Intrahepatic and peripheral blood phenotypes of natural killer and T cells: differential surface expression of killer cell immunoglobulin-like receptors

Deciphering the circulating immunological landscape of thoracic aortic aneurysm: Insights from a two-sample Mendelian randomization study

Background

Thoracic Aortic Aneurysm (TAA) poses significant health risks due to aortic dilation. Recent evidence suggests a pivotal role for the immune-inflammatory response in the mechanism of aortic aneurysm formation. In this study, we aim to investigate the causal relationship between circulating immune cells and TAA.

Methods

This study employs a two-sample Mendelian Randomization (MR) approach, utilizing genome-wide association study (GWAS) summary statistics for 731 immune cell types and two TAA data from large-scale studies. Causal effects of both peripheral immune cells on TAA and TAA on peripheral immune cells are explored. To ensure more accurate results, we intersected the findings from two TAA data from large-scale studies, excluding results where the direction of the odds ratio (OR) was inconsistent.

Findings

The study identifies specific immune cells associated with TAA. Notably, CD45+ NKT cell (OR: 0.95, 95CI%: 0.90-0.99 in FinnGen study; OR: 0.91, 95CI%: 0.84-0.99 in CHIP + MGI study) and CD45+ HLA-DR + CD8+ T cells (OR: 0.95, 95CI%: 0.90-0.99 in FinnGen study; OR: 0.90, 95CI%: 0.82-0.99 in CHIP + MGI study) demonstrate a protective role against TAA. In addition, CD28+ CD45RA- CD8+ T cells (relative cell counts and absolute cell counts) and HVEM + CM + CD8+ T cells are adversely affected by TAA.

Interpretation

The findings indicate that the potential protective influence exerted by specific subsets of peripheral NKT cells and CD8+ T cells in mitigating the development of TAA, while simultaneously highlighting the reciprocal effects of TAA on peripheral Treg cells subsets and T cell subsets. The complex interaction between immune cells and TAA could provide valuable clues for earlier detection and more efficacious treatment strategies for TAA.

Lipid metabolism in the immune niche of tumor-prone liver microenvironment

The liver is a common primary site not only for tumorigenesis, but also for cancer metastasis. Advanced cancer patients with liver metastases also show reduced response rates and survival benefits when treated with immune checkpoint inhibitors. Accumulating evidence has highlighted the importance of the liver immune microenvironment in determining tumorigenesis, metastasis-organotropism, and immunotherapy resistance. Various immune cells such as T cells, natural killer and natural killer T cells, macrophages and dendritic cells, and stromal cells including liver sinusoidal endothelial cells, Kupffer cells, hepatic stellate cells, and hepatocytes are implicated in contributing to the immune niche of tumor-prone liver microenvironment. In parallel, as the major organ for lipid metabolism, the increased abundance of lipids and their metabolites is linked to processes crucial for nonalcoholic fatty liver disease and related liver cancer development. Furthermore, the proliferation, differentiation, and functions of hepatic immune and stromal cells are also reported to be regulated by lipid metabolism. Therefore, targeting lipid metabolism may hold great potential to reprogram the immunosuppressive liver microenvironment and synergistically enhance the immunotherapy efficacy in the circumstance of liver metastasis. In this review, we describe how the hepatic microenvironment adapts to the lipid metabolic alterations in pathologic conditions like nonalcoholic fatty liver disease. We also illustrate how these immunometabolic alterations promote the development of liver cancers and immunotherapy resistance. Finally, we discuss the current therapeutic options and hypothetic combination immunotherapies for the treatment of advanced liver cancers.

Identification of a distinct NK-like hepatic T-cell population activated by NKG2C in a TCR-independent manner

BACKGROUND & AIMS

The liver provides a unique niche of lymphocytes enriched with a large proportion of innate-like T cells. However, the heterogeneity and functional characteristics of the hepatic T-cell population remain to be fully elucidated.

METHODS

We obtained liver sinusoidal mononuclear cells from the liver perfusate of healthy donors and recipients with HBV-associated chronic liver disease (CLD) during liver transplantation. We performed a CITE-seq analysis of liver sinusoidal CD45⁺ cells in combination with T cell receptor (TCR)-seq and flow cytometry to examine the phenotypes and functions of liver sinusoidal CD8⁺ T cells.

RESULTS

We identified a distinct CD56^hiCD161^-CD8⁺ T-cell population characterized by natural killer (NK)-related gene expression and a uniquely restricted TCR repertoire. The frequency of these cells among the liver sinusoidal CD8⁺ T-cell population was significantly increased in patients with HBV-associated CLD. Although CD56^hiCD161^-CD8⁺ T cells exhibit weak responsiveness to TCR stimulation, CD56^hiCD161^-CD8⁺ T cells highly expressed various NK receptors, including CD94, killer immunoglobulin-like receptors, and NKG2C, and exerted NKG2C-mediated NK-like effector functions even in the absence of TCR stimulation. In addition, CD56^hiCD161^-CD8⁺ T cells highly respond to innate cytokines, such as IL-12/18 and IL-15, in the absence of TCR stimulation. We validated the results from liver sinusoidal CD8⁺ T cells using intrahepatic CD8⁺ T cells obtained from liver tissues.

CONCLUSIONS

In summary, the current study found a distinct CD56^hiCD161^-CD8⁺ T-cell population characterized by NK-like activation via TCR-independent NKG2C ligation. Further studies are required to elucidate the roles of liver sinusoidal CD56^hiCD161^-CD8⁺ T cells in immune responses to microbial pathogens or liver immunopathology.

LAY SUMMARY

The role of different immune cell populations in the liver is becoming an area of increasing interest. Herein, we identified a distinct T-cell population that had features similar to those of natural killer (NK) cells - a type of innate immune cell. This distinct population was expanded in the livers of patients with chronic liver disease and could thus have pathogenic relevance.

The Prognostic Value of Natural Killer Cells and Their Receptors/Ligands in Hepatocellular Carcinoma: A Systematic Review and Meta-Analysis

Background

Natural killer (NK) cells play major roles in eliminating tumor cells. Preliminary studies have shown that NK cells and their receptors/ligands have prognostic value in malignant tumors. However, the relevance of NK cells and their receptors/ligands level to the prognosis of hepatocellular carcinoma (HCC) remains unclear.

Methods

Several electronic databases were searched from database inception to November 8, 2021. Random effects were introduced to this meta-analysis. The relevance of NK cells and their receptors/ligands level to the prognosis of HCC was evaluated using hazard ratios (HRs) with 95% confidence interval (95%CI).

Results

26 studies were included in the analysis. The pooled results showed that high NK cells levels were associated with better overall survival (HR=0.70, 95%CI 0.57–0.86, P=0.001) and disease-free survival (HR=0.61, 95%CI 0.40-0.93, P=0.022) of HCC patients. In subgroup analysis for overall survival, CD57⁺ NK cells (HR=0.70, 95%CI 0.55-0.89, P=0.004) had better prognostic value over CD56⁺ NK cells (HR=0.69, 95%CI 0.38-1.25, P=0.224), and intratumor NK cells had better prognostic value (HR=0.71, 95%CI 0.55-0.90, P=0.005) over peripheral NK cells (HR=0.66, 95%CI 0.41-1.06, P=0.088). In addition, high level of NK cell inhibitory receptors predicted increased recurrence of HCC, while the prognostic role of NK cell activating receptors remained unclear.

Conclusion

NK cells and their inhibitory receptors have prognostic value for HCC. The prognostic role of NK cell activating receptors is unclear and more high-quality prospective studies are essential to evaluate the prognostic value of NK cells and their receptors/ligands for HCC.

Human NK cells: From development to effector functions

NK cells are the major lymphocyte subset of the innate immune system that mediates antiviral and anti-tumor responses. It is well established that they develop mechanisms to distinguish self from non-self during the process of NK cell education. Unlike T and B cells, natural killer cells lack clonotypic receptors and are activated after recognizing their target via germline-encoded receptors through natural cytotoxicity, cytokine stimulation, and Ab-dependent cellular cytotoxicity. Subsequently, they utilize cytotoxic granules, death receptor ligands, and cytokines to perform their effector functions. In this review, we provide a general overview of human NK cells, as opposed to murine NK cells, discussing their ontogeny, maturation, receptor diversity, types of responses, and effector functions. Furthermore, we also describe recent advances in human NK cell biology, including tissue-resident NK cell populations, NK cell memory, and novel approaches used to target NK cells in cancer immunotherapy.

Natural Killer cells and monoclonal antibodies: Two partners for successful antibody dependent cytotoxicity against tumor cells

Monoclonal antibodies targeting tumors are one of the most important discoveries in the field of cancer. Although several effective antibodies have been developed, a relapse may occur. One of their mechanisms of action is Antibody Dependent Cell Cytotoxicity (ADCC), by engaging the Fc γ receptor CD16 expressing Natural Killer cells, innate lymphoid cells involved in cancer immunosurveillance and able to kill tumor cells. A lack of NK cells observed in many cancers may therefore be a cause of the low efficacy of antibodies observed in some clinical situations. Here we review clear evidences of the essential partnership between NK cells and antibodies showed in vitro, in vivo, and in clinical trials in different indications, describe the hurdles and ways to enhance ADCC and the evolution of monoclonal antibody therapy. NK cell adoptive immunotherapy combined with monoclonal antibodies may overcome the resistance to the treatment and enhance their efficacy.

Human liver-derived CXCR6+ NK cells are predominantly educated through NKG2A and show reduced cytokine production

NK cells have been implicated to affect the outcome of numerous liver diseases. In particular, members of the killer-cell Ig-like receptor (KIR) family, predominantly expressed by NK cells, have been associated with the outcome of hepatitis C virus infection and clearance of hepatocellular carcinoma. Inhibitory KIRs tune NK cell function through interaction with HLA class I, a process termed education. Nevertheless, the impact of the hepatic environment on NK cell education is incompletely understood. Therefore, we investigated the composition and function of hepatic KIR-expressing NK cells. Matched PBMC and hepatic lymphocytes were isolated from 20 individuals undergoing liver surgery and subsequently phenotypically analyzed for expression of KIRs and markers for tissue residency using flow cytometry. NK cell function was determined by co-culturing NK cells with the target cell line 721.221 and subsequent assessment of CD107a, IFN-γ, and TNF-α expression. Liver-resident CXCR6⁺ /CD56^Bright NK cells lacked KIRs and were predominantly educated through NKG2A, while CXCR6^- /CD16⁺ NK cells expressed KIRs and resembled peripheral blood NK cells. Hepatic NK cells showed lower response rates compared to peripheral blood NK cells; in particular, CXCR6⁺ NK cells were hyporesponsive to stimulation with target cells. The high proportion of educated NK cells in both subsets indicates the importance of self-inhibitory receptors for the balance between maintenance of self-tolerance and functional readiness. However, the reduced functionality of hepatic NK cells may reflect the impact of the tolerogenic hepatic environment on NK cells irrespective of NK cell education.