J Virol. 2014 Dec; 88(24):14002-16.

PubMed ID: 25253346

Hyperglycosylated stable core immunogens designed to present the CD4 binding site are preferentially recognized by broadly neutralizing antibodies

Ingale J, Tran K, Kong L, Dey B, McKee K, Schief W, Kwong PD, Mascola JR, Wyatt RT

The HIV-1 surface envelope glycoprotein (Env) trimer mediates entry into CD4(+) CCR5(+) host cells. Env possesses conserved antigenic determinants, such as the gp120 primary receptor CD4 binding site (CD4bs), a known neutralization target. Env also contains variable regions and protein surfaces occluded within the trimer that elicit nonneutralizing antibodies. Here we engineered additional N-linked glycans onto a cysteine-stabilized gp120 core (0G) deleted of its major variable regions to preferentially expose the conformationally fixed CD4bs. Three, 6, 7, and 10 new NXT/S glycan (G) motifs were engineered into 0G to encode 3G, 6G, 7G, and 10G cores. Following purification, most glycoproteins, except for 10G, were recognized by broadly neutralizing CD4bs-directed antibodies. Gel and glycan mass spectrometry confirmed that additional N-glycans were posttranslationally added to the redesigned cores. Binding kinetics revealed high-affinity recognition by seven broadly neutralizing CD4bs-directed antibodies and low to no binding by non-broadly neutralizing CD4bs-directed antibodies. Rabbits inoculated with the hyperglycosylated cores elicited IgM and IgG responses to each given protein that were similar in their neutralization characteristics to those elicited by parental 0G. Site-specific glycan masking effects were detected in the elicited sera, and the antisera competed with b12 for CD4bs-directed binding specificity. However, the core-elicited sera showed limited neutralization activity. Trimer priming or boosting of the core immunogens elicited tier 1-level neutralization that mapped to both the CD4bs and V3 and appeared to be trimer dependent. Fine mapping at the CD4bs indicated that conformational stabilization of the cores and addition of N-glycans altered the molecular surface of Env sites of vulnerability to neutralizing antibody, suggesting an explanation for why the elicited neutralization was not improved by this rational design strategy.