Role of Innate Immunity in Pediatric Post-transplant Idiopathic Liver Fibrosis

Impact of immunosuppression level on liver allograft fibrosis after pediatric liver transplantation: a retrospective cohort study

BACKGROUND

Liver allograft fibrosis (LAF) is prevalent among children with long-term survival after liver transplantation (LT). The authors aimed to identify clinical risk factors, with a focus on the impact of immunosuppression (IS) level in the early post-transplant period on LAF.

METHODS

A retrospective study was conducted on pediatric LT recipients with at least 1-year of follow-up. Cox regression models were used to analyze risk factors associated with LAF, and landmark analysis was used to evaluate the impact of IS level on LAF. Longitudinal analysis was also conducted in patients with paired biopsies.

RESULTS

A total of 139 patients involving 174 liver biopsies were included. With 2.3 to 5.9 years of follow-up, LAF was detected in 91.4% of patients (7.9% were significant), up to 88.2% of whom showed normal liver function. Episodes of acute rejection, biliary complications, cytomegalovirus infection, and prolonged cold ischemia time were independent risk factors. Besides, the risk of LAF in patients with relatively low IS levels at postoperative 1-3, 3-6, 6-12, and 12-36 months was higher than the counterparts. Especially, in patients with relatively high IS levels (mean tacrolimus trough concentration ≥5.1 ng/ml) during postoperative 12-36 months, the risk of LAF was 67% lower in the short future ( P =0.006). In paired analysis, patients with increased IS levels were more likely to achieve fibrosis-reduction (HR=7.53, P =0.025).

CONCLUSIONS

Mild to moderate LAF is common among pediatric LT recipients and can appear early and silently. Maintaining adequate levels of IS during 1-3 years after LT seems crucial to ensure protection against LAF.

Prope tolerance after pediatric liver transplantation: Experience at Shiraz Organ Transplant Center

BACKGROUND

Children receive transplants at a younger age, and the period of immunosuppression therapy may extend over decades. However, immunosuppression seems to be responsible for long-term mortality and morbidity. Pediatric liver transplant recipients can benefit from achieving immune tolerance and the opportunity of freedom from lifelong immunosuppression. This study aimed to investigate the frequency of prope tolerance among pediatric liver transplant recipients and the characteristics of these patients.

METHODS

In this retrospective cohort study of pediatric liver transplant recipients, the medical records of transplant recipients treated at Shiraz Organ Transplant Center between 1994 and 2017 were reviewed. Prope tolerance was defined as normal laboratory values and stable clinical status on low-dose monotherapy. Children treated with low-dose monotherapy were categorized as the prope tolerant group. We compared the characteristics of prope tolerant recipients on low-dose monotherapy with patients on standard immunosuppression, i.e. full-dose tacrolimus plus steroids and mycophenolate mofetil. The data were analyzed with the t-test, chi-squared test, and a Cox proportional hazard model at a 5% significance level in SPSS software version 16.

RESULTS

A total of 585 children with a mean age of 8.32 ± 5.23 years were enrolled. 341 patients were categorized as prope tolerant and 244 comprised the full immunosuppression regimen group. Mean age at transplantation and rejection frequency were lower in the prope tolerant group (p < 0.001, p < 0.001). Based on the underlying diseases, metabolic/genetic, biliary tract, and cryptogenic liver diseases were significantly more prevalent in the prope tolerant group (p < 0.001). However, autoimmune liver disease was found to be more prevalent in the full immunosuppression regimen group. Also, those who received living organs (p = 0.001) and recipients of organs from female donors had a greater likelihood of achieving prope tolerant. According to the multiple Cox regression results, age at transplantation (p = 0.022), rejection frequency (p < 0.001), and autoimmune liver diseases (p = 0.028) had a prognostic effect on prope tolerance.

CONCLUSION

Factors as underlying disease, age at transplantation, and rejection frequency were factors that were predictive of prope tolerance in this sample of children. However, the risk of rejection should be considered during the tapering period.

Long-term liver allograft fibrosis: A review with emphasis on idiopathic post-transplant hepatitis and chronic antibody mediated rejection

Liver transplantation (LT) is a life-saving surgical procedure and the current standard of care for most patients with end stage liver disease. With improvements in organ preservation techniques, perioperative care, and immunosuppression, there is better patient and graft survival following LT, and assessment of the liver allograft in long-term survivors is becoming increasingly important. Recurrent or de novo viral or autoimmune injury remains the most common causes of chronic hepatitis and fibrosis following liver transplantation in adults. However, no obvious cause can be identified in many adults with controlled recurrent disease and the majority of pediatric LT recipients, as they have been transplanted for non-recurrent liver diseases. Serial surveillance liver biopsies post LT have been evaluated in several adult and pediatric centers to identify long-term pathological changes. Pathological findings are frequently present in liver biopsies obtained after a year post LT. The significance of these findings is uncertain as many of these are seen in protocol liver biopsies from patients with clinically good allograft function and normal liver chemistry parameters. This narrative review summaries the factors predisposing to long-term liver allograft fibrosis, highlighting the putative role of idiopathic post-LT hepatitis and chronic antibody mediated rejection in its pathogenesis.

The New Challenge in Pediatric Liver Transplantation: Chronic Antibody-Mediated Rejection

Antibody-mediated rejection (AMR) of liver allograft transplantation was considered as anecdotal for many decades. However recently, AMR has gained clinical awareness as a potential cause of chronic liver injury, leading to liver allograft fibrosis and eventual graft failure. (1) Methods: Literature on chronic AMR (cAMR) in pediatric post-liver transplant patients was reviewed for epidemiologic data, physiopathology, diagnosis, and treatment approaches. (2) Results: Accurate incidence of cAMR in pediatric liver transplantation remains unknown. Diagnostic criteria of cAMR were suggested by the Banff Working Group in 2016 and are based on standardized histopathological findings, C4d staining pattern, associated with the presence of donor-specific antibodies (DSA). Physio-pathological mechanisms are not clear for the technically difficult-to-obtain animal models reproducing cAMR. Treatment protocols are not established, being limited to case reports and case series, based on experience in ABO incompatible transplantation and kidney transplantation. Immunosuppression compliance with adequate dose adjustment may prevent cAMR. Conversion of Cyclosporine to Tacrolimus may improve pathological findings if treated in early phase. The association of steroids, Mycophenolate Mofetil (MMF) and mTOR inhibitors have shown some synergistic effects. Second-line treatments such as intravenous immunoglobulin (IVIG) and plasma exchange may decrease antibody titers based on ABO incompatible transplant protocols. The use of anti-CD20 (Rituximab) and proteasome inhibitors (Bortezomib) is controversial due to the lack of qualified studies. Therefore, multicenter randomized trials are needed to establish the best therapeutic strategy. In refractory cases, re-transplantation is the only treatment for allograft failure. (3) Conclusions: This literature review collects recent clinical, histopathological, and therapeutical advances of cAMR in liver allograft transplantation of pediatric patients. There are many physio-pathological aspects of cAMR to be clarified. Further efforts with multicenter prospective protocols to manage patients with cAMR are needed to improve its outcome.

Crosstalk Between Autophagy and Innate Immunity: A Pivotal Role in Hepatic Fibrosis

Liver fibrosis is a repair process of chronic liver injuries induced by toxic substances, pathogens, and inflammation, which exhibits a feature such as deposition of the extracellular matrix. The initiation and progression of liver fibrosis heavily relies on excessive activation of hepatic stellate cells (HSCs). The activated HSCs express different kinds of chemokine receptors to further promote matrix remodulation. The long-term progression of liver fibrosis will contribute to dysfunction of the liver and ultimately cause hepatocellular carcinoma. The liver also has abundant innate immune cells, including DCs, NK cells, NKT cells, neutrophils, and Kupffer cells, which conduct complicated functions to activation and expansion of HSCs and liver fibrosis. Autophagy is one specific type of cell death, by which the aberrantly expressed protein and damaged organelles are transferred to lysosomes for further degradation, playing a crucial role in cellular homeostasis. Autophagy is also important to innate immune cells in various aspects. The previous studies have shown that dysfunction of autophagy in hepatic immune cells can result in the initiation and progression of inflammation in the liver, directly or indirectly causing activation of HSCs, which ultimately accelerate liver fibrosis. Given the crosstalk between innate immune cells, autophagy, and fibrosis progression is complicated, and the therapeutic options for liver fibrosis are quite limited, the exploration is essential. Herein, we review the previous studies about the influence of autophagy and innate immunity on liver fibrosis and the molecular mechanism to provide novel insight into the prevention and treatment of liver fibrosis.