Histone Modulation Blocks Treg-Induced Foxp3 Binding to the IL-2 Promoter of Virus-Specific CD8(+) T Cells from Feline Immunodeficiency Virus-Infected Cats

CD8(+) T cells are critical for controlling HIV infection. During the chronic phase of lentiviral infection, CD8(+) T cells lose their proliferative capacity and exhibit impaired antiviral function. This loss of CD8(+) T cell function is due, in part, to CD4(+)CD25(+) T regulatory (Treg) cell-mediated suppression. Our research group has demonstrated that lentivirus-activated CD4(+)CD25(+) Treg cells induce the repressive transcription factor forkhead box P3 (Foxp3) in autologous CD8(+) T cells following co-culture. We have recently reported that Treg-induced Foxp3 binds the interleukin-2 (IL-2), interferon-γ (IFN- γ), and tumor necrosis factor-α (TNF-α) promoters in virus-specific CD8(+) T cells. These data suggest an important role of Foxp3-mediated CD8(+) T cell dysfunction in lentiviral infection. To elucidate the mechanism of this suppression, we previously reported that decreased methylation facilitates Foxp3 binding in mitogen-activated CD8(+) T cells from feline immunodeficiency virus (FIV)-infected cats. We demonstrated the reduced binding of Foxp3 to the IL-2 promoter by increasing methylation of CD8(+) T cells. In the studies presented here, we ask if another form of epigenetic modulation might alleviate Foxp3-mediated suppression in CD8(+) T cells. We hypothesized that decreasing histone acetylation in virus-specific CD8(+) T cells would decrease Treg-induced Foxp3 binding to the IL-2 promoter. Indeed, using anacardic acid (AA), a known histone acetyl transferase (HAT) inhibitor, we demonstrate a reduction in Foxp3 binding to the IL-2 promoter in virus-specific CD8(+) T cells co-cultured with autologous Treg cells. These data identify a novel mechanism of Foxp3-mediated CD8(+) T cell dysfunction during lentiviral infection.