A Modular pH-Responsive Polymer Platform for Protein-Based Vaccines
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Protein-based subunit vaccines have the potential to combat some of the world's most detrimental infectious diseases, but finding an effective and versatile platform able to balance the requirements for a potent, specific and safe immune response remains a significant challenge. The ability of synthetic subunit vaccines to induce CD8+ cytotoxic T-cell (CTL) responses is crucial for protection against diseases caused by intracellular pathogens. Most subunit vaccine designs primarily generate humoral immune responses, yet activate a limited CTL response. In this work, we explore the use of a neutral, pH-responsive polymer micelle platform for enhancing antigen-specific CD8+ T-cell responses in vitro and in vivo. First, polymer carriers consisting of a N-(2-hydroxypropyl) methacrylamide corona block with pendent pyridyl disulfide groups for reversible conjugation of thiolated protein antigen, and a tercopolymer ampholytic core-forming block composed of propylacrylic acid (PAA), dimethylaminoethyl methacrylate (DMAEMA), and butyl methacrylate (BMA), were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. In vitro evaluation with a model antigen, ovalbumin (ova), demonstrated the ability of carriers to enhance cytosolic antigen accumulation, reduce exocytosis, and promote MHC-I cross-presentation. In vivo, carriers facilitated superior antigen transport to and uptake by antigen presenting cells (APCs) in the draining lymph node. Subcutaneous immunization of mice with ova-conjugated micelles significantly enhanced antigen-specific CD8+ T cell responses relative to free ova, an unconjugated physical mixture of ova and polymer, and a non pH-responsive conjugate control. To impart targeting specificity towards antigen presenting cells, pendent mannose moieties were incorporated into the first block of the copolymer evaluated in the previous aims. These glycopolymers were compared to the non-targeted construct in vitro and in vivo. Finally, the immunostimulatory potency of this antigen delivery system was evaluated in vivo with a clinically relevant HIV-1 antigen and a series of adjuvants anticipated to synergistically enhance immune responses. The combined results of this work demonstrate that pH-responsive polymeric micelles are an enabling technology that can be applied towards vaccine applications that rely on CD8+ T cell activation.
- Bioengineering