Prospects for induction of CD8 T cell-mediated immunity to Zika virus infection by yellow fever virus vaccination

Antigen-specific T cell responses following single and co-administration of tick-borne encephalitis, Japanese encephalitis, and yellow fever virus vaccines: Results from an open-label, non-randomized clinical trial-cohort

BACKGROUND

Flavivirus infections pose a significant global health burden, highlighting the need for safe and effective vaccination strategies. Co-administration of different vaccines, including licensed flavivirus vaccines, is commonly practiced providing protection against multiple pathogens while also saving time and reducing visits to healthcare units. However, how co-administration of different flavivirus vaccines de facto affects immunogenicity, particularly with respect to T cell responses, is only partially understood.

METHODS AND FINDINGS

Antigen-specific T cell responses were assessed in study participants enrolled in a previously conducted open-label, non-randomized clinical trial. In the trial, vaccines against tick-borne encephalitis virus (TBEV), Japanese encephalitis virus (JEV), or yellow fever virus (YFV) were administered either individually or concomitantly in different combinations in healthy study participants. Peripheral blood samples were collected before vaccination and at multiple time points afterward. To analyze antigen-specific CD4+ and CD8+ T cell responses, PBMCs were stimulated with overlapping peptide pools from TBEV, JEV, YFV, and Zika virus (ZIKV) envelope (E), capsid (C), and non-structural protein 5 (NS5) viral antigens. A flow cytometry-based activation-induced marker (AIM) assay was used to quantify antigen-specific T cell responses. The results revealed remarkably similar frequencies of CD4+ and CD8+ T cell responses, regardless of whether vaccines were administered individually or concomitantly. In addition, administering the vaccines in the same or different upper arms did not markedly affect T cell responses. Finally, limited cross-reactivity was observed between the TBEV, JEV, and YFV vaccines, and related ZIKV-specific antigens.

CONCLUSIONS

TBEV or JEV vaccines can be co-administered with the live attenuated YFV vaccine without any markedly altered antigen-specific CD4+ and CD8+ T cell responses to the respective flaviviruses. Additionally, the vaccines can be delivered in the same or different upper arms without any significant altered influence on the T cell response. From a broader perspective, these results provide valuable insights into the outcome of immune responses following simultaneous administration of different vaccines for different but related pathogens.

Safety and immunogenicity following co-administration of Yellow fever vaccine with Tick-borne encephalitis or Japanese encephalitis vaccines: Results from an open label, non-randomized clinical trial

BACKGROUND

Flavivirus infections pose a significant global health burden underscoring the need for the development of safe and effective vaccination strategies. Available flavivirus vaccines are from time to time concomitantly delivered to individuals. Co-administration of different vaccines saves time and visits to health care units and vaccine clinics. It serves to provide protection against multiple pathogens in a shorter time-span; e.g., for individuals travelling to different endemic areas. However, safety and immunogenicity-related responses have not been appropriately evaluated upon concomitant delivery of these vaccines. Therefore, we performed an open label, non-randomized clinical trial studying the safety and immunogenicity following concomitant delivery of the yellow fever virus (YFV) vaccine with tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JE) virus vaccines.

METHODS AND FINDINGS

Following screening, healthy study participants were enrolled into different cohorts receiving either TBEV and YFV vaccines, JEV and YFV vaccines, or in control groups receiving only the TBEV, JEV, or YFV vaccine. Concomitant delivery was given in the same or different upper arms for comparison in the co-vaccination cohorts. Adverse effects were recorded throughout the study period and blood samples were taken before and at multiple time-points following vaccination to evaluate immunological responses to the vaccines. Adverse events were predominantly mild in the study groups. Four serious adverse events (SAE) were reported, none of them deemed related to vaccination. The development of neutralizing antibodies (nAbs) against TBEV, JEV, or YFV was not affected by the concomitant vaccination strategy. Concomitant vaccination in the same or different upper arms did not significantly affect safety or immunogenicity-related outcomes. Exploratory studies on immunological effects were additionally performed and included studies of lymphocyte activation, correlates associated with germinal center activation, and plasmablast expansion.

CONCLUSIONS

Inactivated TBEV or JEV vaccines can be co-administered with the live attenuated YFV vaccine without an increased risk of adverse events and without reduced development of nAbs to the respective viruses. The vaccines can be delivered in the same upper arm without negative outcome. In a broader perspective, the results add valuable information for simultaneous administration of live and inactivated flavivirus vaccines in general.

TRIAL REGISTRATION

Eudra CT 2017-002137-32.

Peculiarities of Zika Immunity and Vaccine Development: Lessons from Dengue and the Contribution from Controlled Human Infection Model

The Zika virus (ZIKV) was first isolated from a rhesus macaque in the Zika forest of Uganda in 1947. Isolated cases were reported until 2007, when the first major outbreaks of Zika infection were reported from the Island of Yap in Micronesia and from French Polynesia in 2013. In 2015, ZIKV started to circulate in Latin America, and in 2016, ZIKV was considered by WHO to be a Public Health Emergency of International Concern due to cases of Congenital Zika Syndrome (CZS), a ZIKV-associated complication never observed before. After a peak of cases in 2016, the infection incidence dropped dramatically but still causes concern because of the associated microcephaly cases, especially in regions where the dengue virus (DENV) is endemic and co-circulates with ZIKV. A vaccine could be an important tool to mitigate CZS in endemic countries. However, the immunological relationship between ZIKV and other flaviviruses, especially DENV, and the low numbers of ZIKV infections are potential challenges for developing and testing a vaccine against ZIKV. Here, we discuss ZIKV vaccine development with the perspective of the immunological concerns implicated by DENV-ZIKV cross-reactivity and the use of a controlled human infection model (CHIM) as a tool to accelerate vaccine development.

Risk of Zika virus-associated birth defects in congenital confirmed cases in the Brazilian Amazon

Objective

To establish the risk of microcephaly in neonates born to women infected with ZIKV during pregnancy.

Methods

A cohort of laboratory-confirmed ZIKV cases of congenital infections (109 mothers infected during pregnancy and 101 newborns) among 308 suspect cases was followed in Belem, Pará, Brazil, from October 2015 to December 2017.

Results

A microcephaly risk of 1.98% (95% CI 0.54-6.93%) was found, or 2 cases among the 101 neonates infected with ZIKV during pregnancy. 72% of the pregnant women had ZIKV infection confirmed by RT-qPCR during gestation.

Conclusions

Results showed a low incidence of ZIKV-associated birth defects, stillbirth, and miscarriage, which contrasts with previous studies in other Brazilian regions. Previous exposure to yellow fever vaccine and/or multiserotype DENV infection could be implicated in the protection from ZIKV congenital infection.

Cell-Mediated Immune Responses and Immunopathogenesis of Human Tick-Borne Encephalitis Virus-Infection

Tick-borne encephalitis virus (TBEV) is a flavivirus that belongs to the Flaviviridae family. TBEV is transmitted to humans primarily from infected ticks. The virus causes tick-borne encephalitis (TBE), an acute viral disease that affects the central nervous system (CNS). Infection can lead to acute neurological symptoms of significant severity due to meningitis or meningo(myelo)encephalitis. TBE can cause long-term suffering and has been recognized as an increasing public health problem. TBEV-affected areas currently include large parts of central and northern Europe as well as northern Asia. Infection with TBEV triggers a humoral as well as a cell-mediated immune response. In contrast to the well-characterized humoral antibody-mediated response, the cell-mediated immune responses elicited to natural TBEV-infection have been poorly characterized until recently. Here, we review recent progress in our understanding of the cell-mediated immune response to human TBEV-infection. A particular emphasis is devoted to studies of the response mediated by natural killer (NK) cells and CD8 T cells. The studies described include results revealing the temporal dynamics of the T cell- as well as NK cell-responses in relation to disease state and functional characterization of these cells. Additionally, we discuss specific immunopathological aspects of TBEV-infection in the CNS.

Zika virus, vaccines, and antiviral strategies

INTRODUCTION

Zika virus (ZIKV) recently emerged as a global public health emergency of international concern. ZIKV is responsible for severe neurological complications in adults and infection during pregnancy and can lead to congenital Zika syndrome. There is no licensed vaccine or drug to prevent or treat ZIKV infection. Areas covered: The aim of this article is to provide an overview and update of the progress of research on anti-ZIKV vaccine and medications until the end of 2017, with a special emphasis on drugs that can be used during pregnancy. Expert commentary: Development of new vaccines and drugs is challenging and several points particular to ZIKV infections augment this difficulty: (1) Cross-reactions between ZIKV and other flaviviruses, the impact of ZIKV vaccination on subsequent flavivirus infections, and vice-versa, is unknown, (2) Drugs against ZIKV should be safe in pregnant women, and (3) Evaluation of the efficacy of vaccine and drugs against ZIKV in clinical trials phase II-IV will be complicated due to the decline of ZIKV circulation.

Human T-cell immunity against the emerging and re-emerging viruses

Over the past decade, we have seen an alarming number of high-profile outbreaks of newly emerging and re-emerging viruses. Recent outbreaks of avian influenza viruses, Middle East respiratory syndrome coronaviruses, Zika virus and Ebola virus present great threats to global health. Considering the pivotal role of host T-cell immunity in the alleviation of symptoms and the clearance of viruses in patients, there are three issues to be primarily concerned about T-cell immunity when a new virus emerges: first, does the population possess pre-existing T-cells against the new virus through previous infections of genetically relevant viruses; second, does a proper immune response arise in the patients to provide protection through an immunopathogenic effect; lastly, how long can the virus-specific immune memory persist. Herein, we summarize the current updates on the characteristics of human T-cell immunological responses against recently emerged or re-emerged viruses, and emphasize the necessity for timely investigation on the T-cell features of these viral diseases, which may provide beneficial recommendations for clinical diagnosis and vaccine development.