A Cationic Micelle Complex Improves CD8+ T Cell Responses in Vaccination Against Unmodified Protein Antigen

Nanoscale carrier platforms promote immune responses to vaccination by facilitating delivery of vaccine components to immunologically relevant sites. The technique is particularly valuable for subunit vaccination, in which coadministration of immunostimulatory adjuvant is known to enhance immune responses to protein antigen. The fabrication of polymer-based nanoparticle vaccines commonly requires covalent attachment of vaccine components to the carrier surface. In contrast, we here describe a cationic micelle vaccination platform in which antigen and adjuvant loading is mediated by noncovalent molecular encapsulation and electrostatic complexation. Cationic micelles were generated through self-assembly of a polyarginine-conjugated poly(ethylene glycol)-b-poly(propylene sulfide) (PEG-PPS) diblock copolymer amphiphile, with or without encapsulation of monophosphoryl lipid A (MPLA), an amphiphilic experimental vaccine adjuvant. Micelle complexes were subsequently formed by complexation of ovalbumin (OVA) and CpG-B oligodeoxynucleotide (a second experimental adjuvant) to the cationic micelles. In a 35-day study in mouse, micelle-mediated codelivery of OVA antigen and CpG-B enhanced cellular and humoral responses to vaccination. These outcomes were highlighted in spleen and lymph node CD8⁺ T cells, with significantly increased populations of IFNγ⁺, TNFα⁺, and polyfunctional IFNγ⁺ TNFα⁺ cells. Elevated cytokine production is a hallmark of robust cytotoxic T lymphocyte (CTL) responses sought in next-generation vaccine technologies. Increased production of OVA-specific IgG1, IgG2c, and IgG3 also confirmed micelle enhancement of humoral responses. In a subsequent 35-day study, we explored micelle-mediated vaccination against OVA antigen coadministered with MPLA and CpG-B adjuvants. A synergistic effect of adjuvant coadministration was observed in micelle-free vaccination but not in groups immunized with micelle complexes. This outcome underlines the advantage of the micelle carrier: we achieved optimal cellular and humoral responses to vaccination by use of this nanoparticle platform with a single adjuvant. In particular, enhanced CTL responses support future development of the cationic micelle platform in experimental cancer vaccines and for vaccination against reticent viral pathogens.