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Ex Vivo Expansion Does Not Alter the Capacity of Umbilical Cord Blood CD34+ Cells to Generate Functional T Lymphocytes and Dendritic Cells

We examined whether ex vivo expansion of umbilical cord blood progenitor cells affected their capacity to generate immune cells such as T lymphocytes (TLs) and dendritic cells (DCs). The capacity to generate TLs from cord blood CD34+ cells expanded for 14 days (d14) was compared with that of nonexpanded CD34+ cells (d0) using fetal thymus organ cultures or transfer into nonobese diabetic/severe combined immunodeficient mice. The cell preparations yielded comparable percentages of immature (CD4+CD8−, CD4+CD8+) TLs and functional mature (CD3+CD4+, CD3+CD8+) TLs with an analogous TCR (T‐cell receptor)‐Vβ repertoire pattern. As regards DCs, d0 and d14 CD34+ cells also yielded similar percentages of CD1a+ DCs with the same expression levels of HLA‐DR, costimulatory and adhesion molecules, and chemokine receptors. DCs derived from either d14 or d0 CD34+ stimulated allogeneic TLs to the same extent, and the cytokine pattern production of these allogeneic TLs was similar with no shift toward a predominant Th1 or Th2 response. Even though the intrinsic capacity of d14 CD34+ cells to generate DCs was 13‐fold lower than that of d0 CD34+ cells, this reduction was offset by the prior amplification of the CD34+ cells, resulting in the overall production of 15‐fold more DCs. These data indicate that ex vivo expansion of CD34+ cells does not impair T lymphopoiesis nor DC differentiation capacity.