Fractionation Of Chronic Myelogenous Leukemia Marrow-Cells By Stroma Adherence - Implications For Marrow Purging

Chronic myelogenous leukemia (CML) progenitor cells have been shown to be defective in their ability to adhere to marrow stroma. It was the aim of the present study to investigate at the cytogenetic level marrow-derived CML clonogenic cells fractionated on the basis of their ability to adhere to preformed, allogeneic, normal marrow-derived stromal layers. Mononuclear marrow cells from CML patients (n = 15) were incubated with mafosfamide (100 mug/ml) or control medium, seeded onto marrow stromal layers and allowed to adhere (3 hrs, 37-degrees-C). Following a short-term liquid culture, the different cell fractions were harvested and incorporated in methylcellulose cultures. CFU-GM grown from these cultures were analyzed by single colony karyotyping. On direct cytogenetic analysis, the overall mean (+/- SD) percentage of Ph-negative metaphases was 7 +/- 20%. Following stroma adherence and short-term suspension culture, the mean (+/- SD) percentages of Ph-negative clones were as follows: 33 +/- 25% for adherent CFU-GM, 59 +/- 40% for adherent, mafosfamide-treated CFU-GM, 12 +/- 16% for non-adherent CFU-GM, and 32 +/- 26% for non-adherent-mafosfamide-treated CFU-GM. If only the patients showing a percentage of Ph-negative clones greater-than-or-equal-to 20% were included in this analysis, the mean (+/- SD) percentages of Ph-negative clones were 47 +/- 19% for adherent CFU-GM, and 81 +/- 21% for adherent-Mafosfamide-treated CFU-GM. In contrast, the majority of Ph-positive CFU-GM were detected within the stroma non-adherent cell fraction. In conclusion, our data demonstrate that: (1) Ph-positive CML progenitor cells have a reduced binding capacity to normal marrow stroma; (2) mafosfamide has a selective effect on the Ph-positive clones and seems to spare Ph-negative clones with maintained stroma adherence activity; (3) these findings might represent a new purging approach for autologous marrow transplantation.