Quantification of progenitors capable of generating T cells in human cord blood

Objective: For transplantation of cord blood (CB) cells, it is important to select a CB sample that can reconstitute not only myelo-erythropoiesis but also lymphopoiesis in recipients. However, until now the reconstitution ability of CB samples has been assessed by colony forming unit-culture (CFU-C) assay or by simply counting CD34⁺ cells. The present study aims at establishing a method capable of assessing the potential of T lymphopoieses of CB samples. Methods: CD34⁺CD38^- cells sorted from CB were cultured on a monolayer of murine stromal cell line TSt-4, transduced with the human Delta-like 1 gene. Results: Immature T cells expressing CD5 and/or CD7 were generated in the culture. As these immature T cells can easily be discriminated from mature T cells that are included in the mononuclear cell population (MNCs), we can use the MNCs as starting material for quantification of progenitors capable of generating T cells (TGP). By applying a limiting dilution analysis, we succeeded in determining the frequency of TGP in MNCs. It was found that the ratios for the number of TGP vs. that of CFU-C differ among CB samples maximally by 3.5 times. Conclusion: The present assay system provides a novel tool for the evaluation of CB samples, especially for their T-cell-generating potential.