A further bridge toward human cancer was recently provided by novel immunodeficient models, like Rag2−/−;Il2rg−/− mice, which are permissive for metastatic spread of human HER-2+ cancer cells and can be engrafted with a functional human immune system, allowing for the first time the study of vaccines against oncoantigens to elicit human immune responses against human cancer cells in vivo. This evidence concerns the gene RAG2 and cancer.