and A.B.W. bnAb epitopes and are an important parameter in immunogen design. Keywords:glycans, U18666A human immunodeficiency virus, vaccines, broadly neutralizing antibodies, mass spectrometry, cryo-electron microscopy, glycosylation, structure == Graphical Abstract == == Highlights == HIV glycans form epitopes for broadly neutralizing antibodies High-resolution structure of 2G12 in complex with envelope glycoprotein mimetic Impact of glycan knockouts and knockins on glycan processing and epitope formation The human immunodeficiency virus is coated in a dense array of glycans that can be targeted by broadly neutralizing antibodies. Seabright et al. investigate how the network of glycans act to limit the biosynthetic processing of glycans and maintain glycan-based antibody epitopes. == Introduction == The envelope spike (Env) of the human immunodeficiency virus type 1 (HIV-1) mediates contamination of target host cells and is consequently a main target for vaccine design. However, Env displays extreme antigenic diversity, meaning only an U18666A immune response of exceptional breadth will be protective (Burton et al., 2012). In addition, a dense coat of host-derived, immunologically self N-linked glycans shield the underlying protein from host antibody responses (Wei et al., 2003). Despite these hurdles, approximately a third of infected individuals develop broadly neutralizing antibody (bnAb) responses against Env after several years of contamination (Simek et al., 2009,van Gils et al., 2009). Whereas the Env glycan shield typically limits antibody neutralization, many bnAbs have, paradoxically, evolved to recognize epitopes that are either entirely or partially composed of N-linked glycans (Blattner et al., 2014,Doores and Burton, 2010,Falkowska Rabbit Polyclonal to SERPINB4 et al., 2014,Huang et al., 2014,McLellan et al., 2011,Pancera et al., 2013,Pejchal et al., 2011,Scharf et al., 2014,Walker et al., 2009,Walker et al., 2011). These bnAbs recognize the glycans at four distinct regions of Env: the gp120/gp41 protomer interface (e.g., PGT151), surrounding the CD4 binding site (e.g., HJ16), the V1/V2 loops at the trimer apex (e.g., PG9 and PG16), and the oligomannose-type glycans centered around the highly conserved N332 site around the outer domain name of gp120 (e.g., PGT135 and 2G12) (Crispin et al., 2018). Given the number of bnAbs targeting the N332 glycan, it has previously been termed the supersite of immune vulnerability (Kong et al., 2013). It is well established that this passive transfer of bnAbs protects non-human primates and humanized mice from viral challenge (Pegu et al., 2017,van Gils and Sanders, 2014). Thus, bnAbs are now being investigated for both therapeutic use (Stephenson and Barouch, 2016), and to guide the design of Env-based immunogens intended to elicit similarly broad and neutralizing responses (Burton, 2017,Sanders and Moore, 2017). The latter approach typically involves producing recombinant mimics of the native, virion-associated Env trimer that present multiple bnAb epitopes, and/or immunogens specifically designed to target the germline-encoded bnAb precursors (gl-bnAbs) (Sanders and Moore, 2017,Stamatatos et al., 2017). Currently, the most widely studied recombinant Env mimics are the BG505 SOSIP.664 trimers, based on the subtype A transmitted/founder virus sequence, BG505. U18666A Various modifications, including the introduction of a disulfide bond (SOS), an isoleucine to proline mutation (IP), and truncation at the 664 position (.664), increase both the stability and solubility of the trimers (Sanders et al., 2013). The resulting trimers display native-like structure and antigenicity (Sanders et al., 2013,Ward and Wilson, 2017) and are lead candidates in ongoing human immunogenicity studies (Dey et al., 2018; ClinicalTrials.gov Identifier:NCT03699241). The BG505 transmitted/founder virus naturally lacks the conserved N332 glycan site, thus this glycan was also included (T332N) in the BG505 SOSIP.664 trimers to introduce the supersite epitope (Sanders et al., 2013). However, the BG505 sequence also lacks glycans at the 241 and 289 positions, despite their presence in 97% and 72% of HIV-1 isolates, respectively. The presence or absence of holes within the glycan shield has recently received a lot of attention because of the putative role of holes in.