Efforts to generate vaccines that elicit broadly neutralizing antibodies have been thwarted by features of theHIV-1 envelope glycoprotein (Env) that limit access to conserved, neutralizing epitopes and difficulties inmimicking neutralizing structures in vaccine constructs. These challenges apply especially to thepretransmembrane region (PTM) of gp41, which is the target of approximately half of the broadly neutralizingmonoclonals that have been identified (2F5, 4E10, Z13), and the coiled-coil domain of the gp41 prehairpinintermediate, which is the target of the broadly-active fusion inhibitor T20 (Enfuvirtide) and a recentlydescribed neutralizing antibody D5. Here we propose to create and evaluate rationally-designed gp41immunogens that present PTM, coiled-coil, and other HIV mimotopes in stable, highly exposed, oligomericstructures for eliciting broadly neutralizing antibodies. These studies will further investigate the influence ofthe virion membrane and virus-like particle (VLP) structure on antibody induction, especially for PTMdeterminants, by comparing gp41 oligomers in the context of VLPs or soluble immunogens. Theimmunogens utilize a novel, oligomeric gp41 scaffold, in which the N- and C-heptad repeats (HR) of SIVserve as a trimerization domain and the transmembrane domain (TM) and cytoplasmic tail of HIV serve astargeting signals for incorporationg oligomers into VLPs. We have shown that this gp41 scaffold allowsinsertion of large regions of Env between the trimerizaton and TM domains, without impairing oligomerassembly or incorporation of the gp41 immunogen into VLPs. The gp41 scaffold also contains an alternativeinsertion site, between the N- and C-HR, which may also be used to provide a highly exposed, loop contextfor evaluating some epitopes.
Specific aims i nclude creating and evaluating the following Env determinantspresented in the oligomeric gp41 scaffold in VLP and soluble formats: 1) PTM region containing the 2F5 and4E10 epitopes; 2) N-HR coiled-coil region 3) combination inserts involving PTM, coiled coil, and other HIVneutralizing mimotopes. Immunogens will be extensively characterized, evaluated as single immunogens,and directly compared with other immunogens in the program. Promising constructs will be further assessedin prime-boost combinations involving other vectors and immunogens in the program, with differentformulations and adjuvants.
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