title: Persistence of residual tumour cells after cytokine-mediated ex vivo expansion of mobilized CD34+ blood cells in multiple myeloma.
abstract: Mobilized CD34+ blood cells were immunomagnetically enriched from leukapheresis products in five multiple myeloma (MM) patients. Thawed samples of selected CD34+ cells were cultured for up to 21 d in a liquid and stroma-free culture system with different combinations of recombinant cytokines. The most successful cell expansion was obtained when a combination of rh-IL-1beta, rh-IL-3, rh-IL-6, rh-SCF, rh-G-CSF and rh-GM-CSF was used. After 14 d this mixture gave a 120-187-fold overall increase of total nuclear cells and a 4-8-fold overall increase of early CFU-GM numbers. In four patients a very sensitive patient-specific PCR analysis showed the presence of monoclonal cells in the initial leukapheresis products. After immunomagnetic separation a tumour cell depletion of 2-4 logs was observed, although all samples still contained malignant cells. Cell suspensions that were cultured with the most potent cytokine combination showed tumour contamination in two-thirds of evaluable cases at the moment of maximal CFU-GM output. Serial cDNA dilution experiments indicated that the positive PCR results at day 14 reflected the persistence of pre-culture tumour cells rather than in vitro expansion of tumour cells in two cases. This study demonstrates that ex vivo expansion of myeloid precursor cells from mobilized CD34+ cells in MM patients does not always result in an effective purging of residual tumour cells. On the other hand, our culture conditions do not seem to favour in vitro expansion of malignant cells, despite the use of a cytokine cocktail that includes potential myeloma growth factors.
authors.affiliation: Department of Haematology and Immunology, Free University Brussels (VUB), Belgium.
authors.forename: I
authors.initials: I
authors.lastname: Van Riet
authors.forename: N
authors.initials: N
authors.lastname: Juge-Morineau
authors.forename: R
authors.initials: R
authors.lastname: Schots
authors.forename: M
authors.initials: M
authors.lastname: De Waele
authors.forename: C
authors.initials: C
authors.lastname: De Greef
authors.forename: K
authors.initials: K
authors.lastname: Thielemans
authors.forename: B
authors.initials: B
authors.lastname: Van Camp
authors.forename: M
authors.initials: M
authors.lastname: Bakkus
mesh_terms: D000328:Adult; D018952:Antigens, CD34; D001773:Blood Cells / Q000502:physiology*; D016207:Cytokines / Q000494:pharmacology*; D005260:Female; D006412:Hematopoietic Stem Cells / Q000502:physiology; D006801:Humans; D007937:Leukapheresis; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000097:blood*; D018365:Neoplasm, Residual / Q000473:pathology
chemical_list: D018952:Antigens, CD34; D016207:Cytokines