Using such a transplantable tumor cell line, called TUBO, and WT BALB/c and F1 BALB/c FVB/N-Tg (MMTV-neu) mice as a recipient, findings of Park8 and Mortenson14et al. suggest that adaptive immunity, in particular the role of CD4+ and CD8+ T cells, is essential for the anti-neu mAb-mediated tumour regression. The gene discussed is CD4; the disease is neoplasm.