Understanding the role of innate immunity in the mechanism of action of the live attenuated Yellow Fever Vaccine 17D

Self-Replicating RNA Derived from the Genomes of Positive-Strand RNA Viruses

Self-replicating RNA derived from the genomes of positive-strand RNA viruses represents a powerful tool for both molecular studies on virus biology and approaches to novel safe and effective vaccines. The following chapter summarizes the principles how such RNAs can be established and used for design of vaccines. Due to the large variety of strategies needed to circumvent specific pitfalls in the design of such constructs the technical details of the experiments are not described here but can be found in the cited literature.

Impact of immune enhancement on Covid-19 polyclonal hyperimmune globulin therapy and vaccine development

The pandemic spread of a novel coronavirus - SARS coronavirus-2 (SARS-CoV-2) as a cause of acute respiratory illness, named Covid-19, is placing the healthcare systems of many countries under unprecedented stress. Global economies are also spiraling towards a recession in fear of this new life-threatening disease. Vaccines that prevent SARS-CoV-2 infection and therapeutics that reduces the risk of severe Covid-19 are thus urgently needed. A rapid method to derive antiviral treatment for Covid-19 is the use of convalescent plasma derived hyperimmune globulin. However, both hyperimmune globulin and vaccine development face a common hurdle - the risk of antibody-mediated disease enhancement. The goal of this review is to examine the body of evidence supporting the hypothesis of immune enhancement that could be pertinent to Covid-19. We also discuss how this risk could be mitigated so that both hyperimmune globulin and vaccines could be rapidly translated to overcome the current global health crisis.

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.

High-Dimensional Immunology for Schizophrenia Research: A Short Perspective

There is evidence that many diseases are accompanied by immunological perturbations and even when the perturbations are not directly pathogenic, they can provide correlative signatures of pathology that can be useful diagnostically. For example, the neuromuscular disease, multiple sclerosis, has a pathophysiology that is immunologically mediated, evinced by the use of increasingly sophisticated immunosuppression therapy and by animal studies in which many of the symptoms can be reproduced by breaking immunological tolerance to myelin basic protein. By contrast, immunological correlates exist for other diseases, such as schizophrenia, but it is not clear which, if any, are causative. The problem is compounded in that genome-wide association studies have shown strong genetic correlation between schizophrenia and bipolar disorder, moderate correlation with schizophrenia and major depressive disease, and low correlation with autism spectrum disorders, yet schizophrenia and autism spectrum disorders share immunological signatures. This example illustrates the problem of ferreting out specific, and hopefully causal, immunological correlates with schizophrenia that differentiate it from genetically or immunologically related psychiatric disorders. Fortunately, recent advances in systems immunology provide potent tools to tackle this problem. This review will illustrate these tools by recent examples and sketch out possible pathways to use them for identification of schizophrenia-specific immunological correlates.

Self-Replicating RNA

Self-replicating RNA derived from the genomes of positive strand RNA viruses represents a powerful tool for both molecular studies on virus biology and approaches to novel safe and effective vaccines. The following chapter summarizes the principles how such RNAs can be established and used for design of vaccines. Due to the large variety of strategies needed to circumvent specific pitfalls in the design of such constructs the technical details of the experiments are not described here but can be found in the cited literature.

HIV vaccine trial exploits a dual and central role for innate immunity

Limited understanding of correlates of protection from HIV transmission hinders development of an efficacious vaccine. D. J. M. Lewis and colleagues (J. Virol. 88:11648-11657, 2014, doi:10.1128/JVI.01621-14) now report that vaginal immunization with an HIVgp140 vaccine linked to the 70-kDa heat shock protein downregulated the human immunodeficiency virus (HIV) coreceptor CCR5 (chemokine [C-C motif] receptor 5) and increased expression of the HIV resistance factor APOBEC3G (apolipoprotein B mRNA-editing, enzyme-catalytic, polypeptide-like 3G), in women. These effects correlated with HIV suppression ex vivo. Thus, vaccine-induced innate responses not only facilitate adaptive immunity-they may prove to be critical for preventing HIV transmission.

Manipulation of EAT-2 expression promotes induction of multiple beneficial regulatory and effector functions of the human innate immune system as a novel immunomodulatory strategy

The signaling lymphocytic activation molecule (SLAM) receptor-associated adaptor Ewing's sarcoma-associated transcript-2 (EAT-2) is primarily expressed in innate immune cells including dendritic cells (DCs), macrophages and NK cells. A recent human HIV vaccine study confirmed that EAT-2 expression was associated with the enhanced immunogenicity induced by the MRKAd5/HIV vaccine. We previously harnessed the capability of EAT-2 to modulate signaling mediated by SLAM receptors and demonstrated that by incorporating EAT-2 expression into vaccines, one could enhance innate and adaptive immune responses in mice, even in the face of pre-existing immunity to the vaccine vectors. Herein, we investigated the innate immune responses of human cells exposed to EAT-2-over-expressing vaccines. Our results demonstrate that EAT-2 over-expression can significantly alter the kinetics of critical pro-inflammatory cytokine and chemokine responses elaborated by human PBMCs. In addition, enhanced DC maturation and increased monocyte phagocytosis were observed in EAT-2-transduced human cells. We also found that EAT-2 over-expression improved antigen presentation by human cells. Moreover, EAT-2 over-expression increased the anti-tumor activity of human NK cells against K562 tumor cell targets. Many of these responses were extinguished with use of an EAT-2 variant carrying a mutant SH2 domain (R31Q), suggesting a critical role for the interaction between EAT-2 and SLAM receptors in mediating these responses. In conclusion, these results provide evidence that EAT-2 interacts with key components of multiple arms of the human innate immune system, and that this role highlights the potential for targeting EAT-2 functions so as to improve a number of human immunotherapeutic approaches, including vaccine development.

Advances and controversies in yellow fever vaccination

Ever since its development in 1937, the live-attenuated 17D yellow fever (YF) vaccine has been one of the most effective vaccines available to man. In this review we highlight the major steps in the development of 17D YF vaccine. We discuss the use of neutralizing antibodies as a surrogate marker for protection, and explore the strengths and weaknesses of the current plaque reduction neutralization test (PRNT), a technique developed in the 1960s that continues to be superior to every modern test in both sensitivity and specificity. The neutralizing antibodies demonstrated by the PRNT can be detected for several decades after vaccination, possibly even for the remainder of the recipient's natural life. We review the available evidence on the duration of protection after primary vaccination, a topic that has been the subject of controversy over the last few months. For persons who are immunocompromised due to disease, medication or advancing age, the duration of protection may be shorter: they should always have their vaccine response checked by PRNT. Due to the higher risk of severe adverse events after vaccination with 17D YF in this group, the development of a new, inactivated vaccine will have substantial benefits in this population.

Pathogen recognition receptor crosstalk in respiratory syncytial virus sensing: a host and cell type perspective

Human respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infection in young children, immunocompromised adults, and the elderly. The innate immune response plays a pivotal role in host defense against RSV, but whether severe outcomes following RSV infection result from excessive or poor innate immune recognition remains unclear. Recent research suggests a situation in which crosstalk between families of pattern recognition receptors (PRRs) occurs in a cell type-dependent manner. The current challenge to empower novel therapeutic approaches and vaccine development is to confirm the role of the individual receptors in RSV pathogenesis in humans.

Immunity to viruses: learning from successful human vaccines

For more than a century, immunologists and vaccinologists have existed in parallel universes. Immunologists have for long reveled in using 'model antigens', such as chicken egg ovalbumin or nitrophenyl haptens, to study immune responses in model organisms such as mice. Such studies have yielded many seminal insights about the mechanisms of immune regulation, but their relevance to humans has been questioned. In another universe, vaccinologists have relied on human clinical trials to assess vaccine efficacy, but have done little to take advantage of such trials for studying the nature of immune responses to vaccination. The human model provides a nexus between these two universes, and recent studies have begun to use this model to study the molecular profile of innate and adaptive responses to vaccination. Such 'systems vaccinology' studies are beginning to provide mechanistic insights about innate and adaptive immunity in humans. Here, we present an overview of such studies, with particular examples from studies with the yellow fever and the seasonal influenza vaccines. Vaccination with the yellow fever vaccine causes a systemic acute viral infection and thus provides an attractive model to study innate and adaptive responses to a primary viral challenge. Vaccination with the live attenuated influenza vaccine causes a localized acute viral infection in mucosal tissues and induces a recall response, since most vaccinees have had prior exposure to influenza, and thus provides a unique opportunity to study innate and antigen-specific memory responses in mucosal tissues and in the blood. Vaccination with the inactivated influenza vaccine offers a model to study immune responses to an inactivated immunogen. Studies with these and other vaccines are beginning to reunite the estranged fields of immunology and vaccinology, yielding unexpected insights about mechanisms of viral immunity. Vaccines that have been proven to be of immense benefit in saving lives offer us a new fringe benefit: lessons in viral immunology.

Dissection of antibody specificities induced by yellow fever vaccination

The live attenuated yellow fever (YF) vaccine has an excellent record of efficacy and one dose provides long-lasting immunity, which in many cases may last a lifetime. Vaccination stimulates strong innate and adaptive immune responses, and neutralizing antibodies are considered to be the major effectors that correlate with protection from disease. Similar to other flaviviruses, such antibodies are primarily induced by the viral envelope protein E, which consists of three distinct domains (DI, II, and III) and is presented at the surface of mature flavivirions in an icosahedral arrangement. In general, the dominance and individual variation of antibodies to different domains of viral surface proteins and their impact on neutralizing activity are aspects of humoral immunity that are not well understood. To gain insight into these phenomena, we established a platform of immunoassays using recombinant proteins and protein domains that allowed us to dissect and quantify fine specificities of the polyclonal antibody response after YF vaccination in a panel of 51 vaccinees as well as determine their contribution to virus neutralization by serum depletion analyses. Our data revealed a high degree of individual variation in antibody specificities present in post-vaccination sera and differences in the contribution of different antibody subsets to virus neutralization. Irrespective of individual variation, a substantial proportion of neutralizing activity appeared to be due to antibodies directed to complex quaternary epitopes displayed on the virion surface only but not on monomeric E. On the other hand, DIII-specific antibodies (presumed to have the highest neutralizing activity) as well as broadly flavivirus cross-reactive antibodies were absent or present at very low titers. These data provide new information on the fine specificity as well as variability of antibody responses after YF vaccination that are consistent with a strong influence of individual-specific factors on immunodominance in humoral immune responses.

The live-attenuated yellow fever vaccine has been administered to more than 600 million people worldwide and is considered to be one of the most successful viral vaccines ever produced. Following injection, the apathogenic vaccine virus replicates in the vaccinee and induces antibodies that mediate virus neutralization and subsequent protection from disease. In principle, many different antibodies are induced by viral antigens, but it is becoming increasingly clear that only a subset of them is capable of inactivating the virus, and some antibody populations appear to dominate the immune response. However, to date there has been very little information on individual-specific variations of immunodominance and how such variations can affect the functionality of antibody responses. In our study, we addressed these issues and analyzed the fine specificities of antibodies induced by YF vaccination as well as the contribution of different antibody subsets to virus neutralization in 51 vaccinees. We demonstrate an extensive degree of individual variation with respect to immunodominance of antibody populations and their contribution to virus neutralization. Such variations can have an impact on vaccine-mediated protection, and thus insight into this phenomenon can provide leads for novel strategies in modern vaccine design.

Immunogenicity of seven new recombinant yellow fever viruses 17D expressing fragments of SIVmac239 Gag, Nef, and Vif in Indian rhesus macaques

An effective vaccine remains the best solution to stop the spread of human immunodeficiency virus (HIV). Cellular immune responses have been repeatedly associated with control of viral replication and thus may be an important element of the immune response that must be evoked by an efficacious vaccine. Recombinant viral vectors can induce potent T-cell responses. Although several viral vectors have been developed to deliver HIV genes, only a few have been advanced for clinical trials. The live-attenuated yellow fever vaccine virus 17D (YF17D) has many properties that make it an attractive vector for AIDS vaccine regimens. YF17D is well tolerated in humans and vaccination induces robust T-cell responses that persist for years. Additionally, methods to manipulate the YF17D genome have been established, enabling the generation of recombinant (r)YF17D vectors carrying genes from unrelated pathogens. Here, we report the generation of seven new rYF17D viruses expressing fragments of simian immunodeficiency virus (SIV)mac239 Gag, Nef, and Vif. Studies in Indian rhesus macaques demonstrated that these live-attenuated vectors replicated in vivo, but only elicited low levels of SIV-specific cellular responses. Boosting with recombinant Adenovirus type-5 (rAd5) vectors resulted in robust expansion of SIV-specific CD8⁺ T-cell responses, particularly those targeting Vif. Priming with rYF17D also increased the frequency of CD4⁺ cellular responses in rYF17D/rAd5-immunized macaques compared to animals that received rAd5 only. The effect of the rYF17D prime on the breadth of SIV-specific T-cell responses was limited and we also found evidence that some rYF17D vectors were more effective than others at priming SIV-specific T-cell responses. Together, our data suggest that YF17D – a clinically relevant vaccine vector – can be used to prime AIDS virus-specific T-cell responses in heterologous prime boost regimens. However, it will be important to optimize rYF17D-based vaccine regimens to ensure maximum delivery of all immunogens in a multivalent vaccine.

Insights into human CD8(+) T-cell memory using the yellow fever and smallpox vaccines

Live virus vaccines provide a unique opportunity to study human CD8(+) T-cell memory in the context of a controlled, primary acute viral infection. Yellow fever virus-17D and Dryvax are two such live-virus vaccines that are highly efficacious, used worldwide and provide long-term immunity against yellow fever and smallpox respectively. In this review, we describe the properties of virus-specific memory CD8(+) T cells generated in smallpox and yellow fever vaccinees. We address fundamental questions regarding magnitude, functional quality and longevity of the CD8(+) T-cell response, which are otherwise challenging to address in humans. These findings provide insights into the attributes of the human immune system as well as provide a benchmark for the optimal quality of a CD8(+) T-cell response that can be used to evaluate novel candidate vaccines.

Role of innate signalling pathways in the immunogenicity of alphaviral replicon-based vaccines

Background

Alphaviral replicon-based vectors induce potent immune responses both when given as viral particles (VREP) or as DNA (DREP). It has been suggested that the strong immune stimulatory effect induced by these types of vectors is mediated by induction of danger signals and activation of innate signalling pathways due to the replicase activity. To investigate the innate signalling pathways involved, mice deficient in either toll-like receptors or downstream innate signalling molecules were immunized with DREP or VREP.

Results

We show that the induction of a CD8⁺ T cell response did not require functional TLR3 or MyD88 signalling. However, IRF3, converging several innate signalling pathways and important for generation of pro-inflammatory cytokines and type I IFNs, was needed for obtaining a robust primary immune response. Interestingly, type I interferon (IFN), induced by most innate signalling pathways, had a suppressing effect on both the primary and memory T cell responses after DREP and VREP immunization.

Conclusions

We show that alphaviral replicon-based vectors activate multiple innate signalling pathways, which both activate and restrict the induced immune response. These results further show that there is a delicate balance in the strength of innate signalling and induction of adaptive immune responses that should be taken into consideration when innate signalling molecules, such as type I IFNs, are used as vaccine adjuvant.

TLR expression and NK cell activation after human yellow fever vaccination

The yellow fever vaccine is very effective with a single injection conferring protection for at least 10 years. Recent evidence suggests that the innate immune cells activated through Toll-like receptors (TLRs), are critical determinants of the robustness of the adaptive response. Therefore, we investigated the NK cell status in eight healthy volunteers after vaccination with YF 17DD virus. Shortly after vaccination, we observed increased expression of TLR-3 and TLR-9 in NK cells and markers such as CD69, HLA-DP-DQ-DR, CD38 and CD16. The up-regulation of CD69 was positively correlated with the presence of TLRs throughout the post-vaccination period and the circulating IFN-gamma was significantly augmented. These results suggest that TLRs may play an important role in NK cell activation during the immune response to vaccination, indicating a potential role for NK cells in helping the development of long-lasting protective memory.

Safety of 17D derived yellow fever vaccines

BACKGROUND

Yellow fever, a mosquito-borne viral haemorrhagic fever, is one of the most lethal viral diseases. At present, an efficient vaccine for prevention is available, but may cause serious adverse events.

METHODS

The authors review the up-to-date knowledge for serious adverse events of the yellow fever vaccine (YFSAE): hypersensitivity reactions, neurotropic and viscerotropic syndromes.

RESULTS

The incidence of YFSAE has been associated with increasing age and thymus disorders, but still a number of cases with any risk factor remain unexplained, which suggests that other factors, from the virus or the host, could be involved in the appearance of these postvaccinal adverse events.

CONCLUSIONS

YFSAE are uncommon but must be prevented. Further research on the virus-host immune response is needed to have a better understanding of the basis for the appearance of these severe side effects after vaccination. Vaccination should be limited to people with a true risk of exposure to wild-type yellow fever virus.

Yellow fever vaccine - how does it work and why do rare cases of serious adverse events take place?

Yellow fever 17D vaccine is one of the most successful vaccines ever developed and over 540 million doses have been used. Nevertheless there has been very little known about the mechanism of protection induced by the vaccine. The last couple of years have seen important advances made in understanding how the vaccine works involving studies of the innate and adaptive immune responses plus a systems biology approach. Like all vaccines, the 17D vaccine causes rare serious adverse events (SAEs) following immunization. At present, the mechanism(s) of SAEs is(are) poorly understood but our advances in understanding the immune response induced by the vaccine have promise to help elucidate the mechanism of SAEs.

Dynamics of the CD8 T-cell response following yellow fever virus 17D immunization

Management of yellow fever is focused on the prevention of illness by the use of the yellow fever virus (YFV) 17D vaccine. The role of neutralizing antibodies in protection is generally accepted with YFV-specific T cells likely contributing to the control of viral replication. We studied CD8(+) T-cell responses to four defined human leucocyte antigen-B35-restricted epitopes in YFV vaccine recipients as a model of the kinetics of cytotoxic T-lymphocyte responses to an acute human viral infection. Multiple features of these epitope-specific responses were analysed after vaccination including magnitude, cytokine production, phenotype and T-cell receptor repertoire. Peak peptide-specific interferon-gamma (IFN-gamma) responses of almost 1% of CD8(+) T cells were seen as early as 2 weeks post-vaccination; however, dominant responses varied between donors. Peptide-specific responses were still detectable at 54 months post-vaccination. Tetramer-positive cells, at high frequencies, were detected as early as 7-9 days, before detectable IFN-gamma-producing cells, suggesting a defect in the functional capacity of some antigen-specific cells early post-vaccination. The predominant memory phenotype of the tetramer-positive population was a differentiated effector (CD45RA(+) CCR7(-) CD62L(-)) phenotype. The T-cell receptor Vbeta analysis revealed a diverse oligoclonal repertoire in tetramer-positive T-cell populations in two individuals. These characteristics of the YFV-specific T-cell response could contribute to vaccine effectiveness.

Acute viscerotropic disease following vaccination against yellow fever

Acute viscerotropic disease following yellow fever vaccination (YEL-AVD) is a rare but serious complication of vaccination with 17D yellow fever vaccine. This paper reviews the existing literature regarding YEL-AVD and discusses possible etiologic mechanisms. A greater understanding of this condition is essential to assuring safe and effective prevention of yellow fever and vaccination against other arboviral diseases for which 17D-based vaccines are being developed.