Exosomes are a family of bioactive vesicles and play important roles in antigen presentation. A recent phase I clinical trial with an exosome vaccine derived from colorectal cancer has shown minor clinical benefit. Exosomes derived from leukaemia cell lines have been little studied so, in the present study, the immunoprotective effect of exosomes secreted by NB4 cells, a human acute promyelocytic leukaemia cell line, was investigated. NB4-derived exosomes expressed the proteins retinoic acid receptor a and interstitial cell adhesion molecule 1 and contained heat shock protein 70, as demonstrated by transmission electron microscopy and Western blotting. Cytotoxicity assay demonstrated that cytotoxic T lymphocytes (CTLs) induced by dendritic cells (DCs) pulsed with exosomes were significantly more effective in killing target NB4 cells than CTLs induced by DCs alone. Exosome-based vaccines may be a promising means of prolonging disease-free survival in acute promyelocytic leukaemia patients after induction therapy.