Ex vivo generation of regulatory T cells from liver transplant recipients using costimulation blockade

The potential of adoptive cell therapy with regulatory T cells (Tregs) to promote transplant tolerance is under active exploration. However, the impact of specific transplant settings and protocols on Treg manufacturing is not well-delineated. Here, we compared the use of peripheral blood mononuclear cells (PBMCs) from patients before or after liver transplantation to the use of healthy control PBMCs to determine their suitability for Treg manufacture using ex vivo costimulatory blockade with belatacept. Despite liver failure or immunosuppressive therapy, the capacity for Treg expansion during the manufacturing process was preserved. These experiments did not identify performance or quality issues that disqualified the use of posttransplant PBMCs-the currently favored protocol design. However, as Treg input correlated with output, significant CD4-lymphopenia in both pre- and posttransplant patients limited Treg yield. We therefore turned to leukapheresis posttransplant to improve absolute yield. To make deceased donor use feasible, we also developed protocols to substitute splenocytes for PBMCs as allostimulators. In addition to demonstrating that this Treg expansion strategy works in a liver transplant context, this preclinical study illustrates how characterizing cellular input populations and their performance can both inform and respond to clinical trial design and Treg manufacturing requirements.

Maintenance Immunosuppression in Solid Organ Transplantation: Integrating Novel Pharmacodynamic Biomarkers to Inform Calcineurin Inhibitor Dose Selection

Calcineurin inhibitors, the primary immunosuppressive therapy used to prevent alloreactivity of transplanted organs, have a narrow therapeutic index. Currently, treatment is individualized based on clinical assessment of the risk of rejection or toxicity guided by trough concentration monitoring. Advances in immune monitoring have identified potential markers that may have value in understanding calcineurin inhibitor pharmacodynamics. Integration of these markers has the potential to complement therapeutic drug monitoring. Existing pharmacokinetic-pharmacodynamic (PK-PD) data is largely limited to correlation between the biomarker and trough concentrations at single time points. Immune related gene expression currently has the most evidence supporting PK-PD integration. Novel biomarker-based approaches to pharmacodynamic monitoring including development of enhanced PK-PD models are proposed to realize the full clinical benefit.

Barcelona Consensus on Biomarker-Based Immunosuppressive Drugs Management in Solid Organ Transplantation

With current treatment regimens, a relatively high proportion of transplant recipients experience underimmunosuppression or overimmunosuppression. Recently, several promising biomarkers have been identified for determining patient alloreactivity, which help in assessing the risk of rejection and personal response to the drug; others correlate with graft dysfunction and clinical outcome, offering a realistic opportunity for personalized immunosuppression. This consensus document aims to help tailor immunosuppression to the needs of the individual patient. It examines current knowledge on biomarkers associated with patient risk stratification and immunosuppression requirements that have been generally accepted as promising. It is based on a comprehensive review of the literature and the expert opinion of the Biomarker Working Group of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. The quality of evidence was systematically weighted, and the strength of recommendations was rated according to the GRADE system. Three types of biomarkers are discussed: (1) those associated with the risk of rejection (alloreactivity/tolerance), (2) those reflecting individual response to immunosuppressants, and (3) those associated with graft dysfunction. Analytical aspects of biomarker measurement and novel pharmacokinetic-pharmacodynamic models accessible to the transplant community are also addressed. Conventional pharmacokinetic biomarkers may be used in combination with those discussed in this article to achieve better outcomes and improve long-term graft survival. Our group of experts has made recommendations for the most appropriate analysis of a proposed panel of preliminary biomarkers, most of which are currently under clinical evaluation in ongoing multicentre clinical trials. A section of Next Steps was also included, in which the Expert Committee is committed to sharing this knowledge with the Transplant Community in the form of triennial updates.

Nuclear Factor of Activated T Cells-Regulated Gene Expression as Predictive Biomarker of Personal Response to Calcineurin Inhibitors

BACKGROUND

Calcineurin inhibitors (CNIs) represent the most widely used immunosuppressive agents in kidney transplantation. Both CNIs show a narrow therapeutic window; thus, monitoring is necessary to balance efficacy and toxicity. Several approaches have been undertaken to measure the biological effects of CNI-based immunosuppression.

METHODS

A quantitative analysis of gene expression was established to calculate the functional effects of calcineurin inhibition, the assessment of nuclear factor of activated T cells (NFAT)-regulated gene expression. This assay is based on the quantitative analysis of interleukin-2, interferon-γ, and granulocyte macrophage colony-stimulating factor gene expression in whole blood samples collected at the time cyclosporine A/tacrolimus troughs (C0) and 2 hours after oral uptake (C2).

RESULTS

In this comprehensive review, analytical aspects of the assay and also clinical benefits and limitations are presented and discussed. Several observational studies underline the beneficial effect of NFAT-regulated gene expression as biomarker of personal response on CNI therapy, especially in infectious complications, malignancies, and acute rejection episodes. Data are more comprehensive in cyclosporine A compared with tacrolimus therapy. However, results on prospective interventional studies are sparse. A randomized controlled study evaluating the opportunity for NFAT-guided immunosuppression is ongoing.

CONCLUSIONS

NFAT-regulated gene expression is a promising biomarker in CNI therapy concerning infectious complications, malignancies, and acute rejection. Prospective interventional studies and randomized controlled studies are ongoing to confirm the encouraging results.

Effects of oral cyclosporine on canine T-cell expression of IL-2 and IFN-gamma across a 12-h dosing interval

The duration of immunosuppressive effects following oral cyclosporine in dogs is unknown. This study used flow cytometry and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) to evaluate the effects of high-dose oral cyclosporine across a 12-h dosing interval. Expression of interleukin-2 (IL-2) and interferon-gamma (IFN-γ) was compared before and after 8 days of cyclosporine at 10 mg/kg every 12 h in six healthy dogs. Samples were collected at 0, 2, 4, and 8 h postdosing for analysis of unactivated and activated T-cell and whole blood cytokine expression using flow cytometry and qRT-PCR, respectively, and at 0, 2, 4, 6, 8, and 10 h postdosing for measurement of cyclosporine concentrations. Flow cytometry and qRT-PCR both demonstrated significant marked reductions in IL-2 and IFN-γ levels at 0, 2, 4, and 8 h after dosing compared to pretreatment levels (P < 0.05) for activated samples, with less consistent effects observed for unactivated samples. Both flow cytometry and qRT-PCR are viable techniques for measuring cyclosporine pharmacodynamics in dogs, yielding comparable results with activated samples. Two hours postdrug administration is the preferred time for concurrent assessment of peak drug concentration and cytokine expression, and T-cell activation is needed for optimal results.

Drug target molecules to guide immunosuppression

The individual and interindividual variability of response to immunosuppressants combined with the prevailing concept of lifelong immunosuppression following any organ transplantation motivates the search for methods to further individualize such therapy. Traditional therapeutic drug monitoring, adapting dose according to concentrations in blood, targets the pharmacokinetic variability. It has been increasingly recognized, however, that there is also a considerable variability in the response to a given concentration. Attempts to overcome this variability in response include the efforts to identify relevant targets and methods for pharmacodynamic monitoring. For several of the currently used immunosuppressants there is experimental data suggesting markers that are relevant as indicators for individual monitoring of the effects of these drugs. There are also some clinical data to support these approaches; however what is generally missing, are studies that in a prospective manner demonstrates the benefits and effects on outcome. The monitoring of antithymocyte globulin by lymphocyte subset counts is actually the only well established example of pharmacodynamic monitoring. For drugs such as MPA and mTOR inhibitors, there are candidates such as IMPDH activity expression and p70SK6 phosphorylation status, respectively. The monitoring of CNIs using assays for NFAT RGE, either alone or combined with concentration measurements, is already well documented. Even here, some further investigations relating to the categories of organ transplant, combination of immunosuppressants etc. will be requested. Although some further standardization of the assay is warranted and there is a need for specific recommendations of target levels and how to adjust dose, the NFAT RGE approach to pharmacodynamic monitoring of CNIs may be close to implementation in clinical routine.

Therapeutic drug monitoring in pediatric renal transplantation

Finding the balance between clinical efficacy and toxicity of immunosuppressive drugs is a challenge in renal transplantation (RTx), but especially in pediatric RTx patients. Due to the expected longer life-span of pediatric transplant patients and the long-term consequences of drug-induced infectious, malignant and cardiovascular adverse effects, protocols which minimize immunosuppressive therapy make conceptual sense. In this context, therapeutic drug monitoring is a tool which provides support for the individualization of therapy. It has, however, limitations, and specific data in the pediatric cohort are comparatively sparse. There is large heterogeneity among the studies conducted to date in terms of methods, follow-up, endpoints, immunosuppressive regimens and patients. In addition, data from adult studies are not readily transferrable to the pediatric situation. This educational review gives a concise overview on aspects of therapeutic drug monitoring in pediatric RTx.

Cyclosporine-induced gingival overgrowth correlates with NFAT-regulated gene expression: a pilot study

OBJECTIVE

To determine whether incidence and severity of cyclosporine A (CsA)-induced gingival overgrowth (GO) is related to expression nuclear factor of activated T cells-regulated genes (NFAT-regulated genes).

MATERIAL AND METHODS

Expression of NFAT-regulated genes was determined in 36 transplant patients medicated with CsA by real-time PCR before and 2 h after drug intake and residual NFAT activity was estimated as ratio of both measurements. Demographic, periodontal and pharmacologic parameters were recorded and GO assessed from models. Subjects were divided into two groups according to the degree of GO (responders: GO score≥10%). Groups were compared using parametric and non-parametric tests. The association of various CsA-specific and periodontal parameters on incidence and extent of GO were determined using regression analysis.

RESULTS

Responders had a more than twofold lower residual NFAT activity than non-responders (7.9% and 18.1%, respectively; p<0.001). Multiple regression analysis revealed gingival inflammation, salivary CsA concentration, and residual NFAT activity to be significant factors influencing the expression of GO. Seventy-seven percent of the variability of GO could be explained by these parameters.

CONCLUSIONS

This study showed that pharmacodynamic parameters such as residual NFAT activity may be promising prognostic indicators to identify patients with increased risk for GO.

Biomarkers as a tool for management of immunosuppression in transplant patients

Therapeutic drug monitoring is a well-established approach in transplantation medicine to guide immunosuppressive therapy. However, it cannot always predict the effects of immunosuppressive drugs on immune cells, because it does not reflect any aspect of an individual patient's immune system. Pharmacodynamic monitoring is a more recent strategy to provide information about the biologic effect of a specific drug or drug combination on the individual transplant patient. Currently, there is a large number of different biomarkers that either directly (specific markers) or indirectly (global markers) relate to the pharmacodynamic effects of immunosuppressive drugs and are under investigation as potential candidates to be introduced in clinical practice. Such biomarkers may be useful to identify patients at risk of developing acute rejection, infection, or cancer as well as patients who are suitable for minimization of immunosuppressant therapy and may be helpful to manage the timing and rate of immunosuppressant weaning. Serial longitudinal monitoring may allow maintenance of an individualized immunosuppressive regimen. Thus, biomarker monitoring is a potential complementary tool to therapeutic drug monitoring. This review summarizes the current state of knowledge about the use of a number of global or drug-specific pharmacodynamic biomarkers. It is not a comprehensive overview of the literature available, but rather an evidence-based reflection by experts who are intensively involved in scientific work in this field.

Cyclosporine A affects the in vitro expression of T cell activation-related molecules and cytokines in dogs

Cyclosporine is a powerful immunosuppressive drug that is being used with increasing frequency to treat a wide range of immune-mediated diseases in the dog. To date, ideal dosing protocols that will achieve immunosuppression with cyclosporine in dogs remain unclear, and standard methods that can measure effectiveness of immunosuppression have not been established. The aim of our study was to evaluate the effects of in vitro cyclosporine exposure on a panel of molecules expressed by activated T cells to ascertain their potential as biomarkers of immunosuppression in dogs. Blood was drawn from six healthy dogs, and peripheral blood mononuclear cells (PBMC) were isolated and activated. Half of the cells were incubated with 200 ng/mL cyclosporine prior to activation, and the other half were not exposed to cyclosporine. Samples were analyzed using flow cytometry, and the expression of intracellular cytokines IL-2, IL-4, and IFN-γ was evaluated after 6, 12, and 24h of drug exposure. Each cytokine exhibited a time-dependent suppression profile, and all but two samples activated in the presence of cyclosporine showed lower cytokine expression than untreated controls. We also evaluated the expression of the surface T cell activation molecules CD25 and CD95 by flow cytometry after 36 h of drug exposure. Expression of these surface molecules decreased significantly when activated in the presence of cyclosporine. Our results suggest that suppressed expression of the markers related to T cell activation could potentially be utilized as an indicator of the efficacy of cyclosporine therapy in dogs.

Review: Pharmacodynamic monitoring of immunosuppression in kidney transplantation

Advances in immunosuppressive therapies have improved kidney transplant outcomes. However, immunosuppressant drug-induced toxicities continue to reduce tolerability and impact patient and graft survival. A major ongoing challenge in kidney transplantation is to establish ways of tailoring immunosuppressant therapy so as to maintain efficacy while minimizing toxicity. Pharmacodynamic monitoring by direct measurement of immune cell function has the potential to personalize immunosuppression. The purpose of this review is to provide the clinician with an overview of the methodology and use of immune function monitoring in the field of kidney transplantation.

Pharmacodynamic monitoring of cyclosporine A by NFAT-regulated gene expression and the relationship with infectious complications in pediatric renal transplant recipients

Pharmacokinetic monitoring of CsA is unsatisfactory, because at comparable CsA blood concentrations, the frequency and severity of adverse effects vary considerably among patients. We have therefore recently developed a precise, reliable, and robust whole-blood pharmacodynamic assay that measures the suppression of CsA-target genes in T lymphocytes. Because of the different characteristics of CsA pharmacokinetics in children and the higher propensity for infectious complications, this assay requires validation in the pediatric patient population. We therefore quantified in a prospective study of 45 pediatric renal transplant recipients the residual expression of NFAT-regulated genes in lymphocytes by RT-PCR and correlated these findings with the frequency of recurrent infections in the maintenance period post-transplant. Patients with recurrent infections showed a significantly stronger inhibition of NFAT-regulated gene expression (18.2%) than patients without recurrent infections (31.7%; p = 0.012). This difference was specific, because various PK parameters of CsA and the concomitant immunosuppressive therapy were comparable between patients. Multivariate regression analysis showed that patient age and residual NFAT-regulated gene expression were the only independent determinants of recurrent infections. By ROC curve analysis, a cutoff value of 23% residual NFAT-regulated gene expression had the highest sensitivity (71.1%) and specificity (65.4%) for the discrimination of patients with and without recurrent infections. Pharmacodynamic monitoring of CsA by measurement of residual NFAT-regulated gene expression in T lymphocytes has the potential to identify over-immunosuppressed pediatric renal transplant recipients and is therefore a useful tool for the optimization of CsA therapy.

Whole blood flow cytometric measurement of NFATc1 and IL-2 expression to analyze cyclosporine A-mediated effects in T cells

The calcineurin inhibitor Cyclosporine A (CsA) is one of the crucial immunosuppressive drugs given after organ transplantation. The small therapeutic window of CsA generates the dilemma that efficient and toxic drug doses differ only slightly. Moreover, these threshold concentrations differ considerably between individuals; therefore, functional assays are urgently needed. We explored whether the transcription factor NFATc1, a direct as well as indirect target of CsA, can be used as a potential biomarker to determine the individual immunosuppressive activity of CsA. First, in isolated human T cells we showed that flow cytometry is practicable to measure NFATc1, the most abundant NFATc isoform in activated T cells. Second, for whole blood we developed a flow cytometric assay to determine in parallel the inducible transcription factor NFATc1 and the cytokine IL-2 in stimulated T cells. We found that added CsA inhibits both the expression of NFATc1 and IL-2 in T cells of stimulated whole blood samples with IC(50) values of 200 and 150 nM, respectively. The intra- and inter-assay variability was low, and clinical practicability was good. Further experiments have to demonstrate whether the parallel cytometric measurement of NFATc1 and IL-2 in whole blood is a good predictor of individual CsA efficacy and toxicity in CsA-treated patients.

Pharmacodynamic monitoring of calcineurin inhibition therapy: principles, performance, and perspectives

The calcineurin inhibitors (CNIs) cyclosporin A and tacrolimus are immunosuppressive drugs used extensively in allograft recipients. These drugs show large interindividual pharmacokinetic variation and are associated with severe adverse affects, including nephrotoxicity and cardiovascular disease. In current practice, CNIs are combined with other immunosuppressive drugs such as steroids and mycophenolate mofetil. Dosage is titrated based on blood concentration measurement. For further optimization of calcineurin (CN) inhibition therapy, new monitoring strategies are required. Pharmacodynamic-monitoring strategies constitute novel approaches for optimization of CNIs therapy. This review focuses on the general aspects of immunosuppressive drug pharmacodynamic monitoring and describes the methodologies used for monitoring CN inhibition therapy. Two different types of pharmacodynamic-monitoring strategies can be distinguished: (1) enzymatic strategies, which monitor inhibition of drug-target enzyme activity, and (2) immunologic strategies, which measure cellular responsiveness after in vitro simulated immunologic responses. Enzymatic tests are drug type-specific markers in which CN activity is directly determined. Immunologic strategies measure immune responsiveness at several levels, such as mRNA transcripts (intracellular) concentrations/excretion of cytokines, expression of surface activation markers, and cell proliferation. This review also discusses analytical issues and clinical experience with these techniques. The call for new methodologies to evaluate immunosuppressive therapy has led to the development of a large variety of pharmacodynamic-monitoring strategies. The first reports of their clinical relevance are available, but further understanding of the analytical and clinical variables involved are required for the development of accurate, reproducible, and clinically relevant markers.

New insights into the pharmacokinetics and pharmacodynamics of the calcineurin inhibitors and mycophenolic acid: possible consequences for therapeutic drug monitoring in solid organ transplantation

Although therapeutic drug monitoring (TDM) of immunosuppressive drugs has been an integral part of routine clinical practice in solid organ transplantation for many years, ongoing research in the field of immunosuppressive drug metabolism, pharmacokinetics, pharmacogenetics, pharmacodynamics, and clinical TDM keeps yielding new insights that might have future clinical implications. In this review, the authors will highlight some of these new insights for the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus and the antimetabolite mycophenolic acid (MPA) and will discuss the possible consequences. For CNIs, important relevant lessons for TDM can be learned from the results of 2 recently published large CNI minimization trials. Furthermore, because acute rejection and drug-related adverse events do occur despite routine application of CNI TDM, alternative approaches to better predict the dose-concentration-response relationship in the individual patient are being explored. Monitoring of CNI concentrations in lymphocytes and other tissues, determination of CNI metabolites, and CNI pharmacogenetics and pharmacodynamics are in their infancy but have the potential to become useful additions to conventional CNI TDM. Although MPA is usually administered at a fixed dose, there is a rationale for MPA TDM, and this is substantiated by the increasing knowledge of the many nongenetic and genetic factors contributing to the interindividual and intraindividual variability in MPA pharmacokinetics. However, recent, large, randomized clinical trials investigating the clinical utility of MPA TDM have reported conflicting data. Therefore, alternative pharmacokinetic (ie, MPA free fraction and metabolites) and pharmacodynamic approaches to better predict drug efficacy and toxicity are being explored. Finally, for MPA and tacrolimus, novel formulations have become available. For MPA, the differences in pharmacokinetic behavior between the old and the novel formulation will have implications for TDM, whereas for tacrolimus, this probably will not to be the case.

Monitoring immunosuppression with measures of NFAT decreases cancer incidence

Long-term immunosuppression causes a significantly increased risk for the development of malignancies in transplanted patients. A link between immunosuppression and incidence of cancer is well documented and involves the effect of immunosuppression on anti-tumor surveillance and antiviral adaptive immune responses. We present a 67-year-old patient with a history of recurrent non-melanoma skin cancer. After adjustment of immunosuppressive therapy under close pharmacodynamic control, the development of new malignant lesions could be prevented. The availability of a quantitative, quick laboratory test for an assessment of the individual functional activity of immunocompetent cells that are crucial for transplant rejection, defense against viral infection, and tumor surveillance along with the ability to adjust doses of immunosuppressive agents such that patients are largely protected against malignant disease and/or viral infection are important. NFAT-regulated gene expression measured in peripheral blood allowed us to predict "safe" immunosuppression. Thus patients could maintain a stable allograft function. This represents a breakthrough in transplantation medicine and advances our attempts to individualize treatment in transplanted patients.

The pharmacodynamic effect of sirolimus: individual variation of cytokine mRNA expression profiles in human whole blood samples

Sirolimus (SRL) has become an important alternative to calcineurin inhibitors due to its unique mechanism of action. Since rejection and poor graft outcome are still frequent problems despite therapeutic-range blood concentrations, pharmacodynamic measurements of its immunosuppressive effects would be of great clinical value to optimize treatment in individual patients. We performed a human whole blood assay using real time cytokine RT-PCR for the pharmacodynamic assessment of SRL. IL-2, IL-4 and IL-6 mRNA levels were quantitatively determined upon T-cell-specific stimulation in healthy individuals (n=11; in vitro) and in kidney-transplant patients (n=3; ex vivo). Furthermore, IL-2 protein secretion and T-cell proliferation was measured. After 24h incubation we observed a stronger suppression of IL-2 and IL-4 mRNA expression upon SRL addition (p<0.005; p<0.005) versus 4h (p<0.05; p<0.05). SRL effects displayed a remarkable interindividual variation, which proved to be independent of the concentration applied. Notably, 3/11 and 2/11 individuals had unaffected IL-2 and IL-4 mRNA expression after 4h incubation with SRL, respectively. In contrast, a general suppression of IL-2 protein secretion and T-cell proliferation was induced. Analysis of kidney-transplant patients verified interindividual variation and proved comparability of in vitro and ex vivo effects. We describe an individual degree of SRL-sensitivity that may correlate with clinical efficacy. Rather than analysis of one single peak, we suggest determination of two absolute cytokine mRNA peak levels for the pharmacodynamic assessment of SRL. However, prospective clinical studies are necessary to determine whether individual degrees of SRL-sensitivity correlate with clinical outcome.

Ciclosporin A tapering monitored by NFAT-regulated gene expression: a new concept of individual immunosuppression

BACKGROUND

The impact of long-term immunosuppression in renal transplant recipients with respect to safety and efficacy remains undetermined. Pharmacodynamic monitoring of the relative reduction of T-cell-specific gene expression in renal transplant recipients treated with cyclosporine A (CsA) was applied in this study.

METHODS

During the study, 20 stable renal transplant recipients with tapered CsA dose and 20 patients with stable CsA dose (matched for age, gender, CsA dose, time after transplantation) were compared for a median period of 18 months (range 6-44). CsA dose was tapered in two stages of 15% each, and the expression of the nuclear factor of activated T cells (NFAT)-regulated genes was determined by reverse-transcription polymerase chain reaction method at CsA trough level and 2 hr after oral uptake.

RESULTS

The initial residual gene expression at 2 hr after CsA intake increased from 6.31% (range 1.30-16.6) to 21.3% (range 6.58-31.8) in patients with CsA dosage reduction. In one patient, the residual gene expression increased more than 40% and resulted in a reversible Banff 1A rejection episode. Blood pressure was significantly lower after CsA dosage reduction (P<0.05). In the pair-matched control group NFAT-regulated gene expression was comparable before and after the follow-up period (7.45% [range 0.21-18.3] vs. 5.87% [range 0.66-13.2]; P=NS). Estimated glomerular filtration rate was significantly worse in the control group (P<0.05).

CONCLUSION

Our observation suggests that the measurement of the relative gene expression in CsA-treated patients is a promising tool to monitor the CsA dosage reduction in long-term renal transplant patients. An increase in residual expression of NFAT-regulated gene expression may result in an acute rejection episode.

Variation in Leukocyte Subset Concentrations Affects Calcineurin Activity Measurement: Implications for Pharmacodynamic Monitoring Strategies

Background: In renal transplantation patients, therapeutic drug monitoring of the calcineurin (CN) inhibitor cyclosporin A (CsA) is mandatory because of the drug’s narrow therapeutic index. Pharmacodynamic monitoring of CN inhibition therapy could provide a tool to define and maintain the therapeutic efficacy of CsA therapy. We investigated the effect of variation in cell counts of leukocyte subsets on leukocyte CN activity measurement in renal transplant recipients.

Methods: We measured leukocyte CN activity, whole blood CsA concentrations, and leukocyte subset cell counts in 25 renal transplant recipients. Blood was collected before graft implantation and CsA therapy, 1 day before transplantation when CsA therapy was already started, and 5 days after transplantation. Monocyte, granulocyte, CD4+ T-cell, CD8+ T-cell, B-cell, and natural killer–cell CN activities and CsA inhibition sensitivities were determined in vitro by a spectrophotometric CN assay.

Results: Leukocyte CN activity was inhibited after drug intake. Inter- and intrapatient variation in leukocyte subset cell counts resulted in variation of sample composition. The mean (SD) CN activity varied among leukocyte cell subsets, ranging from 650 (230) to 166 (26) pmol/min/106 cells for monocytes and CD4+ T cells, respectively. CsA half maximal inhibitory concentration (IC50) values ranged from 15 to 78 μg/L for monocytes and B cells, respectively.

Conclusion: Inter- and intraindividual leukocyte subset cell count variation can affect measured CN activity independent of CsA concentration. Cell-specific activity and drug sensitivity should be considered for sample validation to optimize method specificity when pharmacodynamic monitoring strategies are applied in a clinical setting.

Pharmacodynamic cyclosporine A-monitoring: relation of gene expression in lymphocytes to cyclosporine blood levels in cardiac allograft recipients

Recently, we established a pharmacodynamic assay to monitor immunosuppressive effectiveness of cyclosporine A (CsA) in patients on standard CsA regimen. The aim of the present study was to extend this correlation to reduced CsA regimen and to compare pharmacodynamic and kinetic parameters to allow prediction of rejections and infections. In 53 heart allograft recipients, nuclear factor of activated T cells (NFAT)-regulated gene expression was quantified at trough (C0) and 2-h post-CsA dose (C2). Gene expression at C2 was calculated relative to C0 (residual gene expression, RGE) or relative to a healthy reference group (absolute gene expression, AGE). RGE correlated with CsA C2-levels in bimodal fashion: above 575 ng/ml correlation was seen with flat regression gradient. Below 575 ng/ml, correlation was excellent with markedly steeper gradient. At C0 in the low-C2 group (<575 ng/ml), AGE remained unchanged, whereas in the high-C2 group (>575 ng/ml) AGE was markedly reduced. In both groups, AGE at C2 was strongly inhibited. In patients contracting infection during follow-up, RGE was lower than in those without infections independent of CsA levels. CsA-monitoring by quantitation of NFAT-regulated gene expression is feasible with standard and reduced CsA regimens. It correlates better with the incidence of infections than measurement of CsA concentrations and might help in avoiding over-immunosuppression.

Effects of ciclosporin A, tacrolimus and sirolimus on cytokine production in neonatal immune cells

BACKGROUND

It was the aim of this study to evaluate the effects of the well-known immunosuppressive drugs ciclosporin A (CsA), tacrolimus and sirolimus on the intracytoplasmic cytokine expression of neonatal immune cells.

METHODS

Immunosuppressive drugs were added to whole blood cultures of neonatal cord blood samples (n = 17) and peripheral blood samples of adults (n = 17) in vitro prior to stimulation of lymphocytes with phorbol 12-myristate 13-acetate (PMA)/ionomycin or monocytes.

RESULTS

Upon exposure to ciclosporin A (500 ng/mL) or tacrolimus (25 ng/mL) the number of cytokine expressing T cells was almost completely blocked in neonatal T cells while sirolimus (10 ng/mL) only inhibited intracytoplasmatic tumour necrosis factor alpha (TNF-alpha) expression (mean% positive cells; 4.0 +/- 2.1% vs. 1.09 +/- 0.6%, p = 0.003), but mildly stimulated the intracellular expression of interleukin (IL)-2 (24.4 +/- 6.5% vs. 28.1 +/- 7.1%, p = 0.041). In cord blood lymphocytes, the inhibitory effect of ciclosporin A and tacrolimus was dose-dependent (e.g. IL-2: control, 12.3 +/- 5.33%, ciclosporin A 5 ng/mL, 10.1 +/- 5.5%; 50 ng/mL, 7.1 +/- 4.7%; 500 ng/mL, 1.2 +/- 0.3%; tacrolimus 0.25 ng/mL, 9.3 +/- 4.9%; 2.5 ng/mL, 6.1 +/- 3.3%; 25 ng/mL, 1.0 +/- 0.6%), while the function of adult lymphocytes was only impaired at high doses of both compounds. In contrast, the number of cytokine expressing monocytes was not influenced by ciclosporin A and tacrolimus except for a minor decrease of TNF-alpha producing neonatal monocytes after addition of tacrolimus (17.9% vs. 13.9%, p = 0.031). Interestingly, sirolimus was shown to inhibit intracellular IL-6 production in adults (63.1 +/- 12.7% vs. 52.0 +/- 16.0%, p = 0.005), but in neonatal monocytes intracellular IL-6 expression was stimulated (53.5 +/- 22.0% vs. 64.7 +/- 19.1%, p = 0.041).

CONCLUSIONS

The potent dose-dependent inhibitory effect of ciclosporin A and tacrolimus in cord blood lymphocytes provides the basis for further studies on functional immaturity of the neonatal immune system and for future strategies to optimize umbilical cord blood transplantion. Sirolimus was demonstrated to have a distinct effect on neonatal immune cells as shown by increased expression of IL-2 in lymphocytes and IL-6 in monocytes, while only lymphocytic TNF-alpha expression was inhibited.

Pharmacodynamic monitoring of the immunosuppressive therapy in patients after heart transplantation: Whole blood flow cytometric analysis of lymphocyte function

Despite therapeutic monitoring and daily measurements of blood concentrations (pharmacokinetics) of immunosuppressive medications, immunosuppressive therapy remains still a challenge after heart transplantation (HTx) due to drug interactions, toxicities and individual responses to drug effects. We established whole blood flow cytometric assays of lymphocyte function to assess the pharmacodynamics of immunosuppressive therapy and investigated both pharmacokinetic and pharmacodynamic approaches after HTx. Our results showed that pharmacodynamic measurements provide a more direct assessment of the functional activity of immunosuppressants on immune cells compared to drug level monitoring alone. The information from both pharmacokinetic and pharmacodynamic monitoring has the potential to increase the efficacy and safety of individual immunosuppressive therapy after HTx.

Pharmacodynamics of T-cell function for monitoring immunosuppression

OBJECTIVES

Recent studies show that measuring pharmacodynamic (PD) effects offers a unique possibility to predict immunosuppression. Thus, in this study we have monitored the PD properties of immunosuppressants on diverse T-cell functions in heart transplant (HTx) recipients.

MATERIALS

PDs and blood concentrations (PK) of three different basis-immunosuppressive drugs were studied: cyclosporin A (CsA); tacrolimus (TRL) and sirolimus (SRL). T-cell function was analysed by expression of proliferating cell nuclear antigen (PCNA) labelling, expression of cytokines (IL-2, IFN-gamma) and surface antigen (for example, CD25) by FACS analysis.

RESULTS

In group I, at time points C0 and C2, increased CsA-PK significantly inhibited expression of IL-2, IFN-gamma, PCNA and CD25 (P < 0.05). Correlations (r(2)) at C2 between inhibition of T-cell functions (PD) with PK and with drug doses were: CsA-PK: 0.71-0.91 and CsA-dose: 0.73-0.87. In group II, increased TRL-PK over time did not further inhibit expression of CD25, but inhibited PCNA expression more on day 3, and IL-2 and IFN-gamma expression was significantly higher on days 2 and 3 compared to PD effects of CsA (P < 0.05). Blood SRL concentrations in C0 group III, increased on day 1 and remained stable at days 3 and 4. Expression of PCNA was not altered in the SRL-PK category, whereas expression of CD25 was higher and expression of cytokines was lower than PD effects of CsA.

CONCLUSIONS

Our results show that PD effects on T-cell function can be used to monitor immunosuppression bringing potential to increase the efficacy and safety of immunosuppressive therapy after HTx.

Therapeutic monitoring of calcineurin inhibitors for the nephrologist

The calcineurin inhibitors (CNI) cyclosporine and tacrolimus remain the backbone of immunosuppression for most kidney transplant recipients. Despite many years of experience, protocols that optimize efficacy with minimal toxicity remain a subject of debate. Nevertheless, studies of the pharmacokinetic properties of the CNI, particularly cyclosporine, have led to improved dosing strategies. The purpose of this article is to review the current understanding of CNI pharmacokinetics and its relevance to proper dosing and monitoring of these medications. This article also reviews the trials that have helped to define the optimal dosages and discusses the effect of adjunctive immunosuppressive agents on CNI pharmacokinetics and dosing.

Pharmacodynamic Monitoring of Cyclosporine A in Renal Allograft Recipients Shows a Quantitative Relationship Between Immunosuppression and the Occurrence of Recurrent Infections and Malignancies

BACKGROUND

At present it is unclear which dose and consecutive blood levels of cyclosporine A (CsA) are optimal with respect to immunosuppressive efficacy and drug specific side effects at the level of individual patients. Several pharmacodynamic measures of CsA effects have been proposed, but have not become clinical routine yet. Besides the lack of practicability, the biological relevance of these assays has not been determined so far.

METHODS

Residual expression of nuclear factor of activated T-cells (NFAT)-regulated genes two hours after drug intake was used as molecular pharmacodynamic marker to assess CsA effects on lymphocytes and correlated with the frequency of recurrent infections and malignancies in patients with five or more years of follow-up posttransplantation.

RESULTS

Recurrent infectious complications were observed in 44% and malignancies in 20% of the 133 patients studied. Patients with a strong suppression of NFAT-regulated genes by CsA--as judged by a residual level of transcription of less than 15% after drug intake--develop more frequent infections (53% vs. 29%; P = 0.005) and malignancies (22% vs. 4%; P = 0.002). The lack of correlation between the incidence of these complications and CsA blood concentration might point to the interindividual differences in the sensitivity towards calcineurin inhibition.

CONCLUSION

The data presented here reveal a clear relation between the frequency of infectious and malignant complications and the degree of suppression of NFAT-regulated genes by CsA in transplanted patients. Therefore, pharmacodynamic monitoring of CsA efficacy in transplanted patients might be a useful tool to adjust immunosuppressive therapy in individual patients.

In vitro evaluation of the effects of candidate immunosuppressive drugs: flow cytometry and quantitative real-time PCR as two independent and correlated read-outs

BACKGROUND

Immune monitoring may use flow cytometry or molecular biology techniques. Flow cytometry assays cells that are phenotypically characterized, whereas TaqMan RT-PCR starts with RNA extraction from unfractionated heterogeneous cell populations. We therefore wondered how the effects of immunosuppressive drugs on cytokine production in stimulated whole blood, as determined by flow cytometry, would correlate with those obtained with quantitative real-time PCR (TaqMan RT-PCR).

METHODS

Blood drawn from naive cynomolgus monkeys was exposed to incremental amounts of cyclosporine (CsA; 300, 600, 900 and 1200 ng/ml) or tacrolimus (TRL; 8, 20, 40 and 80 ng/ml) before lectin stimulation in vitro. Blood was then either stained for CD3, IFN-gamma, IL-2, IL-4, and TNF-alpha and analyzed on a flow cytometer with various gating strategies, or submitted to RNA extraction for analysis of the above mentioned cytokines mRNA transcripts using TaqMan RT-PCR.

RESULTS

Both methods revealed a parallel dose-dependent inhibition of cytokine production in stimulated blood. The 50% inhibitory concentrations (IC(50)'s) ranged from 511-771 ng/ml (CsA) and 15-29 ng/ml (TRL) with flow cytometry, and from 275-529 ng/ml (CsA) and 11-48 ng/ml (TRL) with TaqMan RT-PCR for T-helper 1 cytokines. Both assays correlated well with a Pearson product moment correlation of 0.76. Extending gating from a CD3(+) gate to a lymphocyte gate improved correlation (r = 0.85) for all cytokines investigated (except IL-2; unchanged) whereas further extending gating resulted, to the contrary, in lower correlations. Independent of gating strategy a high correlation (r = 0.97) was observed when drug IC(50)'s were considered.

CONCLUSIONS

Flow cytometry and TaqMan RT-PCR may be used interchangeably to monitor the effects of candidate immunosuppressive drugs on cytokine mRNA production in lectin-stimulated whole blood.

Immunosuppressive Activity of the Immunophilin-binding Drug Sanglifehrin A in Human Whole Blood: Potent Inhibition of Interleukin-6 Produced by Lymphocytes and Monocytes

The novel immunosuppressant Sanglifehrin A (SFA) is an immunophilin-binding metabolite with a yet unidentified mechanism of action. Several reports demonstrated the effects of SFA on proliferation and cytokine production of purified T cells with in part different results. However, less is known about the impact of SFA on the regulation of innate immune responses. We used a whole blood assay to investigate the impact of SFA on monocyte responses and T-lymphocyte activity/proliferation upon lipopolysaccharide (LPS) stimulation and anti-CD3/anti-CD28 costimulation, respectively. SFA was found to inhibit interleukin (IL)-2 protein expression of T lymphocytes. Whereas IL-2 mRNA expression was significantly reduced after 4 h of costimulation, the mRNA expression of IL-4 and IL-6 but not tumour necrosis factor (TNF)-alpha was inhibited by SFA both after 4 and 24 h of costimulation. The production of IL-2 and IL-6 protein in T lymphocytes was even strongly affected by SFA than the mRNA expression of the respective cytokine. Unlike other immunophilin-binding immunosuppressants, SFA also inhibited LPS-induced IL-6 and TNF-alpha mRNA and protein expression. At the single cell level, SFA was demonstrated to block the intracellular production of IL-6 in CD14+ monocytes but not the expression of other proinflammatory cytokines such as IL-8 and TNF-alpha. On the basis of these data, we propose that SFA may have a significant effect on the initiation and direction of immune responses. Considering the pleiotropic role of bioactive IL-6 production at the interface of innate and acquired immunity in a variety of disease conditions, it was found that these novel aspects of the unique immunosuppressive action could strongly impact on future clinical application of SFA.

Cytokine analysis to predict immunosuppression

BACKGROUND

Recently, it has been realized that TH1/TH2 cytokine production offer the unique possibility to predict drug efficacy. However, there is still an incessant need to explore assay conditions and techniques of analyzing cytokines, which are specific and reliable for monitoring drug efficacy.

METHODS

In this study we used the multiplex bead array technique to detect cytokines of TH1/TH2 cells in whole blood of heart transplanted (HTx) recipients.

RESULTS

We found significantly different levels of cytokine expression in HTx recipients compared with cytokine levels in patients prior to HTx. Furthermore, particular cytokine levels were significantly decreased 2 h after drug dosing, compared with cytokine levels before dosing in mitogen-stimulated whole blood.

CONCLUSIONS

Cytokine analysis with the multiplex array technique in mitogen-stimulated whole blood provides the possibility to predict immunosuppression.

Are anemic patients more sensitive to calcineurin inhibitors?

A calcineurin inhibitor (CNI) is characterized by high affinity binding to red blood cells. There is a possibility that hematocrit levels might affect the immunosuppressive effects of cyclosporine (CsA). The purpose of this study was to examine whether the treatment with CNI was more effective in preventing acute rejection in anemic compared with nonanemic patients and to find a suitable method to monitoring immunosuppression. Ninety-five living donor renal transplant recipients who were treated with CsA were divided into five groups depending on their Ht levels. The incidences of biopsy-proven acute rejection were 1/8 (12.5%), 8/31 (25.8%), 6/28 (21.4%), 10/22 (45.5%), and 2/6 (33.3%) for Ht < or = 25%, 25% < Ht < or = 30%, 30% < Ht < or = 35%, 35% < Ht < or = 40%, and 40% < Ht, respectively. In vitro IL-2 mRNA inhibition tests were performed to evaluate lymphocyte function after stimulation of whole-blood with phorbol myristate acetate and Ca-ionophore in the presence of various concentrations of CsA. Whole blood CsA levels causing 50% inhibition of IL-2 mRNA (IC50) were 256, 310, 175, and 55 ng/mL for Ht 50%, 40%, 30%, and 20%, respectively. It is speculated that plasma concentrations of CsA may increase at low Ht levels, because lower incidences of acute rejection and lower IC50 values of CsA were observed in the anemic state. When the dosage of CsA was adjusted to its whole-blood concentration, the anemic state is likely to enhance the immunosuppressive effect of CsA. A pharmacodynamic study, such as the IL-2 mRNA inhibition test, is preferable for CsA monitoring.

Mycophenolic Acid Interaction With Cyclosporine and Tacrolimus In Vitro and In Vivo

The effect of mycophenolic acid (MPA) in combination with either cyclosporine (CsA) or tacrolimus (TRL) on whole-blood lymphocyte function was assessed in vitro as well as in vivo. For the in vitro studies, rat whole blood was incubated with different concentrations of MPA together with CsA or TRL. In vivo, rats (n = 6 per group) were orally treated with 2.5 or 5 mg/kg of mycophenolate mofetil (MMF), either alone or in combination with 5 mg/kg CsA or 4 mg/kg TRL. Blood was obtained before and at different times after dosing. For both in vitro and in vivo studies, mitogen-stimulated whole blood was analyzed by flow cytometry to determine inhibition of expression of lymphocyte proliferation (proliferating cell nuclear antigen, PCNA) and T-cell activation (eg, CD25). Plasma MPA concentrations were measured by HPLC, and whole-blood CsA and TRL concentrations were quantified using LC-MS/MS. In vitro, low concentrations of 250 and 500 nM MPA acted additively with CsA and overadditively with TRL to suppress lymphocyte function, whereas higher MPA concentrations (1000 nM) in these combinations did not further increase inhibition compared with monotherapy with CsA or TRL alone. In vivo, the MPA AUC0-24 showed a dose-dependent increase. CsA and TRL AUC0-24 were not influenced by the MMF dose. Combination therapy increased inhibition of lymphocyte function compared with MMF monotherapy with a pronounced effect on PCNA compared with CD25. Significant differences between 2.5 and 5 mg/kg MMF in the combination groups were observed at 2 or 6 hours after dosing because of the maximal inhibitory effect on PCNA and CD25 expression (P < 0.05, ANOVA). However, in combination with TRL no different effects on the inhibition of CD25 expression were found between the 2 MMF doses. These novel data indicate that measurement of pharmacodynamic parameters of lymphocyte function in whole blood may help to monitor drug combination therapy and provide a rationale for drug reduction to minimize toxicity without compromising efficacy.

Assessment of immunosuppressive drug interactions: inhibition of lymphocyte function in peripheral human blood

Cyclosporin (CsA) or tacrolimus (TRL) is routinely combined with either sirolimus (SRL) or mycophenolate mofetil (MMF) in immunosuppressive regimes in organ transplantation. The aim of our study was to establish a specific human blood assay of lymphocyte function in order to assess interactions of these drug combinations. Different concentrations (10(6)-10(9) nM) of CsA, TRL, SRL or mycophenolic acid (MPA, the active metabolite of MMF) was added to whole blood of five human volunteers. Drug combinations were studied by adding 250, 500 or 1000 nM of MPA to different concentrations of CsA, TRL, or SRL or by adding 1, 10 or 25 nM of SRL to different concentrations of CsA or TRL. After concanavalin-A stimulation, whole blood cultures were analyzed by flow cytometry detecting lymphocyte proliferation and activation by bivariate expression of proliferating cell nuclear antigen (PCNA)/DNA content and T cell-surface activation antigens (e.g. CD25, CD95, and CD154). We found an order of potency inhibiting lymphocyte function with SRL>TRL>CsA>MPA. In addition, we observed enhanced inhibition of PCNA, CD25, CD95 or CD154, if either CsA or TRL was combined with low concentrations of MPA, or SRL alone or if SRL was combined with low concentrations of MPA. Data analysis revealed an independent functional synergism or partial agonism in most combinations. This human blood assay is able to assess lymphocyte function and to monitor immunosuppressive therapy. The assay also permits pharmacological analysis of drug interactions, which will lead to improved safety and therapeutic efficacy in transplanted patients.

Kinetics of cytokine gene expression in human CD4+ and CD8+ T-lymphocyte subsets using quantitative real-time PCR

The time kinetics of five cytokines [interleukin-2 (IL-2), IL-5, interferon-gamma (IFN-gamma), granulocyte macrophage-colony stimulating factor (GM-CSF) and tumour necrosis factor-alpha (TNF-alpha)] and one cytotoxic effector protein (granzyme B) was analysed by real-time quantitative polymerase chain reaction (PCR) following in vitro stimulation of human CD4 and CD8 T lymphocytes. Two stimuli were used, a mitogen [phytohemagglutinin (PHA)] and a recall antigen [purified protein derivative (PPD)]. The pattern of cytokine mRNA expression was found to be dependent on the T-cell subset and stimulus used. A wide interindividual variability in the cytokine gene expression pattern was demonstrated. Two expression patterns were observed. A bell-shaped expression profile was seen for most cytokines upon PHA activation in both subsets and PPD-activated CD4 T cells, whereas a biphasic/multiphasic expression pattern was noted in CD8 T cells upon PPD stimulation. For most cytokines, the time to induction was within 30 min of activation, and maximum accumulation seemed to be obtained after 4-8 h of activation. A sustained high level could, however, be noticed for up to 24 h. Granzyme B gene expression was also induced within 30 min of activation but showed a continuous gradual increase and late maximal accumulation (48-72 h). The findings of the present study are of importance when designing studies using the cytokine gene expression profile as a marker for antigen-specific T lymphocytes. It might be recommended that cytokine gene expression (IL-2, IL-5 and IFN-gamma) should be measured after 4-8 h of specific activation but also up to 24 h of stimulation is acceptable. Granzyme B should preferentially be measured after 48-72 h of activation.

Sensitivity of Whole-Blood T Lymphocytes in Individual Patients to Tacrolimus (FK 506): Impact of Interleukin-2 mRNA Expression as Surrogate Measure of Immunosuppressive Effect

Background: To optimize immunosuppressive treatment in individual transplant patients, functional measurements of the effects of tacrolimus (FK 506) are of clinical importance. Previous investigations have demonstrated the occurrence of tacrolimus-resistant production of interleukin-2 (IL-2) in vitro, which may explain in part why rejection episodes are still a frequent problem despite attainment of therapeutic blood concentrations and HLA matching. However, an adequate surrogate marker to define the tacrolimus response in individual patients has not been established.

Methods: We investigated the immunosuppressive effects of tacrolimus on anti-CD3/anti-CD28 T-cell costimulation in a human whole-blood assay, analyzing T-cell proliferation, activation marker expression (CD25, CD69), IL-2 protein expression, and cytokine mRNA expression in vitro (n = 11 healthy individuals). We also quantified IL-2 mRNA expression in patients undergoing tacrolimus (n = 4) or cyclosporin A (CsA; n = 4) monotherapy before ex vivo living-donor kidney transplantation.

Results: T-cell proliferation; CD25, CD69, and IL-2 concentrations; and IL-4 mRNA were significantly decreased in vitro. In contrast, cytokine mRNA profiles revealed variable tacrolimus sensitivity. Whole-blood samples from 3 of 11 healthy individuals demonstrated marked suppression of IL-2 mRNA expression (&gt;50%) when tacrolimus was administered in vitro. When CsA was added to whole-blood cultures, the influence on IL-2 mRNA expression was comparable to that of tacrolimus in 9 of 11 individuals. Two individuals responded conversely, indicating that differences in the in vitro response to tacrolimus and CsA among individuals may be attributable to potential heterogeneity in the involvement of the CD28 pathway. Kinetic profiles of IL-2 mRNA expression also revealed individually distinct degrees of calcineurin inhibitor sensitivity in patients undergoing tacrolimus or CsA monotherapy before living-donor kidney transplantation.

Conclusions: Our results suggest an individual degree of calcineurin inhibitor sensitivity of activated whole-blood lymphocytes based on IL-2 mRNA expression. Our approach is potentially valuable for identifying transplant patients in whom IL-2 mRNA expression is unaffected or even enhanced after initiation of immunosuppressive therapy. Such individuals may be less sensitive to the immunosuppressive agent and therefore at increased risk of transplant rejection. Prospective studies are necessary to determine the correlation of IL-2 mRNA expression with the clinical risk of transplant rejection.

Individual variability in cyclosporin A sensitivity: the assessment of functional measures on CD28-mediated costimulation of human whole blood T lymphocytes

The quantitative analysis of cyclosporin A (CsA) effects might be helpful for optimizing immunosuppressive treatment after allogeneic organ transplantation in individual patients, as rejection can occur despite the existence of CsA blood levels within therapeutic ranges. Previous investigations found that costimulation of the CD28 pathway generally mediates CsA-resistant proliferation of T cell receptor (TCR)-activated T lymphocytes. However, here we describe considerable interindividual variation regarding the immunosuppressive effects of CsA (1000 microg/L) on anti-CD3/CD28 T cell costimulation in a human whole blood assay. In the in vitro study, we found a significant reduction of T cell proliferation, activation marker expression (CD25, CD69) on the T cell surface, and interleukin-2 (IL-2) protein expression in whole blood samples of all healthy subjects (n = 11). However, the investigation of cytokine mRNA profiles revealed variable results of in vitro CsA sensitivity. Whole blood samples of 3 of 11 healthy individuals demonstrated a marked suppression of IL-2 mRNA expression (>50%) and a partial inhibition of IL-4, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) mRNA expression on addition of CsA. In contrast, the remaining 8 healthy individuals had cytokine mRNA expression levels that were unaffected or even increased when CsA was administered in vitro. In patients undergoing CsA monotherapy (ex vivo study, n = 9), we found a significant suppression of IL-2 mRNA levels in 4 of 9 patients ex vivo. Thus, we cannot confirm a universal CsA resistance of T cells on anti-CD3/CD28 costimulation. Instead, our results suggest an individual degree of CsA sensitivity that might be more consistent with clinical experience. Prospective studies are necessary to determine if individual degrees of CsA sensitivity correlate with clinical events and are associated with a low or high risk of transplant rejection.