To study the functional profile of virus-specific T-cells in HCV/ HIV co-infection, simultaneous expression of 5 distinct CD8 + T-cell markers were analyzed in 3 individuals within each cohort using a previously developed multicolor flow cytometry method [16] . Expression levels of degranulation marker CD107a and cytokines IFN-c, TNF-a and IL-2, as well as the chemokine MIP-1b were simultaneously measured in response to HCV or HIV peptides in both blood and liver of each individual. Figure 3 depicts a representative multi-parameter analysis of CD8 + T-cell responses in liver and blood of a therapy-naïve, co-infected subject in response to HIV and HCV peptide pools. These data indicate that both HCV and HIV specific CD8 + T-cells expressing one or more functions are detectable in the liver and blood. Compared to blood, the frequency of HIV-specific T-cells producing CD107a and IL-2 was shown to be significantly higher in the liver of therapy-naïve, co-infected individuals. Consistent with previously reported data [10] , HCV-specific responses were compartmentalized to the liver and stronger than peripheral HCV-specific responses (Figure 3c ).