IL21 and coinfection: We were also unable to observe a correlation between HCV-specific IL-21 producing responses and the magnitude of ex vivo HCV-specific CD8+ T cell responses in individuals during chronic HCV mono- and chronic HIV/HCV coinfection although we saw a trend towards higher HCV-specific IFN-gamma production from CD8+ T cells of acutely infected patients with stronger IL-21 responses in CD4+ T cells (S1E–S1G Fig).