RB1 and retinoblastoma: To elaborate on this finding, ARF expression was compared between normal human fetal (FR) and adult retinal (HR) tissues, retinoblastoma cell lines with characterized, non-functional RB1 [11,12] (RB1-/-), and cell lines known for high ARF mRNA expression (HeLa, HEK-T, SaOS-2 and OVCAR-3) or low ARF mRNA (SKOV3).