Differential effects of mesenchymal stem cells on a heterogeneous cell population within lung cancer cell lines

Although mesenchymal stem cells (MSCs) promote lung cancer growth in vivo, in vitro studies indicate that they inhibit the proliferation of lung cancer cells. Because malignant tumors contain a heterogeneous cell population with variable capacity for self-renewal, the aim of this study was to determine whether the inconsistencies between in vitro and in vivo studies are a result of differential effects of MSCs on the heterogeneous cell population within lung cancer cell lines. Human MSCs were isolated from the bone marrow, and their cell surface antigen expression and multi-lineage differentiation capacity was examined at passage 10. CD133+ cells were isolated from A549 and H446 cell lines using immunomagnetic separation. The effects of MSCs on the growth and microsphere formation of heterogeneous cell populations within two lung cancer cell lines (A549 and H446) were compared. MSCs inhibited the in vitro proliferation of both cell lines, but significantly accelerated tumor formation and stimulated tumor growth in vivo (P < 0.05). In CD133+ cells isolated from both A549 and H446 cells, co-culture with MSCs for 1–3 days significantly increased their proliferation (P < 0.05). MSCs also significantly increased microsphere formation in both cell lines (P < 0.05). Selective stimulation of CD133+ cell growth may account for the discrepant effects of MSCs on lung cancer progression.