Human primary fibroblasts (IMR90, ATCC #CCL-186) • Doubling time: +/- 30-40hrs (at 3% O2) • Medium: DMEM, high glucose, + glutamine, w/o pyruvate, Pen/Strep, 10% FBS (change media every three days). All primary human fibroblasts lose telomeric DNA with every doubling, and so will eventually senesce.