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T follicular helper (TFH) cells play an essential role in promoting B cell responses and antibody affinity maturation in germinal centers (GC). A subset of memory CD4+ T cells expressing the chemokine receptor CXCR5 has been described in human blood as phenotypically and clonally related to GC TFH cells. However, the antigen specificity and relationship of these circulating TFH (cTFH) cells with other memory CD4+ T cells remain poorly defined. Combining antigenic stimulation and T cell receptor (TCR) Vβ sequencing, we found T cells specific to tetanus toxoid (TT), influenza vaccine (Flu), or Candida albicans (C.alb) in both cTFH and non‐cTFH subsets, although with different frequencies and effector functions. Interestingly, cTFH and non‐cTFH cells specific for C.alb or TT had a largely overlapping TCR Vβ repertoire while the repertoire of Flu‐specific cTFH and non‐cTFH cells was distinct. Furthermore, Flu‐specific but not C.alb‐specific PD‐1+ cTFH cells had a "GC TFH‐like" phenotype, with overexpression of IL21, CXCL13, and BCL6. Longitudinal analysis of serial blood donations showed that Flu‐specific cTFH and non‐cTFH cells persisted as stable repertoires for years. Collectively, our study provides insights on the relationship of cTFH with non‐cTFH cells and on the heterogeneity and persistence of antigen‐specific human cTFH cells. [ABSTRACT FROM AUTHOR]

Enterobacteriaceae are a large family of Gram‐negative bacteria that includes both commensals and opportunistic pathogens. The latter can cause severe nosocomial infections, with outbreaks of multi‐antibiotics resistant strains, thus being a major public health threat. In this study, we report that Enterobacteriaceae‐reactive memory Th cells were highly enriched in a CCR6+CXCR3+ Th1*/17 cell subset and produced IFN‐γ, IL‐17A, and IL‐22. This T cell subset was severely reduced in septic patients with K. pneumoniae bloodstream infection who also selectively lacked circulating K. pneumonie‐reactive T cells. By combining heterologous antigenic stimulation, single cell cloning and TCR Vβ sequencing, we demonstrate that a large fraction of memory Th cell clones was broadly cross‐reactive to several Enterobacteriaceae species. These cross‐reactive Th cell clones were expanded in vivo and a large fraction of them recognized the conserved outer membrane protein A antigen. Interestingly, Enterobacteriaceae broadly cross‐reactive T cells were also prominent among in vitro primed naïve T cells. Collectively, these data point to the existence of immunodominant T cell epitopes shared among different Enterobacteriaceae species and targeted by cross‐reactive T cells that are readily found in the pre‐immune repertoire and are clonally expanded in the memory repertoire. [ABSTRACT FROM AUTHOR]

Currently available rabies post-exposure prophylaxis (PEP) for use in humans includes equine or human rabies immunoglobulins (RIG). The replacement of RIG with an equally or more potent and safer product is strongly encouraged due to the high costs and limited availability of existing RIG. In this study, we identified two broadly neutralizing human monoclonal antibodies that represent a valid and affordable alternative to RIG in rabies PEP. Memory B cells from four selected vaccinated donors were immortalized and monoclonal antibodies were tested for neutralizing activity and epitope specificity. Two antibodies, identified as RVC20 and RVC58 (binding to antigenic site I and III, respectively), were selected for their potency and broad-spectrum reactivity. In vitro, RVC20 and RVC58 were able to neutralize all 35 rabies virus (RABV) and 25 non-RABV lyssaviruses. They showed higher potency and breath compared to antibodies under clinical development (namely CR57, CR4098, and RAB1) and commercially available human RIG. In vivo, the RVC20-RVC58 cocktail protected Syrian hamsters from a lethal RABV challenge and did not affect the endogenous hamster post-vaccination antibody response. [ABSTRACT FROM AUTHOR]

We previously reported that Cd3e-deficient mice adoptively transferred with CD4+ T cells generate high numbers of T follicular helper (Tfh) cells, which go on to induce a strong B-cell and germinal center (GC) reaction. Here, we show that in this system, GC B cells display an altered distribution between the dark and light zones, and express low levels of activation-induced cytidine deaminase. Furthermore, GC B cells from Cd3e-/- mice accumulate fewer somatic mutations as compared with GC B cells from wild-type mice, and exhibit impaired affinity maturation and reduced differentiation into long-lived plasma cells. Reconstitution of Cd3e-/- mice with regulatory T (Treg) cells restored Tfh-cell numbers, GC B-cell numbers and B-cell distribution within dark and light zones, and the rate of antibody somatic mutations. Tfh-cell numbers and GC B-cell numbers and dynamics were also restored by pre-reconstitution of Cd3e-/- mice with Cxcr5-/- Treg cells or non-regulatory, memory CD4+ T cells. Taken together, these findings underline the importance of a quantitatively regulated Tfh-cell response for an efficient and long-lasting serological response. [ABSTRACT FROM AUTHOR]

The article introduces scientific conference papers on T cells and skin to be presented at the 22nd Scientific meeting 2014 of the Fondation René Touraine (FRT), a European non-governmental organization that promotes therapeutic progress in dermatology, on 5th December 2014 in Paris, France. Papers by researchers Shimon Sakaguchi, Federica Sallusto and Thomas Gebhardt are included. Specific topics include immune abnormalities found in atopic dermatitis and adoptive transfer of dendritic cells.