RAG2 and precursor B-cell acute lymphoblastic leukemia: As AID is the key molecule responsible for somatic hypermutation, class switch recombination and, in birds, gene conversion [52–54], it is interesting to note that very recently AID was also reported to drive - together with RAG1 and RAG2 - leukemic clonal evolution by contributing to the acquisition of genetic lesions in B-ALL [55].