title: Memory CD8+ T cell responses expand when antigen presentation overcomes T cell self-regulation.
abstract: Antimicrobial memory CD8+ T cell responses are not readily expanded by either repeated infections or immunizations. This is a major obstacle to the development of T cell vaccines. Prime-boost immunization with heterologous microbes sharing the same CD8+ epitope can induce a large expansion of the CD8+ response; however, different vectors vary greatly in their ability to boost for reasons that are poorly understood. To investigate how efficient memory T cell expansion can occur, we evaluated immune regulatory events and Ag presentation after secondary immunization with strong and weak boosting vectors. We found that dendritic cells were essential for T cell boosting and that Ag presentation by these cells was regulated by cognate memory CD8+ T cells. When weak boosting vectors were used for secondary immunization, pre-established CD8+ T cells were able to effectively curtail Ag presentation, resulting in limited CD8+ T cell expansion. In contrast, a strong boosting vector, vaccinia virus, induced highly efficient Ag presentation that overcame regulation by cognate T cells and induced large numbers of memory CD8+ T cells to expand. Thus, efficient targeting of Ag to dendritic cells in the face of cognate immunity is an important requirement for T cell expansion.
authors: Department of Molecular Microbiology and Immunology, Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA.
authors: Ian A
authors: IA
authors: Cockburn
authors: Sumana
authors: S
authors: Chakravarty
authors: Michael G
authors: MG
authors: Overstreet
authors: Adolfo
authors: A
authors: García-Sastre
authors: Fidel
authors: F
authors: Zavala
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D003713:Dendritic Cells / Q000276:immunology; D005260:Female; D007117:Immunization, Secondary; D007156:Immunologic Memory; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D014616:Vaccinia virus / Q000276:immunology