The strategy of selecting low producing IFN-γ-transfected NB cells for this study was followed to prevent loss of transfectants, as already described by others (Coze et al, 1995; Ucar et al, 1995), due to the potent induction of NB tumour cell differentiation (Ponzoni et al, 1992; Ponzoni et al, 1993; Montaldo et al, 1994) and sensitisation to apoptosis (Fulda et al, 2001; Banelli et al, 2002; Fulda and Debatin, 2002) caused by high level secretion of the cytokine. The gene discussed is IFNG; the disease is neuroblastoma.