Liver tolerance and the manipulation of immune outcomes

Recurrent and De Novo Autoimmune Hepatitis

Clinical indications for liver transplantation (LT) in patients with autoimmune hepatitis (AIH) are identical to those of patients with other chronic liver diseases that end in acute or semiacute liver failure, decompensated cirrhosis, or hepatocellular carcinoma. Recurrent disease after LT has been reported in 10%-50% of patients with AIH, and the frequency of detection is influenced in part by the use of protocol or clinically indicated liver biopsy. De novo AIH connotes the development of AIH in patients transplanted for liver diseases other than AIH, and it has been reported in 5%-10% of pediatric and 1%-2% of adult recipients. Recurrent disease can negatively impact on graft and patient survival, and retransplantation has been required in 8%-23%. De novo AIH is within the spectrum of graft dysfunction that includes plasma cell-rich rejection, and it can also progress to cirrhosis and graft failure. Treatment for recurrent or de novo disease is based on the conventional regimens for AIH, and corticosteroid therapy alone or combined with azathioprine is standard. Better control of disease activity prior to LT has been associated with less recurrence, and maintenance corticosteroid treatment after LT can reduce its frequency. In conclusion, recurrent AIH is far more frequent than de novo AIH. Both may have negative impacts on graft and patient survival, and early detection and treatment are key objectives. Future investigations must codify the diagnostic criteria for each graft dysfunction, seek diagnostic biomarkers, and evaluate treatments that improve outcomes without increasing the risk of pre- and post-LT infections.

Hepatic stroma-educated regulatory DCs suppress CD8+ T cell proliferation in mice

Liver dendritic cells (DCs) display immunosuppressive activities and inhibit the CD4⁺ T cell response. The present study assessed whether and how liver DCs suppress CD8⁺ T cells. We found that bone marrow-derived mature DCs incubated with liver stromal cells were characterized by a longer life span, reduced CD11c, IA/IE, CD80, CD86, and CD40 expression, and increased CD11b expression. These unique liver stromal cell-educated mature DCs (LSed-DCs) stimulated CD8⁺ T cells to express CD25 and CD69, but inhibited their proliferation. CD8⁺ T cell suppression depended on soluble factors released by LSed-DCs, but not cell-cell contact. Compared with mature DCs, LSed-DCs produced more nitric oxide and IL-10. Addition of a nitric oxide synthase inhibitor, PBIT, but not an IL-10-blocking mAb, reversed LSed-DC inhibition of CD8⁺ T cell proliferation. We also found that LSed-DCs reduced CD8⁺ T cell-mediated liver damage in a mouse model of autoimmune hepatitis. These results demonstrate that the liver stroma induces mature DCs to differentiate into regulatory DCs that suppress CD8⁺ T cell proliferation, and thus contribute to liver tolerance.

Systematic review: recurrent autoimmune liver diseases after liver transplantation

BACKGROUND

Autoimmune liver diseases (AILD) constitute the third most common indication for liver transplantation (LT) worldwide. Outcomes post LT are generally good but recurrent disease is frequently observed.

AIMS

To describe the frequency and risk factors associated with recurrent AILD post-LT and provide recommendations to reduce the incidence of recurrence based on levels of evidence.

METHODS

A systematic review was performed for full-text papers published in English-language journals, using the keywords 'autoimmune hepatitis (AIH)', 'primary biliary cholangitis and/or cirrhosis (PBC)', 'primary sclerosing cholangitis (PSC)', 'liver transplantation' and 'recurrent disease'. Management strategies to reduce recurrence after LT were classified according to grade and level of evidence.

RESULTS

Survival rates post-LT are approximately 90% and 70% at 1 and 5 years and recurrent disease occurs in a range of 10-50% of patients with AILD. Recurrent AIH is associated with elevated liver enzymes and IgG before LT, lymphoplasmacytic infiltrates in the explants and lack of steroids after LT (Grade B). Tacrolimus use is associated with increased risk; use of ciclosporin and preventive ursodeoxycholic acid with reduced risk of PBC recurrence (all Grade B). Intact colon, active ulcerative colitis and early cholestasis are associated with recurrent PSC (Grade B).

CONCLUSIONS

Recommendations based on grade A level of evidence are lacking. The need for further study and management includes active immunosuppression before liver transplantation and steroid use after liver transplantation in autoimmune hepatitis; selective immunosuppression with ciclosporin and preventive ursodeoxycholic acid treatment for primary biliary cholangitis; and improved control of inflammatory bowel disease or even colectomy in primary sclerosing cholangitis.

Oral administration of a non-absorbable plant cell-expressed recombinant anti-TNF fusion protein induces immunomodulatory effects and alleviates nonalcoholic steatohepatitis

AIM

To evaluate the immunomodulatory effect of oral administration of PRX-106 in the high-fat diet model.

METHODS

For 22 wk, C57BL/6 HFD-fed mice received daily oral treatments with BY-2 cells expressing recombinant anti-tumor necrosis factor alpha fusion protein (PRX-106). Mice were followed for serum liver enzyme and triglyceride levels, liver histology and intrahepatic and systemic FACS.

RESULTS

The orally administered non-absorbable PRX-106 was biologically active. Altered distribution of CD4+CD25+FoxP3+ between the liver and spleen and an increase in the intrasplenic-to-intrahepatic CD4+CD25+FoxP3+ ratio and a decrease in the intrasplenic-to-intrahepatic CD8+CD25+FoxP3+ ratio were observed. An increase in intrahepatic NKT cells and a decrease in the intrasplenic-to-intrahepatic NKT ratio were noted. Assessment of the CD4-to-CD8 ratios showed sequestration of CD8+ lymphocytes in the liver. These effects were associated with a decrease in serum triglyceride levels, decrease in the aspartate aminotransferase levels, serum glucose levels, and HOMA-IR score. A decrease in hepatic triglycerides content was observed in the high dose-treated mice.

CONCLUSION

Orally administered PRX-106 shows biological activity and exerts an immunomodulatory effect, alleviating liver damage. The data suggest that PRX-106 may provide an oral immunotherapy for nonalcoholic steatohepatitis.

Factors Influencing RBC Alloimmunization: Lessons Learned from Murine Models

Red blood cell (RBC) alloimmunization may occur following transfusion or pregnancy/delivery. Although observational human studies have described the immunogenicity of RBC antigens and the clinical significance of RBC alloantibodies, studies of factors influencing RBC alloimmunization in humans are inherently limited by the large number of independent variables involved. This manuscript reviews data generated in murine models that utilize transgenic donor mice, which express RBC-specific model or authentic human blood group antigens. Transfusion of RBCs from such donors into nontransgenic but otherwise genetically identical recipient mice allows for the investigation of individual donor or recipient-specific variables that may impact RBC alloimmunization. Potential donor-related variables include methods of blood product collection, processing and storage, donor-specific characteristics, RBC antigen-specific factors, and others. Potential recipient-related variables include genetic factors (MHC/HLA type and polymorphisms of immunoregulatory genes), immune activation status, phenotype of regulatory immune cell subsets, immune cell functional characteristics, prior antigen exposures, and others. Although murine models are not perfect surrogates for human biology, these models generate phenomenological and mechanistic hypotheses of RBC alloimmunization and lay the groundwork for follow-up human studies. Long-term goals include improving transfusion safety and minimizing the morbidity/mortality associated with RBC alloimmunization.

Multipotent mesenchymal stromal cells in liver cancer: implications for tumor biology and therapy

Remodeling of tumor microenvironment is a hallmark in the pathogenesis of liver cancer. Being a pivotal part of tumor stroma, multipotent mesenchymal stromal cells (MSCs), also known as mesenchymal stem cells (MSCs), are recruited and enriched in liver tumors. Owing to their tumor tropism, MSCs are now emerging as vehicles for anticancer drug/gene delivery against liver cancer. However, the exact impact of MSCs on liver cancer remains elusive, as a variety of effects of these cells that have been reported included a plethora of tumor-promoting effects and anti-oncogenic properties. This review aims to dissect the mechanistic insight regarding this observed discrepancy in different experimental settings of liver cancer. Furthermore, we call for caution using MSCs to treat liver cancer or even premalignant liver diseases, before conclusive evidence for safety and efficacy having been obtained.

Antigen expression level threshold tunes the fate of CD8 T cells during primary hepatic immune responses

CD8 T-cell responses to liver-expressed antigens range from deletional tolerance to full effector differentiation resulting in overt hepatotoxicity. The reasons for these heterogeneous outcomes are not well understood. To identify factors that govern the fate of CD8 T cells activated by hepatocyte-expressed antigen, we exploited recombinant adenoassociated viral vectors that enabled us to vary potential parameters determining these outcomes in vivo. Our findings reveal a threshold of antigen expression within the liver as the dominant factor determining T-cell fate, irrespective of T-cell receptor affinity or antigen cross-presentation. Thus, when a low percentage of hepatocytes expressed cognate antigen, high-affinity T cells developed and maintained effector function, whereas, at a high percentage, they became functionally exhausted and silenced. Exhaustion was not irreversibly determined by initial activation, but was maintained by high intrahepatic antigen load during the early phase of the response; cytolytic function was restored when T cells primed under high antigen load conditions were transferred into an environment of low-level antigen expression. Our study reveals a hierarchy of factors dictating the fate of CD8 T cells during hepatic immune responses, and provides an explanation for the different immune outcomes observed in a variety of immune-mediated liver pathologic conditions.

Tumor promotion through the mesenchymal stem cell compartment in human hepatocellular carcinoma

Although the infiltration of mesenchymal stem (stromal) cells (MSCs) into different tumors is widely recognized in animal models, the question whether these MSCs have a positive or negative effect on disease progression remains unanswered. The aim of this study is to investigate whether human hepatocellular carcinoma (HCC) harbors MSCs and whether these MSCs affect tumor growth. We observed that cells capable of differentiation into both adipocyte and osteocyte lineages and expressing MSC markers can be cultured from surgically resected HCC tissues. In situ staining of human HCC tissues with a STRO-1 antibody showed that the tumor and tumor-stromal region are significantly enriched with candidate MSCs compared with adjacent tissue (n = 12, P < 0.01). In mice, coengraftment of a human HCC cell line (Huh7) with MSCs resulted in substantially larger tumors compared with paired engraftment of Huh7 alone (n = 8, P < 0.01). Consistently, coculturing Huh7 with irradiated MSCs significantly increased the number and the size of colonies formed. This enhancement of Huh7 colony formation was also observed by treatment of MSC-conditioned medium (MSC-CM), suggesting that secreted trophic factors contribute to the growth-promoting effects. Genome-wide gene expression array and pathway analysis confirmed the upregulation of cell growth and proliferation-related processes and downregulation of cell death-related pathways by treatment of MSC-CM in Huh7 cells. In conclusion, these results show that MSCs are enriched in human HCC tumor compartment and could exert trophic effects on tumor cells. Thus, targeting of HCC tumor MSCs may represent a new avenue for therapeutic intervention.

Naïve CD8 T cell activation by liver bone marrow-derived cells leads to a "neglected" IL-2low Bimhigh phenotype, poor CTL function and cell death

BACKGROUND & AIMS

The occurrence of primary CD8 T cell activation within the liver, unique among the non-lymphoid organs, is now well accepted. However, the outcome of intrahepatic T cell activation remains controversial. We have previously reported that activation initiated by hepatocytes results in a tolerogenic phenotype characterized by low expression of CD25 and IL-2, poor cytotoxic T lymphocyte (CTL) function, and excessive expression of the pro-apoptotic protein Bim.

METHODS

To investigate whether this phenotype was due to activation in the absence of co-stimulation, we generated bone marrow (bm) radiation chimeras in which adoptively transferred naïve transgenic CD8 T cells were activated in the presence of co-stimulation by liver bm-derived cells.

RESULTS

Despite expressing pro-inflammatory cytokines, high levels of CD25 and CD54, donor T cells activated by liver bm-derived cells did not produce detectable IL-2 and displayed poor CTL function, suggesting incomplete acquisition of effector function. Simultaneously, these cells expressed high levels of Bim and died by neglect. Transfer of Bim-deficient T cells resulted in increased T cell numbers.

CONCLUSIONS

These results imply that expression of CD25 and CD54 is co-stimulation dependent and distinguishes T cell activated by hepatocytes and liver bm-derived cells. In contrast, low expression of IL-2, poor CTL function and excess Bim production represent a more universal phenotype defining T cells undergoing primary activation by both types of hepatic antigen presenting cells (APC). These results have important implications for transplantation, in which all liver antigen presenting cells contribute to activation of T cells specific for the allograft.

Liver transplantation in autoimmune liver diseases

Liver transplantation is indicated for terminal phases of autoimmune hepatitis, primary biliary cirrhosis and primary sclerosing cholangitis. Indications for transplantation in autoimmune liver diseases are similar to those used in other acute or chronic liver diseases. Therapeutic advances have reduced the need for transplantation for autoimmune hepatitis and primary biliary cirrhosis but not for primary sclerosing cholangitis. Overall, outcomes of transplantation for autoimmune liver diseases are excellent. However, recurrence of autoimmune liver diseases in the allograft has variable impacts on graft and patient survivals. Treatment of recurrent diseases requires changes in immunosuppression or addition of ursodeoxycholic acid. Among autoimmune liver diseases, only autoimmune hepatitis occurs de novo in recipients transplanted for other diseases. Patients transplanted for autoimmune hepatitis or primary sclerosing cholangitis are at risk for reactivation or de novo onset of ulcerative colitis. Better understanding of the pathogenesis of recurrent autoimmune liver diseases is needed to devise effective means of prevention and treatment.