Contribution of the SYK Tyrosine kinase expression to human iNKT self-reactivity.

Invariant Natural Killer T (iNKT) cells are particular T lymphocytes at the frontier between innate and adaptative immunities. They participate in the elimination of pathogens or tumor cells, but also in the development of allergic reactions and autoimmune diseases. From their first descriptions, the phenomenon of self-reactivity has been described. Indeed, they are able to recognize exogenous and endogenous lipids. However, the mechanisms underlying the self-reactivity are still largely unknown, particularly in humans. Using a CD1d tetramer-based sensitive immunomagnetic approach, we generated self-reactive iNKT cell lines from blood circulating iNKT cells of healthy donors. Analysis of their functional characteristics in vitro showed that these cells recognized endogenous lipids presented by CD1d molecules through their TCR that do not correspond to α-glycosylceramides. TCR sequencing and transcriptomic analysis of T cell clones revealed that a particular TCR signature and an expression of the SYK protein kinase were two mechanisms supporting human iNKT self-reactivity. The SYK expression, strong in the most self-reactive iNKT clones and variable in ex vivo isolated iNKT cells, seems to decrease the activation threshold of iNKT cells and increase their overall antigenic sensitivity. This study indicates that a modulation of the TCR intracellular signal contributes to iNKT self-reactivity.

Role of the MHC restriction during maturation of antigen-specific human T cells in the thymus.

In the thymus, a T-cell repertoire able to confer protection against infectious and noninfectious agents in a peptide-dependent, self-MHC-restricted manner is selected. Direct detection of Ag-specific thymocytes, and analysis of the impact of the expression of the MHC-restricting allele on their frequency or function has never been studied in humans because of the extremely low precursor frequency. Here, we used a tetramer-based enrichment protocol to analyze the ex vivo frequency and activation-phenotype of human thymocytes specific for self, viral and tumor-antigens presented by HLA-A*0201 (A2) in individuals expressing or not this allele. Ag-specific thymocytes were quantified within both CD4CD8 double or single-positive compartments in every donor. Our data indicate that the maturation efficiency of Ag-specific thymocytes is poorly affected by HLA-A2 expression, in terms of frequencies. Nevertheless, A2-restricted T-cell lines from A2(+) donors reacted to A2(+) cell lines in a highly peptide-specific fashion, whereas their alloreactive counterparts showed off-target activity. This first ex vivo analysis of human antigen-specific thymocytes at different stages of human T-cell development should open new perspectives in the understanding of the human thymic selection process.

Antigen-specific single B cell sorting and expression-cloning from immunoglobulin humanized rats: a rapid and versatile method for the generation of high affinity and discriminative human monoclonal antibodies.

BACKGROUND: There is an ever-increasing need of monoclonal antibodies (mAbs) for biomedical applications and fully human binders are particularly desirable due to their reduced immunogenicity in patients. We have applied a strategy for the isolation of antigen-specific B cells using tetramerized proteins and single-cell sorting followed by reconstruction of human mAbs by RT-PCR and expression cloning. RESULTS: This strategy, using human peripheral blood B cells, enabled the production of low affinity human mAbs against major histocompatibility complex molecules loaded with peptides (pMHC). We then implemented this technology using human immunoglobulin transgenic rats, which after immunization with an antigen of interest express high affinity-matured antibodies with human idiotypes. Using rapid immunization, followed by tetramer-based B-cell sorting and expression cloning, we generated several fully humanized mAbs with strong affinities, which could discriminate between highly homologous proteins (eg. different pMHC complexes). CONCLUSIONS: Therefore, we describe a versatile and more effective approach as compared to hybridoma generation or phage or yeast display technologies for the generation of highly specific and discriminative fully human mAbs that could be useful both for basic research and immunotherapeutic purposes.

Characterization of the human CD4(+) T-cell repertoire specific for major histocompatibility class I-restricted antigens.

While CD4(+) T lymphocytes usually recognize antigens in the context of major histocompatibility (MHC) class II alleles, occurrence of MHC class-I restricted CD4(+) T cells has been reported sporadically. Taking advantage of a highly sensitive MHC tetramer-based enrichment approach allowing detection and isolation of scarce Ag-specific T cells, we performed a systematic comparative analysis of HLA-A*0201-restricted CD4(+) and CD8(+) T-cell lines directed against several immunodominant viral or tumoral antigens. CD4(+) T cells directed against every peptide-MHC class I complexes tested were detected in all donors. These cells yielded strong cytotoxic and T helper 1 cytokine responses when incubated with HLA-A2(+) target cells carrying the relevant epitopes. HLA-A2-restricted CD4(+) T cells were seldom expanded in immune HLA-A2(+) donors, suggesting that they are not usually engaged in in vivo immune responses against the corresponding peptide-MHC class I complexes. However, these T cells expressed TCR of very high affinity and were expanded following ex vivo stimulation by relevant tumor cells. Therefore, we describe a versatile and efficient strategy for generation of MHC class-I restricted T helper cells and high affinity TCR that could be used for adoptive T-cell transfer- or TCR gene transfer-based immunotherapies.

A cluster of broadly neutralizing IgG against BK polyomavirus in a repertoire dominated by IgM.

The BK polyomavirus (BKPyV) is an opportunistic pathogen, which is only pathogenic in immunosuppressed individuals, such as kidney transplant recipients, in whom BKPyV can cause significant morbidity. To identify broadly neutralizing antibodies against this virus, we used fluorescence-labeled BKPyV virus-like particles to sort BKPyV-specific B cells from the PBMC of KTx recipients, then single-cell RNAseq to obtain paired heavy- and light-chain antibody sequences from 2,106 sorted B cells. The BKPyV-specific repertoire was highly diverse in terms of both V-gene usage and clonotype diversity and included most of the IgM B cells, including many with extensive somatic hypermutation. In two patients where sufficient data were available, IgM B cells in the BKPyV-specific dataset had significant differences in V-gene usage compared with IgG B cells from the same patient. CDR3 sequence-based clustering allowed us to identify and characterize three broadly neutralizing "41F17-like" clonotypes that were predominantly IgG, suggesting that some specific BKPyV capsid epitopes are preferentially targeted by IgG.

Non-Expressed Donor KIR3DL1 Alleles May Represent a Risk Factor for Relapse after T-Replete Haploidentical Hematopoietic Stem Cell Transplantation.

KIR3DL1 alleles are expressed at different levels on the natural killer (NK) cell surface. In particular, the non-expressed KIR3DL1*004 allele appears to be common in Caucasian populations. However, the overall distribution of non-expressed KIR3DL1 alleles and their clinical relevance after T-replete haploidentical hematopoietic stem cell transplantation (hHSCT) with post-transplant cyclophosphamide remain poorly documented in European populations. In a cohort of French blood donors (N = 278), we compared the distribution of expressed and non-expressed KIR3DL1 alleles using next-generation sequencing (NGS) technology combined with multi-color flow cytometry. We confirmed the predominance of the non-expressed KIR3DL1*004 allele. Using allele-specific constructs, the phenotype and function of the uncommon KIR3DL1*019 allotype were characterized using the Jurkat T cell line and NKL transfectants. Although poorly expressed on the NK cell surface, KIR3DL1*019 is retained within NK cells, where it induces missing self-recognition of the Bw4 epitope. Transposing our in vitro observations to a cohort of hHSCT patients (N = 186) led us to observe that non-expressed KIR3DL1 HSC grafts increased the incidence of relapse in patients with myeloid diseases. Non-expressed KIR3DL1 alleles could, therefore, influence the outcome of hHSCT.

Early triggering of exclusive IFN-gamma responses of human Vgamma9Vdelta2 T cells by TLR-activated myeloid and plasmacytoid dendritic cells.

gammadelta T cells, a major innate-like T cell subset, are thought to play in vivo an important role in innate and adaptive immune responses to various infection agents like parasites, bacteria, or viruses but the mechanisms contributing to this immune process remain ill defined. Owing to their ability to recognize a broad set of microbial molecular patterns, TLRs represent a major innate pathway through which pathogens induce dendritic cells (DC) maturation and acquisition of immunostimulatory functions. In this study, we studied the effects of various TLR ligands on the activation of human Vgamma9Vdelta2 T cells, a main human gammadelta PBL subset, which has been recently involved in the licensing of mycobacteria-infected DC. Both TLR3 and TLR4, but not TLR2 ligands, induced a rapid, strong, and exclusive IFN-gamma production by Vgamma9Vdelta2 T cells. This gammadelta subset contributed to a large extent to the overall PBL IFN-gamma response induced after short-term TLR stimulation of human PBMC. Importantly, this phenomenon primarily depended on type I IFN, but not IL-12, produced by monocytic DC upon TLR engagement. Vgamma9Vdelta2 T cells were similarly activated by plasmacytoid DC upon TLR8/9 activation or Yellow Fever virus infection. Moreover TLR-induced Vgamma9Vdelta2 IFN-gamma noncytolytic response led to efficient DC polarization into IL-12p70-producing cells. Our results support an adjuvant role played by Vgamma9Vdelta2 T cells along microbial infections through a particular cross-talk with pathogen-associated molecular patterns-activated DC. Moreover they provide new insights into the mechanisms underlying functional activation of this unique peripheral innate-like T cell subset during viral infections.

Bridging innate and adaptive immunity through gammadelta T-dendritic cell crosstalk.

Like Natural Killer cells, gammadelta T cells and Natural Killer T cells display several innate-like features that confer them a broad reactivity against tumors and pathogens. By recognizing stress-induced conserved antigens upregulated a wide array of physiopathological contexts, these lymphoid subsets develop strong and early responses to a broad set of targets. One of the most exciting roles possibly played in vivo by non-conventional T lymphocytes, which exhibit a biased natural memory phenotype, is active regulation of adaptive immune responses through interactions with antigen presenting cells (APCs), such as dendritic cells. Here we will review recent studies reporting functional interactions between gammadelta T cells and APC and a possible involvement of these lymphocytes in bridging innate and adaptative immunity along infections and tumor development. Our discussion will focus on human gammadelta T cells and more specifically on Vgamma9Vdelta2 T cells, a major subset found in human peripheral blood.

Generation of Discriminative Human Monoclonal Antibodies from Rare Antigen-specific B Cells Circulating in Blood.

Monoclonal antibodies (mAbs) are powerful tools useful for both fundamental research and in biomedicine. Their high specificity is indispensable when the antibody needs to distinguish between highly related structures (e.g., a normal protein and a mutated version thereof). The current way of generating such discriminative mAbs involves extensive screening of multiple Ab-producing B cells, which is both costly and time consuming. We propose here a rapid and cost-effective method for the generation of discriminative, fully human mAbs starting from human blood circulating B lymphocytes. The originality of this strategy is due to the selection of specific antigen binding B cells combined with the counter-selection of all other cells, using readily available Peripheral Blood Mononuclear Cells (PBMC). Once specific B cells are isolated, cDNA (complementary deoxyribonucleic acid) sequences coding for the corresponding mAb are obtained using single cell Reverse Transcription-Polymerase Chain Reaction (RT-PCR) technology and subsequently expressed in human cells. Within as little as 1 month, it is possible to produce milligrams of highly discriminative human mAbs directed against virtually any desired antigen naturally detected by the B cell repertoire.

Position in cell cycle controls the sensitivity of colon cancer cells to nitric oxide-dependent programmed cell death.

Mounting evidence suggests that the position in the cell cycle of cells exposed to an oxidative stress could determine their survival or apoptotic cell death. This study aimed at determining whether nitric oxide (NO)-induced cell death in colon cancer cells might depend on their position in the cell cycle, based on a clone of the cancer cell line HT29 exposed to an NO donor, in combination with the manipulation of the cell entry into the cell cycle. We show that PAPA NONOate (pNO), from 10(-4) m to 10(-3) m, exerted early and reversible cytostatic effects through ribonucleotide reductase inhibition, followed by late resumption of cell growth at 5 x 10(-4) m pNO. In contrast, 10(-3) m pNO led to late programmed cell death that was accounted for by the progression of cells into the cell cycle as shown by (a) the accumulation of apoptotic cells in the G(2)-M phase at 10(-3) m pNO treatment; and (b) the prevention of cell death by inhibiting the entry of cells into the cell cycle. The entry of pNO-treated cells into the G(2)-M phase was associated with actin depolymerization and its S-glutathionylation in the same way as in control cells. However, the pNO treatment interfered with the build-up of a high reducing power, associated in control cells with a dramatic increase in reduced glutathione biosynthesis in the G(2)-M phase. This oxidative stress prevented the exit from the G(2)-M phase, which requires a high reducing power for actin deglutathionylation and its repolymerization. Finally, our demonstration that programmed cell death occurred through a caspase-independent pathway is in line with the context of a nitrosative/oxidative stress. In conclusion, this work, which deciphers the connection between the position of colonic cancer cells in the cell cycle and their sensitivity to NO-induced stress and their programmed cell death, could help optimize anticancer protocols based on NO-donating compounds.

Development of Predictive Value of Urinary Cytokine Profile Induced During Intravesical Bacillus Calmette-Guérin Instillations for Bladder Cancer.

BACKGROUND: We sought to demonstrate a correlation between the response to treatment and the profile of urinary cytokine production during bacillus Calmette-Guérin (BCG) therapy. MATERIAL AND METHODS: From December 2008 to February 2011, 23 patients were included in a prospective study. All patients received 6 instillations of BCG weekly. The mean follow-up period of the population was 16.9 ± 8.4 months. Refractory disease or recurrence was observed in 5 patients. Urine samples were collected and stored at -80°C, before and 4 hours after the first, third, and sixth BCG instillations. The cytokines (interleukin [IL]-2, IL-4, IL-6, IL-10, IL-17, interferon-gamma [IFNγ] and tumor necrosis factor-alpha) were quantified within the collected urine samples using cytometric bead array analysis. The quantitative variables were analyzed using Student's t test, and regression statistical analysis was performed. RESULTS: Urinary cytokine production had increased strongly 4 hours after the sixth instillation but only mildly to moderately after the first and third instillations. IL-2 and IL-6 showed the most dramatic changes after the BCG instillations. Different urinary cytokine production profiles were demonstrated. A trend was observed for the BCG-refractory/recurrence group, with high baseline IL-6 levels, followed by low IL-6 levels before the instillations; low baseline IL-2 levels with only minor changes during treatment; the absence of IFNγ and IL-17 production; and a low peak of cytokine production at the end of treatment. CONCLUSION: Analysis of the urinary cytokine production levels during BCG therapy reflect a specific immune response induced in each patient. Their assessment could allow a more reliable selection of patients eligible for this type of treatment and could help justify the use of maintenance BCG therapy.

Self/non-self discrimination by human gammadelta T cells: simple solutions for a complex issue?

Although gammadelta T cells express clonally distributed T-cell receptors (TCRs), a hallmark of adaptive immunity, they are classically considered as innate-like effectors, owing to the high frequency of preactivated gammadelta T cells, with restricted antigen recognition repertoire in particular tissue locations. Actually, such features are shared only by a fraction of gammadelta T-cell subsets located in the skin and reproductive organ mucosa in rodents or in peripheral blood in humans. By contrast, other gammadelta subsets, e.g. those found in rodent and human spleen, show diverse antigenic reactivity patterns and mixed naive/memory phenotypes. Thus, gammadelta T cells are made of both 'primitive' subsets endowed with innate-like properties and 'evolved' subsets able to mount anamnestic responses like conventional major histocompatibility complex-restricted alphabeta T cells. In this article, we show that human gammadelta T cells, although heterogeneous, do share recurrent innate features that distinguish them from mainstream alphabeta T cells. In particular, most of them are activated on TCR- or natural killer receptor-mediated recognition of a restricted set of conserved yet poorly defined endogenous stress determinants. This rather simple recognition mechanism allows human gammadelta T cells to discriminate healthy cells from altered cells and to exert a variety of immunostimulatory or regulatory functions. The recent availability of synthetic gammadelta T-cell agonists mimicking these natural stress-induced ligands have fostered development of immunotherapeutic strategies, with broad indications against infectious and tumor diseases, which are briefly reviewed here.

Potentiation of antigen-stimulated V gamma 9V delta 2 T cell cytokine production by immature dendritic cells (DC) and reciprocal effect on DC maturation.

Vgamma9Vdelta2 T cells, a major gammadelta PBL subset in human adults, have been previously implicated in dendritic cell (DC) licensing, owing to their high frequency in peripheral tissues and their ability to produce inflammatory cytokines upon recognition of a broad array of conserved Ags. Although these observations implied efficient recognition of Ag-expressing immature DC (iDC) by Vgamma9Vdelta2 T cells, the role played by DC subsets in activation of these lymphocytes has not been carefully studied so far. We show that iDC, and to a lesser extent mature DC, potentiated Th1 and Th2 cytokine, but not cytolytic or proliferative responses, of established Vgamma9Vdelta2 T cell clones and ex vivo memory Vgamma9Vdelta2 PBL stimulated by synthetic agonists. The ability of iDC to potentiate Vgamma9Vdelta2 production of inflammatory cytokines required for their own maturation suggested that Vgamma9Vdelta2 T cells, despite their strong lytic activity, could promote efficient iDC licensing without killing at suboptimal Ag doses. Accordingly Vgamma9Vdelta2 cells induced accelerated maturation of Ag-expressing iDC but not "bystander" DC, even within mixed cell populations comprising both Ag-expressing and nonexpressing iDC. Furthermore Vgamma9Vdelta2 cells induced full differentiation into IL-12-producing cells of iDC infected by Vgamma9Vdelta2-stimulating mycobacteria that were otherwise unable to induce complete DC maturation. In conclusion the ability of iDC to selectively potentiate cytokine response of memory Vgamma9Vdelta2 T cells could underlie the adjuvant effect of these lymphocytes, and possibly other natural memory T cells, on conventional T cell responses.