PT - JOURNAL ARTICLE AU - Norie Sugitani AU - Frank P. Vendetti AU - Andrew J. Cipriano AU - Joshua J. Deppas AU - Tatiana N. Moiseeva AU - Sandra Schamus-Haynes AU - Yiyang Wang AU - Drake Palmer AU - Hatice U. Osmanbeyoglu AU - Anna Bostwick AU - Nathaniel W. Snyder AU - Yi-Nan Gong AU - Katherine M. Aird AU - Greg M. Delgoffe AU - Jan H. Beumer AU - Christopher J. Bakkenist TI - ATR kinase inhibition induces thymineless death in proliferating CD8<sup>+</sup> T cells AID - 10.1101/2022.02.24.481821 DP - 2022 Jan 01 TA - bioRxiv PG - 2022.02.24.481821 4099 - http://biorxiv.org/content/early/2022/02/26/2022.02.24.481821.short 4100 - http://biorxiv.org/content/early/2022/02/26/2022.02.24.481821.full AB - ATR kinase is a central regulator of the DNA damage response (DDR) and cell cycle checkpoints. However, little is known about the role of ATR in the cell cycle and the impact of DDR inhibitors in immune cells in the absence of DNA damage. We previously showed that the ATR inhibitor AZD6738 (ATRi) combines with radiation to generate delayed, CD8+ T cell-dependent antitumor responses in mouse models of cancer. Here, we show that ATRi induces untimely CDK1 activity during S phase in CD8+ T cells and this induces origin firing and simultaneous degradation of dNTP synthesis and salvage enzymes. These pleiotropic effects of ATRi in proliferating CD8+ T cells induce deoxyuridine contamination in genomic DNA, R loops, RNA-DNA polymerase collisions, and death. Remarkably, thymidine significantly rescues ATRi-induced CD8+ T cell death. Our data identifies critical considerations for the design of clinical ATRi regimens with genotoxic chemo- and radiation and immunotherapies.Competing Interest StatementThe authors have declared no competing interest.