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).
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.