Pharmacologic inhibition of Jak3 results in reduced myeloid colony formation in normal mouse BM cells stimulated with either GM-CSF alone or the combination of SCF, IL-3, and IL-6. Normal BM cells were obtained from wild-type (C57BL/6) mice and were cultured for 24 hours in the presence of either DMSO or WHI-P154, a specific inhibitor of Jak3. ^20-22  Cells were then plated on methylcellulose to permit colony formation and stimulated with either GM-CSF or a combination of SCF, IL-3, and IL-6. After one week, colonies were counted and the number of colonies counted for DMSO-treated and Jak3 inhibitor-treated plates is shown. (A) Colony counts for GM-CSF-treated cells, plus or minus 1 standard deviation. (B) Colony counts for cells treated with SCF, IL-3, and IL-6, plus or minus 1 standard deviation. rm indicates recombinant murine.