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Abstract
An HIV vaccine capable of eliciting durable neutralizing antibody responses continues to be an important unmet need. Multivalent nanoparticles displaying a high density of envelope trimers may be promising immunogen forms to elicit strong and durable humoral responses to HIV, but critical particle design criteria remain to be fully defined. To this end, we developed strategies to covalently anchor a stabilized gp140 trimer, BG505 MD39, on the surfaces of synthetic liposomes to study the effects of trimer density and vesicle stability on vaccine-elicited humoral responses in mice. CryoEM imaging revealed homogeneously distributed and oriented MD39 on the surface of liposomes irrespective of particle size, lipid composition, and conjugation strategy. Immunization with covalent MD39-coupled liposomes led to increased germinal center and antigen-specific T follicular helper cell responses and significantly higher avidity serum MD39-specific IgG responses compared to immunization with soluble MD39 trimers. A priming immunization with liposomal-MD39 was important for elicitation of high avidity antibody responses, regardless of whether booster immunizations were administered with either soluble or particulate trimers. The stability of trimer anchoring to liposomes was critical for these effects, as germinal center and output antibody responses were further increased by liposome compositions incorporating sphingomyelin that exhibited high in vitro stability in the presence of serum. Together these data highlight key liposome design features for optimizing humoral immunity to lipid nanoparticle immunogens.
Highlights
Stabilized by gp120-gp[41] disulfide bonds and mutation of critical residues promoting interactions between gp[41] subunits[9,15,16]
We employed a SOSIP trimer known as BG50516, or a stabilized version of this trimer called MD39, which incorporates multiple mutations designed to limit sampling of non-native conformations, such as those that expose the V3 loop, and to increase expression and thermal stability[13,18]
To produce high density trimer-liposomes with a high overall coupling efficiency (~95%), we found the optimal ratio of MD39-6xHis:Ni-NTA during coupling to be approximately 1:40
Summary
Stabilized by gp120-gp[41] disulfide bonds and mutation of critical residues promoting interactions between gp[41] subunits[9,15,16]. ® ® infections, and several others) and formerly approved vaccines (e.g. Epaxal for hepatitis A and Inflexal V for influenza; both were discontinued in 2014 due to manufacturing quality issues)[30] Given their ability to be prepared in a range of particle sizes and capacity to be conjugated to any antigen of interest, we and others have demonstrated that stabilized trimers can be densely conjugated to the surface of unilamellar liposomes using both non-covalent[18,31] and covalent[20,32] coupling strategies. Additional optimization of the liposome composition to improve stability in the presence of serum was shown to even further enhance germinal center responses in mice These results define key design criteria for the generation of effective lipid nanoparticle immunogens for HIV and other infectious diseases
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