The present invention relates to peptides comprising at least one CD4+ T epitope, which is immunodominant in vitro, of the cyclin B1 tumor antigen, said peptides being capable of stimulating a specific human CD4+ T lymphocyte response in subjects who have varied HLA II molecules, and to the use of these peptides as a cancer vaccine and as a reagent for the diagnosis of cancer or the immunomonitoring of the cellular response against cyclin B1 during cancer or during an anticancer treatment.