Synergistic mechanisms by which sirolimus and cyclosporin inhibit rat heart and kidney allograft rejection

Target of rapamycin inhibitors (TOR-I; sirolimus and everolimus) for primary immunosuppression in kidney transplant recipients

BACKGROUND

Kidney transplantation is the therapy of choice for many patients with end-stage kidney disease (ESKD) with an improvement in survival rates and satisfactory short term graft survival. However, there has been little improvement in long-term survival. The place of target of rapamycin inhibitors (TOR-I) (sirolimus, everolimus), which have different modes of action from other commonly used immunosuppressive agents, in kidney transplantation remains uncertain. This is an update of a review first published in 2006.

OBJECTIVES

To evaluate the short and long-term benefits and harms of TOR-I (sirolimus and everolimus) when used in primary immunosuppressive regimens for kidney transplant recipients.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 20 September 2019 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register were identified through searches of CENTRAL, MEDLINE and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTs in which drug regimens, containing TOR-I commenced within seven days of transplant, were compared to alternative drug regimens, were included without age restriction, dosage or language of report.

DATA COLLECTION AND ANALYSIS

Three authors independently assessed study eligibility, risk of bias, and extracted data. Results were reported as risk ratios (RR) with 95% confidence intervals (CI) for dichotomous outcomes and mean difference (MD) with 95% CI for continuous outcomes. Statistical analyses were performed using the random-effects model. The certainty of the evidence was assessed using GRADE MAIN RESULTS: Seventy studies (17,462 randomised participants) were included; eight studies included two comparisons to provide 78 comparisons. Outcomes were reported at six months to three years post transplant. Risk of bias was judged to be low for sequence generation in 25 studies, for allocation concealment in 23 studies, performance bias in four studies, detection bias in 65 studies, attrition bias in 45 studies, selective reporting bias in 48 studies, and for other potential bias in three studies. Risk of bias was judged to be at high risk of bias for sequence generation in two studies, allocation concealment in two studies, performance bias in 61 studies, detection bias in one study, attrition bias in four studies, for selective reporting bias in 11 studies and for other potential risk of bias in 46 studies. Compared with CNI and antimetabolite, TOR-I with antimetabolite probably makes little or no difference to death (RR 1.31, 95% CI 0.87 to 1.98; 19 studies) or malignancies (RR 0.86, 95% CI 0.50 to 1.48; 10 studies); probably increases graft loss censored for death (RR 1.32, 95% CI 0.96 to 1.81; 15 studies), biopsy-proven acute rejection (RR 1.60, 95% CI 1.25 to 2.04; 15 studies), need to change treatment (RR 2.42, 95% CI 1.88 to 3.11; 14 studies) and wound complications (RR 2.56, 95% CI 1.94 to 3.36; 12 studies) (moderate certainty evidence); but reduces CMV infection (RR 0.43, 95% CI 0.29 to 0.63; 13 studies) (high certainty evidence). Compared with antimetabolites and CNI, TOR-I with CNI probably makes little or no difference to death (RR 1.06, 95% CI 0.84 to 1.33; 31 studies), graft loss censored for death (RR 1.09, 95% CI 0.82 to 1.45; 26 studies), biopsy-proven acute rejection (RR 0.95, 95% CI 0.81 to 1.12; 24 studies); and malignancies (RR 0.83, 95% CI 0.64 to 1.07; 17 studies); probably increases the need to change treatment (RR 1.56, 95% CI 1.28 to 1.90; 25 studies), and wound complications (RR 1.56, 95% CI 1.28 to 1.91; 17 studies); but probably reduces CMV infection (RR 0.44, 95% CI 0.34 to 0.58; 25 studies) (moderate certainty evidence). Lower dose TOR-I and standard dose CNI compared with higher dose TOR-I and reduced dose CNI probably makes little or no difference to death (RR 1.07, 95% CI 0.64 to 1.78; 9 studies), graft loss censored for death (RR 1.09, 95% CI 0.54 to 2.20; 8 studies), biopsy-proven acute rejection (RR 0.87, 95% CI 0.67 to 1.13; 8 studies), and CMV infection (RR 1.42, 95% CI 0.78 to 2.60; 5 studies) (moderate certainty evidence); and may make little or no difference to wound complications (RR 0.95, 95% CI 0.53 to 1.71; 3 studies), malignancies (RR 1.04, 95% CI 0.36 to 3.04; 7 studies), and the need to change treatments (RR 1.18, 95% CI 0.58 to 2.42; 5 studies) (low certainty evidence). Lower dose of TOR-I compared with higher doses probably makes little or no difference to death (RR 0.84, 95% CI 0.67 to 1.06; 13 studies), graft loss censored for death (RR 0.92, 95% CI 0.71 to 1.19; 12 studies), biopsy-proven acute rejection (RR 1.26, 95% CI 1.10 to 1.43; 11 studies), CMV infection (RR 0.87, 95% CI 0.63 to 1.21; 9 studies), wound complications (RR 0.92, 95% CI 0.66 to 1.29; 7 studies), and malignancy (RR 0.84, 95% CI 0.54 to 1.32; 10 studies) (moderate certainty evidence); and may make little or no difference to the need to change treatments (RR 0.91, 95% CI 0.78 to 1.05; 10 studies) (low certainty evidence). It is uncertain whether sirolimus and everolimus differ in their effects on kidney function and lipid levels because the certainty of the evidence is very low based on a single small study with only three months of follow-up.

AUTHORS' CONCLUSIONS

In studies with follow-up to three years, TOR-I with an antimetabolite increases the risk of graft loss and acute rejection compared with CNI and an antimetabolite. TOR-I with CNI potentially offers an alternative to an antimetabolite with CNI as rates of graft loss and acute rejection are similar between interventions and TOR-I regimens are associated with a reduced risk of CMV infections. Wound complications and the need to change immunosuppressive medications are higher with TOR-I regimens. While further new studies are not required, longer-term follow-up data from participants in existing methodologically robust RCTs are needed to determine how useful immunosuppressive regimens, which include TOR-I, are in maintaining kidney transplant function and survival beyond three years.

Management of mTOR inhibitors oral mucositis: current state of knowledge

Introduction: Mucositis is a well-known side effect of classic anticancer treatments (chemotherapy and radiotherapy). Thanks to the major developments in personalizing treatments through the development of targeted treatment, various specific intraoral lesions have been described. Purpose: mTOR inhibitors are targeted anticancer treatments that are used to treat various cancer types. They can cause intraoral ulcerations that can be serious, and that can lead to a dose reduction or the anticancer treatment being stopped altogether. The management of these disabling and painful lesions is a major part of ensuring the efficiency of the cancer treatments. The objective of this article is to evaluate the current knowledge about the different treatments used nowadays, especially the preventive treatments. Conclusion: An efficient management of the lesions is a major part of the management of patients treated with mTOR inhibitors and should be carried out by the oral cavity specialists.

A pharmacologic perspective on newly emerging T-cell manipulation technologies

T cells are a multifaceted family pivotal in the operations of the immune system and many of its associated diseases. The pathway to understanding T cells has been marked by several pharmacological advances including the discoveries of ciclosporin, tacrolimus and the mTOR inhibitors which revolutionized transplant therapy along with providing relief for severe eczema, asthma and other immunological disorders towards the end of the last century. This article will revisit the current understanding and new developments in T cell pharmacology 10 years on from the TeGenero (TGN 1412) debacle and look at more recent successes with ex vivo antigen presenting cell incubation technologies; T cell receptor (TCR) engineering and adoptive T cell therapy both with chimaeric antibodies and also with modified T cell receptors themselves. Features of T cell biology will be explored and processes often highly unique to humans will be used to highlight what many are beginning to see as an exciting new monoclonal (T cell) frontier for drug development.

Everolimus and sirolimus in combination with cyclosporine have different effects on renal metabolism in the rat

Enhancement of calcineurin inhibitor nephrotoxicity by sirolimus (SRL) is limiting the clinical use of this drug combination. We compared the dose-dependent effects of the structurally related everolimus (EVL) and sirolimus (SRL) alone, and in combination with cyclosporine (CsA), on the rat kidney. Lewis rats were treated by oral gavage for 28 days using a checkerboard dosing format (0, 3.0, 6.0 and 10.0 CsA and 0, 0.5, 1.5 and 3.0 mg/kg/day SRL or EVL, n = 4/dose combination). After 28 days, oxidative stress, energy charge, kidney histologies, glomerular filtration rates, and concentrations of the immunosuppressants were measured along with ¹H-magnetic resonance spectroscopy (MRS) and gas chromatography- mass spectrometry profiles of cellular metabolites in urine. The combination of CsA with SRL led to higher urinary glucose concentrations and decreased levels of urinary Krebs cycle metabolites when compared to controls, suggesting that CsA+SRL negatively impacted proximal tubule metabolism. Unsupervised principal component analysis of MRS spectra distinguished unique urine metabolite patterns of rats treated with CsA+SRL from those treated with CsA+EVL and the controls. SRL, but not EVL blood concentrations were inversely correlated with urine Krebs cycle metabolite concentrations. Interestingly, the higher the EVL concentration, the closer urine metabolite patterns resembled those of controls, while in contrast, the combination of the highest doses of CsA+SRL showed the most significant differences in metabolite patterns. Surprisingly in this rat model, EVL and SRL in combination with CsA had different effects on kidney biochemistry, suggesting that further exploration of EVL in combination with low dose calcineurin inhibitors may be of potential benefit.

Tumor growth effects of rapamycin on human biliary tract cancer cells

Background

Liver transplantation is an important treatment option for patients with liver-originated tumors including biliary tract carcinomas (BTCs). Post-transplant tumor recurrence remains a limiting factor for long-term survival. The mammalian target of rapamycin-targeting immunosuppressive drug rapamycin could be helpful in lowering BTC recurrence rates. Therein, we investigated the antiproliferative effect of rapamycin on BTC cells and compared it with standard immunosuppressants.

Methods

We investigated two human BTC cell lines. We performed cell cycle and proliferation analyses after treatment with different doses of rapamycin and the standard immunosuppressants, cyclosporine A and tacrolimus.

Results

Rapamycin inhibited the growth of two BTC cell lines in vitro. By contrast, an increase in cell growth was observed among the cells treated with the standard immunosuppressants.

Conclusions

These results support the hypothesis that rapamycin inhibits BTC cell proliferation and thus might be the preferred immunosuppressant for patients after a liver transplantation because of BTC.

Sirolimus and cyclosporine A alter barrier function in renal proximal tubular cells through stimulation of ERK1/2 signaling and claudin-1 expression

Alteration of the tight junction complex in renal epithelial cells can affect renal barrier function and perturb normal kidney homeostasis. The immunosuppressant drugs cyclosporine A (CsA) and sirolimus (SRL) used in combination demonstrated beneficial effects in organ transplantation but this combination can also result in increased adverse effects. We previously showed that CsA treatment alone caused an alteration of the tight junction complex, resulting in changes in transepithelial permeability in Madin-Darby canine kidney distal tubular/collecting duct cells. The potential effect of SRL on transepithelial permeability in kidney cells is unknown. In this study, subcytotoxic doses of SRL or CsA were found to decrease the paracellular permeability of the porcine proximal tubular epithelial cells, LLC-PK1 cell monolayers, which was detected as an increase in transepithelial electrical resistance (TER). The cotreatment with SRL and CsA was found to increase TER in a synergistic manner. CsA treatment increased total cellular expression and membrane localization of the tight junction protein claudin-1 and this further increased with the combination of SRL/CsA. SRL and CsA treatment alone or in combination stimulated the phosphorylation of ERK1/2. The MEK-ERK1/2 pathway inhibitor, U0126, reduced the SRL, CsA, and CsA/SRL-induced increase in TER. U0126 also reduced the CsA and CsA/SRL-induced increase in the membrane localization of claudin-1. Alterations in claudin-2 and claudin-4 were also detected. However, the results suggest that the modulation in expression and localization of claudin-1 appears to be pivotal in the SRL- and CsA-induced modulation of the epithelial barrier function and that modulation is regulated by ERK1/2 signaling pathway.

Dysregulated cytokine responses during cytomegalovirus infection in renal transplant recipients

OBJECTIVE

Pre- and posttransplant predisposing factors for cytomegalovirus (CMV) activation and disease are not well defined. The aim of this study was to examine whether there are differences in plasma cytokine levels pretransplant, before and during CMV replication in renal transplant recipients.

MATERIAL AND METHODS

We studied 76 renal transplant recipients in whom CMV-DNA was studied at regular intervals posttransplant. Thirty-eight patients developed CMV viremia posttransplant (CMV-DNA-positive). Thirty-eight patients had no detectable CMV-DNA posttransplant (CMV-DNA-negative). Cytokine and cytokine receptors/antagonists plasma levels were measured pretransplant, and pre-, during, and after CMV-viremia in CMV-DNA-positive patients and at similar time points in CMV-DNA-negative transplant recipients.

RESULTS

Compared with pretransplant, after transplantation soluble (s) plasma interleukin (IL)-2 receptor (R), IL-6, and interferon-gamma (IFN-gamma) decreased in both groups (CMV-DNA-positive: P=0.002; P=0.028; P=0.032; CMV-DNA-negative: P=0.001; P=0.040; P=0.030) whereas IL-10 remained constant in both groups (P=n.s.). During CMV viremia, sIL-2R (P=0.015) and IL-6 (P=0.006) increased compared with previremia but remained constant in CMV-DNA-negative patients matched for the day of investigation (P=n.s.). Simultaneously, IFN-gamma increased in CMV-DNA-negative patients (P=0.008) and remained constant in CMV-DNA-positive patients (P=n.s.). During CMV viremia, IL-10 (P=0.002) and sIL-2R (P=0.007) were significantly higher in CMV-DNA-positive than CMV-DNA-negative patients investigated at similar time points.

CONCLUSION

Our results indicate that CMV replication in renal transplant recipients is associated with increased sIL-2R, IL-6, and IL-10 and decreased IFN-gamma plasma levels, pointing to a monocyte/Th2 activation and a Th1 blockade. The high IL-10 might decrease the IFN-gamma plasma levels in CMV-DNA-positive patients. Th1 deficiency in CMV-DNA-positive patients might promote development of CMV disease.

Sirolimus in chronic allograft nephropathy in pediatric recipients

CAN is a common cause of late graft loss. Nephrotoxicity due to CNIs is known to contribute to CAN. We retrospectively evaluated the efficacy and safety of SRL in pediatric renal Tx recipients showing CAN in their allograft biopsy. Twenty-one patients aged 10.4 +/- 4.6 yr at Tx time receiving CNIs as primary immunosuppression were converted to SRL at 58.9 +/- 49.1 months after Tx, due to progressive decline of renal function and biopsy proven CAN. Mean follow-up after switch was 19.7 +/- 9.5 months. All patients received CsA as part of the immunosuppressive regimen, at a mean dose 4.4 +/- 1.2 mg/kg/day. Mean daily dose of SRL three month after conversion was 2.6 +/- 0.8 mg/body surface area/day and the mean through levels where 6.9 +/- 2.5 ng/mL. Graft biopsies showed Grade I CAN in 12 children and Grade II CAN in nine. After SRL introduction, there were neither acute rejection episodes nor graft losses. GFR improved at three months and was sustained thereafter only in children with Grade I CAN. Post-Tx time at conversion was the only significant variable between patients who had Grade I CAN and Grade II CAN (33.6 +/- 33.3 vs. 92.7 +/- 47.5 months, p = 0.003). Nine patients had no AEs, six patients had nine SAE: five diarrhea, one herpes zoster, one pancreatic pseudo cyst, one pneumonia, and one Influenza A infection; 11 patients had 13 AEs: six oral aphthous ulcers, three urinary tract infections, two herpes simplex, one lymphedema, and one nephrotic proteinuria. Significant improvement of GFR occurred in Grade I CAN group at three months from conversion and was sustained during follow-up. Those who had Grade II CAN experienced no change in GFR. The incidence of AEs and SAE is of concern and further studies are necessary to assess their relevance.

Evidence for IFN-? up- and IL-4 downregulation late post-transplant in patients with good kidney graft outcome

We found recently that patients with good graft outcome showed higher IFN-gamma and IL-2, and lower IL-10 plasma levels late post-transplant than early post-transplant. In this retrospective study, we compared cytokine plasma levels in 33 symptom-free outpatients with those of 33 renal transplant recipients with early acute rejection (EAR), 29 with chronic rejection (CR), and 34 healthy controls (HC) to assess whether there is evidence for Th1 activation late post-transplant in patients with good graft outcome. Cytokines were measured pre-transplant, one wk, one month, six months, one yr, and two yr after transplantation. Twelve and 24 months post-transplant, IFN-gamma plasma levels were significantly higher (p = 0.001; p = 0.001, respectively) and IL-4 plasma levels significantly lower (p = 0.028; p = 0.003, respectively) in patients with stable graft function than those in controls. Six, 12, and 24 months post-transplant, patients with stable graft function had similar IFN-gamma and IL-4 plasma levels as patients with successfully treated EAR (p = n.s.), and higher IFN-gamma (p = 0.013; p = 0.001; p = 0.0005, respectively) and lower IL-4 (p = 0.007; p = 0.417; p = 0.0001, respectively) plasma levels than patients with CR. These data suggest that increased plasma IFN-gamma and decreased plasma IL-4 late post-transplant might be involved in the induction of mechanisms that facilitate good long-term graft outcome.

The place of sirolimus in kidney transplantation: Can we reduce calcineurin inhibitor renal toxicity?

Sirolimus, a macrocylic lactone, blocks T-cell activation by a mechanism of action distinct from calcineurin inhibitors (CNIs). Therefore, it may be expected that sirolimus would display a safety profile without the vasomotor form of nephrotoxicity characteristic of CNIs. Initial studies in rodent models and in psoriasis patients showed that sirolimus alone did not impair renal function. Subsequently, two pivotal, randomized double dummy, phase III trials in human renal transplantation demonstrated that sirolimus exacerbated the nephrotoxicity of full doses of CNIs. Both pharmacokinetic and pharmacodynamic mechanisms have been implicated in the pathogenesis of this disorder. Subsequent experience has shown that cyclosporin A dose reduction, elimination, or avoidance mitigates these effects, particularly in patients distant from the transplant procedure. However, there is concern about recovery from ischemia-reperfusion injury. Animal models suggesting that sirolimus may delay recovery in this setting have been supported by non-randomized experiences at single centers, which have observed an increased incidence of delayed graft function among sirolimus-treated recipients. In contrast, large single- and multi-center studies have not confirmed this finding; impaired renal recovery has been observed in only occasional instances. Thus, present data indicate that sirolimus does not impair the function of an uninjured kidney, but whether the drug acts alone or potentiates conditions that delay recovery after ischemic injury remains to be established by large randomized trials specifically targeted to recipients at high risk for this complication.

Theoretical basis, experimental design, and computerized simulation of synergism and antagonism in drug combination studies

The median-effect equation derived from the mass-action law principle at equilibrium-steady state via mathematical induction and deduction for different reaction sequences and mechanisms and different types of inhibition has been shown to be the unified theory for the Michaelis-Menten equation, Hill equation, Henderson-Hasselbalch equation, and Scatchard equation. It is shown that dose and effect are interchangeable via defined parameters. This general equation for the single drug effect has been extended to the multiple drug effect equation for n drugs. These equations provide the theoretical basis for the combination index (CI)-isobologram equation that allows quantitative determination of drug interactions, where CI < 1, = 1, and > 1 indicate synergism, additive effect, and antagonism, respectively. Based on these algorithms, computer software has been developed to allow automated simulation of synergism and antagonism at all dose or effect levels. It displays the dose-effect curve, median-effect plot, combination index plot, isobologram, dose-reduction index plot, and polygonogram for in vitro or in vivo studies. This theoretical development, experimental design, and computerized data analysis have facilitated dose-effect analysis for single drug evaluation or carcinogen and radiation risk assessment, as well as for drug or other entity combinations in a vast field of disciplines of biomedical sciences. In this review, selected examples of applications are given, and step-by-step examples of experimental designs and real data analysis are also illustrated. The merging of the mass-action law principle with mathematical induction-deduction has been proven to be a unique and effective scientific method for general theory development. The median-effect principle and its mass-action law based computer software are gaining increased applications in biomedical sciences, from how to effectively evaluate a single compound or entity to how to beneficially use multiple drugs or modalities in combination therapies.

Target of rapamycin inhibitors (sirolimus and everolimus) for primary immunosuppression of kidney transplant recipients: a systematic review and meta-analysis of randomized trials

BACKGROUND

Target of rapamycin inhibitors (TOR-I) have a novel mode of action but uncertain clinical role. We performed a systematic review of randomized trials where immunosuppressive regimens containing TOR-I were compared with other regimens as initial therapy for kidney transplant recipients.

METHODS

Databases (inception, June 2005) and conference proceedings (1996-2005) were searched. Two independent reviewers assessed trials for eligibility and quality. Results at 1 year, are expressed as relative risk (RR), where values<1 favor TOR-I, or lower dose of TOR-I, and for continuous outcomes are expressed as weighted mean difference (WMD), both expressed with 95% confidence intervals (CI).

RESULTS

Thirty-three trials (142 reports) were included (27 trials of sirolimus, 5 of everolimus, and 1 of head-to-head comparison). When TOR-I replaced calcineurin inhibitors (CNI) (8 trials with 750 participants), there was no difference in acute rejection (RR, 1.03; 95% CI, 0.74-1.44), but serum creatinine was lower (WMD, -18.31 micromol/L; 95% CI, -30.96 to -5.67) and bone marrow more suppressed (leukopenia: RR 2.02; 95% CI, 1.12-3.66; thrombocytopenia: RR, 6.97; 95% CI, 2.97-16.36; and anaemia: RR, 1.67; 95% CI, 1.27-2.20). When TOR-I replaced antimetabolites (11 trials with 3966 participants), acute rejection and cytomegalovirus infection (CMV) were reduced (RR, 0.84; 95% CI, 0.71-0.99; RR, 0.49; 95% CI, 0.37-0.65, respectively), but hypercholesterolemia was increased (RR, 1.65; 95% CI, 1.32-2.06). When low- was compared with high-dose TOR-I, with equal CNI dose (10 trials with 3,175 participants), rejection was increased (RR, 1.23; 95% CI, 1.06-1.43) but calculated glomerular filtration rate (GFR) higher (WMD, 4.27 mL/min; 95% CI, 1.12-7.41), and when lower-dose TOR-I and standard-dose CNI were compared with higher-dose TOR-I and reduced CNI, acute rejection was reduced (RR, 0.67; 95% CI, 0.52-0.88), but calculated GFR was also reduced (WMD, -9.46 mL/min; 95% CI, -12.16 to -6.76). There was no significant difference in mortality, graft loss, or malignancy risk for TOR-I in any comparison.

CONCLUSIONS

TOR-I have been evaluated in four different primary immunosuppressive algorithms: as replacement for CNI and antimetabolites, in combination with CNI at low and high doses, and with a variable dose of CNI. Generally, surrogate endpoints for graft survival favor TOR-I (lower risk of acute rejection and higher GFR), and surrogate endpoints for patient outcomes are worsened by TOR-I (bone marrow suppression and lipid disturbance). Long-term hard-endpoint data from methodologically robust randomized trials are still required.

Target of rapamycin inhibitors (TOR-I; sirolimus and everolimus) for primary immunosuppression in kidney transplant recipients

BACKGROUND

Target of rapamycin inhibitors (TOR-I) (sirolimus, everolimus) are immunosuppressive agents with a novel mode of action but an uncertain clinical role.

OBJECTIVES

To investigate the benefits and harms of immunosuppressive regimens containing TOR-I when compared to other regimens as initial therapy for kidney transplant recipients.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (in The Cochrane Library, issue 2, 2005), MEDLINE (1966-June 2005), EMBASE (1980-June 2005), the specialised register of the Cochrane Renal Group (June 2005)., and contacted authors and pharmaceutical companies to identify relevant studies.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTs where drug regimens containing TOR-I were compared to alternative drug regimens in the immediate post-transplant period were included, without age restriction, dosage or language of report.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trials for eligibility and quality, and extracted data. Results are expressed as relative risk (RR) or weight mean difference (MD) with 95% confidence intervals (CI).

MAIN RESULTS

Thirty three trials (142 reports) were included (sirolimus (27), everolimus (5), head-to-head (1)). When TOR-I replaced CNI there was no difference in acute rejection, but serum creatinine was lower (MD -18.31 micromol/L, -30.96 to -5.67), and bone marrow more suppressed (leucopenia: RR 2.02 1.12 to 3.66; thrombocytopenia: RR 6.97 2.97 to 16.36; anaemia: RR 1.67, 1.27 to 2.20). When TOR-I replaced antimetabolites, acute rejection (RR 0.84, 0.71 to 0.99) and cytomegalovirus infection (CMV) (RR 0.49; 0.37 to 0.65) were reduced, but hypercholesterolaemia was increased (RR 1.65, 1.32 to 2.06). For low versus high-dose TOR-I, with equal CNI dose, rejection was increased (RR 1.23, 1.06 to 1.43) but calculated GFR higher (MD 4.27 mL/min, 1.12 to 7.41), and for low-dose TOR-I/standard-dose CNI versus higher-dose TOR-I/reduced CNI, acute rejection (RR 0.67, 0.52 to 0.88) and calculated GFR (MD -9.46 mL/min, -12.16 to -6.76) were reduced. There was no significant difference in mortality, graft loss or malignancy risk for TOR-I in any comparison.

AUTHORS' CONCLUSIONS

TOR-I have been evaluated in four different primary immunosuppressive algorithms; as replacement for CNI and for antimetabolites, in combination with CNI at low and high dose and with variable dose of CNI. Generally, surrogate endpoints for graft survival favour TOR-I (lower risk of acute rejection and higher GFR) and surrogate endpoints for patient outcomes are worsened by TOR-I (bone marrow suppression, lipid disturbance). Long-term hard-endpoint data from methodologically robust RCTs are still needed.

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

JAK3 is a cytoplasmic tyrosine kinase with limited tissue expression but is readily found in activated T cells. Patients lacking JAK3 are immune compromised, suggesting that JAK3 represents a therapeutic target for immunosuppression. Herein, we show that a Mannich base, NC1153, blocked IL-2-induced activation of JAK3 and its downstream substrates STAT5a/b more effectively than activation of the closely related prolactin-induced JAK2 or TNF-alpha-driven NF-kappaB. In addition, NC1153 failed to inhibit several other enzymes, including growth factor receptor tyrosine kinases, Src family members, and serine/threonine protein kinases. Although NC1153 inhibited proliferation of normal human T cells challenged with IL-2, IL-4, or IL-7, it did not block T cells void of JAK3. In vivo, a 14-day oral therapy with NC1153 significantly extended survival of MHC/non-MHC mismatched rat kidney allografts, whereas a 90-day therapy induced transplantation tolerance (>200 days). Although NC1153 acted synergistically with cyclosporin A (CsA) to prolong allograft survival, it was not nephrotoxic, myelotoxic, or lipotoxic and did not increase CsA-induced nephrotoxicity. In contrast to CsA, NC1153 was not metabolized by cytochrome P450 3A4. Thus, NC1153 prolongs allograft survival without several toxic effects associated with current immunosuppressive drugs.

Emerging therapies for graft-versus-host disease

Acute graft-versus-host disease (GVHD) and chronic GVHD remain the major barriers to successful haematopoietic cell transplantation. The induction of GVHD may be divided into three phases: (i) recipient conditioning, (ii) donor T cell activation, and (iii) effector cells mediating GVHD. Standard agents and agents under development to prevent and treat GVHD are discussed. The various pharmacological agents impact on different phases of the GVHD cascade. Sirolimus is a new immunophilin binding agent that appears to be synergistic with tacrolimus and cyclosporin. It also seems to promote allograft tolerance. Mycophenolate mofetil (MMF) is an antimetabolite that is currently under study for prophylaxis and treatment of acute and chronic GVHD; results are encouraging. Other agents such as the purine analogue pentostatin and the monoclonal antibodies alemtuzumab, daclizumab and infliximab are discussed at length within the GVHD context. The most effective approach to GVHD prevention will likely be a combination regimen where the three phases of the GVHD cascade are disrupted. Once GVHD has occurred, all three phases of the cascade are activated. Developments of combination therapy for the treatment of both acute and chronic GVHD will likely yield better results than monotherapy. The numerous new treatment modalities presented should improve the outlook for acute and chronic GVHD.

Maldaptation of the link between inflammation and bone turnover may be a key determinant of osteoporosis

Currently the etiology of osteoporosis is attributed to various endocrine, metabolic, and mechanical factors. We hypothesize that many cases of osteoporosis are also partially attributable to a maladaptation of the link between inflammation and bone turnover. We explore the spatial and temporal link between inflammation and osteoporosis in conditions such as aging, menopause, reflex sympathetic dystrophy, HIV, pregnancy, transplantation, and steroid administration. While nutritional and mechanical factors clearly play a role in many of these situations, the spatial and temporal concordance of osteoporosis and inflammation is buttressed by emerging molecular evidence. Modern bone biology of humans may reflect dual functional legacies of mineral storage and structural support. Osteoporosis may result from disequilibrium between structural demand for key minerals and their biologic demand during maladaptive states of inflammation.

Immunomodulatory Effects of Combination of Pooled Human Gammaglobulin and Rapamycin on Cell Proliferation and Apoptosis in the Mixed Lymphocyte Reaction

BACKGROUND

Multidrug immunosuppressive regimens benefit transplant recipients, reducing side effects and creating synergy between medications with different mechanisms of action. We have shown that pooled human gammaglobulin (intravenous immunoglobulin [IVIG]) inhibits the mixed lymphocyte reaction (MLR) and induces apoptosis primarily in B cells. Rapamycin (RAPA), a potent macrolide immunosuppressant, inhibits B- and T-cell proliferation through G1 cell-cycle blockade and purportedly induces apoptosis. Here we examined the possible synergistic effects of IVIG and RAPA on cell proliferation and apoptosis induction in the MLR.

METHODS

MLR was performed with IVIG (0.2-5 mg/mL), RAPA (0.02-40 ng/mL), alone or in combination. Cell proliferation was detected by H-thymidine incorporation, and apoptosis by Annexin V and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling flow cytometry.

RESULTS

IVIG or RAPA inhibited cell proliferation in a dose-dependent manner. RAPA (0.02-40 ng/mL) in combination with IVIG (5 mg/mL) significantly augmented the inhibition compared with RAPA alone (70% vs. 34% at 0.2 ng/mL; 90% vs. 76% at 2 ng/mL). Apoptosis was significantly higher in IVIG-treated (5 mg/mL) CD19+ cells and less so in CD3+ cells. However, RAPA (0.2-40 ng/mL) neither induced apoptosis nor altered apoptosis induced by IVIG.

CONCLUSIONS

Combined RAPA and IVIG at subtherapeutic concentrations inhibits cell proliferation in the MLR. RAPA neither induces apoptosis nor augments apoptosis induced by IVIG in the MLR. Lower-concentration RAPA (0.2-2 ng/mL) in combination with IVIG (5 mg/mL) versus therapeutic levels (2-50 ng/mL and 10-40 mg/mL, respectively) could represent an effective immunomodulatory drug combination.

METABOLIC INTERACTION BETWEEN CYCLOSPORINE AND SIROLIMUS

BACKGROUND

When the immunosuppressants cyclosporine (CsA) and sirolimus (SRL) are co-administered to transplant patients, lower doses are used than when either drug is given alone. Since both drugs share similar transport and metabolic pathways, there is the potential for an interaction leading to unpredictable effects. Furthermore, both drugs affect the activity of cytochrome P450 3A1/2 (CYP3A1/2), the rat parallel to human CYP3A4, and the multidrug transporter P-glycoprotein (Pgp).

METHODS

To clarify the role of metabolic enzymes and membrane transporters involved in the disposition of both drugs, we examined hepatic CYP3A1/2, Pgp, and multidrug resistance gene (mdr) mRNA during chronic therapy with CsA and SRL in salt-depleted rats. Specifically, rats were given intravenous doses of CsA 2.5 mg/kg and SRL 1 mg/kg, alone or in combination, for two weeks via constant rate intravenous infusion.

RESULTS

CsA treatment inhibited hepatic CYP3A1/2 protein expression, catalytic activity, and mRNA levels. SRL dosing suppressed CYP3A1/2 protein expression and catalytic activity, without affecting mRNA. With combined dosing, however, there was a much greater reduction. Hepatic Pgp protein levels were elevated after treatment with either drug alone, as well as with combined dosing. Compared to controls, there were significant increases in mdr1a and mdr1b mRNA levels in all treatment groups, with the combined drugs causing the greatest increase.

CONCLUSIONS

Both CYP3A1/2 and Pgp participate in the disposition of CsA and SRL in rats. Changes in the individual activities of CYP3A1/2 and Pgp may contribute to an interaction between CsA and SRL resulting in unanticipated effects during chronic therapy.

Therapeutic Drug Monitoring of Immunosuppressant Drugs by High-Performance Liquid Chromatography–Mass Spectrometry

The currently expanding range of immunosuppressant agents has placed new challenges on therapeutic drug-monitoring (TDM) services. Many of these drugs require the measurement of concentrations with subsequent dosage adjustment to maximize efficacy while minimizing toxicity. HPLC-mass spectrometry (HPLC-MS) is a relatively new technique for drug quantification and thus TDM of immunosuppressant drugs. Although mass spectrometry relies on producing, differentiating, and detecting ions in the gas phase, the development of the atmospheric pressure ionization interface (electrospray and chemical ionization) has enabled the direct coupling of solution introduction of compounds, via HPLC, to the mass analyzer. The impetus for using HPLC-MS for immunosuppressant measurement has come from the highly potent low-dose immunosuppressant drugs tacrolimus and sirolimus, which have low nanogram per milliliter circulating concentrations. A number of strategies have been reported for sample preparation and ways to automate these processes with solid-phase extraction and 2-dimensional chromatography. The disadvantages of HPLC-MS are initial cost of equipment and availability of suitably skilled scientific staff. The advantages of HPLC-mass spectrometry are high sensitivity, specificity, small sample requirements, minimal sample preparation, rapid throughput, and simultaneous measurement. Further, scientists have the ability to develop methods to measure new immunosuppressant drugs by HPLC-MS before commercial assays become available. With potential applications increasing in immunosuppressive drug monitoring, it can be envisaged that HPLC-MS may become standard equipment in TDM laboratories of the future.

Synergistic effects of RAD and Neoral in inhibition of host-vs.-graft and graft-vs.-host immune responses in rat small-bowel transplantation

The combined effects of RAD and Neoral were tested in a rat orthotopic small-bowel transplantation model. Seven groups (n = 6) were involved in this study, and each one was included in three rejection models for the evaluation of host-vs.-graft disease (HVG) (LBN-F1 to LEW), graft-vs.-host disease (GVH) (LEW to LBN-F1), and combined HVG and GVH immune responses (BN to LEW). Both drugs were administered orally throughout the study. Low doses of RAD (1.0-2.5 mg/kg/day) combined with Neoral (2.0-5.0 mg/kg/day) produced strong synergistic effects in the prolongation of small-bowel graft survival in HVG (combination index, CI = 0.095, 0.1212), GVH (CI = 0.027, 0.020), and combined HVG and GVH immune responses (CI = 0.070, 0.301). The combination therapy of RAD and Neoral produces a strong synergistic effect toward the inhibition of HVG, GVH, and combined HVG and GVH immune responses in a rat small-bowel transplantation model.

Sirolimus, tacrolimus, and low-dose methotrexate for graft-versus-host disease prophylaxis in mismatched related donor or unrelated donor transplantation

We studied the feasibility and activity of adding sirolimus to tacrolimus and low-dose methotrexate as graft-versus-host disease (GVHD) prophylaxis in recipients of alternative donor transplants. Forty-one patients with hematologic malignancies were conditioned with cyclophosphamide and total body irradiation. Marrow stem cells were from an HLA-A, -B, and -DR compatible, unrelated donor (n = 26, 68%), from a 5 of 6 antigen-matched unrelated donor (n = 8, 20%), or from a 5 of 6 antigen-matched family member (n = 5, 12%). Therapeutic serum levels of sirolimus were attained in most patients. All evaluable patients engrafted. An absolute neutrophil count of 500/microL was achieved on day +18 (range, 11-32 days). Sustained platelet counts of more than 20 000/ microL were attained on day +29 (range, 14-98 days). Grades 0-I acute GVHD occurred in 75% of patients. Grades II, III, and IV acute GVHD occurred in 13%, 8%, and 5%, respectively (total grades II-IV GVHD, 26%). Median survival is 366 days (95% CI 185, not estimable) and actuarial survival at 1 year is 52%. Oral sirolimus is tolerable, adequate blood levels are achievable, and there is a low rate of acute GVHD compared with historical data in this high-risk population. This novel agent is worthy of further study in allogeneic transplantation.

Sirolimus: its discovery, biological properties, and mechanism of action

Sirolimus is the USAN-assigned generic name for the natural product rapamycin. Sirolimus is produced by a strain of Streptomyces hygroscopicus, isolated from a soil sample collected from Rapa Nui commonly known as Easter Island. Although sirolimus was isolated as an antifungal agent with potent anticandida activity, subsequent studies revealed impressive antitumor and immunosuppressive activities. Sirolimus demonstrates activity against several murine tumors, such as B16 43 melanocarcinoma, Colon 26 tumor, EM ependymoblastoma, and mammary and colon 38 solid tumors. Sirolimus is a potent inhibitor of antigen-induced proliferation of T cells, B cells, and antibody production. Demonstration of the potent immunosuppressive activity of sirolimus in animal models of organ transplantation led to clinical trials and subsequent approval by regulatory authorities for prophylaxis of renal graft rejection. Interest in sirolimus as an immunosuppressive therapy in organ transplantation derives from its unique mechanism of action, its unique side-effect profile, and its ability to synergize with other immunosuppressive agents. The molecular mechanism underlying the antifungal, antiproliferative, and immunosuppressive activities of sirolimus is the same. Sirolimus forms an immunosuppressive complex with intracellular protein, FKBP12. This complex blocks the activation of the cell-cycle-specific kinase, TOR. The downstream events that follow the inactivation of TOR result in the blockage of cell-cycle progression at the juncture of G1 and S phase.

Rapamycin in combination with cyclosporine or tacrolimus in liver, pancreas, and kidney transplantation

A 10-year experience with the immunosuppressive drug rapamycin that begins in the laboratory then extends through multicentre trials in combination with cyclosporine in kidney transplant recipients, exploration of its use as a single agent and in combination with tacrolimus, and its potential in nonrenal organs is described. Rapamycin is a potent inhibitor of endothelial injury in rat aortic allografts. When added to full-dose cyclosporine it achieves low rejection rates, but it augments the nephrotoxicity and hyperlipidemia of cyclosporine. On the other hand, it allows discontinuation of calcineurin inhibitors in stable kidney and liver patients suffering from nephrotoxicity late posttransplant. At least in Caucasian patients, discontinuation of cyclosporine is possible as early as 3 months post-kidney transplant. In combination with low-dose tacrolimus, exceptionally low rates of rejection were seen in recipients of kidney, pancreas, and liver recipients with preservation of excellent renal function. These pilot studies have been confirmed in several single-centre and, more recently, multicentre trials in kidney and pancreas transplantation. The side-effect profile of hyperlipidemia, lymphocoeles, delayed wound healing, and possible liver effects are coming into focus, and ways of minimizing these problems being introduced. The lessons learned include the need for early adequate blood levels, the lack of correlation between dose and drug exposure, and the potency that allows marked dose reductions in calcineurin inhibitors and steroids.

Sirolimus therapy in cardiac transplantation

Rapamycin powerfully inhibits the progression of antigen-activated T cells through the cell cycle. In animal heart transplantation models, rapamycin therapy has been associated with profound immunosuppressive effects on host humoral and cellular responses. In consequence, further studies have been conducted to evaluate the efficiency of rapamycin in preventing acute heart allograft rejection, treating refractory acute heart allograft rejection, inducing transplantation tolerance, and preventing and treating transplant coronary artery disease. The results of these studies indicated that rapamycin can effectively prevent acute graft rejection and inhibit refractory acute graft rejection in heart transplant recipients by exerting potent immunosuppressive and antiproliferative effects without adversely affecting renal function. This supports the use of rapamycin therapy in heart transplant recipients, especially in those with renal dysfunction, for whom treatment with calcineurin inhibitors is contraindicated. Rapamycin may also halt and even reverse the progression of cardiac allograft vasculopathy, which warrants further clinical trials in humans. Finally, rapamycin may be able to induce transplantation tolerance, thus making it one of the most promising modalities for improving the long-term survival of heart transplant recipients.

Preclinical results of sirolimus treatment in transplant models

Sirolimus (SRL; rapamycin) is a macrolide antibiotic, which modest anticandidal and tumoricidal activities were superseded by its immunosuppressive potential to block allograft rejection. The most intriguing biological characteristic of SRL emerged after demonstration of its potent synergism with cyclosporine (CsA). Naïve T cells, residing in the G(0) phase of the cell cycle, become activated by three signals. Signal 1 (T cell antigen receptor/alloantigen) and Signal 2 (CD28/B7) progress T cell to the early G(1) phase inducing production of interleukin-2 (IL-2) and other T cell growth factors (TGFs). Signal 3 (cytokine/cytokine receptor) initiate cell division and differentiation in the late G(1)/S phase. Whereas CsA binding to calcineurin blocks Signal 1/2, SRL binding to mammalian target of rapamycin (mTOR) blocks Signal 3. Our preclinical studies have established the in vivo principles of the effects exhibited by SRL alone on allograft survival, synergism between SRL and CsA as well as two drugs pharmacokinetic and pharmacodynamic interactions. In our experimental model, a 14-day i.v. continuous infusion of SRL by osmotic pump into rat recipients extended the survivals of heart allografts in a dose-dependent fashion. In comparison to untreated controls (MST of 6.3 +/- 0.5 days), 0.08 mg/kg SRL extended MST to 34.4 +/- 12.1 days, and 0.8 mg/kg to 74.1 +/- 20.2 days, with 6/18 allografts surviving for more than 100 days. Since almost identical results were produced by 10-fold higher SRL doses delivered by oral gavage, we estimated its bioavailability at 10%. Similarly, SRL prolonged the survivals of kidney, pancreas, and small bowel allografts in rats. At the same time large animal models cautioned about potential toxicities, namely intestinal vasculitis. The synergistic interactions of CsA and SRL may be explained by sequential effects in the early G(0)/G(1) versus late G1/S phases of cell cycle progression, respectively. The in vivo interaction of SRL with other immunosuppressive drugs was evaluated by the median effect analysis and the combination index (CI) values (CI = 1 shows additive, CI < 1, synergistic, and CI > 1, antagonistic, interactions). Oral SRL proved to be synergistic in both CsA-resistant mouse (CI = 0.4-1.5) and CsA-sensitive rat (CI = 0.3-0.6) models. The pharmacokinetic interactions of SRL and/or CsA were evaluated in rats for i.v. and oral formulations. Although low CsA and SRL i.v. doses did not affect each other levels, potent interaction was observed after oral gavage: CsA increased SRL levels by 2-11 folds; and, SRL increased CsA levels by 2-3-folds. Our results suggested that both pharmacodynamic and pharmacokinetic interactions contribute to the synergism between SRL and CsA. We also estimated the impact of CsA/SRL interaction on renal dysfunction, myelosuppression, and hyperlipidemia. Salt-depleted rats treated with SRL (0.4-6.4 mg/kg) and/or CsA (2.5-20 mg/kg) were examined for glomerular filtration rates (GFR), lipid levels, and bone marrow cellularity. CsA-induced kidney function deficiency was exacerbated by SRL. This exacerbation of renal dysfunction correlated with increased CsA levels in kidneys when combined with SRL. Furthermore, CsA potentiated SRL-mediated toxicities, namely myelosuppression and increased cholesterol. In conclusion, SRL therapy is synergistic with CsA but both drug levels should be carefully monitored to avoid toxic effects.

[New immunosuppressive agents for treating psoriasis]

Accumulative evidence suggests that psoriasis may be a genetically determined immunologenic inflammatory disorder based on an ongoing autoreactive Th-1 response. Various cytokines (e.g. IL-2, interferon-gamma etc.) are released and exert proliferative signals on to keratinocytes, which start proliferation that finally results in an incomplete differentiation. During this pathobiological process keratinocytes themselves express receptors that make them sensitive for growth inducing stimulation and also start the production of a set of cytokines that contribute to and maintain inflammation. Immunosuppressive agents, mostly by affecting T-cells may interfere with or even disrupt by rather unspecific mechanisms, this complex process of mutual stimulation of leucocytes and keratinocytes. In this manuscript we show mode of action, efficacy and side effects of Methotrexate, Ciclosporin A, Tacrolimus and Pimecrolimus, and discuss therapeutic options with mycophenolate mofetil and fumaric acid esters.

Simultaneous quantification of sirolimus, everolimus, tacrolimus and cyclosporine by liquid chromatography-mass spectrometry (LC-MS)

We developed a universal liquid chromatography-mass spectrometry (LC-MS) assay with automated online extraction to quantify simultaneously the immunosuppressants sirolimus, everolimus, tacrolimus, and cyclosporine. Whole blood (300 microl) plus 6 microl 32-desmethoxyrapamycin (1 ng/microl) as internal standard was treated with 600 microl methanol/0.2 M ZnSO4 (80/20 v/v). After vortexing (30 s) and centrifugation (20000 g, 5 min) 50 microl of the supernatant were loaded on an extraction column, were washed by 0.35 ml/min water for 3 min and, after activation of a column-switching valve, were back-flushed by 0.25 ml/min methanol/ water (90/10 v/v) onto a C18 analytical column. After 22 min the extraction column was washed for 2 min with methanol and for 3 min with water before starting the next run. Column temperatures were kept at 33 degrees C. Sodium adduct ions [M+Na]+ ions were detected in the selected ion mode. For sirolimus, everolimus and tacrolimus the assay was linear from 0.3 to 200 microg/l and for cyclosporine from 5 to 1000 microg/l (all r2>0.999). Recovery of all immunosuppressants and the internal standard was >90% and in general, inter-day and intraday precision was <10%. The simultaneous quantification of blood levels by LC-MS seems to be the method of choice in transplanted patients receiving multiple immunosuppressants.

Update on pharmacokinetic/pharmacodynamic studies with FTY720 and sirolimus

Expanding the cytokine paradigm beyond the use of calcineurin inhibitors as baseline therapy provides new strategies in immunosuppression. Drugs such as FTY720 alter the sensitivity of lymphocytes to homing chemokines, and agents such as sirolimus (SRL) disrupt downstream cytokine signal transduction. Confirming studies in rodents and nonhuman primates, administration of either FTY720 or both of these drugs afford synergistic interactions with cyclosporine to renal transplant patients to rapidly and dramatically deplete peripheral blood lymphocytes (PBL) but neither granulocytes nor monocytes. Present information suggests that FTY720 facilitates lymphocyte homing mechanisms, leading to T and B cell sequestration in secondary lymphoid structures. Interestingly, FTY720 displays pharmacokinetic characteristics suggesting that therapeutic drug monitoring (TDM) will not be essential for clinical applications. In contrast, SRL is a critical-dose drug that requires TDM. SRL disrupts costimulatory and cytokine-stimulated T cell activation by inhibiting a multifunctional kinase, mammalian target of sirolimus (mTOR). Two pivotal trials including more than 1,300 patients demonstrated that addition of SRL to a CsA-based regimen reduces the incidence, time to onset, and severity of acute rejection episodes. When used alone, SRL seems therapeutically equivalent to CsA. In the coming decade, SRL is likely to be used in a variety of drug combination regimens both simultaneously and sequentially, not only to avert acute rejection episodes, but also to forestall chronic nephropathic processes. These two new agents are likely to usher in a new era of transplant therapy.

Selective inhibitor of Janus tyrosine kinase 3, PNU156804, prolongs allograft survival and acts synergistically with cyclosporine but additively with rapamycin

Janus kinase 3 (Jak3) is a cytoplasmic tyrosine (Tyr) kinase associated with the interleukin-2 (IL-2) receptor common gamma chain (gamma(c)) that is activated by multiple T-cell growth factors (TCGFs) such as IL-2, -4, and -7. Using human T cells, it was found that a recently discovered variant of the undecylprodigiosin family of antibiotics, PNU156804, previously shown to inhibit IL-2-induced cell proliferation, also blocks IL-2-mediated Jak3 auto-tyrosine phosphorylation, activation of Jak3 substrates signal transducers and activators of transcription (Stat) 5a and Stat5b, and extracellular regulated kinase 1 (Erk1) and Erk2 (p44/p42). Although PNU156804 displayed similar efficacy in blocking Jak3-dependent T-cell proliferation by IL-2, -4, -7, or -15, it was more than 2-fold less effective in blocking Jak2-mediated cell growth, its most homologous Jak family member. A 14-day alternate-day oral gavage with 40 to 120 mg/kg PNU156804 extended the survival of heart allografts in a dose-dependent fashion. In vivo, PNU156804 acted synergistically with the signal 1 inhibitor cyclosporine A (CsA) and additively with the signal 3 inhibitor rapamycin to block allograft rejection. It is concluded that inhibition of signal 3 alone by targeting Jak3 in combination with a signal 1 inhibitor provides a unique strategy to achieve potent immunosuppression.