We conclude that oral sirolimus markedly delays the loss of renal function and retards cyst development in Han:SPRD rats with ADPKD. Our data also suggest that activation of the S6K signalling pathway plays an important role in the pathogenesis of PKD. Sirolimus could be a useful drug to retard progressive renal failure in patients with ADPKD.

These data demonstrate that PD-L1 is an inducible renal tubular epithelial antigen that negatively regulates T-cell responses elicited by IFN-gamma-stimulated TEC. We speculate that the PD-1/PD-L1 pathway may play a role in protecting the epithelium from immune-mediated tubulointerstitial injury.

Abstract. MHC class II-expressing renal tubular epithelial cells (TEC) are able to present foreign peptide antigens to T cells. The costimulatory signals that are required for effective T cell activation upon antigen presentation by TEC have not been characterized. Various cultured TEC lines were examined for expression of the recently described costimulatory molecule B7RP-1 (B7h), a ligand of the T cell molecule inducible costimulator (ICOS), and expression was compared with that of B7.1, B7.2, and CD40. B7RP-1 and CD40 were abundantly expressed by cultured murine and human TEC, whereas B7.1 and B7.2 could not be detected. Stimulation with lipopolysaccharide or tumor necrosis factor-␣ did not induce B7.1 or B7.2 expression and did not alter B7RP-1 expression. Interestingly, interleukin-2 production by T cell hybridomas after antigen presentation by TEC was enhanced by blocking antibodies to B7RP-1 and ICOS. In contrast, blocking antibodies to B7RP-1 or ICOS exerted inhibitory effects on anti-CD3-activated murine splenocyte proliferation. Immunohistochemical staining of normal human kidneys demonstrated strong constitutive B7RP-1 expression in distal tubules, collecting ducts, and urothelium. In human kidneys with allograft rejection or interstitial nephritis, distinct B7RP-1 staining was also detected in proximal tubules, in areas of mononuclear infiltration. In conclusion, the B7RP-1/ICOS pathway negatively regulates T cell activation upon MHC class II-restricted antigen presentation by TEC. Because B7RP-1 is also expressed by tubules in vivo, it can be speculated that the B7RP-1/ICOS pathway could play an inhibitory role in TEC-mediated immune activation in the kidney.Renal proximal tubular epithelial cells (TEC) play an important role in the pathogenesis of immune renal injury, both as initiators of T cell responses and as targets of T cells. Various studies, including our own, have demonstrated that TEC express MHC class II antigens, particularly in response to interferon-␥ (IFN-␥) (1-3). TEC also have the ability to ingest and process antigen in the lysosomal compartment, then presenting it in the form of small antigenic peptides, in the context of MHC class II molecules, to CD4 ϩ T cells (3-5). Specific CD4 ϩ T cells may recognize antigen via T cell receptors. Various signaling pathways are then activated, transmitting the so-called signal 1 to the interior of the T cells (6).Typical antigen-presenting cells initiate a second signal (signal 2), which is needed to fully activate the T cells. This second signal is usually received by T cells through the interaction of CD28 with B7 (7). Several studies have demonstrated, however, that cultured TEC lack the classic B7 molecules, including B7.1 and B7.2. Furthermore, B7.1 and B7.2 are not observed on tubules in vivo, in animal models of renal injury (8 -10). This has raised many questions regarding the nature and importance of signal 2 in the interaction of T cells with TEC.Ligation of T cell receptors in the absence of signal 2 may result in clonal anergy (11...

Background/Aims: Rapamycin inhibits cyst growth in polycystic kidney disease by targeting the mammalian target of rapamycin (mTOR). To determine if this is a class effect of the mTOR inhibitors, we examined the effect of everolimus, the analogue of rapamycin, on disease progression in the Han:SPRD rat model of polycystic kidney disease. Methods: Four-week-old male heterozygous cystic (Cy/+) and wild-type normal (+/+) Han:SPRD rats were administered everolimus or vehicle (3 mg/kg/day) by gavage for 5 weeks. Kidney function and whole-blood trough levels of everolimus were monitored. After treatment kidney weight and cyst volume density were assessed. Tubule epithelial cell proliferation was assessed by BrdU staining. Results: Everolimus trough levels between 5 and 7 µg/l were sufficient to significantly reduce kidney and cyst volume density by approximately 50 and 40%, respectively. The steady decrease of kidney function in Cy/+ rats was reduced by 30% compared with vehicle-treated Cy/+ rats. Everolimus treatment markedly reduced the number of 5-bromo-2-deoxyuridine-labeled nuclei in cyst epithelia. Body weight gain and kidney function were impaired in everolimus-treated wild-type rats. Conclusion: Moderate dosage of everolimus inhibits cystogenesis in Han:SPRD rats. The inhibitory effect of everolimus appears to represent a class effect of mTOR inhibitors.

Because Akt is a proximal target of mTOR, its inhibition with specific antagonists could be useful to prevent or halt cystogenesis in ADPKD.