Spherical nucleic acids as an infectious disease vaccine platform

Despite recent efforts demonstrating that organization and presentation of vaccine components are just as important as composition in dictating vaccine efficacy, antiviral vaccines have long focused solely on the identification of the immunological target. Herein, we describe a study aimed at exploring how vaccine component presentation in the context of spherical nucleic acids (SNAs) can be used to elicit and maximize an antiviral response. Using COVID-19 as a topical example of an infectious disease with an urgent need for rapid vaccine development, we designed an antiviral SNA vaccine, encapsulating the receptor-binding domain (RBD) subunit into a liposome and decorating the core with a dense shell of CpG motif toll-like receptor 9 agonist oligonucleotides. This vaccine induces memory B cell formation in human cells, and in vivo administration into mice generates robust binding and neutralizing antibody titers. Moreover, the SNA vaccine outperforms multiple simple mixtures incorporating clinically employed adjuvants. Through modular changes to SNA structure, we uncover key relationships and proteomic insights between adjuvant and antigen ratios, concepts potentially translatable across vaccine platforms and disease models. Importantly, when humanized ACE2 transgenic mice were challenged in vivo against a lethal live virus, only mice that received the SNA vaccine had a 100% survival rate and lungs that were clear of virus by plaque analysis. This work underscores the potential for SNAs to be implemented as an easily adaptable and generalizable platform to fight infectious disease and demonstrates the importance of structure and presentation in the design of next-generation antiviral vaccines.

Infectious diseases have long threatened humanity due to their ability to rapidly spread and mutate across populations, infecting many people (1). The rapid and global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, emphatically revealed this and highlighted the importance of effective vaccination strategies to mitigate the spread and infectivity of viruses. Vaccination strategies are increasingly important as we consider the potential for emerging infectious diseases still to come (2, 3). The ability to rapidly adapt vaccine platforms through advancement of previous knowledge can be a huge asset. In particular, protein-based subunit vaccines can reduce vaccine production costs, while diminishing vaccine side effects. However, ultimate outcomes of protein-based subunit vaccine performance are difficult to correlate between candidates (4).An example of this is the influenza vaccine, which has relied on various simple mixtures of antigenic protein subunit target and adjuvant in solution to induce immune responses (5). As a result, influenza vaccine effectiveness has varied dramatically by year, with a low of 10% effectiveness in 2004–2005 and a high of 60% effectiveness in 2010–2011 (6, 7). This high variability is often attributed to the level of antigenic match between circulating viruses and vaccine strains. However, recent work has shown that the same antigen target can be more or less antigenic depending on the mode of presentation and delivery to the immune system (7, 8). By harnessing this concept, which we have termed rational vaccinology (9), we can greatly aid efforts to correlate vaccine design with performance by providing structurally informed and optimized vaccine platforms that can be readily and quickly adapted to new disease targets.Rational vaccinology has been implemented successfully for vaccines against cancer, where nanoscale changes have dramatically altered immune activation and tumor reduction (9–11). The application of this approach toward infectious disease has yet to be fully realized, and the potential for it to dramatically impact the success of vaccine development remains untapped. Herein, we have implemented spherical nucleic acid (SNA) nanotechnology as a tool to explore the impact of vaccine presentation when applied to infectious disease, using COVID-19 as a case study. SNAs comprise a nanoparticle core surrounded by a dense radial arrangement of oligonucleotides (12–14). Like many nanovaccine platforms, the SNA is biocompatible and comprises naturally found molecules in cellular biology. Importantly, however, the SNA provides key advantages over other nanovaccine platforms. Specifically, the SNA platform is highly modular, enabling the elucidation of important structure–function relationships. Moreover, the SNA is effective at entering cells rapidly and in high quantities through scavenger receptor A–mediated endocytosis and is resistant to nuclease degradation, due to the dense arrangement of oligonucleotides (15, 16). Moreover, by using a DNA shell containing immunostimulatory CpG motif DNA, SNAs robustly activate the innate immune system through toll-like receptor 9 (TLR9) (9, 17) and exhibit efficient lymph node drainage and high codelivery of adjuvant and antigen to antigen-presenting cells (9, 11). These properties have been harnessed in this work to maximize humoral responses and generate antibodies that are effective at neutralization in pseudoviral assays, capable of withstanding mutations to still bind the target, and protective in mice against a lethal viral challenge. Overall, we report enhancement in immune responses, leading to a 100% survival rate in a lethal viral challenge, which can be achieved through utilization of the SNA’s privileged architecture.