Lonza’s Renal Proximal Tubule Epithelial Cells (RPTEC) are isolated from the cortex of the kidney. A characteristic of kidney cortex epithelial isolation results in a population consisting of approximately 50%- 70% RPTEC. Lonza uses a proprietary enrichment process to further purify the RPTEC population. Lonza guarantees that all lots of RPTEC cells will test positive for Gamma-glutamyl transpeptidase (gamma-GTP) further confirming the cell type.