Background:  Co-infection with HIV-1 and hepatitis C virus (HCV) leads to increased levels of circulating HCV and increased rates of liver disease progression. The effect of HCV infection on HIV-1 is unclear, although progression to AIDS may be accelerated. We have previously shown that the V1-V2 and V4-V5 regions of the HIV-1 envelope gene (env) undergo high levels of change in 6-month intervals until CD4 counts fall below 150/µL. Here, we examined the effect of HCV infection on HIV env evolution by comparing HIV-infected men and HIV/HCV-co-infected people with hemophilia (PWH) during late chronic infection while CD4 counts were low.

Methods:  For co-receptor usage determination, plasma or serum from low CD4 count (<200/µL) time points were obtained from 20 HIV⁺HCV⁺ PWH enrolled in the Multicenter Hemophilia Cohort Study and 20 HIV⁺ men enrolled in either the San Francisco Men’s Health Study or the DC Gay Men’s Study. V3 regions were amplified, cloned, and sequenced. For the viral diversity study, semi-annual plasma or serum samples were obtained from 14 HIV⁺HCV⁺ PWA (Multicenter Hemophilia Cohort Study) and 12 HIV⁺ men (San Francisco and DC studies). All sequential samples had CD4 counts <150/µL. Viral diversity over time was measured by heteroduplex tracking assays (HTA) for the V1-V2 and V4-V5 regions, with analysis of the HTA patterns by total change and HTA index calculations.

Results:  V3 sequencing yielded proportions of X4 variants (by genotype) of 65% (13 of 20) in the HIV⁺ group vs 25% (5 of 20) in the co-infected group (p = 0.025). The V1-V2 and V4-V5 HTA analyses indicated that the rate of sequence turnover and new sequence emergence were higher for the co-infected subjects by all analyses, and were significantly higher for the V1-V2 region by HTA index.

Conclusions:  Our data indicate that the HIV⁺HCV⁺ PWH demonstrated increased levels of immune-mediated viral selection (higher rates of sequence turnover and less X4 virus) at low CD4 counts than did HIV⁺ men. These differences may reflect the direct effect of HCV, the presence of liver disease, or an altered response in the multiply-transfused hemophilia population These findings merit further investigation into immune function during co-infection of all affected populations.