The progeny of GM-CSF and GM-CSF/TNF-α–cultured CD34⁺/CD86⁺ cells induce proliferative response of allogeneic CD4⁺ cells. CD34⁺/CD86⁺ and CD34⁺/CD86⁻ cells were cultured for 9 days in GM-CSF plus SCF, in the absence (B) or presence (C) of TNF-α. Fresh (A) and cultured cells (B and C) were resuspended in 15% PHS. Cells were irradiated at 3,000 cGy, and serial dilutions were cultured with HLA-DR–mismatched CD4⁺ T cells at 5 × 10⁴ responders/well in U-bottomed plates. Cells were harvested on day 6 after 18 hours of exposure to³H-thymidine.