Immunomonitoring of nuclear factor of activated T cells-regulated gene expression: the first clinical trial in liver allograft recipients

Pharmacodynamic Monitoring of Ciclosporin and Tacrolimus: Insights From Nuclear Factor of Activated T-Cell-Regulated Gene Expression in Healthy Volunteers

BACKGROUND

Although therapeutic drug monitoring of calcineurin inhibitor (CNI) concentrations is performed routinely in clinical practice, an identical concentration may lead to different effects in different patients. Although the quantification of nuclear factor of activated T-cell-regulated gene expression (NFAT-RGE) is a promising method for measuring individual CNI effects, CNI pharmacodynamics are as of yet incompletely understood.

METHODS

CNI concentrations and NFAT-RGEs were quantified in 24 healthy volunteers receiving either ciclosporin or tacrolimus in 2 clinical trials. NFAT-RGE was measured using quantitative reverse transcription polymerase chain reaction tests of whole-blood samples. Pharmacokinetics and pharmacodynamics were analyzed using compartmental modeling and simulation. In addition, NFAT-RGE data from renal transplant patients were analyzed.

RESULTS

The average NFAT-RGE during a dose interval was reduced to approximately 50% with ciclosporin, considering circadian changes. The different effect-time course with ciclosporin and tacrolimus could be explained by differences in potency (IC 50 204 ± 41 versus 15.1 ± 3.2 mcg/L, P < 0.001) and pharmacokinetics. Residual NFAT-RGE at the time of maximum concentration (RGE tmax ) of 15% when using ciclosporin and of 30% when using tacrolimus was associated with similar average NFAT-RGEs during a dose interval. Renal transplant patients had similar but slightly stronger effects compared with healthy volunteers.

CONCLUSIONS

Ciclosporin and tacrolimus led to similar average suppression of NFAT-RGE in a dose interval, despite considerably different RGE tmax . Pharmacodynamic monitoring of average NFAT-RGE should be considered. When using NFAT-RGE at specific time points, the different effect-time courses and circadian changes of NFAT-RGEs should be considered.

Getting immunosuppression just right: the role of clinical biomarkers in predicting patient response post solid organ transplantation

INTRODUCTION

Actually, immunosuppression selection isn't based on individual immune alloreactivity, and immunosuppressive drug dosing is mainly based on the development of toxicity and the achievement of specific target concentrations. Since a successful outcome requires optimal patient risk stratification and treatment, several groups have evaluated candidate biomarkers that have shown promise in the assessment of individual immune responses, the prediction of personal pharmacodynamic effects of immunosuppressive drugs and the prognosis and diagnosis of graft outcomes..

AREAS COVERED

This review includes biomarkers that the Scientific Community in Solid Organ Transplantation currently considers to have potential as diagnostic and prognostic biomarkers of graft evolution. We have focused on recent scientific advances and expert recommendations regarding the role of specific and non-specific pharmacodynamic biomarkers that are mainly involved in the T-cell-mediated response.

EXPERT OPINION

Integral pharmacologic monitoring that combines pharmacokinetics, pharmacogenetics and predictive pharmacodynamic biomarkers may provide crucial information and allow personal adjustment of immunosuppressive drugs at an early stage before severe adverse events ensue. Multicentre, randomized, prospective and interventional trials are needed to fine tune the established cut-off values for each biomarker and the optimal monitoring frequency for each biomarker and to accurately evaluate possible clinical confounding factors to enable correct clinical qualification.

Monitoring of gene expression in tacrolimus-treated de novo renal allograft recipients facilitates individualized immunosuppression: Results of the IMAGEN study

AIMS

Calcineurin inhibitors (CNI) have a small therapeutic window, and drug monitoring is required. Pharmacokinetic monitoring does not correlate sufficiently with clinical outcome. Therefore, the expression of nuclear factor of activated T cells (NFAT)-regulated genes in the peripheral blood has been suggested as a potentially useful immune monitoring tool to optimize CNI therapy. NFAT-regulated gene expression (RGE) was evaluated in renal allograft recipients as predictive biomarker to detect patients at risk of acute rejection or infections.

METHODS

NFAT-RGE (interleukin-2, interferon-γ, granular-macrophage colony-stimulating factor) was evaluated by quantitative real-time polymerase chain reaction in whole blood samples at day 7, day 14, month 1, 3, and 6 after transplantation in 64 de novo renal allograft recipients from 3 European centres. Immunosuppression consisted of tacrolimus (Tac), mycophenolic acid, and corticosteroids.

RESULTS

Tac concentrations (C0 and C1.5) correlated inversely with NFAT-RGE (P < .01). NFAT-RGE showed a high interindividual variability (1-61%). Patients with high residual gene expression (NFAT-RGE ≥30%) were at the increased risk of acute rejection in the following months (35 vs. 5%, P = .02), whereas patients with low residual gene expression (NFAT-RGE <30%) showed a higher incidence of viral complications, especially cytomegalovirus and BK virus replication (52.5 vs. 10%, P = .01).

CONCLUSIONS

NFAT-RGE was confirmed as a potential noninvasive early predictive biomarker in the immediate post-transplant period to detect patients at risk of acute rejection and infectious complications in Tac-treated renal allograft recipients. Monitoring of NFAT-RGE may provide additional useful information for physicians to achieve individualized Tac treatment.

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.

Nuclear factor of activated T cells as potential pharmacodynamic biomarker for the risk of acute and subclinical rejection in de novo liver recipients

BACKGROUND & AIMS

Nuclear factor of activated T cell-regulated gene expression (NFAT-RGE) has been proposed as a pharmacodynamic biomarker for tacrolimus (Tac) and cyclosporine (CsA). Our aim was to evaluate the role of NFAT-RGE in modulating intralymphocytary IL-2 and IFN-γ expression and its clinical utility as an early non-invasive predictive biomarker for the risk of acute rejection (AR) and infection in de novo liver transplant (LT) recipients.

METHODS

Fifty-six LT recipients treated with Tac or CsA [with and without mycophenolate mofetil (MMF)] were included: 30 free of rejection or infection, 11 rejectors (T cell-mediated acute rejection), 5 with subclinical rejection (SCR) and 10 with cytomegalovirus (CMV) infection. Within the first 3 months after transplantation, NFAT-RGE of IL-2, IFN-γ and GM-CSF and intralymphocytary synthesis of IL-2 and IFN-γ were evaluated by real-time PCR and flow cytometry respectively.

RESULTS

A significant increase in NFAT-RGE was observed in patients who experienced TCMAR (75% [42-100%]) or SCR (41% [18-78%]) compared with patients without rejection or infection (14% [2-23%]). Positive correlations between the %NFAT-RGE-IFN and both the %CD8CD69IFN-γ and %CD4CD69IFN-γ and between the %NFAT-RGE-IL2 and the %CD8CD69IL2 were observed. NFAT-RGE was significantly lower in CMV⁺ patients than in non-infected patients. Finally, an inverse correlation between the Tac or CsA concentration and inhibition of NFAT-RGE were observed.

CONCLUSIONS

Sequential post-transplantation NFAT-RGE monitoring combined with intralymphocytary IL-2 and IFN-γ before transplantation and at the first and third month post-transplantation may be key predictive and diagnostic biomarkers for the risk of TCMAR and SCR and better guide CNi therapy in LT patients.

An intronic polymorphism of NFATC1 gene shows a risk association with biopsy-proven acute rejection in renal transplant recipients

Background

We aimed to explore the influence of single nucleotide polymorphisms (SNPs) in NFATC1 gene on the occurrence of biopsy-proven acute rejection (BPAR) in renal transplant recipients.

Methods

Blood samples from 131 subjects with stable allograft function (STA) and 69 with BPAR episodes were collected and analyzed using target sequencing (TS) with an established panel. Odds ratios (OR) and 95% confidence intervals (95% CIs) were calculated for logistic regression models adjusted for confounding factors. Pathological changes were extracted and the relationship with tagger SNPs was calculated. Moreover, the CCK-8 assay was performed to explore the proliferation of T lymphocytes, and PCR, Western blotting and enzyme-linked immunosorbent assay were applied to identify the effect of mutant on the activation of T cells.

Results

High-quality readouts were obtained for 55 NFATC1 SNPs and 14 tagger SNPs were remained for further analysis. After adjusting for clinical confounding factors, the distribution of four NFATC1 SNPs, including rs2290154, rs2304738, rs754093 and rs754096, were statistically significant between STA and BPAR groups. Pathological association analysis indicated one SNP, rs2290154, was significantly related with the Banff score and renal tubulitis. Our in vitro study suggested that NFATC1 rs2290154 mutant could remarkably promote the T cell proliferation, increase the transcription of NFATC1 mRNA and expression of NFATC1 protein, as well as the interleukin-2 (IL-2) secretion.

Conclusions

We reported the crucial association of NFATC1 gene with the occurrence of acute rejection (AR) episodes. Moreover, in vitro NFATC1 rs2290154 was significantly involved in the T lymphocytes activation and proliferation through increasing the translation of NFATC1 mRNA and expression of NFATC1 protein, along with the secretion of IL-2.

Suppressed calcineurin-dependent gene expression identifies lung allograft recipients at increased risk of infection

Lung transplant immunosuppression regimens generally include the calcineurin inhibitor tacrolimus. We hypothesized that mean residual expression (MRE) of calcineurin-dependent genes assesses rejection and infection risk better than does tacrolimus trough. We prospectively followed 44 lung allograft recipients at 2 to 18 months posttransplant and measured changes in whole blood interleukin-2, interferon-γ, and granulocyte-macrophage colony-stimulating factor gene expression following a tacrolimus dose. Posttransplant duration, immunosuppressive medication levels, and bronchoscopic rejection and infection assessments were compared with MRE by using generalized-estimating equation-adjusted models. Prednisolone effect on MRE was assessed ex vivo in blood samples from nontransplanted controls. Tacrolimus concentration inhibiting 50% of cytokine production (IC₅₀ ) was measured in a pretransplant subset. Results showed that MRE did not change with diagnosis of rejection but that airway infection was associated with a 20% absolute decrease (95% confidence interval 11%-29%). MRE increased with time after transplant but was not associated with tacrolimus trough. Interestingly, MRE correlated inversely with corticosteroid dose in the study cohort and ex vivo. Pretransplant tacrolimus IC₅₀ depended on the cytokine measured and varied between individuals, suggesting a range in baseline responses to tacrolimus. We conclude that MRE identifies infection risk in lung allograft recipients, potentially integrating calcineurin inhibitor and steroid effects on lymphocyte effector function.

Activity of the Calcineurin Pathway in Patients on the Liver Transplantation Waiting List: Factors of Variability and Response to Tacrolimus Inhibition

BACKGROUND

We sought to evaluate, in patients on a liver transplantation waiting list, potential biomarkers of the base calcineurin pathway activity with use of a new model of nonstimulated peripheral blood mononuclear cells (PBMC) and ex vivo response to tacrolimus (TAC).

METHODS

The calcineurin pathway activity was explored ex vivo in stimulated and nonstimulated PBMC from 19 patients. The inhibition of NFAT1 translocation to PBMC nuclei, expression of intracellular IL-2, and membrane CD25 in different T-cell subsets were measured by multiparametric flow cytometry before and after exposure to TAC. We also studied the influence on the individual response of polymorphisms in 3 key genes of the calcineurin pathway: PPIA, PPP3CA, and IL2RA.

RESULTS

All pharmacodynamics profiles closely fitted an I/Imax sigmoid model. Interindividual variability was higher in nonstimulated than in stimulated conditions, as well as in the presence of TAC. IL-2+CD8+ cells at TAC Imax showed the highest interindividual variability, suggesting its usefulness as a biomarker of individual TAC effects integrating many different sources of regulation and variability. Moreover, in the absence of TAC, patients with end-stage liver disease exhibited lower NFAT1 translocation and T-cell activation than healthy volunteers from a previous study under similar conditions. Multivariate statistical analysis showed strong and significant associations between TAC pharmacodynamic parameters and 2 polymorphisms in the gene-coding cyclophilin A (rs8177826 and rs6850).

CONCLUSIONS

We show the feasibility of using nonstimulated PBMCs to explore the calcineurin pathway under more physiologic conditions and point toward potential biomarkers for TAC pharmacodynamic monitoring. ClinicalTrials.gov Identifier: NCT01760356

NFAT-regulated cytokine gene expression during tacrolimus therapy early after renal transplantation

AIMS

Despite pharmacokinetic monitoring of calcineurin inhibitors, the long-term outcome after transplantation (Tx) is still hampered by the side effects of these drugs. The aim of the present study was to characterize nuclear factor of activated T cells (NFAT)-regulated gene expression as a potential pharmacodynamic biomarker for further individualization of tacrolimus (Tac) therapy.

METHODS

In 29 renal allograft recipients, samples were drawn once pre-Tx, and before and 1.5 h after Tac dosing at approximately 1 week, 6 weeks and 1 year post-Tx. Tac concentrations were measured by immunoassay, while the expression of genes encoding NFAT-regulated cytokines [interleukin 2 (IL2), interferon gamma (IFNG), colony stimulating factor 2 (CSF2)] and cytochrome P450 3A5 (CYP3A5) genotyping were determined by real-time polymerase chain reaction.

RESULTS

The cytokine response after Tac dosing varied up to 46-fold between patients and changed significantly with time post-engraftment. Tac concentrations 1.5 h postdose (C_1.5 ) >15 μg l^-1 were associated with strong cytokine inhibition and residual gene expression (RGE) ≤10%, while lower Tac C_1.5 resulted in more variable responses (RGE 2.5-68.7%). Patients with ongoing subclinical acute rejection (n = 5) demonstrated limited cytokine inhibition (RGE 39.7-72.6%), while patients with polyoma virus viraemia (n = 3) had relatively strong inhibition of cytokines (RGE 2.5-32.5%). By contrast, there was no association between Tac exposure and rejection or viraemia.

CONCLUSIONS

The findings of our study support the potential of NFAT-regulated gene expression measurements as a pharmacodynamic tool for additional monitoring of Tac therapy, especially in the context of overimmunosuppression and viraemia.

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.

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.

The Calcineurin Inhibitor-Sparing (CIS) Trial - individualised calcineurin-inhibitor treatment by immunomonitoring in renal allograft recipients: protocol for a randomised controlled trial

Background

Adequate monitoring tools are required to optimise the immunosuppressive therapy of an individual patient. Particularly, in calcineurin inhibitors, as critical dose drugs with a narrow therapeutic range, the optimal monitoring strategies are discussed in terms of safety and efficacy. Nevertheless, no pharmacokinetic monitoring markers reflect the biological activity of the drug. A new quantitative analysis of gene expression was employed to directly measure the functional effects of calcineurin inhibition: the transcriptional activities of the nuclear factor of activated T-cell (NFAT)-regulated genes in the peripheral blood.

Methods/Design

The CIS study is a randomised prospective controlled trial, comparing a ciclosporin A (CsA)-based immunosuppressive regimen monitored by CsA trough levels to a CsA-based immunosuppressive regimen monitored by residual NFAT-regulated gene expression. Pulse wave velocity as an accepted surrogate marker of the cardiovascular risk is assessed in both study groups. Our hypothesis is that an individualised CsA therapy monitored by residual NFAT-regulated gene expression results in a significantly lower cardiovascular risk compared to CsA therapy monitored by CsA trough levels.

Discussion

There is a lack of evidence in individualising standard immunosuppression in renal allograft recipients. The CIS study will consider the feasibility of individualised ciclosporin A immunosuppression by pharmacodynamic monitoring and evaluate the opportunity to reduce cardiovascular risk while maintaining sufficient immunosuppression.

Trial registration

EudraCT identifier 2011-003547-21, registration date 18 July 2011

https://www.clinicaltrialsregister.eu

Tacrolimus Pharmacodynamics and Pharmacogenetics along the Calcineurin Pathway in Human Lymphocytes

BACKGROUND

Although therapeutic drug monitoring has improved the clinical use of immunosuppressive drugs, there is still interpatient variability in efficacy and toxicity that pharmacodynamic monitoring may help to reduce. To select the best biomarkers of tacrolimus pharmacodynamics, we explored the strength and variability of signal transduction and the influence of polymorphisms along the calcineurin pathway.

METHODS

Peripheral blood mononuclear cells from 35 healthy volunteers were incubated with tacrolimus (0.1–50 ng/mL) and stimulated ex vivo. Inhibition of NFAT1 (nuclear factor of activated T cells 1) translocation to the nucleus and intracellular expression of interleukin-2 in CD4+ and CD8+ T cells and the surface activation marker CD25 in CD3+ cells were measured by flow cytometry. We sequenced the promoter regions of immunophilins and calcineurin subunits and characterized selected single nucleotide polymorphisms in the genes of the calcineurin pathway with allelic discrimination assays.

RESULTS

All responses closely fitted an I/Imax sigmoid model. Large interindividual variability (n = 30) in I0 and IC50 was found for all biomarkers. Moreover, strong and statistically significant associations were found between tacrolimus pharmacodynamic parameters and polymorphisms in the genes coding cyclophilin A, the calcineurin catalytic subunit α isoenzyme, and CD25.

CONCLUSIONS

This study demonstrates the consistency and large interindividual variability of signal transduction along the calcineurin pathway, as well as the strong influence of pharmacogenetic polymorphisms in the calcineurin cascade on both the physiological activity of this route and tacrolimus pharmacodynamics.

Pharmacodynamic monitoring of immunosuppressive effects indicates reduced cyclosporine activity during telaprevir therapy

Drug interactions with immunosuppressive drugs are a major problem associated with protease inhibitor-based antiviral triple therapy for hepatitis C virus (HCV) reinfection after liver transplantation. In this retrospective cohort study, we analyzed biomarkers of the immunosuppressive effects of cyclosporine A (CSA) by quantifying nuclear factor of activated T cells (NFAT)-regulated gene expression during telaprevir (TVR) therapy in 5 liver transplant patients. Furthermore, dose adjustments and blood concentrations of CSA as well as the clinical course were analyzed. We observed a clear impact of TVR not only on doses and blood concentrations but also on the immunosuppressive effects of CSA. Despite apparently adequate CSA trough concentrations, the CSA peak concentration decreased to 68% (range = 44%-90%). This was associated with a 1.9-fold (1.6- to 4.1-fold) increase in the residual gene activity of NFAT-regulated genes, which indicated reduced immunosuppressive activity of CSA with TVR co-medication. The median dose of CSA was reduced to 25% (range = 16%-48%) and 31% (range = 22%-64%) after 1 and 2 weeks, respectively. The CSA drug clearance was reduced to 38.7% (range = 31.0%-49.4%). We report excellent antiviral efficacy. At the end of the observation period, all patients were HCV RNA-negative (1 patient at 18 weeks, 1 patient at 12 weeks, and 3 patients at 4 weeks after the end of therapy). Safety was acceptable, with mild acute rejection and reactivation of cytomegalovirus being the most serious adverse events. One patient with histologically proven recurrent cholestatic hepatitis before therapy underwent retransplantation during the course of antiviral therapy. In conclusion, the immunomonitoring of NFAT-regulated gene expression indicated reduced immunosuppressive activity of CSA during antiviral therapy with TVR in our cohort of liver transplant patients. Thus, the immunosuppressive effects of CSA may be overestimated if one is looking only at trough concentrations during co-medication with protease inhibitors or other strong cytochrome P450 3A inhibitors. Immunomonitoring of NFAT-regulated gene expression could, therefore, help to prevent overimmunosuppression or underimmunosuppression.

Reduced residual gene expression of nuclear factor of activated T cells-regulated genes correlates with the risk of cytomegalovirus infection after liver transplantation

BACKGROUND

Pharmacokinetic monitoring of calcineurin inhibitors (CNIs) is unsatisfactory because, at comparable blood concentrations, side effects vary considerably. We recently confirmed the applicability of a pharmacodynamic (PD) assay that measures the suppression of CNI target genes, specifically the suppression of nuclear factor of activated T cells (NFAT)-regulated genes in liver transplant (LT) recipients. The aim of this prospective study was to prove the clinical reliability of this assay. Therefore, we quantified the residual gene expression (RGE) of NFAT-regulated genes and evaluated the association between the RGE of NFAT-regulated genes and the incidence of cytomegalovirus (CMV) infection.

PATIENTS AND METHODS

In 20 LT recipients, 10 patients on cyclosporine (CsA) and 10 patients on tacrolimus (Tac) therapy, who presented with CMV infection, the RGEs of interleukin-2, interferon-γ (IFNγ), and granulocyte-monocyte colony-stimulating factor were measured and compared with the RGEs of these cytokines in 40 healthy dose-matched LT controls.

RESULTS

CsA-treated CMV patients demonstrated a lower RGE of all NFAT-regulated genes compared with controls (30 ± 17 vs. 44 ± 20, P = 0.067). For IFNγ, the level of significance was reached (26 ± 17 vs. 43 ± 17, P = 0.0125). Daily CsA dosage, CsA baseline (C0 ) and 2 h (C2 ) concentrations were comparable (CsA dosage 169 mg/day vs. 165 mg/day; CsA C0 94 μg/L vs. 85 μg/L; CsA C2 389 μg/L vs. 381 μg/L). In addition, Tac-treated CMV patients demonstrated a lower RGE of all NFAT-regulated genes compared with controls (68 ± 25 vs. 84 ± 22, P = 0.0769). Analogous to CsA-treated CMV patients, the level of significance was reached for IFNγ (61 ± 24 vs. 88 ± 29, P = 0.0154). Daily Tac dosage and Tac 1.5 h concentrations (C1.5 ) were comparable in both groups (Tac dosage 4 mg/day vs. 4 mg/day; Tac C1.5 8 μg/L vs. 10 μg/L), whereas Tac C0 concentrations were significantly higher in controls (Tac C0 4 μg/L vs. 6 μg/L, P = 0.0276).

CONCLUSION

Measuring the RGE of NFAT-regulated genes is appropriate to assess the risk of infections in LT recipients. Measuring the RGE of IFNγ is particularly suitable to assess the risk of CMV infection. PD monitoring of CNIs in LT recipients is an approach to individualize immunosuppression, which may help to reduce infectious complications.

Immune monitoring post liver transplant

Many of the causes of short and late morbidity following liver transplantation are associated with immunosuppression or immunosuppressive medications. Current care often involves close monitoring of liver biochemistry as well as therapeutic drug levels. However, the postoperative course following liver transplantation can often be associated with significant complications including infection and rejection, suggesting an inadequacy in current immune function monitoring. Many assays have been tested in the research setting to identify possible biomarkers that may be used to predict clinical events such as acute cellular rejection, and therefore allow modification of a patient’s immunosuppressive regimen prior to a clinical event. However, these generally require significant laboratory processing and have had difficulty becoming established in common clinical use outside the research setting. One assay, Cylex ImmuKnow has been food and drug administration approved but has had variable results. In this review we discuss the assays that have been used to assess monitoring of immune function after liver transplantation and consider possible future directions.

Nuclear translocation of nuclear factor of activated T cells (NFAT) as a quantitative pharmacodynamic parameter for tacrolimus

Nuclear factor of activated T cells (NFAT) is a family of transcription factors involved in regulating the immune response. The canonical NFAT pathway is calcium-dependent and upon activation, NFAT is dephosphorylated by the phosphatase, calcineurin. This results in its translocation from the cytoplasm to the nucleus and transcription of downstream target genes that include the cytokines IL-2, IL-10, and IFNγ. Calcineurin inhibitors including tacrolimus inhibit the NFAT pathway and are used as immunosuppressants in transplant settings to prevent graft rejection. There is, as yet, no direct means to monitor tacrolimus pharmacodynamics. In this study, a rapid, quantitative, image cytometry-based measurement of nuclear translocation of NFAT1 is used to evaluate NFAT activation in T cells and its tacrolimus-induced inhibition. A strong dose-dependent correlation between NFAT1 inhibition and tacrolimus dose is demonstrated in vitro. Time kinetic analysis of NFAT1 inhibition in plasma from stable renal transplant recipients before and after an in vivo dose with tacrolimus correlated with the expected pharmacokinetic profile of tacrolimus. This was further corroborated by analysis of patients' autologous CD4 and CD8 T cells. This is the first report to show that the measurement of NFAT1 activation potential by nuclear translocation can be used as a direct, sensitive, reproducible and quantitative pharmacodynamic readout for tacrolimus action. These results, and the rapid turnaround time for this assay, warrant its evaluation in a larger clinical setting to assess its role in therapeutic drug monitoring of calcineurin inhibitors.

Next level of immunosuppression: drug/immune monitoring

1. Current immunological monitoring relies heavily on clinical judgment and therapeutic drug levels and does not adequately assess the functional or donor-specific immunosuppression (IS) status of recipients of liver transplantation (LT). 2. Trough levels of drugs are arbitrary and are more clinically relevant for preventing supratherapeutic or subtherapeutic dosing and blood concentrations and for more closely monitoring at-risk populations (children, the elderly, and patients with organ dysfunction). The AUC or the post-dose levels may be more precise, but they have not been used extensively by transplant centers. 3. Data on drug/immune monitoring specific to LT are fairly limited; therefore, clinical practice is often borrowed from experiences with nonhepatic transplantation (mainly renal transplantation). 4. The monitoring of drug levels in patients taking generic immunosuppressants is challenging because the formulations may change with each prescription. The monitoring of drug or antibody levels is not yet clinically available for biological therapies (induction, lymphocyte-depleting, and maintenance agents). 5. Polymorphisms in drug metabolism (cytochrome P450 and P-glycoprotein) may be useful in selecting the initial and maintenance dosages of immunosuppressants and in preventing complications from over or underimmunosuppression. 6. Future immune monitoring assays should be focused on genomic or immunological predispositions and on specific reactivities to donor antigens to guide the appropriate dosing and minimization of IS after LT.