Daan Pieren

74 Chapter 3 Memory (CD44 Hi ) Tc cells of WT aged mice do not differ from those of WT young mice [3]. In contrast, viSNE analysis of Ercc1 -/ Δ 7 memory Tc cells showed an increase in cluster 1 (21.5% versus 12.7%) and 2 (35.7% versus 25.6%), and a decrease in cluster 3 (38.4% versus 56.9%) compared to Ercc1 +/+ mice ( Figure 3E-G ). These differences were reflected in a reduced frequency of CD122 + cells and an increased frequency of PD-1 + cells among the memory Tc cells of Ercc1 -/ Δ 7 mice compared to Ercc1 +/+ mice ( Figure 3I,J ), which is also shown in the expression of these markers on a per cell basis ( Supplementary Figure 4 ). Together, these data indicate that the impact of compromised DNA damage repair on naive and memory Tc cells may not explain findings on aging of Tc cells in WT aged mice. Compromised DNA repair promotes the accumulation of regulatory cells within the memory Tc-cell subset. PD-1 + CD122 + Tc cells are regulatory Tc cells (Tc reg) [34,35] and these cells mainly accumulate within the naive Tc-cell subet of WT aged mice [3]. In contrast, PD-1 + CD122 + Tc reg cells did not accumulate within the naive Tc- cell subset of Ercc1 -/ Δ 7 mice ( Supplementary Figure 5 ), but rather within their memory Tc-cell subset. Therefore, compromised DNA repair does not explain findings on Tc reg cells in WT aged mice. eRapa reduces memory T cells that are induced by compromised DNA repair. Inhibition of mTOR by rapamycin reduces aging-related T-cell changes in WT mice [29]. Moreover, the mTOR pathway is thought to impair the DNA damage response [30]. We therefore hypothesized that in vivo dietary treatment of Ercc1 -/ Δ 7 mice with eRapa may slow down changes to the T-cell compartment induced by compromised DNA repair. To this end, 8-week old Ercc1 -/ Δ 7 mice were fed eRapa for the remainder of their life (42 ppm, reported previously as a life- and healthspan extending dose [36]). eRapa-fed Ercc1 -/ Δ 7 mice showed decreased proportions of CD3 + T cells among live spleen-derived lymphocytes compared to control-fed Ercc1 +/+ and Ercc1 -/ Δ 7 mice ( Figure 4A ), consistent with previous reports in WT mice [29]. Interestingly, eRapa reduced the proportion of memory CD4 + and CD4 - T cells towards levels found in control-fed Ercc1 +/+ mice ( Figure 4B,C ), suggesting that the increase of memory T cells induced by compromised DNA repair may in part be dependent on mTOR activation.