses in recombinant MVA (rMVA) by up to 2-fold. However, previously, we showed that deletion of the C12L, A44L, A46R, B7R, or B15R ORFs from rMVA, using MVA-BAC recombineering technology, did not enhance rMVA immunogenicity at either peak or memory cellular immune responses. Here, we extend our previous study to examine the effect of deleting clusters of genes on rMVA cellular immunogenicity. Two clusters of fifteen genes were deleted in one rMVA mutant that encodes either the 85A antigen of Mycobacterium tuberculosis or an immunodominant H2-Kd-restricted murine malaria epitope (pb9). The deletion mutants were tested in prime only or prime and boost vaccination regimens. The responses showed no improved peak or memory CD8+ T cell frequencies. Our results suggest that the reported small increases in MVA deletion mutants could not be replicated with different antigens, or epitopes. Therefore, the gene deletion strategy may not be taken as a generic approach for improving the immunogenicity of MVA-based vaccines, and should be carefully assessed for every individual recombinant antigen.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Virological and immunological characterization of novel NYVAC-based HIV/AIDS vaccine candidates expressing clade C trimeric soluble gp140(ZM96) and Gag(ZM96)-Pol-Nef(CN54) as virus-like particles

The generation of vaccines against HIV/AIDS able to induce long-lasting protective immunity remains a major goal in the HIV field. The modest efficacy (31.2%) against HIV infection observed in the RV144 phase III clinical trial highlighted the need for further improvement of HIV vaccine candidates, formulation, and vaccine regimen. In this study, we have generated two novel NYVAC vectors, expressing HIV-1 clade C gp140(ZM96) (NYVAC-gp140) or Gag(ZM96)-Pol-Nef(CN54) (NYVAC-Gag-Pol-Nef), and defined their virological and immunological characteristics in cultured cells and in mice. The insertion of HIV genes does not affect the replication capacity of NYVAC recombinants in primary chicken embryo fibroblast cells, HIV sequences remain stable after multiple passages, and HIV antigens are correctly expressed and released from cells, with Env as a trimer (NYVAC-gp140), while in NYVAC-Gag-Pol-Nef-infected cells Gag-induced virus-like particles (VLPs) are abundant. Electron microscopy revealed that VLPs accumulated with time at the cell surface, with no interference with NYVAC morphogenesis. Both vectors trigger specific innate responses in human cells and show an attenuation profile in immunocompromised adult BALB/c and newborn CD1 mice after intracranial inoculation. Analysis of the immune responses elicited in mice after homologous NYVAC prime/NYVAC boost immunization shows that recombinant viruses induced polyfunctional Env-specific CD4 or Gag-specific CD8 T cell responses. Antibody responses against gp140 and p17/p24 were elicited. Our findings showed important insights into virus-host cell interactions of NYVAC vectors expressing HIV antigens, with the activation of specific immune parameters which will help to unravel potential correlates of protection against HIV in human clinical trials with these vectors.

IMPORTANCE

We have generated two novel NYVAC-based HIV vaccine candidates expressing HIV-1 clade C trimeric soluble gp140 (ZM96) and Gag(ZM96)-Pol-Nef(CN54) as VLPs. These vectors are stable and express high levels of both HIV-1 antigens. Gag-induced VLPs do not interfere with NYVAC morphogenesis, are highly attenuated in immunocompromised and newborn mice after intracranial inoculation, trigger specific innate immune responses in human cells, and activate T (Env-specific CD4 and Gag-specific CD8) and B cell immune responses to the HIV antigens, leading to high antibody titers against gp140. For these reasons, these vectors can be considered vaccine candidates against HIV/AIDS and currently are being tested in macaques and humans.