Reinherz Vaccine Discovery Consortium 

OVERVIEW:

A vaccine capable of eliciting antibodies capable of neutralizing a broad range of HIV-1 strains must target a region of the HIV-1 virus that is highly conserved across strains. The Reinherz VDC is aimed at eliciting antibodies directed against a region of the viral gp41 envelope protein known as the membrane proximal ectodomain region (MPER). Structural information on this lipid-embedded region will be exploited for vaccine immunogen design and delivery to the immune system in the form of lipid-coated nanoparticles. This vehicle system has the advantage of concomitantly facilitating delivery of adjuvants including Toll-like receptor (TLR) ligands. In addition, nanoparticles can be used to further deliver both T helper and cytotoxic T lymphocyte (CTL) epitopes in the nanoparticle core in future iterations.

RESEATCH OBJECTIVES:

1. Structural analysis of HIV-1 MPER from clade C viruses with and without the appended transmembrane (TM) gp41 segment in lipid environments.
2. Creation of MPER nanoparticles consisting of a polymer core particle encapsulated by an outer lipid vesicle or "skin" for MPER presentation to the immune system.
3. Elicitation of humoral immune responses to MPER immunogens, assessment of antibody titer, specificity and HIV-1 neutralizing activity.

PROGRESS:

Although rarely elicited during the course of natural infection or upon conventional vaccination, the membrane-proximal ectodomain region (MPER) of the HIV-1 glycoprotein of M_r 41,000 (gp41) envelope protein subunit is the target of 3 human broadly neutralizing antibodies (BNAbs): 4E10, 2F5, and Z13e1. How these BNAbs bind to their lipid-embedded epitopes and mediate antiviral activity is unclear, but this information may offer important insight into a worldwide health imperative. The Reinherz Vaccine Discovery Consortium has utilized EPR and NMR techniques to define the manner in which these BNAbs differentially recognize viral membrane-encrypted residues configured within the L-shaped helix–hinge–helix MPER segment. Two distinct modes of antibody-mediated interference of viral infection were identified. 2F5, like 4E10, induces large conformational changes in the MPER relative to the membrane. However, although 4E10 straddles the hinge and extracts residues W672 and F673, 2F5 lifts up residues N-terminal to the hinge region, exposing L669 and W670. In contrast, Z13e1 effects little change in membrane orientation or conformation, but rather immobilizes the MPER hinge through extensive rigidifying surface contacts. Thus, BNAbs disrupt HIV-1 MPER fusogenic functions critical for virus entry into human CD4 T cells and macrophages either by preventing hinge motion or by perturbing MPER orientation. HIV-1 MPER features, important for targeted vaccine design, have been revealed, with implications extending to BNAb targets on other viral fusion proteins.

In addition, the Irvine group’s work on phospholipid-enveloped biodegradable polymer microparticles and nanoparticles, synthesized by an emulsion–solvent evaporation process, were characterized by confocal and cryoelectron microscopies. This showed that the lipid envelope exhibits two-dimensional fluidity and can be configured into ‘shell’, ‘onion’, or ‘flower’ nanostructures, depending on the quantity and composition of lipids employed in the synthesis.