Sensitivity of HIV Type 1 Subtype C Isolates to the Entry Inhibitor T-20

T-20 is the first in a new class of antiretroviral drugs targeting the entry stage of the virus life cycle. It is a 36 amino acid peptide that binds to the HR1 region of gp41 preventing gp41-mediated fusion with the host cell membrane. T-20 was designed based on the HR2 sequence of HIV-1 subtype B gp41, a region that shows significant genetic variation with HIV-1 subtype C sequences. In order to assess the efficacy of T-20 to inhibit subtype C isolates, a total of 23 isolates were tested for their ability to replicate in the presence of T-20. This included 15 isolates that used CCR5, five that used both CCR5 and CXCR4, and three that used CXCR4. Five of these were from patients failing other antiretroviral therapies. Sequence analysis of the HR2 region indicated that there were 10–16 amino acid changes in the region corresponding to T-20. However, all isolates were effectively inhibited by T-20 at 1 μg/ml. There were no significant differences between viruses that used CCR5 or CXCR4 to enter cells. All isolates, except one, had GIV at positions 36–38 in the HR1 region. One isolate had a GVV motif but this did not affect its sensitivity to T-20. Therefore, T-20 inhibited subtype C viruses despite significant genetic differences in the HR2 region and there was no evidence for baseline resistance to T-20. These data suggest that T-20 would be highly effective in patients with HIV-1 subtype C infection, including those failing existing antiretroviral drug regimens.