The association of GM-CSF plus IL-2 for cytotoxic cell expansion: influence of monocyte and and GM-CSF concentration

We evaluated the association GM-CSF + IL-2 on PBSC in liquid culture for 7 days both for its efficacy in LAK generation and for its protective effect on hemopoietic progenitors. In the first step of the experimental design we demonstrated that when GM-CSF was added to IL-2 (300 U/ml) in liquid culture at the concentration of 20 ng/ml, it caused a minor loss of cells in comparison with IL-2 alone (82% vs 58%) and a higer persistence of CD34+ cells (386/103 cells vs 103/103 cells ). Moreover the association GM-CSF + IL-2 showed a protective effect also on clonogenic ability of committed progenitors with a better recovery of CFU-GM (2671/ml vs 1345/ml,) and BFU-E (1033/ml vs 366/ml) after 7 days of liquid culture compared to IL-2 alone. On the other hand the addition of GM-CSF to IL-2 leaded to a minor NK expansion and similarly the boost of NK-LAK activity after 7 days of liquid culture resulted less efficacious in comparison with IL-2 alone. In the second step we evaluated the influence of the GM-CSF concentration comparing the previous concentration of 20 ng/ml with a lower concentration (2 ng/ml) and a higher concentration (200 ng/ml); we showedthat the association IL-2 + GM-CSF 2 ng/ml enhanced the NK expansion and the NK-LAK activity at in a similar manner to that observed with IL-2 alone, without hindering the protective effect on hemopoietic progenitors. Similar results have been observed using the higher GM-CSF concentration (20 ng/ml) in association with IL-2, but after monocyte depletion before the liquid culture. In conclusion our results suggest that the addition of GM-CSF at standard dose (20 ng/ml) protects the hemopoietic progenitors when cultured with IL-2, but antagonizes IL-2 as regard the NK-LAK expansion and activity. This effect is loss when lower concentration of GM-CSF is added or when PBSC are depleted by monocytes before liquid culture, suggesting that high concentrations of GM-CSF, via monocyte activation, can antagonize the expansion and the activation of cytotoxic effectors incubated with IL-2.