The hTERT-immortalized foreskin fibroblast cell line, BJ-5ta, was derived by transfecting the BJ foreskin fibroblast cell line with the pGRN145 hTERT-expressing plasmid (ATCC MBA-141) at population doubling 58. Cells were cultured in medium containing hygromycin B until stable clones were selected [Pubmed: 9454332]. The cells are capable of at least 10 population doublings post-cryopreservation recovery. As part of our quality control, we test these cells for their ability to grow for a minimum of 10 population doublings after recovery from cryopreservation. We also compare their karyotype, telomerase expression levels, growth rate, morphology, and tissue-specific markers when first recovered from cryopreservation with that of cells at a minimum of 10 population doublings to ensure that there is no change in these parameters and that the cells are capable of extended proliferation.