RAG2 is a core component of the RAG recombinase complex essential for V(D)J recombination, the process generating immunoglobulin and T-cell receptor diversity in developing lymphocytes 1. Although RAG2 is not catalytically active, it is required for all catalytic activities mediated by RAG1 and functions as a chr11 state sensor that recruits the RAG complex to H3K4me3-marked regions 2. The RAG proteins introduce double-strand breaks by creating hairpin coding ends and blunt signal ends at recombination sites 3. RAG2 also mediates pre-B cell allelic exclusion, ensuring single immunoglobulin heavy chain expression through ATM-dependent repositioning of non-recombined alleles to heterochromatin. Mutations in RAG2 cause severe immunodeficiencies ranging from severe combined immunodeficiency (SCID) to Omenn syndrome, with recombination activity levels correlating with clinical phenotype severity 4. RAG2-SCID manifests as life-threatening infections without hematopoietic cell transplantation. Gene-correction approaches using CRISPR/Cas9 in patient-derived hematopoietic stem cells successfully restore V(D)J recombinase activity and rescue lymphoid development, including normal TCR and immunoglobulin expression 5. This demonstrates therapeutic potential for RAG2-deficiency treatment.