Changes in natural killer cell subsets in pediatric liver transplant recipients

Natural Killer Cells in Hepatic Ischemia-Reperfusion Injury

Ischemia-reperfusion injury can be divided into two phases, including insufficient supply of oxygen and nutrients in the first stage and then organ injury caused by immune inflammation after blood flow recovery. Hepatic ischemia-reperfusion is an important cause of liver injury post-surgery, consisting of partial hepatectomy and liver transplantation, and a central driver of graft dysfunction, which greatly leads to complications and mortality after liver transplantation. Natural killer (NK) cells are the lymphocyte population mainly involved in innate immune response in the human liver. In addition to their well-known role in anti-virus and anti-tumor defense, NK cells are also considered to regulate the pathogenesis of liver ischemia-reperfusion injury under the support of more and more evidence recently. The infiltration of NK cells into the liver exacerbates the hepatic ischemia-reperfusion injury, which could be significantly alleviated after depletion of NK cells. Interestingly, NK cells may contribute to both liver graft rejection and tolerance according to their origins. In this article, we discussed the development of liver NK cells, their role in ischemia-reperfusion injury, and strategies of inhibiting NK cell activation in order to provide potential possibilities for translation application in future clinical practice.

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.

Circulating CXCR3-CCR6-CXCR5+CD4+ T cells are associated with acute allograft rejection in liver transplantation

Circulating T follicular helper (cTFH) cells have been demonstrated to be involved in B-cell-mediated alloreactive responses in kidney and liver transplantation; however, whether these cells are involved in acute liver allograft rejection after liver transplantation, and which subsets are involved, remains to be clarified. The present study aimed to investigate the profiles of cTFH cells in acute liver allograft rejection, including the CXC motif receptor 3 (CXCR3)⁺ chemokine receptor 6 (CCR6)^- subset, the CXCR3^-CCR6^- subset, and the CXCR3^-CCR6⁺ subset. Twelve liver transplant patients with acute rejection (AR) and 20 with no acute rejection (NAR) were enrolled in the study. The results showed that the proportion of CXCR3-CCR6-CXCR5⁺CD4⁺ T cells was significantly increased and the proportion of CXCR3^-CCR6⁺CXCR5⁺CD4⁺ T cells was significantly decreased in patients with AR compared with patients with NAR. In addition, the proportion of CXCR3-CCR6-CXCR5⁺CD4⁺ T cells was positively correlated with the proportion of B cells in patients with AR. The level of serum interleukin (IL)-21 was higher in the AR group than in the NAR groups. Furthermore, the proportion of CXCR3-CCR6-CXCR5⁺CD4⁺ T cells was positively correlated with alanine amino transferase (ALT), whereas the proportion of CXCR3^-CCR6⁺ CXCR5⁺CD4⁺ T cells was negatively correlated with ALT. B cells and TFH cells were detected in follicular-like structures in liver allograft tissues from patients with AR. These results suggest that CXCR3-CCR6-CXCR5⁺CD4⁺ T cells may be involved in acute allograft rejection after liver transplantation.

STAT4-associated natural killer cell tolerance following liver transplantation

OBJECTIVE

Natural killer (NK) cells are important mediators of liver inflammation in chronic liver disease. The aim of this study was to investigate why liver transplants (LTs) are not rejected by NK cells in the absence of human leukocyte antigen (HLA) matching, and to identify a tolerogenic NK cell phenotype.

DESIGN

Phenotypic and functional analyses on NK cells from 54 LT recipients were performed, and comparisons made with healthy controls. Further investigation was performed using gene expression analysis and donor:recipient HLA typing.

RESULTS

NK cells from non-HCV LT recipients were hypofunctional, with reduced expression of NKp46 (p<0.05) and NKp30 (p<0.001), reduced cytotoxicity (p<0.001) and interferon (IFN)-γ secretion (p<0.025). There was no segregation of this effect with HLA-C, and these functional changes were not observed in individuals with HCV. Microarray and RT-qPCR analysis demonstrated downregulation of STAT4 in NK cells from LT recipients (p<0.0001). Changes in the expression levels of the transcription factors Helios (p=0.06) and Hobit (p=0.07), which control NKp46 and IFNγ expression, respectively, were also detected. Hypofunctionality of NK cells was associated with impaired STAT4 phosphorylation and downregulation of the STAT4 target microRNA-155. Conversely in HCV-LT NK cell tolerance was reversed, consistent with the more aggressive outcome of LT for HCV.

CONCLUSIONS

LT is associated with transcriptional and functional changes in NK cells, resulting in reduced activation. NK cell tolerance occurs upstream of major histocompatibility complex (MHC) class I mediated education, and is associated with deficient STAT4 phosphorylation. STAT4 therefore represents a potential therapeutic target to induce NK cell tolerance in liver disease.

Differences in Peripheral Blood Lymphocytes between Brand-Name and Generic Tacrolimus Used in Stable Liver Transplant Recipients

OBJECTIVES

In this study, peripheral blood lymphocytes were compared between a brand-name and a generic tacrolimus group in stable liver transplant recipients.

SUBJECTS AND METHODS

Sixteen patients who underwent ABO-compatible living donor liver transplants between 2012 and 2013 and had stable graft function were included in this study. Ten patients received brand-name tacrolimus and 6 patients received generic tacrolimus. CD3, CD4, CD8, γδ, CD4+FoxP3+, and CD3-CD56+ T cells were analyzed in peripheral blood obtained preoperatively and 4, 8, 12, and 24 weeks after liver transplantation. Categorical variables were compared using a χ2 test or Fisher exact test, and continuous variables were compared using the Mann-Whitney U test.

RESULTS

Regarding the baseline and perioperative characteristics, there were no statistically significant differences between the 2 groups. Immunosuppression also was not different. Subtype analysis of T-cell populations carried out in parallel showed similar levels of CD3, CD4, CD8, and γδT cells with brand-name tacrolimus and generic tacrolimus in stable liver transplant recipients. However, the levels of CD4+Foxp3+ and CD3-CD56+ T cells were higher in the brand-name tacrolimus group than in the generic tacrolimus group 8 weeks after transplantation (p < 0.05).

CONCLUSIONS

The level of CD4+Foxp3+ T cells was higher in the brand-name tacrolimus group than in the generic tacrolimus group after transplantation. This finding showed that brand-name tacrolimus could have more potential immunosuppressive activity than generic tacrolimus regarding the contribution of CD4+Foxp3+ T cells to graft tolerance in liver transplant recipients.

Mass cytometry reveals a distinct immunoprofile of operational tolerance in pediatric liver transplantation

Long-term IS in transplant patients has significant morbidity, poorer quality of life, and substantial economic costs. TOL, defined as graft acceptance without functional impairment in the absence of IS, has been achieved in some pediatric LT recipients. Using mass cytometry, peripheral blood immunotyping was performed to characterize differences between tolerant patients and patients who are stable on single-agent IS. Single-cell mass cytometry was performed using blood samples from a single-center pediatric LT population of operationally tolerant patients to comprehensively characterize the immune cell populations in the tolerant state compared with patients on chronic low-dose IS. Specific T-cell populations of interest were confirmed by flow cytometry. This high-dimensional phenotypic analysis revealed distinct immunoprofiles between transplant populations as well as a CD4⁺ TOT (CD4⁺ CD5⁺ CD25⁺ CD38^-/lo CD45RA) that correlates with tolerance in pediatric LT recipients. In TOL patients, the TOT was significantly increased as compared to patients stable on low levels of IS. This TOT cell was confirmed by flow cytometry and is distinct from classic Treg cells. These results demonstrate the power of mass cytometry to discover significant immune cell signatures that have diagnostic potential.

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.

NK cells after transplantation: friend or foe

Natural killer (NK) cells are effector cells of the innate immune system that can lyse target cells without prior sensitization and have an important role in host defense to pathogens and transformed cells. A balance between negative and positive signals transmitted via germ line-encoded inhibitory and activating receptors controls the function of NK cells. Although the concept of "missing-self" would suggest that NK cells could target foreign allografts, the prevailing dogma has been that NK cells are not active participants in the mechanisms that culminate in the rejection of solid organ allografts. Recent studies, however, challenge this conclusion and instead implicate NK cells in contributing to both graft rejection and tolerance to an allograft. In this review, we highlight recent studies with the goal of understanding the complex NK cell interactions that impact alloimmunity.

Characteristics of Vδ1(+) and Vδ2(+) γδ T cell subsets in acute liver allograft rejection

BACKGROUND

To investigate the characteristics of γδ T cells as well as the Vδ1(+) and Vδ2(+) subsets in the peripheral blood in liver allograft recipients.

METHODS

Sixty-three liver transplant recipients were enrolled in this study: 26 cases with acute allograft rejection (Gr-AR), and 37 cases with stable allograft liver function (Gr-SF). The frequencies of γδ T cells, the Vδ1(+) and Vδ2(+) subsets, and interleukin (IL)-10-producing Vδ1(+) γδ T cells in the peripheral blood were analyzed by flow cytometry. The relationship between liver function parameters and the Vδ1(+)/Vδ2(+) ratio was analyzed.

RESULTS

The frequency of the Vδ1(+) subset and the Vδ1(+)/Vδ2(+) ratio in Gr-SF was significantly higher than that in Gr-AR; in contrast, the frequency of the Vδ2(+) subset in Gr-SF was markedly lower than that in Gr-AR. In addition, there was no significant difference in the frequency of γδ T cells between the Gr-AR and Gr-SF groups. Moreover, there was a significant negative correlation between the Vδ1(+)/Vδ2(+) ratio with the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in Gr-AR.

CONCLUSIONS

Vδ1(+) γδ T cells may have a potential role in maintaining stable graft liver function, and Vδ2(+) γδ T cells may be associated with liver allograft rejection. The Vδ1(+)/Vδ2(+) ratio could serve as a prognostic marker for acute rejection after liver transplantation.