Intrahepatic Detection of FOXP3 Gene Expression After Liver Transplantation Using Minimally Invasive Aspiration Biopsy

The role of regulatory T cells in liver transplantation

The liver is considered a tolerogenic organ that can induce peripheral tolerance. The exact mechanisms of tolerance in the liver remain undefined. Regulatory T cells (Tregs) have been demonstrated to be involved in inducing and maintaining peripheral tolerance. They play an important role in the prevention of immune responses and autoimmunity. The main focus of this review is the role of Tregs and their subpopulation in liver transplantation. More specifically, this manuscript will highlight the recent findings about using Treg cells as a biomarker in liver transplantation. There are some reports and animal models about the role of Tregs in the process of rejection of liver transplantation. Previous reports and studies have suggested that by increasing the number of Tregs better liver transplant outcomes will be accomplished by enhancing tolerance. It has been shown that the levels of CD4 + CD25 + FOXP3+ Treg cells correlate with the inhibition of acute allograft rejection in liver transplantation; however, further studies must be done to address the potential role of Treg cells in chronic rejection. Indeed, in the future, Treg cells may have potential use as a beneficial biomarker to screen long-term graft function.

Gene expression profiling of human tissue-resident immune cells: Comparing blood and liver

In this study, we describe a method to reliably characterize intrahepatic leukocyte populations using flow cytometry and next‐generation RNA sequencing on fresh human liver biopsies. Over the last decades, immune responses of viral hepatitis patients, and of other liver diseases, have been incompletely characterized. Most studies include peripheral blood samples only, foregoing the possibility to investigate the site of inflammation directly. Here, we show that with an optimized protocol that combines cell sorting and RNA sequencing, we can perform a side by side comparison of both intrahepatic and peripheral immune cells. Using core liver biopsies from chronic hepatitis B virus patients, we show that the expression levels of IFN‐stimulated genes and leukocyte‐specific genes are markedly different in the liver compartment as compared to the peripheral blood. These observations emphasize the need to sample the liver directly. The variation of gene expression profiles in these chronic hepatitis B patients was considerable, despite the uniform treatment with nucleotide analogs and absence of liver inflammation in these patients. Finally, we show that this method can provide a detailed characterization of previously undetected liver‐specific effects of novel candidate therapeutic compounds.

Regulatory T-cell therapy in liver transplantation

Modern immunosuppression drug regimens have produced excellent short-term survival after liver transplantation but it is generally accepted that the side effects of these medications remain a significant contributing factor for less satisfactory long term outcomes. The liver has unique tolerogenic properties as evidenced by the higher rates of operational tolerance seen in liver transplant recipients compared to other solid organ transplants, and therefore, liver transplantation offers an attractive setting in which to study tolerizing therapies. CD4⁺ CD25⁺ FOXP3⁺ regulatory T cells (Tregs) are crucial for maintenance of self-tolerance and prevention of autoimmune disease and are therefore an appealing potential candidate for use as a tolerizing cell therapy. In this review, we summarize the evidence from drug withdrawal trials of spontaneous operational tolerance in liver transplantation, the unique immunology of the hepatic microenvironment, the evidence for the use of CD4⁺ CD25⁺ FOXP3⁺ regulatory T cells as a tolerance inducing therapy in liver transplantation and the challenges in producing clinical grade Treg cell products.

CMV infection of human sinusoidal endothelium regulates hepatic T cell recruitment and activation

BACKGROUND & AIMS

Human cytomegalovirus infection (HCMV) is associated with an increased morbidity after liver transplantation, by facilitating allograft rejection and accelerating underlying hepatic inflammation. We hypothesized that human hepatic sinusoidal endothelial cells infected with HCMV possess the capacity to modulate allogeneic T cell recruitment and activation, thereby providing a plausible mechanism of how HCMV infection is able to enhance hepatic immune activation.

METHODS

Human hepatic sinusoidal endothelial cells were isolated from explanted livers and infected with recombinant endotheliotropic HCMV. We used static and flow-based models to quantify adhesion and transendothelial migration of allogeneic T cell subsets and determine their post-migratory phenotype and function.

RESULTS

HCMV infection of primary human hepatic sinusoidal endothelial cells facilitated ICAM-1 and CXCL10-dependent CD4 T cell transendothelial migration under physiological levels of shear stress. Recruited T cells were primarily non-virus-specific CXCR3(hi) effector memory T cells, which demonstrated features of LFA3-dependent Th1 activation after migration, and activated regulatory T cells, which retained a suppressive phenotype following transmigration.

CONCLUSIONS

The ability of infected hepatic endothelium to recruit distinct functional CD4 T cell subsets shows how HCMV facilitates hepatic inflammation and immune activation and may simultaneously favor virus persistence.

Effect of cell density and HLA-DR incompatibility on T-cell proliferation and forkhead box P3 expression in human mixed lymphocyte reaction

BACKGROUND

The proliferation rates of human T cells in vitro are affected by some factors such as initial T-cell number, dose of stimulating cells, and duration of culture. The transcription factor forkhead box P3 (FoxP3) has been used to identify regulatory T cells in humans and is thought to correlate with tolerance to allogeneic organ transplant. Thus, it is important to optimize conditions to expand FoxP3 cell proliferation to improve engraftment of allogeneic organ transplants.

METHODS

We studied proliferative responses and FoxP3 expression in divided T cells with the use of flow cytometric analysis of Ki-67 in culture of different concentrations of responding cells (6 × 10(6), 4 × 10(6), 2 × 10(6), 1 × 10(6), and 0.5 × 10(6)cells/mL), different types of stimulating cells (lymphocytes and low density cells), and different numbers of HLA mismatches.

RESULTS

The proportion of CD3(+) cells, CD4(+)CD25(+) cells, and CD4(+)CD25(+)FoxP3(+) cells among mononuclear cells were highest at initial cell concentration of 2 × 10(6) responder cells/mL with lymphocytes as stimulators at day-5 mixed lymphocyte reaction (MLR). They were highest at a concentration of 4 × 10(6) responder cells/mL with low density cells as stimulators. The recovery (%), proportion of CD3(+) cells, CD4(+)CD25(+) cells, and CD4(+)CD25(+)FoxP3(+) cells with 2 HLA-DR incompatibility were significantly higher than those of 1 HLA-DR incompatibility at day-5 MLR.

CONCLUSIONS

Initial cell concentration and HLA-DR incompatibility can affect the generation of FoxP3+ T cells in human MLR. These factors could be considered for efficient generation of Tregs for clinical trials in the future.

Comprehensive phenotyping of regulatory T cells after liver transplantation

Regulatory T cells (Tregs) play an important role in controlling alloreactivity after solid organ transplantation, but they may also impair antiviral immunity. We hypothesized that the Treg frequency and the Treg phenotype are altered in hepatitis C virus (HCV)-infected recipients of liver transplantation (LT) with possible prognostic implications. Tregs from 141 individuals, including healthy individuals, LT recipients with or without persistent HCV infections, and nontransplant patients with chronic HCV, were studied. A comprehensive phenotypic analysis was performed with multicolor flow cytometry, which included standard Treg markers [CD4(+), CD25(hi), CD127(-), and FoxP3(+) in addition to HLA DR, CCR7, CD45RA, CD62L, CD49d, CD39, ICOS and LAP-TGFβ stainings. Healthy individuals and LT patients displayed similar Treg frequencies and largely comparable Treg phenotypes, which were stable over time after transplantation. In contrast, Tregs with a CD45RA(-) CCR7(-) effector phenotype were enriched in LT recipients with chronic HCV versus HCV-negative transplant patients. HCV infection, rather than LT, altered the expression of functional markers on Tregs. A principal component analysis revealed distinct Treg phenotypes in HCV-infected LT recipients with rejection and patients with recurrent graft HCV. In conclusion, Treg phenotypes are altered in HCV-infected LT patients. An investigation of Tregs may possibly help to distinguish recurrent HCV from graft rejection. Further functional studies are needed to define the role of Tregs in determining the balance between antiviral and allogenic immunity.

Immune tolerance in liver disease

Liver tolerance is manifest as a bias toward immune unresponsiveness, both in the context of a major histocompatibility complex-mismatched liver transplant and in the context of liver infection. Two broad classes of mechanisms account for liver tolerance. The presentation of antigens by different liver cell types results in incomplete activation of CD8(+) T cells, usually leading to initial proliferation followed by either clonal exhaustion or premature death of the T cell. Many liver infections result in relatively poor CD4(+) T-cell activation, which may be because liver antigen-presenting cells express a variety of inhibitory cytokines and coinhibitor ligands. Poor CD4(+) T-cell activation by liver antigens likely contributes to abortive activation, exhaustion, and early death of CD8(+) T cells. In addition, a network of active immunosuppressive pathways in the liver is mediated mostly by myeloid cells. Kupffer cells, myeloid-derived suppressor cells, and liver dendritic cells both promote activation of regulatory T cells and suppress CD8(+) and CD4(+) effector T cells. This suppressive network responds to diverse inputs, including signals from hepatocytes, sinusoidal endothelial cells, and hepatic stellate cells.

CONCLUSION

Though liver tolerance may be exploited by pathogens, it serves a valuable purpose. Hepatitis A and B infections occasionally elicit a powerful immune response sufficient to cause fatal massive liver necrosis. More commonly, the mechanisms of liver tolerance limit the magnitude of intrahepatic immune responses, allowing the liver to recover. The cost of this adaptive mechanism may be incomplete pathogen eradication, leading to chronic infection.

Diagnostic value of tolerance-related gene expression measured in the recipient alloantigen-reactive T cell fraction

The efficient development of tolerance-inducing therapies and safe reduction of immunosuppression should be supported by early diagnosis and prediction of tolerance in transplantation. Using mouse models of donor-specific tolerance to allogeneic skin and islet grafts we tested whether measurement of tolerance-related gene expression in their alloantigen-reactive peripheral T cell fraction efficiently reflected the tolerance status of recipients. We found that Foxp3, Nrn1, and Klrg1 were preferentially expressed in conditions of tolerance compared with rejection or unmanipulated controls if their expression is measured in CD69(+) T cells prepared from coculture of recipient peripheral T cells and donor antigen-presenting cells. The same pattern of gene expression was observed in recipients grafted with either skin or islets, recipients of different genetic origins, and even those taking immunosuppressive drugs. These findings suggest that the expression of tolerance-related genes in the alloantigen-reactive T cell fraction could be used to detect tolerance in the clinic.

Prognostic significance of graft Foxp3 expression in renal transplant recipients: a critical review and attempt to reconcile discrepancies

A large body of evidence has been accumulated from experimental models in the past decade to support the critical role of Foxp3-expressing regulatory T cells (Tregs) in the suppression of alloimmune responses. This has prompted transplant clinicians to investigate whether Foxp3 analysis might be used as an immunodiagnostic tool for better assessment of the significance of graft infiltrate and to predict its impact on graft outcome. However, conflicting results have emerged from these studies and may have generated more confusion than clarification. Foxp3 expression has been antagonistically correlated with either good or poor prognosis. We discuss here how methodological issues and specific clinical settings may have accounted for the discrepancies between the results of these studies. Depending on many factors, including the techniques used, the method of sampling normalization, the extent of intra-graft inflammation, the immunosuppressive regimen and the depletion or repletion of T lymphocyte compartment, the significance of Foxp3 expression may vary. We propose here the conditions to be fulfilled in order to use Foxp3 analysis as a relevant biomarker for graft outcome assessment. Far from challenging the key role of Tregs in dampening alloimmune responses, this review highlights the need for technical harmonization and standards.

Enrichment of regulatory T cells in acutely rejected human liver allografts

Acute cellular rejection (ACR) occurs frequently after liver transplantation and can usually be controlled. Triggering of allospecific immune responses and lack of immunoregulation are currently suggested as a cause of ACR, but there are no investigations of intrahepatic immune responses during ACR. Therefore we prospectively analyzed the intrahepatic T cell infiltration pattern in correlation to the severity of ACR in a cohort of patients with graft hepatitis (n = 151). While CD4(+) cells dominated the portal infiltrates in mild-moderate ACR, CD8(+) cells prevailed in severe ACR. Furthermore portal CD8(+) and not CD4(+) infiltration correlated with serum transaminases and with the likelihood of subsequent ACRs. Surprisingly, the rise of portal effector T cells density during ACR was surpassed by the increase in portal infiltration of regulatory T cells by a factor of two. Thus ACRs rather showed an increase and not a lack of regulation, as was suggested by analysis of peripheral blood mononuclear cells. Despite the pattern of enhanced immunoregulation, patients with severe ACR had a higher risk for subsequent rejections and showed a trend to a reduced survival. Thus, patients with severe rejections might need a modification of their immunosuppression to improve prognosis.

Regulatory T cells: hypes and limitations

PURPOSE OF REVIEW

In recent years there has been increased interest in understanding the physiology and function of regulatory T cells. In this review we focus on the characterization of regulatory T-cell subsets and their potential therapeutic use in organ transplantation.

RECENT FINDINGS

Regulatory T cells can play an instrumental role in the establishment of operational tolerance to allografts. The level of expression and the extent of posttranslational acetylation of the regulatory T-cell specific transcription factor Foxp3 are important modulators of their suppressive activity. Low expression of CD127 can be used as a novel marker to define pure regulatory T-cell populations and the expression of CD45RA on CD4CD25 regulatory T cells characterizes a population with a more stable phenotype upon expansion in vitro. Interleukin-35 is a recently discovered immunosuppressive cytokine secreted by CD4CD25 regulatory T cells. Although the presence of allospecific memory T cells in the pretransplant period and the use of immunosuppressants might interfere with the effectiveness of regulatory T-cell-based therapies, encouraging results indicate that the immunosuppressive drug rapamycin does not affect the expansion and function of regulatory T cells and could be included in a combined therapy.

SUMMARY

Important advances have been made towards establishing regulatory T cells as a viable therapy in transplantation and the first clinical trials using human regulatory T cells are currently underway. There are, however, important limitations and safety issues that have to be addressed before this therapy can be fully translated into the clinic.

Moving to tolerance: clinical application of T regulatory cells

Decreasing the incidence of chronic rejection and reducing the need for life-long immunosuppression remain important goals in clinical transplantation. In this article, we will review how regulatory T cells (Treg) came to be recognized as an attractive way to prevent or treat allograft rejection, the ways in which Treg can be manipulated or expanded in vivo, and the potential of in vitro expanded/generated Treg for cellular therapy. We will describe the first regulatory T cell therapies that have been or are in the process of being conducted in the clinic as well as the safety concerns of such therapies and how outcomes may be measured.

Characterization of HCV-specific CD4+Th17 immunity in recurrent hepatitis C-induced liver allograft fibrosis

Hepatitis C virus (HCV) recurrence with accelerated fibrosis following orthotopic liver transplantation (OLT) is a universal phenomenon. To evaluate mechanisms contributing to HCV induced allograft fibrosis/cirrhosis, we investigated HCV-specific CD4+Th17 cells and their induction in OLT recipients with recurrence utilizing 51 HCV+ OLT recipients, 15 healthy controls and 9 HCV- OLT recipients. Frequency of HCV specific CD4+ Tcells secreting IFN-γ, IL-17 and IL-10 was analyzed by ELISpot. Serum cytokines and chemokines were analyzed by LUMINEX. Recipients with recurrent HCV induced allograft inflammation and fibrosis/cirrhosis demonstrated a significant increase in frequency of HCV specific CD4+Th17 cells. Increased pro-inflammatory mediators (IL-17, IL-1β, IL-6, IL-8 and MCP-1), decreased IFN-γ, and increased IL-4, IL-5 and IL-10 levels were identified. OLT recipients with allograft inflammation and fibrosis/cirrhosis demonstrated increased frequency of Foxp3+ regulatory T cells (Tregs) that inhibited HCV specific CD4+Th1 but not Th17 cells. This suggests that recurrent HCV infection in OLT recipients induces an inflammatory milieu characterized by increased IL-6, IL-1β and decreased IFN-γ which facilitates induction of HCV specific CD4+Th17 cells. These cells are resistant to suppression by Tregs and may mediate an inflammatory cascade leading to cirrhosis in OLT recipients following HCV recurrence.

Th17 cells: the emerging reciprocal partner of regulatory T cells in the liver

T helper cells that produce interleukin-17 (IL-17) (Th17 cells) have recently been identified as the third distinct subset of effector T cells, the differentiation of which depends on specific transcription nuclear factor retinoic acid-related orphan nuclear receptor-gammat. Emerging data have suggested that Th17 cells play an important role in innate immunity, adaptive immunity and autoimmunity. Interestingly, there is a reciprocal relationship between Th17 cells and regulatory T cells (Treg), not only in development, but also in their effector function. Transforming growth factor (TGF)-beta induces Treg-specific transcription factor Forkhead box P3(FOXP3), while the addition of IL-6 to TGF-beta inhibits the generation of Treg cells and induces Th17 cells. It is proposed that the fine balance between Th17 and Treg cells is crucial for maintenance of immune homeostasis. In addition to IL-6, other factors such as retinoic acid, rapamycin, or cytokines (e.g., IL-2 and IL-27) could dictate the balance between Th17 and Treg cells. Since Treg cells play an important role in hepatic immunity with overregulation in chronic viral hepatitis and hepatic carcinoma, and inadequate inhibition in autoimmune liver diseases, graft rejection and acute liver failure, it is reasonable to assume that Th17 cells may play a reciprocal role in these diseases. Thus, future research on the Treg/Th17 balance may provide an opportunity to illustrate the pathogenesis of hepatic inflammation and to explore new therapeutic targets for immune-related liver diseases.

Regulatory T cells in alloreactivity after clinical heart transplantation

PURPOSE OF REVIEW

As the knowledge of CD4+CD25bright+FoxP3+ regulatory T cells in experimental transplant models grows, we need to understand how and to what extent these suppressor cells regulate donor-directed immune events in the transplantation clinic. This review focuses on the function of regulatory T cells in the peripheral blood and the transplanted organ of patients after heart transplantation during immunological quiescence and rejection.

RECENT FINDINGS

Here, we present data that peripheral CD4+CD25bright+FoxP3+ T cells of heart transplant patients who experience acute rejection have inadequate immune regulatory function in vitro compared with those of nonrejecting patients. During rejection, potent donor-specific T-cell suppressors are present in the transplanted organ.

SUMMARY

The studies in transplant patients' show that the function of CD4+CD25bright+FoxP3+ regulatory T cells in alloimmunity is to inhibit the activation of effector T cells, to prevent rejection, and to control the antidonor response at the graft itself at later stages of immune reactivity.

The human "Treg MLR": immune monitoring for FOXP3+ T regulatory cell generation

BACKGROUND

Controversy exists about the conditions effecting the development of forkhead/winghead helix transcription factor P3 (FOXP3) expressing T cells and their relevance in transplant recipients.

METHODS

We generated carboxy-fluorescein diacetate succinimidyl ester-labeled CD4+CD25 high FOXP3+ cells in mixed lymphocyte reactions (MLRs) ("the Treg MLR"), with varying human leukocyte antigen (HLA) disparities and cell components. Five color flow cytometry and H-thymidine uptakes were the readouts.

RESULTS

(1) Despite lower stimulation indices (SIs) than two DR-mismatched MLRs, 2 DR-matched MLRs generated more than twofold higher percentages when gating on proliferating CD4+CD25 high FOXP3+ cells; (2) Even with low numbers of proliferating cells, autologous and HLA identical MLRs generated the highest FOXP3+:FOXP3- cell ratios; (3) Elimination of either non-CD3+ responding cells (resulting in "direct presentation" only) or responding CD25+ (Treg generating) cells increased the SI but inhibited proliferating CD4+CD25 high FOXP3+ cell development; (4) MLR-generated CD4+CD25 high FOXP3+ cells added as third components specifically inhibited the same freshly set MLR SI and caused recruitment of new CD4+CD25 high FOXP3+ cells. As an example of the "Treg MLR" immune monitoring potential, addition of third component peripheral blood mononuclear cell containing high percentages of CD4+CD25 high FOXP3+ cells from an HLA identical kidney transplant recipient (in a tolerance protocol) caused donor-specific Treg MLR inhibition or recruitment. This was similar to the third component MLR Tregs generated entirely in vitro.

CONCLUSION

In the Treg MLR, the generation of CD4+CD25 high FOXP3+ cells is more pronounced in the context of self-recognition (HLA matching, indirect presentation). These cells can be assayed for MLR inhibitory and Treg recruitment functions, so as to immunologically monitor the allospecific regulation after transplantation.

Human FOXP3+ regulatory T cells in transplantation

CD4+CD25+FOXP3+ suppressive regulatory T cells (Treg) represent a subset of immune regulatory cells. Based on experimental results, Treg have recently been considered as a potential treatment option in several diseases. Compared with murine Treg, human CD4+CD25+FOXP3+ cells are less well characterized and understood, so a thorough understanding of their biology is vital before clinical applications can be initiated. This review summarizes knowledge on generation, phenotypic characteristics and function of human Treg. The possible role of these cells in organ transplantation, as well as interactions between immunosuppression and Treg are also discussed.

Transplantation immunology: what the clinician needs to know for immunotherapy

The liver is unique among transplanted organs with respect to its interaction with the host immune system. There is evidence, both anecdotal and documented, that some liver recipients who cease taking immunosuppressive drugs maintain allograft function, suggesting robust tolerance is in place. Moreover, recipients of human liver allografts require less immunosuppression than do other organ recipients, and liver transplants confer protection on other organ grafts from the same donor. Hence, the liver shows features of immune privilege. Still, the liver can display destructive immunologic processes such as rejection in approximately one quarter of patients. The understanding of the cellular and molecular mechanisms operant in tolerance vs allograft rejection is important for developing new agents to improve long-term outcome, minimize infectious complications (including recurrence of hepatotropic viruses), and deliver immunosuppression without long-term toxicity. This review describes the unique aspects of the hepatic immune response, the pathways involved in T-cell activation and alloantigen recognition, effector cells and pathways mediating liver allograft rejection, the role of regulatory T cells, and targets of current and future immunosuppressive agents.