Finite lifespans of T cell clones derived from CD34+ human haematopoietic stem cells in vitro

Several studies have documented finite lifespans of at least the vast majority of cultured human T cell lines and clones. However, there is a great deal of variation among the different preparations, ranging from < 25 PD up to > 100 PD. The cultured T cells in all these studies originated from mature T cells isolated from peripheral blood of adult donors. It was, therefore, impossible to assess the contribution of differences in in vivo age to the subsequent differences between clones in in vitro aging. In an attempt to circumvent this difficulty, we have developed a culture system that supports the differentiation of highly purified human CD34+ cells into CD3+ T cells in vitro. This features the use of a serum-free medium supplemented with the cytokines flt-3 ligand, IL 3, stem cell factor (c-kit ligand) and IL 2, together with IL 7 or oncostatin M (OM). In this way it is possible to perform "longitudinal" studies on T cells derived de novo in vitro. We show here that T cell clones derived under these circumstances also manifest variable finite life expectancies, for which the only uncontrolled (nonstochastic) effects of aging must already have occurred at the stem cell level.