Impact of Common Modifications on the Antigenic Profile and Glycosylation of Membrane-Expressed HIV-1 Envelope Glycoprotein

Abstract

Recent HIV-1 vaccine development has centered on “near native” soluble envelope glycoprotein (Env) trimers. These trimers are artificially stabilized laterally (between protomers) and apically (between gp120 and gp41). These same stabilizing mutations have been leveraged for use in membrane-expressed Env mRNA vaccines, although their precise effects in this context are unclear. To address this question, we investigated the effects of Env mutations expressed on virus-like particle (VLP) in 293T cells. Uncleaved (UNC) trimers were laterally unstable upon gentle lysis from membranes. However, gp120/gp41 processing improved lateral stability. Due to inefficient gp120/gp41 processing, UNC is incorporated into VLPs. A linker between gp120 and gp41 (NFL) neither improved trimer stability nor its antigenic profile. An artificially introduced enterokinase cleavage site allowed processing post-expression, resulting in increased trimer stability. Gp41 N-helix mutations I559P and NT1-5 both imparted lateral trimer stability, but concomitantly reduced gp120/gp41 processing and/or impacted V2 apex and interface NAb binding. I559P consistently reduced recognition by HIV+ donor plasmas, further supporting antigenic differences. Mutations in the gp120 bridging sheet failed to stabilize membrane trimers in a pre-fusion conformation, reduced gp120/gp41 processing and exposed non-neutralizing epitopes. Reduced glycan maturation and increased sequon skipping were common effect of mutations. In some cases, this may be due to increased rigidity which limits access to glycan processing enzymes. In contrast, viral gp120 did not show glycan skipping. We observed a minor species of high mannose glycan only gp160 in particle preparations. This was unaffected by any mutations and instead bypasses normal folding and glycan maturation processes. Including the full gp41 cytoplasmic tail led to markedly reduced gp120/gp41 processing and increased the proportion of high mannose gp160. Remarkably, NAbs were unable to bind to full-length Env trimers. Overall, our findings suggest caution in leveraging mutations to ensure they impart valuable membrane trimer phenotypes for vaccine use.