Alloreactivity of myeloma DCs derived from CD34⁺ cells generated in the presence of GM-CSF, TNF-α, SCF, and FLT3-L (G+T+S+F) and grown in FCS (A) or autologous serum (B) with and without IL-6.

Increasing numbers of DCs were tested for their capacity to stimulate 5 × 10⁴ allogeneic CD3⁺ cells. Negative controls, which always gave less than 2000 cpm, are represented by unmanipulated mononuclear cells and allogeneic PB mononuclear cells (PBMCs). Results report the mean ± SD of 5 different experiments. The addition of IL-6 (A) to the culture of CD34⁺ cells significantly inhibited the development of alloreactive APCs (P < .002). The inhibitory effect of IL-6 was abrogated by anti–IL-6 antibodies. Similarly, autologous serum prevented the differentiation of functional DCs. However, anti–IL-6 antibodies did not fully reverse the APC ability of DC (P < .05 compared to G+T+S+F).