HIV Membrane-Proximal External Region Scaffolded Immunogen Killed Whole-Cell Genome-Reduced Vaccines

Background: Killed Whole Cell Genome-Reduced Bacteria (KWC/GRB), a versatile vaccine platform, can produce very low cost, thermostable, easily manufactured vaccines expressing complex immunogens that include potent immunomodulators. This system supports iterative optimization through a Design–Build–Test–Learn (DBTL) workflow aimed at enhancing immunogenicity. We applied this approach to developing an HIV-1 gp41 Membrane-Proximal External Region (MPER) vaccine using the scaffolded MPER antigen, 3AGJ, a recombinant heterologous protein engineered to mimic MPER structures recognized by broadly neutralizing monoclonal antibodies (bNAbs). Methods: Five KWC/GRB vaccines expressing versions of 3AGJ were designed, including versions linked to immunomodulators and multimers of the immunogen. Display on the surface of the bacteria was evaluated by flow cytometry using the broadly neutralizing monoclonal antibody 2F5. Outbred HET3 mice were vaccinated intramuscularly, MPER-specific an-tibody responses were assessed by ELISA, and the ability of the vaccines to induce neutralizing antibodies determined. Neutralization was measured against tier 1 and tier 2 HIV-1 pseudoviruses. Results: All five vaccines were strongly expressed on the bacterial surface and induced clear MPER-specific antibody responses in every mouse. About 33% of the animals showed detectable HIV-1 neutralization. Conclusion: A KWC/GRB 3AGJ scaffold-MPER vaccine can induce HIV-1 neutralizing antibodies. While improvements in the responses would be needed for a clinically useful vaccine, the findings provide an initial validation of the concept. There are many strategies that can be used to enhance and extend immune responses induced by KWC/GRB vaccines that can be employed to yield improved anti-HIV immune responses.