PROJECT SUMMARY Strategies to enhance antigenicity, antibody affinity maturation, and memory induction in response to subunit vaccines are of broad relevance for the design of effective vaccines against infectious diseases, and may be especially important for difficult-to-neutralize pathogens such as HIV. One approach to enhance the efficacy of subunit vaccines is to formulate antigens in a multivalent, nanoparticulate form, which promotes several aspects of humoral immunity, and most notably enhances crosslinking of B cell receptors (BCRs). This approach has been exploited both in licensed vaccines (e.g., the HPV and HBV vaccines), and in a great variety of vaccines in preclinical and clinical development. However, to date it remains unclear what are the ideal characteristics of nanoparticle antigen display. In this project, we use the unique technology of scaffolded DNA origami to engineer nanoparticles on the 10–100 nanometer scale that offer the ability to investigate the impact of scaffold size, antigen copy number up to more than 100, antigen-BCR affinity, as well as the nanoscale spatial organization and dimensionality of antigen presentation on BCR activation. Specifically, we test the relative importance of these parameters on B-cell activation, which are of central importance to the development of a successful subunit vaccines, using the germline targeting engineered outer domain of HIV-1 gp120, termed eOD-GT8, and its variants with different affinities, as a testbed. In vitro evaluation of early B-cell signaling and pathway activation will be characterized, and contrasted with the benchmark strongly activating 60-mer control organized on a protein scaffold. Single-cell fluorescence imaging is used to investigate the detailed mechanism of BCR-binding and B-cell activation based on the optimal immunogen presentation found. These constructs are then used to test the impact of these optimal HIV DNA-NP constructs on T-cell and B-cell response in vivo using mouse models. Taken together, our results will offer the elucidation of the optimal immunogen presentation parameters for effective immune cell response in the development of more effective subunit vaccines, with major translational potential for HIV and other infectious diseases.