Both CD133+ and CD133- subpopulations of A549 and H446 cells contain cancer-initiating cells.

Tumors have been known to contain a small population of cancer stem cells that initiate tumor growth and promote tumor spreading. CD133 alone or in combination with other markers is currently being used for identification and isolation of the putative cancer stem cell population from malignant tumors. To determine whether the CD133+ cells constitute the stem cell populations of lung cancer cells A549 and H446, CD133+ and CD133- subpopulations were sorted from A549 and H446 cells by magnetic cell separation and characterized for their in vitro stem cell-like properties. Interestingly, both the CD133+ and CD133- cells displayed similar abilities of colony formation, self-renewal, proliferation, differentiation, and invasion, as well as resistance to chemotherapy drugs. Furthermore, colony formation assays showed that more than 40% of cells in both the CD133+ cells and CD133- subpopulations could form large colonies capable of regenerating the unsorted populations and forming tumors in nude mice. These results suggest that CD133 alone cannot be used as a stem cell marker for the lung cancer cells A549 and H446, and both the CD133+ and CD133- subpopulations contain similar numbers of cancer stem cells.