Evaluation of PDGFRB, FLT3, CSK, and EGFR mutations in IL-3 independence assay. Ba/F3 cells were transfected with constructs expressing mutant PDGFRB/FLT3 (A) or CSK/EGFR (B). Following 4 weeks of neomycin selection, stably transfected cells plated in media in the absence of exogenous cytokines. The number of viable cells was assessed by trypan blue exclusion. As a positive control, Ba/F3 cells expressing the constitutively active FLT3-D835Y allele were plated in the absence of IL-3 in panel A to demonstrate IL-3–independent growth. Values represent mean plus or minus SEM.