Provided is a method of vaccinating a patient against a tumor by administering an agent to reduce or prevent interaction between Notch and a Notch ligand, or expression or processing of Notch or a Notch ligand. In one embodiment, this is accomplished by administering to the patient a tumor antigen expressed by the tumor and exposing an antigen presenting cell in the patient to an agent that reduces or prevents interaction, expression or processing of Notch or a Notch ligand in a T cell.