Design and characterization of a germ-line targeting soluble, native-like, trimeric HIV-1 Env lacking key glycans from the V1V2-loop.

Background: The HIV-1 envelope glycoprotein (Env) is the primary target for broadly neutralizing antibodies (bNAbs) which can block infection. The current design strategy of soluble forms of Env in native-like trimeric conformation induces neutralizing antibodies with minimal breadth and potency. Extensive shielding by N-glycans on the surface of the HIV-1 Env acts as an immune evasion mechanism by restricting B cell recognition of conserved neutralizing determinants. An alternate approach is to design Env protein with glycan deletion to expose the protein surface.

Methods: A stable native-like trimeric Env with glycan holes at potentially immunogenic locations is expected to elicit better induction of germ-line B-cells due to exposure of the immunogenic regions. However, the extent and consequences of glycan removal from the trimer apex that form an important epitope is not explored. In this work, we have designed a construct with glycans deleted from the trimer apex of an Indian clade C origin Env that has previously been characterized for immunogenicity, to understand the impact of deglycosylation on the structural and functional integrity as well as on the antibody binding properties.

Results: The V1V2 glycan-deleted protein maintains native-like trimeric conformation with improved accessibility of the V1V2-directed germ-line antibodies. Furthermore, we showed that the protein binds specifically to quaternary conformation-dependent bnAbs but minimally to non-neutralizing antibodies.

Conclusions: This study provide an important design aspect of HIV-1 Env-based immunogens with glycan holes in the apex region that could be useful in eliciting apex directed antibodies in immunization studies.