Expression of KITD814V in HSC/Ps results in ligand-independent growth and promiscuous proliferation in response to multiple cytokines. (A) Bone marrow LDMNCs were transduced with empty vector, WT KIT, or KITD814V. Top panel demonstrates the relative transduction efficiency from one of several experiments as determined by EGFP expression (x-axis). After 48 hours of culture, cells were pulsed with [³H] thymidine in the absence of growth factors for an additional 6 hours. Bars denote the mean thymidine incorporation (cpm ± SD) from 1 of at least 3 independent experiments performed in quadruplicate. *P < .05, KITD814V versus vector or WT KIT. (B) Lin⁻ LDMNCs were transduced with empty vector or KITD814V (top panel). EGFP-positive cells were subjected to thymidine incorporation in the absence of growth factors as described in panel A. Bars denote the mean thymidine incorporation (cpm ± SD) from 1 of at least 3 independent experiments performed in quadruplicate. *P < .05, KITD814V versus vector. Bone marrow LDMNCs were transduced with empty vector or KITD814V (C) or with WT KIT or KITD814V (D). EGFP-positive cells were subjected to thymidine incorporation in the presence of indicated cytokines: no growth factor (NO GF), SCF 50 ng/mL, M-CSF 50 ng/mL, G-CSF 20 ng/mL, or IL-3 5 ng/mL. After 48 hours of culture, cells were pulsed with [³H] thymidine for an additional 6 hours. Bars denote the mean thymidine incorporation (cpm ± SD) from one of several experiments performed in quadruplicate. *P < .05, KITD814V versus vector (C) or KITD814V versus WT KIT (D).