Shared and Distinct Phenotypes and Functions of Human CD161++ Vα7.2+ T Cell Subsets.

Human mucosal-associated invariant T (MAIT) cells are an important T cell subset that are enriched in tissues and possess potent effector functions. Typically such cells are marked by their expression of Vα7.2-Jα33/Jα20/Jα12 T cell receptors, and functionally they are major histocompatibility complex class I-related protein 1 (MR1)-restricted, responding to bacterially derived riboflavin synthesis intermediates. MAIT cells are contained within the CD161++ Vα7.2+ T cell population, the majority of which express the CD8 receptor (CD8+), while a smaller fraction expresses neither CD8 or CD4 coreceptor (double negative; DN) and a further minority are CD4+. Whether these cells have distinct homing patterns, phenotype and functions have not been examined in detail. We used a combination of phenotypic staining and functional assays to address the similarities and differences between these CD161++ Vα7.2+ T cell subsets. We find that most features are shared between CD8+ and DN CD161++ Vα7.2+ T cells, with a small but detectable role evident for CD8 binding in tuning functional responsiveness. By contrast, the CD4+ CD161++ Vα7.2+ T cell population, although showing MR1-dependent responsiveness to bacterial stimuli, display reduced T helper 1 effector functions, including cytolytic machinery, while retaining the capacity to secrete interleukin-4 (IL-4) and IL-13. This was consistent with underlying changes in transcription factor (TF) expression. Although we found that only a proportion of CD4+ CD161++ Vα7.2+ T cells stained for the MR1-tetramer, explaining some of the heterogeneity of CD4+ CD161++ Vα7.2+ T cells, these differences in TF expression were shared with CD4+ CD161++ MR1-tetramer+ cells. These data reveal the functional diversity of human CD161++ Vα7.2+ T cells and indicate potentially distinct roles for the different subsets in vivo.

Erratum: MAIT cells: new guardians of the liver.

[This corrects the article DOI: 10.1038/cti.2016.51.].

Early Molecular Stratification of High-risk Primary Biliary Cholangitis.

High-risk primary biliary cholangitis (PBC), defined by inadequate response at one year to Ursodeoxycholic acid (UDCA), is associated with disease progression and liver transplantation. Stratifying high-risk patients early would facilitate improved approaches to care. Using long-term follow-up data to define risk at presentation, 6 high-risk PBC patients and 8 low-risk patients were identified from biopsy, transplant and biochemical archival records. Formalin-fixed paraffin-embedded (FFPE) liver biopsies taken at presentation were graded (Scheuer and Nakanuma scoring) and gene expression analysed using the NanoString® nCounter PanCancer Immunity 770-gene panel. Principle component analysis (PCA) demonstrated discrete gene expression clustering between controls and high- and low-risk PBC. High-risk PBC was characterised by up-regulation of genes linked to T-cell activation and apoptosis, INF-γ signalling and leukocyte migration and down-regulation of those linked to the complement pathway. CDKN1a, up-regulated in high-risk PBC, correlated with significantly increased expression of its gene product, the senescence marker p21WAF1/Cip, by biliary epithelial cells. Our findings suggest high- and low-risk PBC are biologically different from disease outset and senescence an early feature in high-risk disease. Identification of a high-risk 'signal' early from standard FFPE tissue sections has clear clinical utility allowing for patient stratification and second-line therapeutic intervention.

MAIT cells: new guardians of the liver.

The liver is an important immunological organ that remains sterile and tolerogenic in homeostasis, despite continual exposure to non-self food and microbial-derived products from the gut. However, where intestinal mucosal defenses are breached or in the presence of a systemic infection, the liver acts as a second 'firewall', because of its enrichment with innate effector cells able to rapidly respond to infections or tissue dysregulation. One of the largest populations of T cells within the human liver are mucosal-associated invariant T (MAIT) cells, a novel innate-like T-cell population that can recognize a highly conserved antigen derived from the microbial riboflavin synthesis pathway. MAIT cells are emerging as significant players in the human immune system, associated with an increasing number of clinical diseases of bacterial, viral, autoimmune and cancerous origin. As reviewed here, we are only beginning to investigate the potential role of this dominant T-cell subset in the liver, but the reactivity of MAIT cells to both inflammatory cytokines and riboflavin derivatives suggests that MAIT cells may have an important role in first line of defense as part of the liver firewall. As such, MAIT cells are promising targets for modulating the host defense and inflammation in both acute and chronic liver diseases.

Long-Term Fenofibrate Treatment in Primary Biliary Cholangitis Improves Biochemistry but Not the UK-PBC Risk Score.

BACKGROUND: Fenofibrate (FF) has been suggested as a second-line agent in primary biliary cholangitis (PBC) patients who do not achieve adequate biochemical response to ursodeoxycholic acid (UDCA) monotherapy. Limited data exist on FF use beyond 12 months, and its long-term effects are unclear. AIM: To study the biochemical outcome of long-term (>12 months) FF treatment in combination with UDCA (FF + UDCA) in PBC patients and to determine the effect on predicted prognosis using the UK-PBC Risk Score. METHODS: This was a retrospective cohort study of all PBC patients treated in a specialist center with FF + UDCA therapy after failure to achieve biochemical response. Liver and renal biochemical indices and the UK-PBC Risk Score at baseline and at 12, 24, 36, 48, and 60 months of FF + UDCA treatment were compared. Biochemical response was assessed using the POISE trial criteria at the end of FF + UDCA treatment. RESULTS: Data from 23 patients treated with FF + UDCA combination were analyzed. The median dose of fenofibrate was 200 mg/day, and median treatment duration was 21 months (range 1-123 months). Six (26 %) patients discontinued FF within 1 year. In patients who completed 12 months (n = 17) and long-term therapy, significant decrease in ALP was seen at 12 (p = 0.0002), 24 (p = 0.002), and 36 (p = 0.03) months. More than 75 % patients met the POISE criteria of ALP response at all study time points. There was no significant improvement in the 5-, 10-, and 15-year UK-PBC Risk Scores after FF + UDCA treatment. No significant renal impairment or adverse events were reported. CONCLUSION: The long-term treatment of PBC patients with fenofibrate as an adjunct to UDCA is safe and effective in improving ALP, but the treatment did not significantly reduce the estimated probability of liver-related death or need for liver transplantation.

LLT1 and CD161 Expression in Human Germinal Centers Promotes B Cell Activation and CXCR4 Downregulation.

Germinal centers (GCs) are microanatomical structures critical for the development of high-affinity Abs and B cell memory. They are organized into two zones, light and dark, with coordinated roles, controlled by local signaling. The innate lectin-like transcript 1 (LLT1) is known to be expressed on B cells, but its functional role in the GC reaction has not been explored. In this study, we report high expression of LLT1 on GC-associated B cells, early plasmablasts, and GC-derived lymphomas. LLT1 expression was readily induced via BCR, CD40, and CpG stimulation on B cells. Unexpectedly, we found high expression of the LLT1 ligand, CD161, on follicular dendritic cells. Triggering of LLT1 supported B cell activation, CD83 upregulation, and CXCR4 downregulation. Overall, these data suggest that LLT1-CD161 interactions play a novel and important role in B cell maturation within the GC in humans.

Human MAIT and CD8αα cells develop from a pool of type-17 precommitted CD8+ T cells.

Human mucosal associated invariant T (MAIT) CD8(+) and Tc17 cells are important tissue-homing cell populations, characterized by high expression of CD161 ((++)) and type-17 differentiation, but their origins and relationships remain poorly defined. By transcriptional and functional analyses, we demonstrate that a pool of polyclonal, precommitted type-17 CD161(++)CD8αß(+) T cells exist in cord blood, from which a prominent MAIT cell (TCR Vα7.2(+)) population emerges post-natally. During this expansion, CD8αα T cells appear exclusively within a CD161(++)CD8(+)/MAIT subset, sharing cytokine production, chemokine-receptor expression, TCR-usage, and transcriptional profiles with their CD161(++)CD8αß(+) counterparts. Our data demonstrate the origin and differentiation pathway of MAIT-cells from a naive type-17 precommitted CD161(++)CD8(+) T-cell pool and the distinct phenotype and function of CD8αα cells in man.