Interleukin-21 administration to rhesus macaques chronically infected with simian immunodeficiency virus increases cytotoxic effector molecules in T cells and NK cells and enhances B cell function without increasing immune activation or viral replication.

We have previously shown that interleukin-21, a pleiotropic C γ-chain signaling cytokine, induces the expression of the cytotoxic molecules granzyme B (GrB) and perforin in vitro in CD8 T cells and NK cells of chronically HIV infected individuals. In this pilot study, four chronically SIV infected rhesus macaques (RM) in late-stage disease were given two doses of recombinant MamuIL-21, 50 μg/kg, intravenously 7 days apart, followed by one subcutaneous dose, 100 μg/kg, 23 days after the second dose. Three animals served as controls. After each dose of IL-21, increases were noted in frequency and mean fluorescence intensity of GrB and perforin expression in memory and effector subsets of CD8 T cells in peripheral blood (PB), in peripheral and mesenteric lymph node (LN) cells, in PB memory and effector CD4 T cells and in NK cells. Frequencies of SIV-gag specific CD107a(+)IFN-γ(+) CD8 T cells increased 3.8-fold in PB and 1.8-fold in LN. In addition, PB CD27(+) memory B cells were 2-fold higher and serum SIV antibodies increased significantly after IL-21 administration. No changes were observed in markers of T cell activation, T cell proliferation or plasma virus load. Thus, administration of IL-21 to chronically SIV infected viremic animals was safe, well tolerated and could augment the cytotoxic potential of T cells and NK cells, promote B cell differentiation with increases in SIV antibody titers without discernable increase in cellular activation. Further studies are warranted to elucidate the effects and potential benefit of IL-21 administration in the context of SIV/HIV infection and in SIV/HIV vaccine design.