Visualization of Polyoma Virus-Specific CD8+ T Cells In Vivo During Infection and Tumor Rejection

Abstract

T cells are critical for clearing infection and preventing tumors induced by polyoma virus, a natural murine papovavirus. We previously identified the immunodominant epitope for polyoma virus-specific CTL in tumor-resistant H-2k mice as the Dk-restricted peptide, MT389–397, derived from the polyoma middle T oncoprotein. In this study, we developed tetrameric Dk complexes containing the MT389–397 peptide to directly visualize and enumerate MT389–397-specific CTL during polyoma virus infection. We found that Dk/MT389 tetramer+CD8+ T cells undergo a massive expansion during primary infection such that by day 7 postinfection these Ag-specific CD8+ T cells constitute ∼20% of the total and ∼40% of the activated CD8+ T cells in the spleen. This expansion of Dk/MT389 tetramer+CD8+ T cells parallels the emergence of MT389–397-specific ex vivo cytolytic activity and clearance of polyoma virus. Notably, Dk/MT389 tetramer+CD8+ T cells are maintained in memory at very high levels. The frequencies of Dk/MT389 tetramer+CD8+ effector and memory T cells in vivo match those of CD8+ T cells producing intracellular IFN-γ after 6-h in vitro stimulation by MT389–397 peptide. Consistent with preferential Vβ6 expression by MT389–397-specific CD8+CTL lines and clones, Dk/MT389 tetramer+CD8+ T cells exhibit biased expression of this Vβ gene segment. Finally, we show that Dk/MT389 tetramer+CD8+ T cells efficiently infiltrate a polyoma tumor challenge to virus-immune mice. Taken together, these findings strongly implicate virus-induced MT389–397-specific CD8+ T cells as essential effectors in eliminating polyoma-infected and polyoma-transformed cells in vivo.