Treatment strategies to minimize or prevent chronic allograft dysfunction in pediatric renal transplant recipients: an overview

Immunosuppressants in Organ Transplantation

The goal of immunosuppressive therapy post-transplantation in pediatric renal transplant recipients is to prevent acute and chronic rejection while minimizing drug side effects. Most therapies alter immune response mechanisms but are not immunologically specific, and a careful balance is required to find the dose that prevents rejection of the graft while minimizing the risks of overimmunosuppression leading to infection and cancer. While this chapter because of space constraints focuses on immunosuppressive therapy in pediatric renal transplant recipients, many aspects can be applied on pediatric recipients of other solid organ transplants such as the liver and heart. The major maintenance immunosuppressive agents currently used in various combination regimens are tacrolimus, cyclosporine, mycophenolate mofetil, azathioprine, everolimus, sirolimus, and glucocorticoids (steroids). Although data from adult renal transplantation trials are used to help guide management decisions in pediatric patients, immunosuppressive therapy in pediatric renal transplant recipients often must be modified because of the unique dosage requirements and clinical effects of these agents in children, including their impact on growth and development. The optimal immunosuppressive therapy post-transplant is not established. The goal remains to find the best combination of immunosuppressive agents that optimizes allograft survival by preventing acute rejection while limiting drug toxicities.

Amniotic fluid cells: current progress and emerging challenges in renal regeneration

Amniotic fluid (AF) contains a heterogeneous population of cells that have been identified to possess pluripotent and progenitor-like characteristics. These cells have been applied in various regenerative medicine applications ranging from in vitro cell differentiation to tissue engineering to cellular therapies for different organs including the heart, the liver, the lung, and the kidneys. In this review, we examine the different methodologies used for the derivation of amniotic fluid stem cells and renal progenitors, and their application in renal repair and regeneration. Moreover, we discuss the recent achievements and newly emerging challenges in our understanding of their biology, their immunoregulatory characteristics, and their paracrine-mediated therapeutic potential for the treatment of acute and chronic kidney diseases.

Minimum mycophenolic acid levels are associated with donor-specific antibody formation

Although de novo DSA are associated with inferior graft survival, there are no effective strategies to prevent their formation. Underexposure to MPA (prodrug: MMF) also contributes to rejection rates early after transplantation, but the effect of this phenomenon on the formation of DSA long-term post-transplantation is unknown. Data are expressed as mean (standard deviation). All available data from 32 renal transplant recipients (age at transplantation 7.5 [4.5] yr) on tacrolimus and MPA immunosuppression with an average follow-up of 9.4 (s.d. 4.6) yr were analyzed. DSA were measured using the Luminex assay (>500 MFI was considered DSA-positive). Tacrolimus and MPA levels were measured with the Abbot Tacro II and EMIT assay, respectively. Among 1964 MPA and 3462 tacrolimus trough levels, the average MPA trough level was 3.2 (1.5) mg/L and the average tacrolimus level was 6.7 (2.8) ng/mL. At last follow-up, only 5/32 patients had undetectable DSA, with 5/32 having no class I antibodies and 6/32 having no class II antibodies. DSA formation was associated with a lower minimum MPA trough level (0.27 [0.23] vs. 0.47 [0.18] mg) and cystatin C eGFR (48 [21] vs. 70 [23] mL/min/1.73 m(2)) for class I DSA formers. The average eGFR of patients without class I DSA was 70 (23) mL/min/1.73 m(2), whereas the average eGFR of patients with class I DSA was 48 (21) mL/min/1.73 m(2) (p = 0.0071). MPA trough levels <1.3 mg/L long-term post-transplantation are associated with the formation of DSA. The association between the formation of DSA and minimum MPA exposure may support a strategy for preventing the formation of DSA.

Alternatively activated macrophages in the pathogenesis of chronic kidney allograft injury

BACKGROUND

Prevention of chronic kidney allograft injury (CAI) is a major goal in improving kidney allograft survival; however, the mechanisms of CAI are not clearly understood. The current study investigated whether alternatively activated M2-type macrophages are involved in the development of CAI.

METHODS

A retrospective study examined kidney allograft protocol biopsies (at 1 h and at years 1, 5, and 10--a total of 41 biopsies) obtained from 13 children undergoing transplantation between 1991 and 2008 who were diagnosed with CAI: interstitial fibrosis and tubular atrophy (IF/TA) not otherwise specified (IF/TA-NOS).

RESULTS

Immunostaining identified a significant increase in interstitial fibrosis with accumulation of CD68 + CD163+ M2-type macrophages. CD163+ cells were frequently localized to areas of interstitial fibrosis exhibiting collagen I deposition and accumulation of α-smooth muscle actin (SMA) + myofibroblasts. There was a significant correlation between interstitial CD163+ cells and the parameters of interstitial fibrosis (p < 0.0001), and kidney function (r =-0.82, p < 0.0001). The number of interstitial CD163+ cells at years 1 and 5 also correlated with parameters of interstitial fibrosis at years 5 and 10 respectively. Notably, urine CD163 levels correlated with interstitial CD163+ cells (r = 0.79, p < 0.01) and parameters of interstitial fibrosis (p < 0.0001). However, CD3+ T lymphocytic infiltration did not correlate with macrophage accumulation or fibrosis. In vitro, dexamethasone up-regulated expression of CD163 and cytokines (TGF-β1, FGF-2, CTGF) in human monocyte-derived macrophages, indicating a pro-fibrotic phenotype.

CONCLUSIONS

Our findings identify a major population of M2-type macrophages in patients with CAI, and suggest that these M2-type macrophages might promote the development of interstitial fibrosis in IF/TA-NOS.

Advantageous effects of immunosuppression with tacrolimus in comparison with cyclosporine A regarding renal function in patients after heart transplantation

BACKGROUND

Nephrotoxicity is a serious adverse effect of calcineurin inhibitor therapy in patients after heart transplantation (HTX).

AIM

In this retrospective registry study, renal function within the first 2 years after HTX in patients receiving de novo calcineurin inhibitor treatment, that is, cyclosporine A (CSA) or tacrolimus (TAC), was analyzed. In a consecutive subgroup analysis, renal function in patients receiving conventional tacrolimus (CTAC) was compared with that of patients receiving extended-release tacrolimus (ETAC).

METHODS

Data from 150 HTX patients at Heidelberg Heart Transplantation Center were retrospectively analyzed. All patients were continuously receiving the primarily applied calcineurin inhibitor during the first 2 years after HTX and received follow-up care according to center practice.

RESULTS

Within the first 2 years after HTX, serum creatinine increased significantly in patients receiving CSA (P<0.0001), whereas in patients receiving TAC, change of serum creatinine was not statistically significant (P=not statistically significant [ns]). McNemar's test detected a significant accumulation of patients with deterioration of renal function in the first half year after HTX among patients receiving CSA (P=0.0004). In patients receiving TAC, no significant accumulation of patients with deterioration of renal function during the first 2 years after HTX was detectable (all P=ns). Direct comparison of patients receiving CTAC versus those receiving ETAC detected no significant differences regarding renal function between patients primarily receiving CTAC or ETAC treatment during study period (all P=ns).

CONCLUSION

CSA is associated with a more pronounced deterioration of renal function, especially in the first 6 months after HTX, in comparison with patients receiving TAC as baseline immunosuppressive therapy.

An in-house assay for BK polyomavirus quantification using the Abbott m2000 RealTime system

BK polyomavirus (BKPyV) quantification is useful for monitoring renal transplant patient response to therapy. The Abbott m2000 RealTime System employed by some clinical laboratories to perform US Food and Drug Administration-approved assays can also be used to develop in-house assays such as the one presented here. This study aimed to validate an in-house quantitative real-time PCR assay targeting the BKPyV major capsid VP1 gene for assessment of viral load using the Abbott m2000 RealTime System. BKPyV load was measured in 95 urine and plasma samples previously tested for BKPyV by one of three laboratories (46 BKPyV-positive samples consisting of 35 plasma and 11 urine samples; 49 samples negative for BKPyV consisting of 47 plasma and two urine samples). Two additional plasma specimens from the College of American Pathologists proficiency testing survey were also analysed. Precision studies were performed by diluting a high-viral-titre patient sample into BKPyV-negative pooled plasma to create high-positive (6.16 log10 copies ml(-1)) and low-positive (3.16 log10 copies ml(-1)) samples. For precision studies of inter-assay variability, a high-positive (7.0 log10 copies ml(-1)) and a low-positive (3.0 log10 copies ml(-1)) sample were measured in 20 separate runs. The assay's limit of quantification and limit of detection were 2.70 and 2.25 log10 copies ml(-1), respectively. The assay was linear from 2.70 to 9.26 log10 copies ml(-1). Of the 48 known positives, 43 were detected as positive, with three reported by the reference laboratory as values lower than the limit of detection. Two known positives at 3.27 and 3.80 log10 copies ml(-1) tested negative by the m2000 BKPyV assay. Of the 49 known negative samples, 48 were negative by the m2000 BKPyV load assay, with one sample confirmed positive by a reference laboratory. Qualitative analysis prior to discrepancy testing demonstrated a sensitivity of 89.58 % and a specificity of 97.96 %. Precision studies demonstrated inter-assay coefficients of variation of 0.63 % (high positive) and 4.38 % (low positive). Genotyping was performed on 22 patient samples, of which 21 (95.45 %) were type I and one (4.55 %) was type II. In conclusion, the m2000 BKPyV viral load assay sensitivity, specificity, linear range, precision and cost effectiveness make it an attractive methodology for clinical laboratories using the Abbott m2000 RealTime System.

Effective therapy for acute antibody-mediated rejection with mild chronic changes: case report and review of the literature

To reduce the long-term toxicities of immunosuppressant drugs, corticosteroid-sparing and calcineurin-inhibitor-sparing immunosuppression protocols have become increasingly popular in managing kidney transplant recipients. The most vexing clinical condition caused by antibodies in organ transplants is antibody-mediated rejection. Limitations of the current antibody-mediated rejection therapies include (1) antibody-mediated rejection reversal tends to be gradual rather than prompt, (2) expense, (3) rejection reversal rates below 80%, (4) common appearance of chronic rejection after antibody-mediated rejection treatment, and (5) long-term persistence of donor specific antibodies after therapy. Because these limitations may be due to a lack of effects on mature plasma cells, the effects of bortezomib on mature plasma cells may represent a quantum advance in antihumoral therapy. Our experiences represent the first clinical use of bortezomib as an antihumoral agent in renal allograft recipients in Kuwait. We present 2 cases with resistant-acute antibody-mediated rejection to the standard therapies that were managed successfully with bortezomib.

Steroid-resistant acute allograft rejection in renal transplantation

Steroid-resistant rejection after pediatric renal transplantation forms a rare but severe complication with a guarded prognosis particularly if this occurs late after transplantation. There is a paucity of data on how to manage these challenging rejection episodes, particularly in the pediatric literature. Mohan Shenoy et al. published a case series of 15 patients who were treated with anti-thymocyte globulin for steroid-resistant acute allograft rejection over a 15-year period in a single center in this issue of Pediatric Nephrology. While the results for the early rejection group were encouraging, the results in the eight patients with late rejection episodes after transplantation were unfavorable and afflicted with a high incidence of side-effects. Important diagnostic tools such as C4d staining of the renal transplant biopsy and the measurement of donor-specific antibodies were underutilized. The editorial reviews the importance of the differentiation between humoral and cellular rejection and the challenges of treating late antibody-mediated acute rejection in these patients. A multi-center approach is required to establish a registry of these events and ideally prospective randomized interventions should be designed to provide some evidence base for the management of this challenging complication after pediatric renal transplantation.

Calcineurin inhibitor-free immunosuppression in pediatric renal transplantation: a viable option?

The introduction, in the mid-1980s, of calcineurin inhibitors - namely ciclosporin (cyclosporine) and later tacrolimus - has significantly improved short-term renal graft survival by lowering acute rejection rates in both adult and pediatric kidney transplantation. Nonetheless, long-term transplant survival is still not satisfactory, with calcineurin inhibitor-induced chronic nephrotoxicity being one of the main causes of progressive nephron loss and declining renal transplant function. Hence, different immunosuppressant regimens have been proposed to avoid or ameliorate calcineurin inhibitor-induced nephrotoxicity. These comprise the use of non-depleting or depleting antibodies for calcineurin inhibitor minimization, calcineurin inhibitor avoidance, or calcineurin inhibitor withdrawal from mycophenolate mofetil-based immunosuppressant protocols. De novo use of a mammalian target of rapamycin (mTOR) inhibitor (sirolimus or everolimus) or conversion from a calcineurin inhibitor to an mTOR inhibitor may constitute another therapeutic option to avoid or reduce calcineurin inhibitor-induced nephrotoxicity. To date, complete calcineurin inhibitor avoidance seems to be inappropriate because other relatively potent immunosuppressant agents such as lymphocyte-depleting antibodies are needed for rejection prophylaxis, which are frequently accompanied by a higher incidence of infections and an unacceptably high acute rejection rate under calcineurin inhibitor avoidance. In some studies, calcineurin inhibitor withdrawal in adult and pediatric kidney allograft recipients with stable or declining transplant function has been associated with an amelioration of renal function; however, this is attained at the cost of a higher acute rejection rate in 10-20% of patients. It has been frequently stressed that conversion from a calcineurin inhibitor-based regimen to an mTOR inhibitor-based immunosuppressant regimen should be performed early (e.g. 3 or 6 months post-transplant) in patients with well-preserved renal transplant function without significant proteinuria in order to prevent, or at least limit, calcineurin inhibitor-induced tissue damage and provide long-term benefit. It should be borne in mind though that the use of an mTOR inhibitor carries the risk of potential adverse events such as aggravation of proteinuria, hyperlipidemia, myelosuppression, and hypergonadotropic hypogonadism. Even though everolimus may be better tolerated than sirolimus, studies on everolimus for calcineurin inhibitor-free immunosuppression in the pediatric kidney transplant patient population are lacking. At present, the safest therapeutic strategy for pediatric renal allograft recipients with chronic calcineurin inhibitor-induced nephrotoxicity appears to be a mycophenolate mofetil-based regimen with low-dose calcineurin inhibitor therapy and corticosteroids; available published data show that dual immunosuppression with mycophenolate mofetil and corticosteroids, as well as an mTOR inhibitor plus mycophenolate mofetil plus corticosteroid-based regimens, are associated with an increased risk of acute rejection episodes. In individual patients with evidenced chronic allograft dysfunction and over-immunosuppression leading to recurrent infections, dual maintenance immunosuppression with mycophenolate mofetil and corticosteroids may be appropriate. As stated in the annual report issued by the North American Pediatric Renal Trials and Collaborative Studies (NAPRTCS) Registry, currently the most popular immunosuppressant protocol consists of a calcineurin inhibitor combined with mycophenolate mofetil and corticosteroids: 59.1% and 53.2% of patients with a functioning graft receive a calcineurin inhibitor plus mycophenolate mofetil plus corticosteroid-based immunosuppression at 1 and 5 years post-transplant, respectively. 91.4% and 87.8% of patients are administered a calcineurin inhibitor-containing regimen 1 and/or 5 years after transplantation, respectively. Undoubtedly, the use of calcineurin inhibitor-free immunosuppressant regimens with or without antibody induction, plus an mTOR inhibitor and mycophenolate mofetil, requires more comprehensive long-term investigations to determine whether acceptable rejection rates and conservation of renal function can be achieved.

The new immunosuppressant PLNPK prolongs allograft survival in mice

The pentapeptide PLNPK (Pro-Leu-Asn-Pro-Lys) is extracted from the spleen. Preliminary studies have shown that PLNPK could inhibit T lymphocyte transformation and antibody production. In the present study, we detected the inhibitory effect of PLNPK on one-way mixed leukocyte reaction (MLR) in vitro and observed the effect of PLNPK on the duration of allograft survival in mouse models of skin or cardiac transplantation. Pathological damage and T cell infiltration of the grafts were also detected. Results showed that PLNPK could significantly inhibit T lymphocyte proliferation, with an optimized inhibition of 40%. Also PLNPK could significantly prolong the mean survival time of skin allograft and cardiac allograft, producing survival rates of 42% and 38.7%, respectively. PLNPK at a dose of 200 μg/kg/d or 100 μg/kg/d could significantly suppress ConA-induced T cell proliferation and T cell IL-2 secretion in transplant recipient mice, compared to the saline group (P<0.05). This information suggests that PLNPK can effectively antagonize transplant rejection, possibly by reducing IL-2 secretion by T cells and inhibiting T cell proliferation and activation.

Nonimmune complications after transplantation

As posttransplant longevity has increased, nonimmune complications related to the transplant and posttransplant course have emerged as important factors in defining long-term outcomes. The incidence of, and risk factors for these complications may vary by transplanted organ based on immunosuppressive protocols and preexisting risk factors. This article discusses the relevant nonimmune complications associated with posttransplant care, with a focus on risk factors and management strategies.