T-cell Responses in Individuals Infected with Zika Virus and in Those Vaccinated Against Dengue Virus

Comprehensive analysis of early T cell responses to acute Zika Virus infection during the first epidemic in Bahia, Brazil

BACKGROUND

In most cases, Zika virus (ZIKV) causes a self-limited acute illness in adults, characterized by mild clinical symptoms that resolve within a few days. Immune responses, both innate and adaptive, play a central role in controlling and eliminating virus-infected cells during the early stages of infection.

AIM

To test the hypothesis that circulating T cells exhibit phenotypic and functional activation characteristics during the viremic phase of ZIKV infection.

METHODS

A comprehensive analysis using mass cytometry was performed on peripheral blood mononuclear cells obtained from patients with acute ZIKV infection (as confirmed by RT-PCR) and compared with that from healthy donors (HD). The frequency of IFN-γ-producing T cells in response to peptide pools covering immunogenic regions of structural and nonstructural ZIKV proteins was quantified using an ELISpot assay.

RESULTS

Circulating CD4+ and CD8+ T lymphocytes from ZIKV-infected patients expressed higher levels of IFN-γ and pSTAT-5, as well as cell surface markers associated with proliferation (Ki-67), activation ((HLA-DR, CD38) or exhaustion (PD1 and CTLA-4), compared to those from HD. Activation of CD4+ and CD8+ memory T cell subsets, including Transitional Memory T Cells (TTM), Effector Memory T cells (TEM), and Effector Memory T cells Re-expressing CD45RA (TEMRA), was prominent among CD4+ T cell subset of ZIKV-infected patients and was associated with increased levels of IFN-γ, pSTAT-5, Ki-67, CTLA-4, and PD1, as compared to HD. Additionally, approximately 30% of ZIKV-infected patients exhibited a T cell response primarily directed against the ZIKV NS5 protein.

CONCLUSION

Circulating T lymphocytes spontaneously produce IFN-γ and express elevated levels of pSTAT-5 during the early phase of ZIKV infection whereas recognition of ZIKV antigen results in the generation of virus-specific IFN-γ-producing T cells.

Current Understanding of the Role of T Cells in Chikungunya, Dengue and Zika Infections

Arboviral infections such as Chikungunya (CHIKV), Dengue (DENV) and Zika (ZIKV) are a major disease burden in tropical and sub-tropical countries, and there are no effective vaccinations or therapeutic drugs available at this time. Understanding the role of the T cell response is very important when designing effective vaccines. Currently, comprehensive identification of T cell epitopes during a DENV infection shows that CD8 and CD4 T cells and their specific phenotypes play protective and pathogenic roles. The protective role of CD8 T cells in DENV is carried out through the killing of infected cells and the production of proinflammatory cytokines, as CD4 T cells enhance B cell and CD8 T cell activities. A limited number of studies attempted to identify the involvement of T cells in CHIKV and ZIKV infection. The identification of human immunodominant ZIKV viral epitopes responsive to specific T cells is scarce, and none have been identified for CHIKV. In CHIKV infection, CD8 T cells are activated during the acute phase in the lymph nodes/blood, and CD4 T cells are activated during the chronic phase in the joints/muscles. Studies on the role of T cells in ZIKV-neuropathogenesis are limited and need to be explored. Many studies have shown the modulating actions of T cells due to cross-reactivity between DENV-ZIKV co-infections and have repeated heterologous/homologous DENV infection, which is an important factor to consider when developing an effective vaccine.

CD4+ T Cells Cross-Reactive with Dengue and Zika Viruses Protect against Zika Virus Infection

The underlying mechanisms by which prior immunity to dengue virus (DENV) affords cross-protection against the related flavivirus Zika virus (ZIKV) are poorly understood. Here, we examine the ability of DENV/ZIKV-cross-reactive CD4⁺ T cells to protect against versus exacerbate ZIKV infection by using a histocompatibility leukocyte antigen (HLA)-DRB1*0101 transgenic, interferon α/β receptor-deficient mouse model that supports robust DENV and ZIKV replication. By mapping the HLA-DRB1*0101-restricted T cell response, we identify DENV/ZIKV-cross-reactive CD4⁺ T cell epitopes that stimulate interferon gamma (IFNγ) and/or tumor necrosis factor (TNF) production. Vaccination of naive HLA-DRB1*0101 transgenic mice with these peptides induces a CD4⁺ T cell response sufficient to reduce tissue viral burden following ZIKV infection. Notably, this protective response requires IFNγ and/or TNF secretion but not anti-ZIKV immunoglobulin G (IgG) production. Thus, DENV/ZIKV-cross-reactive CD4⁺ T cells producing canonical Th1 cytokines can suppress ZIKV replication in an antibody-independent manner. These results may have important implications for increasing the efficacy and safety of DENV/ZIKV vaccines and for developing pan-flavivirus vaccines.

Pre-existing Immunity to Japanese Encephalitis Virus Alters CD4 T Cell Responses to Zika Virus Inactivated Vaccine

The epidemic spread of Zika virus (ZIKV), associated with devastating neurologic syndromes, has driven the development of multiple ZIKV vaccines candidates. An effective vaccine should induce ZIKV-specific T cell responses, which are shown to improve the establishment of humoral immunity and contribute to viral clearance. Here we investigated how previous immunization against Japanese encephalitis virus (JEV) and yellow fever virus (YFV) influences T cell responses elicited by a Zika purified-inactivated virus (ZPIV) vaccine. We demonstrate that three doses of ZPIV vaccine elicited robust CD4 T cell responses to ZIKV structural proteins, while ZIKV-specific CD4 T cells in pre-immunized individuals with JEV vaccine, but not YFV vaccine, were more durable and directed predominantly toward conserved epitopes, which elicited Th1 and Th2 cytokine production. In addition, T cell receptor repertoire analysis revealed preferential expansion of cross-reactive clonotypes between JEV and ZIKV, suggesting that pre-existing immunity against JEV may prime the establishment of stronger CD4 T cell responses to ZPIV vaccination. These CD4 T cell responses correlated with titers of ZIKV-neutralizing antibodies in the JEV pre-vaccinated group, but not in flavivirus-naïve or YFV pre-vaccinated individuals, suggesting a stronger contribution of CD4 T cells in the generation of neutralizing antibodies in the context of JEV-ZIKV cross-reactivity.

CD8+ T cells mediate protection against Zika virus induced by an NS3-based vaccine

Zika virus (ZIKV) is associated with congenital malformations in infants born to infected mothers, and with Guillain-Barré syndrome in infected adults. Development of ZIKV vaccines has focused predominantly on the induction of neutralizing antibodies, although a suboptimal antibody response may theoretically enhance disease severity through antibody-dependent enhancement (ADE). Here, we report induction of a protective anti-ZIKV CD8+ T cell response in the HLA-B*0702 Ifnar1-/- transgenic mice using an alphavirus-based replicon RNA vaccine expressing ZIKV nonstructural protein NS3, a potent T cell antigen. The NS3 vaccine did not induce a neutralizing antibody response but elicited polyfunctional CD8+ T cells that were necessary and sufficient for preventing death in lethally infected adult mice and fetal growth restriction in infected pregnant mice. These data identify CD8+ T cells as the major mediators of ZIKV NS3 vaccine-induced protection and suggest a new strategy to develop safe and effective anti-flavivirus vaccines.

Multifunctional T cell response in convalescent patients two years after ZIKV infection

Zika is an important emerging infectious disease in which the role of T cells remains elusive. This study aimed to evaluate the phenotype of multifunctional T cells in individuals 2 yr after exposure to Zika virus (ZIKV). We used a library of 671 synthetic peptides covering the whole polyprotein of ZIKV in pools corresponding to each viral protein (i.e., capsid, membrane precursor or prM, envelope, NS1 [nonstructural protein], NS2A + NS2B, NS3, NS4A + NS4B, and NS5) to stimulate PBMCs from individuals previously exposed to ZIKV. We observed an increased frequency of ZIKV-specific IFNγ, IL-17A, TNF, and IL-10 production by T cell populations. IFNγ and TNF production were especially stimulated by prM, capsid, or NS1 in CD8+ T cells and by capsid or prM in CD4+ T cells. In addition, there was an increase in the frequency of IL-10+ CD8+ T cells after stimulation with prM, capsid, NS1, NS3, or NS5. Multifunctional properties were observed in ZIKV-specific T cells responding especially to prM, capsid, NS1 or, to a smaller extent, NS3 antigens. For example, we found a consistent IFNγ + TNF+ CD8+ T cell population in response to most virus antigens and CD4+ and CD8+ T cells that were IFNγ + IL-17A+ and IL-17A+IL-10+, which could also produce TNF, in response to capsid, prM, NS1, or NS3 stimulation. Interestingly, CD8+ T cells were more prone to a multifunctional phenotype than CD4+ T cells, and multifunctional T cells were more efficient at producing cytokines than single-function cells. This work provides relevant insights into the quality of ZIKV-specific T cell responses and ZIKV immunity.

Protective to a T: The Role of T Cells during Zika Virus Infection

CD4 and CD8 T cells are an important part of the host's capacity to defend itself against viral infections. During flavivirus infections, T cells have been implicated in both protective and pathogenic responses. Given the recent emergence of Zika virus (ZIKV) as a prominent global health threat, the question remains as to how T cells contribute to anti-ZIKV immunity. Furthermore, high homology between ZIKV and other, co-circulating flaviviruses opens the possibility of positive or negative effects of cross-reactivity due to pre-existing immunity. In this review, we will discuss the CD4 and CD8 T cell responses to ZIKV, and the lessons we have learned from both mouse and human infections. In addition, we will consider the possibility of whether T cells, in the context of flavivirus-naïve and flavivirus-immune subjects, play a role in promoting ZIKV pathogenesis during infection.

Peptide-Based Subunit Vaccine Design of T- and B-Cells Multi-Epitopes against Zika Virus Using Immunoinformatics Approaches

The Zika virus disease, also known as Zika fever is an arboviral disease that became epidemic in the Pacific Islands and had spread to 18 territories of the Americas in 2016. Zika virus disease has been linked to several health problems such as microcephaly and the Guillain-Barré syndrome, but to date, there has been no vaccine available for Zika. Problems related to the development of a vaccine include the vaccination target, which covers pregnant women and children, and the antibody dependent enhancement (ADE), which can be caused by non-neutralizing antibodies. The peptide vaccine was chosen as a focus of this study as a safer platform to develop the Zika vaccine. In this study, a collection of Zika proteomes was used to find the best candidates for T- and B-cell epitopes using the immunoinformatics approach. The most promising T-cell epitopes were mapped using the selected human leukocyte antigen (HLA) alleles, and further molecular docking and dynamics studies showed a good peptide-HLA interaction for the best major histocompatibility complex-II (MHC-II) epitope. The most promising B-cell epitopes include four linear peptides predicted to be cross-reactive with T-cells, and conformational epitopes from two proteins accessible by antibodies in their native biological assembly. It is believed that the use of immunoinformatics methods is a promising strategy against the Zika viral infection in designing an efficacious multiepitope vaccine.

Generation of Zika virus-specific T cells from seropositive and virus-naïve donors for potential use as an autologous or "off-the-shelf" immunotherapeutic

BACKGROUND

Zika virus (ZIKV) infection can cause severe birth defects in newborns with no effective currently available treatment. Adoptive transfer of virus-specific T cells has proven to be safe and effective for the prevention or treatment of many viral infections, and could represent a novel treatment approach for patients with ZIKV infection. However, extending this strategy to the ZIKV setting has been hampered by limited data on immunogenic T-cell antigens within ZIKV. Hence, we have generated ZIKV-specific T cells and characterized the cellular immune responses against ZIKV antigens.

METHODS

T-cell products were generated from peripheral blood of ZIKV-exposed donors, ZIKV-naive adult donors and umbilical cord blood by stimulation with pentadecamer (15mer) overlapping peptide libraries spanning four ZIKV polyproteins (C, M, E and NS1) using a Good Manufacturing Practice-compliant protocol.

RESULTS

We successfully generated T cells targeting ZIKV antigens with clinically relevant numbers. The ex vivo-expanded T cells comprised both CD4⁺ and CD8⁺ T cells that were able to produce Th1-polarized effector cytokines and kill ZIKV-infected HLA-matched monocytes, confirming functionality of this unique T-cell product as a potential "off-the-shelf" therapeutic. Epitope mapping using peptide arrays identified several novel HLA class I and class II-restricted epitopes within NS1 antigen, which is essential for viral replication and immune evasion.

DISCUSSION

Our findings demonstrate that it is feasible to generate potent ZIKV-specific T cells from a variety of cell sources including virus naïve donors for future clinical use in an "off-the-shelf" setting.

Cross-Reactive T Cell Immunity to Dengue and Zika Viruses: New Insights Into Vaccine Development

Dengue virus (DENV) is a member of the Flavivirus family that includes Zika virus (ZIKV), West Nile virus, Japanese encephalitis virus, and yellow fever virus. As the most prevalent of the flaviviruses, DENV is responsible for tens of millions of infections each year. The clinical manifestations of infection with one of the four DENV serotypes (DENV1–4) range from no symptoms to hemorrhagic fever and shock (“severe dengue”), which is fatal in ~25,000 patients annually. Many factors contribute to the development of severe dengue, including the DENV serotype and host expression of certain HLA alleles; however, it now seems clear that pre-existing immunity to DENV—and possibly other flaviviruses—is a major precipitating factor. While primary infection with one DENV serotype elicits strong cellular and humoral immune responses that likely confer long-lived protection against the same serotype, subsequent infection with a different serotype carries an increased risk of developing severe dengue. Thus, primary DENV infection elicits cross-reactive immunity that may be protective or pathogenic, depending on the context of the subsequent infection. Many flaviviruses share high sequence homology, raising the possibility that cross-reactive immunity to one virus may contribute to protection against or pathogenesis of a second virus in a similar manner. In addition, several flaviviruses are now endemic in overlapping geographic regions, underscoring the need to gain more knowledge about the mechanisms underlying cross-reactive immunity to different DENV serotypes and flaviviruses. Here, we review our current understanding of T cell immunity to DENV, focusing on cross-reactivity with other serotypes and flaviviruses such as ZIKV, and the role of DENV-elicited CD4⁺ and CD8⁺ T cells in protection. Recent work in this area supports a beneficial role for cross-reactive T cells and provides new insights into the design of safe and efficient flavivirus/pan-flavivirus vaccines.

Antigenic cross-reactivity between Zika and dengue viruses: is it time to develop a universal vaccine?

Zika and the four serotypes of dengue are closely related flaviviruses that share a high degree of structural and sequence homology and co-circulate in many regions of the world. Here, we review recent studies investigating antigenic cross-reactivity between the two viruses. We discuss the pathogenic and protective roles of cross-reactive anti-viral antibody and T cell responses, respectively, in modulating the outcome of secondary dengue or Zika infection. Based on recent findings and increased incidence of severe disease in seronegative recipients of the first dengue vaccine to be licensed, we propose that the time has come to focus on developing pan-flavivirus vaccines that protect against Zika and four dengue serotypes by eliciting protective cross-reactive T cell responses while concomitantly reducing production of cross-reactive antibodies that can exacerbate disease.

A longitudinal systems immunologic investigation of acute Zika virus infection in an individual infected while traveling to Caracas, Venezuela

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus linked to devastating neurologic diseases. Immune responses to flaviviruses may be pathogenic or protective. Our understanding of human immune responses to ZIKV in vivo remains limited. Therefore, we performed a longitudinal molecular and phenotypic characterization of innate and adaptive immune responses during an acute ZIKV infection. We found that innate immune transcriptional and genomic responses were both cell type- and time-dependent. While interferon stimulated gene induction was common to all innate immune cells, the upregulation of important inflammatory cytokine genes was primarily limited to monocyte subsets. Additionally, genomic analysis revealed substantial chromatin remodeling at sites containing cell-type specific transcription factor binding motifs that may explain the observed changes in gene expression. In this dengue virus-experienced individual, adaptive immune responses were rapidly mobilized with T cell transcriptional activity and ZIKV neutralizing antibody responses peaking 6 days after the onset of symptoms. Collectively this study characterizes the development and resolution of an in vivo human immune response to acute ZIKV infection in an individual with pre-existing flavivirus immunity.

Zika virus (ZIKV) is an emerging flaviviral infection that causes significant clinical disease. It is estimated that approximately one half of the world’s population is at risk for ZIKV infection. There are only a limited number of studies describing the human immune response to ZIKV infection. Carlin et al. combined conventional and genomic approaches to longitudinally analyze the innate and adaptive immune responses to acute ZIKV infection and its resolution in a person who was infected while traveling in Venezuela during the 2016 ZIKV epidemic year. Genome-wide sequencing in individual cell types revealed that although many populations respond to interferon stimulation, only specific cell populations within peripheral blood mononuclear cells upregulate important inflammatory cytokine gene expression. Additionally, analysis of open chromatin using ATAC-seq suggests that chromatin remodeling at sites containing cell-type specific transcription factor binding motifs may help us understand changes in gene expression. Consistent with previous reports, this individual with prior exposure to dengue virus (DENV), rapidly developed neutralizing anti-ZIKV responses that were cross-reactive with multiple DENV serotypes. Collectively this study combines traditional and genomic approaches to characterize the cell-type specific development of an in vivo human immune response to acute ZIKV infection.

Memory T Cells in Flavivirus Vaccination

Flaviviruses include many medically important viruses, such as Dengue virus (DENV), Japanese encephalitis (JEV), tick-borne encephalitis (TBEV), West Nile (WNV), yellow fever (YFV), and Zika viruses (ZIKV). Currently, there are licensed human vaccines for DENV, JEV, TBEV and YFV, but not for WNV or ZIKV. Memory T cells play a central role in adaptive immunity and are important for host protection during flavivirus infection. In this review, we discuss recent findings from animal models and clinical trials and provide new insights into the role of memory T cells in host protective immunity upon vaccination with the licensed flavivirus vaccines.

Cross-reactive Dengue virus-specific CD8+ T cells protect against Zika virus during pregnancy

As Zika virus (ZIKV) emerges into Dengue virus (DENV)-endemic areas, cases of ZIKV infection in DENV-immune pregnant women may rise. Here we show that prior DENV immunity affects maternal and fetal ZIKV infection in pregnancy using sequential DENV and ZIKV infection models. Fetuses in ZIKV-infected DENV-immune dams were normal sized, whereas fetal demise occurred in non-immune dams. Moreover, reduced ZIKV RNA is present in the placenta and fetuses of ZIKV-infected DENV-immune dams. DENV cross-reactive CD8⁺ T cells expand in the maternal spleen and decidua of ZIKV-infected dams, their depletion increases ZIKV infection in the placenta and fetus, and results in fetal demise. The inducement of cross-reactive CD8⁺ T cells via peptide immunization or adoptive transfer results in decreased ZIKV infection in the placenta. Prior DENV immunity can protect against ZIKV infection during pregnancy in mice, and CD8⁺ T cells are sufficient for this cross-protection. This has implications for understanding the natural history of ZIKV in DENV-endemic areas and the development of optimal ZIKV vaccines.

Current concerns and perspectives on Zika virus co-infection with arboviruses and HIV

Dissemination of vector-borne viruses, such as Zika virus (ZIKV), in tropical and sub-tropical regions has a complicated impact on the immunopathogenesis of other endemic viruses such as dengue virus (DENV), chikungunya virus (CHIKV) and human immunodeficiency virus (HIV). The consequences of the possible co-infections with these viruses have specifically shown significant impact on the treatment and vaccination strategies. ZIKV is a mosquito-borne flavivirus from African and Asian lineages that causes neurological complications in infected humans. Many of DENV and CHIKV endemic regions have been experiencing outbreaks of ZIKV infection. Intriguingly, the mosquitoes, Aedes Aegypti and Aedes Albopictus, can simultaneously transmit all the combinations of ZIKV, DENV, and CHIKV to the humans. The co-circulation of these viruses leads to a complicated immune response due to the pre-existence or co-existence of ZIKV infection with DENV and CHIKV infections. The non-vector transmission of ZIKV, especially, via sexual intercourse and placenta represents an additional burden that may hander the treatment strategies of other sexually transmitted diseases such as HIV. Collectively, ZIKV co-circulation and co-infection with other viruses have inevitable impact on the host immune response, diagnosis techniques, and vaccine development strategies for the control of these co-infections.

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.

T-cell Responses in Individuals Infected with Zika Virus and in Those Vaccinated Against Dengue Virus

BACKGROUND

The outbreak of Zika virus (ZIKV) infection in Brazil has raised concerns that infection during pregnancy could cause microcephaly and other severe neurodevelopmental malformations in the fetus. The mechanisms by which ZIKV causes fetal abnormalities are largely unknown. The importance of pre-infection with dengue virus (DENV), or other flaviviruses endemic to Brazil, remains to be investigated. It has been reported that antibodies directed against DENV can increase ZIKV infectivity by antibody dependent enhancement (ADE), suggesting that a history of prior DENV infection might worsen the outcome of ZIKV infection.

METHODS

We used bioinformatics tools to design 18 peptides from the ZIKV envelope containing predicted HLA-I T-cell epitopes and investigated T-cell cross-reactivity between ZIKV-infected individuals and DENV-vaccinated subjects by IFNγ ELISPOT.

RESULTS

Three peptides induced IFNγ production in both ZIKV-infected subjects and in DENV-vaccinated individuals. Flow cytometry indicated that 1 ZIKV peptide induced a CD4+ T-cell response in DENV-vaccinated subjects.

CONCLUSIONS

We demonstrated that vaccination against DENV induced a T-cell response against ZIKV and identified one such CD4+ T-cell epitope. The ZIKV-reactive CD4+ T cells induced by DENV vaccination and identified in this study could contribute to the appearance of cross-reactive antibodies mediating ADE.