Liver grafts contain a unique subset of natural killer cells that are transferred into the recipient after liver transplantation

Qizhu anticancer prescription enhances immunosurveillance of liver cancer cells by regulating p21-dependent secretory phenotypes

ETHNOPHARMACOLOGICAL RELEVANCE

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide, largely due to the limitations of available therapeutic strategies. The traditional Chinese medicine Qizhu Anticancer Prescription (QZACP) can improve the quality of life and prolong the survival time of patients with HCC. However, the precise mechanisms underlying the anti-cancer properties of QZACP remain unclear.

PURPOSE

This study examined the anti-hepatocarcinogenic properties of QZACP, with a specific focus on its influence on the p21-activated secretory phenotype (PASP)-mediated immune surveillance, to elucidate the underlying molecular pathways involved in HCC.

MATERIALS AND METHODS

Cell proliferation was measured using the Cell Counting Kit-8, 5-ethynyl-2'-deoxyuridine, and clonogenic assays. The cell cycle was evaluated using flow cytometry, and senescence was identified by staining with senescence-associated beta-galactosidase (SA-β-gal). A primary liver cancer model produced by diethylnitrosamine was established in C57 BL/6 mice to assess the tumor-inhibitory effect of QZACP. The liver's pathological characteristics were examined using hematoxylin and eosin staining. PASP screening was performed using GeneCards, DisGeNet, Online Mendelian Inheritance in Man, and The Cancer Genome Atlas databases. Western blot analysis, enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining, and Transwell migration assays were performed.

RESULTS

Serum containing QZACP enhanced p21 expression, triggered cell cycle arrest, accelerated cell senescence, and suppressed cell proliferation in Huh7 and MHCC-97H liver cancer cells. QZACP reduced the quantity and dimensions of liver tumor nodules and enhanced p21 protein expression, SA-β-Gal staining in tumor lesions, and cytotoxic CD8+ T cell infiltration. Bioinformatic analyses indicated that PASP factors, including hepatocyte growth factor, decorin (DCN), dermatopontin, C-X-C motif chemokine ligand 14 (CXCL14), and Wnt family member 2 (WNT2), play an important role in the development of HCC. In addition, these factors are associated with the presence of natural killer cells and CD8+ T cells within tumors. Western blotting and ELISA confirmed that QZACP increased DCN, CXCL14, and WNT2 levels in tumor tissues and peripheral blood.

CONCLUSIONS

QZACP's suppression of HCC progression may involve cell senescence mediated via p21 upregulation, DCN, CXCL14, and WNT2 secretion, and reversal of the immunosuppressive microenvironment. This study provides insights that can be used in the development of new treatment strategies for HCC.

Dynamic immune recovery process after liver transplantation revealed by single-cell multi-omics analysis

Elucidating the temporal process of immune remodeling under immunosuppressive treatment after liver transplantation (LT) is critical for precise clinical management strategies. Here, we performed a single-cell multi-omics analysis of peripheral blood mononuclear cells (PBMCs) collected from LT patients (with and without acute cellular rejection [ACR]) at 13 time points. Validation was performed in two independent cohorts with additional LT patients and healthy controls. Our study revealed a four-phase recovery process after LT and delineated changes in immune cell composition, expression programs, and interactions along this process. The intensity of the immune response differs between the ACR and non-ACR patients. Notably, the newly identified inflamed NK cells, CD14+RNASE2+ monocytes, and FOS-expressing monocytes emerged as predictive indicators of ACR. This study illuminates the longitudinal evolution of the immune cell landscape under tacrolimus-based immunosuppressive treatment during LT recovery, providing a four-phase framework that aids the clinical management of LT patients.

Dynamic immune cell profiling identified natural killer cell shift as the key event in early allograft dysfunction after liver transplantation

Early allograft dysfunction (EAD) is a life-threatening and fast-developing complication after liver transplantation. The underlying mechanism needs to be better understood, and there has yet to be an efficient therapeutic target. This study retrospectively reviewed 109 patients undergoing liver transplantation, with dynamic profiling of CD3/4/8/16/19/45/56 on the peripheral immune cells (before transplant and 2-4 days after). Altogether, 35 out of the 109 patients developed EAD after liver transplantation. We observed a significant decrease in the natural killer cell proportion (NK cell shift, p = 0.008). The NK cell shift was linearly correlated with cold ischemic time (p = 0.016) and was potentially related to the recipients' outcomes. In mouse models, ischemic/reperfusion (I/R) treatments induced the recruitment of NK cells from peripheral blood into liver tissues. NK cell depletion blocked a series of immune cascades (including CD8+ CD127+ T cells) and inhibited hepatocyte injury effectively in I/R and liver transplantation models. We further found that I/R treatment increased hepatic expression of the ligands for natural killer group 2 member D (NKG2D), a primary activating cell surface receptor in NK cells. Blockade of NKG2D showed a similar protective effect against I/R injury, indicating its role in NK cell activation and the subsequent immunological injury. Our findings built a bridge for the translation from innate immune response to EAD at the bedside. Peripheral NK cell shift is associated with the incidence of EAD after liver transplantation. NKG2D-mediated NK cell activation is a potential therapeutic target.

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

Role of the immune system in liver transplantation and its implications for therapeutic interventions

Liver transplantation (LT) stands as the gold standard for treating end-stage liver disease and hepatocellular carcinoma, yet postoperative complications continue to impact survival rates. The liver's unique immune system, governed by a microenvironment of diverse immune cells, is disrupted during processes like ischemia-reperfusion injury posttransplantation, leading to immune imbalance, inflammation, and subsequent complications. In the posttransplantation period, immune cells within the liver collaboratively foster a tolerant environment, crucial for immune tolerance and liver regeneration. While clinical trials exploring cell therapy for LT complications exist, a comprehensive summary is lacking. This review provides an insight into the intricacies of the liver's immune microenvironment, with a specific focus on macrophages and T cells as primary immune players. Delving into the immunological dynamics at different stages of LT, we explore the disruptions after LT and subsequent immune responses. Focusing on immune cell targeting for treating liver transplant complications, we provide a comprehensive summary of ongoing clinical trials in this domain, especially cell therapies. Furthermore, we offer innovative treatment strategies that leverage the opportunities and prospects identified in the therapeutic landscape. This review seeks to advance our understanding of LT immunology and steer the development of precise therapies for postoperative complications.

Cytotoxic NK cells phenotype and activated lymphocytes are the main characteristics of patients with alcohol-associated liver disease

T cells, natural killer (NK) and NKT cells have opposing actions in the development of alcohol-associated liver fibrosis. We aimed to evaluate the phenotype of NK cells, NKT cells and activated T cells in patients with alcohol use disorder (AUD) according to the presence of advanced liver fibrosis (ALF). Totally, 79 patients (51-years, 71% males) were admitted to treatment of AUD. ALF was defined as FIB4-score > 2.67. Immunophenotyping of NK cells (CD3-CD56+CD16+, CD3-CD56+CD16-, CD3-CD56-CD16+), NKT-like (CD3+CD56+), and the activation status of CD4+, CD8+ and regulatory T cells (Tregs) were evaluated according to the HLA-DR expression. Patients had an AUD duration of 18 ± 11 years with a daily alcohol consumption of 155 ± 77 gr/day prior to hospital admission. The values of absolute cells were 2 ± 0.9 cells/L for total lymphocytes, 1054 ± 501 cells/µL for CD4+, 540 ± 335 cells/µL for CD8+, 49.3 ± 24.8 cells/µL for Tregs, 150.3 ± 97.5 cells/µL for NK cells and 69.8 ± 78.3 cells/µL for NKT-like. The percentage of total NK cells (11.3 ± 5.5% vs. 7 ± 4.3%, p < 0.01), CD3-CD56+CD16+ regarding total lymphocytes (9.7 ± 5.1% vs. 5.8 ± 3.9%, p < 0.01), activated CD4+ cells (5.2 ± 3.2% vs. 3.9 ± 3%, p = 0.04) and activated CD8+ cells (15.7 ± 9.1% vs. 12.2 ± 9%, p = 0.05) were significantly higher in patients with ALF. The percentage of CD3-CD56+CD16- regarding NK cells (5.1 ± 3.4% vs. 7.6 ± 6.2%, p = 0.03) was significantly lower in patients with ALF. Activated Tregs (39.9 ± 11.5 vs. 32.4 ± 9.2, p = 0.06) showed a tendency to be higher in patients with ALF. The proportion of activated CD4+ cells (r = 0.40, p < 0.01) and activated CD8+ cells (r = 0.51, p < 0.01) was correlated with the proportion of NKT-like in patients without ALF. Patients with ALF presented an increased NK cytotoxic phenotype and activated T cells concomitant with a decreased NK cytokine-secreting phenotype.

Protective and pathogenic functions of innate lymphoid cells in transplantation

Innate lymphoid cells (ILCs) are a family of lymphocytes with essential roles in tissue homeostasis and immunity. Along with other tissue-resident immune populations, distinct subsets of ILCs have important roles in either promoting or inhibiting immune tolerance in a variety of contexts, including cancer and autoimmunity. In solid organ and hematopoietic stem cell transplantation, both donor and recipient-derived ILCs could contribute to immune tolerance or rejection, yet understanding of protective or pathogenic functions are only beginning to emerge. In addition to roles in directing or regulating immune responses, ILCs interface with parenchymal cells to support tissue homeostasis and even regeneration. Whether specific ILCs are tissue-protective or enhance ischemia reperfusion injury or fibrosis is of particular interest to the field of transplantation, beyond any roles in limiting or promoting allograft rejection or graft-versus host disease. Within this review, we discuss the current understanding of ILCs functions in promoting immune tolerance and tissue repair at homeostasis and in the context of transplantation and highlight where targeting or harnessing ILCs could have applications in novel transplant therapies.

The co-inhibitory receptor TIGIT regulates NK cell function and is upregulated in human intrahepatic CD56bright NK cells

The crosstalk between NK cells and their surrounding environment is enabled through activating and inhibitory receptors, which tightly control NK cell activity. The co-inhibitory receptor TIGIT decreases NK cell cytotoxicity and is involved in NK cell exhaustion, but has also been associated with liver regeneration, highlighting that the contribution of human intrahepatic CD56bright NK cells in regulating tissue homeostasis remains incompletely understood. A targeted single-cell mRNA analysis revealed distinct transcriptional differences between matched human peripheral blood and intrahepatic CD56bright NK cells. Multiparameter flow cytometry identified a cluster of intrahepatic NK cells with overlapping high expression of CD56, CD69, CXCR6, TIGIT and CD96. Intrahepatic CD56bright NK cells also expressed significantly higher protein surface levels of TIGIT, and significantly lower levels of DNAM-1 compared to matched peripheral blood CD56bright NK cells. TIGIT+ CD56bright NK cells showed diminished degranulation and TNF-α production following stimulation. Co-incubation of peripheral blood CD56bright NK cells with human hepatoma cells or primary human hepatocyte organoids resulted in migration of NK cells into hepatocyte organoids and upregulation of TIGIT and downregulation of DNAM-1 expression, in line with the phenotype of intrahepatic CD56bright NK cells. Intrahepatic CD56bright NK cells represent a transcriptionally, phenotypically, and functionally distinct population of NK cells that expresses higher levels of TIGIT and lower levels of DNAM-1 than matched peripheral blood CD56bright NK cells. Increased expression of inhibitory receptors by NK cells within the liver environment can contribute to tissue homeostasis and reduction of liver inflammation.

Immunotolerance in liver transplantation: a primer for the clinician

The use of immunosuppressive medications for solid organ transplantation is associated with cardiovascular, metabolic, and oncologic complications. On the other hand, the development of graft rejection is associated with increased mortality and graft dysfunction. Liver transplant recipients can withdraw from immunosuppression without developing graft injury while preserving an adequate antimicrobial response - a characteristic known as immunotolerance. Immunotolerance can be spontaneously or pharmacologically achieved. Contrary to the classic dogma, clinical studies have elucidated low rates of true spontaneous immunotolerance (no serologic or histological markers of immune injury) among liver transplant recipients. However, clinical, serologic, and tissue biomarkers can aid in selecting patients in whom immunosuppression can be safely withdrawn. For those who failed an immunosuppression withdrawal trial or are at high risk of rejection, pharmacological interventions for immunotolerance induction are under development. In this review, we provide an overview of the mechanisms of immunotolerance, the clinical studies investigating predictors and biomarkers of spontaneous immunotolerance, as well as the potential pharmacological interventions for inducing it.

The Functional Diversity of Tissue-Resident Natural Killer Cells Against Infection

For decades, studies of natural killer (NK) cells have focused on those found in peripheral blood (PBNK cells) as the prototype for NK cell biology. Only recently have researchers begun to explore the diversity of tissue-resident NK (tr-NK) cells. While tr-NK cells were initially identified from mice parabiosis and intravascular staining experiments, they can also be identified by tissue retention markers such as CD69, CD103, and others. More importantly, tr-NK cells have distinct functions compared to PBNK cells. Within the liver, there are diverse subsets of tr-NK cells expressing different combinations of tissue-retention markers and transcription factors, the clinical relevance of which are still unclear. Functionally, liver tr-NK are primed with immediate responsiveness to infection and equipped with regulatory mechanisms to prevent liver damage. When decidual NK (dNK) cells were first discovered, they were mainly characterized by their reduced cytotoxicity and functions related to placental development. Recent studies, however, revealed different mechanisms by which dNK cells prevent uterine infections. The lungs are one of the most highly exposed sites for infection due to their role in oxygen exchange. Upon influenza infection, lung tr-NK cells can degranulate and produce more inflammatory cytokines than PBNK cells. Less understood are gut tr-NK cells which were recently characterized in infants and adults for their functional differences. In this mini-review, we aim to provide a brief overview of the most recent discoveries on how several tr-NK cells are implicated in the immune response against infection. This article is protected by copyright. All rights reserved.

Targeting NK Cells for HIV-1 Treatment and Reservoir Clearance

Combined antiretroviral therapy (cART) can inhibit the replication of human immunodeficiency virus type 1 (HIV-1) and reduce viral loads in the peripheral blood to undetectable levels. However, the presence of latent HIV-1 reservoirs prevents complete HIV-1 eradication. Several drugs and strategies targeting T cells are now in clinical trials, but their effectiveness in reducing viral reservoirs has been mixed. Interestingly, innate immune natural killer (NK) cells, which are promising targets for cancer therapy, also play an important role in HIV-1 infection. NK cells are a unique innate cell population with features of adaptive immunity that can regulate adaptive and innate immune cell populations; therefore, they can be exploited for HIV-1 immunotherapy and reservoir eradication. In this review, we highlight immunotherapy strategies for HIV infection that utilize the beneficial properties of NK cells.

Donor NK and T Cells in the Periphery of Lung Transplant Recipients Contain High Frequencies of Killer Cell Immunoglobulin-Like Receptor-Positive Subsets

Introduction

For end-stage lung diseases, double lung transplantation (DLTx) is the ultimate curative treatment option. However, acute and chronic rejection and chronic dysfunction are major limitations in thoracic transplantation medicine. Thus, a better understanding of the contribution of immune responses early after DLTx is urgently needed. Passenger cells, derived from donor lungs and migrating into the recipient periphery, are comprised primarily by NK and T cells. Here, we aimed at characterizing the expression of killer cell immunoglobulin-like receptors (KIR) on donor and recipient NK and T cells in recipient blood after DLTx. Furthermore, we investigated the functional status and capacity of donor vs. recipient NK cells.

Methods

Peripheral blood samples of 51 DLTx recipients were analyzed pre Tx and at T0, T24 and 3wk post Tx for the presence of HLA-mismatched donor NK and T cells, their KIR repertoire as well as activation status using flow cytometry.

Results

Within the first 3 weeks after DLTx, donor NK and T cells were detected in all patients with a peak at T0. An increase of the KIR2DL/S1-positive subset was found within the donor NK cell repertoire. Moreover, donor NK cells showed significantly higher frequencies of KIR2DL/S1-positive cells (p<0.01) 3wk post DLTx compared to recipient NK cells. This effect was also observed in donor KIR⁺ T cells 3wk after DLTx with higher proportions of KIR2DL/S1 (p<0.05) and KIR3DL/S1 (p<0.01) positive T cells. Higher activation levels of donor NK and T cells (p<0.001) were detected compared to recipient cells via CD25 expression as well as a higher degranulation capacity upon activation by K562 target cells.

Conclusion

Higher frequencies of donor NK and T cells expressing KIR compared to recipient NK and T cells argue for their origin in the lung as a part of a highly specialized immunocompetent compartment. Despite KIR expression, higher activation levels of donor NK and T cells in the periphery of recipients suggest their pre-activation during the ex situ phase. Taken together, donor NK and T cells are likely to have a regulatory effect in the balance between tolerance and rejection and, hence, graft survival after DLTx.

Natural killer cells in liver transplantation: Can we harness the power of the immune checkpoint to promote tolerance?

The roles that natural killer (NK) cells play in liver disease and transplantation remain ill‐defined. Reports on the matter are often contradictory, and the mechanisms elucidated are complex and dependent on the context of the model tested. Moreover, NK cell attributes, such as receptor protein expression and function differ among species, make study of primate or rodent transplant models challenging. Recent insights into NK function and NK‐mediated therapy in the context of cancer therapy may prove applicable to transplantation. Of specific interest are immune checkpoint molecules and the mechanisms by which they modulate NK cells in the tumor micro‐environment. In this review, we summarize NK cell populations in the peripheral blood and liver, and we explore the data regarding the expression and function of immune checkpoint molecules on NK cells. We also hypothesize about the roles they could play in liver transplantation and discuss how they might be harnessed therapeutically in transplant sciences.

The role of natural killer cells in liver inflammation

The liver is an important immunological site that can promote immune tolerance or activation. Natural killer (NK) cells are a major immune subset within the liver, and therefore understanding their role in liver homeostasis and inflammation is crucial. Due to their cytotoxic function, NK cells are important in the immune response against hepatotropic viral infections but are also involved in the inflammatory processes of autoimmune liver diseases and fatty liver disease. Whether NK cells primarily promote pro-inflammatory or tolerogenic responses is not known for many liver diseases. Understanding the involvement of NK cells in liver inflammation will be crucial in effective treatment and future immunotherapeutic targeting of NK cells in these disease settings. Here, we explore the role that NK cells play in inflammation of the liver in the context of viral infection, autoimmunity and fatty liver disease.

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

High Intrapatient Variability in Tacrolimus Exposure Is Not Associated With Immune-mediated Graft Injury After Liver Transplantation

BACKGROUND

A high intrapatient variability (IPV) in tacrolimus exposure is associated with impaired long-term clinical outcome after kidney transplantation. It remains to be determined if this is equally detrimental for liver transplant recipients. The objective of this study was to investigate the association between IPV in tacrolimus exposure and immune-mediated graft injury after liver transplantation.

METHODS

For 326 liver transplant recipients, transplanted between 2000 and 2015, tacrolimus IPV was calculated from at least 5 tacrolimus trough samples obtained between months 6 and 18 after liver transplantation and expressed as the coefficient of variation. Primary composite endpoint consisted of immune-mediated graft injury (chronic rejection, biopsy proven, and suspected late acute rejection) after month 6. Secondary outcomes were the association between tacrolimus IPV on (1) loss of renal function per year of follow-up and (2) cytomegalovirus viremia after month 6.

RESULTS

Of the 326 included liver transplant recipients, 70 patients (21.5%) reached the primary endpoint. Median tacrolimus coefficient of variation was 28%. There was no significant difference in reaching the primary composite endpoint between the low- and high-IPV groups (P = 0.068). Model for End-Stage Liver Disease score pretransplantation and the number of acute rejections were identified as independent predictors for immune-mediated graft injury (P = 0.049 and 0.016). A higher IPV in combination with a low kidney function at baseline (estimated glomerular filtration rate < 40 mL/min) was associated with greater loss of renal function per year of follow-up (P = 0.007). Tacrolimus variability was not associated with late cytomegalovirus viremia.

CONCLUSIONS

High IPV in tacrolimus exposure beyond month 6 postliver transplantation was not associated with immune-mediated graft injury.

The Role of Diverse Liver Cells in Liver Transplantation Tolerance

Liver transplantation is the ideal treatment approach for a variety of end-stage liver diseases. However, life-long, systemic immunosuppressive treatment after transplantation is required to prevent rejection and graft loss, which is associated with severe side effects, although liver allograft is considered more tolerogenic. Therefore, understanding the mechanism underlying the unique immunologically privileged liver organ is valuable for transplantation management and autoimmune disease treatment. The unique hepatic acinus anatomy and a complex cellular network constitute the immunosuppressive hepatic microenvironment, which are responsible for the tolerogenic properties of the liver. The hepatic microenvironment contains a variety of hepatic-resident immobile non-professional antigen-presenting cells, including hepatocytes, liver sinusoidal endothelial cells, Kupffer cells, and hepatic stellate cells, that are insufficient to optimally prime T cells locally and lead to the removal of alloreactive T cells due to the low expression of major histocompatibility complex (MHC) molecules, costimulatory molecules and proinflammatory cytokines but a rather high expression of coinhibitory molecules and anti-inflammatory cytokines. Hepatic dendritic cells (DCs) are generally immature and less immunogenic than splenic DCs and are also ineffective in priming naïve allogeneic T cells via the direct recognition pathway in recipient secondary lymphoid organs. Although natural killer cells and natural killer T cells are reportedly associated with liver tolerance, their roles in liver transplantation are multifaceted and need to be further clarified. Under these circumstances, T cells are prone to clonal deletion, clonal anergy and exhaustion, eventually leading to tolerance. Other proposed liver tolerance mechanisms, such as soluble donor MHC class I molecules, passenger leukocytes theory and a high-load antigen effect, have also been addressed. We herein comprehensively review the current evidence implicating the tolerogenic properties of diverse liver cells in liver transplantation tolerance.

Transplant Tolerance Induction: Insights From the Liver

A comparison of pre-clinical transplant models and of solid organs transplanted in routine clinical practice demonstrates that the liver is most amenable to the development of immunological tolerance. This phenomenon arises in the absence of stringent conditioning regimens that accompany published tolerizing protocols for other organs, particularly the kidney. The unique immunologic properties of the liver have assisted our understanding of the alloimmune response and how it can be manipulated to improve graft function and survival. This review will address important findings following liver transplantation in both animals and humans, and how these have driven the understanding and development of therapeutic immunosuppressive options. We will discuss the liver's unique system of immune and non-immune cells that regulate immunity, yet maintain effective responses to pathogens, as well as mechanisms of liver transplant tolerance in pre-clinical models and humans, including current immunosuppressive drug withdrawal trials and biomarkers of tolerance. In addition, we will address innovative therapeutic strategies, including mesenchymal stem cell, regulatory T cell, and regulatory dendritic cell therapy to promote liver allograft tolerance or minimization of immunosuppression in the clinic.

On the Way to Become a Natural Killer Cell

Natural Killer (NK) cells are innate lymphocytes playing pivotal roles in host defense and immune-surveillance. The homeostatic modulation of germ-line encoded/non-rearranged activating and inhibitory NK cell receptors (NKRs) determines the capability of these innate lymphocytes to either spare "self" cells or to kill viral-infected, tumor-transformed and heterologous cell targets. However, despite being discovered more than 40 years ago, several aspects of NK cell biology remain unknown or are still being debated. In particular, our knowledge of human NK cell ontogenesis and differentiation is still in its infancy as the majority of our experimental evidence on this topic mainly comes from findings obtained in vitro or with animal models in vivo. Although both the generation and the maintenance of human NK cells are sustained by hematopoietic stem cells (HSCs), the precise site(s) of NK cell development are still poorly defined. Indeed, HSCs and hematopoietic precursors are localized in different anatomical compartments that also change their ontogenic commitments before and after birth as well as in aging. Currently, the main site of NK cell generation and maturation in adulthood is considered the bone marrow, where their interactions with stromal cells, cytokines, growth factors, and other soluble molecules support and drive maturation. Different sequential stages of NK cell development have been identified on the basis of the differential expression of specific markers and NKRs as well as on the acquisition of specific effector-functions. All these phenotypic and functional features are key in inducing and regulating homing, activation and tissue-residency of NK cells in different human anatomic sites, where different homeostatic mechanisms ensure a perfect balance between immune tolerance and immune-surveillance. The present review summarizes our current knowledge on human NK cell ontogenesis and on the related pathways orchestrating a proper maturation, functions, and distributions.

NK cells switch from granzyme B to death receptor-mediated cytotoxicity during serial killing

Natural killer cells can kill infected and transformed cells via two different cell death mechanisms. Prager et al. show that NK cells quickly kill their first targets by releasing cytotoxic granules and only use the slower death receptor–mediated cytotoxicity for their final kill.

NK cells eliminate virus-infected and tumor cells by releasing cytotoxic granules containing granzyme B (GrzB) or by engaging death receptors that initiate caspase cascades. The orchestrated interplay between both cell death pathways remains poorly defined. Here we simultaneously measure the activities of GrzB and caspase-8 in tumor cells upon contact with human NK cells. We observed that NK cells switch from inducing a fast GrzB-mediated cell death in their first killing events to a slow death receptor–mediated killing during subsequent tumor cell encounters. Target cell contact reduced intracellular GrzB and perforin and increased surface-CD95L in NK cells over time, showing how the switch in cytotoxicity pathways is controlled. Without perforin, NK cells were unable to perform GrzB-mediated serial killing and only killed once via death receptors. In contrast, the absence of CD95 on tumor targets did not impair GrzB-mediated serial killing. This demonstrates that GrzB and death receptor–mediated cytotoxicity are differentially regulated during NK cell serial killing.

Daclizumab Therapy for Multiple Sclerosis

Daclizumab is a humanized monoclonal antibody that prevents formation of high-affinity interleukin (IL)-2 receptor (IL-2R). Because activated T cells up-regulate high-affinity IL-2R and IL-2 is used to grow activated T cells in vitro, daclizumab was envisioned to selectively inhibit activated T cells. However, the mechanism of action (MOA) of daclizumab is surprisingly broad and it includes many unanticipated effects on innate immunity. Specifically, daclizumab modulates the development of innate lymphoid cells, leading to expansion of immunoregulatory CD56^bright natural killer (NK) cells. Activated CD56^bright NK cells migrate to the intrathecal compartment in multiple sclerosis (MS) and regulate autoreactive T cells via cytotoxicity. Finally, daclizumab also restricts initial steps of T-cell activation by blocking trans-presentation of IL-2 by dendritic cells to antigen-specific T cells. In conclusion, daclizumab has complex immunomodulatory effects with resultant inhibition of central nervous system inflammation in MS.

Cytotoxicity of Human Hepatic Intrasinusoidal CD56bright Natural Killer Cells against Hepatocellular Carcinoma Cells

Hepatic intrasinusoidal (HI) natural killer (NK) cells from liver perfusate have unique features that are similar to those of liver-resident NK cells. Previously, we have reported that HI CD56^bright NK cells effectively degranulate against SNU398 hepatocellular carcinoma (HCC) cells. Thus, the aim of this study was to further investigate the phenotype and function of HI NK cells. We found that HI CD56^bright NK cells degranulated much less to Huh7 cells. HI CD56^bright NK cells expressed NKG2D, NKp46, TNF-related apoptosis-inducing ligand (TRAIL), and FAS ligand (FASL) at higher levels than CD56^dim cells. SNU398 cells expressed more NKG2D ligands and FAS and less PD-L1 than Huh7 cells. Blockade of NKG2D, TRAIL, and FASL significantly reduced the cytotoxicity of HI NK cells against SNU398 cells, but blockade of PD-L1 did not lead to any significant change. However, HI NK cells produced IFN-γ well in response to Huh7 cells. In conclusion, the cytotoxicity of HI CD56^bright NK cells was attributed to the expression of NKG2D, TRAIL, and FASL. The results suggest the possible use of HI NK cells for cancer immunotherapy and prescreening of HCC cells to help identify the most effective NK cell therapy recipients.

Characterization of Antigen-Presenting Cell Subsets in Human Liver-Draining Lymph Nodes

T-cell immunity in the liver is tightly regulated to prevent chronic liver inflammation in response to antigens and toxins derived from food and intestinal bacterial flora. Since the main sites of T cell activation in response to foreign components entering solid tissues are the draining lymph nodes (LN), we aimed to study whether Antigen-Presenting Cell (APC) subsets in human liver lymph-draining LN show features that may contribute to the immunologically tolerant liver environment. Healthy liver LN, iliac LN, spleen and liver perfusates were obtained from multi-organ donors, while diseased liver LN were collected from explanted patient livers. Inguinal LN were obtained from kidney transplant recipients. Mononuclear cells were isolated from fresh tissues, and immunophenotypic and functional characteristics of APC subsets were studied using flowcytometry and in ex vivo cultures. Healthy liver-draining LN contained significantly lower relative numbers of CD1c⁺ conventional dendritic cells (cDC2), plasmacytoid DC (PDC), and CD14⁺CD163⁺DC-SIGN⁺ macrophages (MF) compared to inguinal LN. Compared to spleen, both types of LN contained low relative numbers of CD141^hi cDC1. Both cDC subsets in liver LN showed a more activated/mature immunophenotype than those in inguinal LN, iliacal LN, spleen and liver tissue. Despite their more mature status, cDC2 isolated from hepatic LN displayed similar cytokine production capacity (IL-10, IL-12, and IL-6) and allogeneic T cell stimulatory capacity as their counterparts from spleen. Liver LN from patients with inflammatory liver diseases showed a further reduction of cDC1, but had increased relative numbers of PDC and MF. In steady state conditions human liver LN contain relatively low numbers of cDC2, PDC, and macrophages, and relative numbers of cDC1 in liver LN decline during liver inflammation. The paucity of cDC in liver LN may contribute to immune tolerance in the liver environment.

Innate Immune Cells in Immune Tolerance After Liver Transplantation

Currently, liver transplantation is the most effective treatment for end-stage liver disease. Immunosuppressive agents are required to be taken after the operations, which have significantly reduced rejection rates and improved the short-term (<1 year) survival rates. However, post-transplant complications related to the immunosuppressive therapy have led to the development of new protocols aimed at protecting renal function and preventing de novo cancer and dysmetabolic syndrome. Donor specific immune tolerance, which means the mature immune systems of recipients will not attack the grafts under the conditions without any immunosuppression therapies, is considered the optimal state after liver transplantation. There have been studies that have shown that some patients can reach this immune tolerance state after liver transplantation. The intrahepatic immune system is quite different from that in other solid organs, especially the innate immune system. It contains a variety of liver specific cells, such as liver-derived dendritic cells, Kupffer cells, liver sinusoidal endothelial cells, liver-derived natural killer (NK) cells, natural killer T (NKT) cells, and so on. Depending on their specific structures and functions, these intrahepatic innate immune cells play important roles in the development of intrahepatic immune tolerance. In this article, in order to have a deeper understanding of the tolerogenic functions of liver, we summarized the molecular mechanisms of immune tolerance induced by intrahepatic innate immune cells after liver transplantation.

Clinical use of an immune monitoring panel in liver transplant recipients: A prospective, observational study

Immunosuppressive therapy greatly contributed to making liver transplantation the standard treatment for end-stage liver diseases. However, it remains difficult to predict and measure the efficacy of pharmacological immunosuppression. Therefore, we used a panel of standardized, commonly available, biomarkers with the aim to describe their changes in the first 3 weeks after the transplant procedure and assess if they may help therapeutic drug monitoring in better tailoring the dose of the immunosuppressive drugs. We prospectively studied 72 consecutive patients from the day of liver transplant (post-operative day #0) until the post-operative day #21. Leukocytes, neutrophils, lymphocytes (CD4+, CD8+), natural killer cells, monocytes, immunoglobulins and tacrolimus serum levels were measured on peripheral blood (at day 0, 3, 7, 14, 21 after surgery). Patients who developed infections showed significantly higher CD64+ monocytes on post operative day #7. IgG levels were lower on post operative day #3 among patients who later developed infections. We also found that a sharp decrease in IgA from post operative day #0 to 3 (-226 mg/dL in the ROC curve analysis) strongly correlates with the onset of infections among HCV- patients. No specific markers of rejection emerged from the tested panel of markers. Our results show that some early changes in peripheral blood white cells and immunoglobulins may predict the onset of infections and may be useful in modulating the immunosuppressive therapy. However, a panel of commonly available, standardized biomarkers do not support in improving therapeutic drug monitoring ability to individualize immunosuppressive drugs dosing.

Treatment of advanced hepatocellular carcinoma: immunotherapy from checkpoint blockade to potential of cellular treatment

The absence of potent therapeutic option accounts for the dismal prognosis of advanced hepatocellular carcinoma (HCC) with high mortality and recurrence rate. For a decade, sorafenib is the only approved systemic drug in the first-line setting and warrants as the standard-of-care for HCC in the advanced stage. Given the common failures of chemotherapies and targeted therapies in the field of HCC treatment, promising breakthroughs were eagerly needed and until recently, immunotherapies have opened a new era of anticancer treatment. The liver organ is perceived as "immunotolerant" owing to its functional role, and the hepatic immune balance is found to be deregulated during chronic liver inflammation and HCC tumorigenesis. Restoring a competent immunity by mitigation of immunosuppression signals is a contemporary approach. In this regard, novel immune checkpoint inhibitors have revolutionized cancer pharmacological treatment options with remarkable clinical outcomes in hematologic malignancy and multiple solid tumors including advanced HCC. Nivolumab, an immunotherapeutic agent to block programmed cell death protein 1 (PD-1), showed high efficacy potential for patients progressed with sorafenib and granted accelerated approval by the US Food and Drug Administration (FDA) recently. The development of this class of immunotherapeutic drug is currently based on myriad studies established on the role of T-cell mediated immunosuppression through immune checkpoints. Heterogeneous results have led to further explorations to the profile of oncogenic processes and signaling pathways associated with PD1/PD-L1 axis. Emerging evidence from preclinical studies implicate natural killer (NK) cells as a mediator to the PD-1 checkpoint signaling immunoevasion. The strategy of adopting immunomodulating ability of NK cells by immune checkpoints inhibitors is potential to additive effects in stimulating anticancer immunity. This idea is not entirely newfound but has recently gained prominence because of advances in defining phenotypic heterogeneity of NK cell populations. The physiological significance and synergistic value of NK cells await further investigation in clinical trials. In this review, an overview of the treatment paradigm shift of HCC management is presented. Current knowledge concerning immunological mechanisms of immune checkpoints attributed to T cell is further discussed and relevant ongoing clinical trials are summarized. We proposed that NK cells should be viewed as part of the network of checkpoint immunoevasion and delineate current evidence of translational clinical research in this area. It is conceivable that immune checkpoint inhibitors in combination with NK cell-based therapeutic strategies will be great promise for treatment of advanced HCC.

NK cells in liver homeostasis and viral hepatitis

As an important member of the innate immune system, natural killer (NK) cells are well known for their rapid and efficient immune responses against infectious agents and tumors. NK cells are widely distributed throughout the body and are particularly enriched within the liver, where they display unique phenotypic and functional properties, playing important roles in various liver diseases. Herein, we present an overview of liver NK cell properties with regard to phenotype, function, and subset composition at steady state, and we also summarize the complex reciprocal interactions between liver NK cells and other cell types within the local environment of the liver. We also provide an overview of recent advances demonstrating the roles of NK cells in viral hepatitis, including a discussion of NK cell altered states and their beneficial versus harmful effects during hepatitis B virus and hepatitis C virus infection.

Hepatic irradiation persistently eliminates liver resident NK cells

Hepatic irradiation for the treatment of hepatobiliary malignancies often indirectly damages liver tissue and promotes the development of liver fibrosis. However, little is known concerning the effects of hepatic irradiation on the liver immune system, including natural killer (NK) cells. The aim of this study was therefore to investigate how hepatic irradiation influences the functions and characteristics of liver resident NK cells. An established murine hepatic irradiation model was used to examine the specific effects of hepatic irradiation on immune cell populations and metastasis. This analysis demonstrated that hepatic irradiation decreased the number of liver resident NK cells (DX5^–TRAIL⁺), but did not affect the total NK number or proportions of NK cells in the liver or spleen. This effect was correlated with the hepatic irradiation dose. Surprisingly, the liver resident NK population had not recovered by two months after hepatic irradiation. We also found that hepatic irradiation limited the cytotoxic effects of liver-derived lymphocytes against a mouse hepatoma cell line and promoted hepatic metastases in an in vivo model, although adoptive transfer of activated NK cells could alleviate metastatic growth. Finally, we demonstrated that hepatic irradiation disrupted the development of liver-resident NK cells, even after the adoptive transfer of precursor cells from the bone marrow, liver, and spleen, suggesting that irradiation had altered the developmental environment of the liver. In summary, our data demonstrated that hepatic irradiation abolished the DX5^–TRAIL⁺ liver-resident NK cell population and dampened antitumor activities in the liver for at least two months. Additionally, hepatic irradiation prevented differentiation of precursor cells into liver-resident NK cells.

Tissue-resident Eomes(hi) T-bet(lo) CD56(bright) NK cells with reduced proinflammatory potential are enriched in the adult human liver

The adult human liver is enriched with natural killer (NK) cells, accounting for 30-50% of hepatic lymphocytes, which include tissue-resident hepatic NK-cell subpopulations, distinct from peripheral blood NK cells. In murine liver, a subset of liver-resident hepatic NK cells have altered expression of the two highly related T-box transcription factors, T-bet and eomesodermin (Eomes). Here, we investigate the heterogeneity of T-bet and Eomes expression in NK cells from healthy adult human liver with a view to identifying human liver-resident populations. Hepatic NK cells were isolated from donor liver perfusates and biopsies obtained during orthotopic liver transplantation (N = 28). Hepatic CD56(bright) NK cells were Eomes(hi) T-bet(lo) , a phenotype virtually absent from peripheral blood. These NK cells express the chemokine receptor CXCR6 (chemokine (C-X-C motif) receptor 6), a marker of tissue residency, which is absent from hepatic CD56(dim) and blood NK cells. Compared to blood populations, these hepatic CD56(bright) NK cells have increased expression of activatory receptors (NKp44, NKp46, and NKG2D). They show reduced ability to produce IFN-γ but enhanced degranulation in response to challenge with target cells. This functionally distinct population of hepatic NK cells constitutes 20-30% of the total hepatic lymphocyte repertoire and represents a tissue-resident immune cell population adapted to the tolerogenic liver microenvironment.

Emerging insights into natural killer cells in human peripheral tissues

Natural killer (NK) cells have long been considered to be a homogenous population of innate lymphocytes with limited phenotypic and functional diversity. However, recent findings have revealed that these cells comprise a large number of distinct populations with diverse characteristics. Some of these characteristics may relate to their developmental origin, and others represent differences in differentiation that are influenced by factors such as tissue localization and imprints by viral infections. In this Review, we provide a comprehensive overview of the emerging knowledge about the development, differentiation and function of human NK cell populations, with a particular focus on NK cells in peripheral tissues.

CD56bright NK IL-7Rα expression negatively associates with HCV level, and IL-7-induced NK function is impaired during HCV and HIV infections

Several lines of evidence support the concept that NK cells play an important role in control of hepatitis C virus (HCV) infection via cytokine secretion and cytotoxicity. IL-7 is a homeostatic cytokine with a role in T cell development, activation, proliferation, and cytokine secretion. The IL-7Rα chain [cluster of differentiation (CD)127] is expressed on NK cells, with greatest abundance on the CD56^brightCD16^dim/- (CD56^bright) subset. Here, we measured CD127 expression on CD56^bright, CD56^dimCD16⁺ (CD56^dim), or CD56^negCD16⁺ (CD56^neg) NK cell subsets of 25 uninfected donors (UD); 34 chronic HCV-infected, treatment-naïve; 25 HIV-infected, virally suppressed on antiretroviral therapy (ART); and 42 HCV-HIV-coinfected subjects on ART. Interestingly, CD127 expression on CD56^bright NK cells negatively correlated with HCV plasma levels in HCV monoinfection and HCV-HIV coinfection. IL-7 induced CD69 expression, as well as IFN-γ production, in CD56^bright NK cells and also enhanced the IFN-α-induced CD69 expression on these cells. The latter was impaired in HIV infection. Furthermore, IL-7 induced B cell lymphoma 2 (BCL-2) expression and cell cycling of CD56^bright NK cells, and this effect was impaired in HCV- and HIV-infected subjects. Whereas IL-7-stimulated CD56^bright NK cell degranulation appeared intact in all cohorts, we observed impaired IL-7-activated NK cell cytolytic function in HCV- and HIV-infected subjects. Finally, IL-7-induced phosphorylation of STAT-5 (pSTAT-5) signaling was impaired in NK cells of subjects with chronic viral infection, and this was reversible upon 6 mo of viral suppression with IFN-free HCV therapy. These results implicate that IL-7-dependent NK cell activation and effector function may be other host immune surveillance mechanisms that are impaired in viral infections.

Graft-Versus-Host Disease Following Liver Transplantation: Development of a High-Incidence Rat Model and a Selective Prevention Method

Graft-versus-host disease (GvHD) following liver transplantation (LT) is a rare but serious complication with no presently available animal model and no preventive measures. To develop a rat model of GvHD after LT (LT-GvHD), we preconditioned hosts with sublethal irradiation plus reduction of natural killer (NK) cells with anti-CD8α mAb treatment, which invariably resulted in acute LT-GvHD. Compared with those in the peripheral counterpart, graft CD4⁺ CD25^- passenger T cells showed lower alloreactivities in mixed leukocyte culture. Immunohistology revealed that donor CD4⁺ T cells migrated and formed clusters with host dendritic cells in secondary lymphoid organs, with early expansion and subsequent accumulation in target organs. For selectively preventing GvHD, donor livers were perfused ex vivo with organ preservation media containing anti-TCRαβ mAb. T cell-depleted livers almost completely suppressed clinical GvHD such that host rats survived for >100 days. Our results showed that passenger T cells could develop typical LT-GvHD if resistant cells such as host radiosensitive cells and host radioresistant NK cells were suppressed. Selective ex vivo T cell depletion prevented LT-GvHD without affecting host immunity or graft function. This method might be applicable to clinical LT in prediagnosed high-risk donor-recipient combinations and for analyzing immunoregulatory mechanisms of the liver.

Changes in T Cells After ABO-Incompatible Liver Transplantation

PURPOSE

T lymphocytes are an essential component of allograft rejection and tolerance. The aims of the present study are to analyze the characteristics of T-cell subsets between ABO-incompatible living donor liver transplantation (ABO-I LDLT) and ABO-compatible LDLT (ABO-C LDLT).

MATERIALS AND METHODS

Between April 2013 and June 2014, 61 patients underwent adult LDLT. ABO-I LDLT patients received rituximab and all patients received basiliximab as induction therapy and tacrolimus as maintenance therapy. The distribution of peripheral blood T lymphocyte subsets pretransplant and 4, 8, 12, and 24 weeks post-transplant were serially monitored.

RESULTS

Eight patients underwent ABO-I LDLT. Patient characteristics did not vary between the ABO-I and ABO-C groups. Absolute lymphocyte counts and CD4+ T cells in the ABO-I group were lower than those in ABO-C group after LDLT (p =.034 and p =.039, respectively). However, the comparison between the ABO-I and ABO-C groups revealed that the CD8+ T cells, CD4/CD8 ratio, Vδ1 cells, Vδ2 cells, γδ T cells, Vδ1/Vδ2 ratio, CD3-CD56+ cells, and CD4+Foxp3+ T cells did not change significantly over time.

CONCLUSIONS

Absolute lymphocyte counts and CD4+ T cell levels are different between ABO-I and ABO-C groups after LDLT. The present study suggests that T-cell lymphocyte changes in peripheral blood in ABO-I LDLT patients were similar to those in ABO-C LDLT patients.

Role of NK, NKT cells and macrophages in liver transplantation

Liver transplantation has become the treatment of choice for acute or chronic liver disease. Because the liver acts as an innate immunity-dominant organ, there are immunological differences between the liver and other organs. The specific features of hepatic natural killer (NK), NKT and Kupffer cells and their role in the mechanism of liver transplant rejection, tolerance and hepatic ischemia-reperfusion injury are discussed in this review.

Liver immunology and its role in inflammation and homeostasis

The human liver is usually perceived as a non-immunological organ engaged primarily in metabolic, nutrient storage and detoxification activities. However, we now know that the healthy liver is also a site of complex immunological activity mediated by a diverse immune cell repertoire as well as non-hematopoietic cell populations. In the non-diseased liver, metabolic and tissue remodeling functions require elements of inflammation. This inflammation, in combination with regular exposure to dietary and microbial products, creates the potential for excessive immune activation. In this complex microenvironment, the hepatic immune system tolerates harmless molecules while at the same time remaining alert to possible infectious agents, malignant cells or tissue damage. Upon appropriate immune activation to challenge by pathogens or tissue damage, mechanisms to resolve inflammation are essential to maintain liver homeostasis. Failure to clear 'dangerous' stimuli or regulate appropriately activated immune mechanisms leads to pathological inflammation and disrupted tissue homeostasis characterized by the progressive development of fibrosis, cirrhosis and eventual liver failure. Hepatic inflammatory mechanisms therefore have a spectrum of roles in the healthy adult liver; they are essential to maintain tissue and organ homeostasis and, when dysregulated, are key drivers of the liver pathology associated with chronic infection, autoimmunity and malignancy. In this review, we explore the changing perception of inflammation and inflammatory mediators in normal liver homeostasis and propose targeting of liver-specific immune regulation pathways as a therapeutic approach to treat liver disease.

Immunological aspects of liver cell transplantation

Within the field of regenerative medicine, the liver is of major interest for adoption of regenerative strategies due to its well-known and unique regenerative capacity. Whereas therapeutic strategies such as liver resection and orthotopic liver transplantation (OLT) can be considered standards of care for the treatment of a variety of liver diseases, the concept of liver cell transplantation (LCTx) still awaits clinical breakthrough. Success of LCTx is hampered by insufficient engraftment/long-term acceptance of cellular allografts mainly due to rejection of transplanted cells. This is in contrast to the results achieved for OLT where long-term graft survival is observed on a regular basis and, hence, the liver has been deemed an immune-privileged organ. Immune responses induced by isolated hepatocytes apparently differ considerably from those observed following transplantation of solid organs and, thus, LCTx requires refined immunological strategies to improve its clinical outcome. In addition, clinical usage of LCTx but also related basic research efforts are hindered by the limited availability of high quality liver cells, strongly emphasizing the need for alternative cell sources. This review focuses on the various immunological aspects of LCTx summarizing data available not only for hepatocyte transplantation but also for transplantation of non-parenchymal liver cells and liver stem cells.

Natural Killer Cells and Liver Transplantation: Orchestrators of Rejection or Tolerance?

Natural killer (NK) cells are highly heterogeneous innate lymphocytes with a diverse repertoire of phenotypes and functions. Their role in organ transplantation has been poorly defined due to conflicting clinical and experimental data. There is evidence that NK cells can contribute to graft rejection and also to tolerance induction. In most solid organ transplantation settings, the role of NK cells is only considered from the perspective of the recipient immune system. In contrast to other organs, the liver contains major resident populations of immune cells, particularly enriched with innate lymphocytes such as NK cells, NKT cells, and gamma-delta T cells. Liver transplantation therefore results in a unique meeting of donor and recipient immune systems. The unusual immune repertoire and tolerogenic environment of the liver may explain why this potentially inflammatory "meeting" often results in attenuated immune responses and reduced requirement for immunosuppression. Recent trials of immunosuppression withdrawal in liver transplant patients have identified NK cell features as possible predictors of tolerance. Here we propose that hepatic NK cells play a key role in the induction of tolerance post-liver transplant and examine potential mechanisms by which these cells influence liver transplant outcome.

Natural Killer Cells and Liver Fibrosis

In the 40 years since the discovery of natural killer (NK) cells, it has been well established that these innate lymphocytes are important for early and effective immune responses against transformed cells and infections with different pathogens. In addition to these classical functions of NK cells, we now know that they are part of a larger family of innate lymphoid cells and that they can even mediate memory-like responses. Additionally, tissue-resident NK cells with distinct phenotypical and functional characteristics have been identified. Here, we focus on the phenotype of different NK cell subpopulations that can be found in the liver and summarize the current knowledge about the functional role of these cells with a special emphasis on liver fibrosis. NK cell cytotoxicity can contribute to liver damage in different forms of liver disease. However, NK cells can limit liver fibrosis by killing hepatic stellate cell-derived myofibroblasts, which play a key role in this pathogenic process. Therefore, liver NK cells need to be tightly regulated in order to balance these beneficial and pathological effects.

Kinetics of B, T, NK lymphocytes and isoagglutinin titers in ABO incompatible living donor liver transplantation using rituximab and basiliximab

BACKGROUND

The kinetics of isoagglutinin titers and lymphocyte subpopulations including B, T, and natural killer (NK) cells after ABO incompatible (ABO-I) living donor liver transplantation (LDLT) have not been evaluated.

METHODS

From January 2012 to July 2013, consecutive ABO-I LDLT patients were enrolled at the National Cancer Center. Our desensitizing protocol included rituximab, plasma exchanges, basiliximab, and intravenous immune globulin without splenectomy.

RESULTS

Twenty patients (14 males, 6 females) underwent ABO-I LDLT due to HCC (n=15) or liver cirrhosis (n=5). There was no hyperacute and antibody-mediated rejection. The isoagglutinin titers were effectively lowered less than 1:16 before operation. CD 19+ B cells were rapidly eliminated after rituximab and suppressed during 6months postoperatively. CD3+ and CD4+ T cells were elevated higher than CD8+ T cells. CD4/CD8 ratio was increased during first 1month postoperatively and decreased thereafter. CD16+CD56+ NK cells were lowered and restored after 4months of LDLT. Among 15 patients with HCC, 5 patients (33.3%) experienced early tumor recurrence (1/8 within Milan and 4/7 beyond Milan).

CONCLUSIONS

Our protocol showed effective results in preventing antibody-mediated rejection and suppressing B lymphocytes. Application to advanced hepatocellular carcinoma should be considered due to decreased natural immunity after ABO-I LDLT.

Organ-specific phenotypic and functional features of NK cells in humans

Natural killer (NK) cells kill virus-infected and tumor target cells without prior sensitization. Each NK cell expresses a multitude of activating and inhibitory receptors, and the interplay of signals determines the outcome of NK cell activity. NK cell-mediated cytolysis of target cell involves polarized degranulation at effector-target interface. Peripheral blood NK cell constitutes about 10% of lymphocytes, and approximately 90% of peripheral blood NK cells are CD56(dim)CD16(+); however, there is a distinct subset of NK cells, CD56(bright)CD16(-), expressed by certain lymphoid organs which are able to produce large amounts of cytokines including interferon-γ, tumor necrosis factor, and granulocyte-macrophage colony-stimulating factor, but the cytotoxicity is attained only on their prolonged activation. In this review, we discuss the accumulated data on distinct phenotypes of NK cells in human uterus, liver, intestine, skin, and lung and also attempt to correlate their phenotype with corresponding activity and functions, with significant stress on the role of NK cells in pathology in the specific organs. Our detailed understanding of altered NK cell activity in different organs and their inherent cytotoxic activity against tumor target cells will help us design better immunotherapeutic strategies in NK cell-mediated cancer therapies.

Rotterdam: main port for organ transplantation research in the Netherlands

This overview describes the full spectrum of current pre-clinical and clinical kidney-, liver-, heart- and lung transplantation research performed in Erasmus MC - University Medical Centre in Rotterdam, The Netherlands. An update is provided on the development of a large living donor kidney transplantation program and on optimization of kidney allocation, including the implementation of a domino kidney-donation program. Our current research efforts to optimize immunosuppressive regimens and find novel targets for immunosuppressive therapy, our recent studies on prevention of ischemia-reperfusion-induced graft injury, our newest findings on stimulation of tissue regeneration, our novel approaches to prevent rejection and viral infection, and our latest insights in the regulation of allograft rejection, are summarized.

Intrahepatic natural killer cell activation, but not function, is associated with HBsAg levels in patients with HBeAg-negative chronic hepatitis B

BACKGROUND & AIMS

Natural killer (NK) cells play an important role in the immune response to viruses. As the hepatitis B virus (HBV) replicates in hepatocytes, examination of the liver of chronic hepatitis B (CHB) patients is crucial to better understand the role of NK cells in HBV. HBeAg-negative CHB differs in many aspects from HBeAg-positive CHB, and until now little is known about the intrahepatic NK cell response in HBeAg-negative patients. Intrahepatic immune control might be different in HBeAg-negative as compared with HBeAg-positive patients.

METHODS

Liver NK cells were investigated in 21 HBeAg-positive and 35 HBeAg-negative CHB patients. Biopsy specimens were processed for routine histopathology and staging according to Ishak scores. Intrahepatic and blood NK cell frequencies, activation status and function of NK cells were analysed by flow cytometry.

RESULTS

In HBeAg-negative CHB patients, compared to blood, liver NK cells displayed a more activated phenotype and stimulation further increased the activation status, but production of IFN-γ was markedly less. There was no difference with HBeAg-positive CHB. Only in HBeAg-negative CHB, but not in HBeAg-positive CHB, NK cell activation was inversely correlated with HBsAg levels.

CONCLUSIONS

The present study indicates that liver NK cells of CHB have a higher activation status compared to blood. However, they are not capable to increase cytokine production above levels reached by activated blood NK cells. In HBeAg-negative CHB, the levels of HBsAg may contribute to the incapacity of activated liver NK cells to increase cytokine production.

MicroRNA profiles in graft preservation solution are predictive of ischemic-type biliary lesions after liver transplantation

BACKGROUND & AIMS

Ischemic-type biliary lesions (ITBL) are the second most common cause of graft loss after liver transplantation. Though the exact pathophysiology of ITBL is unknown, bile duct injury during graft preservation is considered to be a major cause. Here we investigated whether the release of cholangiocyte-derived microRNAs (CDmiRs) during graft preservation is predictive of the development of ITBL after liver transplantation.

METHODS

Graft preservation solutions (perfusates) and paired liver biopsies collected at the end of cold ischemia were analysed by RT-qPCR for CDmiR-30e, CDmiR-222, and CDmiR-296 and hepatocyte-derived miRNAs (HDmiRs) HDmiR-122 and HDmiR-148a. MicroRNAs in perfusates were evaluated on their stability by incubation and fractionation experiments. MicroRNA profiles in perfusates from grafts that developed ITBL (n=20) and grafts without biliary strictures (n=37) were compared.

RESULTS

MicroRNAs in perfusates were proven to be stable and protected against degradation by interacting proteins. Ratios between HDmiRs/CDmiRs were significantly higher in perfusates obtained from grafts that developed ITBL (p<0.01) and were identified as an independent risk factor by multivariate analysis (p<0.01, HR: 6.89). The discriminative power of HDmiRs/CDmiRs in perfusates was validated by analysis of separate brain death- (DBD) and cardiac death donors (DBD; p ≤ 0.016) and was superior to expression in liver biopsies (C=0.77 in perfusates vs. C<0.50 in biopsies).

CONCLUSIONS

This study demonstrates that differential release of CDmiRs during graft preservation is predictive of the development of ITBL after liver transplantation. This provides new evidence for the link between graft-related bile duct injury and the risk for later development of ITBL.

Differential function of natural killer cells in the liver graft perfusate of Korean population

BACKGROUND

Liver perfusate (LP) lymphocytes show unique subsets compared with peripheral blood (PB) lymphocytes. LP natural killer (NK) and NKT cells may display unique cytotoxicity and cytokine production, thus leading to distinct roles in liver transplantation. In this study, we sought to evaluate the functions of graft perfusate NK and NKT cells in clinical liver transplantation.

METHODS

The living donor right lobe graft was initially washed with 1 L of histidine-tryptophan-ketoglutarate solution to collect the perfusate. We also collected donor PB. Lymphocytes separated by the Ficoll-Hypaque density gradient method underwent immunophenotyping using multicolor flow cytometry. To assess cytokine secretion, we performed the enzyme-linked immunosorbent assay.

RESULTS

There were more NK and NKT cells in LP confirming previous reports. In particular, CD56(bright)CD16(low) NK cells accounted for approximately 50% of total NK cells compared with 5% to 10% among PB NK cells. In response to cytokine stimulation LP NK cells produce tumor necrosis factor-α at different levels and less interleukin-10 compared with PB NK cells. The major source of interferon-γ production upon stimulation with liver caner cells were CD56(dim) NK cells and CD56(-)CD3(-) cells rather than NKT or T cells. Unlike PB NK cells, LP CD56(bright)CD16(low) NK cells along with CD56(dim)CD16(high) NK cells and NKT cells were efficient killers against Korean liver cancer cells.

CONCLUSION

LP NK and NKT cells showed unique functions in cytotoxicity and cytokine production.