Daan Pieren

83 Compromised DNA repair promotes the accumulation of regulatory T cells on aging-related T-cell changes. Second, although endogenous nuclear DNA damage accumulation in Ercc1 -/ Δ 7 mice has been confirmed in liver and kidney cells [22]. it is unknown whether T cells of Ercc1 -/ Δ 7 mice also accumulate DNA damage. Therefore, it remains to be established whether T-cell changes we ascribe to Ercc1 -deficiency are due to T-cell intrinsic accumulation of DNA damage, or due to DNA damage present in the microenvironment these T cells reside in. Additionally, the inflammatory profile affecting T cells might differ between normal aging by response to antigen exposure over time, senescence- driven aging, and DNA damage-accelerated aging. Finally, we used a 42 ppm eRapa dose in our in vivo experiments as this dose was previously reported to further expand the health- and lifespan of WT mice compared to lower eRapa dosages [36]. Compared to other studies investigating the effect of eRapa on T-cell phenotype and function in WT mice [29,46], our dose is 3-fold higher. As different doses of rapamycin show different outcomes of lifespan in WT mice [27,46], it is likely that changes within the T-cell population are also dose- dependent. Additionally, to what extent the 42 ppm dose of eRapa inhibits mTORC1 and mTORC2 signals remains unknown and warrants future immune studies. Collectively, this study reveals a novel and pivotal role for compromised DNA repair in promoting accumulation of Tregs with an aging-related phenotype. Although smaller mTOR-mediated effects by eRapa may be missed by the relatively small group sizes in our study, compromised DNA repair appears to impose accumulation of naive Tregs through a mechanism that may be independent of mTOR activation. Our study indicates that preventing DNA-damage over the course of life may help to prevent accumulation of immunosuppressive Tregs hampering protective immunity at old age. Moreover, our study warrants further studies of biological processes that may underlie aging-related immune defects in order to better understand the process of aging. ACKNOWLEDGEMENTS We thank the biotechnicians of the Institute for Translational Vaccinology for their assistance, Jeroen Hoeboer for assisting with the experiments, Sander Barnhoorn, Nicole van Vliet, Yvette van Loon and the animal caretakers for general assistance with mouse experiments, and Gerco den Hartog for critically reviewing the manuscript. This study was supported by grants S/112006 and S/340005 provided by the Strategic Program of RIVM (SPR); grant V/152106 provided by the Dutch Ministry of Health, Welfare and Sport; grant 733050810 3