After activation, populations of antigen-specific T cells flow between sites of antigen expression, local lymphoid structures and other lymphoid and non-lymphoid organs. In this study, we documented the in vivo dynamics of a CD8+ T cell response to antigen delivered using herpes simplex virus amplicon vectors and revealed several unexpected features. First, the T cells localized to the site of vector injection, as well as the draining lymph node within 24-48 h. Second, the major site to which T cells later redistributed were intra-abdominal lymphoid organs, including milky spots, mesenteric and lumbar lymph nodes. We determined the relationship between bioluminescent signal and antigen-specific T cell numbers in various lymphoid organs, and concluded that bioluminescent signal is a valid surrogate measure of T cell abundance in superficial lymph nodes, but not in deeper structures such as the spleen. © The Japanese Society for Immunology. 2007. All rights reserved.