Elsevier

Vaccine

Volume 24, Issue 11, 10 March 2006, Pages 1880-1888
Vaccine

CpG oligodeoxynucleotides activate dendritic cells in vivo and induce a functional and protective vaccine immunity against a TERT derived modified cryptic MHC class I-restricted epitope

https://doi.org/10.1016/j.vaccine.2005.10.036Get rights and content

Abstract

The use of synthetic peptides derived from tumor-associated Ags is attractive for the development of antitumoral vaccines as far as strong adjuvants are found to render them immunogenic. Here, we investigated the possibility to enhance the CD8 response against the human and mouse shared TERT572Y HLA-A*0201 restricted modified cryptic peptide by using ODN-CpG as adjuvant. Humanized transgenic mice were immunized with the TERT572Y modified cryptic peptide in the presence of ODN-CpG and compared to mice immunized in IFA. By contrast with IFA, we first showed that, in vivo, ODN-CpG leads to the recruitment of dendritic cells in the lymph nodes draining the injection site. Those cells and especially the CD11c+ CD11b CD8a+ lymphoid and the CD11c+ B220+ plasmacytoid dendritic cells were activated as shown by up-regulation of CD40 at their cell surface. Immunization against TERT572Y peptide in the presence of ODN-CpG rather than IFA led to a strong CD8 response and can delayed mortality in an induced tumor model. Study of the CD8 response obtained after antigenic challenge suggested that a functional memory response is induced upon vaccination with ODN-CpG. Thus, MHC class I-restricted epitope in combination of ODN-CpG is a promising and rather simple cancer vaccine formulation.

Introduction

The identification of CTL-defined tumor-associated Ag has allowed for the development of new strategies for cancer therapy based on the use of synthetic peptides. Since numerous tumor Ag are self proteins involved in the negative selection of the T cell repertoire [1], the efficiency of this approach depends on the capacity of the vaccination strategy to bypass the immune tolerance against self tumor antigens. In this regard, the tumor Ag-derived peptide has to be carefully selected and the conditions for vaccination optimized.

We previously found that low affinity tumor Ag-derived peptides (so-called cryptic peptides) which are weakly presented at the cell surface and thus weakly involved in the T cell negative selection are better candidates than high affinity ones (so-called dominant peptides) [2], [3]. The substitution of the first amino acid of these low affinity peptides, involved in their interaction with the MHC class I molecule, importantly increased their immunogenicity [4]. The CD8 T cells generated against the modified cryptic peptides are able to cross recognize their low affinity native counterpart [2].

Among the different actors involved in the expansion of a functional CD8 T cell response, the appropriate presentation of antigen by activated dendritic cells (DC) is required. DC mature upon different danger signals and adjuvants are thought to mimic these danger signals. Besides IFA which has been so far commonly used in experimental models of vaccination, new potent bacterial derived adjuvants such as ODN-CpG have been identified [5]. Moreover, their strong DC activating effect [6] suggests that a concomitant T helper CD4 T cell response could be avoided which would be of particular interest in humans in view of simplifying vaccine formulation.

In this paper, we investigated the possibility of enhancing the CD8 response against the human and mouse shared TERT572Y HLA-A*0201 restricted modified cryptic peptide by using ODN-CpG as an adjuvant. HLA-A*0201 transgenic HHD mice [7] were immunized with the TERT572Y modified cryptic peptide in the presence of ODN-CpG and compared to HHD mice immunized in IFA. We first assessed the influence of the two different adjuvants on the recruitment and activation status of APC in the lymph node draining the injection site. A strong activation of lymphoid and plasmacytoid dendritic cells was only observed in mice injected with ODN-CpG. Then, we directly monitored the peptide-specific CD8+ T cell response in both conditions of vaccination by tetramer staining ex vivo and examined the functionality of specific T cells by measuring their IFN-γ production. ODN-CpG are more effective than IFA to recruit specific CD8+ T cells against TERT572Y peptide and to induce a functional memory response. This conclusion is confirmed in vivo thanks to results obtained in a tumoral challenge which prove that two vaccinations of HHD mice with ODN-CpG and TERT572Y delayed significatively mortality as compared with vaccinations with IFA.

Section snippets

Cell lines

Previously described EL4/HHD cells [7] were kindly provided by Pr. François Lemonnier (Institut Pasteur, Paris, France) and maintained in DMEM medium supplemented with 1% HEPES, 1% strepto-penicillin and 10% heat inactivated fetal calf serum (FCS).

Synthetic peptides, ODN-CpG

TERT572 (RLFFYRKSV), TERT572Y (YLFFYRKSV) and the control gp100209 (ITDQVPFSV) were made by Epytop (Nîmes, France). The immunostimulatory synthetic ODN-CpG 1826 optimized for stimulation of the mouse immune system (TCCATGACGTTCCTGACGTT) were used (CpG

ODN-CpG induce the recruitment and the activation of dendritic cells in the lymph nodes draining the injection site

We compared the absolute number of cells recruited in the draining lymph nodes of mice injected with 50 μg ODN-CpG, IFA or PBS 18 h before (Table 1). A significant increase in the absolute number of cells was defined by the mean value in the experimental group higher than the mean value plus 3 S.D. in PBS injected mice. First, variability between individuals was observed. Two out of six mice injected with ODN-CpG and one out six mice injected with IFA presented an increase in the absolute number

Discussion

The use of synthetic peptides derived from tumor-associated Ags is attractive for the development of antitumoral vaccines. However, these compounds are usually not very immunogenic unless they are administered in combination with a strong adjuvant. In the present study, we demonstrate the potent role of ODN-CpG as an adjuvant of the CD8 response directed against TERT-derived modified cryptic peptide. By contrast with IFA, we first show that, in vivo, ODN-CpG leads to the recruitment of

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