Super Potent Bispecific Llama VHH Antibodies Neutralize HIV via a Combination of gp41 and gp120 Epitopes

International audienceBroad and potent neutralizing llama single domain antibodies (VHH) against HIV-1targeting the CD4 binding site (CD4bs) have previously been isolated upon llama immunization.Here we describe the epitopes of three additional VHH groups selected from phage libraries. The 2E7group binds to a new linear epitope in the first heptad repeat of gp41 that is only exposed in thefusion-intermediate conformation. The 1B5 group competes with co-receptor binding and the 1F10group interacts with the crown of the gp120 V3 loop, occluded in native Env. We present biophysicaland structural details on the 2E7 interaction with gp41. In order to further increase breadth andpotency, we constructed bi-specific VHH. The combination of CD4bs VHH (J3/3E3) with 2E7 groupVHH enhanced strain-specific neutralization with potencies up to 1400-fold higher than the mixtureof the individual VHHs. Thus, these new bivalent VHH are potent new tools to develop therapeuticapproaches or microbicide intervention