Rapamycin in transplantation: a review of the evidence

The evolving role of platelets in inflammation

Platelets are small in size and simple in structure. Nevertheless, these anucleate cytoplasts utilize complex molecular systems to regulate a variety of biological functions. Here we review evolutionary paths, traditional roles, and previously unrecognized biological capacities of platelets that interface thrombosis with inflammation and potentially identify new roles in inflammatory diseases.

Rapamycin in lung transplantation: preliminary results

INTRODUCTION

Rapamycin is a potent immunosuppressive agent with a different mechanism of action and different adverse effects from those of calcineurin inhibitors (CNIs).

OBJECTIVE

To analyze our experience with rapamycin in patients undergoing lung transplantation and heart-lung transplantation in our center.

PATIENTS AND METHODS

Patients were treated with rapamycin when showing chronic rejection and/or toxicity associated with the CNI after lung transplantation or heartlung transplantation. Patients with chronic rejection were administered rapamycin in combination with CNIs, whereas the CNIs were eliminated in patients with toxicity.

RESULTS

Since October 2001, 7 patients (4 women), of mean age 45+/-15 years, received treatment with rapamycin (heart-lung transplantation, 2 cases; lung transplantation, 5 cases). The indications were chronic rejection in 4 patients and CMIs toxicity in 3 patients (kidney failure in 2 cases and optic neuropathy in 1 case). Pulmonary function stabilization was observed in 3 of 4 patients receiving rapamycin for chronic rejection. In the 3 patients with CNIs toxicity elimination of these drugs did not result in pulmonary functional deterioration. Patients with kidney failure showed an improvement in creatinine levels; visual acuity improved in the patient with optic neuropathy. We observed 2 infectious complications (pneumococcal pneumonia and pulmonary aspergillosis), which resolved with treatment.

CONCLUSION

Rapamycin is an alternative for lung-transplant recipients who develop chronic rejection and/or CNIs toxicity.

Sirolimus-induced thrombotic microangiopathy in a renal transplant recipient

A rare but well-documented serious adverse reaction to the administration of the calcineurin inhibitors tacrolimus and cyclosporine in renal transplant recipients is the development of medication-induced thrombotic microangiopathy. The recently introduced immunosuppressive medication sirolimus has a very similar molecular structure to tacrolimus and also binds to the same intracellular proteins. Despite these similarities with tacrolimus, sirolimus has a different side-effect profile and reportedly lacks documented specific renal toxicity. This is a case report of the isolated administration of sirolimus without a concomitant calcineurin inhibitor being associated with the development of renal transplant biopsy-proven thrombotic microangiopathy. The patient is a 47-year-old African-American woman whose primary cause of renal failure was not thrombotic micrangiopathy, and she received a 5-antigen mismatched cadaveric renal transplant. Because of preexisting nephrosclerosis in the renal transplant, this patient was never administered a calcineurin inhibitor but was always maintained on sirolimus. With recent animal data showing that sirolmus can be nephrotoxic in a renal ischemic-reperfusion model (similar to what happens with a renal transplant), the authors speculate on a mechanism for this adverse reaction.

Rapamycin inhibits IL-4--induced dendritic cell maturation in vitro and dendritic cell mobilization and function in vivo

Rapamycin (RAPA) is a potent immunosuppressive macrolide hitherto believed to mediate its action primarily via suppression of lymphocyte responses to interleukin 2 (IL-2) and other growth factors. We show here that this view is incomplete and provide evidence that RAPA suppresses the functional activation of dendritic cells (DCs) both in vitro and in vivo. In vitro, RAPA inhibits IL-4-dependent maturation and T-cell stimulatory activity of murine bone marrow-derived DCs. These effects are associated with posttranscriptional down-regulation of both subunits of the IL-4 receptor complex (CD124, CD132) and are mediated via binding of RAPA to its intracellular receptor FK506-binding protein 12 (FKBP12). In vivo, RAPA impairs steady-state DC generation and fms-like tyrosine 3 kinase ligand (Flt3L)-induced DC mobilization. In addition, in vivo administration of RAPA impairs DC costimulatory molecule up-regulation, production of proinflammatory cytokines, and T-cell allostimulatory capacity. These novel findings have implications for RAPA-based therapy of chronic DC-triggered autoimmune diseases, transplant rejection, and hematologic malignancies with activating Flt3 mutations.

Immunosuppressive TOR kinase inhibitor everolimus (RAD) suppresses growth of cells derived from posttransplant lymphoproliferative disorder at allograft-protecting doses

BACKGROUND

Posttransplant lymphoproliferative disorders (PTLDs) represent a life-threatening complication of standard immunosuppressive therapy. The impact of novel, rapamycin-related immunosuppressive drugs on the pathogenesis of PTLDs remains undefined.

METHODS

We tested the effect of everolimus (RAD, Novartis Pharma AG, Basel, Switzerland) on human PTLD-derived cells using in vitro assays and an in vivo severe combined immunodeficiency disease mouse xenotransplant model.

RESULTS

Everolimus profoundly inhibited the proliferation, cell-cycle progression, and survival of the PTLD-1 cell line established from a pulmonary PTLD. Equally profound inhibition of PTLD-1 growth was achieved in vivo at well-tolerated everolimus doses of 0.5 to 5 mg/kg per day. Five mg/kg per day of everolimus, given once per day, inhibited PTLD-1 tumor volume gain by more than 10-fold in treated mice compared with untreated mice. Because the subsequent pharmacokinetic analysis indicated rapid everolimus absorption, distribution, and clearance in mice (with a half-life of 3 to 6 hr and maximum drug blood concentration reached after 0.5 to 1 hr), treatment was changed to a twice-daily regimen. Everolimus given twice daily at 0.5 mg/kg per dose inhibited tumor-volume gain by more than 60-fold and at 0.25 mg/kg per dose by more than 10-fold. Similar everolimus doses were required to prevent graft rejection in a mouse heart allotransplantation model; the highest dose tested (1.5 mg/kg twice daily) resulted in long-term graft survival in all mice that underwent transplantation.

CONCLUSIONS

Everolimus displays a potent inhibitory effect on PTLD-derived cells in vitro and in vivo in a dose range leading to prevention of allograft rejection and may prove effective in both the prevention and treatment of PTLDs in transplant patients.

Airway anastomotic dehiscence associated with use of sirolimus immediately after lung transplantation

GOAL

The goal of this study was to assess the efficacy of sirolimus in lung-transplant recipients.

METHODS

The study was designed as a single center, consecutive case study of lung-transplant recipients treated with sirolimus, tacrolimus, and prednisone. All study subjects also received an HMG-CoA reductase inhibitor, and prophylaxis for cytomegalovirus and Pneumocystis carinii.

RESULTS

A total of 15 subjects were enrolled in the study. Within 6 months, significant airway complications occurred in four subjects, three of whom died. At that point, the investigators terminated enrollment in the study. The study population was compared retrospectively with a group of 83 consecutive lung recipients treated with cyclosporine (n=64) or tacrolimus (n=19), mycophenolate mofetil, and prednisone. This confirmed an increased incidence of airway dehiscence and reduced survival in the sirolimus-treated patients. Sirolimus-treated patients had a low incidence of acute rejection. No significant differences were noted in the incidence of bacterial or fungal bronchopulmonary infections.

CONCLUSIONS

We observed an unexpectedly high incidence of postoperative airway dehiscence in lung-transplant recipients treated with sirolimus, in combination with tacrolimus, prednisone, and an HMG-CoA inhibitor. Further studies will be needed to determine the safety and efficacy of using sirolimus after complete airway healing has occurred.

Rapamycin inhibits vascular remodeling in an experimental model of allograft vasculopathy and attenuates associated changes in fibrosis-associated gene expression

BACKGROUND

Rapamycin inhibits extracellular matrix (ECM) accumulation (fibrosis) and vascular remodeling in experimental models of chronic allograft dysfunction (CAD) by poorly understood mechanisms. The aim of this study was to assess the effect of rapamycin on the expression of fibrosis-associated genes and correlate this with observed changes in ECM remodeling in an experimental of model allograft vasculopathy.

METHODS

Vascular remodeling and ECM accumulation (picrosirius red) were measured by computerized histomorphometry of F344-to-Lewis rat aortic allograft sections harvested at serial timepoints. Expression of fibrosis associated genes was studied by means of semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Rapamycin (0.5 mg/kg/day) inhibited intimal hyperplasia, medial ECM accumulation and expansive vascular remodeling (increasing vessel circumference) in rat aortic allografts. This was associated with attenuation of the graft inflammatory infiltrate and a reduction in intragraft gelatinase, collagen III and tissue inhibitor of metalloproteinase 1 (TIMP 1) mRNA levels. At a lower dosage (0.25 mg/kg/day), rapamycin inhibited intimal hyperplasia and medial ECM accumulation, but there was a lesser effect on vascular remodeling. Lower dose allografts were also seen to have a more severe inflammatory infiltrate and larger amounts of intragraft matrix metalloproteinase 9 (MMP 9) mRNA than those treated with the higher dose.

CONCLUSIONS

These data suggest that, in addition to the tissue response to injury, the alloimmune injury itself may contribute directly to the vascular remodeling that occurs in allograft vasculopathy. Rapamycin at higher but not lower doses inhibited both of these pathologic processes.

Ten years of sirolimus therapy in orthotopic liver transplant recipients

BACKGROUND

Sirolimus therapy has been used in orthotopic liver transplant (OLT) recipients diagnosed with a variety of diseases; chronic graft rejection (CR), calcineurin associated renal toxicity, preemptive immune suppression, calcineurin related neurotoxicity, preemptive therapy in transplant recipients with history of hepatocellular carcinoma, and steroid resistant allograft rejection.

METHODS

A search for the medical literature and experiences involving sirolimus was done.

RESULTS

Several animal and human reports evaluating the use sirolimus in liver transplant recipients are found and discussed.

CONCLUSION

Sirolimus has been used for multitude of indications, primarily based on anecdotal experiences. However, reports of sirolimus related side effects have decreased the transplant communities' enthusiasm towards promoting this agent as a safe immune suppression agent.

Rapamycin attenuates load-induced cardiac hypertrophy in mice

BACKGROUND

Cardiac hypertrophy, or an increase in heart size, is an important risk factor for cardiac morbidity and mortality. The mammalian target of rapamycin (mTOR) is a component of the insulin-phosphoinositide 3-kinase pathway, which is known to play a critical role in the determination of cell, organ, and body size.

METHODS AND RESULTS

To examine the role of mTOR in load-induced cardiac hypertrophy, we administered rapamycin, a specific inhibitor of mTOR, to mice with ascending aortic constriction. Activity of p70 ribosomal S6 kinase 1 (S6K1), an effector of mTOR, was increased by 3.8-fold in the aortic-constricted heart. Pretreatment of mice with 2 mg. kg-1. d-1 of rapamycin completely suppressed S6K1 activation and S6 phosphorylation in response to pressure overload. The heart weight/tibial length ratio of vehicle-treated aortic-banded mice was increased by 34.4+/-3.6% compared with vehicle-treated sham-operated mice. Rapamycin suppressed the load-induced increase in heart weight by 67%. Attenuation of cardiac hypertrophy by rapamycin was associated with attenuation of the increase in myocyte cell size induced by aortic constriction. Rapamycin did not cause loss of body weight, lethality, or left ventricular dysfunction.

CONCLUSIONS

mTOR or its target(s) seems to play an important role in load-induced cardiac hypertrophy. Because systemic administration of rapamycin has been used successfully for the treatment of transplant rejection in clinical practice, it may be a useful therapeutic modality to suppress cardiac hypertrophy in patients.

GbetaL, a positive regulator of the rapamycin-sensitive pathway required for the nutrient-sensitive interaction between raptor and mTOR

mTOR and raptor are components of a signaling pathway that regulates mammalian cell growth in response to nutrients and growth factors. Here, we identify a member of this pathway, a protein named GbetaL that binds to the kinase domain of mTOR and stabilizes the interaction of raptor with mTOR. Like mTOR and raptor, GbetaL participates in nutrient- and growth factor-mediated signaling to S6K1, a downstream effector of mTOR, and in the control of cell size. The binding of GbetaL to mTOR strongly stimulates the kinase activity of mTOR toward S6K1 and 4E-BP1, an effect reversed by the stable interaction of raptor with mTOR. Interestingly, nutrients and rapamycin regulate the association between mTOR and raptor only in complexes that also contain GbetaL. Thus, we propose that the opposing effects on mTOR activity of the GbetaL- and raptor-mediated interactions regulate the mTOR pathway.

Interstitial pneumonitis associated with sirolimus: a dilemma for lung transplantation

Rapamycin/sirolimus (SR), trade named Rapammune (Wyeth-Ayerst, Sydney, Australia), is a potent immunosuppressive drug associated with myelosuppression, hypertension, hyperlipidemia, and infection. Rapamycin/sirolimus-induced pneumonitis has been described previously in renal transplant recipients, and this report describes a stable heart-lung transplant recipient who developed a pulmonary infiltrate that reversed after ceasing SR therapy. We believe that immunosuppression-induced pneumonitis in a lung allograft is a serious dilemma for lung transplant physicians

Tacrolimus and sirolimus decrease oxidative phosphorylation of isolated rat kidney mitochondria

1. Tacrolimus and sirolimus are potent immunosuppressors used in transplantation. Tacrolimus has been suspected to alter mitochondrial respiration of different tissues but sirolimus has not been evaluated. 2. We evaluated the in vitro effect of tacrolimus and sirolimus on oxidative phosphorylation of isolated rat kidney mitochondria. 3. Oxygen consumption was measured with a Clark-type electrode. Tacrolimus and sirolimus increased the resting rate (state 4) and had no significant effect on ADP-stimulated respiration (state 3). The decrease of respiratory control ratio was concentration-dependent with a biphasic curve for tacrolimus. The EC(50)s were 3.4 x 10(-11) M and 2.3 x 10(-8) M for tacrolimus and 4.4 x 10(-10) M for sirolimus. The maximal inhibition was 20 and 14% for tacrolimus and sirolimus, respectively. 4. Tacrolimus and sirolimus had an uncoupling effect on oxidative phosphorylation related to a decrease of the inner membrane fluidity. At the opposite of cyclosporin A, no effect on swelling or Ca(2+) fluxes was observed. 5. All events occurred at therapeutic concentrations and then could appear during long-term treatment. Cellular consequences such as chronic nephrotoxicity with tacrolimus are suggested. The risk of cyclosporin A nephrotoxicity potentiation by sirolimus is discussed.

Contrasting impacts of immunosuppressive agents (rapamycin, FK506, cyclosporin A, and dexamethasone) on bidirectional dendritic cell-T cell interaction during antigen presentation

Rapamycin (RAP), tacrolimus (FK506), cyclosporin A, and glucocorticoids represent modern and classic immunosuppressive agents being used clinically. Although these agents have distinct molecular mechanisms of action and exhibit different immunoregulatory profiles, their direct influences on Ag presentation processes remain relatively unknown. Here we report quantitative and qualitative differences among the above four immunosuppressants in their impact on Ag-specific, bidirectional interaction between dendritic cells (DC) and CD4(+) T cells. In the presence of relevant Ag, bone marrow-derived DC delivered activation signals to CD4(+) T cells isolated from the DO11.10 TCR transgenic mice, leading to clonal expansion; secretion of IFN-gamma, IL-2, and IL-4; and surface expression of CD69. Conversely, DO11.10 T cells delivered maturation signals to DC, leading to IL-6 and IL-12 production and CD40 up-regulation. FK506 (10(-10)-10(-8) M) and cyclosporin A (10(-9)-10(-7) M) each blocked efficiently and uniformly all the changes resulting from intercellular signaling in both DC-->T cell and T cell-->DC directions. Dexamethasone (10(-9)-10(-6) M) suppressed all changes, except for CD69 up-regulation, rather incompletely. Remarkably, RAP (10(-10)-10(-8) M) efficiently inhibited DC-induced T cell proliferation and T cell-mediated CD40 up-regulation by DC without abrogating other changes. Interestingly, T cell-independent DC maturation triggered by LPS stimulation was inhibited by dexamethasone, but not by other agents. Our results demonstrate contrasting pharmacological effects of RAP vs calcineurin inhibitors on Ag presentation, thus forming a conceptual framework for rationale-based selection (and combination) of immunosuppressive agents for clinical application.

[Present and future of kidney transplantation]

Renal transplant is the treatment of choice for the patient with end stage renal disease. Spain is the country with the highest donation rate (33 ppm). However, at present this figure is stabilized. The development of non-beating heart programmes, living-donor nephrectomy (specially laparoscopic nephrectomy) programmes, and may be xenotransplantation in a non-immediate future could increase the transplantation activity. The knowledge of preservation mechanisms, specially with the use of perfusion machines allows to rescue for transplantation kidneys with a long warm-ischemia time. Furthermore, these machines are useful for analyzing viability markers. The new immunosuppressive drugs: Tacrolimus, Mycophenolate-Mophetil, Rapamycin and monoclonal antibodies against alpha chain of the interleukine-2 receptor (Basoliximab and Dazcizumab) have reduced the incidence of acute rejection in the immediate renal transplant period. However, its effect in the long-term follow-up period is still a matter of controversy. The incidence of tumour in the renal transplant recipient is increased, specially those of lymphoma, skin cancer and Kaposi sarcoma. Periodical exams for detecting the development of tumours are mandatory in this population. Finally, xenotransplantation is an attractive alternative, although immunological, infective and ethical barriers should previously be resolved.

Long-term comparison of tacrolimus- and cyclosporine-induced nephrotoxicity in pediatric heart-transplant recipients

Nephrotoxicity is an adverse effect of cyclosporine and tacrolimus. Studies comparing their long-term nephrotoxicities are lacking. This study evaluates the nephrotoxicity of these agents over a 7-year period following heart transplantation. Pediatric heart-transplant recipients receiving cyclosporine or tacrolimus as primary immunosuppression were evaluated at two centers from 1982 to 1998. Data collected included serum creatinine, height and weight prior to transplantation, at 1 and 6 months and 1 years post transplantation, and at yearly intervals thereafter. Creatinine clearance was calculated and compared between the two groups. Glomerular filtration rate was measured using Tc-99m diethylenetriaminepentacetic acid. In total, 123 patients were evaluated. Demographic data of the two groups were comparable. Creatinine clearance demonstrated a steady decline. This decline did not differ statistically between the two groups: tacrolimus 98.9 and 90.7mL/min/1.73 m2 at 1 month and 5 years, respectively; cyclosporine 110.7 and 81.7 mL/min/ 1.73 m2 at 1 month and 5 years, respectively. Four patients developed end-stage renal failure. Calculated creatinine clearance consistently overestimated glomerular filtration rate, the latter being greater than 2 standard deviations below the mean normal in 38% of patients. We conclude that the nephrotoxicities of tacrolimus and cyclosporine are comparable over the medium- to long-term in pediatric heart-transplant recipients.

Leucine is a direct-acting nutrient signal that regulates protein synthesis in adipose tissue

In freshly isolated rat adipocytes, leucine or its analog norleucine activates the mammalian target of rapamycin (mTOR)-signaling pathway. This results in phosphorylation of the ribosomal protein S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), two proteins involved in the initiation phase of protein synthesis. The purpose of the studies reported herein was to address the question of whether or not these in vitro effects of leucine and norleucine on adipocytes could be extended to the intact animal and to other tissues. To accomplish this, food-deprived (18 h) male Sprague-Dawley rats were orally administered solutions (2.5 ml/100 g body wt) containing normal saline (0.9% NaCl), a carbohydrate mixture (26.2% D-glucose and 26.2% sucrose), leucine (5.4%), or norleucine (5.4%). The protein synthetic responses of adipose tissue were measured and compared with those of other tissues. In addition, S6K1 and 4E-BP1 phosphorylation was measured, as was the plasma concentration of insulin and tissue ATP concentrations. Leucine administration stimulated protein synthesis in adipose tissue, gastrocnemius, and kidney but not in liver and heart. Norleucine stimulated protein synthesis in all of the tissues tested but, in contrast to leucine, without affecting plasma insulin concentrations. The carbohydrate meal had no effect on protein synthesis in any tissue tested but elicited a robust increase in plasma insulin. These findings provide support for a role of leucine as a direct-acting nutrient signal for stimulation of protein synthesis in adipose tissue as well as other select tissues. In adipose tissue, the effects of the different treatment conditions on the acute regulation of protein synthesis closely correlated with changes in phosphorylation of S6K1 and 4E-BP1; however, this correlation did not exist in all tissues examined. This result implies that leucine or norleucine may acutely stimulate protein synthesis, at least in some tissues, by a mechanism that is independent of both S6K1 and 4E-BP1 phosphorylation.

Fulminant recurrence of atypical hemolytic uremic syndrome during a calcineurin inhibitor-free immunosuppression regimen

Recurrence of hemolytic uremic syndrome (HUS) after kidney transplantation is frequent, occurring almost exclusively in patients with atypical HUS, which is not caused by Escherichia coli gastroenteritis and in which diarrhea is absent. Calcineurin inhibitors are associated with recurrence of HUS. In two children who underwent living donor kidney transplantation for atypical HUS, we pre-emptively employed sirolimus in a calcineurin inhibitor-free immunosuppression regimen. Both children had excellent early graft function, yet both developed severe recurrent disease and subsequently lost their grafts. Avoidance of calcineurin inhibitors did not prevent recurrence of severe HUS and graft loss. Transplantation for severe atypical HUS remains problematic.

Rapamycin inhibits macropinocytosis and mannose receptor-mediated endocytosis by bone marrow-derived dendritic cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that use 2 major pathways for antigen uptake: constitutive macropinocytosis and mannose receptor-mediated endocytosis. Efficient endocytosis is critical for DCs to fulfill their sentinel function in immunity. We investigated the influence of the immunosuppressive macrolide rapamycin on macropinocytosis of fluorescein isothiocyanate (FITC)-albumin and mannose receptor-mediated endocytosis of FITC-dextran by murine bone marrow-derived DCs by flow cytometry. The data show that (1) at a low, physiologically relevant concentration (1 ng/mL), rapamycin impairs macropinocytosis and mannose receptor-mediated endocytosis; (2) the effects are independent of DC maturation and can be demonstrated specifically in immature CD11c(+) major histocompatibility complex (MHC) class II(lo) DCs by 3-color flow cytometry; (3) inhibition of endocytosis is not related to apoptotic cell death; and (4) molar excess of the structurally related molecule FK506 inhibits the actions of rapamycin. The inhibitory effects of rapamycin on DC endocytosis were confirmed in vivo. To our knowledge, this is the first report that a clinically relevant immunosuppressant inhibits DC endocytosis.

mTOR interacts with raptor to form a nutrient-sensitive complex that signals to the cell growth machinery

mTOR/RAFT1/FRAP is the target of the immunosuppressive drug rapamycin and the central component of a nutrient- and hormone-sensitive signaling pathway that regulates cell growth. We report that mTOR forms a stoichiometric complex with raptor, an evolutionarily conserved protein with at least two roles in the mTOR pathway. Raptor has a positive role in nutrient-stimulated signaling to the downstream effector S6K1, maintenance of cell size, and mTOR protein expression. The association of raptor with mTOR also negatively regulates the mTOR kinase activity. Conditions that repress the pathway, such as nutrient deprivation and mitochondrial uncoupling, stabilize the mTOR-raptor association and inhibit mTOR kinase activity. We propose that raptor is a missing component of the mTOR pathway that through its association with mTOR regulates cell size in response to nutrient levels.

Assessment of sirolimus concentrations in whole blood by high-performance liquid chromatography with ultraviolet detection

A novel, reversed-phase high-performance liquid chromatographic (HPLC) method is described for the analysis of sirolimus (SRL) in whole blood. The samples were purified by precipitating blood matrix with zinc sulfate, SRL was then extracted with acetone followed by solid-phase extraction. The method was linear over a range of 1-100 ng/ml and the lower limit of quantification was 2.5 ng/ml. The coefficient of variation (within day) was below 8.0% for the lowest SRL concentration. The day-to-day coefficient of variation was below 6.6%. The assay did not show interference peaks with immunosuppressive drugs commonly given to transplant patients. With the simplified extraction procedure described, 60 samples (including controls and calibration curve) can be quantified in a day. The sensitivity and rapidity of this analytical procedure makes it useful for routine therapeutic monitoring of SRL.

Drug-eluting stents: from bench to bed

The introduction of stents to clinical practice in 1987 was the major breakthrough in the field of percutaneous coronary intervention (PCI). The use of stenting has drastically improved the outcomes of traditional PCI. First stents were approved for bailout and treatment of dissections, reducing dramatically the need for emergent coronary artery bypass grafting (CABG) as a result of vessel closure during PCI. Later stents were proven to reduce the restenosis rate of PCI from 30%-40% with balloon angioplasty to 15%-20% with stents, primarily by eliminating elastic recoil and vascular remodeling as shown by intravascular ultrasound (IVUS) studies. These outcomes have led to a wide acceptance of stenting as the strategy of choice for more than 80% of all PCI procedures performed. The current review focuses on the following topics: (1) strategies in drug selection to reduce neointimal proliferation, (2) stent designs and polymer selection as a platform for drug-eluting stents, (3) review of major preclinical and clinical experimental work performed in the field, and (4) a discussion of the potential and limitations of the technology.

Global and specific translational control by rapamycin in T cells uncovered by microarrays and proteomics

Rapamycin has been shown to affect translation. We have utilized two complementary approaches to identify genes that are predominantly affected by rapamycin in Jurkat T cells. One was to compare levels of polysome-bound and total RNA using oligonucleotide microarrays complementary to 6,300 human genes. Another was to determine protein synthesis levels using two-dimensional PAGE. Analysis of expression changes at the polysome-bound RNA levels showed that translation of most of the expressed genes was partially reduced following rapamycin treatment. However, translation of 136 genes (6% of the expressed genes) was totally inhibited. This group included genes encoding RNA-binding proteins and several proteasome subunit members. Translation of a set of 159 genes (7%) was largely unaffected by rapamycin treatment. These genes included transcription factors, kinases, phosphatases, and members of the RAS superfamily. Analysis of [(35)S]methionine-labeled proteins from the same cell populations using two-dimensional PAGE showed that the integrated intensity of 111 of 830 protein spots changed in rapamycin-treated cells by at least 3-fold (70 increased, 41 decreased). We identified 22 affected protein spots representing protein products of 16 genes. The combined microarray and proteomic approach has uncovered novel genes affected by rapamycin that may be involved in its immunosuppressive effect and other genes that are not affected at the level of translation in a context of general inhibition of cap-dependent translation.

A randomized comparison of a sirolimus-eluting stent with a standard stent for coronary revascularization

BACKGROUND

The need for repeated treatment of restenosis of a treated vessel remains the main limitation of percutaneous coronary revascularization. Because sirolimus (rapamycin) inhibits the proliferation of lymphocytes and smooth-muscle cells, we compared a sirolimus-eluting stent with a standard uncoated stent in patients with angina pectoris.

METHODS

We performed a randomized, double-blind trial to compare the two types of stents for revascularization of single, primary lesions in native coronary arteries. The trial included 238 patients at 19 medical centers. The primary end point was in-stent late luminal loss (the difference between the minimal luminal diameter immediately after the procedure and the diameter at six months). Secondary end points included the percentage of in-stent stenosis of the luminal diameter and the rate of restenosis (luminal narrowing of 50 percent or more). We also analyzed a composite clinical end point consisting of death, myocardial infarction, and percutaneous or surgical revascularization at 1, 6, and 12 months.

RESULTS

At six months, the degree of neointimal proliferation, manifested as the mean (+/-SD) late luminal loss, was significantly lower in the sirolimus-stent group (-0.01+/-0.33 mm) than in the standard-stent group (0.80+/-0.53 mm, P<0.001). None of the patients in the sirolimus-stent group, as compared with 26.6 percent of those in the standard-stent group, had restenosis of 50 percent or more of the luminal diameter (P<0.001). There were no episodes of stent thrombosis. During a follow-up period of up to one year, the overall rate of major cardiac events was 5.8 percent in the sirolimus-stent group and 28.8 percent in the standard-stent group (P<0.001). The difference was due entirely to a higher rate of revascularization of the target vessel in the standard-stent group.

CONCLUSIONS

As compared with a standard coronary stent, a sirolimus-eluting stent shows considerable promise for the prevention of neointimal proliferation, restenosis, and associated clinical events.

T-cell activation through the antigen receptor. Part 2: role of signaling cascades in T-cell differentiation, anergy, immune senescence, and development of immunotherapy

Part 2 of this review on cellular activation by the T-cell antigen receptor (TCR) will highlight how TCR signaling pathways are adapted to achieve specific biologic outcomes, including different states of T-cell differentiation and the induction of T-cell tolerance. We will also explore how treatment with altered peptide ligands affects TCR signaling to change T-cell differentiation or to induce an anergy state. These changes are accomplished through alteration of protein tyrosine kinase activity, the stoichiometry of phosphorylation of immunoreceptor tyrosine-based activation motifs, intracellular free ionized calcium flux, mitogen-activated protein kinase activity, and transcriptional activation of key cytokine promoters. The CTLA-4 plays an important role in the induction and maintenance of anergy. The second theme will highlight how altered TCR signal transduction, including changes in the compartmentalization of signaling components at the TCR synapse, contributes to decreased T-cell activation during immune senescence. Finally, we will illustrate how the molecular details of TCR activation can be used to modify the function of the immune system. This includes a description of the mechanism of action of altered peptide ligands, CTLA-4Ig, and pharmacologic inhibitors of mitogen-activated protein kinases, nuclear factor kappaB, and protein kinase C cascades.

Twenty-eight-day efficacy and phamacokinetics of the sirolimus-eluting stent

BACKGROUND

In-stent restenosis is caused by neointimal hyperplasia. Sirolimus (rapamycin; Wyeth Research, Radnor, Pennsylvania, USA) inhibits vascular smooth muscle cell proliferation and we evaluated the efficacy of sirolimus in reducing neointimal formation in a rabbit iliac model and in-vivo pharmacokinetics in the porcine coronary model.

DESIGN

Randomized, blinded, prospective animal study.

METHODS

Bilateral rabbit iliac artery stent implantation was performed using crossflex stents (Cordis Corporation, Warren, New Jersey, USA) coated with sirolimus incorporated in a nonerodable polymer. Arteries were randomized to one of four stent groups: uncoated stents (n = 8); polymer control stents (n = 10); low-dose sirolimus-eluting stents (n = 9); and high-dose sirolimus-eluting stents (n = 10). Histomorphometry was performed at 28 days. Arterial tissue and stents were retrieved at 8, 14 and 28 days and blood samples were obtained daily during the first week.

RESULTS

Treatment with low-dose sirolimus was associated with a 23% (P = NS) reduction in neointimal area and treatment with high-dose sirolimus with a 45% (P < 0.05) reduction. Sustained drug release from the stent and prolonged intramural arterial deposition were confirmed for up to 28 days. No detectable sirolimus was found in the blood after 2 days.

CONCLUSION

Controlled-release local delivery of a cell-cycle inhibitor from a nonerodable polymer-coated stent reduced neointimal formation in rabbit iliac arteries in a dose-dependent manner and represents a promising strategy for preventing restenosis.

Long-term care of pediatric renal transplant patients: from bench to bedside

In this review, we discuss current and future issues in the management of pediatric renal transplant recipients, including the optimization of long-term graft function and the minimization of complications caused by immunosuppression. Long-term management involves not only the monitoring of graft function but also the identification of patients at risk for the development of complications. The identification of patients with immunoreactive or immunoregulatory responses can be performed molecular monitoring of the immune response. Also, the use of frequent surveillance kidney biopsies, surrogate markers of chronic rejection, and glomerular filtration rate will be a part of future management. Identifying high-risk patients enables the physician to optimize immunosuppression to limit acute rejection. Short-and long-term management of pediatric transplant patients also includes adequate monitoring of growth and the monitoring for post-transplant lymphoproliferative disease. Ongoing clinical trials are underway that focus on these novel approaches in caring for pediatric transplant recipients.

Akt/protein kinase B promotes organ growth in transgenic mice

One of the least-understood areas in biology is the determination of the size of animals and their organs. In Drosophila, components of the insulin receptor phosphoinositide 3-kinase (PI3K) pathway determine body, organ, and cell size. Several biochemical studies have suggested that Akt/protein kinase B is one of the important downstream targets of PI3K. To examine the role of Akt in the regulation of organ size in mammals, we have generated and characterized transgenic mice expressing constitutively active Akt (caAkt) or kinase-deficient Akt (kdAkt) specifically in the heart. The heart weight of caAkt transgenic mice was increased 2.0-fold compared with that of nontransgenic mice. The increase in heart size was associated with a comparable increase in myocyte cell size in caAkt mice. The kdAkt mutant protein attenuated the constitutively active PI3K-induced overgrowth of the heart, and the caAkt mutant protein circumvented cardiac growth retardation induced by a kinase-deficient PI3K mutant protein. Rapamycin attenuated caAkt-induced overgrowth of the heart, suggesting that the mammalian target of rapamycin (mTOR) or effectors of mTOR mediated caAkt-induced heart growth. In conclusion, Akt is sufficient to induce a marked increase in heart size and is likely to be one of the effectors of the PI3K pathway in mediating heart growth.

Immunisations in solid-organ transplant recipients

Solid-organ transplant recipients are at increased risk of various infectious diseases, some of which are vaccine preventable mmunisations are among the most efficient interventions available. Solid-organ tranplant recipients would greatly benefit from effective immunisations, provided the recommendations are based on a careful risk-benefit analysis in which the effectiveness of the vaccine is weighed against possible adverse reactions, including graft rejection. In this review, we summarise the data from studies on relevant immunisations in solid-organ transplant recipients. The major issues are the immunogenicity and safety of immunisations, the factors associated with poor immune response, and recommendations for immunisation schemes.

Rapamycin inhibits primary and metastatic tumor growth by antiangiogenesis: involvement of vascular endothelial growth factor

Conventional immunosuppressive drugs have been used effectively to prevent immunologic rejection in organ transplantation. Individuals taking these drugs are at risk, however, for the development and recurrence of cancer. In the present study we show that the new immunosuppressive drug rapamycin (RAPA) may reduce the risk of cancer development while simultaneously providing effective immunosuppression. Experimentally, RAPA inhibited metastatic tumor growth and angiogenesis in in vivo mouse models. In addition, normal immunosuppressive doses of RAPA effectively controlled the growth of established tumors. In contrast, the most widely recognized immunosuppressive drug, cyclosporine, promoted tumor growth. From a mechanistic perspective, RAPA showed antiangiogenic activities linked to a decrease in production of vascular endothelial growth factor (VEGF) and to a markedly inhibited response of vascular endothelial cells to stimulation by VEGF. Thus, the use of RAPA, instead of cyclosporine, may reduce the chance of recurrent or de novo cancer in high-risk transplant patients.

Inflammation in lung transplantation for CF. Immunosuppression and modulation of inflammation

Lung transplantation is an accepted therapy for selected individuals with end-stage lung disease due to cystic fibrosis (CF). Recent data show that CF recipients of lung transplantation have survival as good as those of any other diagnostic group. After transplantation, CF patients confront the major threats to life and health of graft infection and rejection. Inflammation is the common mediator of injury to the lung in both these instances. Graft infection after lung transplantation involves the same micro-organisms as are typical with CF as well as opportunistic agents. Prophylactic strategies and aggressive diagnosis via bronchoscopy are both critical in the effective treatment of post-transplant lung infections. Graft rejection involves the detection and recognition of foreign antigen and the subsequent activation of specific T-lymphocyte clones leading to inflammatory injury to the donor organ. Immunosuppression is used to prevent and/or modulate host response to the donor organ and titrated to serum therapeutic drug monitoring and transbronchial biopsy findings. Precise clinical monitoring and aggressive diagnostic approaches are crucial to minimizing graft injury and enhancing life after transplantation. Although most CF lung transplant recipients experience both graft infection and rejection and the 5-yr survival rate remains at approx 50%, improvement in diagnosis and therapy continue over time. With the introduction of new approaches to antimicrobial therapy, new immunosuppressant agents and promising strategies to promote immune tolerance, survival after lung transplantation is likely to improve in the coming decades.

Mechanisms of resistance to rapamycins

Rapamycins represent a novel family of anticancer agents, currently including rapamycin and its derivatives, CCI-779 and RAD001. Rapamycins inhibit the function of the mammalian target of rapamycin (mTOR), and potently suppress tumor cell growth by arresting cells in G1 phase or potentially inducing apoptosis of cells, in culture or in xenograft tumor models. However, recent data indicate that genetic mutations or compensatory changes in tumor cells influence the sensitivity of rapamycins. First, mutations of mTOR or FKBP12 prevent rapamycin from binding to mTOR, conferring rapamycin resistance. Second, mutations or defects of mTOR-regulated proteins, including S6K1, 4E-BP1, PP2A-related phosphatases, and p27(Kip1) also render rapamycin insensitivity. In addition, the status of ATM, p53, PTEN/Akt and 14-3-3 are also associated with rapamycin sensitivity. To better explore the role of rapamycins against tumors, this review will summarize the current knowledge of the mechanism of action of rapamycins, and progress in understanding mechanisms of acquired or intrinsic resistance.

Rapamycin and less immunosuppressive analogs are toxic to Candida albicans and Cryptococcus neoformans via FKBP12-dependent inhibition of TOR

Candida albicans and Cryptococcus neoformans cause both superficial and disseminated infections in humans. Current antifungal therapies for deep-seated infections are limited to amphotericin B, flucytosine, and azoles. A limitation is that commonly used azoles are fungistatic in vitro and in vivo. Our studies address the mechanisms of antifungal activity of the immunosuppressive drug rapamycin (sirolimus) and its analogs with decreased immunosuppressive activity. C. albicans rbp1/rbp1 mutant strains lacking a homolog of the FK506-rapamycin target protein FKBP12 were found to be viable and resistant to rapamycin and its analogs. Rapamycin and analogs promoted FKBP12 binding to the wild-type Tor1 kinase but not to a rapamycin-resistant Tor1 mutant kinase (S1972R). FKBP12 and TOR mutations conferred resistance to rapamycin and its analogs in C. albicans, C. neoformans, and Saccharomyces cerevisiae. Our findings demonstrate the antifungal activity of rapamycin and rapamycin analogs is mediated via conserved complexes with FKBP12 and Tor kinase homologs in divergent yeasts. Taken together with our observations that rapamycin and its analogs are fungicidal and that spontaneous drug resistance occurs at a low rate, these mechanistic findings support continued investigation of rapamycin analogs as novel antifungal agents.

Managing the highly sensitized transplant recipient and B cell tolerance

The detection of anti-donor-HLA antibodies in a renal allograft recipient's serum, either at the time of or after transplantation, is usually associated with specific antibody-mediated clinical syndromes. These can be divided temporally into three categories: hyperacute rejection, acute humoral rejection and chronic humoral rejection. With the identification of new immunosuppressive drug combinations, more-effective control of alloantibody production has been recently achieved in humans. Thus, prevention and/or treatment of antibody-mediated allograft injury are now possible. Ultimately, the induction of mixed hematopoietic chimerism may allow us to overcome the problem of allosensitization and accept an allograft without chronic immunosuppression.

Short-term effects of statin therapy in patients with hyperlipoproteinemia after liver transplantation: results of a randomized cross-over trial

BACKGROUND/AIMS

Hyperlipoproteinemia is frequent following liver transplantation and may lead to atherosclerosis. Lipid-lowering agents may be useful, but could interfere with the function of the transplanted organ and with immunosuppression. We therefore evaluated in a prospective, randomized, open-labeled cross-over trial the effect of two frequently used 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (pravastatin 10 mg d(-1) and cerivastatin 0.1 mg d(-1)) in hyperlipoproteinemic patients after liver transplantation.

METHODS

Sixteen patients (6.3 +/- 2.0 years post-transplantation, cyclosporine n = 11, tacrolimus n = 5) with hyperlipoproteinemia (cholesterol 246 +/- 42, triglycerides 191 +/- 87, low-density lipoprotein (LDL)-cholesterol 161 +/- 35, high-density lipoprotein (HDL)-cholesterol 44 +/- 11 mg d(-1)) were included. Treatment periods of 6 weeks were separated by a 4-week washout period.

RESULTS

Both medications were tolerated well, no effects on serum concentrations of liver enzymes or immunosuppressive agents were observed. Cerivastatin and pravastatin decreased (P < 0.001) cholesterol by 21 +/- 10% and 15 +/- 10%, LDL-cholesterol by 27 +/- 14% and 17 +/- 15%, respectively, while triglyceride and HDL-cholesterol concentrations did not change significantly. LDL/HDL-cholesterol markedly improved (P < 0.001) by 29 +/- 16% (cerivastatin) and 16 +/- 16% (pravastatin). Cerivastatin was more potent than pravastatin in patients receiving cyclosporine A, while there was no significant difference in patients receiving tacrolimus.

CONCLUSIONS

Low-dose cerivastatin and pravastatin significantly improve lipid profiles following liver transplantation without affecting liver function or immunosuppression.