Technical Advance: Ascorbic acid induces development of double‐positive T cells from human hematopoietic stem cells in the absence of stromal cells

In vitro human T cell development from hematopoietic stem cells in the presence and absence of feeder cells is promoted by ascorbic acid. The efficacy of donor HSCT is partly reduced as a result of slow post‐transplantation immune recovery. In particular, T cell regeneration is generally delayed, resulting in high infection‐related mortality in the first years post‐transplantation. Adoptive transfer of in vitro‐generated human T cell progenitors seems a promising approach to accelerate T cell recovery in immunocompromised patients. AA may enhance T cell proliferation and differentiation in a controlled, feeder‐free environment containing Notch ligands and defined growth factors. Our experiments show a pivotal role for AA during human in vitro T cell development. The blocking of NOS diminished this effect, indicating a role for the citrulline/NO cycle. AA promotes the transition of proT1 to proT2 cells and of preT to DP T cells. Furthermore, the addition of AA to feeder cocultures resulted in development of DP and SP T cells, whereas without AA, a preT cell‐stage arrest occurred. We conclude that neither DLL4‐expressing feeder cells nor feeder cell conditioned media are required for generating DP T cells from CB and G‐CSF‐mobilized HSCs and that generation and proliferation of proT and DP T cells are greatly improved by AA. This technology could potentially be used to generate T cell progenitors for adoptive therapy.