VIP knockout(KO) mice have an increased CMV tetramer response. VIP KO and VIP WT mice were infected (day 0) with either a sub-lethal low dose (5 × 10^4 PFU) or a lethal high dose (5 × 10^5 PFU) of CMV. Peripheral blood was stained for T cell markers and tetramer and analyzed by flow cytometry. On day 3, high dosed VIP KO mice had a higher number of tetramer positive CD8 T cells and better survival than WT mice (all high dose VIP WT died prior to day 10). VIP KO mice had a significant increase in tetramer positive CD8 T cells between days 3 and 10. *** p<0.01, difference between VIP KO and VIP WT littermate at designated dose level and day.