Ontogeny of different subsets of yellow fever virus-specific circulatory CXCR5+ CD4+ T cells after yellow fever vaccination.

Monitoring the frequency of circulatory CXCR5+ (cCXCR5+) CD4+ T cells in periphery blood provides a potential biomarker to draw inferences about T follicular helper (TFH) activity within germinal center. However, cCXCR5+ T cells are highly heterogeneous in their expression of ICOS, PD1 and CD38 and the relationship between different cCXCR5 subsets as delineated by these markers remains unclear. We applied class II tetramer reagents and mass cytometry to investigate the ontogeny of different subsets of cCXCR5+ T cell following yellow fever immunization. Through unsupervised analyses of mass cytometry data, we show yellow fever virus-specific cCXCR5 T cells elicited by vaccination were initially CD38+ICOS+PD1+, but then transitioned to become CD38+ICOS-PD1+ and CD38-ICOS-PD1+ before coming to rest as a CD38-ICOS-PD1- subset. These results imply that most antigen-specific cCXCR5+ T cells, including the CD38-ICOS-PD1- CXCR5+ T cells are derived from the CXCR5+CD38+ICOS+PD1+ subset, the subset that most resembles preTFH/TFH in the germinal center.

Discriminative T cell recognition of cross-reactive islet-antigens is associated with HLA-DQ8 transdimer-mediated autoimmune diabetes.

Human leukocyte antigen (HLA)-DQ8 transdimer (HLA-DQA1*0501/DQB1*0302) confers exceptionally high risk in autoimmune diabetes. However, little is known about HLA-DQ8 transdimer-restricted CD4 T cell recognition, an event crucial for triggering HLA-DQ8 transdimer-specific anti-islet immunity. Here, we report a high degree of epitope overlap and T cell promiscuity between susceptible HLA-DQ8 and HLA-DQ8 transdimer. Despite preservation of putative residues for T cell receptor (TCR) contact, stronger disease-associated responses to cross-reactive, immunodominant islet epitopes are elicited by HLA-DQ8 transdimer. Mutagenesis at the α chain of HLA-DQ8 transdimer in complex with the disease-relevant GAD65250-266 peptide and in silico analysis reveal the DQ α52 residue located within the N-terminal edge of the peptide-binding cleft for the enhanced T cell reactivity, altering avidity and biophysical affinity between TCR and HLA-peptide complexes. Accordingly, a structurally promiscuous but nondegenerate TCR-HLA-peptide interface is pivotal for HLA-DQ8 transdimer-mediated autoimmune diabetes.

Neuroinvasive West Nile Infection Elicits Elevated and Atypically Polarized T Cell Responses That Promote a Pathogenic Outcome.

Most West Nile virus (WNV) infections are asymptomatic, but some lead to neuroinvasive disease with symptoms ranging from disorientation to paralysis and death. Evidence from animal models suggests that neuroinvasive infections may arise as a consequence of impaired immune protection. However, other data suggest that neurologic symptoms may arise as a consequence of immune mediated damage. We demonstrate that elevated immune responses are present in neuroinvasive disease by directly characterizing WNV-specific T cells in subjects with laboratory documented infections using human histocompatibility leukocyte antigen (HLA) class II tetramers. Subjects with neuroinvasive infections had higher overall numbers of WNV-specific T cells than those with asymptomatic infections. Independent of this, we also observed age related increases in WNV-specific T cell responses. Further analysis revealed that WNV-specific T cell responses included a population of atypically polarized CXCR3+CCR4+CCR6- T cells, whose presence was highly correlated with neuroinvasive disease. Moreover, a higher proportion of WNV-specific T cells in these subjects co-produced interferon-γ and interleukin 4 than those from asymptomatic subjects. More globally, subjects with neuroinvasive infections had reduced numbers of CD4+FoxP3+ Tregs that were CTLA4 positive and exhibited a distinct upregulated transcript profile that was absent in subjects with asymptomatic infections. Thus, subjects with neuroinvasive WNV infections exhibited elevated, dysregulated, and atypically polarized responses, suggesting that immune mediated damage may indeed contribute to pathogenic outcomes.

Assessment of CD4+ T cell responses to glutamic acid decarboxylase 65 using DQ8 tetramers reveals a pathogenic role of GAD65 121-140 and GAD65 250-266 in T1D development.

Susceptibility to type 1 diabetes (T1D) is strongly associated with MHC class II molecules, particularly HLA-DQ8 (DQ8: DQA1*03:01/DQB1*03:02). Monitoring T1D-specific T cell responses to DQ8-restricted epitopes may be key to understanding the immunopathology of the disease. In this study, we examined DQ8-restricted T cell responses to glutamic acid decarboxylase 65 (GAD65) using DQ8 tetramers. We demonstrated that GAD65 121-140 and GAD65 250-266 elicited responses from DQ8+ subjects. Circulating CD4+ T cells specific for these epitopes were detected significantly more often in T1D patients than in healthy individuals after in vitro expansion. T cell clones specific for GAD65 121-140 and GAD65 250-266 carried a Th1-dominant phenotype, with some of the GAD65 121-140-specific T cell clones producing IL-17. GAD65 250-266-specific CD4+ T cells could also be detected by direct ex vivo staining. Analysis of unmanipulated peripheral blood mononuclear cells (PBMCs) revealed that GAD65 250-266-specific T cells could be found in both healthy and diabetic individuals but the frequencies of specific T cells were higher in subjects with type 1 diabetes. Taken together, our results suggest a proinflammatory role for T cells specific for DQ8-restricted GAD65 121-140 and GAD65 250-266 epitopes and implicate their possible contribution to the progression of T1D.

Yellow fever vaccination elicits broad functional CD4+ T cell responses that recognize structural and nonstructural proteins.

Yellow fever virus (YFV) can induce acute, life-threatening disease that is a significant health burden in areas where yellow fever is endemic, but it is preventable through vaccination. The live attenuated 17D YFV strain induces responses characterized by neutralizing antibodies and strong T cell responses. This vaccine provides an excellent model for studying human immunity. While several studies have characterized YFV-specific antibody and CD8(+) T cell responses, less is known about YFV-specific CD4(+) T cells. Here we characterize the epitope specificity, functional attributes, and dynamics of YFV-specific T cell responses in vaccinated subjects by investigating peripheral blood mononuclear cells by using HLA-DR tetramers. A total of 112 epitopes restricted by seven common HLA-DRB1 alleles were identified. Epitopes were present within all YFV proteins, but the capsid, envelope, NS2a, and NS3 proteins had the highest epitope density. Antibody blocking demonstrated that the majority of YFV-specific T cells were HLA-DR restricted. Therefore, CD4(+) T cell responses could be effectively characterized with HLA-DR tetramers. Ex vivo tetramer analysis revealed that YFV-specific T cells persisted at frequencies ranging from 0 to 100 cells per million that are detectable years after vaccination. Longitudinal analysis indicated that YFV-specific CD4(+) T cells reached peak frequencies, often exceeding 250 cells per million, approximately 2 weeks after vaccination. As frequencies subsequently declined, YFV-specific cells regained CCR7 expression, indicating a shift from effector to central memory. Cells were typically CXCR3 positive, suggesting Th1 polarization, and produced gamma interferon and other cytokines after reactivation in vitro. Therefore, YFV elicits robust early effector CD4(+) T cell responses that contract, forming a detectable memory population.

Differential binding of pyruvate dehydrogenase complex-E2 epitopes by DRB1*08:01 and DRB1*11:01 Is predicted by their structural motifs and correlates with disease risk.

DRB1*08:01 (DR0801) and DRB1*11:01 (DR1101) are highly homologous alleles that have opposing effects on susceptibility to primary biliary cirrhosis (PBC). DR0801 confers risk and shares a key feature with other HLA class II alleles that predispose to autoimmunity: a nonaspartic acid at beta57. DR1101 is associated with protection from PBC, and its sequence includes an aspartic acid at beta57. To elucidate a mechanism for the opposing effects of these HLA alleles on PBC susceptibility, we compared the features of epitopes presented by DR0801 and DR1101. First, we identified DR0801- and DR1101-restricted epitopes within multiple viral Ags, observing both shared and distinct epitopes. Because DR0801 is not well characterized, we deduced its motif by measuring binding affinities for a library of peptides, confirming its key features through structural modeling. DR0801 was distinct from DR1101 in its ability to accommodate charged residues within all but one of its binding pockets. In particular, DR0801 strongly preferred acidic residues in pocket 9. These findings were used to identify potentially antigenic sequences within PDC-E2 (an important hepatic autoantigen) that contain a DR0801 motif. Four peptides bound to DR0801 with reasonable affinity, but only one of these bound to DR1101. Three peptides, PDC-E2145-159, PDC-E2(249-263), and PDC-E2(629-643), elicited high-affinity T cell responses in DR0801 subjects, implicating these as likely autoreactive specificities. Therefore, the unique molecular features of DR0801 may lead to the selection of a distinct T cell repertoire that contributes to breakdown of self-tolerance in primary biliary cirrhosis, whereas those of DR1101 promote tolerance.

CD4+ T cells recognize unique and conserved 2009 H1N1 influenza hemagglutinin epitopes after natural infection and vaccination.

Influenza A/California/4/2009 (H1N1/09) is a recently emerged influenza virus capable of causing serious illness or death in otherwise healthy individuals. Serious outcomes were most common in young adults and children, suggesting that pre-existing heterologous immunity may influence the severity of infection. Using tetramers, we identified CD4(+) T-cell epitopes within H1N1/09 hemagglutinin (HA) that share extensive homology with seasonal influenza and epitopes that are unique to H1N1/09 HA. Ex vivo tetramer staining revealed that T cells specific for conserved epitopes were detectable within the memory compartment, whereas T cells specific for unique epitopes were naive and infrequent prior to infection or vaccination. Following infection, the frequencies of T cells specific for unique epitopes were 11-fold higher, reaching levels comparable to those of T cells specific for immunodominant epitopes. In contrast, the frequencies of T cells specific for conserved epitopes were only 2- to 3-fold higher following infection. In general, H1HA-reactive T cells exhibited a memory phenotype, expressed CXCR3 and secreted IFN-γ, indicating a predominantly Th1-polarized response. A similar Th1 response was seen in vaccinated subjects, but the expansion of T cells specific for HA epitopes was comparatively modest after vaccination. Our findings indicate that CD4(+) T cells recognize both strain-specific and conserved epitopes within the influenza HA protein and suggest that naive T cells specific for HA epitopes undergo significant expansion, whereas memory T cells specific for the conserved epitopes undergo more restrained expansion.

A novel molecular diagnostic of glioblastomas: detection of an extracellular fragment of protein tyrosine phosphatase mu.

We recently found that normal human brain and low-grade astrocytomas express the receptor protein tyrosine phosphatase mu (PTPmu) and that the more invasive astrocytomas, glioblastoma multiforme (GBM), downregulate full-length PTPmu expression. Loss of PTPmu expression in GBMs is due to proteolytic cleavage that generates an intracellular and potentially a cleaved and released extracellular fragment of PTPmicro. Here, we identify that a cleaved extracellular fragment containing the domains required for PTPmicro-mediated adhesion remains associated with GBM tumor tissue. We hypothesized that detection of this fragment would make an excellent diagnostic tool for the localization of tumor tissue within the brain. To this end, we generated a series of fluorescently tagged peptide probes that bind the PTPmu fragment. The peptide probes specifically recognize GBM cells in tissue sections of surgically resected human tumors. To test whether the peptide probes are able to detect GBM tumors in vivo, the PTPmu peptide probes were tested in both mouse flank and intracranial xenograft human glioblastoma tumor model systems. The glial tumors were molecularly labeled with the PTPmu peptide probes within minutes of tail vein injection using the Maestro FLEX In Vivo Imaging System. The label was stable for at least 3 hours. Together, these results indicate that peptide recognition of the PTPmu extracellular fragment provides a novel molecular diagnostic tool for detection of human glioblastomas. Such a tool has clear translational applications and may lead to improved surgical resections and prognosis for patients with this devastating disease.

Stimulation of N-cadherin-dependent neurite outgrowth by small molecule peptide mimetic agonists of the N-cadherin HAV motif.

N-cadherin is a cell adhesion molecule that promotes axon outgrowth and synapse formation during the development of the central nervous system. In addition, N-cadherin promotes glial cell adhesion and myelination of axons. Therefore, stimulating N-cadherin function with N-cadherin agonists could be used therapeutically to promote regeneration of the nervous system and remyelination after injury or disease. In the extracellular domain of N-cadherin, the amino acid sequence HAV is required for N-cadherin-mediated adhesion and neurite outgrowth. The ADH-1 cyclic peptide, derived from the N-cadherin HAV site, is an effective antagonist of N-cadherin-mediated neurite outgrowth and is currently being tested in clinical trials for cancer chemotherapy. Of interest, a dimeric version of this cyclic peptide, N-Ac-CHAVDINGHAVDIC-NH(2), functions as an N-cadherin agonist. This dimeric peptide agonist and the peptide antagonist ADH-1 both have limitations as drugs due to their metabolic instability and lack of oral delivery. To address this issue Adherex Technologies Inc. generated a small molecule library of peptidomimetics to the HAV region of N-cadherin, which would be more amenable to therapeutic use. We screened the Adherex library for compounds that altered neurite outgrowth and identified eight N-cadherin agonists that stimulated N-cadherin-dependent neurite outgrowth. Five of these agonists also stimulated retinal cell migration. These small molecule agonists may be effective reagents for promoting axon growth and remyelination after injury or disease.

Novel peptide mimetic small molecules of the HAV motif in N-cadherin inhibit N-cadherin-mediated neurite outgrowth and cell adhesion.

The cell adhesion molecule, N-cadherin, stabilizes cell-cell junctions and promotes cellular migration during tissue morphogenesis in development. N-cadherin is also implicated in mediating tumor progression and metastasis in cancer. Therefore, developing antagonists of N-cadherin adhesion may be of therapeutic value in cancer treatment. The amino acid sequence HAV in the extracellular domain of N-cadherin is required for N-cadherin-mediated adhesion and migration. A cyclic peptide, ADH-1, derived from the N-cadherin HAV site is an effective antagonist of N-cadherin-mediated processes and is now in clinical trials for cancer chemotherapy. Because it is a peptide, ADH-1 has certain limitations as a drug, namely its metabolic instability and lack of oral delivery. Adherex set out to identify small molecule antagonists of N-cadherin, which would be more amenable to therapeutic use. Using three-dimensional computational screening, Adherex identified a set of small molecules as potential antagonists with sufficient structural similarity to the HAV region of N-cadherin. We tested the ability of these small molecules to interfere with two N-cadherin-dependent processes: neurite outgrowth (axonal migration) and N-cadherin-dependent cell adhesion. We identified 21 N-cadherin antagonists of varying potency. More importantly, our studies demonstrate that these compounds are significantly more potent than ADH-1 at perturbing N-cadherin-mediated processes. The IC(50) of ADH-1 is 2.33 mM while the IC(50) of the small molecules ranges from 4.5 to 30 microM. Given the efficacy of ADH-1 for treating cancer, these small molecule antagonists will be highly effective in treatment of cancer metastasis and conditions of aberrant neurite outgrowth, such as neuropathic pain.

The receptor protein-tyrosine phosphatase PTPmu interacts with IQGAP1.

The receptor protein-tyrosine phosphatase PTPmu is a member of the Ig superfamily of cell adhesion molecules. The extracellular domain of PTPmu contains motifs commonly found in cell adhesion molecules. The intracellular domain of PTPmu contains two conserved catalytic domains, only the membrane-proximal domain has catalytic activity. The unique features of PTPmu make it an attractive molecule to transduce signals upon cell-cell contact. PTPmu has been shown to regulate cadherin-mediated cell adhesion, neurite outgrowth, and axon guidance. Protein kinase C is a component of the PTPmu signaling pathway utilized to regulate these events. To aid in the further characterization of PTPmu signaling pathways, we used a series of GST-PTPmu fusion proteins, including catalytically inactive and substrate trapping mutants, to identify PTPmu-interacting proteins. We identified IQGAP1, a known regulator of the Rho GTPases, Cdc42 and Rac1, as a novel PTPmu-interacting protein. We show that this interaction is due to direct binding. In addition, we demonstrate that amino acid residues 765-958 of PTPmu, which include the juxtamembrane domain and 35 residues of the first phosphatase domain, mediate the binding to IQGAP1. Furthermore, we demonstrate that constitutively active Cdc42, and to a lesser extent Rac1, enhances the interaction of PTPmu and IQGAP1. These data indicate PTPmu may regulate Rho-GTPase-dependent functions of IQGAP1 and suggest that IQGAP1 is a component of the PTPmu signaling pathway. In support of this, we show that a peptide that competes IQGAP1 binding to Rho GTPases blocks PTPmu-mediated neurite outgrowth.