A novel approach to visualize polyclonal virus-specific CD8 T cells in vivo

Recent technical breakthroughs in generating soluble MHC class I-peptide te tramers now allow the direct visualization of virus-specific CD8 T cells af ter infection in vivo. However, this technique requires the knowledge of th e immunodominant viral epitopes recognized by T cells. Here, we describe an alternative approach to visualize polyclonal virus specific CD8 T cells in vivo using a simple adoptive transfer system. In our approach, C57BL/6 (Th y1.2) mice were infected with lymphocytic choriomeningitis virus, vesicular stomatitis virus, or vaccinia virus to induce virus specific memory T cell s. Tracer T cells (2 x 10(6)) from these virus-immune mice were adoptively transferred into nonirradiated (C57BL/6 x B6.PL-Thy-1(a) )F-1 mice. After i nfection of the F-1- recipient mice with the appropriate virus, the transfe rred cells expanded vigorously, and on day 8 postinfection 60-80% of total CD8 T cells were of donor T cell origin. Under the same conditions memory C D4 T cells gave rise to at least 10 times less cell numbers than memory CD8 T cells, The transfer system described here not only allows to visualize e ffector and memory CD8 T cells in vivo but also to isolate them for further in vitro characterization without knowing the epitopes recognized by these Ag-specific CD8 T cells.