Immunosuppressive enzyme-responsive nanoparticles for enhanced accumulation in liver allograft to overcome acute rejection

Acute rejection is a life-threatening complication after liver transplantation. Immunosuppressants such as tacrolimus are used to inhibit acute rejection of liver grafts in clinic. However, inefficient intragraft accumulation may reduce the therapeutic outcomes of tacrolimus. Here, an enzyme-responsive nanoparticle is developed to selectively enhance the accumulation of tacrolimus in liver allograft through enzyme-induced aggregation to refine immunotherapeutic efficacy of tacrolimus. The nanoparticles are composed of amphiphilic tacrolimus prodrugs synthesized by covalently conjugating tacrolimus and matrix metalloproteinase 9 (MMP9)-cleavable peptide-containing methoxy poly (ethylene glycol) to poly (l-glutamic acid). Upon exposure to MMP9, which is overexpressed in rejected liver allografts, the nanoparticles undergo a morphological transition from spherical micellar nanoparticles to microscale aggregate-like scaffolds. Intravenous administration of MMP9-responsive nanoparticles into a rat model of acute liver graft rejection results in enhanced nanoparticle accumulation in allograft as compared to nonresponsive nanoparticles. Consequently, the MMP9-responsive nanoparticles significantly inhibit intragraft inflammatory cell infiltration and proliferation, maintain intragraft immunosuppressive environment, alleviate graft damage, improve liver allograft function, abate weight loss and prolong recipient survival. This work proves that morphology-switchable enzyme-responsive nanoparticles represent an innovative strategy for selectively enhancing intragraft accumulation of immunosuppressive agents to improve treatment of liver allograft rejection.

Prediction of late allograft dysfunction following liver transplantation by immunological blood biomarkers

BACKGROUND

An accelerated course of hepatic fibrosis may occur in liver transplantation (LT) patients despite normal or slightly abnormal liver blood tests.

AIM

To identify screening tools based on blood biomarkers to predict late allograft dysfunction in LT recipients.

METHODS

174 LT recipients were enrolled. Liver biopsy, liver functional tests, cytokine quantitation in serum, as well as soluble MHC class I polypeptide-related sequence A and B (sMICA/sMICB) and soluble UL16 binding protein 2 (sULBP2) were performed.

RESULTS

Patients with late graft dysfunction had a significantly higher donor age, lower albumin level, higher alanine (ALT) and aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT), total bilirubin and alkaline phosphatase (ALP), higher sMICA, sULBP2, higher interleukin (IL) 6, interferon γ and lower IL10 in serum as compared to recipients without allograft dysfunction. In order to provide a better statistical accuracy for discriminating 5-year allograft dysfunction from other less progressive subtype of allograft injury, we established a predictive model, based on 7 parameters (serum ALP, ALT, AST, GGT, sMICA, IL6 and albumin) which provided an Area Under the Receiver Operating Characteristics (AUROC) curve of 0.905.

CONCLUSIONS

Blood-based biomarkers can significantly improve prediction of late liver allograft outcome in LT patients. The new developed score comprising serum parameters, with an excellent AUROC, can be reliably used for diagnosing late allograft dysfunction in transplanted patients.

The Immunological Basis of Liver Allograft Rejection

Liver allograft rejection remains a significant cause of morbidity and graft failure in liver transplant recipients. Rejection is caused by the recognition of non-self donor alloantigens by recipient T-cells. Antigen recognition results in proliferation and activation of T-cells in lymphoid tissue before migration to the allograft. Activated T-cells have a variety of effector mechanisms including direct T-cell mediated damage to bile ducts, endothelium and hepatocytes and indirect effects through cytokine production and recruitment of tissue-destructive inflammatory cells. These effects explain the histological appearances of typical acute T-cell mediated rejection. In addition, donor specific antibodies, most typically against HLA antigens, may give rise to antibody-mediated rejection causing damage to the allograft primarily through endothelial injury. However, as an immune-privileged site there are several mechanisms in the liver capable of overcoming rejection and promoting tolerance to the graft, particularly in the context of recruitment of regulatory T-cells and promotors of an immunosuppressive environment. Indeed, around 20% of transplant recipients can be successfully weaned from immunosuppression. Hence, the host immunological response to the liver allograft is best regarded as a balance between rejection-promoting and tolerance-promoting factors. Understanding this balance provides insight into potential mechanisms for novel anti-rejection therapies.

The Human Immune Response to Cadaveric and Living Donor Liver Allografts

The liver is an important contributor to the human immune system and it plays a pivotal role in the creation of both immunoreactive and tolerogenic conditions. Liver transplantation provides the best chance of survival for both children and adults with liver failure or cancer. With current demand exceeding the number of transplantable livers from donors following brain death, improved knowledge, technical advances and the desire to prevent avoidable deaths has led to the transplantation of organs from living, ABO incompatible (ABOi), cardiac death donors and machine based organ preservation with acceptable results. The liver graft is the most well-tolerated, from an immunological perspective, of all solid organ transplants. Evidence suggests successful cessation of immunosuppression is possible in ~20–40% of liver transplant recipients without immune mediated graft injury, a state known as “operational tolerance.” An immunosuppression free future following liver transplantation is an ambitious but perhaps not unachievable goal. The initial immune response following transplantation is a sterile inflammatory process mediated by the innate system and the mechanisms relate to the preservation-reperfusion process. The severity of this injury is influenced by graft factors and can have significant consequences. There are minimal experimental studies that delineate the differences in the adaptive immune response to the various forms of liver allograft. Apart from ABOi transplants, antibody mediated hyperacute rejection is rare following liver transplant. T-cell mediated rejection is common following liver transplantation and its incidence does not differ between living or deceased donor grafts. Transplantation in the first year of life results in a higher rate of operational tolerance, possibly due to a bias toward Th2 cytokines (IL4, IL10) during this period. This review further describes the current understanding of the immunological response toward liver allografts and highlight the areas of this topic yet to be fully understood.

Non-Invasive Assessment of Graft Fibrosis After Living Donor Liver Transplantation: Is There Still a Role for Liver Biopsy?

Non-invasive methods have evolved as a surrogate for liver biopsy such as indirect markers (aspartate transaminase to platelet ratio index, fibro-α score), transient elastography (TE), and magnetic resonance elastography (MRE). The aim of this study is to prospectively compare the value of MRE, TE, and indirect markers in detecting and staging allograft fibrosis compared to liver biopsies in patients who have undergone living donor liver transplantation for complications related to hepatitis C virus. A total of 31 living donor liver transplantation recipients with hepatitis C virus recurrence underwent a liver biopsy, TE, and MRE within 3 months of a liver biopsy. Fibrosis was assessed according to the biopsy and staged according to Metavir criteria. There was a significant correlation between both MRE and fibro-α scores, as well as histologic classification by liver biopsy (P = .02, .002). The diagnostic accuracy of MRE and fibro-α scores in diagnosing significant fibrosis (F ≥ 3) was measured as the area under the curve (.708 and .833, respectively). Both methods showed good diagnostic performance. TE and aspartate transaminase to platelet ratio index were insignificantly correlated with the degree of fibrosis in liver biopsy (P value of .134, .535). At a cutoff value of 5.5 kPa, MRE predicted graft fibrosis (Metavir stage ≥ 3) with 71.43% sensitivity, 75% specificity, 45.5% positive predictive value, and 90% negative predictive value; at a cutoff value  > 1.47, fibro-α scores predicted significant graft fibrosis (Metavir stage ≥ 3) with 85.7% sensitivity and 70.83% specificity, with a positive predictive value of 46.2% and a negative predictive value of 94.4%. These data suggest that non-invasive methods could be considered a reliable tool in assessing significant graft fibrosis post-living donor liver transplantation.

Transient elastography for non-invasive evaluation of post-transplant liver graft fibrosis in children

As graft survival in pediatric LT is often affected by progressive fibrosis, numerous centers carry out protocol liver biopsies. Follow-up biopsy protocols differ from center to center, but all biopsies are progressively spaced out, as time from transplant increases. Therefore, there is a need for non-invasive techniques to evaluate graft fibrosis progression in those children who have no clinical or serological signs of liver damage. Indirect markers, such as the APRI, should be relied on with caution because their sensitivity in predicting fibrosis can be strongly influenced by the etiology of liver disease, severity of fibrosis, and patient age. A valid alternative could be TE, a non-invasive technique already validated in adults, which estimates the stiffness of the cylindrical volume of liver tissue, 100-fold the size of a standard needle biopsy sample. The aims of this study were to evaluate the reliability of TE in children after LT and to compare both the TE and the APRI index results with the histological scores of fibrosis on liver biopsies. A total of 36 pediatric LT recipients were studied. All patients underwent both TE and biopsy within a year (median interval -0.012 months) at an interval from LT of 0.36 to 19.47 years (median 3.02 years). Fibrosis was assessed on the biopsy specimens at histology and staged according to METAVIR. There was a statistically significant correlation between TE stiffness values and METAVIR scores (P = .005). The diagnostic accuracy of TE for the diagnosis of significant fibrosis (F ≥ 2) was measured as the area under the curve (AUROC = 0.865), and it demonstrated that the method had a good diagnostic performance. APRI was not so accurate in assessing graft fibrosis when compared to METAVIR (AUROC = 0.592). A liver stiffness cutoff value of 5.6 kPa at TE was identified as the best predictor for a significant graft fibrosis (METAVIR F ≥ 2) on liver biopsy, with a 75% sensitivity, a 95.8% specificity, a 90% positive predictive value, and an 88.5% negative predictive value. These data suggest that TE may represent a non-invasive, reliable tool for the assessment of graft fibrosis in the follow-up of LT children, alerting the clinicians to the indication for a liver biopsy, with the aim of reducing the number of protocol liver biopsies.

Immunosuppression status of liver transplant recipients with hepatitis C affects biopsy-proven acute rejection

Background/Aims

The relationship between patient survival and biopsy-proven acute rejection (BPAR) in liver transplant recipients with hepatitis C remains unclear. The aims of this study were to compare the characteristics of patients with and without BPAR and to identify risk factors for BPAR.

Methods

We retrospectively reviewed the records of 169 HCV-RNA-positive patients who underwent LT at three centers.

Results

BPAR occurred in 39 (23.1%) of the HCV-RNA-positive recipients after LT. The 1-, 3-, and 5-year survival rates were 92.1%, 90.3%, and 88.5%, respectively, in patients without BPAR, and 75.7%, 63.4%, and 58.9% in patients with BPAR (P<0.001). Multivariate analyses showed that BPAR was associated with the non-use of basiliximab and tacrolimus and the use of cyclosporin in LT recipients with HCV RNA-positive.

Conclusion

The results of the present study suggest that the immunosuppression status of HCV-RNA-positive LT recipients should be carefully determined in order to prevent BPAR and to improve patient survival.

From immunosuppression to tolerance

The past three decades have seen liver transplantation becoming a major therapeutic approach in the management of end-stage liver diseases. This is due to the dramatic improvement in survival after liver transplantation as a consequence of the improvement of surgical and anaesthetic techniques, of post-transplant medico-surgical management and of prevention of disease recurrence and other post-transplant complications. Improved use of post-transplant immunosuppression to prevent acute and chronic rejection is a major factor in these improved results. The liver has been shown to be more tolerogenic than other organs, and matching of donor and recipients is mainly limited to ABO blood group compatibility. However, long-term immunosuppression is required to avoid severe acute and chronic rejection and graft loss. With the current immunosuppression protocols, the risk of acute rejection requiring additional therapy is 10-40% and the risk of chronic rejection is below 5%. However, the development of histological lesions in the graft in long-term survivors suggest atypical forms of graft rejection may develop as a consequence of under-immunosuppression. The backbone of immunosuppression remains calcineurin inhibitors (CNI) mostly in association with steroids in the short-term and mycophenolate mofetil or mTOR inhibitors (everolimus). The occurrence of post-transplant complications related to the immunosuppressive therapy has led to the development of new protocols aimed at protecting renal function and preventing the development of de novo cancer and of dysmetabolic syndrome. However, there is no new class of immunosuppressive drugs in the pipeline able to replace current protocols in the near future. The aim of a full immune tolerance of the graft is rarely achieved since only 20% of selected patients can be weaned successfully off immunosuppression. In the future, immunosuppression will probably be more case oriented aiming to protect the graft from rejection and at reducing the risk of disease recurrence and complications related to immunosuppressive therapy. Such approaches will include strategies aiming to promote stable long-term immunological tolerance of the liver graft.

Pre-transplant left ventricular diastolic dysfunction is associated with post transplant acute graft rejection and graft failure

INTRODUCTION

Acute cellular rejection (ACR) is a significant cause of morbidity and graft failure in liver transplant recipients (LTR). Diastolic dysfunction (DD) is frequently present in patients with cirrhosis undergoing liver transplantation. However, it is unclear if DD leads to ACR.

METHODS

Data was collected retrospectively for consecutive LTR between January 2000 and December 2010. Demographic data and mortality related data was obtained from social security index. Primary outcome was biopsy proven ACR. Graft failure and all-cause mortality were also evaluated. DD was evaluated as a predictor of these outcomes. Other echocardiographic indices were also assessed as predictors of ACR by using Cox proportional hazard modeling adjusted for covariates.

RESULTS

A total of 970 LTR (mean age 53.2 ± 10 years, women 34.6 % and white 64.5 %) were followed for 5.3 ± 3.4 years. Patients with DD (n = 145, 14.9 %) were significantly more likely to develop ACRs (HR 10.56; 95 % CI 6.78-16.45, p value = 0.0001) as well as graft failure (HR 2.09; 95 % CI 1.22-3.59, p value = 0.007) and all-cause mortality (HR 1.52; 95 % CI 1.08-2.13, p = 0.01). There was an increase in the risk of these outcomes with worsening of DD, when adjusted for various risk factors such as donor and recipient age, gender, race, Framingham risk score, pre-transplant MELD, transplant etiology and cold ischemia time.

CONCLUSION

Pre-transplant DD is significantly associated with increased risk of allograft rejection, graft failure and mortality. This signifies the importance of cardiac evaluation during the pre-transplant period.