Immunomodulation in stable renal transplant recipients with concomitant tacrolimus and sirolimus therapy

Impact of sirolimus, tacrolimus and mycophenolate mofetil on osteoclastogenesis--implications for post-transplantation bone disease

BACKGROUND

Post-transplantation bone disease is associated with a high degree of morbidity including pain and fractures. Glucocorticoid-induced osteoporosis on top of pre-existing renal osteodystrophy is considered the major pathogenic factor, while the role of non-glucocorticoid immunosuppressants is less well defined.

METHODS

In this study, we investigated the influence of sirolimus (SRL) versus calcineurin inhibitor (CI)-based immunosuppressive regimens on biomarkers of bone resorption in renal transplant patients. In addition, the impact of SRL, tacrolimus and mycophenolate mofetil (MMF) on osteoclast activation and function was assessed in cell culture systems.

RESULTS

Using this approach, we demonstrated reduced serum levels of bone resorption markers in patients treated with SRL after kidney transplantation compared to a CI-based regimen. In line with this observation, we detected profoundly reduced osteoclast differentiation and subsequently diminished hydroxyapatite resorption in the presence of SRL compared to MMF and tacrolimus in vitro. Moreover, SRL significantly reduced osteoclast precursor proliferation in vitro compared to tacrolimus and led to augmented apoptosis in osteoclast precursors.

CONCLUSIONS

Taken together, SRL was shown to inhibit osteoclast formation in vivo and in vitro. SRL thus may have the potential to balance osteoclast promoting effects of glucocorticoids and CI, thereby counteracting the development of accelerated osteoporosis in renal transplant recipients.

Use of sirolimus in solid organ transplantation

Sirolimus is a mammalian target of rapamycin (mTOR) inhibitor that inhibits cell cycle progression and has proven to be a potent immunosuppressive agent for use in solid organ transplant recipients. The drug was initially studied as an adjunct to ciclosporin (cyclosporine) to prevent acute rejection in kidney transplant recipients. Subsequent studies have shown efficacy when combined with a variety of other immunosuppressive agents. The most common adverse effects of sirolimus are hyperlipidaemia and myelosuppression. The drug has unique antiatherogenic and antineoplastic properties, and may promote immunological tolerance and reduce the incidence of chronic allograft nephropathy. Although sirolimus is relatively non-nephrotoxic when administered as monotherapy, it pharmacodynamically enhances the toxicity of calcineurin inhibitors. Ironically, the drug has been used to facilitate calcineurin inhibitor-free protocols designed to preserve renal function after solid organ transplantation. Whether sirolimus can be used safely over the long term with low doses of calcineurin inhibitors requires further study. The use of sirolimus as a corticosteroid-sparing agent also remains to be proven in controlled trials. Postmarketing studies have revealed a number of unforeseen adverse effects including impaired wound healing and possibly proteinuria, oedema, pneumonitis and thrombotic microangiopathy. Overall, sirolimus is a powerful agent when used judiciously with other available immunosuppressants. As is true for all immunosuppressive drugs available for treatment of solid organ transplant recipients, the efficacy of the drug must be balanced against its considerable adverse effects.

Targeted in vitro and in vivo gene transfer into T lymphocytes: potential of direct inhibition of allo-immune activation

Background

Successful inhibition of alloimmune activation in organ transplantation remains one of the key events in achieving a long-term graft survival. Since T lymphocytes are largely responsible for alloimmune activation, targeted gene transfer of gene of cyclin kinase inhibitor p21 into T cells might inhibit their aberrant proliferation. A number of strategies using either adenoviral or lentiviral vectors linked to mono or bispecific antibodies directed against T cell surface markers/cytokines did not yield the desired results. Therefore, this study was designed to test if a CD3promoter-p21 chimeric construct would in vitro and in vivo transfer p21 gene to T lymphocytes and result in inhibition of proliferation. CD3 promoter-p21 chimeric constructs were prepared with p21 in the sense and antisense orientation. For in vitro studies EL4-IL-2 thyoma cells were used and for in vivo studies CD3p21 sense and antisense plasmid DNA was injected intramuscularly in mice. Lymphocyte proliferation was quantified by ³H-thymidine uptake assay; IL-2 mRNA expression was studied by RT-PCR and using Real Time PCR assay, we monitored the CD3, p21, TNF-α and IFN-γ mRNA expression.

Results

Transfection of CD3p21 sense and antisense in mouse thyoma cell line (EL4-IL-2) resulted in modulation of mitogen-induced proliferation. The intramuscular injection of CD3p21 sense and antisense plasmid DNA into mice also modulated lymphocyte proliferation and mRNA expression of pro-inflammatory cytokines.

Conclusion

These results demonstrate a novel strategy of in vitro and in vivo transfer of p21 gene to T cells using CD3-promoter to achieve targeted inhibition of lymphocyte proliferation and immune activation.

Ex vivo expanded dendritic cells home to T-cell zones of lymphoid organs and survive in vivo after allogeneic bone marrow transplantation

Little is known about adoptive transfer of allogeneic ex vivo expanded dendritic cells (eDCs). We investigated the trafficking pattern of eDCs in mice after allogeneic bone marrow transplantation by using bioluminescence imaging. eDCs were expanded from bone marrow precursors in the presence of GM-CSF, interleukin-4, and Flt3L and retrovirally transduced to express luciferase (luc) and green fluorescence protein (gfp). Flow cytometry showed polyclonal DC populations after expansion that consisted of CD11c+CD11b+ and CD11c-CD11b+ cells that co-expressed CD40, CD80, CD86, and MHCII. eDCs were functional in mixed lymphocyte reactions and produced tumor necrosis factor-alpha on phytohemagglutinin stimulation. The eDCs were then injected intravenously into BALB/c recipient mice that had received allogeneic bone marrow transplantation 6 weeks previously. On day 1 after transfer, eDCs were detected by bioluminescence imaging throughout the lungs and spleen. In the later course, signals were observed throughout thymus, lower abdomen, and spleen throughout a period of more than 42 days. Immunofluorescence microscopy confirmed CD11c positivity on the gfp+ donor cells, which localized in T-cell zones of mesenteric lymph nodes, Peyer's patches, spleen, and thymus. These findings are important for adoptive immunotherapies because they indicate that eDCs migrate efficiently in vivo and are capable of surviving long term.

Reciprocal role of cyclins and cyclin kinase inhibitor p21WAF1/CIP1 on lymphocyte proliferation, allo-immune activation and inflammation

Background

Immune activation that results due to the aberrant proliferation of lymphocytes leads to inflammation and graft rejection in organ transplant recipients. We hypothesize that the cell cycle control and inflammation are parallel events, inhibition of cellular proliferation by cyclin kinase inhibitor specifically p21 will limit inflammation and prevent allograft rejection.

Methods

We performed in vitro and in vivo studies using lymphocytes, and rat heart transplant model to understand the role of cyclins and p21 on mitogen and allo-induced lymphocyte activation and inflammation. Lymphocyte proliferation was studied by ³H-thymidine uptake assay and mRNA expression was studied RT-PCR.

Results

Activation of allo- and mitogen stimulated lymphocytes resulted in increased expression of cyclins, IL-2 and pro-inflammatory cytokines, which was inhibited by cyclosporine. The over-expression of p21 prolonged graft survival in a completely mismatched rat heart transplant model resulted by inhibiting circulating and intra-graft expression of proinflammatory cytokines.

Conclusion

Cyclins play a significant role in transplant-induced immune activation and p21 over-expression has potential to inhibit T cell activation and inflammation. The results from this study will permit the design of alternate strategies by controlling cell cycle progression to achieve immunosuppression in transplantation.

Recombinant p21 protein inhibits lymphocyte proliferation and transcription factors

Cellular proliferation determines the events leading to the initiation and development of inflammation, immune activation, cancer, atherogenesis, and other disorders associated with aberrant cell proliferation. Cyclin inhibitor p21 plays a unique role in limiting cell cycle progression. However, its effectiveness can only be demonstrated with direct in vitro and in vivo delivery to control aberrant proliferation. We demonstrate that using a protein-transducing domain p21 protein a) localizes within the nuclear compartments of cells, b) interacts with transcription factors, NF-kappaB, and NFATs (NFATc and NFATp), and c) inhibits lymphocyte proliferation and expression of proinflammatory cytokines. This study using lymphocyte proliferation as a model suggests that the recombinant p21 protein can directly be delivered as a therapeutic protein to provide a novel, viable, and powerful strategy to limit proliferation, inflammation, alloimmune activation, cancer, and vascular proliferative disorders such as atherosclerosis.

Clinical application of sirolimus in renal transplantation: an update

In addition to an analysis of the final results of phase I/II and phase III clinical trials of sirolimus (SRL), this review focuses on the recent results of several studies in renal transplantation, which include diverse combinations of SRL with other immunosuppressive agents. While SRL was initially introduced as an adjunctive agent to calcineurin inhibitors, it is now serving as the base for therapies that spare or avoid these nephrotoxic drugs. However, to optimize the use of SRL as base therapy, further work is necessary to determine target concentrations, requirement for concomitant steroids and/or nucleoside synthesis blockers, and countermeasure therapy to overcome the drug's adverse effects.

Long-term treatment of bile duct-ligated rats with rapamycin (sirolimus) significantly attenuates liver fibrosis: analysis of the underlying mechanisms

Rapamycin is an immunosuppressant with antiproliferative properties. We investigated whether rapamycin treatment of bile duct-ligated (BDL) rats is capable of inhibiting liver fibrosis and thereby affecting hemodynamics. Following BDL, rats were treated for 28 days with rapamycin (BDL SIR). BDL animals without drug treatment (BDL CTR) and sham-operated animals served as controls. After 28 days, hemodynamics were measured, and livers were harvested for histology/immunohistochemistry. Liver mRNA levels of transforming growth factor (TGF)-beta1, connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF)-beta, cyclin-dependent kinase inhibitor p27(kip) (p27), and cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (p21) were quantified by real-time polymerase chain reaction. Liver protein levels of p27, p21, p70 S6 kinase (p70(s6k)), phosphorylated p70(s6k) (p-p70(s6k)), eukaryotic initiation factor 4E-binding protein (4E-BP1), p-4E-BP1 (Thr37/46), and p-4E-BP1 (Ser65/Thr70) were determined by Western blotting. Portal vein pressure was lower in BDL SIR than in BDL CTR animals. Volume fractions of connective tissue, bile duct epithelial, and desmin- and actin-positive cells were lower in BDL SIR than in BDL CTR rats. On the mRNA level, TGF-beta1, CTGF, and PDGF were decreased by rapamycin. p27 and p21 mRNA did not differ. On the protein level, rapamycin increased p27 and decreased p21 levels. Levels of nonphosphorylated p70(s6k) and 4E-BP1 did not vary between groups, but levels of p-p70(s6k) were decreased by rapamycin. Rapamycin had no effect on p-4E-BP1 (Thr37/46) and p-4E-BP1 (Ser65/Thr70) levels. In BDL rats, rapamycin inhibits liver fibrosis and ameliorates portal hypertension. This is paralleled by decreased levels of TGF-beta1, CTGF, and PDGF. Rapamycin influences the cell cycle by up-regulation of p27, down-regulation of p21, and inhibition of p70(s6k) phosphorylation.

Anti-transforming growth factor antibody at low but not high doses limits cyclosporine-mediated nephrotoxicity without altering rat cardiac allograft survival: potential of therapeutic applications

BACKGROUND

Long-term treatment of cardiac transplant recipients with cyclosporine results in a progressive decline in kidney function in a large number of patients. This complication is one of the most important prognostic parameters that determine the outcome of cardiac transplantation. Transforming growth factor-beta (TGF-beta) is one of the most potent mediators of the fibrogenic effects of cyclosporine.

METHODS AND RESULTS

With the use of an experimental rodent model, heterotopic heart transplantation was performed, creating histocompatibility-disparate allografts. Because TGF-beta in part mediates both the immunosuppressive and nephrotoxic effects of cyclosporine, recipients were treated with cyclosporine with and without anti-TGF-beta antibody to determine whether anti-TGF-beta antibody could reduce the nephrotoxic effects of cyclosporine. Intrarenal expression of TGF-beta, collagen, fibronectin, matrix metalloproteinase-2, and tissue inhibitor of metalloproteinase-2 was studied with the use of reverse transcription-polymerase chain reaction. Intrarenal expression of TGF-beta protein was studied by immunohistochemistry and with the use of ELISA to quantify circulating levels of TGF-beta protein in plasma. Cyclosporine-induced graft survival (immunosuppressive effect) was abrogated with a higher concentration (2.5 mg/kg) of anti-TGF-beta antibody, whereas a lower concentration (1 mg/kg) inhibited both cyclosporine-induced expression of fibrogenic molecules and renal toxicity.

CONCLUSIONS

These results provide credence to the pivotal role of TGF-beta in immunosuppression-associated renal toxicity in recipients of cardiac transplantation. Furthermore, these findings support a potentially significant therapeutic use of optimal concentration of anti-TGF-beta antibody to ameliorate cyclosporine-associated nephrotoxicity in cardiac transplant recipients.