Antigen Dose and Persistence Contribute to Induction of a Durable HIV-1-Specific Neutralizing Antibody Response

The immunogenicity of HIV-1 Env glycoprotein (Env) is limited in part by its structural instability and extensive glycan shielding and is likely the greatest obstacle to an HIV-1 vaccine. Stabilized Env trimers can elicit serum neutralizing antibodies but often require many immunizations and the response is short-lived. To understand the parameters that confer a durable neutralizing antibody response, we used a Newcastle Disease Virus-like particle (NDV-VLP) platform to present stabilized versions of HIV-1 Env at high valency and varied the conformational stability, adjuvants, dose, and antigen persistence. Influenza virus hemagglutinin (HA), or SARS-CoV2 Spike (S)-bearing VLPs were used as controls. HA or S bearing VLPs rapidly induced neutralizing antibodies, whereas they were not induced by those bearing Env. A replicating adenovirus type 4 expressing Env rapidly induced autologous neutralizing antibodies, suggesting glycan shielding or the naïve B cell repertoire were not barriers. We then tested the parameters that might approximate a replicating virus infection. Only when multiple features of a virus infection were combined did we observe durable neutralizing antibodies, with the largest impact attributable to dose and escalating dose. Our results suggest that numerous features of a replicating virus infection, including stabilization, spike density, TLR stimulation, total dose, and persistence of antigen, can be combined to improve the immunogenicity of HIV-1 Env.