Yellow Fever 17D Vaccine Research Articles

Yellow fever vaccine induces integrated multilineage and polyfunctional immune responses

Correlates of immune-mediated protection to most viral and cancer vaccines are still unknown. This impedes the development of novel vaccines to incurable diseases such as HIV and cancer. In this study, we have used functional genomics and polychromatic flow cytometry to define the signature of the immune response to the yellow fever (YF) vaccine 17D (YF17D) in a cohort of 40 volunteers followed for up to 1 yr after vaccination. We show that immunization with YF17D leads to an integrated immune response that includes several effector arms of innate immunity, including complement, the inflammasome, and interferons, as well as adaptive immunity as shown by an early T cell response followed by a brisk and variable B cell response. Development of these responses is preceded, as demonstrated in three independent vaccination trials and in a novel in vitro system of primary immune responses (modular immune in vitro construct [MIMIC] system), by the coordinated up-regulation of transcripts for specific transcription factors, including STAT1, IRF7, and ETS2, which are upstream of the different effector arms of the immune response. These results clearly show that the immune response to a strong vaccine is preceded by coordinated induction of master transcription factors that lead to the development of a broad, polyfunctional, and persistent immune response that integrates all effector cells of the immune system.

Systems biology approach predicts immunogenicity of the yellow fever vaccine in humans

A major challenge in vaccinology is to prospectively determine vaccine efficacy. Here we have used a systems biology approach to identify early gene 'signatures' that predicted immune responses in humans vaccinated with yellow fever vaccine YF-17D. Vaccination induced genes that regulate virus innate sensing and type I interferon production. Computational analyses identified a gene signature, including complement protein C1qB and eukaryotic translation initiation factor 2 alpha kinase 4-an orchestrator of the integrated stress response-that correlated with and predicted YF-17D CD8(+) T cell responses with up to 90% accuracy in an independent, blinded trial. A distinct signature, including B cell growth factor TNFRS17, predicted the neutralizing antibody response with up to 100% accuracy. These data highlight the utility of systems biology approaches in predicting vaccine efficacy.

Does yellow fever 17D vaccine protect against melanoma?

BCG vaccine, vaccinia vaccine and certain pathogens that were shown in previous studies to protect against melanoma have antigenic determinants homologous in their amino acids sequence with the melanoma antigen HERV-K-MEL, encoded by a human endogenous retrovirus K (HERV-K), which is expressed in about 95% of malignant melanocytes. Yellow fever vaccine (YFV) likewise contains an antigenic determinant with a close homology to HERV-K-MEL and might therefore also confer protection against melanoma. To investigate this possibility we carried out a cohort study (28,306 subjects) and a nested case-control study (37 melamona cases and 151 tumors not expressing HERV-K-MEL) in Veneto region (North-Eastern Italy). The standardized incidence ratio was 1.33 (95% confidence interval, 0.84–2.11), 1.59 (0.97–2.59) and 0.59 (0.19–1.84), while the age- gender-adjusted odds ratios were 1.00, 0.96 (0.43–2.14) and 0.26 (0.07–0.96), at 0–4, 5–9, and ≥10 years elapsed from YFV administration, respectively. The risk of melanoma may therefore be lowered 10 years after vaccination with yellow fever vaccine.

Yellow fever vaccine: past, present and future

Background: Yellow fever is a re-emerging infectious disease, as vector control and routine immunisation have dwindled in endemic areas in the last few decades. There is a constant threat of outbreaks in the large susceptible non-immune population of the megacities in tropical countries with an ongoing virus life cycle in the rainforests. For this population and for travellers to endemic areas, vaccination is the only effective protective measure against the disease and the spread of the virus. Objective/methods: We discuss the history of yellow fever vaccine development, and focus on practical aspects of vaccine safety, contraindications for vaccination, and future vaccine developments. Results/conclusions: Vaccination with the live attenuated yellow fever-17D vaccine (YF-17D) induces low-grade viraemia in half of the vaccinees and elicits protective neutralising antibody levels in 99%. Reports of serious adverse events in the elderly and immunocompromised, and the inability to produce large quantities of yellow fever vaccine at short notice in combination with limited vaccine stockpiles highlight the need for further study of this highly effective and safe vaccine.

Case of Yellow Fever Vaccine–Associated Viscerotropic Disease with Prolonged Viremia, Robust Adaptive Immune Responses, and Polymorphisms in CCR5 and RANTES Genes

The live attenuated yellow fever vaccine 17D (YF-17D) is one of the most effective vaccines. Despite its excellent safety record, some cases of viscerotropic adverse events develop, which are sometimes fatal. The mechanisms underlying such events remain a mystery. Here, we present an analysis of the immunologic and genetic factors driving disease in a 64-year-old male who developed viscerotropic symptoms. We obtained clinical, serologic, virologic, immunologic and genetic data on this case patient. Viral RNA was detected in the blood 33 days after vaccination, in contrast to the expected clearance of virus by day 7 after vaccination in healthy vaccinees. Vaccination induced robust antigen-specific T and B cell responses, which suggested that persistent virus was not due to adaptive immunity of suboptimal magnitude. The genes encoding OAS1, OAS2, TLR3, and DC-SIGN, which mediate antiviral innate immunity, were wild type. However, there were heterozygous genetic polymorphisms in chemokine receptor CCR5, and its ligand RANTES, which influence the migration of effector T cells and CD14+CD16bright monocytes to tissues. Consistent with this, there was a 200-fold increase in the number of CD14+CD16bright monocytes in the blood during viremia and even several months after virus clearance. In this patient, viscerotropic disease was not due to the impaired magnitude of adaptive immunity but instead to anomalies in the innate immune system and a possible disruption of the CCR5-RANTES axis.

Intradermally administered yellow fever vaccine at reduced dose induces a protective immune response: a randomized controlled non-inferiority trial.

BackgroundImplementation of yellow fever vaccination is currently hampered by limited supply of vaccine. An alternative route of administration with reduced amounts of vaccine but without loss of vaccine efficacy would boost vaccination programmes.Methods and FindingsA randomized, controlled, non-inferiority trial was conducted in a Dutch university center between August 2005 and February 2007. A total of 155 primary vaccinated and 20 previously vaccinated volunteers participated. Participants were randomly assigned in a 1∶1 ratio to receive intradermal (i.d.) vaccination with live attenuated yellow fever 17D vaccine at a reduced dose (1/5th; 0·1 mL) or the conventional subcutaneous (s.c.) vaccination (0·5 mL). Antibody neutralization titers were determined at 2, 4 and 8 weeks and 1 year after vaccination by counting the reduction in virus-induced plaques in the presence of serial serum dilutions. Adverse events were documented in a 3-week dairy. Viraemia was measured 5 days after vaccination. From 2 weeks up to one year after vaccination, the maximum serum-dilution at which 80% of the virus plaques were neutralized, which indicates protection against yellow fever, did not differ between those given a reduced i.d. dose or standard s.c. dose of vaccine. In all cases the WHO standard of seroprotection (i.e. 80% virus neutralization) was reached (in 77/77 and 78/78, respectively). Similar results were found in the previously vaccinated individuals. Viraemia was detected in half of the primary vaccinated participants, which was not predictive of serological response. In revaccinees no viraemia was detected.ConclusionsIntradermal administration of one fifth of the amount of yellow fever vaccine administered subcutaneously results in protective seroimmunity in all volunteers. Albeit this vaccination route should enable vaccination of five-times as many individuals at risk for disease, these results should now be confirmed in field studies in areas with potential yellow fever virus transmission to change vaccination policy.Trial RegistrationNederlands Trial Register ISRCTN46326316

Evaluation of an Indirect Immunofluorescence Assay for Detection of Immunoglobulin M (IgM) and IgG Antibodies against Yellow Fever Virus

The first commercial indirect immunofluorescence assay (IFA) using Euroimmun Biochip technology was evaluated for the serodiagnosis of immunoglobulin G (IgG) and IgM antibodies against yellow fever virus (YFV) and was compared with the plaque reduction neutralization test (PRNT), which is currently the gold standard test for YFV. An overall correlation between the tests of 98.7% was established based on the analysis of 150 sera from individuals after vaccination with the 17D yellow fever vaccine. The sensitivity and specificity, calculated using the 150 sera from vaccinees and 150 sera from healthy blood donors, were 95% and 95%, respectively, for the IgG IFA and 94% and 97% for the IgM IFA. Antibody titers found in the PRNT correlated poorly with the IgM and IgG titers detected by IFA. The analysis of preexisting heterologous flaviviral immunity revealed the presence of antibodies reactive with YFV, tick-borne encephalitis virus, West Nile virus, Japanese encephalitis virus, and dengue virus serotypes 1 to 4 in 20 out of the 150 vaccinees. The indirect IFA showed that nine of these individuals with previous flaviviral exposure who received 17D vaccine failed to produce detectable IgM antibodies. Despite this preexisting immunity, all vaccinees developed protective immunity as detected by PRNT and anti-YFV IgG antibodies as detected by IFA. The high specificity and sensitivity of the IFA make it a useful tool for rapid diagnosis of yellow fever during outbreaks, for epidemiological studies, and for serosurveillance after vaccination.

Yellow Fever 17-D Vaccine Is Neurotropic and Produces Encephalitis in Immunosuppressed Hamsters

Immunosuppressed (cyclophosphamide) adult golden hamsters inoculated intraperitoneally (i.p.) with wild-type Asibi yellow fever virus (YFV) developed a rapidly fatal illness. Histopathologic and immunohistochemical studies of tissues from these animals showed typical hepatic changes of severe yellow fever (inflammation, hepatocyte necrosis, and steatosis) without brain involvement. In contrast, 50% of immunosuppressed hamsters receiving the YFV-17D-attenuated vaccine developed a slowly progressive encephalitic-type illness. Brain tissue from these latter animals revealed focal neuronal changes, inflammation, and YFV antigen-positive neurons; however, the liver and spleen appeared normal. YFV was isolated from brain cultures of many of these animals. Immunocompetent (non-immunosuppressed) hamsters inoculated with both viruses developed a subclinical infection. Results of this study indicate that wild-type YFV is hepatotropic in immunosuppressed hamsters, whereas the attenuated YFV-17 is primarily neurotropic. These findings support current recommendations against yellow fever vaccination of immunosuppressed/immunocompromised people and suggest that this hamster model might be useful for monitoring the safety of other live-attenuated YFV vaccines.

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.

INNATE IMMUNE RESPONSES IN HUMAN DENDRITIC CELLS UPON INFECTION BY CHIMERIC YELLOW-FEVER DENGUE VACCINE SEROTYPES 1–4

Dengue infection is an important public health issue worldwide. The ChimeriVax-Dengue (CYD) vaccine uses yellow fever (YF) 17D vaccine as a live vector. Dendritic cells (DCs) play a key role in initiating immune responses and could be an important primary target of dengue infection. We investigated in vitro the consequences of CYD infection of DCs on their activation/maturation and cytokine production. In CYD-infected DCs, we observed an up-regulation of HLA-DR, CD80, CD86, and CD83. Cells exposed to CYD secreted type I interferons, monocyte chemoattractant protein 1 (MCP-1)/CC chemokine ligand 2 (CCL-2), interleukin-6 (IL-6), and low amounts of tumor necrosis factor-alpha (TNF-alpha), but no IL-10, IL-12, or IL-1alpha. Parental dengue viruses induced a similar array of cytokines, but more TNF-alpha, less IL-6, and less MCP-1/CCL-2 than induced by CYD. Chimeras thus induced DCs maturation and a controlled response accompanied by limited inflammatory cytokine production and consistent expression of anti-viral interferons, in agreement with clinical observations of safety and immunogenicity.

Restricted replication and lysosomal trafficking of yellow fever 17D vaccine virus in human dendritic cells

The yellow fever virus attenuated 17D vaccine strain is a safe and effective vaccine and a valuable model system for evaluating immune responses against attenuated viral variants. This study compared the in vitro interactions of the commercially available yellow fever vaccine (YF-VAX), Dengue virus and the live-attenuated dengue vaccine PDK50 with dendritic cells (DCs), the main antigen-presenting cells at the initiation of immune responses. Similar to PDK50, infection with YF-VAX generated activated DCs; however, for YF-VAX, activation occurred with limited intracellular virus replication. The majority of internalized virus co-localized with endolysosomal markers within 90 min, suggesting that YF-VAX is processed rapidly in DCs. These results indicate that restricted virus replication and lysosomal compartmentalization may be important contributing factors to the success of the YF-VAX vaccine.

Yellow fever vaccine YF-17D activates multiple dendritic cell subsets via TLR2, 7, 8, and 9 to stimulate polyvalent immunity

The live attenuated yellow fever vaccine 17D (YF-17D) is one of the most effective vaccines available, with a 65-yr history of use in >400 million people globally. Despite this efficacy, there is presently no information about the immunological mechanisms by which YF-17D acts. Here, we present data that suggest that YF-17D activates multiple Toll-like receptors (TLRs) on dendritic cells (DCs) to elicit a broad spectrum of innate and adaptive immune responses. Specifically, YF-17D activates multiple DC subsets via TLRs 2, 7, 8, and 9 to elicit the proinflammatory cytokines interleukin (IL)-12p40, IL-6, and interferon-α. Interestingly, the resulting adaptive immune responses are characterized by a mixed T helper cell (Th)1/Th2 cytokine profile and antigen-specific CD8+ T cells. Furthermore, distinct TLRs appear to differentially control the Th1/Th2 balance; thus, whilst MyD88-deficient mice show a profound impairment of Th1 cytokines, TLR2-deficient mice show greatly enhanced Th1 and Tc1 responses to YF-17D. Together, these data enhance our understanding of the molecular mechanism of action of YF-17D, and highlight the potential of vaccination strategies that use combinations of different TLR ligands to stimulate polyvalent immune responses.

A recombinant Yellow Fever 17D vaccine expressing Lassa virus glycoproteins

The Yellow Fever Vaccine 17D (YFV17D) has been used as a vector for the Lassa virus glycoprotein precursor (LASV-GPC) resulting in construction of YFV17D/LASV-GPC recombinant virus. The virus was replication-competent and processed the LASV-GPC in cell cultures. The recombinant replicated poorly in guinea pigs but still elicited specific antibodies against LASV and YFV17D antigens. A single subcutaneous injection of the recombinant vaccine protected strain 13 guinea pigs against fatal Lassa Fever. This study demonstrates the potential to develop an YFV17D-based bivalent vaccine against two viruses that are endemic in the same area of Africa.

Neutralizing antibody response to booster vaccination with the 17d yellow fever vaccine

A retrospective review was conducted of yellow fever vaccination among laboratory workers receiving annual serologic assessment to determine the initial and long-term response after boosting. Patients were divided into three groups based on pre-vaccination serology: Group 1, 1:10; Group 2, 1:20–1:40 and Group 3, >1:40. The percent with ≥four-fold increase in titers after booster vaccination were: 78% (646/829, Group 1), 65% (79/121, Group 2) and 10% (8/79, Group 3) ( p < 0.0001). The median times to titer failure (<1:40) were 798 days (Group 1), 3340 days (Group 2) and 7709 days (Group 3) ( p < 0.0001). Pre-vaccination serology influenced the initial and long-term response to yellow fever booster vaccination.

Characterization of a viscerotropic yellow fever vaccine variant from a patient in Brazil

Although the live attenuated yellow fever (YF) 17D vaccine is considered to be one of the safest vaccines in the world today, several cases of disease associated with administration of the vaccine have been reported, including YF vaccine-associated viscerotropic disease (YF-VAVD), which was first described in 1996. All YF-VAVD isolates sequenced to date have shown very little genomic change when compared to their parental vaccine strains. In this study, we report the characterization of an isolate, BeH291597 (Brazil75), from a 1975 fatal case of YF-VAVD in Brazil. Comparison of Brazil75 with the genomic sequence of the parental 17DD vaccine strain revealed two amino acid substitutions (at positions M-49 and NS4B-240) that were unique to Brazil75. Although still a rare occurrence, this isolate suggests that YF-VAVD has been present much longer than previously recognized.

Expression of Foreign Protein Epitopes at the Surface of Recombinant Yellow Fever 17D Viruses Based on Three-Dimensional Modeling of Its Envelope Protein

The yellow fever (YF) 17D vaccine is a live attenuated virus, and its genetic manipulation constitutes a new platform for vaccine development. In this article, we review one of the possible approaches to enable this development, which is the insertion of foreign protein epitopes into different locations of the genome. We describe the three-dimensional (3D) modeling of the YF 17D virus E protein structure based on tick-borne encephalitis (TBE) and the identification of a potential insertion site located at the YF 17D fg loop. Further 3D analysis revealed that it is possible to accommodate inserts of different sizes and amino acid composition in the flavivirus E protein fg loop. We demonstrate that seven YF 17D viruses bearing foreign epitopes that vary in sequence and length show differential growth characteristics in cell culture. The testing of recombinant viruses for mouse neurovirulence suggests that insertions at the 17D E protein fg loop do not compromise the attenuated phenotype of YF 17D virus, further confirming the potential use of this site for the development of new live attenuated 17D virus-based vaccines.

Live attenuated yellow fever 17D infects human DCs and allows for presentation of endogenous and recombinant T cell epitopes

The yellow fever (YF) 17D vaccine is one of the most successful live attenuated vaccines available. A single immunization induces both long-lasting neutralizing antibody and YF-specific T cell responses. Surprisingly, the mechanism for this robust immunity has not been addressed. In light of several recent reports suggesting flavivirus interaction with dendritic cells (DCs), we investigated the mechanism of YF17D interaction with DCs and the importance of this interaction in generating T cell immunity. Our results show that YF17D can infect immature and mature human DCs. Viral entry is Ca2+ dependent, but it is independent of DC-SIGN as well as multiple integrins expressed on the DC surface. Similar to infection of cell lines, YF infection of immature DCs is cytopathic. Although infection itself does not induce DC maturation in vitro, TNF-α–induced maturation protects DCs from YF-induced cytopathogenicity. Furthermore, we show that DCs infected with YF17D or YF17D carrying a recombinant epitope can process and present antigens for CD8+ T cell stimulation. These findings offer insight into the immunologic mechanisms associated with the highly capable YF17D vaccine that may guide effective vaccine design.

Vaccination coverage survey versus administrative data in the assessment of mass yellow fever immunization in internally displaced persons—Liberia, 2004

Yellow fever (YF) is a mosquito-borne vaccine-preventable disease with high mortality. In West Africa, low population immunity increases the risk of epidemic transmission. A cluster survey was conducted to determine the effectiveness of a mass immunization campaign using 17D YF vaccine in internally displaced person (IDP) camps following a reported outbreak of YF in Liberia in February 2004. Administrative data of vaccination coverage were reviewed. A cluster sample size was determined among 17,384 shelters using an 80% vaccination coverage threshold. A questionnaire eliciting demographic information, household size, and vaccination status was distributed to randomly selected IDPs. Data were analyzed to compare vaccination coverage rates of administrative versus survey data. Among 87,000 persons estimated living in IDP camps, administrative data recorded 49,395 (57%) YF vaccinated persons. A total of 237 IDPs were surveyed. Of survey respondents, 215 (91.9%, 95% CI 88.4–95.4) reported being vaccinated during the campaign and 196 (83.5%, 95% CI 78.6–88.5) possessed a valid campaign vaccination card. The median number of IDPs living in a shelter was 4 (range, 1–8) and 69,536 persons overall were estimated to be living in IDP camps. Coverage rates from a rapid survey exceeded 90% by self-report and 80% by evidence of a vaccination card, indicating that the YF immunization campaign was effective. Survey results suggested that administrative data overestimated the camp population by at least 20%. An emergency, mop-up vaccination campaign was avoided. Coverage surveys can be vital in the evaluation of emergency vaccination campaigns by influencing both imminent and future immunization strategies.

Yellow Fever 17D Vaccine Safety and Immunogenicity in the Elderly

The incidence of serious and severe multisystem adverse events (AEs) following yellow fever (YF) 17D vaccine is higher in persons of advanced age. One hypothesis for the occurrence of these AEs in the elderly is immunological senescence and a reduced ability to clear the vaccine virus infection. We determined age-specific rates of serious and nonserious AEs in two large clinical trials of two YF 17D vaccines from different manufacturers. In addition, we analyzed AEs reported in a large general practice data base in the United Kingdom. Neutralizing antibody responses were compared in young and elderly subjects. In the clinical trials, involving a total of 4,532 subjects, there were no neurological and viscerotropic AEs; interestingly, the incidence of common injection site and systemic AEs was significantly lower in elderly than in younger subjects. The neutralizing antibody categorical and quantitative responses were equivalent across younger and elderly subjects. In contrast, the larger retrospective analysis of 43,555 persons receiving YF 17D in the UK general practice database revealed a higher incidence of significant neurologic and multisystem AEs with advancing age. The age-specific reporting rate ratio (RRR) was approximately twice that in the 25-44 year-old reference group for subjects in the 45-64 year age group (RRR 1.82; 95% CI 0.88,3.77) and 3-fold higher for the 65-74 year-old age group (RRR 2.82; 95% CI 0.81, 9.81). These results are consistent with previous reports on YF vaccine safety in the US (Martin M, et al. Emerg Infect Dis 2001;6:945-951; Khromova et al., Vaccine 2005;23:3256-3263). In elderly persons, YF 17D vaccine is associated with a higher frequency of significant AEs in the elderly but a lower incidence of common non-serious side-effects. The neutralizing antibody response, which is the mediator of protective immunity to YF, is not diminished in healthy, elderly persons.

Safety testing for neurovirulence of novel live, attenuated flavivirus vaccines: Infant mice provide an accurate surrogate for the test in monkeys

Current requirements for control of live viral vaccines, including yellow fever 17D, produced from potentially neurotropic wild-type viruses include tests for neurovirulence in nonhuman primates. We have used yellow fever 17D virus as a live vector for novel flavivirus vaccines (designated ChimeriVax™) against dengue, Japanese encephalitis (JE), and West Nile (WN) viruses. For control of these vaccines, it would be preferable to substitute a test in mice for the test in a higher species (monkeys). In this study, we compare the neurovirulence of ChimeriVax™ vaccine candidates in suckling mice inoculated by the intracerebral (IC) route with graded doses of the test article or yellow fever 17D vaccine as a reference control. Mortality ratio and survival distribution are the outcome measures. The monkey safety test is performed as described for control of yellow fever vaccines [World Health Organization. Tech Rep Ser, WHO, Geneva; 1997]. In both mice and monkeys, all chimeric vaccines were significantly less neurovirulent than yellow fever 17D vaccine. The test in suckling mice discriminated between strains of two different vaccines (ChimeriVax™-JE and ChimeriVax™-DEN1) differing by a single amino acid change, and was more sensitive for detecting virulence differences than the test in monkeys. The results indicate that the suckling mouse test is simple to perform, highly sensitive and, with appropriate validation, could complement or possibly even replace the neurovirulence component of the monkey safety test. The test in infant mice is particularly useful as a means of demonstrating biological consistency across seed virus and vaccine lots.