Antisense oligonucleotide-mediated abrogation of HPK1 expression in FD-EPO cells and SKT6 cells leads to reduced Epo-dependent proliferation and inhibition of erythroid differentiation. Various concentrations (0 to 30 μmol/L) of HPK1 antisense S-oligonucleotides (○), HPK1 sense S-oligonucleotides (□), or scrambled S-oligonucleotides (•) were mixed with FD-EPO cells (A) or with SKT6 cells (B) in the presence of Epo. Cellular proliferation was measured using a MTT assay. The hemoglobinized cells were stained with DAF, and the percentage of hemoglobinized cells without oligonucleotides is shown as 100%. Values shown are the means of six experiments.