Inhibition of autonomous cell line growth by Jak2^V617F-shRNA. HEL, K562, UKE-1, and SET-2 cells were infected with the pRRL-mt4 or the control pRRL-Scr virus, selected for GFP expression, and grown in liquid culture in the absence or the presence of cytokines. Viable cells were counted every 2 or 3 days. Expression of the Jak2^V617F-shRNA from the pRRL-mt4 virus inhibited the proliferation of the JAK2^V617F-expressing HEL, UKE-1, and SET-2 cell lines, but had no effect on JAK2^WT-expressing K562 cell growth. Results from typical experiments are represented and expressed as mean numbers (± SEM). *P ≤ .05 using the Student t test. Analysis of variance of linear models from 3 independent experiments using duplicate or triplicate counts shows that the shRNA significantly decreased cell numbers in all cell lines (P ≤ 10⁶), except K562 (P = .7). IL-3 (30 ng/mL, UKE-1), GM-CSF (10 ng/mL, SET-2), and TPO (10 ng/mL, only for SET-2) significantly completely abolished the effect (n = 3). For TPO and UKE-1, the effect was only reduced.