K562-MSCs promote K562 cells to proliferate partially via the enhanced secretion of TGF-β1. With PBS, NMSCs and NMSC supernatant as controls, the abilities of K562-MSCs and K562-MSC supernatant to support the proliferation of K562 cells were examined using a CCK-8 kit. (A) NMSCs showed no significant different effects with PBS on the proliferation of K562 cells (nsP>0.05, n=4), whereas K562-MSCs enhanced the proliferation of K562 cells compared with NMSCs and PBS (**P<0.01, n=4). The K562-MSC supernatant significantly promoted the proliferation of K562 cells compared with the NMSC supernatant. (B) Ly364947, a TGF-β1 inhibitor, was used to examine whether K562-MSCs induced the proliferation of K562 cells in a TGF-β1-dependent manner. PBS and TGF-β1 served as negative and positive controls, respectively, and Ly364947 could efficiently inhibit the K562-MSC-induced proliferation of K562 cells via the supernatant (**P<0.01, n=3).