Exosomal vaccines containing the S protein of the SARS coronavirus induce high levels of neutralizing antibodies

Abstract

Infection with the SARS-associated coronavirus (SARS-CoV) induces an atypical pulmonary disease with a high lethality rate. Although the initial SARS epidemic was contained, sporadic outbreaks of the disease still occur, suggesting a continuous need for a vaccine against this virus. We therefore explored exosome-based vaccines containing the spike S proteins of SARS-CoV. S-containing exosomes were obtained by replacing the transmembrane and cytoplasmic domains of the S protein by those of VSV-G. The immunogenicity and efficacy of the S-containing exosomes were tested in mice and compared to an adenoviral vector vaccine expressing the S protein. Both, S-containing exosomes and the adenoviral vector vaccine induced neutralizing antibody titers. After priming with the SARS-S exosomal vaccine and boosting with the adenoviral vector the neutralizing antibody titers exceeded those observed in the convalescent serum of a SARS patient. Both approaches were effective in a SARS-S-expressing tumor challenge model and thus warrant further investigation.

Antigen-loaded exosomes alone induce Th1-type memory through a B cell–dependent mechanism

“…Exosomes are actively secreted by a diverse range of cells, and especially DC-derived exosomes have acquired much attention because they harbor all the necessary molecules required for the activation of potent immune responses, for example, MHC I and MHC II, CD54, CD80, and CD86, on their surface. 2 The initial investigations have shown the biologic significance of exosomes in different areas of research, such as tumor and transplantation immunology, [3][4][5][6][7] vaccine therapy against infection, [8][9][10] as well as a biomarker for diagnostic purposes. 11 Exosome-based tumor vaccines have recently been tested in phase 1 clinical trials in melanoma, nonsmall cell lung cancer, and colorectal cancer patients.…”

Enhancement of immunostimulatory properties of exosomal vaccines by incorporation of fusion-competent G protein of vesicular stomatitis virus

“…Eight hours after transfection the FCS-containing medium was changed into the serum-free CD293 medium (Invitrogen). The conditioned medium was harvested 24 h later and the ELV were concentrated by ultracentrifugation through 20% sucrose cushion as described previously [9]. For the step gradient ultracentrifugation, the pelleted ELVs were resuspended in PBS and loaded onto a sucrose gradient containing 60, 50, 40, 30, 20 and 10% of sucrose and centrifuged for 2 h at 30,000 rpm.…”

“…Western blot analysis was performed as described previously [9]. Blots were incubated with a rabbit anti-OVA, mouse anti-VSV-G antiserum (Sigma-Aldrich) or mouse anti-HSP90 antibodies (Santa Cruz Biotechnology Inc., Heidelberg, Germany).…”

“…For the surface staining rabbit anti-OVA and FITC-conjugated anti-rabbit IgG Ab were used. The expression analysis was performed as described [9].…”

“…We recently demonstrated that replacing the transmembrane and cytoplasmic domain of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) S protein with that of the G protein of vesicular stomatitis virus (VSV-G) resulted in enhanced shedding of the S protein in a vesicle-associated form into the supernatant of transfected 293T cells. The presence of proteins such as HSP90 and CD82 indicated an exosome-like nature of these vesicles [9]. Viral fusion proteins might provide an attractive strategy to enhance uptake of the exosomal vaccines by professional antigen presenting cells and thus improve the immunogenicity.…”