Neutral Polymer Micelle Carriers with PH-Responsive, Endosome-Releasing Activity Modulate Antigen Trafficking to Enhance CD8+ T Cell Responses


Synthetic subunit vaccines need to induce CD8+ cytotoxic T cell (CTL) responses for effective vaccination against intracellular pathogens. Most subunit vaccines primarily generate humoral immune responses, with a weaker than desired CD8+ cytotoxic T cell response. Here, a neutral, pH-responsive polymer micelle carrier that alters intracellular antigen traffickingwas shown to enhance CD8+ T cell responses with a correlated increase in cytosolic delivery and a decrease in exocytosis. Polymer diblock carriers consisted of a N-(2-hydroxypropyl) methacrylamide corona block with pendent pyridyl disulfide groups for reversible conjugation of thiolated ovalbumin, and a tercopolymer ampholytic core-forming block composed of propylacrylic acid (PAA), dimethylaminoethyl methacrylate (DMAEMA), and butylmethacrylate (BMA). The diblock copolymers self-assembled into 25-30 nm diameter micellar nanoparticles. Conjugation of ovalbumin to themicelles significantly enhanced antigen cross-presentation in vitro relative to free ovalbumin, an unconjugated physical mixture of ovalbumin and polymer, and a non-pHresponsive micelle-ovalbumin control. Mechanistic studies in a murine dendritic cell line (DC 2.4) demonstrated micelle-mediated enhancements in intracellular antigen retention and cytosolic antigen accumulation. Approximately 90% of initially internalized ovalbumin-conjugated micelles were retained in cells after 1.5 h, compared to only ~40% for controls. Furthermore, cells dosed with conjugates displayed 67-fold higher cytosolic antigen levels relative to soluble ovalbumin 4 h post uptake. Subcutaneous immunization of mice with ovalbumin-polymer conjugates significantly enhanced antigen-specific CD8+ T cell responses (0.4% IFN-γ+ of CD8+) compared to immunization with soluble protein, ovalbumin and polymer mixture, and the controlmicelle without endosome-releasing activity. Additionally, pH-responsive carrier facilitated antigen delivery to antigen presenting cells in the draining lymph nodes. As early as 90 min post injection, ova-micelle conjugates were associated with 28% and 55% of dendritic cells and macrophages, respectively. After 24 h, conjugates preferentially associated with dendritic cells, affording 30-, 3-, and 3-fold enhancements in uptake relative to free protein, physical mixture, and the non-pHresponsive conjugate controls, respectively. These results demonstrate the potential of pH-responsive polymericmicelles for use in vaccine applications that rely on CD8+ T cell activation.


Materials Science and Engineering

Keywords and Phrases

Nanoparticles; Ph-responsive; Polymer micelles; Subunit vaccine

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Document Type

Article - Journal

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© 2014 Elsevier B.V., All rights reserved.

Publication Date

01 Oct 2014

PubMed ID