Cell-Intrinsic Transforming Growth Factor-β Signaling Mediates Virus-Specific CD8+ T Cell Deletion and Viral Persistence In Vivo

SummaryAlthough deficient CD8+ T cell responses have long been associated with chronic viral infections, the underlying mechanisms are still unclear. Here we report that sustained transforming growth factor-β (TGF-β) expression and phosphorylation of its signaling mediator, Smad-2, were distinctive features of virus-specific CD8+ T cells during chronic versus acute viral infections in vivo. The result was TGF-β-dependent apoptosis of virus-specific CD8+ T cells that related to upregulation of the proapoptotic protein Bim during chronic infection. Moreover, selective attenuation of TGF-β signaling in T cells increased the numbers and multiple functions of antiviral CD8+ T cells and enabled rapid eradication of the persistence-prone virus and memory generation. Finally, we found that cell-intrinsic TGF-β signaling was responsible for virus-specific-CD8+ T cell apoptosis and decreased numbers but was not necessary for their functional exhaustion. Our findings reveal persisting TGF-β-Smad signaling as a hallmark and key regulator of CD8+ T cell responses during chronic viral infections in vivo.