T Cell-Mediated Immunity towards Yellow Fever Virus and Useful Animal Models

Yellow Fever: Global Impact, Epidemiology, Pathogenesis, and Integrated Prevention Approaches

Yellow fever poses a substantial global health concern as one of the re-emerging diseases with pandemic potential in a scenario of the worldwide distribution of some vectors (such as Aedes aegypti); in the context of climatic change, an unclear knowledge about the immune behaviour of the virus, between other determinants. This review details the historical foundations, intricate evolution of geographical spread, and transmission mechanisms of the disease to understand the behaviour of outbreaks over time in a multifactorial context that could be difficult to understand. This article approaches to epidemiological, pathophysiological, immunological, social determinants, and climatic crisis by understanding possible control mechanisms and anticipating potential future epidemics. This article explores the evidence of yellow fever virus (YFV) pathogenesis and its complex interactions with the immune response in the host, the vector, and in the context of immunisation. These discussions contribute to a more comprehensive understanding of the disease's progression. Despite the global presence of the vector and other factors that could facilitate an epidemic spread, yellow fever outbreaks have remained confined to specific endemic areas. This limited distribution is not entirely understood. However, it may be influenced by the complex immune interactions between the virus, the vector, and the host, preventing its spread to other regions.

Baculovirus surface display of a chimeric E-NS1 protein of YFV protects against YFV infection

Yellow fever (YF) is a disease caused by the homonymous flavivirus that can be prevented by a vaccine containing attenuated viruses. Since some individuals cannot receive this vaccine, the development of alternatives is desirable. Here, we developed a recombinant baculovirus (rBV) surface display platform utilizing a chimeric E-NS1 protein as a vaccine candidate. A pBacPAK9 vector containing the baculoviral GP64 signal peptide, the YFV prM, E, NS1 and the ectodomain of VSV-G sequences was synthesized. This transfer plasmid and the bAcGOZA bacmid were cotransfected into Sf9 cells, and an rBV-E-NS1 was obtained, which was characterized by PCR, WB, IFI and FACS analysis. Mice immunized with rBV-E-NS1 elicited a specific humoral and cellular immune response and were protected after YFV infection. In summary, we have developed an rBV that expresses YFV major antigen proteins on its surface, which opens new alternatives that can be tested in a mouse model.

Next generation yellow fever vaccine induces an equivalent immune and transcriptomic profile to the current vaccine: observations from a phase I randomised clinical trial

BACKGROUND

Yellow fever (YF), a mosquito-borne acute viral haemorrhagic illness, is endemic to many tropical and subtropical areas of Africa and Central and South America. Vaccination remains the most effective prevention strategy; however, as repeated outbreaks have exhausted vaccine stockpiles, there is a need for improved YF vaccines to meet global demand. A live-attenuated YF vaccine candidate (referred to as vYF) cloned from a YF-17D vaccine (YF-VAX®) sub-strain, adapted for growth in Vero cells cultured in serum-free media, is in clinical development. We report the innate and adaptive immune responses and the transcriptome profile of selected genes induced by vYF.

METHODS

Healthy adults aged 18-60 years were randomised at a 1:1:1:1 ratio to receive one dose of vYF at 4, 5 or 6 Log CCID50 or YF-VAX (reference vaccine), administered subcutaneously in the upper arm (ClinicalTrials.gov identifier: NCT04142086). Blood/serum samples were obtained at scheduled time points through 180 days (D180) post-vaccination. The surrogate endpoints assessed were: serum cytokine/chemokine concentrations, measured by bead-based Multiplex assay; peripheral blood vYF-specific IgG and IgM memory B cell frequencies, measured by FluoroSpot assay; and expression of genes involved in the immune response to YF-17D vaccination by RT-qPCR.

FINDINGS

There was no increase in any of the cytokine/chemokine concentrations assessed through D14 following vaccination with vYF or YF-VAX, except for a slight increase in IP-10 (CXCL10) levels. The gene expression profiles and kinetics following vaccination with vYF and YF-VAX were similar, inclusive of innate (antiviral responses [type-1 interferon, IFN signal transduction; interferon-stimulated genes], activated dendritic cells, viral sensing pattern recognition receptors) and adaptive (cell division in stimulated CD4+ T cells, B cell and antibody) immune signatures, which peaked at D7 and D14, respectively. Increases in vYF-specific IgG and IgM memory B cell frequencies at D28 and D180 were similar across the study groups.

INTERPRETATION

vYF-induced strong innate and adaptive immune responses comparable to those induced by YF-VAX, with similar transcriptomic and kinetic profiles observed.

FUNDING

Sanofi.

Harnessing T-Cells for Enhanced Vaccine Development against Viral Infections

Despite significant strides in vaccine research and the availability of vaccines for many infectious diseases, the threat posed by both known and emerging infectious diseases persists. Moreover, breakthrough infections following vaccination remain a concern. Therefore, the development of novel vaccines is imperative. These vaccines must exhibit robust protective efficacy, broad-spectrum coverage, and long-lasting immunity. One promising avenue in vaccine development lies in leveraging T-cells, which play a crucial role in adaptive immunity and regulate immune responses during viral infections. T-cell recognition can target highly variable or conserved viral proteins, and memory T-cells offer the potential for durable immunity. Consequently, T-cell-based vaccines hold promise for advancing vaccine development efforts. This review delves into the latest research advancements in T-cell-based vaccines across various platforms and discusses the associated challenges.

Standardization, validation, and comparative evaluation of a faster and high-performance test for quantification of yellow fever neutralizing antibodies

Although it is considered the reference for quantification of neutralizing antibodies, classical method of the plaque reduction neutralization test (PRNT) is labor intensive, requires specific equipment and inputs, besides a long time for its finalization, even in the micro-PRNT version (in 96-well plates). It has a higher sample throughput, however the smaller wells make the reading of plaques more difficult. With an immunoenzymatic revelation step and a semi-automated reading, the μFRN-HRP (micro Focus Reduction Neutralization - Horseradish Peroxidase) is a faster and more efficient test for the quantification of YF neutralizing antibodies. This study aimed to standardize, validate, and compare it with the reference method in 6-well plates (PRNT). Once the execution protocol was standardized, precision, accuracy, selectivity, and robustness were evaluated to validate the μFRN-HRP. In addition, 200 sera of vaccinees were processed by the μFRN-HRP and by the micro-PRNT to compare with the reference test, estimating agreement by Intraclass Correlation Coefficient (ICC). The standardization and validation of the μFRN-HRP was carried out successfully. Weak to moderate agreement was observed between μFRN-HRP and PRNT for titers in reciprocal dilution, while the same comparison between the classical tests resulted in a better ICC. However, titers in milli-international units obtained by μFRN-HRP showed a substantial agreement with PRNT, while the agreement between micro-PRNT and PRNT was inferior. Therefore, μFRN-HRP can be used in the confirmation of natural YF infection and immune response to vaccination, replacing the micro-PRNT, gaining agility, while preserving the specificity of the result.

The next frontier in vaccine design: blending immune correlates of protection into rational vaccine design

Despite the extraordinary speed and success in SARS-Cov-2 vaccine development, the emergence of variants of concern perplexed the vaccine development community. Neutralizing antibodies waned antibodies waned and were evaded by viral variants, despite the preservation of protection against severe disease and death across vaccinated populations. Similar to other vaccine design efforts, the lack of mechanistic correlates of immunity against Coronavirus Disease 2019, raised questions related to the need for vaccine redesign and boosting. Hence, our limited understanding of mechanistic correlates of immunity - across pathogens - remains a major obstacle in vaccine development. The identification and incorporation of mechanistic correlates of immunity are key to the accelerated design of highly impactful globally relevant vaccines. Systems-biology tools can be applied strategically to define a complete understanding of mechanistic correlates of immunity. Embedding immunological dissection and target immune profile identification, beyond canonical antibody binding and neutralization, may accelerate the design and success of durable protective vaccines.

Yellow fever vaccination in Brazil: Short-term safety and immunogenicity in juvenile autoimmune rheumatic diseases

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We examined 17DD yellow fever vaccine in juvenile autoimmune rheumatic disease patients under low immunosuppression during the recent epidemic in Sao Paulo-Brazil.

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No serious adverse events were reported and frequencies of mild adverse events were comparable between patients and healthy controls.

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Immunogenicity parameters against yellow fever vaccine were not hampered in juvenile autoimmune rheumatic disease patients.

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Peripheral white-blood-cells kinetics after yellow fever vaccination was demonstrated with transient decreases in lymphocytes at D5 and neutrophil levels at D10 with complete recovery at D30.

Yellow fever vaccine (YFV) is a live attenuated vaccine usually contraindicated for juvenile autoimmune rheumatic disease (JARD) patients. During the recent epidemic in Sao Paulo-Brazil, YFV was indicated for patients under low immunosuppression. Thirty JARD patients with inactive diseases undergoing low immunosuppression and 30 healthy controls (HC) were vaccinated with a fractional dose 17DD YFV (∼5495 IU) and evaluated 30 days later. JARD patients and controls had comparable median age (12.4 vs. 12 years, p = 0.250). Disease parameters remained stable 30 days after 17DD YFV (p > 0.05) and only mild adverse events were reported in both groups (p > 0.05). JARD and HC had similar seroprotection [93% vs. 100%;p = 0.49], seroconversion rates [96% vs. 100%;p = 0.489], and GMT [1249 vs.1293;p = 0.821]. Both groups had similar white-blood-cells kinetics with transient decreases in lymphocytes at D5 and neutrophils at D10, followed by full recovery at D30 (P < 0.05). In conclusion, 17DD YFV was safe and immunogenic in JARD. This study may contribute to recommendations for patients living/travelling to endemic areas.

Review of -omics studies on mosquito-borne viruses of the Flavivirus genus

Arboviruses are transmitted by arthropods (arthropod-borne virus) which can be mosquitoes or other hematophagous arthropods, in which their life cycle occurs before transmission to other hosts. Arboviruses such as Dengue, Zika, Saint Louis Encephalitis, West Nile, Yellow Fever, Japanese Encephalitis, Rocio and Murray Valley Encephalitis viruses are some of the arboviruses transmitted biologically among vertebrate hosts by blood-taking vectors, mainly Aedes and Culex sp., and are associated with neurological, viscerotropic, and hemorrhagic reemerging diseases, posing as significant health and socioeconomic concern, as they become more and more adaptive to new environments, to arthropods vectors and human hosts. One of the main families that include mosquito-borne viruses is Flaviviridae, and here, we review the case of the Flavivirus genus, which comprises the viruses cited above, using a variety of research approaches published in literature, including genomics, transcriptomics, proteomics, metabolomics, etc., to better understand their structures as well as virus-host interactions, which are essential for development of future antiviral therapies.

A Yellow Fever 17D Virus Replicon-Based Vaccine Platform for Emerging Coronaviruses

The tremendous global impact of the current SARS-CoV-2 pandemic, as well as other current and recent outbreaks of (re)emerging viruses, emphasize the need for fast-track development of effective vaccines. Yellow fever virus 17D (YF17D) is a live-attenuated virus vaccine with an impressive efficacy record in humans, and therefore, it is a very attractive platform for the development of novel chimeric vaccines against various pathogens. In the present study, we generated a YF17D-based replicon vaccine platform by replacing the prM and E surface proteins of YF17D with antigenic subdomains from the spike (S) proteins of three different betacoronaviruses: MERS-CoV, SARS-CoV and MHV. The prM and E proteins were provided in trans for the packaging of these RNA replicons into single-round infectious particles capable of expressing coronavirus antigens in infected cells. YF17D replicon particles expressing the S1 regions of the MERS-CoV and SARS-CoV spike proteins were immunogenic in mice and elicited (neutralizing) antibody responses against both the YF17D vector and the coronavirus inserts. Thus, YF17D replicon-based vaccines, and their potential DNA- or mRNA-based derivatives, may constitute a promising and particularly safe vaccine platform for current and future emerging coronaviruses.

Development of a neutralizing antibody targeting linear epitope of the envelope protein domain III of ZIKV

Zika virus (ZIKV) infection represents an emerging infectious disease that poses an increasing threat to human health, especially after the ZIKV outbreak in Brazil in 2015. Unfortunately, there continues to be a lack of highly effective antiviral drugs or vaccines against ZIKV. In this study, we expressed the ZIKV envelope protein domain III (ZIKV EDIII) in E. coli strain BL21. The purified recombinant protein was used to immunize mice to produce monoclonal antibodies (mAbs). After 6 screening and 5 subcloning cycles, 10 monoclonal cell lines that stably produced antibodies, termed 2F5, 5B8, 6G6, 7E12, 8B6, 17E6, 19E7, 20F4, 26G6, and 37E6, were identified. The mAb 8B6 could neutralize ZIKV and recognize the ZIKV EDIII epitope (GRLITANPVITESTE). Another 9 mAbs did not exhibit neutralizing activity; however, they could specifically recognize the ZIKV EDIII and ZIKV lysate, suggesting their potential use in the diagnosis of ZIKV.

Activation and Kinetics of Circulating T Follicular Helper Cells, Specific Plasmablast Response, and Development of Neutralizing Antibodies following Yellow Fever Virus Vaccination

A single dose of the replication-competent, live-attenuated yellow fever virus (YFV) 17D vaccine provides lifelong immunity against human YFV infection. The magnitude, kinetics, and specificity of B cell responses to YFV 17D are relatively less understood than T cell responses. In this clinical study, we focused on early immune events critical for the development of humoral immunity to YFV 17D vaccination in 24 study subjects. More specifically, we studied the dynamics of several immune cell populations over time and the development of neutralizing Abs. At 7 d following vaccination, YFV RNA in serum as well as several antiviral proteins were detected as a sign of YFV 17D replication. Activation of Th1-polarized circulating T follicular helper cells followed germinal center activity, the latter assessed by the surrogate marker CXCL13 in serum. This coincided with a plasmablast expansion peaking at day 14 before returning to baseline levels at day 28. FluoroSpot-based analysis confirmed that plasmablasts were specific to the YFV-E protein. The frequencies of plasmablasts correlated with the magnitude of neutralizing Ab titers measured at day 90, suggesting that this transient B cell subset could be used as an early marker of induction of protective immunity. Additionally, YFV-specific memory B cells were readily detectable at 28 and 90 d following vaccination, and all study subjects tested developed protective neutralizing Ab titers. Taken together, these studies provide insights into key immune events leading to human B cell immunity following vaccination with the YFV 17D vaccine.

What Constitutes Protective Immunity Following Yellow Fever Vaccination?

Yellow fever (YF) remains a threat to global health, with an increasing number of major outbreaks in the tropical areas of the world over the recent past. In light of this, the Eliminate Yellow Fever Epidemics Strategy was established with the aim of protecting one billion people at risk of YF through vaccination by the year 2026. The current YF vaccine gives excellent protection, but its use is limited by shortages in supply due to the difficulties in producing the vaccine. There are good grounds for believing that alternative fractional dosing regimens can produce strong protection and overcome the problem of supply shortages as less vaccine is required per person. However, immune responses to these vaccination approaches are yet to be fully understood. In addition, published data on immune responses following YF vaccination have mostly quantified neutralising antibody titers. However, vaccine-induced antibodies can confer immunity through other antibody effector functions beyond neutralisation, and an effective vaccine is also likely to induce strong and persistent memory T cell responses. This review highlights the gaps in knowledge in the characterisation of YF vaccine-induced protective immunity in the absence or presence of neutralising antibodies. The assessment of biophysical antibody characteristics and cell-mediated immunity following YF vaccination could help provide a comprehensive landscape of YF vaccine-induced immunity and a better understanding of correlates of protective immunity.

Yellow fever virus vaccination: an emblematic model to elucidate robust human immune responses

By preventing infectious diseases, vaccines contribute substantially to public health. Besides, they offer great opportunities to investigate human immune responses. This is particularly true for live-attenuated virus vaccines which cause resolving acute infections and induce robust immunity. The fact that one can precisely schedule the time-point of vaccination enables complete characterization of the immune response over time, short-term and over many years. The live-attenuated Yellow Fever virus vaccine strain YF-17D was developed in the 1930's and gave rise to the 17D-204 and 17DD vaccine sub-strains, administered to over 600 million individuals worldwide. YF vaccination causes a systemic viral infection, which induces neutralizing antibodies that last for a lifetime. It also induces a strong T cell response resembling the ones of acute infections, in contrast to most other vaccines. In spite of its use since 1937, learning how YF vaccination stimulates such strong and persistent immune responses has gained substantial knowledge only in the last decades. Here we summarize the current state of knowledge on the immune response to YF vaccination, and discuss its contribution as a human model to address complex questions on optimal immune responses.

Activation of an Effective Immune Response after Yellow Fever Vaccination Is Associated with the Genetic Background and Early Response of IFN-γ and CLEC5A

The yellow fever vaccine (YF17DD) is highly effective with a single injection conferring protection for at least 10 years. The YF17DD induces polyvalent responses, with a TH1/TH2 CD4⁺ profile, robust T CD8⁺ responses, and synthesis of interferon-gamma (IFN-γ), culminating in high titers of neutralizing antibodies. Furthermore, C-type lectin domain containing 5A (CLEC5A) has been implicated in innate outcomes in other flaviviral infections. Here, we conducted a follow-up study in volunteers immunized with YF17DD, investigating the humoral response, cellular phenotypes, gene expression, and single nucleotide polymorphisms (SNPs) of IFNG and CLEC5A, to clarify the role of these factors in early response after vaccination. Activation of CLEC5A⁺ monocytes occurred five days after vaccination (DAV). Following, seven DAV data showed activation of CD4⁺ and CD8⁺T cells together with early positive correlations between type II IFN and genes of innate antiviral response (STAT1, STAT2, IRF7, IRF9, OAS1, and RNASEL) as well as antibody levels. Furthermore, individuals with genotypes rs2430561 AT/AA, rs2069718 AG/AA (IFNG), and rs13237944 AC/AA (CLEC5A), exhibited higher expression of IFNG and CLEC5A, respectively. Together, we demonstrated that early IFN-γ and CLEC5A responses, associated with rs2430561, rs2069718, and rs13237944 genotypes, may be key mechanisms in the long-lasting immunity elicited by YF17DD.

Absence of YF-neutralizing antibodies in vulnerable populations of Brazil: A warning for epidemiological surveillance and the potential risks for future outbreaks

Yellow Fever (YF) is an acute febrile illness caused by yellow fever virus (YFV), a mosquito-borne flavivirus transmitted to humans and non-human primates. In Brazil, YF is a public health threat and may cause recurrent epidemics, even with the availability of a vaccine. We evaluated the sero-status for YFV in 581 individuals living in a risk area for YF in Brazil. The area presents history of cases and is located in the southeast region of country where outbreaks of YF have been reported since 2016. Through, a PRNT assay, we found 25.8% of individuals lacking YF-neutralizing antibodies. Furthermore, neutralizing antibodies were not detected in 10 individuals with proven vaccination. Our findings reinforce the importance of surveillance systems and the need of an urgent intensification of immunization programs in regions with YFV circulation. Monitoring susceptible individuals that could act as potential disseminators for YFV in risk areas should also be considered.

A Yellow Fever Virus 17D Infection and Disease Mouse Model Used to Evaluate a Chimeric Binjari-Yellow Fever Virus Vaccine

Despite the availability of an effective, live attenuated yellow fever virus (YFV) vaccine (YFV 17D), this flavivirus still causes up to ≈60,000 deaths annually. A number of new approaches are seeking to address vaccine supply issues and improve safety for the immunocompromised vaccine recipients. Herein we describe an adult female IFNAR-/- mouse model of YFV 17D infection and disease that recapitulates many features of infection and disease in humans. We used this model to evaluate a new YFV vaccine that is based on a recently described chimeric Binjari virus (BinJV) vaccine technology. BinJV is an insect-specific flavivirus and the chimeric YFV vaccine (BinJ/YFV-prME) was generated by replacing the prME genes of BinJV with the prME genes of YFV 17D. Such BinJV chimeras retain their ability to replicate to high titers in C6/36 mosquito cells (allowing vaccine production), but are unable to replicate in vertebrate cells. Vaccination with adjuvanted BinJ/YFV-prME induced neutralizing antibodies and protected mice against infection, weight loss and liver pathology after YFV 17D challenge.

Transcriptomic immune profiles of human flavivirus-specific T-cell responses

The Flavivirus genus of viruses includes dengue (DENV), Zika (ZIKV), yellow fever (YFV), Japanese encephalitis (JEV), and West Nile (WNV) viruses. Infections with these species combined are prevalent in tropical and sub-tropical areas, affecting millions of people and ranging from asymptomatic to severe forms of the disease. They therefore pose a serious threat to global public health. Several studies imply a role for T cells in the protection but also pathogenesis against the different flavivirus species. Identifying flavivirus-specific T-cell immune profiles and determining how pre-exposure of one species might affect the immune response against subsequent infections from other species is important to further define the role of T cells in the immune response against infection. Understanding the immune profiles of the flavivirus-specific T-cell response in natural infection is important to understand the T-cell response in the context of vaccination. In this review, we summarize the current knowledge on human immune profiles of flavivirus-specific T-cell reactivity, comparing natural infection with the acute form of the disease and vaccination in different flavivirus infections.

Randomized, double-blinded, controlled non-inferiority trials evaluating the immunogenicity and safety of fractional doses of Yellow Fever vaccines in Kenya and Uganda

Introduction: Yellow fever is endemic in specific regions of sub-Saharan Africa and the Americas, with recent epidemics occurring on both continents. The yellow fever vaccine is effective, affordable and safe, providing life-long immunity following a single dose vaccination. However, the vaccine production process is slow and cannot be readily scaled up during epidemics. This has led the World Health Organization (WHO) to recommend the use of fractional doses as a dose-sparing strategy during epidemics, but there are no randomized controlled trials of fractional yellow fever vaccine doses in Africa. Methods and analysis: We will recruit healthy adult volunteers, adults living with HIV, and children to a series of randomized controlled trials aiming to determine the immunogenicity and safety of fractional vaccine doses in comparison to the standard vaccine dose. The trials will be conducted across two sites; Kilifi, Kenya and Mbarara, Uganda. Recruited participants will be randomized to receive fractional or standard doses of yellow fever vaccine. Scheduled visits will include blood collection for serum and peripheral blood mononuclear cells (PBMCs) before vaccination and on various days - up to 2 years - post-vaccination. The primary outcome is the rate of seroconversion as measured by the plaque reduction neutralization test (PRNT 50) at 28 days post-vaccination. Secondary outcomes include antibody titre changes, longevity of the immune response, safety assessment using clinical data, the nature and magnitude of the cellular immune response and post-vaccination control of viremia by vaccine dose. Ethics and dissemination: The clinical trial protocols have received approval from the relevant institutional ethics and regulatory review committees in Kenya and Uganda, and the WHO Ethics Review Committee. The research findings will be disseminated through open-access publications and presented at relevant conferences and workshops. Registration: ClinicalTrials.gov NCT02991495 (registered on 13 December 2016) and NCT04059471 (registered on 15 August 2019).

Yellow Fever: Integrating Current Knowledge with Technological Innovations to Identify Strategies for Controlling a Re-Emerging Virus

Yellow fever virus (YFV) represents a re-emerging zoonotic pathogen, transmitted by mosquito vectors to humans from primate reservoirs. Sporadic outbreaks of YFV occur in endemic tropical regions, causing a viral hemorrhagic fever (VHF) associated with high mortality rates. Despite a highly effective vaccine, no antiviral treatments currently exist. Therefore, YFV represents a neglected tropical disease and is chronically understudied, with many aspects of YFV biology incompletely defined including host range, host–virus interactions and correlates of host immunity and pathogenicity. In this article, we review the current state of YFV research, focusing on the viral lifecycle, host responses to infection, species tropism and the success and associated limitations of the YFV-17D vaccine. In addition, we highlight the current lack of available treatments and use publicly available sequence and structural data to assess global patterns of YFV sequence diversity and identify potential drug targets. Finally, we discuss how technological advances, including real-time epidemiological monitoring of outbreaks using next-generation sequencing and CRISPR/Cas9 modification of vector species, could be utilized in future battles against this re-emerging pathogen which continues to cause devastating disease.

Yellow fever disease in a renal transplant recipient: Case report and literature review

Yellow fever (YF) is a viral disease, with clinical presentation among immunosuppressed patients not fully understood. YF vaccination (YFV), a live vaccine, is contraindicated in patients receiving immunosuppressive treatment due to the risk of developing the disease after vaccination. We report a case of a 50-year-old male recipient who presented wild-type YF five years after a deceased donor kidney transplant. He lived in a YF endemic area and inadvertently received YFV. One day after YFV, the patient presented nausea, vomiting, fever, diarrhea, polyarthralgia, thrombocytopenia, and increased levels of liver function enzymes. The serological test was compatible with YF disease, and quantitative viral load confirmed the diagnosis of wild-type YF. The patient received supportive care for twelve days, with hospital discharge in good clinical condition and stable renal function. One month after discharge, the patient developed de novo donor-specific anti-HLA antibodies (DSA) and histological evidence of endothelial lesion, with a diagnosis of acute antibody-mediated rejection (AMR), treated with plasmapheresis and human IVIg therapy. Six months after therapy, he presented normal renal function with a reduction of DSA MFI. In the reported case, we observed a clinical wild-type YF diagnosed even after YF vaccine administration, with good clinical outcome. De novo DSA and AMR occurred after the recovering of disease, with an adequate response to therapy and preserved allograft function. We reviewed the published literature on YF and YFV in solid organ transplantation.

Identification of Protective CD8 T Cell Responses in a Mouse Model of Zika Virus Infection

Many flaviviruses including dengue (DENV), and Zika (ZIKV) have attracted significant attention in the past few years. As many flaviviruses are spread by arthropods, most of the world's population is at risk of encountering a flavivirus, and infection with these viruses has created a significant disease burden worldwide. Vaccination against flaviviruses is thought to be one of the most promising avenues for reducing the disease burden associated with these viruses. The optimism surrounding a vaccine approach is supported by the highly successful vaccines for yellow fever and Japanese encephalitis. Central to the development of new successful vaccines is the understanding of the correlates of protection that will be necessary to engineer into new vaccines. To aid in this endeavor we have directed our efforts to identify correlates of protection that will reduce the disease burden associated with ZIKV and DENV. Within this study we have identified a novel murine ZIKV specific CD8⁺ T cell epitope, and shown that the ZIKV epitope specific CD8⁺ T cell response has a distinct immunodominance hierarchy present during acute infection and is detectible as part of the memory T cell responses. Our studies confirm that ZIKV-specific CD8⁺ T cells are an important correlate of protection for ZIKV and demonstrate that both naïve and ZIKV immune CD8⁺ T cells are sufficient for protection against a lethal ZIKV infection. Overall this study adds to the body of literature demonstrating a role for CD8⁺ T cells in controlling flavivirus infection.

Brazilian recommendations on the safety and effectiveness of the yellow fever vaccination in patients with chronic immune-mediated inflammatory diseases

BACKGROUND

In Brazil, we are facing an alarming epidemic scenario of Yellow fever (YF), which is reaching the most populous areas of the country in unvaccinated people. Vaccination is the only effective tool to prevent YF. In special situations, such as patients with chronic immune-mediated inflammatory diseases (CIMID), undergoing immunosuppressive therapy, as a higher risk of severe adverse events may occur, assessment of the risk-benefit ratio of the yellow fever vaccine (YFV) should be performed on an individual level. Faced with the scarcity of specific orientation on YFV for this special group of patients, the Brazilian Rheumatology Society (BRS) endorsed a project aiming the development of individualized YFV recommendations for patients with CIMID, guided by questions addressed by both medical professionals and patients, followed an internationally validated methodology (GIN-McMaster Guideline Development). Firstly, a systematic review was carried out and an expert panel formed to take part of the decision process, comprising BRS clinical practitioners, as well as individuals from the Brazilian Dermatology Society (BDS), Brazilian Inflammatory Bowel Diseases Study Group (GEDIIB), and specialists on infectious diseases and vaccination (from Tropical Medicine, Infectious Diseases and Immunizations National Societies); in addition, two representatives of patient groups were included as members of the panel. When the quality of the evidence was low or there was a lack of evidence to determine the recommendations, the decisions were based on the expert opinion panel and a Delphi approach was performed. A recommendation was accepted upon achieving ≥80% agreement among the panel, including the patient representatives. As a result, eight recommendations were developed regarding the safety of YFV in patients with CIMID, considering the immunosuppression degree conferred by the treatment used. It was not possible to establish recommendations on the effectiveness of YFV in these patients as there is no consistent evidence to support these recommendations.

CONCLUSION

This paper approaches a real need, assessed by clinicians and patient care groups, to address specific questions on the management of YFV in patients with CIMID living or traveling to YF endemic areas, involving specialists from many areas together with patients, and might have global applicability, contributing to and supporting vaccination practices. We recommended a shared decision-making approach on taking or not the YFV.

Impact of synthetic and biological immunomodulatory therapy on the duration of 17DD yellow fever vaccine-induced immunity in rheumatoid arthritis

Background

The 17DD-yellow fever (YF) vaccine induces a long-lasting protective immunity, resulting from humoral and cellular immunological memory. The treatment of rheumatoid arthritis (RA) patients with disease-modifying anti-rheumatic drugs (DMARD) may affect pre-existing 17DD-vaccine protective immunity and increase the risk of acquiring YF infection. Our goal was to determine whether DMARD would affect the duration of YF-specific protective immunity in RA patients.

Methods

A total of 122 RA patients, previously immunized with the 17DD-YF vaccine (1–5, 5–9, and ≥ 10 years) and currently under DMARD therapy, were enrolled in the present investigation. Immunomodulatory therapy encompasses the use of conventional synthetic DMARD alone (csDMARD) or combines with biological DMARD (cs+bDMARD). A total of 226 healthy subjects were recruited as a control group (CONT). Neutralizing antibody responses were measured by a plaque-reduction neutralization test (PRNT), and cellular immunity was evaluated by an in vitro 17DD-YF-specific peripheral blood lymphoproliferative assay.

Results

The data demonstrated that csDMARD therapy did not affect the duration of protective immunity induced by the 17DD-YF vaccine compared to that of CONT, as both presented a significant time-dependent decline at 10 years after vaccination. Conversely, cs+bDMARD therapy induced a premature depletion in the main determinants of the vaccine protective response, with diminished PRNT seropositivity levels between 5 and 9 years and impaired effector memory in CD8⁺ T cells as early as 1–5 years after 17DD-YF vaccination.

Conclusions

These findings could support changing the vaccination schedule of this population, with the possibility of a planned booster dose upon the suspension of bDMARD in cases where this is allowed, even before 10 years following 17DD-YF vaccination. The benefit of a planned booster dose should be evaluated in further studies.

Trial registration

RBR-946bv5. Date of registration: March 05, 2018. Retrospectively registered

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

Clinical evidence for the immunogenicity and immune persistence of vaccination with yellow fever virus strain 17D in Chinese peacekeepers deployed to Africa

Yellow fever is a serious disease caused by infection with the yellow fever virus (YFV). A live-attenuated YFV vaccine strain, 17D (YFV-17D) is the only virus strain available for the production of the YFV vaccine. This study evaluated the immunogenicity and immune persistence of vaccination with YFV-17D and identified their influencing factors in Chinese peacekeepers deployed to Africa. Serum specimens were collected before and ≥21 days after primary vaccination with YFV-17D in 349 Chinese peacekeepers who were subsequently deployed to Africa for the first time from 2016 to 2017 (population 1). Serum specimens were collected from 1 to 11 years after vaccination with YFV-17D in 2062 returned Chinese peacekeepers who were deployed to Africa from 2005 to 2015 (population 2). We found that YFV-17D exhibited an excellent protective effect in the Chinese peacekeepers deployed to Africa early following vaccination. In the Chinese peacekeepers one year after vaccination, the serum antibody titer against YFV increased with increasing age at vaccination; in those two or more years after vaccination, the serum antibody titer against YFV decreased over years and was similar to but greater than the minimum protective level 11 years after vaccination. The number of peacekeeping missions exhibited an almost negligible influence on the serum antibody titer against YFV. (This study has been registered at International Clinical Trials Registry Platform (http://www.who.int/ictrp/en/) under registration Nos. ChiCTR1800017024.).

CD4+T cells mediate protection against Zika associated severe disease in a mouse model of infection

Zika virus (ZIKV) has gained worldwide attention since it emerged, and a global effort is underway to understand the correlates of protection and develop diagnostics to identify rates of infection. As new therapeutics and vaccine approaches are evaluated in clinical trials, additional effort is focused on identifying the adaptive immune correlates of protection against ZIKV disease. To aid in this endeavor we have begun to dissect the role of CD4+T cells in the protection against neuroinvasive ZIKV disease. We have identified an important role for CD4+T cells in protection, demonstrating that in the absence of CD4+T cells mice have more severe neurological sequela and significant increases in viral titers in the central nervous system (CNS). The transfer of CD4+T cells from ZIKV immune mice protect type I interferon receptor deficient animals from a lethal challenge; showing that the CD4+T cell response is necessary and sufficient for control of ZIKV disease. Using a peptide library spanning the complete ZIKV polyprotein, we identified both ZIKV-encoded CD4+T cell epitopes that initiate immune responses, and ZIKV specific CD4+T cell receptors that recognize these epitopes. Within the ZIKV antigen-specific TCRβ repertoire, we uncovered a high degree of diversity both in response to a single epitope and among different mice responding to a CD4+T cell epitope. Overall this study identifies a novel role for polyfunctional and polyclonal CD4+T cells in providing protection against ZIKV infection and highlights the need for vaccines to develop robust CD4+T cell responses to prevent ZIKV neuroinvasion and limit replication within the CNS.

Astragalus polysaccharides enhance the immune response to avian infectious bronchitis virus vaccination in chickens

Astragalus polysaccharides (APS) are biological macromolecules extracted from Astragalus species that have strong immunoregulatory properties. In this study, APS were employed as an adjuvant for an avian infectious bronchitis virus (IBV) vaccine, and its effects on the cellular immune and humoral immune responses to vaccination in chicken were investigated. One hundred and fifty chicken were randomly divided into five groups (n = 30, each group). The chickens in all groups, except for the unvaccinated control group, were vaccinated with an IBV DNA vaccine. Three of the four vaccinated groups were administered different doses of APS (APSL, 10 mg/kg; APSM, 50 mg/kg; and APSH, 100 mg/kg) after the first vaccination, and the remaining vaccinated group served as a control, without any additional treatment. At 14, 28, and 42 days after the first vaccination, serum anti-IBV antibody titers; peripheral lymphocyte proliferation; and the mRNA expression of IL-1β, IL-2, IL-8, and TNF-α in the spleen were assessed by enzyme-linked immunosorbent assay (ELISA), the cell counting kit-8 (CCK-8), and real time quantitative RT-PCR (qRT-PCR), respectively. At most time points, the titer of IBV-specific antibodies, lymphocyte proliferation, and IL-1β, IL-2, IL-8, and TNF-α mRNA expression levels were higher in three APS groups than in the vaccine control group, and these increases were dose-dependent. These data suggest that APS could be used as an adjuvant for IBV vaccination to provide better protection against IBV infection.