Fatty Acid-Mimetic Micelles for Dual Delivery of Antigens and Imidazoquinoline Adjuvants

Abstract

Vaccine design has undergone a shift towards the use of purified protein subunit vaccines, which offer increased safety and greater control over antigen specificity, but at the expense of immunogenicity. Here we report the development of a new polymer-based vaccine delivery platform engineered to enhance immunity through the co-delivery of protein antigens and the Toll-like receptor 7 (TLR7) agonist imiquimod (IMQ). Owing to the preferential solubility of IMQ in fatty acids, a series of block copolymer micelles with a fatty acid-mimetic core comprising lauryl methacrylate (LMA) and methacrylic acid (MAA), and a poly(ethylene glycol) methyl ether methacrylate (PEGMA) corona decorated with pyridyl disulfide ethyl methacrylate (PDSM) moieties for antigen conjugation were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Carriers composed of 50 mole% LMA (LMA50) demonstrated the highest IMQ loading (2.2 w/w%) and significantly enhanced the immunostimulatory capacity of IMQ to induce dendritic cell maturation and proinflammatory cytokine production. Conjugation of a model antigen, ovalbumin (OVA), to the corona of IMQ-loaded LMA50 micelles enhanced in vitro antigen uptake and cross-presentation on MHC class I (MHC-I). A single intranasal (IN) immunization of mice with carriers co-loaded with IMQ and OVA elicited significantly higher pulmonary and systemic CD8+ T cell responses and increased serum IgG titer relative to a soluble formulation of antigen and adjuvant. Collectively, these data demonstrate that rationally designed fatty acid-mimetic micelles enhance intracellular antigen and IMQ delivery and have potential as synthetic vectors for enhancing the immunogenicity of subunit vaccines.

Structural Optimization of Polymeric Carriers to Enhance the Immunostimulatory Activity of Molecularly Defined RIG-I Agonists

“… 19 , 20 Given their superior immunostimulatory potency, the NP/3pRNA complexes developed here also hold potential as vaccine delivery platforms, investigations that will be pursued in future work. Important to such efforts, the synthetic versatility of RAFT synthesis also allows for incorporation of reactive handles into carriers for covalent linkage of peptides and proteins, 20 , 46 offering a strategy to achieve codelivery of antigen and adjuvant, which has been widely demonstrated to enhance vaccine responses. 47 Similarly, by using reactive or functionalized chain transfer agents in polymer synthesis, these carriers are also highly amenable to incorporation of targeting ligands (e.g., antibodies, carbohydrates) to improve cell or organ specificity of RIG-I activation.…”

pH-Responsive Amphiphilic Carboxylate Polymers: Design and Potential for Endosomal Escape

“…These polymers have pH-responsive carboxylate pendant groups from MAA, and hydrophobicity from non-ionizable methacrylates, such as BMA, dodecyl methacrylate (DMA), lauryl methacrylate (LMA), and cholesteryl methacrylate (CMA). Previous studies found that incorporating a small portion of hydrophobic monomers (i.e., 1% DMA, 2% CMA or 10% LMA) in PMAA copolymers could enhance the interaction with lipid membranes significantly, compared with PMAA homopolymer (Cho et al, 2016;Sevimli et al, 2017;Wannasarit et al, 2019).…”

“…These polymers have pH-responsive carboxylate pendant groups from MAA, and hydrophobicity from non-ionizable methacrylates, such as BMA, dodecyl methacrylate (DMA), lauryl methacrylate (LMA), and cholesteryl methacrylate (CMA). Previous studies found that incorporating a small portion of hydrophobic monomers (i.e., 1% DMA, 2% CMA or 10% LMA) in PMAA copolymers could enhance the interaction with lipid membranes significantly, compared with PMAA homopolymer (Cho et al, 2016 ; Sevimli et al, 2017 ; Wannasarit et al, 2019 ). However, a further increase of the hydrophobic moieties (i.e., 8% CMA and 40% LMA) in the copolymer led to decreased solubility and enhanced supermolecular assembly in aqueous solutions, which in turn decreased the interaction between polymer and lipid membranes (Sevimli et al, 2012 ; Wannasarit et al, 2019 ).…”

Engineering self-assembled materials to study and direct immune function

“…Several approaches have emerged to co-assemble and co-deliver antigen and adjuvant using non-covalent interactions, including electrostatic or hydrophobic interactions, and other driving forces. For example, micelles and other particulate strategies have been used to deliver model antigens and either individual TLRas or defined combinations of TLRs [83] , [93] , [94] , [95] . Interestingly, one example of this approach demonstrates that co-incorporation of antigen and adjuvant enhances the potency of the response with minimal systemic inflammation [96] , an off-target side effect often associated with adjuvant delivery.…”