RAG1 and acute lymphoblastic leukemia: RAG1 and RAG2 proteins form a DNA recombinase initiating V(D)J recombination, generating numerous Igh variable region exons essential for immune responses against various pathogens.[52, 53] In B‐ALL, the ETV6‐RUNX1 fusion gene induces excessive RAG recombinase activity, leading to tumor progression.