CD8⁺ T-cell dependence on CD4⁺ cell counts differs by viral specificity in individuals coinfected with HCV and HIV-1. Magnitude of virus-specific immunity (SFC/10⁶ PBMCs) plotted against CD4⁺ count. A significant positive correlation was discovered for HCV-specific CD8⁺ functional immunity (A) but not for the magnitude of CD8⁺ cells specific for HIV-1 (B) or EBV (C). Of note, this remains highly statistically significant (P < .0001) after removal of the outlier with the highest level of immunity (subject D3-01-49).