Although most tumour cells do not express MHC class II molecules, CD4+ T cells can effect an antitumour response in the absence of CD8+ T cells by secreting cytokines, such as interferon-γ (Mumberg et al, 1999; Qin and Blankenstein, 2000), or by activation and recruitment of effector cells such as macrophages and eosinophils (Greenberg, 1991; Hung et al, 1998). The gene discussed is CD4; the disease is neoplasm.