Journal of Hematology - Supplements - Haematologica

24
the degree of lineage commitment. In freshly
harvested CB we found that very few LTC-IC are
in the S-phase of the cell cycle; however, in contrast
to that which was observed in the bone
marrow, also very few CFC were found in the S-
phase of the cell cycle. A possible explanation is
that a different regulation exists for bone marrow
hematopoiesis and for CB hematopoiesis,
but the factors which could determine this difference
are presently unknown. Also, these
authors found that cultured CD34 + cells reentering
G0 have a shorter pre-replicating phase
than freshly isolated G0 CD34 + cells. This observation
could explain the high proportion (up to
90%, Figure 1) of LTC-IC and CFC entering the
S-phase when incubated in the presence of
cytokines for 36-48 hours.
In summary, our data show that very few CBderived
CFC and LTC-IC are in the S-phase of
the cell cycle. Furthermore, results on cell cycle
distribution and statin expression of CD34 +
cells, while confirming the low numbers of progenitor
cells in the S-phase of the cell cycle, clearly
indicate that a significant number of CD34 +
cells are in the G1 phase of the cell cycle. Our
results also provide new information on the
kinetics of recruitment into the S-phase of the
cell cycle of CB-derived CFC and LTC-IC, and on
culture conditions which can modify their
cycling status without reducing their numbers.
These findings could play an important role in
the engineering of CB-derived progenitor cells
for gene therapy and in the designing of clinically
relevant protocols for their ex vivo expansion.
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haematologica vol. 85(supplement to n. 11):November 2000