Early virus-associated bystander events affect the fitness of the CD8 T cell response to persistent virus infection.

Chronic Ag exposure during persistent viral infection erodes virus-specific CD8 T cell numbers and effector function, with a concomitant loss of pathogen control. Less clear are the respective contributions of Ag-specific and Ag-nonspecific (bystander) events on the quantity, quality, and maintenance of antiviral CD8 T cells responding to persistent virus infection. In this study, we show that low-dose inoculation with mouse polyomavirus (PyV) elicits a delayed, but numerically equivalent, antiviral CD8 T cell response compared with high-dose inoculation. Low-dose infection generated virus-specific CD8 T cells endowed with multicytokine functionality and a superior per cell capacity to produce IFN-gamma. PyV-specific CD8 T cells primed by low-dose inoculation also expressed higher levels of IL-7Ralpha and bcl-2 and possessed enhanced Ag-independent survival. Importantly, the quantity and quality of the antiviral CD8 T cell response elicited by dendritic cell-mediated immunization were mitigated by infection with a mutant PyV lacking the dominant CD8 T cell viral epitope. These findings suggest that the fitness of the CD8 T cell response to persistent virus infection is programmed in large part by early virus-associated Ag-nonspecific factors, and imply that limiting bystander inflammation at the time of inoculation, independent of Ag load, may optimize adaptive immunity to persistent viral infection.