Immunosuppressive activity of serum taken from a liver transplant recipient after withdrawal of immunosuppressants

Proteomics in Liver Transplantation: A Systematic Review

Background

Although proteomics has been employed in the study of several models of liver injury, proteomic methods have only recently been applied not only to biomarker discovery and validation but also to improve understanding of the molecular mechanisms involved in transplantation.

Methods

The study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology and the guidelines for performing systematic literature reviews in bioinformatics (BiSLR). The PubMed, ScienceDirect, and Scopus databases were searched for publications through April 2020. Proteomics studies designed to understand liver transplant outcomes, including ischemia-reperfusion injury (IRI), rejection, or operational tolerance in human or rat samples that applied methodologies for differential expression analysis were considered.

Results

The analysis included 22 studies after application of the inclusion and exclusion criteria. Among the 497 proteins annotated, 68 were shared between species and 10 were shared between sample sources. Among the types of studies analyzed, IRI and rejection shared a higher number of proteins. The most enriched pathway for liver biopsy samples, IRI, and rejection was metabolism, compared to cytokine-cytokine receptor interactions for tolerance.

Conclusions

Proteomics is a promising technique to detect large numbers of proteins. However, our study shows that several technical issues such as the identification of proteoforms or the dynamic range of protein concentration in clinical samples hinder the successful identification of biomarkers in liver transplantation. In addition, there is a need to minimize the experimental variability between studies, increase the sample size and remove high-abundance plasma proteins.

Translational medical research and liver transplantation: systematic review

Translational medicine has become a priority, but there is still a big difference between the arrival of new treatments and investment. Basic science should not be neglected because the translation from basic research is not sustained in the absence of basic research. The purpose of this literature review was to analyze the translational medicine in the liver transplant field: liver ischemia-reperfusion injury (IRI), immunosuppression, clinical and surgical complications, small-for-size syndrome (SFSS), rejection, and ongoing innovations (liver machine, liver preservation, artificial livers, and regenerative medicine). We performed a systematic literature review that were updated in October 2016. The searches were performed in the Cochrane Central Register of Controlled Trials and Review, PubMed/Medline, Embase, and LILACS databases. All the selected studies on the management of translational medical research in liver transplantation (LT) were analyzed. Initially the search found 773 articles. Methodological viewing and analysis of the articles, followed by the application of scientific models, including translational medicine in the liver transplant field. In conclusions, this review demonstrates the application of scientific research with translation medical benefits regarding the LT. The literature has a great tendency, improvements and investments in the study of translational medicine in LT. Innovative studies and technologies from basic science help to clarify clinical doubts. Moreover, evidence increases the importance of scientific research in quality of clinical practice care.

Proteomics in transplantation

Proteomics and biochemical profiling have emerged as exciting and powerful tools in clinical biomarker research. In the field of transplantation, proteomics aims not only at developing noninvasive means for immune monitoring but also to gain mechanistic insights into the pathophysiology of the alloimmune response and hence defining new therapeutic targets. This chapter provides an overview of proteomic biomarker-driven approaches and its underlying concepts and discusses the advantages, clinical implications, challenges, and limitations of this novel modality as it relates to solid organ transplantation.

Clinical operational tolerance in liver transplantation: state-of-the-art perspective and future prospects

BACKGROUND

Liver transplantation is the definite treatment for end-stage liver diseases with satisfactory results. However, untoward effects of life-long immunosuppression prevent the development of alternative strategies to achieve better long-term outcome. Achieving clinical operational tolerance is the ultimate goal.

DATA SOURCES

A PubMed and Google Scholar search using terms: "immune tolerance", "liver transplantation", "clinical trial", "operational tolerance" and "immunosuppression withdrawal" was performed, and relevant articles published in English in the past decade were reviewed. Full-text publications relevant to the field were selected and relevant articles from reference lists were also included. Priority was given to those articles which are relevant to the review.

RESULTS

Because of the inherent tolerogenic property, around 20%-30% of liver transplantation recipients develop spontaneous operational tolerance after immunosuppression withdrawal, and the percentage may be even higher in pediatric living donor liver transplantation recipients. Several natural killer and gammadeltaT cell related markers have been identified to be associated with the tolerant state in liver transplantation patients. Despite the progress, clinical operational tolerance is still rare in liver transplantation. Reprogramming the recipient immune system by creating chimerism and regulatory cell therapies is among newer promising means to achieve clinical liver transplantation tolerance in the future.

CONCLUSION

Although clinical operational tolerance is still rare in liver transplantation recipients, ongoing basic research and collaborative clinical trials may help to decipher the mystery of transplantation tolerance and extend the potential benefits of drug withdrawal to an increasing number of patients in a more predictable fashion.

Recent advances in biomarker discovery in solid organ transplant by proteomics

The identification and clinical use of more sensitive and specific biomarkers in the field of solid organ transplantation is an urgent need in medicine. Solid organ transplantation has seen improvements in the short-term survival of transplanted organs due to recent advancements in immunosuppressive therapy. However, the currently available methods of allograft monitoring are not optimal. Recent advancements in assaying methods for biomolecules such as genes, mRNA and proteins have helped to identify surrogate biomarkers that can be used to monitor the transplanted organ. These high-throughput 'omic' methods can help researchers to significantly speed up the identification and the validation steps, which are crucial factors for biomarker discovery efforts. Still, the progress towards identifying more sensitive and specific biomarkers remains a great deal slower than expected. In this article, we have evaluated the current status of biomarker discovery using proteomics tools in different solid organ transplants in recent years. This article summarizes recent reports and current status, along with the hurdles in efficient biomarker discovery of protein biomarkers using proteomics approaches. Finally, we will touch upon personalized medicine as a future direction for better management of transplanted organs, and provide what we think could be a recipe for success in this field.

Tolerance in liver transplantation

Operational tolerance (OT) in liver transplant patients occurs much more frequently than OT of other transplanted organs; however the rate of OT varies considerably with the centre and patient population. Rates of OT range from 15% of the total liver transplant (LTX) patient population down to less than 5%. This review examines the reports of liver OT and compares the factors that could contribute to this variation. Multiple factors were examined, including the time from transplantation when weaning of immunosuppression (IS) was commenced, the rapidity of weaning, the contribution of maintenance and induction IS and the patient population transplanted. The approaches that might be used to increase the likelihood of OT are discussed and the approaches to monitoring OT in LTX patients are reviewed.

Finding the right time for weaning off immunosuppression in solid organ transplant recipients

Solid organ transplantation (SOT) requires lifelong immunosuppression (IS) to prevent rejection and graft loss. The currently adopted immunosuppressive protocols are numerous and are based on the administration of at least two molecules with diverse mechanisms of action. Owing to the fact that the majority of immunosuppressants act non-selectively, the immune system is normally oversuppressed, and as a result is less able to both defend the host against infection and to control the spread of malignant cells. Consequently, long-term IS is burdened by chronic toxicity, which may be highly invalidating and may significantly influence patient's quality of life, compliance to treatment, overall success rate, and patient and graft survival. In an ideal scenario, SOT recipients should initially receive just enough IS to favor the onset of clinical operational tolerance (COT), a condition where the immune system of the host does not attack the graft in the absence of any immunosuppressant. COT has been documented after liver transplantation (LT) and renal transplantation (RT). First, COT was accidentally detected in patients who were nonadherent to treatment and who spontaneously decided to stop all IS without any medical guidance or surveillance. Later, it was described in recipients who required IS withdrawal following the occurrence of malignant diseases. Based on strikingly convincing experimental data, several tolerogenic protocols have recently been applied in patients but overall the results have been disappointing. The current literature demonstrates that COT can be safely achieved in stable LT recipients, with completely different strategies. Importantly, the onset of an episode of acute rejection during the attempt of IS withdrawal would not worsen the clinical outcome. On the contrary, COT remains a major challenge after RT because the onset of acute rejection will substantiate in graft loss. Currently, a major field of investigation aims to define markers of COT, which will allow the selection of individuals who are more prone to develop COT. Preliminary results in both RT and LT have just been announced; however, these markers will require validation in prospective studies.

Interpreting the proteome and peptidome in transplantation

Publication of the human proteome has prompted efforts to develop high-throughput techniques that can catalogue and quantify proteins and peptides present in different tissue types. The field of proteomics aims to identify, quantify, analyze, and functionally define a large number of proteins in cellular processes in different disease states on a global scale. Peptidomics, a newer name in the -omics world, measures and identifies naturally occurring low molecular weight peptides, also providing an insight into enzymatic processes and molecular events occurring in the system of interest. One area of major interest is the use of proteomics to identify diagnostic and prognostic biomarkers for different diseases as well as for various clinical phenotypes in organ transplantation that can advance targeted therapy for various forms of graft injury. Outcomes in organ transplantation can be potentially improved by identifying noninvasive biomarkers that will serve as triggers that predate graft injury, and can offer a means to customize patient treatment by differentiating among causes of acute and chronic graft injury. Proteomic and peptidomic strategies can be harnessed for frequent noninvasive measurements in tissue fluids, allowing for serial monitoring of organ disease. In this review, we describe the basic techniques used in proteomic and peptidomic approaches, point out special considerations in using these methods, and discuss their applications in recently published studies in organ transplantation.

Operational tolerance after liver transplantation

The achievement of an immunosuppression (IS)-free state after transplantation represents the ultimate goal of any immunosuppressive regimen. While clinical operational tolerance (COT) remains the exception after other types of solid organ transplantation, several cases of COT have been described after liver transplantation (LT). Overall, the experience gained so far worldwide demonstrates that COT can be achieved safely in one quarter of selected individuals, irrespective of the immunological background of donor and recipient, patient age, indication for LT, study endpoint, length of the weaning period and of pre/post-weaning follow-up, presence or not of chimerism. However, most transplant physicians still believe that the achievement of COT is still out of reach for the majority of LT recipients because of the potential risk for transplant survival, the non-randomized nature of most of the studies reported so far, and the selective nature of the patients enrolled in such studies, making them non-representative of the whole population of LT recipients. Despite these concerns, the present article demonstrates that this attitude is potentially no longer justified, given the growing evidence that a permanent and stable IS-free state can be achieved in a proportion of individuals who have received a LT for non-immune mediated liver diseases.

The Tor Vergata weaning off immunosuppression protocol in stable HCV liver transplant patients: the updated follow up at 78 months

BACKGROUND

We report the update of the Tor Vergata immunosuppression (IS) weaning protocol in stable hepatitis C virus (HCV) liver transplant (LT) recipients.

METHODS

The weaning off IS was attempted in 34 patients who had received a LT 63.5+/-20.1 month earlier, for HCV-related end stage liver disease. Patients were observed over a period of 6.5 years. During this time, yearly protocol liver biopsies were performed. Primary endpoints were determined as the feasibility of weaning off IS and its impact on the long term disease progression. Secondary endpoints were defined as the impact on patient morbidity and quality of life.

RESULTS

Of the 8 originally tolerant patients, 7 remain alive and in good condition, while 1 died of severe HCV recurrence 10 years post-LT and 6 years after complete removal of IS. Four out of 26 intolerant individuals died of HCV recurrence (2x), lung carcinoma (1x) and acute myocardial infarction (1x), after a mean follow up period from LT of 115 (range 100-124). The 10-year survival from LT was comparable (89% vs. 87.5%). Liver graft pathology showed no significant differences between the two groups in terms of staging, fibrosis progression rate, and grading. Quantitative HCV RNA assay showed a significant non-logarithmic difference between the two groups (p = 0.03). The two groups were comparable in terms of liver function tests and lipid profile, whereas they differed with regards to glycaemia. While all tolerant individuals were euglicemic, 11 intolerant individuals developed new onset diabetes that required specific treatment (p = 0.03). Finally, significantly more intolerant patients are suffering from either cardiovascular (14/22 vs. 0/7, p = 0.01) or infectious diseases (13/22 vs. 0/7, p = 0.01).

CONCLUSIONS

After a 6.5-year follow up, the complete withdrawal of IS in HCV LT recipient remains safe and beneficial to patients, because it reduces the IS-related morbidity and increases the quality of life. The impact on HCV disease recurrence is less marked than after 3.5 years.