The IC50 reported for PF956980 against JAK3 is ~4nM [24], however this compound has been reported to be effective against IL-4-induced cytotoxic resistance in chronic lymphocytic leukaemia cells at concentrations of ~0.3μM [34] in agreement with the potency of PF956980 in the present study. This evidence concerns the gene IL4 and B-cell chronic lymphocytic leukemia.