In vivo blockade of PD-1 and B7-H1 at the time of antigen encounter by self-antigen-specific CD8 T cells results in the development of functional CTL. (A) Clone 4 cells were adoptively transferred into C3-HA^low mice with the indicated blocking antibodies administered intraperitoneally on day 0. Specific lysis in vivo was assayed by transfer of CFSE- or PKH26-labeled, HA peptide-pulsed targets on day 6. Targets from WT, B7-H1 KO, and B7-DC KO animals were differentially labeled (see “Materials and methods”) and injected simultaneously. Percentage specific lysis calculated as described previously,²⁶  n = 5. No significant differences in target lysis within the antibody treatment groups were detected by ANOVA. (B) In vitro CTL. clone 4 T cells were adoptively transferred as above, harvested on day 4 and sorted by FACS to < 95% purity. CTL were coincubated with HA peptide pulsed targets for at 37° for 4 hours, and percentage target lysis was calculated as described previously.²⁷