The role of LAT-PLCγ1 interaction in γδ T cell development and homeostasis

ZAP70, too little, too much can lead to autoimmunity*

Establishing both central and peripheral tolerance requires the appropriate TCR signaling strength to discriminate self‐ from agonist‐peptide bound to self MHC molecules. ZAP70, a cytoplasmic tyrosine kinase, directly interacts with the TCR complex and plays a central and requisite role in TCR signaling in both thymocytes and peripheral T cells. By studying ZAP70 hypomorphic mutations in mice and humans with a spectrum of hypoactive or hyperactive activities, we have gained insights into mechanisms of central and peripheral tolerance. Interestingly, both hypoactive and hyperactive ZAP70 can lead to the development of autoimmune diseases, albeit through distinct mechanisms. Immature thymocytes and mature T cells rely on normal ZAP70 function to complete their development in the thymus and to modulate T cell responses in the periphery. Hypoactive ZAP70 function compromises key developmental checkpoints required to establish central tolerance, allowing thymocytes with potentially self‐reactive TCRs a greater chance to escape negative selection. Such ‘forbidden clones’ may escape into the periphery and may pose a greater risk for autoimmune disease development since they may not engage negative regulatory mechanisms as effectively. Hyperactive ZAP70 enhances thymic negative selection but some thymocytes will, nonetheless, escape negative selection and have greater sensitivity to weak and self‐ligands. Such cells must be controlled by mechanisms involved in anergy, expansion of Tregs, and upregulation of inhibitory receptors or signaling molecules. However, such potentially autoreactive cells may still be able to escape control by peripheral negative regulatory constraints. Consistent with findings in Zap70 mutants, the signaling defects in at least one ZAP70 substrate, LAT, can also lead to autoimmune disease. By dissecting the similarities and differences among mouse models of patient disease or mutations in ZAP70 that affect TCR signaling strength, we have gained insights into how perturbed ZAP70 function can lead to autoimmunity. Because of our work and that of others on ZAP70, it is likely that perturbations in other molecules affecting TCR signaling strength will be identified that also overcome tolerance mechanisms and cause autoimmunity. Delineating these molecular pathways could lead to the development of much needed new therapeutic targets in these complex diseases.

The Clinical Aspect of Adaptor Molecules in T Cell Signaling: Lessons Learnt From Inborn Errors of Immunity

Adaptor molecules lack enzymatic and transcriptional activities. Instead, they exert their function by linking multiple proteins into intricate complexes, allowing for transmitting and fine-tuning of signals. Many adaptor molecules play a crucial role in T-cell signaling, following engagement of the T-cell receptor (TCR). In this review, we focus on Linker of Activation of T cells (LAT) and SH2 domain-containing leukocyte protein of 76 KDa (SLP-76). Monogenic defects in these adaptor proteins, with known roles in T-cell signaling, have been described as the cause of human inborn errors of immunity (IEI). We describe the current knowledge based on defects in cell lines, murine models and human patients. Germline mutations in Adhesion and degranulation adaptor protein (ADAP), have not resulted in a T-cell defect.

Spontaneous Differentiation of T Follicular Helper Cells in LATY136F Mutant Mice

Mice with a mutation at the LAT-PLCγ1 binding site (Y136) have a defect in thymocyte development due to dampened TCR signaling. CD4⁺ T cells that do reach the periphery are hyper-activated and skewed to Th2. Over time, these mice develop an autoimmune-like syndrome, characterize by overproduction of Th2 cytokines, T cell infiltration into various organs, and B cell activation, isotype switching, and autoantibody production. In this study, we examined IL4 production by CD4⁺ T cells in the LATY136F mice using the KN2 reporter mice, in which human CD2 expression marks T cells that are actively producing IL4 protein. We showed that these mice had spontaneous Tfh differentiation. Despite the fact that the majority of CD4⁺ T cells were skewed to Th2 and were GATA3⁺, only a small subset of them were actively secreting IL4. These T cells were Tfh cells that expressed BCL6 and were localized to B cell-rich germinal centers within the spleen. Interestingly, these Tfh cells expressed high levels of both BCL6 and GATA3. By using LAT conditional knockout mice that inducibly express only the LATY136F allele, we further showed that Tfh cell differentiation was likely the result of defective LAT-PLCγ1 signaling in the periphery. In addition, B cells were required for spontaneous development of Tfh cells and uncontrolled T cell expansion in these mice. Together, these results indicated a novel role for tonic LAT-PLCγ1 signaling in modulating Tfh cell differentiation during development of autoimmune syndrome.

Association of DNA-Methylation Profiles With Immune Responses Elicited in Breast Cancer Patients Immunized With a Carbohydrate-Mimicking Peptide: A Pilot Study

Immune response to a given antigen, particularly in cancer patients, is complex and is controlled by various genetic and environmental factors. Identifying biomarkers that can predict robust response to immunization is an urgent need in clinical cancer vaccine development. Given the involvement of DNA methylation in the development of lymphocytes, tumorigenicity and tumor progression, we aimed to analyze pre-vaccination DNA methylation profiles of peripheral blood mononuclear cells (PBMCs) from breast cancer subjects vaccinated with a novel peptide-based vaccine referred to as P10s-PADRE. This pilot study was performed to evaluate whether signatures of differentially methylated (DM) loci can be developed as potential predictive biomarkers for prescreening subjects with cancer who will most likely generate an immune response to the vaccine. Genomic DNA was isolated from PBMCs of eight vaccinated subjects, and their DNA methylation profiles were determined using Infinium^® MethylationEPIC BeadChip array from Illumina. A linear regression model was applied to identify loci that were differentially methylated with respect to anti-peptide antibody titers and with IFN-γ production. The data were summarized using unsupervised-learning methods: hierarchical clustering and principal-component analysis. Pathways and networks involved were predicted by Ingenuity Pathway Analysis. We observed that the profile of DM loci separated subjects in regards to the levels of immune responses. Canonical pathways and networks related to metabolic and immunological functions were found to be involved. The data suggest that it is feasible to correlate methylation signatures in pre-treatment PBMCs with immune responses post-treatment in cancer patients going through standard-of-care chemotherapy. Larger and prospective studies that focus on DM loci in PBMCs is warranted to develop pre-screening biomarkers before BC vaccination.

Clinical Trial Registration:www.ClinicalTrials.gov, Identifier: NCT02229084.

Transcriptomic signature of gut microbiome-contacting cells in colon of spontaneously hypertensive rats

Fecal matter transfer from hypertensive patients and animals into normotensive animals increases blood pressure, strengthening the evidence for gut-microbiota interactions in the control of blood pressure. However, cellular and molecular events involved in gut dysbiosis-associated hypertension remain poorly understood. Therefore, our objective in this study was to use gene expression profiling to characterize the gut epithelium layer in the colon in hypertension. We observed significant suppression of components of T cell receptor (TCR) signaling in the colonic epithelium of spontaneously hypertensive rats (SHR) when compared with Wistar Kyoto (WKY) normotensive rats. Western blot analysis confirmed lower expression of key proteins including T cell surface glycoprotein CD3 gamma chain (Cd3g) and lymphocyte cytosolic protein 2 (Lcp2). Furthermore, lower expression of cytokines and receptors responsible for lymphocyte proliferation, differentiation, and activation (e.g., Il12r, Il15ra, Il7, Il16, Tgfb1) was observed in the colonic epithelium of the SHR. Finally, Alpi and its product, intestinal alkaline phosphatase, primarily localized in the epithelial cells, were profoundly lower in the SHR. These observations demonstrate that the colonic epithelium undergoes functional changes linked to altered immune, barrier function, and dysbiosis in hypertension.

A comparative view on vitamin C effects on αβ- versus γδ T-cell activation and differentiation

Vitamin C (VitC) is an essential vitamin that needs to be provided through exogenous sources. It is a potent anti-oxidant, and an essential cofactor for many enzymes including a group of enzymes that modulate epigenetic regulation of gene expression. Moreover, VitC has a significant influence on T-cell differentiation, and can directly interfere with T-cell signaling. Conventional CD4 and CD8 T cells express the αβ TCR and recognize peptide antigens in the context of MHC presentation. The numerically small population of γδ T cells recognizes antigens in an MHC-independent manner. γδ T cells kill a broad variety of malignant cells, and because of their unique features, are interesting candidates for cancer immunotherapy. In this review, we summarize what is known about the influence of VitC on T-cell activation and differentiation with a special focus on γδ T cells. The known mechanisms of action of VitC on αβ T cells are discussed and extrapolated to the effects observed on γδ T-cell activation and differentiation. Overall, VitC enhances proliferation and effector functions of γδ T cells and thus may help to increase the efficacy of γδ T cells applied as cancer immunotherapy in adoptive cell transfer.

γδ T Cells Shape Preimmune Peripheral B Cell Populations

We previously reported that selective ablation of certain γδ T cell subsets, rather than removal of all γδ T cells, strongly affects serum Ab levels in nonimmunized mice. This type of manipulation also changed T cells, including residual γδ T cells, revealing some interdependence of γδ T cell populations. For example, in mice lacking Vγ4(+) and Vγ6(+) γδ T cells (B6.TCR-Vγ4(-/-)/6(-/-)), we observed expanded Vγ1(+) cells, which changed in composition and activation and produced more IL-4 upon stimulation in vitro, increased IL-4 production by αβ T cells as well as spontaneous germinal center formation in the spleen, and elevated serum Ig and autoantibodies. We therefore examined B cell populations in this and other γδ-deficient mouse strains. Whereas immature bone marrow B cells remained largely unchanged, peripheral B cells underwent several changes. Specifically, transitional and mature B cells in the spleen of B6.TCR-Vγ4(-/-)/6(-/-) mice and other peripheral B cell populations were diminished, most of all splenic marginal zone (MZ) B cells. However, relative frequencies and absolute numbers of Ab-producing cells, as well as serum levels of Abs, IL-4, and BAFF, were increased. Cell transfers confirmed that these changes are directly dependent on the altered γδ T cells in this strain and on their enhanced potential of producing IL-4. Further evidence suggests the possibility of direct interactions between γδ T cells and B cells in the splenic MZ. Taken together, these data demonstrate the capability of γδ T cells of modulating size and productivity of preimmune peripheral B cell populations.

The Importance of IL-6 in the Development of LAT-Mediated Autoimmunity

Linker for activation of T cells (LAT) is a transmembrane adaptor protein that is highly tyrosine phosphorylated upon engagement of the TCR. Phosphorylated LAT binds Grb2, Gads, and phospholipase C (PLC)γ1 to mediate T cell activation, proliferation, and cytokine production. T cells from mice harboring a mutation at the PLCγ1 binding site of LAT (Y136F) have impaired calcium flux and Erk activation. Interestingly, these T cells are highly activated, resulting in the development of a lymphoproliferative syndrome in these mice. CD4(+) T cells in LATY136F mice are Th2 skewed, producing large amounts of IL-4. In this study, we showed that the LATY136F T cells could also overproduce IL-6 due to activated NF-κB, AKT, and p38 pathways. By crossing LATY136F mice with IL-6-deficient mice, we demonstrated that IL-6 is required for uncontrolled T cell expansion during the early stage of disease development. Reduced CD4(+) T cell expansion was not due to a further block in thymocyte development or an increase in the number of regulatory T cells, but was caused by reduction in cell survival. In aged IL-6(-/-) LATY136F mice, CD4(+) T cells began to hyperproliferate and induced splenomegaly; however, isotype switching and autoantibody production were diminished. Our data indicated that the LAT-PLCγ1 interaction is important for controlling IL-6 production by T cells and demonstrated a critical role of IL-6 in the development of this lymphoproliferative syndrome.

Five Layers of Receptor Signaling in γδ T-Cell Differentiation and Activation

The contributions of γδ T-cells to immunity to infection or tumors critically depend on their activation and differentiation into effectors capable of secreting cytokines and killing infected or transformed cells. These processes are molecularly controlled by surface receptors that capture key extracellular cues and convey downstream intracellular signals that regulate γδ T-cell physiology. The understanding of how environmental signals are integrated by γδ T-cells is critical for their manipulation in clinical settings. Here, we discuss how different classes of surface receptors impact on human and murine γδ T-cell differentiation, activation, and expansion. In particular, we review the role of five receptor types: the T-cell receptor (TCR), costimulatory receptors, cytokine receptors, NK receptors, and inhibitory receptors. Some of the key players are the costimulatory receptors CD27 and CD28, which differentially impact on pro-inflammatory subsets of γδ T-cells; the cytokine receptors IL-2R, IL-7R, and IL-15R, which drive functional differentiation and expansion of γδ T-cells; the NK receptor NKG2D and its contribution to γδ T-cell cytotoxicity; and the inhibitory receptors PD-1 and BTLA that control γδ T-cell homeostasis. We discuss these and other receptors in the context of a five-step model of receptor signaling in γδ T-cell differentiation and activation, and discuss its implications for the manipulation of γδ T-cells in immunotherapy.