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Publication Abstract from PubMed

The HIV-1-envelope (Env) trimer is a target for vaccine design as well as a conformational machine that facilitates virus entry by transitioning between prefusion-closed, CD4-bound, and co-receptor-bound conformations before rearranging into a postfusion state. Vaccine designers have sought to restrict the conformation of the HIV-1-Env trimer to its prefusion-closed state, as this state is recognized by most broadly neutralizing -but not by non-neutralizing- antibodies. We previously identified a disulfide bond, I201C-A433C (DS), which stabilizes Env in the vaccine-desired prefusion-closed state. When placed into the context of BG505 SOSIP.664, a soluble Env-trimer mimic developed by Sanders, Moore and colleagues, the engineered DS-SOSIP trimer showed reduced conformational triggering by CD4. Here, we further stabilize DS-SOSIP through a combination of structure-based design and 96-well-based expression and antigenic assessment. From 103 designs, we identified one, named DS-SOSIP.4mut, with four additional mutations at the interface of potentially mobile domains of the prefusion-closed structure. We also determined the crystal structures of DS-SOSIP.4mut at 4.1-A resolution - and of an additional DS-SOSIP.6mut variant at 4.3-A resolution - and these confirmed the formation of engineered disulfide bonds. Notably, DS-SOSIP.4mut elicited a higher ratio of tier-2 autologous titers versus tier-1 V3-sensitive titers as compared to BG505 SOSIP.664. DS-SOSIP.4mut also showed reduced recognition of CD4 and increased thermostability. The improved antigenicity, thermostability, and immunogenicity of DS-SOSIP.4mut suggests utility as an immunogen or a serologic probe; moreover, the specific 4mut alterations identified here, M154, M300, M302 and L320, can also be transferred to other HIV-1 Env trimers of interest to improve their properties.IMPORTANCE One approach to elicit broadly neutralizing antibodies against HIV-1 is to stabilize the structurally flexible HIV-1-envelope (Env) trimer in a conformation that displays predominantly broadly neutralizing epitopes, and few to no non-neutralizing epitopes. The prefusion-closed conformation of HIV-1 Env has been identified as one such preferred conformation, and a current leading vaccine candidate is the "BG505 DS-SOSIP" variant, comprising two disulfides and an Ile to Pro mutation of strain BG505. Here, we introduced additional mutations to further stabilize BG505 DS-SOSIP in the vaccine-preferred prefusion-closed conformation. In guinea pigs, our best mutant, DS-SOSIP.4mut, elicited a significantly higher ratio of autologous versus V3-directed neutralizing antibody responses than the SOSIP-stabilized form. We also observed an improvement in thermostability and a reduction in CD4 affinity. With improved antigenicity, stability, and immunogenicity, DS-SOSIP.4mut-stabilized trimers may have utility as HIV-1 immunogens, or in other antigen-specific contexts, such as with B-cell probes.

Structure-Based Design of a Soluble Prefusion-Closed HIV-1-Env Trimer with Reduced CD4 Affinity and Improved Immunogenicity.,Chuang GY, Geng H, Pancera M, Xu K, Cheng C, Acharya P, Chambers M, Druz A, Tsybovsky Y, Wanninger TG, Yang Y, Doria-Rose NA, Georgiev IS, Gorman J, Joyce MG, O'Dell S, Zhou T, McDermott AB, Mascola JR, Kwong PD J Virol. 2017 Mar 8. pii: JVI.02268-16. doi: 10.1128/JVI.02268-16. PMID:28275193^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.