Increased RARα2 expression induces stem cell characteristics in MM. (A) Western blots showed ALDH protein levels in OCI-MY5 and ARP1 cells transfected with either RARα2 or empty vector. (B) ALDH activity was evaluated in RARα2 overexpressing cells OCI-MY5 and ARP1 by flow cytometry analysis. (C) SP fractions of OCI-MY5 and ARP1 cells were examined by flow cytometry and the results show the percentages of SP in RARα2 overexpressing cells (1.09% in OCI-MY5 and 0.71% in ARP1) and EV control cells (0.31% in OCI-MY5 and 0.35% in ARP1).