Enfuvirtide (T-20) cross-reactive glycoprotein 41 antibody does not impair the efficacy or safety of enfuvirtide.

The present study investigated the effect of enfuvirtide cross-reactive glycoprotein 41 (gp41) antibody on the efficacy or safety of enfuvirtide in patients participating in 1 of 2 24-week phase 3 clinical trials (T-20 vs. optimized regimen only [TORO] 1 and TORO 2). Serum samples from human immunodeficiency virus-infected patients receiving enfuvirtide plus optimized background (OB) and from patients receiving OB only were evaluated for enfuvirtide cross-reactive gp41 antibodies. Most patients had detectable levels of antibody at baseline; 78% of patients treated with enfuvirtide plus OB had a > or =30% decrease in level of antibody, compared with 43% of patients treated with OB only. Baseline antibody status did not influence virological responses to enfuvirtide-containing treatment. Favorable virological responses were more common among patients who experienced a > or =30% decrease from baseline than among those who experienced either an increase or a lesser decrease. A decrease in virus load correlated with a decrease in level of antibody. Safety was unaffected by the presence of positive antibody at any time point or change in level of antibody. There was no evidence that enfuvirtide cross-reactive gp41 antibody affects the efficacy or safety of enfuvirtide.