Date Published: September 19, 2013
Publisher: Public Library of Science
Author(s): Rogier W. Sanders, Ronald Derking, Albert Cupo, Jean-Philippe Julien, Anila Yasmeen, Natalia de Val, Helen J. Kim, Claudia Blattner, Alba Torrents de la Peña, Jacob Korzun, Michael Golabek, Kevin de los Reyes, Thomas J. Ketas, Marit J. van Gils, C. Richter King, Ian A. Wilson, Andrew B. Ward, P. J. Klasse, John P. Moore, Alexandra Trkola.
A desirable but as yet unachieved property of a human immunodeficiency virus type 1 (HIV-1) vaccine candidate is the ability to induce broadly neutralizing antibodies (bNAbs). One approach to the problem is to create trimeric mimics of the native envelope glycoprotein (Env) spike that expose as many bNAb epitopes as possible, while occluding those for non-neutralizing antibodies (non-NAbs). Here, we describe the design and properties of soluble, cleaved SOSIP.664 gp140 trimers based on the subtype A transmitted/founder strain, BG505. These trimers are highly stable, more so even than the corresponding gp120 monomer, as judged by differential scanning calorimetry. They are also homogenous and closely resemble native virus spikes when visualized by negative stain electron microscopy (EM). We used several techniques, including ELISA and surface plasmon resonance (SPR), to determine the relationship between the ability of monoclonal antibodies (MAbs) to bind the soluble trimers and neutralize the corresponding virus. In general, the concordance was excellent, in that virtually all bNAbs against multiple neutralizing epitopes on HIV-1 Env were highly reactive with the BG505 SOSIP.664 gp140 trimers, including quaternary epitopes (CH01, PG9, PG16 and PGT145). Conversely, non-NAbs to the CD4-binding site, CD4-induced epitopes or gp41ECTO did not react with the trimers, even when their epitopes were present on simpler forms of Env (e.g. gp120 monomers or dissociated gp41 subunits). Three non-neutralizing MAbs to V3 epitopes did, however, react strongly with the trimers but only by ELISA, and not at all by SPR and to only a limited extent by EM. These new soluble trimers are useful for structural studies and are being assessed for their performance as immunogens.
One approach to creating a preventative vaccine against human immunodeficiency virus type 1 (HIV-1) infection is to design an immunogen capable of inducing adequate titers of broadly neutralizing antibodies (bNAbs) . NAbs prevent HIV-1 from infecting target cells by binding to the viral envelope glycoprotein (Env) complex, a trimeric structure comprising three gp120 and three gp41 subunits held together by meta-stable, non-covalent interactions. Induction of NAbs therefore requires the use of an Env-based immunogen. Of these, the most widely tested have been monomeric gp120 subunits, which failed to induce bNAbs and did not prevent infection , , . A better mimic of the native, trimeric Env spike may be a superior immunogen for bNAb induction , , , , . However, creating a true mimic of an Env trimeric spike has proven challenging.
We describe here the design and properties of a next-generation, fully cleaved and highly stable soluble gp140 trimer based on the BG505 subtype A sequence. EM imaging shows that the BG505 SOSIP.664 gp140 trimers are homogeneous and that their architecture is very similar to that of native Env spikes on virions. We used a range of techniques to assess the antigenic properties of the soluble trimers, particularly their abilities to bind bNAbs and non-NAbs and the relationship between trimer binding and virus neutralization. The various techniques were generally concordant, with one notable exception relating to V3 MAbs. Overall, there were few discrepancies between the antigenicity of the trimers and the neutralization sensitivity of the corresponding BG505.T332N virus. Thus, in general, all the bNAbs that neutralized the virus also bound to the soluble trimers, with the obvious exception of bNAbs to the MPER, a region that was eliminated from the trimers to improve their biophysical properties. The presence of so many bNAb epitopes on a soluble, generally homogenous and highly stable trimer is highly beneficial for structural studies, and may also be valuable for their immunogenicity properties. Whether the favorable antigenic profile translates into the induction of bNAbs will be determined experimentally.