Anti-PD-1 plus CCL21-DC tumor antigen (Ag) vaccine therapy enhances dendritic cell (DC) activity in the TME. CD4 and CD8 T cells were purified from the spleens of mice following vaccination with DC tumor lysate vaccine. DCs from TME of (i) diluent control, (ii) anti-PD-1, (iii) CCL21-DC tumor lysate vaccine, and (iv) anti-PD-1 plus CCL21-DC tumor lysate vaccine were pulsed with MHC Class I K-Ras peptide (LVVVGADGV) or MHC Class II (MTEYKLVVVGADGVG) and co-cultured with splenic CD8 or CD4 T cells of the vaccinated mice at a ratio of 1:5 for 24 h. IFNγ secreted by T cells in the co-culture was determined by IFNγ-specific ELISA. In comparison to diluent control or monotherapy, anti-PD-1 plus CCL21-DC tumor lysate Ag induced the highest DC activity of presenting MHC Class I and MHC Class II K-RasG12D tumor peptides to T cells. Control peptide (FECNTAQAC)-pulsed DCs did not stimulate T cell IFNγ production (data not shown). Bars represent SE; p < 0.01 compared with diluent-treated control, p < 0.05 compared with monotherapy. Results are representative of a single experiment (n = 4 mice/group).