Cells will undergo genotypic changes resulting in reduced responsiveness over time in normal cell-culture conditions. Genetic instability is a biological phenomenon that occurs in all stably transfected cells. Therefore, it is critical to prepare an adequate number of frozen stocks at early passages.
Transcription factors of the NFAT (nuclear factor of activated T cells) family are expressed in most immune system cells and in a range of other cell types. NFAT plays the immunomodulatory role, primarily in T-cell activation and differentiation. In addition, NFAT target genes are involved in the regulation of apoptosis and differentiation in nonimmune cell types. A key aspect of the regulated transcription response to immune stimuli is the Ca2+/calmodulin-dependent signal cascade which leads to the activation of the NFAT and induction of its target genes. This NFAT signaling pathway is the target of the immunosuppressive drugs cyclosporin A and FK506, which act at the level of calcineurin activation. The pathway can be interfered by a number of viruses, including human immunodeficiency virus, hepatitis C virus, and African swine fever virus (ASFV).