Extrathymic T cell differentiation in vitro from human CD34 + stem cells

Although it is well established that T cells are derived from CD34 + stem cells in vivo , and that T cells can develop in the absence of a functioning thymus, it has not proven possible thus far to generate human T cells in vitro from CD34 + cells in the absence of any thymic influence. We now present a limiting dilution cloning culture system that supports the differentiation of highly purified human CD34 + cells to CD3 + T cells in vitro in the complete absence of any thymic components. The culture system features the use of a serum‐free medium supplemented with a cocktail of cytokines including flt‐3 ligand, interleukin‐3 (IL‐3), stem cell factor (SCF), and IL‐2. CD4 + T cell clones capable of mitogen‐stimulated proliferation and response to IL‐2, and expressing a varied TCR‐Vβ repertoire were obtained under these conditions. This culture system therefore supports human T lymphopoiesis in the absence of any thymic influence and may prove useful for the evaluation of extrathymic T cell differentiation in vitro. J. Leukoc. Biol. 64: 733–739; 1998.