CD43 regulates the threshold for T cell activation by targeting Cbl functions

T cell responses to control fungal infection in an immunological memory lens

In recent years, fungal vaccine research emanated significant findings in the field of antifungal T-cell immunity. The generation of effector T cells is essential to combat many mucosal and systemic fungal infections. The development of antifungal memory T cells is integral for controlling or preventing fungal infections, and understanding the factors, regulators, and modifiers that dictate the generation of such T cells is necessary. Despite the deficiency in the clear understanding of antifungal memory T-cell longevity and attributes, in this review, we will compile some of the existing literature on antifungal T-cell immunity in the context of memory T-cell development against fungal infections.

Loss of BAP1 expression is associated with an immunosuppressive microenvironment in uveal melanoma, with implications for immunotherapy development

Immunotherapy using immune checkpoint inhibitors (ICIs) induces durable responses in many metastatic cancers. Metastatic uveal melanoma (mUM), typically occurring in the liver, is one of the most refractory tumours to ICIs and has dismal outcomes. Monosomy 3 (M3), polysomy 8q, and BAP1 loss in primary uveal melanoma (pUM) are associated with poor prognoses. The presence of tumour-infiltrating lymphocytes (TILs) within pUM and surrounding mUM - and some evidence of clinical responses to adoptive TIL transfer - strongly suggests that UMs are indeed immunogenic despite their low mutational burden. The mechanisms that suppress TILs in pUM and mUM are unknown. We show that BAP1 loss is correlated with upregulation of several genes associated with suppressive immune responses, some of which build an immune suppressive axis, including HLA-DR, CD38, and CD74. Further, single-cell analysis of pUM by mass cytometry confirmed the expression of these and other markers revealing important functions of infiltrating immune cells in UM, most being regulatory CD8+ T lymphocytes and tumour-associated macrophages (TAMs). Transcriptomic analysis of hepatic mUM revealed similar immune profiles to pUM with BAP1 loss, including the expression of IDO1. At the protein level, we observed TAMs and TILs entrapped within peritumoural fibrotic areas surrounding mUM, with increased expression of IDO1, PD-L1, and β-catenin (CTNNB1), suggesting tumour-driven immune exclusion and hence the immunotherapy resistance. These findings aid the understanding of how the immune response is organised in BAP1 - mUM, which will further enable functional validation of detected biomarkers and the development of focused immunotherapeutic approaches. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Immunomodulatory effect of mesenchymal stem cells in chemical-induced liver injury: a high-dimensional analysis

Background

The efficacy of mesenchymal stem cell (MSC)-based therapy for acute liver injury (ALI) involves coordination with the hepatic immune system, a complex and coordinated network of immune-cell interactions. However, studies of the immunomodulatory effects of MSCs have focused on a limited number of cell subsets rather than a systematic assessment.

Methods

Carbon tetrachloride (CCl₄) was used to induce ALI in mice. To determine the efficacy of MSCs, ALI mice were injected with MSCs via the tail vein, and histopathological changes, survival rate, and the serum levels of liver enzymes were determined. To assess the immune response induced by MSCs, a mass cytometry panel of 43 metal isotope-tagged antibodies was used to characterize the hepatic immune compartment at days 1, 2, 3, and 7 after administration of MSCs or PBS.

Results

MSC treatment significantly alleviated CCl₄-induced ALI and improved the survival rate. MSC treatment also modulated the hepatic immune system in terms of the distribution of immune-cell subsets and the phenotype of single cells. During the injured phase, MSCs inhibited a systemic response by reducing the numbers of Ly6C^lowCD8⁺ T_RM cells, conventional NK cells, and IgM⁺IgD⁺ B cells; suppressing the activation of Ly6C^hiCD8⁺ T_RM cells; downregulating MHC II and IgM expression in IgM⁺IgD⁺ B cells; and increasing the number of immunosuppressive monocyte-derived macrophages. During the recovery phase, MSCs promoted the retention of Ly6C^lowCD8⁺ T_RM cells and maintained the immunosuppressive activity of monocyte-derived macrophages. The response to MSC treatment differed between the injured and recovery phases, emphasizing the benefit of dynamic assessment of the immunomodulatory effects of MSCs.

Conclusions

We determined the immunomodulatory effects of MSC treatment on the subtype distribution and phenotypes of hepatic immune cells.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1379-6) contains supplementary material, which is available to authorized users.

Crk adaptor proteins regulate CD3ζ chain phosphorylation and TCR/CD3 down-modulation in activated T cells

T cell receptor (TCR) recognition of a peptide antigen in the context of MHC molecules initiates positive and negative cascades that regulate T cell activation, proliferation and differentiation, and culminate in the acquisition of effector T cell functions. These processes are a prerequisite for the induction of specific T cell-mediated adaptive immune responses. A key event in the activation of TCR-coupled signaling pathways is the phosphorylation of tyrosine residues within the cytoplasmic tails of the CD3 subunits, predominantly CD3ζ. These transiently formed phosphotyrosyl epitopes serve as docking sites for SH2-domain containing effector molecules, predominantly the ZAP70 protein tyrosine kinase, which is critical for signal propagation. We found that CrkI and CrkII adaptor proteins also interact with CD3ζ in TCR activated-, but not in resting-, T cells. Crk binding to CD3ζ was independent of ZAP70 and also occurred in ZAP70-deficient T cells. Binding was mediated by Crk-SH2 domain interaction with phosphotyrosine-containing motifs on CD3ζ, via a direct physical interaction, as demonstrated by Far-Western blot. CrkII binding to CD3ζ could also be demonstrated in a heterologous system, where coexpression of a catalytically active Lck was used to phosphorylate the CD3ζ chain. TCR activation-induced Crk binding to CD3ζ resulted in increased and prolonged phosphorylation of CD3ζ, as well as ZAP70 and LAT, suggesting a positive role for CrkI/II binding to CD3ζ in regulation of TCR-coupled signaling pathways. Furthermore, Crk-dependent increased phosphorylation of CD3ζ coincided with inhibition of TCR downmodulation, supporting a positive role for Crk adaptor proteins in TCR-mediated signal amplification.

An alternative mode of CD43 signal transduction activates pro-survival pathways of T lymphocytes

CD43 is one of the most abundant co-stimulatory molecules on a T-cell surface; it transduces activation signals through its cytoplasmic domain, contributing to modulation of the outcome of T-cell responses. The aim of this study was to uncover new signalling pathways regulated by this sialomucin. Analysis of changes in protein abundance allowed us to identify pyruvate kinase isozyme M2 (PKM2), an enzyme of the glycolytic pathway, as an element potentially participating in the signalling cascade resulting from the engagement of CD43 and the T-cell receptor (TCR). We found that the glycolytic activity of this enzyme was not significantly increased in response to TCR+CD43 co-stimulation, but that PKM2 was tyrosine phosphorylated, suggesting that it was performing moonlight functions. We report that phosphorylation of both Y¹⁰⁵ of PKM2 and of Y⁷⁰⁵ of signal transducer and activator of transcription 3 was induced in response to TCR+CD43 co-stimulation, resulting in activation of the mitogen-activated protein kinase kinase 5/extracellular signal-regulated kinase 5 (MEK5/ERK5) pathway. ERK5 and the cAMP response element binding protein (CREB) were activated, and c-Myc and nuclear factor-κB (p65) nuclear localization, as well as Bad phosphorylation, were augmented. Consistent with this, expression of human CD43 in a murine T-cell hybridoma favoured cell survival. Altogether, our data highlight novel signalling pathways for the CD43 molecule in T lymphocytes, and underscore a role for CD43 in promoting cell survival through non-glycolytic functions of metabolic enzymes.

High salt promotes autoimmunity by TET2-induced DNA demethylation and driving the differentiation of Tfh cells

Follicular helper T cells (Tfh) have been well documented to play a critical role in autoimmunity, such as systemic lupus erythematosus (SLE), by helping B cells. In this study, high salt (sodium chloride, NaCl), under physiological conditions, was demonstrated to increase the differentiation of Tfh. A high-salt diet markedly increased lupus features in MRL/lpr mice. The mechanism is NaCl-induced DNA demethylation via the recruitment of the hydroxytransferase Ten-Eleven Translocation 2 (TET2). Gene silencing of TET2 obviously diminished NaCl-induced Tfh cell polarization in vitro. In addition, the gene expression of sh2d1a, map3k1, spn and stat5b was enhanced after NaCl treatment, consistent with the findings in lupus CD4(+)T cells. However, only spn was directly regulated by TET2, and spn was not the sole target for NaCl. Our findings not only explain the epigenetic mechanisms of high-salt induced autoimmunity but also provide an attractive molecular target for intervention strategies of patients.

Exosomes from Dendritic Cells Loaded with Chaperone-Rich Cell Lysates Elicit a Potent T Cell Immune Response Against Intracranial Glioma in Mice

Chaperone-rich cell lysates (CRCLs) may play an important role in the development of anti-tumor vaccines. Tumor-derived CRCLs have been reported to activate dendritic cells (DCs) to elicit potent anti-tumor activity. However, the role of DC-derived exosomes (DEXs) secreted from DCs loaded with CRCLs in the treatment of tumors has not been clearly determined. In the present study, DEXs were generated from DCs loaded with CRCLs derived from GL261 glioma cells. These DEXs, designated DEX (CRCL-GL261), were then used to treat DCs to create DEX (CRCL-GL261)-DCs. The DEX (CRCL-GL261)-DCs were found to promote cell proliferation and cytotoxic T lymphocyte (CTL) activity of CD4(+) and CD8(+) T cells in vitro compared with DEX (GL261)-DCs, which were loaded with DEXs derived from DCs loaded with GL261 tumor cell lysates. DEX (CRCL-GL261)-DCs significantly prolonged the survival of mice with tumors and inhibited tumor growth in vivo. In addition, DEX (CRCL-GL261)-DCs induced enhanced T cell infiltration in intracranial glioma tissues compared with other treatments. DEX (CRCL-GL261)-DCs induced strong production of anti-tumor cytokines, including interleukin-2 and interferon-γ. Moreover, depletion of CD4(+) and CD8(+) T cells significantly impaired the anti-tumor effect of DEX (CRCL-GL261)-DCs. Finally, DEX (CRCL-GL261)-DCs were found to negatively regulate Casitas B cell lineage lymphoma (Cbl)-b and c-Cbl signaling, leading to the activation of phosphatidyl inositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) signaling in T cells. In summary, we present evidence that DEX (CRCL-GL261)-DCs induce more potent and effective anti-tumor T cell immune responses and delineate the underlying mechanism by which DEX (CRCL-GL261)-DCs exerted their anti-tumor activity through modulating Cbl-b and c-Cbl signaling. These results provide novel and promising insight for the development of an anti-tumor vaccine.

CD43 signals prepare human T cells to receive cytokine differentiation signals

T cells are increasingly used for passive immunotherapy and bone marrow transplantation. Proper ex-vivo management of the cells is important for the desired therapeutic effects. For differentiation into effector cells of the Th1 and Th2 phenotypes, T-cells require signals from IFNγ and IL-4, respectively. Naïve cells have an extremely low expression of the specific receptors that recognize these cytokines, indicating that in order to differentiate, cells need to perceive other signals that will enable them to sense the cytokine milieu. CD43 has been proposed as one of the molecules that make the initial contacts with antigen presenting cells. We report here that in cord blood, adult naïve and total human T cells, CD43 signals induced the expression of both IFNγ and IL-4 receptors, mediate their capping, increased their signaling and augmented differentiation mediated by these receptors. CD43 signals also stimulated the expression of IFNγ and in neonatal cells that of IL-4 as well. These data demonstrate an important role for CD43 signals in T-cell preparedness for differentiation into effector cells.

Overexpression of X-linked genes in T cells from women with lupus

Women develop lupus more frequently than men and the reason remains incompletely understood. Evidence that men with Klinefelter's Syndrome (XXY) develop lupus at approximately the same rate as women suggests that a second X chromosome contributes. However, since the second X is normally inactivated, how it predisposes to lupus is unclear. DNA methylation contributes to the silencing of one X chromosome in women, and CD4+ T cell DNA demethylation contributes to the development of lupus-like autoimmunity. This suggests that demethylation of genes on the inactive X may predispose women to lupus, and this hypothesis is supported by a report that CD40LG, an immune gene encoded on the X chromosome, demethylates and is overexpressed in T cells from women but not men with lupus. Overexpression of other immune genes on the inactive X may also predispose women to this disease. We therefore compared mRNA and miRNA expression profiles in experimentally demethylated T cells from women and men as well as in T cells from women and men with lupus. T cells from healthy men and women were treated with the DNA methyltransferase inhibitor 5-azacytidine, then X-linked mRNAs were surveyed with oligonucleotide arrays, and X-linked miRNA's surveyed with PCR arrays. CD40LG, CXCR3, OGT, miR-98, let-7f-2*, miR 188-3p, miR-421 and miR-503 were among the genes overexpressed in women relative to men. MiRNA target prediction analyses identified CBL, which downregulates T cell receptor signaling and is decreased in lupus T cells, as a gene targeted by miR-188-3p and miR-98. Transfection with miR-98 and miR-188-3p suppressed CBL expression. The same mRNA and miRNA transcripts were also demethylated and overexpressed in CD4+ T cells from women relative to men with active lupus. Together these results further support a role for X chromosome demethylation in the female predisposition to lupus.