Most tumour cells are poor APC because of the low or absent expression of costimulatory molecules (Hurwitz et al, 2000), but enforced expression of some of these (e.g. CD80, B7H2 or 4-1BBL) by gene transfer has resulted in enhanced antitumour responses and tumour rejection in different animal models (Wu et al, 1995; Weinberg et al, 2000; Liu et al, 2001). This evidence concerns the gene ICOSLG and neoplasm.