Paving the way for nucleic acid-based HIV-1 envelope vaccines

Human immunodeficiency virus type 1 (HIV-1) remains a major global health challenge, with no effective prophylactic vaccine despite decades of dedicated research. The viral envelope glycoprotein (Env) trimer is the sole target of neutralizing antibodies and a central focus for vaccine development. However, its remarkable sequence diversity, inherent instability, and dense glycan shield, among other factors, hinder the induction of broadly neutralizing antibodies (bNAbs). This thesis explores novel strategies to stabilize Env trimers, enhance their antigenic properties, and improve their suitability for RNA- and other nucleic acid-based vaccine platforms.
We first investigated natural mechanisms of Env stabilization by introducing destabilizing mutations and identifying compensatory changes that emerged during viral evolution. Building on these and other prior insights, we engineered hyperstable trimers and found that increased stability led to stronger and more consistent neutralizing antibody responses. By selectively masking immunodominant epitopes with glycans, we redirected immune responses toward subdominant epitopes with greater potential to induce bNAbs.
We also developed the Triple Tandem Trimer (TTT) platform, which encodes all three protomers of an HIV-1 Env or influenza hemagglutinin (HA) trimer within a single gene, ensuring exclusive trimer expression. TTT immunogens formed native-like trimers, induced diminished non-neutralizing responses, and enabled the design of chimeric trimers that could simplify sequential vaccine regimens by integrating different immunization stages into a single immunogen.
Finally, we engineered RNA-delivered, membrane-bound, germline-targeting Env immunogens that potently activated rare bNAb precursors in knock-in mouse models and outperformed soluble counterparts in triggering these targeted responses.
Collectively, these approaches advance the design of stable, immunofocused Env immunogens optimized for nucleic acid-based vaccine delivery, and offer promising tools and strategies for the development of an effective HIV-1 vaccine.