Finding Solutions to Improving Long-Term Outcomes

Finding Solutions to Improving Long-Term Outcomes

Imran Javed, MD

University of Washington Medical Center, Seattle, Washington

The ultimate goal of organ transplantation is to improve quality of life and life expectancy. Thus, long-term allograft survival always has been a prime topic of discussion in the transplant community. The exact mechanism of long-term renal graft loss is poorly understood, although it is believed that alloantigens play an important role. Chronic renal graft loss or transplant nephropathy is associated with chronic fibrosis on allograft biopsy. The introduction of new immunosuppressants has lessened the rate of early acute graft rejection. However, late graft loss is still common and can lead to graft failure and the need for a second organ transplant.

Imran Javed, MDProtocol biopsies performed 1 and 5 years following renal transplant have shown that some grafts undergo chronic changes that limit their long-term survival. Kidney-transplant recipients having fewer microscopic changes over the first year post transplant tend to have better graft function over 5 years.

The many factors that affect graft survival must be addressed and managed, and more trials involving close surveillance of kidney-transplant recipients must be performed. In addition, primary pathologies or comorbidities such as diabetes and hypertension must be well controlled, new drugs must be tested carefully for their effect on transplanted tissues, and screening tools (namely, biomarkers) must be scrutinized in the context of early changes that slowly affect the allograft.

Organ transplantation is intended to improve the survival and quality of life of patients with end-stage organ disease. The allograft is always considered to be a foreign tissue by the host immune system. Therefore, chronic graft rejection and chronic graft loss are still possible, even though patients are adhering to their maintenance immunosuppressant regimens. Chronic graft rejection is relatively less defined than is hyperacute or acute rejection. It probably is caused by multiple factors, which include both antibodies and lymphocytes. A definitive diagnosis of chronic rejection is possible by analyzing a tissue sample that shows fibrosis (scarring) and microscopic vascular injury in the substance of the kidney. On the other hand, livers with chronic rejection have fewer bile ducts on biopsy (ie, vanishing bile duct syndrome).

An early-morning symposium held during the 2014 World Transplant Congress focused on our current understanding of long-term renal graft loss. It was moderated by Vivekanand Jha, MBBS, MD, DM, PhD, Executive Director of The George Institute for Global Health in India and Professor of Nephrology at the University of Oxford in the United Kingdom, and Helio Tedesco-Silva, MD, of the Hospital do Rim e Hipertensão in São Paulo, Brazil.

PATHOLOGY OF LONG-TERM RENAL GRAFT LOSS
Based on a presentation by Bruce Kaplan, MD, Kathy and Harry Jentsch Professor of Medicine and Professor of Surgery and Pharmacology, University of Arizona College of Medicine, Tucson, Arizona.

The pathogenesis of chronic allograft rejection—also known as chronic rejection, transplant nephropathy, chronic renal allograft dysfunction, transplant glomerulopathy, chronic allograft injury, and chronic renal allograft nephropathy—is unknown. Chronic allograft rejection is the second most common cause of renal graft loss, following death of a patient with a working graft.

On tissue biopsy, chronic renal allograft rejection is associated with interstitial fibrosis, tubular atrophy, and glomerular changes (eg, glomerular double contours, peritubular capillary basement membrane multilayering, and/or fibrous intimal thickening in arteries). The Banff criteria for chronic allograft nephropathy are listed in Table 1.


Chronic renal allograft rejection also is characterized by complement split product positivity (C4d+) and the presence of circulating antidonor antibodies. However, these graft changes can present with organ dysfunction despite biopsy findings that are negative for C4d or serum that tests negative for donor-specific antibody (DSA).

In the past, lowering the rate of acute cell-mediated rejection (ACR) episodes was believed to impact long-term survival significantly. The development of protective protocols decreased the rate of ACR, particularly during the first year post transplant. However, Lamb et al1 found that decreasing the frequency of ACR to < 10% did not improve long-term outcomes.

Interstitial fibrosis and tubular atrophy presenting with interstitial inflammation are much stronger predictors of graft loss than is interstitial fibrosis or tubular atrophy alone. The multicenter Long-Term Deterioration of Kidney Allograft Function study, which was designed to identify the causes of late allograft dysfunction, showed that interstitial inflammation in areas of interstitial fibrosis and tubular atrophy was predictive of reduced time to graft failure, even after adjustment for serum creatinine level.2

Fibrosis also has been linked to the use of calcineurin inhibitors (CNIs) for immunosuppression in transplant recipients. It has been hypothesized that this slowly progressive change may be a manifestation of CNI toxicity related to the use of tacrolimus. However, CNI toxicity usually is the diagnosis of exclusion on kidney allograft biopsy, since associated changes are nonspecific.3

Seeking Protocols to Save Grafts
Several studies have investigated differences in long-term survival after kidney transplant when patients underwent surveillance biopsy or a biopsy on allograft dysfunction.

El-Zoghby et al4 concluded that not all grafts experience chronic injury, and different causes may be identified among those that do. Glomerulopathy was the leading cause of graft failure, whereas alloimmunity was the mechanism for the kidney graft loss. The fibrosis was not related to CNI toxicity.

For most biopsies performed at the time of allograft dysfunction, DSA appears to be a more common cause of later graft loss, although inflammation also may continue to play a role.

At the Mayo Clinic, Stegall and colleagues5 analyzed the prevalence and progression of histologic changes in protocol surveillance biopsies 1 and 5 years after kidney transplantation in 447 patients who received solitary kidney transplants between 1998 and 2004. All patients used tacrolimus for maintenance immunosuppression. Moderate-to-severe interstitial fibrosis was uncommon at both 1 and 5 years (13% and 17%, respectively). Mild fibrosis involving ≤ 25% of the interstitium was relatively common (37% at 1 year), but it rarely progressed to more severe forms by 5 years.

Some surveillance biopsy studies also suggested intragraft inflammation linked to fibrosis and graft loss. Subclinical inflammation was seen in ≤ 15% of renal allografts at 1 year and was related to the development of interstitial fibrosis or graft loss.6,7

It is unclear whether this subclinical inflammation stimulates cell-mediated alloimmunity against the allograft that may not meet Banff criteria for ACR.7 An increased rate of transplant glomerulopathy also has been seen in grafts with prior subclinical inflammation.8 Thus, there may be a link between the cellular alloimmune response and the development of DSAs.

If subclinical inflammation occurring early after transplantation reflects a failure of conventional immunosuppression to control the alloimmune response, treatment trials should seek to prevent or reverse this process. By doing so, long-term graft survival may be achieved.

Role of Alloantibodies
Chronic allograft nephropathy is associated with an alloimmune response. When biopsies are performed to evaluate new-onset graft dysfunction or proteinuria > 5 years after transplantation, results consistently indicate a major role for antibody-mediated late graft injury. In the Deterioration of Kidney Allograft Function (DeKAF) trial,9 patients underwent biopsies an average of 7.5 ± 6.0 years post transplant to look for allograft dysfunction. Patients with DSAs and/or C4d+ status were at substantial risk of graft failure over 2 years following biopsy. The severity of clinical injury correlated with the intensity of the antibody response.

CAUSES OF LONG-TERM GRAFT FAILURE AFTER LONG-TERM GRAFT SURVIVAL
Based on a presentation by Donald E. Hricik, MD, Professor of Medicine and Chief of the Division of Nephrology, Case Western Reserve University School of Medicine, Cleveland, Ohio.

The exact mechanism of chronic graft loss in unknown. However, a DSA-mediated immune response appears to be a key mechanism in the process of fibrosis. The causes/contributing factors of long-term graft failure may be organized into four categories: (1) quality of graft and organ matching (alloantigen-dependent), (2) early rejection, (3) maintenance immunosuppression and medication adherence, and (4) recurrence of primary disease and control of comorbidities.

Quality of Graft and Organ Matching
Generally, younger grafts behave better than do older ones. Older living donor kidney allografts do not perform better than do standard-criteria donor organs,10 but overall living-donor kidney transplants have a greater long-term graft survival rate than do deceased-donor kidneys taken primarily from brain-dead donors.

Expanded-criteria donors are either > 60 years of age or meet two of the following three criteria: age = 50–59 years, history of hypertension, or serum creatinine level > 1.5 mg/dL. Kidney grafts from these types of donors tend to have poorer survival than do grafts from standard-criteria donors.

Although it is believed that kidney outcomes suffer with donations after cardiac death (DCD), improved outcomes of DCD kidney grafts have been seen over the past few years. According to the United Network for Organ Sharing database, 5-year post-transplant outcomes of DCD kidneys, in terms of patient (81%) and graft (67%) survival, are not significantly different from those of kidneys from brain-deceased donors.

Human leukocyte antigen (HLA) matching is critical and outweighs the detrimental effect of prolonged cold ischemia time on graft survival. Regardless of the quality of donor organs, ischemia time is an independent factor for short- and long-term graft survival. The only way to reduce the impact of prolonged ischemia time resulting from transportation of the organ is to have better HLA typing, which results in long-term graft-survival benefits.

Sensitization
The more an organ donor is exposed to antigens, the greater the chance that allograft rejection will occur, particularly in kidney-transplant recipients who have high panel-reactive antibody levels. Preformed HLA alloantibodies (DSAs), and particularly those of class II, also are associated with decreased allograft outcomes. Using highly sensitive HLA-specific assays, Lefaucheur and others11 evaluated allograft survival at 8 years among 43 patients with and 194 patients without preformed DSAs. Allograft survival was 68% and 77%, respectively, whereas the incidence of antibody-mediated rejection was nine times higher for those with preformed DSAs.

Early Graft Rejection
Acute graft rejection within 1 year of transplant has an adverse impact on long-term graft survival. This consequence can be minimized by choosing a strong immunosuppressive induction agent. Use of antithymocyte immunoglobulin (ATG) is beneficial as an induction immunosuppressant for kidney transplantation, particularly for patients with high panel-reactive antibody levels, African-Americans, and recipients of a second kidney allograft.

Maintenance Immunosuppression and Adherence
Although long-term use of tacrolimus induces hyalinosis and fibrosis in the renal allograft,12 there is no better choice currently for maintenance immunosuppression. Sirolimus worsens proteinuria.

Nonadherence is another important issue that must be addressed. Patients who do not adhere to immunosuppressive treatment begin to suffer failure of graft function. Two- or three-times-daily dosing sometimes is used to minimize gastrointestinal side effects, but these regimens increase the patient's burden. Teenagers and young adults tend to be less adherent than older patients.

The recent advent of a once-daily formulation of tacrolimus appears to improve adherence while retaining the drug's effectiveness. More research is needed to develop similar slow-release immunosuppressants that will allow patients to be dosed just once daily. In addition, medications that combine two immunosuppressants in one tablet or capsule to simplify dosing may be helpful to promote adherence.

Recurrence of Primary Disease or Comorbidities
If a primary disease is not well controlled, early changes in the allograft will result. The leading cause of end-stage renal failure is diabetes; hypertension is another main player in kidney disease. If not well controlled, these diseases can damage an allograft.

A multivariate analysis by Mange et al13 showed that 1 year following transplant, an increase of 10 mm Hg in mean arterial blood pressure resulted in a 1.3-fold higher risk of allograft failure. The presence of protein in the urine also is a predictor of long-term graft loss. In addition, elevated homocysteine levels are associated with decreased allograft survival. In a prospective study of 733 renal transplant patients, Winkelmayer and colleagues14 compared baseline fasting plasma total homocysteine levels with renal allograft survival over a median follow-up of 6.1 years. After statistical adjustment, elevated homocysteine levels (≥ 12 µmol/L) were associated with an increased risk of allograft loss (hazard ratio [HR] = 1.63; 95% confidence interval [CI] = 1.09–2.44) and mortality (HR = 2.44; 95% CI = 1.45–4.12).

Weiner and others15 reported on a randomized, controlled trial known as the Folic Acid for Vascular Outcomes Reduction in Transplant Recipients (FAVORIT). The results showed no benefit related to the use of high-dose B-complex vitamin supplementation.

Recurrence of primary pathology, particularly glomerulopathies, has an adverse impact on transplant outcomes. Recurrent glomerulonephritis is the third most common cause of allograft loss at 10 years. A retrospective study by Hanrahan and colleagues16 evaluated the outcomes of about 5,000 renal transplants documented in the Renal Allograft Disease Registry. In all, 167 patients had clinical and biopsy-proven evidence of recurrent or de novo glomerular disease. The risk ratio for allograft failure was 1.9 for those with glomerular disease. At 5 years, patients with glomerular disease had a much higher rate of allograft failure (60%) than did those without glomerular disease (32%).

Briganti and others17 reported that among 1,505 renal transplant recipients who had end-stage renal disease due to glomerulonephritis, 52 patients (3.5%) had allograft loss resulting from biopsy-proven recurrent glomerulonephritis.

ADDRESSING INTERVENTIONS THAT WORK LATE AFTER TRANSPLANT
Based on a presentation by Klemens Budde, MD, PhD, Professor of Medicine and Head, Clinical Transplant Program, Charité-Universitätsmedizin Berlin, Berlin, Germany.

The most important nonimmunologic issue affecting graft survival is patient adherence to the maintenance immunosuppressant regimen. In addition, diabetes and hypertension must be well controlled. Any change in baseline blood pressure should be evaluated thoroughly, and suspected renal artery stenosis should be addressed.

Recurrent primary disease should always be considered. Clinicians should distinguish focal segmental glomerulosclerosis (FSGS) observed on transplant biopsy as a primary change or as a recurrence. The onset of proteinuria typically occurs within days or a few weeks in recurrent FSGS and develops rapidly. In comparison, protein excretion does not begin to increase until at least 3 months after transplantation and then rises slowly in chronic de novo disease.

Polyoma virus allograft nephropathy typically presents with subacutely progressive allograft dysfunction. A more specific diagnosis is made if the virus is detected in blood or urine using the polymerase chain reaction.

Early Screening for Graft Loss
Beside creatinine clearance, other markers for graft function also should be checked.

CD30. Amirzargar and colleagues18 reported that graft recipients with high CD30 levels in the presence of HLA class I or II antibodies within 2 weeks post transplant had poor graft survival (P = 0.004 and P = 0.002, respectively). High levels of post-transplant immunoglobulin A anti-Fab antibody were more frequently observed among patients with functioning grafts (P = 0.00001), correlated with decreased serum creatinine levels (P = 0.01), and were associated with improved graft survival (P = 0.008).

Serum proteins. The analysis of serum proteins has been another focus of blood sample monitoring. The upregulation of transforming growth factor-β19 remains an inconsistent finding in kidney-graft recipients with biopsy-proven interstitial fibrosis and tubular atrophy (IF/TA).

Serum β2-microglobulin. The serum level of β2-microglobulin at discharge is a strong predictor of long-term mortality and renal allograft loss.20

Urinary protein assay. Liquid chromatography and tandem mass spectroscopy may be used to analyze proteins in urine specimens. Quintana et al21 identified 6,000 protein ions from 32 recipients with IF/TA and chronic antibody-mediated injury and from 18 stable recipients. Preliminary studies demonstrated that 14 proteins differed between those with IF/TA and individuals with antibody-mediated processes.22 A further analysis of these patient samples identified uromodulin at 638.03 m/z and a high expression of 642.61 m/z as diagnostic of chronic allograft dysfunction in nearly all cases. By two-dimensional difference gel electrophoresis, 19 different proteins related to the histologic diagnosis of IF/TA were identified.23

Urinary messenger RNA. Li et al24 have advocated the use of messenger RNA isolation and analysis from urine specimens to noninvasively diagnose ongoing allograft pathology.

Alternative Immunosuppressants
Belatacept therapy is associated with superior renal function and similar patient and graft survival, as compared with cyclosporine, at 1 year post transplant, despite a higher rate of early acute graft rejection.25 Treatment with belatacept-based regimens also is generally considered safe, with no increased incidence of serious adverse events or of cytomegalovirus or BK polyoma virus infections.

SUMMARY
Long-term graft loss is not completely understood, but alloimmunity has a definite role in this phenomenon. Besides tissue diagnosis, certain markers in serum and urine can predict the long-term outcome of the graft. More studies must be performed to evaluate the potential role of these biomarkers and to provide a better understanding of the exact mechanism of long-term graft loss than we have now.

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Dr. Javed is a Senior Fellow in Abdominal Organ Transplantation at the University of Washington Medical Center, Seattle, Washington.

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