D Z13e1) bind to epitopes at the base of gp41, along a segment adjacent to the viral membrane known as the membrane proximal external region (MPER) that links the gp41 transmembrane domain to its ectodomain [2,3]. Two, 4E10 and 2F5, have been extensively characterized. Each has been shown to be polyreactive [4?], with an elongated heavy chain complementarity determining region 3 (CDRH3) that has a