Yellow Fever Virus 17D Strain Research Articles

Construction and evaluation of a self-replicative RNA vaccine against SARS-CoV-2 using yellow fever virus replicon.

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a global threat. To forestall the pandemic, developing safe and effective vaccines is necessary. Because of the rapid production and little effect on the host genome, mRNA vaccines are attractive, but they have a relatively low immune response after a single dose. Replicon RNA (repRNA) is a promising vaccine platform for safety and efficacy. RepRNA vaccine encodes not only antigen genes but also the genes necessary for RNA replication. Thus, repRNA is self-replicative and can play the role of an adjuvant by itself, which elicits robust immunity. This study constructed and evaluated a repRNA vaccine in which the gene encoding the spike (S) protein of SARS-CoV-2 was inserted into a replicon of yellow fever virus 17D strain. Upon electroporation of this repRNA into baby hamster kidney cells, the S protein and yellow fever virus protein were co-expressed. Additionally, the self-replication ability of repRNA vaccine was confirmed using qRT-PCR, demonstrating its potency as a vaccine. Immunization of C57BL/6 mice with 1 μg of the repRNA vaccine induced specific T-cell responses but not antibody responses. Notably, the T-cell response induced by the repRNA vaccine was significantly higher than that induced by the nonreplicative RNA vaccine in our experimental model. In the future, it is of the essence to optimize vaccine administration methods and improve S protein expression, like protection of repRNA by nanoparticles and evasion of innate immunity of the host to enhance the immune-inducing ability of the repRNA vaccine.

Development of inactivated cultural yellow fever vaccine

The only currently available live vaccine against yellow fever (YF) based on chicken embryos infected with an attenuated 17D strain of the YF virus is one of the most effective vaccine preparations. However, the live vaccine is associated with "viscerotropic syndrome" (approximately 0.4 cases per 100 000 vaccinated). Therefore, the development and introduction of highly purified inactivated vaccine against YF is intended to ensure the maximum safety of vaccination against one of the most common human viral diseases.Goals and objectives. Development and evaluation of immunogenicity of the cultural inactivated vaccine against YF at the laboratory model level. Adaptation of 17D strain of YF virus to Vero cell culture, cultivation, removal of cellular DNA, inactivation with β-propiolactone, concentration, chromatographic purification, determination of protein and antigen of YF virus, assessment of immunogenicity in mice in parallel with commercial live vaccine. Immunogenicity: the determination of specific antibodies of class G (IgG) and virus neutralizing antibodies in the sera of immunized mice showed high level of antibodies exceeding that of immunized with commercial live vaccine. The optimal dose of antigen in the vaccine (total protein) was 50 μg/ml (5 μg/0.1 ml -dose and volume per 1 vaccination of mice). Thus, the laboratory version of cultural inactivated vaccine against YF is as effective (and even superior) as the commercial live vaccine. Laboratory version of cultural inactivated vaccine against YF, which is not inferior in immunogenicity (in animal model) to commercial live vaccine, has been developed.

Refractoriness of Indian Aedes aegypti to Oral Infection with Yellow Fever Virus 17D Strain

Yellow fever virus (YFV) is the causative agent of yellow fever. It is one of the most important hemorrhagic arboviral infection of global public health significance. It is categorised under category ‘C’ of potential bioterrorism agent. Effect of geographical variation on vector competence in Ae. aegypti has been well documented for several viruses including YFV. In the present study, the vector competence of Ae. aegypti mosquitoes collected from Gwalior, India for YFV 17D vaccine strain was evaluated to understand the risk of its transmission. Further the risk associated with transmission of YFV 17D vaccine strain from viremic vaccinees to mosquitoes and subsequently to naive individuals was assessed. Ae. aegypti were orally infected with high titer of YFV 17D strain and the infection status was investigated at 7 and 14 day post infection (dpi) using a highly sensitive quantitative RT-PCR assay. None of the Ae. aegypti mosquito orally infected with YFV 17D strain was found to be positive for YFV. The infection rate was found to be zero per cent at both 7 dpi and 14 dpi. These results demonstrated the inability of the YFV 17D strain to cause infection or replication in the midgut of Ae. aegypti. Due to the highly attenuated replication of this strain in Ae. aegypti midgut, there is a minimal risk of its transmission. Further, it is unlikely for a mosquito that feeds on a viremic vaccine to get infected with this vaccine strain. The risk of transmission of YFV 17D strain by Indian Ae. aegypti mosquitoes is negligible. Further vector competence study using epidemic strain of YFV will aid in risk assessment analysis of YFV in India.

Pre-Clinical Efficacy and Safety of Experimental Vaccines Based on Non-Replicating Vaccinia Vectors against Yellow Fever

BackgroundCurrently existing yellow fever (YF) vaccines are based on the live attenuated yellow fever virus 17D strain (YFV-17D). Although, a good safety profile was historically attributed to the 17D vaccine, serious adverse events have been reported, making the development of a safer, more modern vaccine desirable.Methodology/Principal FindingsA gene encoding the precursor of the membrane and envelope (prME) protein of the YFV-17D strain was inserted into the non-replicating modified vaccinia virus Ankara and into the D4R-defective vaccinia virus. Candidate vaccines based on the recombinant vaccinia viruses were assessed for immunogenicity and protection in a mouse model and compared to the commercial YFV-17D vaccine. The recombinant live vaccines induced γ-interferon-secreting CD4- and functionally active CD8-T cells, and conferred full protection against lethal challenge already after a single low immunization dose of 105 TCID50. Surprisingly, pre-existing immunity against wild-type vaccinia virus did not negatively influence protection. Unlike the classical 17D vaccine, the vaccinia virus-based vaccines did not cause mortality following intracerebral administration in mice, demonstrating better safety profiles.Conclusions/SignificanceThe non-replicating recombinant YF candidate live vaccines induced a broad immune response after single dose administration, were effective even in the presence of a pre-existing immunity against vaccinia virus and demonstrated an excellent safety profile in mice.

Distinctive TLR7 Signaling, Type I IFN Production, and Attenuated Innate and Adaptive Immune Responses to Yellow Fever Virus in a Primate Reservoir Host

Why cross-species transmissions of zoonotic viral infections to humans are frequently associated with severe disease when viruses responsible for many zoonotic diseases appear to cause only benign infections in their reservoir hosts is unclear. Sooty mangabeys (SMs), a reservoir host for SIV, do not develop disease following SIV infection, unlike nonnatural HIV-infected human or SIV-infected rhesus macaque (RM) hosts. SIV infections of SMs are characterized by an absence of chronic immune activation, in association with significantly reduced IFN-α production by plasmacytoid dendritic cells (pDCs) following exposure to SIV or other defined TLR7 or TLR9 ligands. In this study, we demonstrate that SM pDCs produce significantly less IFN-α following ex vivo exposure to the live attenuated yellow fever virus 17D strain vaccine, a virus that we show is also recognized by TLR7, than do RM or human pDCs. Furthermore, in contrast to RMs, SMs mount limited activation of innate immune responses and adaptive T cell proliferative responses, along with only transient antiviral Ab responses, following infection with yellow fever vaccine 17D strain. However, SMs do raise significant and durable cellular and humoral immune responses comparable to those seen in RMs when infected with modified vaccinia Ankara, a virus whose immunogenicity does not require TLR7/9 recognition. Hence, differences in the pattern of TLR7 signaling and type I IFN production by pDCs between primate species play an important role in determining their ability to mount and maintain innate and adaptive immune responses to specific viruses, and they may also contribute to determining whether disease follows infection.

Envelope protein as molecular target for YFV (Yellow fever virus) drug discovery

AbstractYellow fever (YF), a mosquito-borne viral haemorrhagic fever, is one of the most lethal viral diseases. Despite the availability of vaccines, yellow fever virus (YFV) strikes an estimated 2, 00,000 persons world-wide each year and causes 30,000 deaths approximately. There are no approved antiviral therapies for the treatment of YFV disease in humans. YFV 17D strain RNA genome is of 10,862 nucleotides, which encodes three structural proteins (C, PrM, and E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). Identification of different protein functions facilitates a mechanistic understanding of YFV infection and opens novel means for drug development. Functional assignment of complete YFV proteome was done through support Vector machine (SVM). Significant functions of YFV Envelope (E) protein are Transmembrane, Aptamer-binding protein, Coat protein, Zinc-binding, Manganese-binding and Metal-binding etc. The E protein being non homologous to human and important in receptor binding, hemagglutination of erythrocytes at acidic pH, induction of the protective immune response, and involvement in an intraendosomal acid-catalyzed fusion step necessary for infection was selected as a potent molecular target against YFV drug discovery. 3D structure of target protein E protein is predicted using MODELLER9V6 and validated through PROCHECK analysis. The Binding site tool of Discovery Studio 2.0 was used to find sites all over protein. Heparin was identified as an important ligand against the molecular target and was docked to the functionally important binding site using LigandFit protocol. The YFV E protein -Heparin docking complex associated with strong hydrogen bonding with SER 483, GLN 443 and ALA 441 residues. The strong docking interaction may impede the infection causes due to association of YFV E protein and Core membrane. Further, the predicted model can be used as reference towards designing candidate drugs against YFV.

Envelope protein as molecular target for YFV (Yellow fever virus) drug discovery

Yellow fever (YF), a mosquito-borne viral haemorrhagic fever, is one of the most lethal viral diseases. Despite the availability of vaccines, yellow fever virus (YFV) strikes an estimated 2, 00,000 persons world-wide each year and causes 30,000 deaths approximately. There are no approved antiviral therapies for the treatment of YFV disease in humans. YFV 17D strain RNA genome is of 10,862 nucleotides, which encodes three structural proteins (C, PrM, and E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). Identification of different protein functions facilitates a mechanistic understanding of YFV infection and opens novel means for drug development. Functional assignment of complete YFV proteome was done through support Vector machine (SVM). Significant functions of YFV Envelope (E) protein are Transmembrane, Aptamer-binding protein, Coat protein, Zinc-binding, Manganese-binding and Metal-binding etc. The E protein being non homologous to human and important in receptor binding, hemagglutination of erythrocytes at acidic pH, induction of the protective immune response, and involvement in an intraendosomal acid-catalyzed fusion step necessary for infection was selected as a potent molecular target against YFV drug discovery. 3D structure of target protein E protein is predicted using MODELLER9V6 and validated through PROCHECK analysis. The Binding site tool of Discovery Studio 2.0 was used to find sites all over protein. Heparin was identified as an important ligand against the molecular target and was docked to the functionally important binding site using LigandFit protocol. The YFV E protein -Heparin docking complex associated with strong hydrogen bonding with SER 483, GLN 443 and ALA 441 residues. The strong docking interaction may impede the infection causes due to association of YFV E protein and Core membrane. Further, the predicted model can be used as reference towards designing candidate drugs against YFV.

Evaluation of yellow fever virus 17D strain as a new vector for HIV-1 vaccine development

The failure to develop an effective vaccine against HIV-1 infection has led the research community to seek new ways of raising qualitatively different antibody and cellular immune responses. Towards this goal, we investigated the yellow fever 17D vaccine strain (YF17D), one of the most effective vaccines ever made, as a platform for HIV-1 vaccine development. A test antigen, HIV-1 p24 (clade B consensus), was inserted near the 5′ end of YF17D, in frame and upstream of the polyprotein (YF-5′/p24), or between the envelope and the first non-structural protein (YF-E/p24/NS1). In vitro characterization of these recombinants indicated that the gene insert was more stable in the context of YF-E/p24/NS1. This was confirmed in immunogenicity studies in mice. CD8+ IFN-γ T-cell responses against p24 were elicited by the YF17D recombinants, as were specific CD4+ T cells expressing IFN-γ and IL-2. A balanced CD4+ and CD8+ T-cell response was notable, as was the polyfunctionality of the responding cells. Finally, the protective efficacy of the YF17D recombinants, particularly YF-E/p24/NS1, in mice challenged with a vaccinia expressing HIV-1 Gag was demonstrated. These results suggest that YF17D warrants serious consideration as a live-attenuated vector for HIV-1 vaccine development.

Yellow fever virus/dengue-2 virus and yellow fever virus/dengue-4 virus chimeras: biological characterization, immunogenicity, and protection against dengue encephalitis in the mouse model.

Two yellow fever virus (YFV)/dengue virus chimeras which encode the prM and E proteins of either dengue virus serotype 2 (dengue-2 virus) or dengue-4 virus within the genome of the YFV 17D strain (YF5.2iv infectious clone) were constructed and characterized for their properties in cell culture and as experimental vaccines in mice. The prM and E proteins appeared to be properly processed and glycosylated, and in plaque reduction neutralization tests and other assays of antigenic specificity, the E proteins exhibited profiles which resembled those of the homologous dengue virus serotypes. Both chimeric viruses replicated in cell lines of vertebrate and mosquito origin to levels comparable to those of homologous dengue viruses but less efficiently than the YF5.2iv parent. YFV/dengue-4 virus, but not YFV/dengue-2 virus, was neurovirulent for 3-week-old mice by intracerebral inoculation; however, both viruses were attenuated when administered by the intraperitoneal route in mice of that age. Single-dose inoculation of either chimeric virus at a dose of 10(5) PFU by the intraperitoneal route induced detectable levels of neutralizing antibodies against the homologous dengue virus strains. Mice which had been immunized in this manner were fully protected from challenge with homologous neurovirulent dengue viruses by intracerebral inoculation compared to unimmunized mice. Protection was associated with significant increases in geometric mean titers of neutralizing antibody compared to those for unimmunized mice. These data indicate that YFV/dengue virus chimeras elicit antibodies which represent protective memory responses in the mouse model of dengue encephalitis. The levels of neurovirulence and immunogenicity of the chimeric viruses in mice correlate with the degree of adaptation of the dengue virus strain to mice. This study supports ongoing investigations concerning the use of this technology for development of a live attenuated viral vaccine against dengue viruses.

CIRCULATING VIRUS, INTERFERON AND ANTIBODY AFTER VACCINATION WITH THE 17-D STRAIN OF YELLOW-FEVER VIRUS.

CIRCULATING interferon has been induced in laboratory animals by the inoculation of several different viruses.1 , 2 In man circulating interferon has been detected after the intravenous administration of viruses to a patient with acute leukemia3 as well as in a number of patients with naturally occurring clinical viral infections.4 In the latter the lack of virus isolations precluded the establishment of any relation between the type of virus, time of infection and virus, interferon and antibody production. In an attempt to establish these relations recent studies both in this laboratory and elsewhere have been concerned with infections produced by live-virus vaccines, . . .