A next step towards bioartificial kidney: preclinical safety evaluation

Currently available treatment options for patients affected by chronic kidney disease (CKD) comprise peritoneal dialysis, hemodialysis and kidney transplantation. However, as there is a significant shortage in organ donors for kidney transplantation and dialysis treatment does not offer complete removal of uremic toxins, novel treatment options are being developed. A promising solution is offered by the bioartificial kidney (BAK), which aims to replace the loss of kidney function observed in CKD, by combining a scaffold such as polymer hollow fiber membranes (HFM) and renal proximal tubule epithelial cells (PTEC), thus creating biofunctionalized kidney tubules that would help replacing excretory, endocrine, metabolic and regulatory functions of the kidney. One of the attractive options for the use in renal replacement therapies are the conditionally immortalized human PTEC (ciPTEC) equipped with a broad range of transporters involved in the removal of waste products. Despite the promising features of ciPTECs for BAK application, the safety issues such as immune response activation, tumorigenic potential and other undesired effects, should be carefully evaluated. The present thesis describes the preclinical safety evaluation of ciPTECs for BAK application. Chapter 2 represents a systematic review concerning the use of genetically modified cells in animal models of kidney disease for the purposes of cell therapy. Due to the high heterogeneity in study characteristics (animal species, disease model and cell therapy) and the fact that the majority of the studies were characterized by suboptimal or inappropriate study design, it was rather challenging to reveal a general overview on safety aspects. Furthermore, ciPTECs were shown to be able to activate vitamin D in 1α-hydroxylase-dependent manner, and that this reaction is not affected by uremic conditions typical of kidney patients. In addition, vitamin D can exert beneficial effects on ciPTECs in uremic conditions in terms of restoration of cell viability, improved inflammatory and oxidative status of the cells, and recovery of transepithelial barrier function (chapter 3). Next, ciPTECs were shown to express CD40 and HLA class I molecules with an increase after exposure to interferon-γ (IFN-γ) and bacterial lipopolysaccharide (LPS), while the expression of HLA class II molecules, and the costimulatory molecules CD80 and CD86 was very low or completely absent. Besides, ciPTECs were also shown to lack direct allostimulatory effects (immunogenicity) as they failed to induce activation and proliferation of human peripheral blood mononuclear cells (PBMCs) (chapter 4). Chapter 5 describes successful upscaling of BAK device with functional ciPTEC epithelial monolayers, transepithelial transport of indoxyl sulfate and polarized secretion of inflammatory mediators for safe future applications. Finally, chapter 6 shows that ciPTECs do not show cancer cell-like behavior and tumorigenicity in immunodeficient rats, considering the genetic modifications implemented for their creation, and thus appear to be rather safe option for future BAK applications. Taken together, the safety evaluation of ciPTECs, as presented in this thesis, offers a significant contribution to the preclinical development and evaluation of the BAK device and provides further advances in the field of innovative renal replacement therapies