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Year : 2010 | Volume
: 21
| Issue : 6 | Page : 1030-1037 |
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New concepts to individualize calcineurin inhibitor therapy in renal allograft recipients |
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Claudia Sommerer1, Thomas Giese2, Stefan Meuer2, Martin Zeier1
1 Department of Nephrology, University Hospital, INF 162, Heidelberg, Germany 2 Department of Immunology, University of Heidelberg, INF 400, Heidelberg, Germany
Click here for correspondence address and email
Date of Web Publication | 4-Nov-2010 |
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Abstract | | |
A maximum of efficacy with a minimum of toxicity is the ultimate goal of immunosuppressive therapy. Calcineurin inhibitors are widely used as immunosuppressive drugs, and there is still a discussion about the optimal blood levels of cyclosporine A (CsA) and tacrolimus (Tac), balancing safety and efficacy. Monitoring of calcineurin inhibitor therapy is usually performed by blood trough levels, pharmacokinetics such as measurement of two-hour peak levels, or by various areas under the curve assessments (AUC, 4 to 12 hours). All these mentioned pharmacokinetic measurements cannot predict the individual biological effects of the immunosuppressive drug. Several approaches have been undertaken to measure immunosuppression by calcineurin inhibitors. In this manuscript, general and specific immune monitoring strategies of calcineurin inhibitors and their clinical benefits are discussed.
How to cite this article: Sommerer C, Giese T, Meuer S, Zeier M. New concepts to individualize calcineurin inhibitor therapy in renal allograft recipients. Saudi J Kidney Dis Transpl 2010;21:1030-7 |
How to cite this URL: Sommerer C, Giese T, Meuer S, Zeier M. New concepts to individualize calcineurin inhibitor therapy in renal allograft recipients. Saudi J Kidney Dis Transpl [serial online] 2010 [cited 2021 Jan 16];21:1030-7. Available from: https://www.sjkdt.org/text.asp?2010/21/6/1030/72287 |
Introduction | |  |
Since the introduction of calcineurin inhibitors (CNI) cyclosporine A (CsA) and tacrolimus (Tac), acute rejection rates have improved remarkably. [1] Unexpectedly, the overall renal allograft survival remained stable during the last decade. [2] With the expanding application of CNIs, undesirable side effects have come into focus. [3],[4],[5],[6] Especially in CNIs, the optimal monitoring strategies are discussed in terms of safety and efficacy. [7] Pharmacokinetic (PK) monitoring of CNI (CsA, Tac) treatment by C0 levels is widely accepted. Certainly, the most reliable PK parameter for CNI dosing is the assessment of the CNI area under the concentration time curve (AUC) within 12 hours, a strategy hardly practicable in clinical routine. [8],[9],[10],[11] Nevertheless, all PK monitoring strategies do not reflect the biological activity of the drug. [7],[12]
Recently, pharmacodynamic (PD) monitoring has been proposed as a new strategy to provide information about the biological effect of a specific drug.
General Pharmacodynamic Assays for CNI Monitoring | |  |
Non-specific PD biomarkers are utilized to reflect the activity of the immune system. It is assumed that a combined effect of multiple immunosuppressive drugs can be anticipated. Several biomarkers are applied to detect occurring clinical events, such as acute rejection episodes, as early as possible.
The pharmacological effect on immune cells is quantified by PD assays, which measure immune functions responsible for graft rejections. Most of the currently used immunosuppressive drugs inhibit lymphocyte proliferation. Several study groups investigated flowcytometric or radio-nucleotide-based lymphocyte proliferation in stimulated whole blood cultures or peripheral blood mononuclear cells (PBMCs). [13] Others assessed T-cell activation markers, such as CD25 and CD71 on CD4 + and CD8 + lymphocyte subsets or on natural killer cells. [14],[15] In various studies, the potential prediction of tolerance by natural regulatory T cells (CD4 + CD25 high FOXP3 + ) is evaluated. Pre-clinical transplant models suggested their role in preventing allograft rejection and tolerance induction. [16] However, its clinical usefulness for guiding immunosuppressive drug weaning has not been verified so far.
Some of these suggested PD markers have already been evaluated in a substantial number of clinical studies. Two promising immune monitoring markers namely, the soluble CD30 molecule and T-cell adenosine triphosphate release, are discussed in the following sections.
Soluble CD30 molecule
One of the key interesting immune monitoring biomarkers is the soluble CD30 (sCD 30) molecule. sCD30 has been proposed as a T-cell activation marker with prognostic value regarding acute rejection episodes and renal allograft survival. [17] The sCD30 molecule is a member of the tumor necrosis factor/nerve growth factor receptor super family and preferentially expressed on human CD4 + and CD8 + T cells that secrete Th2-type cytokines, whereas no or low CD30 expression is found on Th1-type cytokine-secreting T cells. [18] A soluble form of CD30 is released into the bloodstream after activation of CD30 + T cells. [19] The five-year graft survival rate in 901 recipients with a high pre-transplant serum sCD30 ( - 100 U/mL) was 64 ± 2%, significantly lower than the 75 ± 1% rate in 2998 recipients with low sCD30 (< 100 U/mL) (P < 0.0001) including patients on CsA and Tac treatment. [17] The sCD30 effect on graft survival was also evident in presensitized patients with lymphocytotoxic antibodies and in patients who received grafts that were poorly HLA-matched. Recipients with a high pre-transplant sCD30 continued to lose grafts at a higher rate during the five-year follow-up period, indicating that pre-transplant sCD30 is not only a predictor of acute rejections but also a predictor of deterioration in chronic allograft nephropathy. [20] A more recent study confirmed a significant correlation between high levels of pre-transplant sCD30 and increased incidence of post-transplant viral and bacterial infections and increased serum creatinine. [21] Therefore, sCD30 is a marker for alloreactive immune responses and identification of patients at high-risk of rejection-related complications. However, the predictive value for the post-transplant outcome at the individual level remains rather low.
Adenosine triphosphate (ATP) release of CD4 + T cells
A commercially available laboratory test measuring the concentration of adenosine triphosphate (ATP) released after phytohemagglutinin (PHA) stimulation of CD4 + T cells (ImmuKnow TM ; Cylex, Inc., Columbia, MD) was approved by the US Food and Drug Administration (FDA) to measure global immune competence in solid organ transplant patients receiving immunosuppressive therapy. [22] Although this is not a specific immunological response, previous reports in organ transplantation have shown that results of the ImmuKnow TM assay correlate with the clinical states of over- and under-immunosuppression in pediatric and adult allograft recipients independent of the type of immunosuppression. This immune monitoring assay has been proven clinically useful in identifying patients at risk of graft failure or infections, even prior to the development of clinical symptoms. [23] Low ImmuKnow TM ATP values seems to indicate a state of overimmunosuppression with an in creased risk of bacterial or viral infections such as cytomegalovirus (CMV), Epstein-Barr virus (EBV) and polyoma virus (BKV), where-as a higher than normal ATP level is associated with rejection of the graft in organ transplantation. [24] Although many of the studies support the potential use of ImmuKnow TM assay in guiding immunosuppressive therapy after transplantation, its contribution remains controversial and is not uniformly accepted. [25] There is a lack of large prospective interventional studies until now. Moreover, the adequacy of ATP release in PHA-stimulated CD4 + T-cells is discussed, since ATP reflects the over-all energy metabolism of cells and is not specific for immunosuppressive drugs.
Specific PD assays for CNI monitoring | |  |
A PD monitoring assay is only useful if it provides reliable and valid results, if it is easy to perform and if a clinical benefit has been proven. The principal action of CNIs, CsA and Tac, within the T-lymphocytes is the inhibition of the phosphatase calcineurin. Calcineurin is a key component of T-cell activation and acts as a target of the CsA-cyclophilin and TacFK506-binding protein 12 complexes. The inhibition of calcineurin down-regulates the dephosphorylation of the nuclear factor of activated T-cells (NFAT) and consequently prevents the translocation of the transcription factor NFAT into the nucleus of activated Tlymphocytes. Subsequently, the transcription of several central genes of the immune system, such as interleukin 2 (IL-2) or interferon-y (IFNγ) ) are blocked [Figure 1]. | Figure 1 :A model of drug-specific pharmacodynamic monitoring of cyclosporine A and tacrolimus.
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T-cell immune monitoring reflects the intensity of specific CNI-induced immunosuppression in an individual patient and these new approaches are supposed to overcome the limitations of PK monitoring and guide optimal drug dosing. [26] A considerable number of approaches have been undertaken to assess the PD consequences of CNI-based immunosuppression and several PD parameters have been identified for the monitoring of immunosuppressive therapy. These efforts resulted in the identification of promising biomarkers for specific PD monitoring of calcineurin inhibitor dependent immunosuppression.
Calcineurin phosphatase activity
One of these specific T-cell immune monitoring strategies quantified the individual immunosuppressive effect of CNIs on calcineurin phosphatase activity. [27],[28],[29] Different methods to assess calcineurin phosphatase activity have been evaluated: high performance liquid chromatography (HPLC)-ultraviolet measurement of dephosphorylated peptide, [30] the radioactive measurement of [32] P-labeled phosphate [31] and a spectrophotometric method. [32] The calcineurin phosphatase activity is measured in various blood fractions as whole blood, [33] PBMCs, [34] and leukocyte subsets. [35] A cell-specific activity has been recognized and, for this reason, inter- and intra-individual variations in leukocyte subset cell counts may influence measured calcineurin phosphatase activity. [35] The activity of calcineurin phosphatase in lymphocytes correlates inversely with blood CsA concentrations. A high inter- and intra-individual variability in calcineurin phosphatase activity for CsA and Tac has been reported. Renal transplant patients exhibited an overall calcineurin phosphatase activity of 50% of healthy volunteers and the peak CsA blood concentrations resulted in a 70 to 96% reduction in calcineurin phosphatase activity. [27],[36] In Tactreated patients, the maximum inhibitory effect on calcineurin phosphatase activity was about 60%. [27],[29] Calcineurin phosphatase activity correlated inadequately with drug dosages or PK data in PK/PD studies. [33] These findings prove that immunosuppressive drugs induce a variety of inter-individual patient responses. Only limited data are available on PD monitoring of calcineurin phosphatase activity and clinical outcomes. Despite a poor but existing relationship between drug concentration and calcineurin phosphatase activity, no clear association between calcineurin phosphatase activity and clinical adverse events has been reported. [37] The clinical meaning has been maintained by the observation that a lower calcineurin phosphatase activity results in a higher rate of graft-versus-host diseases in bone marrow recipients on CsA therapy. [38] This is confirmed by the clinical study of Sanquer et al [39] demonstrating that calcineurin activity predicts graft versus-host-disease in allogenic stem-cell transplantation. In organ transplant patients, calcineurin phosphatase activity has been evaluated in stable renal transplant patients with a higher baseline activity in low-dose CsA in comparison to standard-dose CsA, however, it is of note, that calcineurin phosphatase activity was similar at CsA C 2 . [40] High calcineurin phosphatase activity resulted in acute rejection episodes in liver transplant recipients on CsA and Tac therapy. [41]
T-cell specific cytokines
Some other studies have focused on T-cell specific cytokine production as PD parameters. With enzyme-linked immunosorbent assay (ELISA) and flow-cytometric techniques, the concentrations of cytokines or chemokines have been measured in whole blood, serum and intracellular in stimulated PBMCs derived from patients after transplantation. [15],[42],[43] Several interesting effector cytokine patterns of CD4 + T cells have been defined. For example, CD4 + Tcell effector cytokines such as IL-2, IFN-γ and TNF-α have been defined as predictor of acute rejection, and a decreased ratio of CD4 + T-cell to CD8 + T-cell cytokines has been confirmed as predictor of graft acceptance. IL-2 protein was measured in mitogen-activated whole blood. [44] The addition of mycophenolic acid to CsA or Tac-based immunosuppression reduced IL-2 production, demonstrating that it is not merely a CNI specific response of the T-cell effector cytokine IL-2. [34] Some study results confirmed an even tight co-rrelation between CsA C0 or C 2 levels and IL-2 production, [43],[44] while other studies failed to prove this strong association. [14] Concerning clinical outcome, only limited data are available. In a small study cohort, an association between pre-transplant IL2 production and the risk of acute rejection has been proposed. [45] Other study groups revealed the T-cell effector cytokine IFN-γ as a more specific marker of the CsA-induced immunosuppressive effect. [40] However, monitoring of cytokine production is a problematic issue as a result of restrictions to certain cell cycle phases, different half-lives for the circulation of cytokines and changes in the up- and down-regulation of cytokine expression. [46]
Cytokine mRNA expression
Detection of the messenger RNA (mRNA) level as a marker of the degree of calcineurin inhibition has been introduced to assess the degree of calcineurin inhibition. [44],[45] Hartel et al [47] described a human whole blood assay based on quantitative real-time cytokine reverse transcription polymerase chain reaction (rt-PCR) for PD monitoring. The authors observed a decreased basal mRNA expression of TNFα in patients on CsA therapy and retarded cytokine mRNA expression kinetics during T-cell costimulation. These data suggested that distinct shifts in peak cytokine mRNA expression may represent a sensitive PD marker of individual CsA response. For prospective studies on cytokine mRNA concentrations, the parameter "area of cytokine mRNA expression over time" was suggested as PD monitoring tool, which should include absolute cytokine mRNA concentrations measured at two different time points. The same study group investigated the potential PD effects of Tac on IL-2 mRNA expression in an in vitro human whole-blood assay. [45] IL-2 mRNA profiles revealed variable Tac sensitivity. Kinetic profiles of IL-2 mRNA expression demonstrated individually distinct degrees of CNI sensitivity in patients undergoing Tac monotherapy before living-donor kidney transplantation. Individuals with unaffected IL-2 mRNA expression may be at increased risk of transplant rejection. Other studies have investigated the expression of cytokines in kidney-transplant biopsies. [48] Recently, quantitative analysis of gene expression was employed to measure directly the functional effects of calcineurin inhibition: the transcriptional activities of NFAT-regulated genes in the peripheral blood. [49],[50],[51] This assay is based on the quantitative analysis of the gene expression of the three NFAT-regulated cytokine genes IL-2, IFN-γ and granulocyte macrophage colony-stimulating factor (GM-CSF). Blood samples are taken at CNI trough, and the relative inhibition of gene expression after oral drug intake is calculated at CNI peak level.
A short time ago, the assessment of NFAT regulated gene expression has been established to ameliorate CNI-specific PD monitoring. Several clinical studies affirmed this approach as a useful tool with potential to individualize CNI therapy. The expression of NFAT-regulated genes correlated inversely with both CsA and Tac levels. [50] Similar to calcineurin phosphatase activity, a high inter-individual variability of NFAT-regulated gene expression in patients with corresponding CsA or Tac doses has been observed. Even in long-term renal transplant patients, there was a high variability in residual NFAT-regulated gene expression varying from 2 to 50%, which confirms various degrees of immunosuppression and T-cell activation. On the other side, intra-individual variability of residual NFAT-regulated gene expression was low in repetitive measurements in one single patient with a stable CNI dose. [51] The monitoring of residual NFAT-regulated gene expression has been proven in clinical studies as a useful and safe tool to reduce CsA therapy. [52] CsA-treated patients with low residual expression of NFAT-regulated genes were more likely to get recurrent infections or tumors, [51],[53] and patients with a low residual NFAT-regulated gene expression have an increased risk of non-melanoma skin cancer. [54] Elderly long-term renal transplant patients were at an increased risk for non-melanoma skin cancer if residual NFAT-regulated gene expression was below 15%. In a biopsy-controlled study, the stepwise reduction of CsA dose and the following increase of residual NFAT-regulated gene expression proceeded without adverse effects. [52] One patient had an acute cellular rejection with a residual NFAT-activity above 40% after the tapering of the CsA dose. In addition, the reduction of CsA dose resulted in a decrease of systolic and pulse pressure. An optimal range of residual NFAT-regulated gene expression has been proposed between 20 and 30% in long-term stable renal transplant patients. However, data on de novo renal transplant patients and recipients of other solid organs are not available.
Conclusion | |  |
The optimal monitoring strategy of CNI therapy is still a controversial issue. Monitoring by traditional pharmacokinetic data is hampered by the fact of missing perfect association between drug exposure and PD effects. Several approaches have been undertaken to develop tools for pharmacodynamic monitoring of CNI therapy. General and drug-specific PD monitoring strategies which determine pharmacological efficacy constitute encouraging tools to assist clinical decisions on individual dosaging. Although the concept of PD monitoring is attractive and although preliminary reports reveal associations between the different PD markers and clinical outcomes, none of these methods is broadly validated or accepted in clinical practice. Studies in larger patient populations are desired to confirm individual benefits of these promising approaches.
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Correspondence Address: Claudia Sommerer Department of Nephrology, University of Heidelberg , Im Neuenheimer Feld 162 D-69120 Heidelberg Germany
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PMID: 21060169 
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