Protective Capacity of Memory CD8⁺ T Cells Is Dictated by Antigen Exposure History and Nature of the Infection

Infection or vaccination confers heightened resistance to pathogen rechallenge because of quantitative and qualitative differences between naive and primary memory T cells. Herein, we show that secondary (boosted) memory CD8⁺ T cells were better than primary memory CD8⁺ T cells in controlling some, but not all acute infections with diverse pathogens. However, secondary memory CD8⁺ T cells were less efficient than an equal number of primary memory cells at preventing chronic LCMV infection and are more susceptible to functional exhaustion. Importantly, localization of memory CD8⁺ T cells within lymph nodes, which is reduced by antigen restimulation, was critical for both viral control in lymph nodes and for the sustained CD8⁺ T cell response required to prevent chronic LCMV infection. Thus, repeated antigen stimulation shapes memory CD8⁺ T cell populations to either enhance or decrease per cell protective immunity in a pathogen-specific manner, a concept of importance in vaccine design against specific diseases.