The unique properties of mammalian cells make them valuable for a variety of applications in medicine, industry, and diagnostics. However, the utility of such cells is restricted due to the difficulty in storing them non-frozen for an extended time and still maintaining their stability and responsiveness. In order to extend the active life span of a mammalian biosensor cell line at room and refrigerated temperatures, we have over expressed genes that are reported to provide protection from apoptosis, stress, or oxidation. We demonstrated that over expression of genes from the extremophile, Artemia franciscana, as well as GADD45 beta, extends room-temperature storage of fully active cells 3.5-fold, while over production of several antiapoptotic proteins extended 4 C storage 2- to 3-fold. Methodologies like these that improve the stability of mammalian-cell-based technologies in the absence of freezers may enable widespread use of these tools in applications that have been considered impractical based solely on limited storage characteristics. Biotechnoi. Bioeng. 2010;106: 474-481. (C) 2010 Wiley Periodicals, Inc.