Cell-permeable capsids as universal antigen carrier for the induction of an antigen-specific CD8+ T-cell response

Sami Akhras,Kiyoshi Himmelsbach,Meike Gratz,Fabian Elgner,Masako Toda,Klaus Boller,Stephan Scheurer,Eberhard Hildt,Stefan Vieths,Marlene Biehl

doi:10.1038/s41598-017-08787-0

Abstract

Vaccine platforms that can be flexibly loaded with antigens can contribute to decrease response time to emerging infections. For many pathogens and chronic infections, induction of a robust cytotoxic T lymphocytes-mediated response is desirable to control infection. Antigen delivery into the cytoplasm of antigen presenting cells favors induction of cytotoxic T cells. By fusion of the cell-permeable translocation motif (TLM)-peptide to the capsid-forming core protein of hepatitis B virus, and by insertion of the strep-tag in the spike tip (a domain that protrudes from the surface of the capsid), cell-permeable carrier capsids were generated that can be flexibly loaded with various antigens. Loading with antigens was demonstrated by electron microscopy, density gradient centrifugation and surface plasmon resonance spectroscopy. Confocal immunofluorescence microscopy showed that cell-permeable carrier capsids mediate transfer of cargo antigen into the cytoplasm. Using cell-permeable carrier capsids loaded with ovalbumin as model antigen, activation of antigen presenting cells and ovalbumin-specific CD8+ T-cells, which correlates with enhanced specific killing activity, was found. This demonstrates the capacity of TLM-carrier-capsids to serve as universal antigen carrier to deliver antigens into the cytoplasm of antigen presenting cells, which leads to enhanced MHC class I-mediated presentation and induction of antigen-specific cytotoxic T lymphocytes response.

Highlights

Vaccination is one of the most effective means to combat infectious diseases
To use these particles as platform for antigen transfer into antigen presenting cells (APCs), a short adapter, based on the strep-tag III, was inserted in the spike tip domain of the translocation motif (TLM)-fused hepatitis B core antigen (HBcAg) protein to generate an universal carrier platform that can be flexibly loaded on its surface with variable antigens that are fused to streptavidin (Fig. 1a,b)
The confocal microscopy shows that in contrast to the free streptavidin-Ova, the streptavidin-Ova fusion protein loaded to the surface of the TLM-carrier capsids translocates across the plasma membrane into the cell (Fig. 5b). These results indicate that the TLM-carrier capsid can be efficiently loaded with the streptavidin-Ova fusion protein that serves as model antigen and that the antigen cargo is translocated by the TLM-carrier capsid into the cytoplasm of the target cells

Summary

Introduction

Vaccination is one of the most effective means to combat infectious diseases. Infections by new emerging pathogens such as Ebola or Zika virus that can rapidly reach epidemic levels require a concept for the rapid development of vaccines. Virus-like particles (VLPs) can be used as a vaccine platform for direct delivery of the antigen. The size of the inserted protein is limited and some structural requirements must be fulfilled: i.e. the distance between the N- and C-terminal domains of the inserted protein must fit in the opened spike tip[12]. To overcome this obstacle, alternatives to the direct insertion can be applied such as the chemical coupling of the foreign antigens to the capsid surface[13]. Other coupling systems, such as the covalet bond-forming tag/domain, the SpyTag/SpyCatcher[15, 16], can be applied as well

Methods

Results

Conclusion