The role of CD8 + T cells in dengue virus infection and subsequent disease manifestations is not fully understood. According to the original antigenic sin theory, skewing of T-cell responses induced by primary infection with one serotype causes less effective response upon secondary infection with a different serotype, predisposing individuals to severe disease. A comprehensive analysis of CD8 + responses in the general population from the Sri Lankan hyperendemic area, involving the measurement of ex vivo IFNγ responses associated with more than 400 epitopes, challenges the original antigenic sin theory. Although skewing of responses toward primary infecting viruses was detected, this was not associated with impairment of responses either qualitatively or quantitatively. Furthermore, we demonstrate higher magnitude and more polyfunctional responses for HLA alleles associated with decreased susceptibility to severe disease, suggesting that a vigorous response by multifunctional CD8 + T cells is associated with protection from dengue virus disease.

T-cells have to recognize peptides presented on MHC molecules to be activated and elicit their effector functions. Several studies demonstrate that some peptides are more immunogenic than others and therefore more likely to be T-cell epitopes. We set out to determine which properties cause such differences in immunogenicity. To this end, we collected and analyzed a large set of data describing the immunogenicity of peptides presented on various MHC-I molecules. Two main conclusions could be drawn from this analysis: First, in line with previous observations, we showed that positions P4–6 of a presented peptide are more important for immunogenicity. Second, some amino acids, especially those with large and aromatic side chains, are associated with immunogenicity. This information was combined into a simple model that was used to demonstrate that immunogenicity is, to a certain extent, predictable. This model (made available at http://tools.iedb.org/immunogenicity/) was validated with data from two independent epitope discovery studies. Interestingly, with this model we could show that T-cells are equipped to better recognize viral than human (self) peptides. After the past successful elucidation of different steps in the MHC-I presentation pathway, the identification of variables that influence immunogenicity will be an important next step in the investigation of T-cell epitopes and our understanding of cellular immune responses.

Dengue virus (DENV) is a rapidly spreading pathogen with unusual pathogenesis, and correlates of protection from severe dengue disease and vaccine efficacy have not yet been established. Although DENV-specific CD8 + T-cell responses have been extensively studied, the breadth and specificity of CD4 + T-cell responses remains to be defined. Here we define HLA-restricted CD4 + T-cell epitopes resulting from natural infection with dengue virus in a hyperepidemic setting. Ex vivo flow-cytometric analysis of DENVspecific CD4+ T cells revealed that the virus-specific cells were highly polarized, with a strong bias toward a CX3CR1 A ll four of the dengue virus serotypes (DENV 1-4) have spread rapidly within countries and across regions in the past few decades, resulting in an increased frequency of epidemics and severe dengue disease. Multiple serotypes circulate simultaneously in many tropical countries, and recent outbreaks have been reported in Europe and the continental United States (1, 2). These circumstances make dengue the most prevalent and rapidly spreading mosquito-borne viral disease in humans (3). Recent reports estimate that 390 million infections occur each year, with ∼25% of cases resulting in symptomatic disease (2).All four dengue serotypes can cause a spectrum of disease, ranging from self-limiting dengue fever to potentially lethal severe dengue disease, such as states of dengue hemorrhagic fever and Dengue shock syndrome, which are associated with the plasma leakage syndromes leading to visceral organ injury (4). It is not yet fully understood why only a subset of people infected with DENV progresses to severe disease. One risk factor for severe disease is the acquisition of DENV-reactive Abs before secondary infection with a different serotype (heterologous infection). These Abs can either be acquired from a previous infection with a different serotype or, in the case of infants, acquired from an immune mother (5, 6). It has been shown that subneutralizing levels of DENV-specific Abs exacerbate disease in a phenomenon termed Ab-dependent enhancement of infection (7,8). In brief, dengue-specific crossreactive Abs produced after an initial DENV infection combine with those produced after a second viral infection to form immune complexes that perpetuate infection by increasing the number of infected cells and, therefore, viral output per cell (6).The observation that only a minority of patients develops severe disease suggests that host genetic factors may play an important role in disease severity. Relatedly, a role for T cells in control of disease has been suggested by several studies that correlate the expression of certain HLA molecules with susceptibility to or protection from DENV disease (9-15). HLA molecules are one of the most polymorphic host factors in humans, with several thousand variants thus far known (16,17). Each HLA variant is present with variable frequency, depending on ethnic lineage and geographic locality. For HLA class I MHC restricted responses, it has been recently shown tha...

CD4+ cytotoxic T lymphocytes (CD4-CTLs) have been reported to play a protective role in several viral infections. However, little is known in humans about the biology of CD4-CTL generation, their functional properties, and heterogeneity, especially in relation to other well-described CD4+ memory T cell subsets. We performed single-cell RNA sequencing in more than 9000 cells to unravel CD4-CTL heterogeneity, transcriptional profile, and clonality in humans. Single-cell differential gene expression analysis revealed a spectrum of known transcripts, including several linked to cytotoxic and costimulatory function that are expressed at higher levels in the TEMRA (effector memory T cells expressing CD45RA) subset, which is highly enriched for CD4-CTLs, compared with CD4+ T cells in the central memory (TCM) and effector memory (TEM) subsets. Simultaneous T cell antigen receptor (TCR) analysis in single cells and bulk subsets revealed that CD4-TEMRA cells show marked clonal expansion compared with TCM and TEM cells and that most of CD4-TEMRA were dengue virus (DENV)–specific in donors with previous DENV infection. The profile of CD4-TEMRA was highly heterogeneous across donors, with four distinct clusters identified by the single-cell analysis. We identified distinct clusters of CD4-CTL effector and precursor cells in the TEMRA subset; the precursor cells shared TCR clonotypes with CD4-CTL effectors and were distinguished by high expression of the interleukin-7 receptor. Our identification of a CD4-CTL precursor population may allow further investigation of how CD4-CTLs arise in humans and, thus, could provide insights into the mechanisms that may be used to generate durable and effective CD4-CTL immunity.

The expression of CD45RA is generally associated with naive T cells. However, a subset of effector memory T cells re-expresses CD45RA (termed TEMRA) after antigenic stimulation with unknown molecular characteristics and functions. CD4 TEMRA cells have been implicated in protective immunity against pathogens such as dengue virus (DENV). Here we show that not only the frequency but also the phenotype of CD4 TEMRA cells are heterogeneous between individuals. These cells can be subdivided into two major subsets based on the expression of the adhesion G protein-coupled receptor GPR56, and GPR56 + TEMRA cells display a transcriptional and proteomic program with cytotoxic features that is distinct from effector memory T cells. Moreover, GPR56 + TEMRA cells have higher levels of clonal expansion and contain the majority of virus-specific TEMRA cells. Overall, this study reveals the heterogeneity of CD4 TEMRA cells and provides insights into T-cell responses against DENV and other viral pathogens.

The incidence of infection with any of the four dengue virus serotypes (DENV1 to -4) has increased dramatically in the last few decades, and the lack of a treatment or vaccine has contributed to significant morbidity and mortality worldwide. A recent comprehensive analysis of the human T cell response against wild-type DENV suggested an human lymphocyte antigen (HLA)-linked protective role for CD8 ؉ T cells. We have collected one-unit blood donations from study participants receiving the monovalent or tetravalent live attenuated DENV vaccine (DLAV), developed by the U.S. National Institutes of Health. Peripheral blood mononuclear cells from these donors were screened in gamma interferon enzyme-linked immunosorbent spot assays with pools of predicted, HLA-matched, class I binding peptides covering the entire DENV proteome. Here, we characterize for the first time CD8؉ T cell responses after live attenuated dengue vaccination and show that CD8 ؉ T cell responses in vaccinees were readily detectable and comparable to natural dengue infection. Interestingly, whereas broad responses to structural and nonstructural (NS) proteins were observed after monovalent vaccination, T cell responses following tetravalent vaccination were, dramatically, focused toward the highly conserved NS proteins. Epitopes were highly conserved in a vast variety of field isolates and able to elicit multifunctional T cell responses. Detailed knowledge of the T cell response will contribute to the identification of robust correlates of protection in natural immunity and following vaccination against DENV. IMPORTANCEThe development of effective vaccination strategies against dengue virus (DENV) infection and clinically significant disease is a task of high global public health value and significance, while also being a challenge of significant complexity. A recent efficacy trial of the most advanced dengue vaccine candidate, demonstrated only partial protection against all four DENV serotypes, despite three subsequent immunizations and detection of measurable neutralizing antibodies to each serotype in most subjects. These results challenge the hypothesis that seroconversion is the only reliable correlate of protection. Here, we show that CD8 ؉ T cell responses in vaccinees were readily detectable and comparable to natural dengue virus infection. Detailed knowledge of the T cell response may further contribute to the identification of robust correlates of protection in natural immunity and vaccination against DENV. Infections with dengue virus (DENV) occur with high incidence in more than 100 countries around the world. Recent reports estimate the number of annual infections with any of the four DENV serotypes (DENV1 to -4) to be as high as 390 million, of which 96 million manifest as clinically significant diseases, including life-threatening conditions such as dengue hemorrhagic fever and dengue shock syndrome (1). This constitutes an increasing public health problem in tropical and subtropical regions and underscores the urgent need f...

Summary A major obstacle to tuberculosis (TB) control is the problem of chronic TB infection (CTBI). NOS2-/-and gp91phox -/-mice given aminoguanidine [to suppress the effects of nitric oxide synthase 2 (NOS2)] -indicating minimal metabolic effect on the cysH mutant survival in these mice. The cysH mutant was also susceptible to peroxynitrite and hydrogen peroxide in vitro . These results show that CysH is important for Mtb protection during the chronic infection phase, and that resistance to nitrosative and oxidative stress may be the mechanism of this protection. Thus, this metabolic gene of an intracellular pathogen could have a secondary role in protection against the host immune response. Finally the lack of an endogenous human orthologue of cysH and its possible role in defence against adaptive immunity renders CysH an attractive enzyme for further studies as a target for therapeutics active against CTBI.

Infection with chikungunya virus (CHIKV) causes an acute illness characterized by fever, rash, and arthralgia. However, CHIKV infection can sometimes progress to chronic arthritis or even lethal disease. CHIKV continues to cause substantial morbidity worldwide as its vector mosquitoes expand and spread. There are currently no approved vaccines or antiviral drugs available for the prevention or treatment of CHIKV. Although antibody therapy has shown promise in the prevention or treatment of CHIKV disease in preclinical models, challenges remain for implementing such therapies. Here, from the B cells of a survivor of natural CHIKV infection, we isolated ultrapotent neutralizing human monoclonal antibodies (mAbs) and encoded their sequences into mRNA molecules delivered by infusion. One human mAb, CHKV-24, was expressed to biologically significant levels in vivo after infusion of mRNAs in lipid nanoparticles in mice. We evaluated the protective capacity of CHKV-24 mAb immunoglobulin G protein or mRNA in mouse models of CHIKV infection. Treatment with CHKV-24 mRNA protected mice from arthritis, musculoskeletal tissue infection, and lethality and reduced viremia to undetectable levels at 2 days after inoculation. Infusion of macaques with CHKV-24 mRNA achieved a mean maximal mAb concentration of 10.1 to 35.9 micrograms per milliliter, with a half-life of 23 days, a level well above what is needed for protection in mice. Studies with CHKV-24 mRNA in macaques demonstrated a dose-response effect after the first dose of mRNA and maintained levels after second dose. These preclinical data with CHKV-24 mRNA suggest that it might be useful to prevent human disease.