 NHEJ is also used to repair DSBs generated during V(D)J recombination when gene regions are rearranged to create the unique antigen binding sites of antibodies and T-cell receptors.DNA damage occurs very frequently and is generated from exposure to a variety of both exogenous and endogenous genotoxic sources.One of these include ionizing radiation, such as γ radiation and X-rays, which ionize the deoxyribose groups in the DNA backbone and can induce DSBs.