ATM Influences the Efficiency of TCRβ Rearrangement, Subsequent TCRβ-Dependent T Cell Development, and Generation of the Pre-Selection TCRβ CDR3 Repertoire

Generation and resolution of DNA double-strand breaks is required to assemble antigen-specific receptors from the genes encoding V, D, and J gene segments during recombination. The present report investigates the requirement for ataxia telangiectasia-mutated (ATM) kinase, a component of DNA double-strand break repair, during TCR beta recombination and in subsequent TCR beta-dependent repertoire generation and thymocyte development. CD4(-)CD8(-) double negative stage 2/3 thymocytes from ATM-deficient mice have both an increased frequency of cells with DNA break foci at TCR beta loci and reduced V beta-DJ beta rearrangement. Sequencing of TCR beta complementarity-determining region 3 demonstrates that ATM-deficient CD4(+)CD8(+) double positive thymocytes and peripheral T cells have altered processing of coding ends for both in-frame and out-of-frame TCR beta rearrangements, providing the unique demonstration that ATM deficiency alters the expressed TCR beta repertoire by a selection-independent mechanism. ATMKO thymi exhibit a partial developmental block in DN cells as they negotiate the beta-selection checkpoint to become double negative stage 4 and CD4(+)CD8(+) thymocytes, resulting in reduced numbers of CD4(+)CD8(+) cells. Importantly, expression of a rearranged TCR beta transgene substantially reverses this defect in CD4(+)CD8(+) cells, directly linking a requirement for ATM during endogenous TCR beta rearrangement to subsequent TCR beta-dependent stages of development. These results demonstrate that ATM plays an important role in TCR beta rearrangement, generation of the TCR beta CDR3 repertoire, and efficient TCR beta-dependent T cell development.