Material and Methods: The alkaline comet assay was used to evaluate the DNA damage index induced in human leukocytes after incubation for 6 hours at 37:C with PA (2-5 mM) and MMA (0.5-5 mM) Background: Chronic tubulointerstitial nephritis is a frequent finding in patients with isolated methylmalonic aciduria. Among them, patients with mut0 and CblB disease have the highest risk of developing kidney disease. The underlying renal pathology has yet not been elucidated. Therefore, we aimed to establish an in vitro model for the human disease. Methods: We prepared cells from urine of healthy donors and patients with mut0, mut-, CblA, and CblB disease and purified proximal tubule epithelial cells (hPTEC). For long-term cultivation we used a method to immortalize these primary cells with pRSVneo vector containing SV40 (pRNS1) using electroporation. Afterwards, hPTEC were characterized regarding morphology and marker protein expression.