Vaccines that elicit a CD8⁺ T cell response have the potential to prevent or treat a number of infectious diseases and malignancies, but little is known about how vaccine encoded proteins are presented to the immune system. In February 4 online Nature Immunology, Christopher Norbury and colleagues from National Institutes of Health, Bethesda, USA, show how antigen-presenting cells (APC) infected with a vector virus prime naïve CD8⁺ T cells in vivo.

Norbury et al. used confocal microscopy to visualize the mouse CD8⁺ T cell response to a well-defined antigen expressed by a recombinant vaccinia virus (rVV). They found infected macrophages and dendritic cells in the draining lymph nodes but only the dendritic cells (DC) presented antigen to naïve CD8⁺ T cells. Presentation was swift — as rapidly as 6 h after inoculation — and then quickly declined in parallel with the number...