Recombinant simian varicella viruses induce immune responses to simian immunodeficiency virus (SIV) antigens in immunized vervet monkeys

Insertion of foreign genes into the simian varicella virus genome by Tn7-mediated site-specific transposition

A Tn7-transposition approach was utilized for site-specific insertion of foreign genes into the genome of simian varicella virus (SVV), the causative agent of simian varicella in nonhuman primates. The severe acute respiratory syndrome coronavirus (SARS-CoV-2) nucleocapsid (N) gene and receptor binding domain (RBD) of the spike gene were inserted into the ORF 14 region of the SVV genome cloned into a bacterial artificial chromosome and then transfected into Vero cells to generate the infectious recombinant SVV (rSVV). The rSVV replicated efficiently in infected Vero cells and expressed the N and RBD antigens as indicated by immunoblot and immunofluorescence assays. Tn7-mediated transposition provides a rapid and efficient method for constructing rSVVs which may be evaluated as live-attenuated vaccines.

Recombinant Simian Varicella Virus-Simian Immunodeficiency Virus Vaccine Induces T and B Cell Functions and Provides Partial Protection against Repeated Mucosal SIV Challenges in Rhesus Macaques

HIV vaccine mediated efficacy, using an expanded live attenuated recombinant varicella virus-vectored SIV rSVV-SIVgag/env vaccine prime with adjuvanted SIV-Env and SIV-Gag protein boosts, was evaluated in a female rhesus macaques (RM) model against repeated intravaginal SIV challenges. Vaccination induced anti-SIV IgG responses and neutralizing antibodies were found in all vaccinated RMs. Three of the eight vaccinated RM remained uninfected (vaccinated and protected, VP) after 13 repeated challenges with the pathogenic SIVmac251-CX-1. The remaining five vaccinated and infected (VI) macaques had significantly reduced plasma viral loads compared with the infected controls (IC). A significant increase in systemic central memory CD4+ T cells and mucosal CD8+ effector memory T-cell responses was detected in vaccinated RMs compared to controls. Variability in lymph node SIV-Gag and Env specific CD4+ and CD8+ T cell cytokine responses were detected in the VI RMs while all three VP RMs had more durable cytokine responses following vaccination and prior to challenge. VI RMs demonstrated predominately SIV-specific monofunctional cytokine responses while the VP RMs generated polyfunctional cytokine responses. This study demonstrates that varicella virus-vectored SIV vaccination with protein boosts induces a 37.5% efficacy rate against pathogenic SIV challenge by generating mucosal memory, virus specific neutralizing antibodies, binding antibodies, and polyfunctional T-cell responses.

Current In Vivo Models of Varicella-Zoster Virus Neurotropism

Varicella-zoster virus (VZV), an exclusively human herpesvirus, causes chickenpox and establishes a latent infection in ganglia, reactivating decades later to produce zoster and associated neurological complications. An understanding of VZV neurotropism in humans has long been hampered by the lack of an adequate animal model. For example, experimental inoculation of VZV in small animals including guinea pigs and cotton rats results in the infection of ganglia but not a rash. The severe combined immune deficient human (SCID-hu) model allows the study of VZV neurotropism for human neural sub-populations. Simian varicella virus (SVV) infection of rhesus macaques (RM) closely resembles both human primary VZV infection and reactivation, with analyses at early times after infection providing valuable information about the extent of viral replication and the host immune responses. Indeed, a critical role for CD4 T-cell immunity during acute SVV infection as well as reactivation has emerged based on studies using RM. Herein we discuss the results of efforts from different groups to establish an animal model of VZV neurotropism.

Recombinant varicella-zoster virus vaccines as platforms for expression of foreign antigens

Varicella-zoster virus (VZV) vaccines induce immunity against childhood chickenpox and against shingles in older adults. The safety, efficacy, and widespread use of VZV vaccines suggest that they may also be effective as recombinant vaccines against other infectious diseases that affect the young and the elderly. The generation of recombinant VZV vaccines and their evaluation in animal models are reviewed. The potential advantages and limitations of recombinant VZV vaccines are addressed.

Increased cellular immune responses and CD4+ T-cell proliferation correlate with reduced plasma viral load in SIV challenged recombinant simian varicella virus - simian immunodeficiency virus (rSVV-SIV) vaccinated rhesus macaques

Background

An effective AIDS vaccine remains one of the highest priorities in HIV-research. Our recent study showed that vaccination of rhesus macaques with recombinant simian varicella virus (rSVV) vector – simian immunodeficiency virus (SIV) envelope and gag genes, induced neutralizing antibodies and cellular immune responses to SIV and also significantly reduced plasma viral loads following intravenous pathogenic challenge with SIV_MAC251/CX1.

Findings

The purpose of this study was to define cellular immunological correlates of protection in rSVV-SIV vaccinated and SIV challenged animals. Immunofluorescent staining and multifunctional assessment of SIV-specific T-cell responses were evaluated in both Experimental and Control vaccinated animal groups. Significant increases in the proliferating CD4+ T-cell population and polyfunctional T-cell responses were observed in all Experimental-vaccinated animals compared with the Control-vaccinated animals.

Conclusions

Increased CD4+ T-cell proliferation was significantly and inversely correlated with plasma viral load. Increased SIV-specific polyfunctional cytokine responses and increased proliferation of CD4+ T-cell may be crucial to control plasma viral loads in vaccinated and SIV_MAC251/CX1 challenged macaques.

Cloning the simian varicella virus genome in E. coli as an infectious bacterial artificial chromosome

Simian varicella virus (SVV) is closely related to human varicella-zoster virus and causes varicella and zoster-like disease in nonhuman primates. In this study, a mini-F replicon was inserted into a SVV cosmid, and infectious SVV was generated by co-transfection of Vero cells with overlapping SVV cosmids. The entire SVV genome, cloned as a bacterial artificial chromosome (BAC), was stably propagated upon serial passage in E. coli. Transfection of pSVV-BAC DNA into Vero cells yielded infectious SVV (rSVV-BAC). The mini-F vector sequences flanked by loxP sites were removed by co-infection of Vero cells with rSVV-BAC and adenovirus expressing Cre-recombinase. Recombinant SVV generated using the SVV-BAC genetic system has similar molecular and in vitro replication properties as wild-type SVV. To demonstrate the utility of this approach, a SVV ORF 10 deletion mutant was created using two-step Red-mediated recombination. The results indicate that SVV ORF 10, which encodes a homolog of the HSV-1 virion VP-16 transactivator protein, is not essential for in vitro replication but is required for optimal replication in cell culture.

Replicating viral vectors as HIV vaccines: summary report from the IAVI-sponsored satellite symposium at the AIDS vaccine 2009 conference

In October 2009, The International AIDS Vaccine Initiative (IAVI) convened a satellite symposium entitled 'Replicating Viral Vectors for use in AIDS Vaccines' at the AIDS Vaccine 2009 Conference in Paris. The purpose of the symposium was to gather together researchers, representatives from regulatory agencies, and vaccine developers to discuss issues related to advancement of replication-competent viral vector- based HIV vaccines into clinical trials. The meeting introduced the rationale for accelerating the development of replicating viral vectors for use as AIDS vaccines. It noted that the EMEA recently published draft guidelines that are an important first step in providing guidance for advancing live viral vectors into clinical development. Presentations included case studies and development challenges for viral vector-based vaccine candidates. These product development challenges included cell substrates used for vaccine manufacturing, the testing needed to assess vaccine safety, conducting clinical trials with live vectors, and assessment of vaccination risk versus benefit. More in depth discussion of risk and benefit highlighted the fact that AIDS vaccine efficacy trials must be conducted in the developing world where HIV incidence is greatest and how inequities in global health dramatically influence the political and social environment in developing countries.

Recombinant varicella vaccines induce neutralizing antibodies and cellular immune responses to SIV and reduce viral loads in immunized rhesus macaques

The development of an effective AIDS vaccine remains one of the highest priorities in HIV research. The live, attenuated varicella-zoster virus (VZV) Oka vaccine, safe and effective for prevention of chickenpox and zoster, also has potential as a recombinant vaccine against other pathogens, including human immunodeficiency virus (HIV). The simian varicella model, utilizing simian varicella virus (SVV), offers an approach to evaluate recombinant varicella vaccine candidates. Recombinant SVV (rSVV) vaccine viruses expressing simian immunodeficiency virus (SIV) env and gag antigens were constructed. The hypothesis tested was that a live, attenuated rSVV-SIV vaccine will induce immune responses against SIV in the rhesus macaques and provide protection against SIV challenge. The results demonstrated that rSVV-SIV vaccination induced low levels of neutralizing antibodies and cellular immune responses to SIV in immunized rhesus macaques and significantly reduced viral loads following intravenous challenge with pathogenic SIVmac251-CX-1.

Simian varicella virus: molecular virology

Simian varicella virus (SVV) is a primate herpesvirus that is closely related to varicella-zoster virus (VZV), the causative agent of varicella (chickenpox) and herpes zoster (shingles). Epizootics of simian varicella occur sporadically in facilities housing Old World monkeys. This review summarizes the molecular properties of SVV. The SVV and VZV genomes are similar in size, structure, and gene arrangement. The 124.5 kilobase pair (kbp) SVV genome includes a 104.7 kbp long component covalently linked to a short component, which includes a 4.9 kbp unique short segment flanked by 7.5 kbp inverted repeat sequences. SVV DNA encodes 69 distinct open reading frames, three of which are duplicated within the viral inverted repeats. The viral genome is coordinately expressed, and immediate early (IE), early, and late genes have been characterized. Genetic approaches have been developed to create SVV mutants, which will be used to study the role of SVV genes in viral pathogenesis, latency, and reactivation. In addition, SVV expressing foreign genes are being investigated as potential recombinant varicella vaccines.

Replicating viral vectors as HIV vaccines Summary Report from IAVI Sponsored Satellite Symposium, International AIDS Society Conference, July 22, 2007

At the International AIDS Society Conference on Pathogenesis, Treatment and Prevention held in Sydney, Australia, in July 2007, the International AIDS Vaccine Initiative (IAVI) convened a satellite symposium entitled 'Accelerating the Development of Replicating Viral Vectors for AIDS Vaccines.' Its purpose was to highlight the rationale for accelerating the development of replicating viral vectors for use as vaccines against HIV-1, and to bring together vaccine scientists, regulatory officials, and public health specialists from industrialized and developing nations to discuss the major issues facing the development and testing of replicating viral vector-based vaccines.

Recombinant simian varicella viruses expressing respiratory syncytial virus antigens are immunogenic

Recombinant simian varicella viruses (rSVVs) were engineered to express respiratory syncytial virus (RSV) antigens. The RSV surface glycoprotein G and second matrix protein M2 (22k) genes were cloned into the SVV genome, and recombinant viruses were characterized in vitro and in vivo. rSVVs were also engineered to express the membrane-anchored or secreted forms of the RSV-G protein as well as an RSV G lacking its chemokine mimicry motif (CX3C), which may have different effects on priming the host immune response. The RSV genes were efficiently expressed in rSVV/RSV-infected Vero cells as RSV-G and -M2 transcripts were detected by RT-PCR, and RSV antigens were detected by immunofluorescence and immunoblot assays. The rSVVs replicated efficiently in Vero cell culture. Rhesus macaques immunized with rSVV/RSV-G and rSVV/RSV-M2 vaccines produced antibody responses to SVV and RSV antigens. The results demonstrate that recombinant varicella viruses are suitable vectors for the expression of RSV antigens and may represent a novel vaccine strategy for immunization against both pathogens.

Simian varicella in old world monkeys

Simian varicella virus (SVV) causes a natural erythematous disease in Old World monkeys and is responsible for simian varicella epizootics that occur sporadically in facilities housing nonhuman primates. This review summarizes the biology of SVV and simian varicella as a veterinary disease of nonhuman primates. SVV is closely related to varicella-zoster virus, the causative agent of human varicella and herpes zoster. Clinical signs of simian varicella include fever, vesicular skin rash, and hepatitis. Simian varicella may range from a mild infection to a severe and life-threatening disease, and epizootics may have high morbidity and mortality rates. SVV establishes a lifelong latent infection in neural ganglia of animals in which the primary disease resolves, and the virus may reactivate later in life to cause a secondary disease corresponding to herpes zoster. Prompt diagnosis is important for control and prevention of epizootics. Antiviral treatment for simian varicella may be effective if administered early in the course of infection.

Killing kinetics of simian immunodeficiency virus-specific CD8+ T cells: implications for HIV vaccine strategies

Both the magnitude and function of vaccine-induced HIV-specific CD8+ CTLs are likely to be important in the outcome of infection. We hypothesized that rapid cytolysis by CTLs may facilitate control of viral challenge. Release kinetics of the cytolytic effector molecules granzyme B and perforin, as well as the expression of the degranulation marker CD107a and IFN-gamma were simultaneously studied in SIV Gag(164-172) KP9-specific CD8+ T cells from Mane-A*10+ pigtail macaques. Macaques were vaccinated with either prime-boost poxvirus vector vaccines or live-attenuated SIV vaccines. Prime-boost vaccination induced Gag-specific CTLs capable of only slow (after 3 h) production of IFN-gamma and with limited (<5%) degranulation and granzyme B release. Vaccination with live-attenuated SIV resulted in a rapid cytolytic profile of SIV-specific CTLs with rapid (<0.5 h) and robust (>50% of tetramer-positive CD8+ T cells) degranulation and granzyme B release. The cytolytic phenotype following live-attenuated SIV vaccinations were similar to that associated with the partial resolution of viremia following SIV(mac251) challenge of prime-boost-vaccinated macaques, albeit with less IFN-gamma expression. High proportions of KP9-specific T cells expressed the costimulatory molecule CD28 when they exhibited a rapid cytolytic phenotype. The delayed cytolytic phenotype exhibited by standard vector-based vaccine-induced CTLs may limit the ability of T cell-based HIV vaccines to rapidly control acute infection following a pathogenic lentiviral exposure.

Simian varicella virus expresses a latency-associated transcript that is antisense to open reading frame 61 (ICP0) mRNA in neural ganglia of latently infected monkeys

Simian varicella virus (SVV) and varicella-zoster virus (VZV) are closely related alphaherpesviruses that cause varicella (chickenpox) in nonhuman primates and humans, respectively. After resolution of the primary disease, SVV and VZV establish latent infection of neural ganglia and may later reactivate to cause a secondary disease (herpes zoster). This study investigated SVV gene expression in neural ganglia derived from latently infected vervet monkeys. SVV transcripts were detected in neural ganglia, but not in liver or lung tissues, of latently infected animals. A transcript mapping to open reading frame (ORF) 61 (herpes simplex virus type 1 [HSV-1] ICP0 homolog) was consistently detected in latently infected trigeminal, cervical, and lumbar ganglia by reverse transcriptase PCR. Further analysis confirmed that this SVV latency-associated transcript (LAT) was oriented antisense to the gene 61 mRNA. SVV ORF 21 transcripts were also detected in 42% of neural ganglia during latency. In contrast, SVV ORF 28, 29, 31, 62, and 63 transcripts were not detected in ganglia, liver, or lung tissues of latently infected animals. The results demonstrate that viral gene expression is limited during SVV latency and that a LAT antisense to an ICP0 homolog is expressed. In this regard, SVV gene expression during latency is similar to that of HSV-1 and other neurotropic animal alphaherpesviruses but differs from that reported for VZV.