A) Pdcd1−/−Ctla4+/− mice were treated with anti-CD4, anti-CD8 or control antibodies. Antibody treatments were started at 21 days of age and administered three times weekly. Time is measured since birth, but no animals are censored prior to the start of the experiment at day 21. P =0.03, anti-CD8 v control, p=0.02, anti-CD8 v. anti-CD4, two-sided cox proportional hazard tests. Risk tables show size of groups. B) Whole splenocytes or splenocytes from which CD8 cells were depleted from Pdcd1−/−Ctla4+/− mice with MC were transferred to Rag1−/− recipient mice. Day 0 is the day of adoptive transfer. P=0.0017, two-sided cox proportional hazard test. Risk tables show size of groups. C) Representative H&E from CD8 depleted splenocyte recipients compared to whole splenocyte recipients. Only cardiac sections are shown. Scale bars show 50μm. Representative of n=10 animals per group. D) Representative IHC for CD8 on cardiac sections from CD8 depleted splenocyte recipients compared to whole splenocyte recipients. Scale bars show 50μm. Representative of n=10 animals per group. E) TCR β chain sequencing on cardiac tissue from a donor Pdcd1−/−Ctla4+/− mouse (Donor, in bold) and Rag1−/− whole splenocyte recipients (Rec1-4). The top ten most abundant TCRs from the donor plus the most abundant TCR from Rec2 are shown. Flow between samples indicates shared TCRs. Bolded CDR3s indicate most clonal TCRs.