Effect of HB-EGF on MSC expansion. Enhancement of MSC proliferation was induced by HB-EGF in a dose-dependent fashion with concentrations between 5 to 50 ng/mL, starting from both 5 × 10³ (A) and 10⁴ (B) cells. MSC expansion with 5 ng/mL (▦), 25 ng/mL (▪), and 50 ng/mL (□) HB-EGF was assessed by MTT method at 72 hours and expressed as additional proliferation (the percentage of increase of MSC proliferation following HB-EGF addition [P1] compared with the spontaneous MSC proliferation that normally occurs without HB-EGF [P2]). In other words, (P1–P2)/P2 × 100. P < .01 refers to the difference between the spontaneous expansion without HB-EGF and the additional proliferation with 5, 25, and 50 ng/mL HB-EGF. The figure shows means ± SD of 5 different experiments.