ADA2 is a lysosomal deoxyadenosine deaminase acting on DNA involved in regulating TLR9-mediated immune sensing of DNA

Although adenosine deaminase 2 (ADA2) is considered an extracellular ADA, evidence questions the physiological relevance of this activity. Our study reveals that ADA2 localizes within the lysosomes, where it is targeted through modifications of its glycan structures. We show that ADA2 interacts with DNA molecules, altering their sequences by converting deoxyadenosine (dA) to deoxyinosine (dI). We characterize its DNA substrate preferences and provide data suggesting that DNA, rather than free adenosine, is its natural substrate. Finally, we demonstrate that dA-to-dI editing of DNA molecules and ADA2 regulate lysosomal immune sensing of nucleic acids (NAs) by modulating Toll-like receptor 9 (TLR9) activation. Our results describe a mechanism involved in the complex interplay between NA metabolism and immune response, possibly impacting ADA2 deficiency (DADA2) and other diseases involving this pathway, including autoimmune diseases, cancer, or infectious diseases. [Display omitted] •ADA2 is primarily a lysosomal protein, challenging the notion of its predominant extracellular presence•ADA2 is capable of editing DNA by converting deoxyadenosine to deoxyinosine•Lysosomal ADA2’s DNA editing activity modulates DNA sensing and innate immune responses Greiner-Tollersrud et al. discover ADA2’s function as a lysosomal deoxyadenosine deaminase acting on DNA (LADAD). This finding reveals insights into cellular DNA sensing and innate immune regulation, with potential implications for therapeutic approaches and gene editing applications.