The magnitude of IL-27 produced by cDC1 cells predicts the magnitude of the vaccine adjuvant-elicited CD8 +  T cell response Mice were immunized i.v. with OVA plus the indicated adjuvants. Seven days later, the spleens were harvested and stained with SIINFEKL–MHC class I K b  tetramers, as previously described ( 20 ), to identify OVA-specific T cells. ( A ) Representative dot plots showing tetramer staining on all live singlet B220 − CD8 + CD3 +  spleen cells isolated from mice immunized with the indicated adjuvants. ( B ) Quantification of T cell data shown in (A) after immunization with the indicated adjuvants. Error bars indicate SD derived from three mice each. ( C  and  D ) The number of tetramer +  T cells generated by each adjuvant, as shown in (B), was plotted against eGFP gMFI of cDC1 cells (C) or the percentage of eGFP +  cDC1 cells (D) 6 h postimmunization with each adjuvant, as shown in  Fig. 3 .  r 2  and  p  values were determined by linear regression analysis (Prism). ( E ) Mice were challenged with the indicated innate stimuli, and the splenocytes were isolated at 6 h, as in  Fig. 3 . Spleens were incubated in vitro for 6 h in the presence of brefeldin A, after which they were stained to identify XCR1 +/−  DCs, as in  Fig. 2 . The cells were then fixed, permeabilized, and stained for intracellular IL-12. The percentage of IL-12 +  XCR1 +  DCs is shown. ( F ) Tetramer +  T cell numbers in the spleen 7 d after immunization with the indicated adjuvants were plotted against the percentage of IL-12 +  cells shown in (E).  r 2  and  p  values were determined by linear regression analysis (Prism). Data in (E) and (F) are from one of two experiments performed. ( G ) Mice were immunized with OVA + LTA, as in (A), with or without the addition of 10 μg of rIL-27. T cell responses were measured as in (A) and (B). * p