Activated CD8 T cells acquire NK1.1 expression and preferentially locate in the liver in mice after allogeneic hematopoietic cell transplantation

CD8+CD161+ T-Cells: Cytotoxic Memory Cells With High Therapeutic Potential

NK1.1 and its human homolog CD161 are expressed on NK cells, subsets of CD4+ and CD8+ T cells, and NKT cells. While the expression of NK1.1 is thought to be inhibitory to NK cell function, it is reported to play both costimulatory and coinhibitory roles in T-cells. CD161 has been extensively studied and characterized on subsets of T-cells that are MR1-restricted, IL-17 producing CD4+ (TH17 MAIT cells) and CD8+ T cells (Tc17 cells). Non-MAIT, MR1-independent CD161-expressing T-cells also exist and are characterized as generally effector memory cells with a stem cell like phenotype. Gene expression analysis of this enigmatic subset indicates a significant enhancement in the expression of cytotoxic granzyme molecules and innate like stress receptors in CD8+NK1.1+/CD8+CD161+ cells in comparison to CD8+ cells that do not express NK1.1 or CD161. First identified and studied in the context of viral infection, the role of CD8+CD161+ T-cells, especially in the context of tumor immunology, is still poorly understood. In this review, the functional characteristics of the CD161-expressing CD8+ T cell subset with respect to gene expression profile, cytotoxicity, and tissue homing properties are discussed, and application of this subset to immune responses against infectious disease and cancer is considered.

Unveiling the heterogeneity of NKT cells in the liver through single cell RNA sequencing

CD1d-dependent type I NKT cells, which are activated by lipid antigen, are known to play important roles in innate and adaptive immunity, as are a portion of type II NKT cells. However, the heterogeneity of NKT cells, especially NKT-like cells, remains largely unknown. Here, we report the profiling of NKT (NK1.1⁺CD3e⁺) cells in livers from wild type (WT), Jα18-deficient and CD1d-deficient mice by single-cell RNA sequencing. Unbiased transcriptional clustering revealed distinct cell subsets. The transcriptomic profiles identified the well-known CD1d-dependent NKT cells and defined two CD1d-independent NKT cell subsets. In addition, validation of marker genes revealed the differential organ distribution and landscape of NKT cell subsets during liver tumor progression. More importantly, we found that CD1d-independent Sca-1⁻CD62L⁺ NKT cells showed a strong ability to secrete IFN-γ after costimulation with IL-2, IL-12 and IL-18 in vitro. Collectively, our findings provide a comprehensive characterization of NKT cell heterogeneity and unveil a previously undefined functional NKT cell subset.

Mouse Models of Nonalcoholic Steatohepatitis: Head-to-Head Comparison of Dietary Models and Impact on Inflammation and Animal Welfare

A variety of dietary nonalcoholic steatohepatitis (NASH) mouse models are available, and choosing the appropriate mouse model is one of the most important steps in the design of NASH studies. In addition to the histopathological and metabolic findings of NASH, a sufficient mouse model should guarantee a robust clinical status and good animal welfare. Three different NASH diets, a high-fat diet (HFD60), a western diet (WD), and a cafeteria diet (CAFD), were fed for 12 or 16 weeks. Metabolic assessment was conducted at baseline and before scheduled sacrifice, and liver inflammation was analyzed via fluorescence-associated cell sorting and histopathological examination. Clinical health conditions were scored weekly to assess the impact on animal welfare. The HFD60 and WD were identified as suitable NASH mouse models without a significant strain on animal welfare. Furthermore, the progression of inflammation and liver fibrosis was associated with a decreased proportion of CD3⁺ NK1.1⁺ cells. The WD represents a model of advanced-stage NASH, and the HFD60 is a strong model of nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome. However, the CAFD should not be considered a NASH model.

iNKT Cells Suppress Pathogenic NK1.1+CD8+ T Cells in DSS-Induced Colitis

T cells producing IFNγ play a pathogenic role in the development of inflammatory bowel disease (IBD). To investigate the functions of CD1d-dependent invariant natural killer T (iNKT) cells in experimental colitis induced in Yeti mice with dysregulated expression of IFNγ, we generated iNKT cell-deficient Yeti/CD1d KO mice and compared colitis among WT, CD1d KO, Yeti, and Yeti/CD1d KO mice following DSS treatment. We found that deficiency of iNKT cells exacerbated colitis and disease pathogenesis was mainly mediated by NK1.1⁺CD8⁺ T cells. Furthermore, the protective effects of iNKT cells correlated with up-regulation of regulatory T cells. Taken together, our results have demonstrated that CD1d-dependent iNKT cells and CD1d-independent NK1.1⁺CD8⁺ T cells reciprocally regulate the development of intestinal inflammatory responses mediated by IFNγ-dysregulation. These findings also identify NK1.1⁺CD8⁺ T cells as novel target cells for the development of therapeutics for human IBD.

Proteomic analysis reveals distinctive protein profiles involved in CD8+ T cell-mediated murine autoimmune cholangitis

Autoimmune cholangitis arises from abnormal innate and adaptive immune responses in the liver, and T cells are critical drivers in this process. However, little is known about the regulation of their functional behavior during disease development. We previously reported that mice with T cell-restricted expression of a dominant negative form of transforming growth factor beta receptor type II (dnTGFβRII) spontaneously develop an autoimmune cholangitis that resembles human primary biliary cholangitis (PBC). Adoptive transfer of CD8⁺ but not CD4⁺ T cells into Rag1^-/- mice reproduced the disease, demonstrating a critical role for CD8⁺ T cells in PBC pathogenesis. Herein, we used SOMAscan technology to perform proteomic analysis of serum samples from dnTGFβRII and B6 control mice at different ages. In addition, we analyzed CD8 protein profiles after adoptive transfer of splenic CD8⁺ cells into Rag1^-/- recipients. The use of the unique SOMAscan aptamer technology revealed critical and distinct profiles of CD8 cells, which are key to biliary mediation. In total, 254 proteins were significantly increased while 216 proteins were significantly decreased in recipient hepatic CD8⁺ cells compared to donor splenic CD8⁺ cells. In contrast to donor splenic CD8⁺ cells, recipient hepatic CD8⁺ cells expressed distinct profiles for proteins involved in chemokine signaling, focal adhesion, T cell receptor and natural killer cell-mediated cytotoxicity pathways.

Dissecting CD8+ NKT Cell Responses to Listeria Infection Reveals a Component of Innate Resistance

A small pool of NK1.1(+) CD8(+) T cells is harbored among the conventional CD8(+) T cell compartment. Conclusions drawn from the analysis of immune responses mediated by cytotoxic CD8(+) T cells are often based on the total population, which includes these contaminating NK1.1(+) CD8(+) T cells. An unresolved question is whether NK1.1(+) CD8(+) cells are conventional T cells that acquire NK1.1 expression upon activation or delineation into memory phenotype or whether they are a distinct cell population that induces immune responses in a different manner than conventional T cells. To address this question, we used the Listeria monocytogenes model of infection and followed CD8(+) NK1.1(+) T cells and NK1.1(-) CD8(+) T cells during each phase of the immune response: innate, effector, and memory. Our central finding is that CD8(+) NK1.1(+) cells and conventional NK1.1(-) CD8(+) T cells both contribute to the adaptive immune response to Listeria, but only CD8(+) NK1.1(+) cells were equipped with the ability to provide a rapid innate immune response, as demonstrated by early and Ag-independent IFN-γ production, granzyme B expression, and degranulation. More importantly, purified conventional CD8(+) T cells alone, in the absence of any contaminating CD8(+) NK1.1(+) cells, were not sufficient to provide early protection to lethally infected mice. These results highlight the role of CD8(+) NK1.1(+) T cells in mounting early innate responses that are important for host defense and support the therapeutic potential of this subset to improve the effectiveness of protective immunity.