Apoptotic cells are generated at every division of in vitro cultured T cell lines.

Long- and short-term T cell lines form the backbone of many assays for T cell function and also represent important tools for use in human immunotherapy. Despite much study concerning the requirements for T cell activation and growth in culture there is relatively little information about the kinetics of proliferation and cell death in such cultures. Here we studied these parameters in a long-term CD8(+) T cell line using a tetrameric MHC reagent and the fluorescent dye CFSE. We observed proliferation of the T cells within 24 h of restimulation with antigen and IL-2 and the cells continued to divide once every 12 h on average. Interestingly, a proportion of cells entered apoptosis with each cell division, showing that a degree of programmed cell death occurred constantly in vitro, not merely at the end of the culture period when antigen or the necessary growth factors became limiting. This information should assist in the design of more efficient protocols for generating large numbers of specific T cells for clinical use.