Mammalian Target of Rapamycin Inhibitors and Kidney Function After Thoracic Transplantation: A Systematic Review and Recommendations for Management of Lung Transplant Recipients

mTOR inhibitors after lung transplantation: a real-life experience

Background

The mammalian target of rapamycin (mTOR) inhibitors in combination with calcineurin inhibitors (CNIs), antimetabolites and corticosteroids for immunosuppression after lung transplantation (TPL) have gained importance in patients with chronic kidney disease (CKD). The goal of this study was to characterize lung transplant recipients (LTR) treated with mTOR inhibitors, with a special focus on kidney function.

Methods

LTR transplanted at the University Hospital Zurich between December 1992 and April 2022 were analyzed. Demographics, estimated glomerular filtration rate (eGFR) before and after mTOR initiation, TPL circumstances, immunosuppressive regimens, and allograft function were recorded. We used linear regression to calculate the Mitch curves and a linear mixed-effects model to compare the eGFR.

Results

Of all LTR, 70/593 (12%) received mTOR inhibitors. Intolerance or adverse events of antimetabolites were the most common indications for mTOR inhibitor introduction. Discontinuation in 34/70 (49%) was often related to planned or urgent surgery to prevent impaired wound healing. The majority of patients had a preserved baseline eGFR at mTOR inhibitor introduction with CKD Kidney Disease Improving Global Outcomes (KDIGO) stage G1 or 2. The mean annual eGFR decline changed significantly from -16.19 mL/min/1.73 m2/year [95% confidence interval (CI): -22.27 to -10.11] 12 months before to -6.16 mL/min/1.73 m2/year (95% CI: -13.37 to 1.05) 12 months after mTOR initiation (P=0.009) showing better outcomes with earlier mTOR inhibitor initiation after lung TPL.

Conclusions

This retrospective study suggests stabilization of kidney function after mTOR inhibitor initiation in LTR documented by a slower eGFR decline after mTOR inhibitor introduction with better outcomes early after lung TPL. Intolerance or adverse events of antimetabolites are important indications for the introduction of mTOR inhibitors. A relatively high discontinuation rate (49%) can be explained by planned discontinuation of mTOR inhibitors prior to surgery to avoid impaired wound healing.

Everolimus Treatment for Chronic Lung Allograft Dysfunction in Lung Transplantation

Our study aims to evaluate the effect of everolimus treatment on lung function in lung transplant (LT) patients with established chronic lung allograft dysfunction (CLAD).

METHODS

This retrospective study included LT patients in two reference LT units who started everolimus therapy to treat CLAD from October 2008 to October 2016. We assessed the variation in the maximum forced expiratory volume in the first second (FEV1) before and after the treatment.

RESULTS

Fifty-seven patients were included in this study. The variation in the FEV1 was -102.7 (149.6) mL/month before starting everolimus compared to -44.7 (109.6) mL/month within the first three months, +1.4 (63.5) mL/month until the sixth month, and -7.4 (46.2) mL/month until the twelfth month (p < 0.05). Glomerular filtrate remained unchanged after everolimus treatment [59.1 (17.5) mL/min per 1.73 m2 at baseline and 60.9 (19.6) mL/min per 1.73 m2, 57.7 (20.5) mL/min per 1.73 m2, and 57.3 (17.8) mL/min per 1.73 m2, at 1, 3, and 6 months, respectively] (p > 0.05). Everolimus was withdrawn in 22 (38.6%) patients. The median time to withdrawal was 14.1 (5.5-25.1) months.

CONCLUSIONS

This study showed an improvement in FEV1 decline in patients with CLAD treated with everolimus. However, the drug was withdrawn in a high proportion of patients.

Tumorigenic role of tacrolimus through mTORC1/C2 activation in post-transplant renal cell carcinomas

BACKGROUND

Kidney transplant recipients (KTRs) face an increased risk of renal cell carcinoma (RCC), in which the immunosuppressive regimen plays an important role. This study aimed to identify intracellular signalling alterations associated with post-transplant (post-tx) tumour formation.

METHODS

Expression of mTOR-related proteins were analysed in kidneys obtained from end-stage renal disease (ESRD) patients and RCCs developed in KTRs or non-transplant patients. The effects of tacrolimus (TAC) and rapamycin (RAPA) on mTOR activity, proliferation, and tumour growth were investigated through different in vitro and in vivo experiments.

RESULTS

Elevated mTORC1/C2 activity was observed in post-tx RCCs and in kidneys of TAC-treated ESRD patients. In vitro experiments demonstrated that TAC increases mTOR activity in a normal tubular epithelial cell line and in the investigated RCC cell lines, moreover, promotes the proliferation of some RCC cell line. In vivo, TAC elevated mTORC1/C2 activity in ischaemic kidneys of mice and enhanced tumour growth in xenograft model.

CONCLUSIONS

We observed significantly increased mTOR activity in ischaemic kidneys and post-tx RCCs, which highlights involvement of mTOR pathway both in the healing or fibrotic processes of kidney and in tumorigenesis. TAC-treatment further augmented the already elevated mTOR activity of injured kidney, potentially contributing to tumorigenesis during immunosuppression.

Sirolimus Long-Term Tolerability and Impact on Kidney Function in Lung Transplantation: A Single-Center Experience

BACKGROUND

After lung transplant, 2 common complications are calcineurin inhibitor (CNI) induced nephrotoxicity and bronchiolitis obliterans syndrome. The objective of this study was to investigate the long-term effects of sirolimus conversion after lung transplantation.

METHODS

This was a retrospective cohort study of patients who had undergone lung transplantation at a single center from June 2003 to December 2016. We compared patients converted to a sirolimus-based regimen to those maintained on our standard tacrolimus-based regimen. Kidney function, pulmonary function, and immunosuppression concentrations were compared between the groups. Additionally, indications, toxicity monitoring parameters, and discontinuation rates for sirolimus were collected.

RESULTS

During the study period, 176 of the 205 patients who underwent lung transplants were converted to a sirolimus-containing regimen (86%). The most common reason for sirolimus initiation was impairment of kidney function or CNI-associated neurotoxicity. Sirolimus was initiated at a median of 150 days post-transplantation and continued for a medium time of 5.02 (2.27-7.85) years. Of those patients converted to sirolimus, 39 (22%) had sirolimus subsequently discontinued secondary to an adverse event. No difference in pulmonary function was found between the groups at 1- and 3-years post-transplantation. In the sirolimus group, the median estimated glomerular filtration rate improved by 8.6 mL/min/1.73 m2 at 3 months post-conversion (P < .001), which was maintained at both 1 and 3 years (P = .014 and .025, respectively).

CONCLUSION

Sirolimus is a viable immunosuppressant option after lung transplant, which successfully allows for the reduction or withdrawal of the CNI, resulting in sustained improvement in kidney function.

Chitosan nanoparticles encapsulated with BEZ235 prevent acute rejection in mouse heart transplantation

Acute rejection may manifest following heart transplantation, despite the implementation of relatively well-established immunosuppression protocols. The significance of the mTOR signaling pathway in rejection is widely acknowledged. BEZ235, a second-generation mTOR inhibitor with dual inhibitory effects on PI3K and mTOR, holds promise for clinical applications. This study developed a nanodelivery system, BEZ235@NP, to facilitate the intracellular delivery of BEZ235, which enhances efficacy and reduces adverse effects by improving the poor solubility of BEZ235. In the complete MHCII-mismatched model, BEZ235@NP significantly prolonged cardiac allografts survival compared to free BEZ235, which was attributed to more effective suppression of effector T cell activation and promotion of greater expansion of Tregs. These nanoparticles demonstrated excellent biosafety and exhibited no short-term biotoxicity upon investigation. To elucidate the mechanism, primary T cells were isolated from the spleen and it was observed that BEZ235@NP treatment resulted in the arrest of these cells in the G0/G1 phase. As indicated by Western blot analysis, BEZ235@NP substantially reduced mTOR phosphorylation. This, in turn, suppressed downstream pathways and ultimately exerted an anti-proliferative and anti-activating effect on cells. Furthermore, it was observed that inhibition of the mTOR pathway stimulated T-cell autophagy. In conclusion, the strategy of intracellular delivery of BEZ235 presents promising applications for the treatment of acute rejection.

Rapamycin Treatment Alleviates Chronic GVHD-Induced Lupus Nephritis in Mice by Recovering IL-2 Production and Regulatory T Cells While Inhibiting Effector T Cells Activation

In this study, we test the therapeutic effects of rapamycin in a murine model of SLE-like experimental lupus nephritis induced by chronic graft-versus-host disease (cGVHD). Our results suggest that rapamycin treatment reduced autoantibody production, inhibited T lymphocyte and subsequent B cell activation, and reduced inflammatory cytokine and chemokine production, thereby protecting renal function and alleviating histological lupus nephritis by reducing the occurrence of albuminuria. To explore the potential mechanism of rapamycin's reduction of kidney damage in mice with lupus nephritis, a series of functional assays were conducted. As expected, rapamycin remarkably inhibited the lymphocytes' proliferation within the morbid mice. Interestingly, significantly increased proportions of peripheral CD4+FOXP3+ and CD4+CD25high T cells were observed in rapamycin-treated group animals, suggesting an up-regulation of regulatory T cells (Tregs) in the periphery by rapamycin treatment. Furthermore, consistent with the results regarding changes in mRNA abundance in kidney by real-time PCR analysis, intracellular cytokine staining demonstrated that rapamycin treatment remarkably diminished the secretion of Th1 and Th2 cytokines, including IFN-γ, IL-4 and IL-10, in splenocytes of the morbid mice. However, the production of IL-2 from splenocytes in rapamycin-treated mice was significantly higher than in the cells from control group animals. These findings suggest that rapamycin treatment might alleviate systemic lupus erythematosus (SLE)-like experimental lupus nephritis through the recovery of IL-2 production, which promotes the expansion of regulatory T cells while inhibiting effector T cell activation. Our studies demonstrated that, unlike other commonly used immunosuppressants, rapamycin does not appear to interfere with tolerance induction but permits the expansion and suppressive function of Tregs in vivo.

Adaptive Immunosuppression in Lung Transplant Recipients Applying Complementary Biomarkers: The Zurich Protocol

Achieving adequate immunosuppression for lung transplant recipients in the first year after lung transplantation is a key challenge. Prophylaxis of allograft rejection must be balanced with the adverse events associated with immunosuppressive drugs, for example infection, renal failure, and diabetes. A triple immunosuppressive combination is standard, including a steroid, a calcineurin inhibitor, and an antiproliferative compound beginning with the highest levels of immunosuppression and a subsequent tapering of the dose, usually guided by therapeutic drug monitoring and considering clinical results, bronchoscopy sampling results, and additional biomarkers such as serum viral replication or donor-specific antibodies. Balancing the net immunosuppression level required to prevent rejection without overly increasing the risk of infection and other complications during the tapering phase is not well standardized and requires repeated assessments for dose-adjustments. In our adaptive immunosuppression approach, we additionally consider results from the white blood cell counts, in particular lymphocytes and eosinophils, as biomarkers for monitoring the level of immunosuppression and additionally use them as therapeutic targets to fine-tune the immunosuppressive strategy over time. The concept and its rationale are outlined, and areas of future research mentioned.