Cells repopulated from tumor-derived clonogenic cells are sensitive to RT or RT+TMZ treatment; only a few slow-growing clonogenic cells can survive and regain their self-renewal capacity.

<p>A. Dissociated cells from GSC cultures derived from three patients' tumors as indicated were plated in culture dishes at clonal density of 900 cells/2 ml/60 mm dish. Cells were incubated for overnight and subjected to treatment as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080397#pone.0080397.s001" target="_blank">Figure S1</a>. Untreated cells (UT) or treated with TMZ alone (10 µM every 3 days) served as control. Colonies that contained at least 50 cells were counted on day 14 in all dishes (a-c) while small colonies that contained at least 6 cells were also counted in plates treated with RT and RT+TMZ (d). Data represent mean values ± SD of triplicate dishes. B. Light-microscopic morphology of clonogenic survivors after treatment. Few single cells survived treatment (a–c, j–l) (days 2–3) and slowly regained self-repopulating capacity (d–f, m–o) (days 14–21), (g–i, p–r) (days 25–30).