BACKGROUND:
During ex vivo expansion of cord blood (CB) CD34+ cells, differentiation of the expanded cells happened and hematopoietic potential of the progenitor cells decreased. In this study, we evaluate the effect of the expression of Fas antigen, Bcl-2, and Bax on CD34+ or AC133+ hematopoietic progenitor cells during ex vivo expansion.
METHODS : CD34+ and AC133+ cells isolated from human CB were cultured in serum free medium supplemented with several cytokines for 7 days. After expansion culture, we re isolated CD34+ and AC133+ cells and compared the numbers of granulocyte-macrophage colony- forming units (CFU-GM) and granulocyte, erythrocyte, monocyte, and macrophage colony-forming units (CFU-GEMM), and expression of Fas antigen, Bcl-2, and Bax with unexpanded cells.
RESULTS : CFU-GM was expanded 23.94 fold in CD34+ cells and 15.22 fold in AC133+ cells at day 7 of culture but CFU-GEMM was not expanded. The expression of Fas antigen and Bax was 7.44% and 2.75%, respectively, in fresh isolated CD34+ cells and increased to 19.71 % and 33.67%, respectively, in expanded CD34+ cells at day 7 culture, but Bcl-2 was not changed. In case of AC133+ cells, the expression of Fas antigen and Bax were also increased from 5.87% and 6.19% to 24.85% and 22.83%, respectively, and Bcl-2 was slightly decreased. Apoptosis was not changed in CD34+ cells and AC133+ cells during ex vivo expansion.
CONCLUSION :
These results indicate that the nature of expansion was similar between CD34+ and AC133+ cells, and expression of Fas antigen and Bax increased on CD34+ and AC133+ cells during ex vivo expansion. Selection of the expanded progenitor cells without apoptosis may be useful for the hematopoietic stem cell transplantation.

Keywords: Apoptosis, Fas antigen, Bax, ex vivo expansion, Hematopoietic progenitor cells