Vaccine Lipid-Biopolymer Cross-Linked Nanoparticles Against Infectious Diseases and Cancer

Abstract

Prophylactic vaccines can induce long-term, antigen-specific cellular and humoral immunity, and provide effective countermeasures against emerging infectious diseases, such as the recent epidemics of Ebola and Zika. Compared to inactivated or live-attenuated pathogens, subunit proteins derived from whole-pathogens provide a safer antigen source but are often limited by unstable delivery in their soluble forms and low immunogenicity. Nanoparticle (NP) vaccines have shown promise to protect antigens from rapid enzymatic degradation, and achieve co-localized delivery of antigens and adjuvants to antigen-presenting cells, thus enhancing cellular and humoral immune responses. In this thesis, I hypothesize that delivery of subunit protein antigens and/or molecular adjuvants by nanoparticles can improve immune stimulation and vaccine efficacy. Specifically, I have developed a new cationic lipid-hyaluronic acid (HA) hybrid NP platform and demonstrated the improved vaccine efficacy using plague, Ebola, and cancer models. In the first section, I present the characterization of these NPs as an intranasal vaccine using the model antigen ovalbumin (OVA) and F1-V, a candidate recombinant antigen against the plague. These NPs exhibited improved colloidal stability, and reduced cytotoxicity associated with cationic liposomes by at least 20 fold in dendritic cell (DC) culture. Furthermore, NPs co-loaded with OVA and a molecular adjuvant, the Toll-like receptor (TLR)-4 agonist monophosphoryl lipid A (MPLA), promoted DC maturation in vitro, and elicited robust OVA-specific CD8+ T cell and antibody responses in vivo. Importantly, intranasal vaccination with NPs co-loaded with F1-V and MPLA increased endpoint serum titers of F1-V-specific total IgG, IgG1, and IgG2c by 11-, 23-, and 15-fold, respectively, compared with the lack of sero-conversion in mice immunized with the equivalent doses of soluble F1-V vaccine. In the second section, I modified the hybrid NP design by promoting inter-lipid layer crosslinking and particle surface decoration with HA, and constructed the multilamellar vaccine particle (MVP) platform. Compared with the previously developed interbilayer-crosslinked multilamellar vesicle (ICMV) platform without HA decoration, MVP accumulated more in CD44-expressing DCs, increased antigen processing in DCs, and elicited significantly stronger antigen-specific CD8+ and CD4+ T cell immune responses tested using the OVA antigen. A single dose of the Ebola glycoprotein (GP)/MPLA co-loaded MVP protected 80% of mice against a lethal viral challenge, suggesting it could be a potent delivery platform for subunit vaccines. Inspired by these promising results, I further explored the MVP for delivery of molecular adjuvants and developed a novel whole-cell cancer vaccination strategy in the third section. Recent studies have shown that cancer cells treated with certain chemotherapeutics, such as mitoxantrone, can undergo immunogenic cell death (ICD) and initiate anti-tumor immune responses. However, it remains unclear how to exploit ICD for cancer immunotherapy. In this section, I synthesized and demonstrated immunogenically dying tumor cells surface-modified with MVP encapsulating CpG, a TLR-9 agonist, efficiently promoted activation and antigen cross-presentation by DCs in vitro, and elicited robust antigen-specific CD8+ T cells in vivo. Furthermore, whole tumor-cell vaccination combined with immune checkpoint blockade led to complete tumor regression in 78% of CT26 tumor-bearing mice and established long-term immunity against tumor recurrence. Our strategy may open new doors to “personalized” cancer immunotherapy tailored to individual patient’s tumor cells. Overall, our results presented in this thesis suggest lipid-HA crosslinked MVP could be a promising platform for vaccine delivery of subunit protein antigens and molecular adjuvants, thus promoting clinical translation of vaccine candidates against infectious diseases and cancer.