The Role of T Cell Costimulation via DNAM-1 in Kidney Transplantation

TIGIT regulates CD4+ T cell immunity against polymicrobial sepsis

Background

Sepsis is one of the major causes of death and increased health care burden in modern intensive care units. Immune checkpoints have been prompted to be key modulators of T cell activation, T cell tolerance and T cell exhaustion. This study was designed to investigate the role of the negative immune checkpoint, T cell immunoglobulin and ITIM domain (TIGIT), in the early stage of sepsis.

Method

An experimental murine model of sepsis was developed by cecal ligation and puncture (CLP). TIGIT and CD155 expression in splenocytes at different time points were assessed using flow cytometry. And the phenotypes of TIGIT-deficient (TIGIT-/-) and wild-type (WT) mice were evaluated to explore the engagement of TIGIT in the acute phase of sepsis. In addition, the characteristics were also evaluated in the WT septic mice pretreated with anti-TIGIT antibody. TIGIT and CD155 expression in tissues was measured using real-time quantitative PCR and immunofluorescence staining. Proliferation and effector function of splenic immune cells were evaluated by flow cytometry. Clinical severity and tissue injury were scored to evaluate the function of TIGIT on sepsis. Additionally, tissue injury biomarkers in peripheral blood, as well as bacterial load in peritoneal lavage fluid and liver were also measured.

Results

The expression of TIGIT in splenic T cells and NK cells was significantly elevated at 24 hours post CLP.TIGIT and CD155 mRNA levels were upregulated in sepsis-involved organs when mice were challenged with CLP. In CLP-induced sepsis, CD4+ T cells from TIGIT-/- mice shown increased proliferation potency and cytokine production when compared with that from WT mice. Meanwhile, innate immune system was mobilized in TIGIT-/- mice as indicated by increased proportion of neutrophils and macrophages with potent effector function. In addition, tissue injury and bacteria burden in the peritoneal cavity and liver was reduced in TIGIT-/- mice with CLP induced sepsis. Similar results were observed in mice treated with anti-TIGIT antibody.

Conclusion

TIGIT modulates CD4+ T cell response against polymicrobial sepsis, suggesting that TIGIT could serve as a potential therapeutic target for sepsis.

T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain as a promising immune checkpoint target for the treatment of SLE

Immune checkpoints (ICs) play a pivotal role in orchestrating immune regulation, crucial for the maintenance of immune tolerance and prevention of autoimmune diseases. One noteworthy example among these immune regulators is T cell immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT). The TIGIT pathway's inhibition or the absence of TIGIT has been linked to the hyperactivation and excessive proliferation of T cells, rendering individuals more susceptible to autoimmune diseases and exacerbating inflammatory responses. Conversely, the activation of TIGIT has exhibited promising outcomes in ameliorating autoimmune disorders, as observed in murine models of systemic lupus erythematosus (SLE). Consequently, a judicious exploration of the co-inhibitory axis appears warranted for the effective management of pathogenic immune responses in SLE. In light of compelling evidence, this review undertakes a comprehensive examination of TIGIT's characteristics within the context of autoimmunity, offering insights into its potential as a therapeutic target for SLE.

Immune Checkpoint Molecule TIGIT Regulates Kidney T Cell Functions and Contributes to AKI

SIGNIFICANCE STATEMENT

T cells mediate pathogenic and reparative processes during AKI, but the exact mechanisms regulating kidney T cell functions are unclear. This study identified upregulation of the novel immune checkpoint molecule, TIGIT, on mouse and human kidney T cells after AKI. TIGIT-expressing kidney T cells produced proinflammatory cytokines and had effector (EM) and central memory (CM) phenotypes. TIGIT-deficient mice had protection from both ischemic and nephrotoxic AKI. Single-cell RNA sequencing led to the discovery of possible downstream targets of TIGIT. TIGIT mediates AKI pathophysiology, is a promising novel target for AKI therapy, and is being increasingly studied in human cancer therapy trials.

BACKGROUND

T cells play pathogenic and reparative roles during AKI. However, mechanisms regulating T cell responses are relatively unknown. We investigated the roles of the novel immune checkpoint molecule T cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory motif domains (TIGIT) in kidney T cells and AKI outcomes.

METHODS

TIGIT expression and functional effects were evaluated in mouse kidney T cells using RNA sequencing (RNA-Seq) and flow cytometry. TIGIT effect on AKI outcomes was studied with TIGIT knockout (TIGIT-KO) mice in ischemia reperfusion (IR) and cisplatin AKI models. Human kidney T cells from nephrectomy samples and single cell RNA sequencing (scRNA-Seq) data from the Kidney Precision Medicine Project were used to assess TIGIT's role in humans.

RESULTS

RNA-Seq and flow cytometry analysis of mouse kidney CD4+ T cells revealed increased expression of TIGIT after IR injury. Ischemic injury also increased TIGIT expression in human kidney T cells, and TIGIT expression was restricted to T/natural killer cell subsets in patients with AKI. TIGIT-expressing kidney T cells in wild type (WT) mice had an effector/central memory phenotype and proinflammatory profile at baseline and post-IR. Kidney regulatory T cells were predominantly TIGIT+ and significantly reduced post-IR. TIGIT-KO mice had significantly reduced kidney injury after IR and nephrotoxic injury compared with WT mice. scRNA-Seq analysis showed enrichment of genes related to oxidative phosphorylation and mTORC1 signaling in Th17 cells from TIGIT-KO mice.

CONCLUSIONS

TIGIT expression increases in mouse and human kidney T cells during AKI, worsens AKI outcomes, and is a novel therapeutic target for AKI.

The Ratio of CD226 and TIGIT Expression in Tfh and PD-1+ICOS+Tfh Cells Are Potential Biomarkers for Chronic Antibody-Mediated Rejection in Kidney Transplantation

Kidney transplantation is the ideal treatment for end-stage renal disease (ESRD). Chronic antibody-mediated rejection (CAMR) is the main cause of graft failure. Tfh and B cells are key immune cells that play important roles in CAMR. In this study, the populations of different Tfh cell phenotypes and B cell subsets in CAMR were investigated in a total of 36 patients. Based on Banff-2019, 15 patients were diagnosed with CAMR (CAMR group), 11 recipients were diagnosed with recurrent or de novo IgA nephropathy (IgAN group), and 10 patients displayed stable renal function (stable group). The Tfh and B cell subsets were analyzed by flow cytometry. The percentage and absolute number of PD-1⁺ICOS⁺Tfh cells were significantly higher in CAMR (p < 0.05), as was the ratio of CD226⁺Tfh cells to TIGIT⁺Tfh cells (p < 0.05). Compared with stable recipients, CAMR patients had lower naïve B cells and higher unswitched memory B cells, which were also significantly related to renal function (p < 0.05). Using the logistic regression model, we concluded that the estimated glomerular filtration rate (eGFR), absolute number of PD-1⁺ICOS⁺Tfh cells, and ratio of CD226⁺Tfh cells to TIGIT⁺Tfh cells were independent risk factors for CAMR. The combination of eGFR, PD-1⁺ICOS⁺Tfh cells, and the ratio of CD226⁺Tfh cells to TIGIT⁺Tfh cells showed better diagnostic efficacy for CAMR than each single parameter. The collective findings show that monitoring different Tfh phenotypes and B cell subsets is beneficial to kidney transplant recipients and implicate the combination of eGFR, number of PD-1⁺ICOS⁺Tfh cells, and ratio of CD226⁺Tfh cells to TIGIT⁺Tfh cells as a biomarker for diagnosing CAMR. The findings may also inform new strategies to identify and treat CAMR.

CD226: An Emerging Role in Immunologic Diseases

CD226, a member of the immunoglobulin superfamily, is a functional protein initially expressed on natural killer and T cells. In recent years, the function of CD226 has been increasingly realized and researched. Accumulating evidence shows that CD226 is closely related to the occurrence of autoimmune diseases, infectious diseases, and tumors. Because of the CD226’s increasing importance, the author herein discusses the structure, mechanism of action, and role of CD226 in various pathophysiological environments, allowing for further understanding of the function of CD226 and providing the basis for further research in related diseases.

Back signaling of HLA class I molecules and T/NK cell receptor ligands in epithelial cells reflects the rejection-specific microenvironment in renal allograft biopsies

The role of endothelial cells in the pathophysiology of antibody-mediated rejection after renal transplantation has been widely investigated. We expand this scenario to the impact of epithelial cells on the microenvironment during rejection. Primary proximal tubular epithelial cells were stimulated via HLA class I, CD155 and CD166 based on their potential signal-transducing capacity to mediate back signaling after encounter with either T/NK cells or donor-specific antibodies. Upon crosslinking of these ligands with mAbs, PTEC secreted IL-6, CXCL1,8,10, CCL2, and sICAM-1. These proteins were also released by PTEC as consequence of a direct interaction with T/NK cells. Downmodulation of the receptor CD226 on effector cells confirmed the involvement of this receptor/ligand pair in back signaling. In vivo, CD155 and CD166 expression was detectable in proximal and distal tubuli of renal transplant biopsies, respectively. The composition of the protein microenvironment in these biopsies showed a substantial overlap with the PTEC response. Cluster and principal component analyses of the microenvironment separated unsuspicious from rejection biopsies and, furthermore, ABMR, TCMR, and borderline rejection. In conclusion, our results provide evidence that epithelial cells may contribute to the rejection process and pave the way to a better understanding of the pathomechanisms of kidney allograft rejection.

Expression of the Inhibitory Receptor TIGIT Is Up-Regulated Specifically on NK Cells With CD226 Activating Receptor From HIV-Infected Individuals

Natural killer (NK) cells are important for maintenance of innate immune system stability and serve as a first line of defense against tumors and virus infections; they can act either directly or indirectly and are regulated via co-operation between inhibitory and stimulatory surface receptors. The recently reported inhibitory receptor, TIGIT, can be expressed on the NK cell surface; however, the expression level and function of TIGIT on NK cells during HIV infection is unknown. In this study, for the first time, we investigated the expression and function of TIGIT in NK cells from HIV-infected individuals. Our data demonstrate that the level of TIGIT is higher on NK cells from patients infected with human immunodeficiency virus (HIV) compared with HIV-negative healthy controls. TIGIT expression is inversely correlated with CD4⁺ T cell counts and positively correlated with plasma viral loads. Additionally, levels of the TIGIT ligand, CD155, were higher on CD4⁺ T cells from HIV-infected individuals compared with those from healthy controls; however, there was no difference in the level of the activating receptor, CD226, which recognizes the same ligands as TIGIT. Furthermore, TIGIT was found to specifically up-regulated on CD226⁺ NK cells in HIV-infected individuals, and either rIL-10, or rIL-12 + rIL-15, could induce TIGIT expression on these cells. In addition, high TIGIT expression inhibited the production of interferon-gamma (IFN-γ) by NK cells, while TIGIT inhibition restored IFN-γ production. Overall, these results highlight the important role of TIGIT in NK cell function and suggest a potential new avenue for the development of therapeutic strategies toward a functional cure for HIV.

MiR-892a Promotes Hepatocellular Carcinoma Cells Proliferation and Invasion Through Targeting CD226

Our study is aim to investigate the influence of miR-892a on proliferative and invasive activities of human hepatocellular carcinoma (HCC) cells through regulating CD226 expression. QRT-PCR was used to detect the expression levels of miR-892a and CD226 mRNA in HCC tissues and adjacent tissues or HCC cells and normal cells whereas Western Blot was used to detect the CD226 protein expression in tissue and cell samples. Then HuH-7 cell line was selected for following assays and respectively transfected with miR-892a mimics, miR-NC, Plenti-GIII-Ubc-CD226, and Plenti-GIII-Ubc followed by qRT-PCR assay to detect the miR-892a and CD226 expression. The luciferase reporter assay was conducted to determine if miR-892a directly targeted CD226 and then CCK-8 assay, wound healing assay, Transwell assay, and flow cytometry were used to detect cell proliferation, migration, invasion ability, cell cycle, and cell apoptosis. What's more, relationships between expression levels of miR-892a or CD226 and overall survival (OS) or disease-free survival (DFS) of HCC patients were investigated based on TCGA database. MiR-892a was high-expressed in HCC tissues or cells while CD226 was low-expressed. MiR-892a directly targeted CD226 and up-regulating miR-892a expression could promote proliferative, migrating, and invasive activities of HCC cells. Different expression levels of miR-892a and CD226 both related to the prognosis of HCC. MiR-892a promotes hepatocellular carcinoma cells proliferation and invasion through regulating CD226 expression. J. Cell. Biochem. 118: 1489-1496, 2017. © 2016 Wiley Periodicals, Inc.