Abstract: A method of inducing a specific immune response in a mammal, comprising: providing a first composition comprising isolated ubiquitinylated proteins in solution in the absence of membrane bound organelles, the isolated ubiquitinylated proteins comprising one or more specific antigens, and further comprising a threshold quantity of polyubiquitinylated short-lived proteins and polyubiquitinylated defective ribosomal products. The isolated ubiquitinylated proteins are affinity-purified from tumor-derived cells grown in culture, the tumor-derived cells being inhibited from degrading ubiquitinylated proteins via the proteasome while being grown in culture. In this way, highly immunogenic short-lived proteins and defective ribosomal products may be loaded onto dendritic cells for cross-presentation and priming of antigen-specific T cells restricted by either classical or non-classical MHC.