Potent MLR stimulatory function is achieved only after mature DCs develop from myelodendritic progenitors present in the anti-TNF–treated GTS cultures. (A) On day 18, cells that had been treated with GM-CSF + SCF + IL-4 on day 10 produced potent T-cell responses. Cells that were left untreated (GTS, anti-TNF on day 3), control GTS cultures, or cells that were treated on day 10 with GM-CSF + G-CSF or M-CSF showed weak stimulatory potential on day 18. Results represent one of three typical experiments. (B) Progenitor cells exhibiting DC differential potential are preserved in anti-TNF–treated GTS cultures beyond day 18. Cells removed from anti-TNF–treated cultures on day 18 and exposed to GM-CSF + IL-4 acquired MLR stimulatory capacity by day 26. Cells obtained from untreated anti-TNF GTS cultures and control GTS cultures on day 26 produced weak T-cell responses, as did anti-TNF GTS cells exposed to GM-CSF + G-CSF or M-CSF on day 18. Results represent one of two experiments.