Native‐like Env trimers as a platform for HIV ‐1 vaccine design

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135

The formation of a correctly folded and natively glycosylated HIV-1 viral spike is dependent on protease cleavage of the gp160 precursor protein in the Golgi apparatus. Cleavage induces a compact structure which not only renders the spike capable of fusion but also limits further maturation of its extensive glycosylation. The redirection of the glycosylation pathway to preserve underprocessed oligomannose-type glycans is an important feature in immunogen design, as glycans contribute to or influence the epitopes of numerous broadly neutralizing antibodies.Here we present a quantitative site-specific analysis of a recombinant, trimeric mimic of the native HIV-1 viral spike (BG505 SOSIP.664) compared to the corresponding uncleaved pseudotrimer and the matched gp120 monomer. We present a detailed molecular map of a trimer-associated glycan remodeling that forms a localized subdomain of the native mannose patch. The formation of native trimers is a critical design feature in shaping the glycan epitopes presented on recombinant vaccine candidates. IMPORTANCEThe envelope spike of human immunodeficiency virus type 1 (HIV-1) is a target for antibody-based neutralization. For some patients infected with HIV-1, highly potent antibodies have been isolated that can neutralize a wide range of circulating viruses. It is a goal of HIV-1 vaccine research to elicit these antibodies by immunization with recombinant mimics of the viral spike. These antibodies have evolved to recognize the dense array of glycans that coat the surface of the viral molecule. We show how the structure of these glycans is shaped by steric constraints imposed upon them by the native folding of the viral spike. This information is important in guiding the development of vaccine candidates.KEYWORDS furin, glycan, glycosylation, human immunodeficiency virus, neutralizing antibodies, oligosaccharides, structure, vaccines T he trimeric envelope (Env) glycoprotein spike of human immunodeficiency virus type 1 (HIV-1) plays a crucial role in mediating host cell infection. Its exposed position on the virus surface also makes it the target for potent, broadly neutralizing antibodies (bNAbs) that are produced in a subset of infected individuals and that now influence the design of Env immunogens intended to induce similar antibody specificities. Env is extensively glycosylated, with glycans contributing to a significant proportion of the glycoprotein's mass (1). The heavily glycosylated surface of Env has been referred to as the "silent face," with the glycans acting to shield the underlying viral protein surface from immune surveillance (2-4). The glycan shield constantly evolves to protect the virus from newly produced neutralizing antibodies. However, compared to the highly diverse protein component of Env, many of the potential

Section: Discussionmentioning

confidence: 99%

Molecular Architecture of the Cleavage-Dependent Mannose Patch on a Soluble HIV-1 Envelope Glycoprotein Trimer

Behrens

Harvey

Milne

et al. 2017

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135

“…This trimer, located on the surface of virus particles, is therefore a focus of vaccine design programs (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). Of particular relevance is a subset of NAbs with activity, in vitro, against multiple circulating HIV-1 strains.…”

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confidence: 99%

“…The instability of the trimer reflects its need to undergo receptormediated conformational changes during the process of virus-cell fusion (19)(20)(21). Both factors create challenges when making Env trimers as recombinant proteins for immunogenicity testing and as the substrates for high-resolution structural studies (11,(22)(23)(24). Most Env immunogen development programs involve producing proteins in a secreted (i.e., soluble) form to improve the yield and simplify purification strategies (8,12,25,26).…”

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confidence: 99%

Improving the Expression and Purification of Soluble, Recombinant Native-Like HIV-1 Envelope Glycoprotein Trimers by Targeted Sequence Changes

Ringe

Ozorowski

Yasmeen

et al. 2017

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Soluble, recombinant native-like envelope glycoprotein (Env) trimers of various human immunodeficiency virus type 1 (HIV-1) genotypes are being developed for structural studies and as vaccine candidates aimed at the induction of broadly neutralizing antibodies (bNAbs). The prototypic design is designated SOSIP.664, but many HIV-1 env genes do not yield fully native-like trimers efficiently. One such env gene is CZA97.012 from a neutralization-resistant (tier 2) clade C virus. As appropriately purified, native-like CZA97.012 SOSIP.664 trimers induce autologous neutralizing antibodies (NAbs) efficiently in immunized rabbits, we sought to improve the efficiency with which they can be produced and to better understand the limitations to the original design. By using structureand antigenicity-guided mutagenesis strategies focused on the V2 and V3 regions and the gp120-gp41 interface, we developed the CZA97 SOSIP.v4.2-M6.IT construct. Fully native-like, stable trimers that display multiple bNAb epitopes could be expressed from this construct in a stable CHO cell line and purified at an acceptable yield using either a PGT145 or a 2G12 bNAb affinity column. We also show that similar mutagenesis strategies can be used to improve the yields and properties of SOSIP.664 trimers of the DU422, 426c, and 92UG037 genotypes.IMPORTANCE Recombinant trimeric proteins based on HIV-1 env genes are being developed for future vaccine trials in humans. A feature of these proteins is their mimicry of the envelope glycoprotein (Env) structure on virus particles that is targeted by neutralizing antibodies, i.e., antibodies that prevent cells from becoming infected. The vaccine concept under exploration is that recombinant trimers may be able to elicit virus-neutralizing antibodies when delivered as immunogens. Because HIV-1 is extremely variable, a practical vaccine may need to incorporate Env trimers derived from multiple different virus sequences. Accordingly, we need to understand how to make recombinant trimers from many different env genes. Here, we show how to produce trimers from a clade C virus, CZA97.012, by using an array of protein engineering techniques to improve a prototypic construct. We also show that the methods may have wider utility for other env genes, thereby further guiding immunogen design.KEYWORDS HIV-1 vaccine, Env trimers

“…(Continued on next page) brane or cytoplasmic domains) that mimics the native structure and antigenicity of virion-associated gp160 (2,24). Trimers with appropriate properties have now been developed, allowing high-resolution cryo-EM and X-ray structures to be obtained and preclinical immunogenicity data to be generated (2, 11).…”

Section: Fig 5 Mutations That Stabilize the Pgt151 Epitope (A)mentioning

confidence: 99%

“…The total molecular size of the molecule is approximately 140 kDa (hence it is termed a gp140). For multiple genotypes, purification using broadly neutralizing antibody (bNAb) affinity columns results in nearly 100% native-like SOSIP.664 trimers (2).…”

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confidence: 99%

High-Throughput Protein Engineering Improves the Antigenicity and Stability of Soluble HIV-1 Envelope Glycoprotein SOSIP Trimers

Sullivan

Sulli

Nilo

et al. 2017

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Soluble envelope glycoprotein (Env) trimers (SOSIP.664 gp140) are attractive HIV-1 vaccine candidates, with structures that mimic the native membranebound Env spike (gp160). Since engineering trimers can be limited by the difficulty of rationally predicting beneficial mutations, here we used a more comprehensive mutagenesis approach with the goal of identifying trimer variants with improved antigenic and stability properties. We created 341 cysteine pairs at predicted points of stabilization throughout gp140, 149 proline residue substitutions at every residue of the gp41 ectodomain, and 362 space-filling residue substitutions at every hydrophobic and aromatic residue in gp140. The parental protein target, the clade B strain B41 SOSIP.664 gp140, does not bind the broadly neutralizing antibody PGT151 and so was used here to identify improved variants that also provide insight into the structural basis for Env antigenicity. Each of the 852 mutants was expressed in human cells and screened for antigenicity using four different monoclonal antibodies (MAbs), including PGT151. We identified 29 trimer variants with antigenic improvements derived from each of the three mutagenesis strategies. We selected four variants (Q203F, T538F, I548F, and M629P) for more comprehensive biochemical, structural, and antigenicity analyses. The T538F substitution had the most beneficial effect overall, including restoration of the PGT151 epitope. The improved B41 SOSIP.664 trimer variants identified here may be useful for vaccine and structural studies.IMPORTANCE Soluble Env trimers have become attractive HIV-1 vaccine candidates, but the prototype designs are capable of further improvement through protein engineering. Using a high-throughput screening technology (shotgun mutagenesis) to create and evaluate 852 variants, we were able to identify sequence changes that were beneficial to the antigenicity and stability of soluble trimers based on the clade B B41 env gene. The strategies described here may be useful for identifying a wider range of antigenically and structurally improved soluble trimers based on multiple genotypes for use in programs intended to create a broadly protective HIV-1 vaccine.