PD-L1 partially protects renal tubular epithelial cells from the attack of CD8+cytotoxic T cells

Background. Activated infiltrating T cells play a crucial role in nephritic inflammation via the direct interaction with proximal tubular epithelial cells (TEC). Under inflammatory conditions, major histocompatibility complex class I and II molecules are upregulated on the surface of renal TEC, enabling them to function as ‘non-professional' antigen-presenting cells (APC) to activate T cells, and, in turn to be targeted by cytotoxic T lymphocytes (CTL) to cause tissue damage. It is known that co-stimulatory (e.g. B7/CD28) and co-inhibitory (e.g. PD-L1/PD-1) signals regulate and determine the magnitude of T cell responses. In this study, we examined the expression of co-stimulatory molecule PD-L1 by renal TEC and the functional role of renal PD-L1/PD-1 pathway in regulating CD8+ T cell responses induced by antigen-presenting renal TEC. Methods. Renal TEC were treated with type I and type II interferons (IFN-α, IFN-β or IFN-γ). PD-L1 expression was then determined with flow cytometry and RT-PCR. To investigate the functional role of renal epithelial PD-L1 on CD8+ CTL responses, H-2Kb-restricted, OVA257-264 peptide-specific CD8+ T cells isolated from OT-1 T cell receptor transgenic mice were co-incubated with IFN-stimulated, OVA257-264 peptide-pulsed congeneic TEC. The activation of OT-1 CD8+ CTL was estimated either by IFN-γ production in the supernatants of co-cultures or by CTL activity. Results. TECs do not constitutively express PD-L1 on their surface. However, a strong and dose-dependent upregulation of PD-L1 was observed on TEC after stimulation with IFN-β or IFN-γ, but not with IFN-α. OVA257-264 peptide pulsed-TEC were able to activate OT-1 CD8+ T cells, indicated by the high amount of IFN-γ production and cytolysis of TEC. Blockade of epithelial PD-L1 with specific mAb significantly increased OT-1 CD8+ T cell activity, indicating that the PD-L1 pathway has a negative effect on CD8+ T cell responses. Moreover, IFN- β- or IFN-γ-stimulated TEC with high surface PD-L1 expression were more resistant to the cytolysis by OT-1 CTL. Conclusion. Together our data reveal that the renal PD-L1/PD-1 pathway has a negative effect on CD8+ CTL activation. PD-L1 might, therefore, act as a protective molecule on TEC, downregulating the cytotoxic renal parenchymal immune respons

Follow-up of bone mineral density changes in de novo kidney transplant recipients treated with two doses of the receptor activator of nuclear factor κB ligand inhibitor denosumab

BACKGROUND: Studies in women with post-menopausal osteoporosis have shown that discontinuation of treatment with denosumab leads to an increased risk of vertebral fractures because of rebound bone turnover and rapid loss of bone mineral density (BMD). METHODS: In a post hoc analysis of the Prolia for Osteoporosis of Transplant Operated Patient study, we analyzed the effect of denosumab withdrawal on BMD changes. Twenty-five de novo kidney transplant recipients (KTR) who were treated for 1 year with 2 six-monthly doses of denosumab on top of standard treatment (daily calcium and vitamin D) were compared to a control group of 29 KTR who received standard treatment alone. BMD changes were analyzed by repeated dual-energy X-ray absorptiometry shortly after transplantation (baseline), after 6 and 12 months (active treatment phase) and after 2-6.5 years (follow-up phase). RESULTS: The average BMD at the lumbar spine declined markedly after discontinuation of treatment with denosumab but increased again thereafter. Thus, the average monthly change in lumbar spine BMD from month 12 onward was only 0.1 ± 2.8‰ in the denosumab group but 1.5 ± 1.9‰ in the control group (p = 0.021). The average monthly change in lumbar spine BMD from baseline to follow-up was similar in the control and denosumab group (1.1 ± 1.2‰ vs. 1.5 ± 2.4‰, p = 0.788). Similar results were seen at the total hip. CONCLUSIONS: In de novo KTR treated with 2 doses of denosumab, we detect a marked decrease in lumbar spine and hip BMD when denosumab is discontinued. Denosumab treatment should therefore not be discontinued without considering an alternative antiresorptive treatment

Relationship of serum bicarbonate levels with 1-year graft function in kidney transplant recipients in Switzerland

BACKGROUND: Metabolic acidosis (MA) is common in kidney transplant recipients (KTRs). Several studies have shown that MA is involved in the progression of chronic kidney disease. However, it is unclear if there is also a relationship between serum bicarbonate and graft function after kidney transplantation (KTx). We hypothesized that low serum bicarbonate is associated with a lower estimated glomerular filtration rate (eGFR) 1 year after KTx. METHODS: We performed a post hoc analysis of a single-center, open-label randomized trial in 90 KTRs and investigated the relationship of serum bicarbonate and graft function in the first year after KTx. RESULTS: Prevalence of MA was high after KTx (63%) and decreased to 28% after 1 year. Bicarbonate (20.6 ± 3.0 to 22.7 ± 2.7 mmol/L) increased in the first year after transplantation whereas eGFR (53.4 ± 15.8 to 56.9 ± 18.5 mL/min/1.73 m2) did not change significantly. Higher serum bicarbonate (p = 0.029) was associated with higher eGFR in the first year after KTx. CONCLUSION: Prevalence of MA is high in KTRs. In the first year after KTx, serum bicarbonate was positively correlated with eGFR, suggesting a potential role of MA in kidney graft function

Successful treatment of hypercalcemia with cinacalcet in renal transplant recipients with persistent hyperparathyroidism

Background. Cinacalcet lowers plasma parathyroid hormone (PTH) levels in primary and secondary hyperparathyroidism. The efficacy and safety of cinacalcet have not been examined in renal transplant patients with persistent hyperparathyroidism. The aim of this study was to evaluate the effect of cinacalcet as a novel therapy for the management of such patients. Methods. Eleven renal allograft recipients with persistent hyperparathyroidism were treated with cinacalcet. The total study time was 10 weeks. Individual cinacalcet doses were adjusted to obtain a serum calcium in the predefined normal target range of 2.10-2.60 mmol/l. Results. Serum calcium decreased significantly from 2.73±0.05 mmol/l to 2.44±0.05 and 2.42± 0.04 mmol/l after 2 and 10 weeks of treatment, respectively. All patients reached the target range rapidly and remained normocalcaemic throughout the study. Serum PTH significantly decreased 16.1 and 21.8% at study weeks 2 and 10, respectively, compared with week 0. Serum phosphate increased. Renal function remained stable and no allograft rejection was observed. From weeks 2 to 10, daily cinacalcet doses administered were 30 mg (n = 8), 15 mg (n = 1) and 60 mg (n = 1), respectively. Conclusion. Cinacalcet was effective in correcting the hypercalcaemia associated with persistent hyperparathyroidism after renal transplantation. It appears to be safe. Thus, cinacalcet represents a promising alternative for parathyroidectomy in these patient

Effective control of persistent hyperparathyroidism with cinacalcet in renal allograft recipients

Background. Cinacalcet rapidly normalizes serum calcium and reduces intact parathyroid hormone (PTH) levels in renal transplant patients with hypercalcaemia and persistent hyperparathyroidism. The aim of this study is to evaluate the 6 months efficacy of cinacalcet and the effect of cinacalcet withdrawal on serum calcium and PTH in such patients. Furthermore, the impact of cinacalcet on bone turnover and quality of life was assessed. Methods. Twelve renal allograft recipients with hypercalcaemia due to persistent hyperparathyroidism were treated with cinacalcet for 26 weeks. Cinacalcet was then withdrawn to check for recurrence of hypercalcaemia. Results. Cinacalcet maintained normocalcaemia in all patients from week 4 to 26, and PTH significantly decreased and remained suppressed. Serum phosphate increased, whereas the serum calcium-phosphate product remained unchanged. The excretion of calcium and phosphate in the 24 h urine had tendency to decrease. After cinacalcet was withdrawn, hypercalcaemia recurred rapidly and PTH increased to baseline values. Renal function remained stable, proteinuria was unchanged and no allograft rejection was observed. During treatment with cinacalcet, total and bone-specific alkaline phosphatase increased, whereas the urinary deoxypyridinoline-creatinine ratio did not change significantly, suggesting enhanced bone formation. Quality of life assessed at weeks 10 and 26 remained unchanged compared with baseline. Conclusions. In conclusion, continued treatment with cinacalcet is required to maintain long-term normocalcaemia and to suppress the enhanced PTH production in renal transplant recipients with persistent hyperparathyroidis

Chronic Norovirus Infection after Kidney Transplantation: Molecular Evidence for Immune-Driven Viral Evolution

Background. Norovirus infection is the most common cause of acute self-limiting gastroenteritis. Only 3 cases of chronic norovirus infection in adult solid organ transplant recipients have been reported thus far. Methods. This case series describes 9 consecutive kidney allograft recipients with chronic norovirus infection with persistent virus shedding and intermittent diarrhea for a duration of 97-898 days. The follow-up includes clinical course, type of immunosuppression, and polymerase chain reaction for norovirus. Detailed molecular analyses of virus isolates from stool specimens over time were performed. Results. The intensity of immunosuppression correlated with the diarrheal symptoms but not with viral shedding. Molecular analysis of virus strains from each patient revealed infection with different variants of GII.4 strains in 7 of 9 patients. Another 2 patients were infected with either the GII.7 or GII.17 strain. No molecular evidence for nosocomial transmission in our outpatient clinic was found. Capsid sequence alignments from follow-up specimens of 4 patients showed accumulation of mutations over time, resulting in amino acid changes predominantly in the P2 and P1-2 region. Up to 25 amino acids mutations were accumulated over a 683-day period in the patient with an 898-day shedding history. Conclusion. Norovirus infection may persist in adult renal allograft recipients with or without clinical symptoms. No evidence for nosocomial transmission in adult renal allograft recipients was found in our study. Molecular analysis suggests continuous viral evolution in immunocompromised patients who are unable to clear this infectio

Inhibition of mTOR with sirolimus slows disease progression in Han:SPRD rats with autosomal dominant polycystic kidney disease (ADPKD)

Background. Autosomal dominant polycystic kidney disease (ADPKD) is characterized by dysregulated tubular epithelial cell growth, resulting in the formation of multiple renal cysts and progressive renal failure. To date, there is no effective treatment for ADPKD. The mammalian target of rapamycin (mTOR) is an atypical protein kinase and a central controller of cell growth and proliferation. We examined the effect of the mTOR inhibitor sirolimus (rapamycin) on renal functional loss and cyst progression in the Han:SPRD rat model of ADPKD. Methods. Five-week-old male heterozygous cystic (Cy/+) and wild-type normal (+/+) rats were administered sirolimus (2 mg/kg/day) orally through the drinking water for 3 months. The renal function was monitored throughout the treatment phase, and rats were sacrificed thereafter. Kidneys were analysed histomorphometrically, and for the expression and phosphorylation of S6K, a well-characterized target of mTOR in the regulation of cell growth. Results. The steady increase in BUN and creatinine in Cy/+ rats was reduced by 39 and 34%, respectively with sirolimus after 3 months treatment. Kidney weight and 2-kidney/total body weight (2K/TBW) ratios were reduced by 34 and 26% in sirolimus-treated Cy/+ rats. Cyst volume density was also reduced by 18%. Of importance, Cy/+ rats displayed enhanced levels of total and phosphorylated S6K. Sirolimus effectively reduced total and phosphorylated levels of S6K. Conclusion. 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 ADPK