T-LYMPHOCYTE DIFFERENTIATION INVITRO FROM ADULT HUMAN PRETHYMIC CD34-MARROW CELLS( BONE)

Pluripotent lymphohematopoietic stem cells are probably confined to bo ne marrow cells expressing CD34 surface molecules. To investigate the capacity of adult human CD34+ bone marrow cells to diffentiate along t he T lymphoid lineage, we plated purified CD34+ cells from healthy adu lts in liquid culture on adherent thymic stromal cells prepared from H LA- or blood group-mismatched postnatal thymic tissue. We show that pu rified CD34+ CD3-CD4-CD8-bone marrow cells contained progenitors with the ability to differentiate into CD4 + and CD8 + T lymphocytes expres sing surface (s)CD3 and T cell receptor alpha/beta in vitro. These pro genitors were found in the CD34+CD2+sCD3-CD4-CD8-, CD34+CD7+sCD3-CD4-C D8-, and CD34+CD2+CD7+sCD3-CD4-CD8-, as well as in the CD34+CD2-sCD3-C D4-CD8-, CD34+CD7-sCD3-CD4-CD8-, and CD34+CD2-CD7-sCD3-CD4-CD8- subset s, indicating that T lymphocyte progenitors sensitive to signals media ted by thymic stroma in vitro are not restricted to CD34+ cells alread y coexpressing early T lymphocyte-associated markers. Finally, we show that T lymphopoiesis was enhanced by c-kit ligand.