Vaccine-Elicited CD8+ T Cells Protect against Respiratory Syncytial Virus Strain A2-Line19F-Induced Pathogenesis in BALB/c Mice

CD8(+) T cells may contribute to vaccines for respiratory syncytial virus (RSV). Compared to CD8(+) T cells responding to RSV infection, vaccine-elicited anti-RSV CD8(+) T cells are less well defined. We used a peptide vaccine to test the hypothesis that vaccine-elicited RSV-specific CD8(+) T cells are protective against RSV pathogenesis. BALB/c mice were treated with a mixture (previously termed TriVax) of an M2(82-90) peptide representing an immunodominant CD8 epitope, the Toll-like receptor (TLR) agonist poly(I.C), and a costimulatory anti-CD40 antibody. TriVax vaccination induced potent effector anti-RSV CD8(+) cytotoxic T lymphocytes (CTL). Mice were challenged with RSV strain A2line19F, a model of RSV pathogenesis leading to airway mucin expression. Mice were protected against RSV infection and against RSVinduced airway mucin expression and cellular lung inflammation when challenged 6 days after vaccination. Compared to A2line19F infection alone, TriVax vaccination followed by challenge resulted in effector CD8(+) T cells with greater cytokine expression and the more rapid appearance of RSVspecific CD8(+) T cells in the lung. When challenged 42 days after TriVax vaccination, memory CD8(+) T cells were elicited with RSVspecific tetramer responses equivalent to TriVaxinduced effector CD8(+) T cells. These memory CD8(+) T cells had lower cytokine expression than effector CD8(+) T cells, and protection against A2line19F was partial during the memory phase. We found that vaccineelicited effector antiRSV CD8(+) T cells protected mice against RSV infection and pathogenesis, and waning protection correlated with reduced CD8(+) T cell cytokine expression.