Abstract:
So far there is no exact identification of hematopietic stem cells. The aim of these studies has been to compare phenotypically characterized, potentially early progenitor cells by in vitro assays.
After establishing and proofing the reliability of the CAFC-assay, regarded as the assay demonstrating the earliest in vitro detectable stem cells we compared CD34pos and AC133pos cells without and after ex-vivo expansion for 4 and 7 days. In addition we used the CFU-assay detecting more differentiated, committed progenitor cells.
In this work we demonstrated that AC133 characterized cells are less differentiated than the heterogenous population of CD34pos cells. The ex vivo expansion of both populations in media supplemented by SCF, Flt-3-ligand and TPO had no effect on the frequency of the CAFC.
In another series we tried to cultivate CD34negCD164 neg and CD34negCD164pos cells in the CAFC- and CFU-Assay. This was not possible, confirming and supplementing previously published data. At the same time transplantations of these cell populations by E.Zanjani showed an engraftment of CD34negCD164pos cells in the fetal-sheep-model.
In conclusion, in vitro-methods are not adequate for less differentiated cells than CD34pos cells. For further investigations one should use in vivo assays as the fetal sheep model or NOD/SCID mice.