Transient ATM inhibition enhances knock-in efficiency in hematopoietic stem cells by attenuating the DNA damage response

Precise genome editing in hematopoietic stem cells (HSCs) offers great potential for treating inherited blood disorders, but low knock-in (KI) efficiency, due to HSC quiescence and a preference for non-homologous end joining (NHEJ) and DNA damage-induced apoptosis, remains a major barrier. Here, we demonstrate that transient inhibition of Ataxia-Telangiectasia Mutated (ATM) kinase markedly enhances KI efficiency in mouse HSCs genome-edited with Cas9/RNP and AAV donor DNA. Phosphoproteomic analysis and capillary western blotting revealed that ATM inhibition suppressed the Cas9-AAV-induced ATM activation and subsequent DNA damage response, reduced p53-dependent apoptosis and preserved knock-in competent cells. In transplantation experiments, ATM inhibition preserved long-term engrafting genome-edited HSCs, increasing their frequency from ∼0.3% to ∼40% in secondary recipients - a >100-fold enhancement compared to untreated cells. Furthermore, in an X-SCID mouse model, ATM inhibition enhanced KI efficiency and restored expression of IL-2 receptor γ chain (CD132). These strikingly novel findings highlight transient ATM inhibition as a powerful and clinically relevant approach to enhance KI-mediated genome editing in HSCs, while preserving their long-term repopulating capacity.