Autologous dermal primary fibroblasts transduced with a retrovirus to express IL-2 or IL-12 have already been used in clinical trials to treat two types of tumour (Sobol et al, 1999; Kang et al, 2001), and IL-2 engineered syngeneic fibroblasts have also been injected intracerebrally to treat experimental glioma (Lichtor et al, 2002). Here, IL2 is linked to central nervous system cancer.