The study reports the isolation and characterization of a human monoclonal antibody, 10E8, which specifically binds to the membrane-proximal external region (MPER) of HIV-1 gp41 and neutralizes ~98% of tested viruses. 10E8 is unique among MPER-specific antibodies in that it does not bind phospholipids, is not autoreactive, and binds to cell-surface envelope. Structural analysis reveals that 10E8 recognizes a conserved site within the MPER, comprising a narrow stretch of highly conserved gp41-hydrophobic residues and a critical Arg/Lys just prior to the transmembrane region. The prevalence of 10E8-like antibodies in chronically infected donors suggests that they are not rare and may be elicited by vaccines designed to target this conserved site. The broad and potent neutralization activity of 10E8, along with its lack of autoreactivity and lipid binding, makes it a promising candidate for vaccine development and passive immunization.The study reports the isolation and characterization of a human monoclonal antibody, 10E8, which specifically binds to the membrane-proximal external region (MPER) of HIV-1 gp41 and neutralizes ~98% of tested viruses. 10E8 is unique among MPER-specific antibodies in that it does not bind phospholipids, is not autoreactive, and binds to cell-surface envelope. Structural analysis reveals that 10E8 recognizes a conserved site within the MPER, comprising a narrow stretch of highly conserved gp41-hydrophobic residues and a critical Arg/Lys just prior to the transmembrane region. The prevalence of 10E8-like antibodies in chronically infected donors suggests that they are not rare and may be elicited by vaccines designed to target this conserved site. The broad and potent neutralization activity of 10E8, along with its lack of autoreactivity and lipid binding, makes it a promising candidate for vaccine development and passive immunization.