CSF2 and plasma cell myeloma: Cells were grown in RPMI 1640 medium (Biosera) supplemented with 8% ultra-low endotoxin heat-inactivated foetal bovine serum (FBS) (Biosera), 2 mM L-glutamine (Gibco), 50 U · mL−1 penicillin (Gibco), 50 μg · mL−1 streptomycin (Gibco) and 20 ng · mL−1 of granulocyte–macrophage colony-stimulating factor (GM-CSF) derived from the J588 myeloma cell line.