Interleukin 17 (IL-17)-producing T helper cells (T(H)-17 cells) have been characterized in mice as a distinct subset of effector cells, but their identity and properties in humans remain elusive. We report here that expression of CCR6 and CCR4 together identified human memory CD4+ T cells selectively producing IL-17 and expressing mRNA encoding the human ortholog of mouse RORgammat, a transcription factor, whereas CCR6 and CXCR3 identified T(H)1 cells producing interferon-gamma and T helper cells producing both interferon-gamma and IL-17. Memory T cells specific for Candida albicans were present mainly in the CCR6+CCR4+ T(H)-17 subset, whereas memory T cells specific for Mycobacterium tuberculosis were present in CCR6+CXCR3+ T helper type 1 subset. The elicitation of IL-17 responses correlated with the capacity of C. albicans hyphae to stimulate antigen-presenting cells for the priming of T(H)-17 responses in vitro and for the production of IL-23 but not IL-12. Our results demonstrate that human T(H)-17 cells have distinct migratory capacity and antigenic specificities and establish a link between microbial products, T helper cell differentiation and homing in response to fungal antigens.

We previously reported that central-memory T cells (T CM cells), which express lymph node homing receptors CCR7 and CD62L, are largely devoid of effector functions but acquire characteristics of effector-memory T cells (T EM cells) (i.e., CCR7 Ϫ T helper [Th]1 or Th2 cells) after stimulation with T cell receptor agonists or homeostatic cytokines. Here we show that three chemokine receptors identify functional subsets within the human CD4 ϩ T CM cell pool. T CM cells expressing CXCR3 secreted low amounts of interferon ␥ , whereas CCR4 ϩ T CM cells produced some interleukin (IL)-4, but not IL-5. In response to IL-7 and IL-15, CXCR3 ϩ T CM and CCR4 ϩ T CM cells invariably generated fully differentiated CCR7 Ϫ Th1 and Th2 cells, respectively, suggesting that they represent pre-Th1 and pre-Th2 cells. Conversely, CXCR5 ϩ T CM cells lacking CXCR3 and CCR4 remained nonpolarized and retained CCR7 and CD62L expression upon cytokine-driven expansion. Unlike naive cells, all memory subsets had a low T cell receptor rearrangement excision circle content, spontaneously incorporated bromodeoxyuridine ex vivo, and contained cells specific for tetanus toxoid. Conversely, recall responses to cytomegalovirus and vaccinia virus were largely restricted to CXCR3 ϩ T CM and T EM cells. We conclude that antigen-specific memory T cells are distributed between T EM cells and different subsets of T CM cells. Our results also explain how the quality of primary T cell responses could be maintained by T CM cells in the absence of antigen.

Dengue virus (DENV) is the principal arthropod-borne viral pathogen afflicting human populations. While repertoires of antibodies to DENV have been linked to protection or enhanced infection, the role of T lymphocytes in these processes remains poorly defined. This study provides a comprehensive overview of CD4(+) and CD8(+) T cell epitope reactivities against the DENV 2 proteome in adult patients experiencing secondary DENV infection. Dengue virus-specific T cell responses directed against an overlapping 15mer peptide library spanning the DENV 2 proteome were analyzed ex vivo by enzyme-linked immunosorbent spot assay, and recognition of individual peptides was further characterized in specific T cell lines. Thirty novel T cell epitopes were identified, 9 of which are CD4(+) and 21 are CD8(+) T cell epitopes. We observe that whereas CD8(+) T cell epitopes preferentially target nonstructural proteins (NS3 and NS5), CD4(+) epitopes are skewed toward recognition of viral components that are also targeted by B lymphocytes (envelope, capsid, and NS1). Consistently, a large proportion of dengue virus-specific CD4(+) T cells have phenotypic characteristics of circulating follicular helper T cells (CXCR5 expression and production of interleukin-21 or gamma interferon), suggesting that they are interacting with B cells in vivo. This study shows that during a dengue virus infection, the protein targets of human CD4(+) and CD8(+) T cells are largely distinct, thus highlighting key differences in the immunodominance of DENV proteins for these two cell types. This has important implications for our understanding of how the two arms of the human adaptive immune system are differentially targeted and employed as part of our response to DENV infection.

BACKGROUND.The clinical management of chronic hepatitis B virus (HBV) patients is based exclusively on virological parameters that cannot independently determine in which patients nucleos(t)ide-analogue (NUC) therapy can be safely discontinued. NUCs efficiently suppress viral replication, but do not eliminate HBV. Thus, therapy discontinuation can be associated with virological and biochemical relapse and, consequently, therapy in the majority is life-long. METHODS.Since antiviral immunity is pivotal for HBV control, we investigated potential biomarkers for the safe discontinuation of NUCs within immune profiles of chronic HBV patients by utilizing traditional immunological assays (ELISPOT, flow cytometry) in conjunction with analyses of global non-antigen-specific immune populations (NanoString and CyTOF). Two distinct cohorts of 19 and 27 chronic HBV patients, respectively, were analyzed longitudinally prior to and after discontinuation of 2 different NUC therapy strategies. RESULTS.Absence of hepatic flares following discontinuation of NUC treatment correlated with the presence, during NUC viral suppression, of HBV core and polymerase-specific T cells that were contained within the ex vivo PD-1 + population.CONCLUSIONS. This study identifies the presence of functional HBV-specific T cells as a candidate immunological biomarker for safe therapy discontinuation in chronic HBV patients. Furthermore, the persistent and functional antiviral activity of PD-1 + HBV-specific T cells highlights the potential beneficial role of the expression of T cell exhaustion markers during human chronic viral infection.

Conclusions:In an analysis of immune cells from patients with chronic HBV infection, we found the duration of HBsAg exposure, rather than the absolute quantity of HBsAg, alters the profile of HBV-specific T cell responses. Although the presence of HBsspecific T cells might not be essential for the clearance of HBV infection in all patients, our study indicates that therapeutic intervention designed to restore anti-HBV immunity should consider patients younger than 30 y.