Bee Venom Phospholipase A2, a Good "Chauffeur" for Delivering Tumor Antigen to the MHC I and MHC II Peptide-Loading Compartments of the Dendritic Cells: The Case of NY-ESO-1.

Christine Almunia,Gerhard Held,Daniel Gillet,Bernard Maillere,Aurélie Babon,André Ménez,Marie Bretaudeau,Florence Anne Castelli,Charles Marchetti,Silke Appel

doi:10.1371/journal.pone.0067645

Abstract

Bee venom phospholipase A2 (bvPLA2) is a small, 15kDa enzyme which hydrolyses many phospholipids through interfacial binding. The mutated bvPLA2H34Q (bvPLA2m), in which histidine-34 is replaced by glutamine, is not catalytically active. This protein has been shown to be a suitable membrane anchor and has been suggested as a suitable tumor-antigen vector for the development of novel dendritic cell-based vaccines. To confirm this feature, in this study the fusion protein PNY, composed of NY-ESO-1(NY(s)) fused to the C-terminus of bvPLA2m, was engineered. bvPLA2m enhanced the binding of NY(s) to the membrane of human monocyte-derived dendritic cells (DCs) and, once taken up by the cells, the antigen fused to the vector was directed to both MHC I and MHC II peptide-loading compartments. bvPLA2m was shown to increase the cross-presentation of the NY(s)-derived, restricted HLA-A*02 peptide, NY-ESO-1157-165(NY157-165), at the T1 cell surface. DCs loaded with the fusion protein induced cross-priming of NY(s)-specific CD8 + T-cells with greater efficiency than DCs loaded with NY(s). Sixty-five percent of these NY(s)-specific CD8+ T-cell lines could also be activated with the DCs pulsed with the peptide, NY157-165. Of these CD8+ T-cell lines, two were able to recognize the human melanoma cell line, SK-MEL-37, in a context of HLA-A*02. Only a small number of bvPLA2m CD8+ T-cell lines were induced, indicating the low immunogenicity of the protein. It was concluded that bvPLA2m can be used as a membrane-binding vector to promote MHC class II peptide presentation and MHC class I peptide cross-presentation. Such a system can, therefore, be tested for the preparation of cell-based vaccines.

Highlights

Experimental vaccines, which have been studied primarily in the context of advanced cancers, have not, to date, been as successful as expected
The mutant bvPLA2m was shown to be able to augment the capture of NY(s) by dendritic cells (DCs), enhance NY(s)-derived peptide cross-presentation and promote the cross-priming of NY-ESO-1-specific CD8+ T-cells capable of recognizing human melanoma cells expressing NY-ESO-1
The bvPLA2m in PNY increases the anchorage of NY(s) to the surface of the DCs at least twice as much as NY(s) alone during the first two hours of incubation, taking into account the fact that NY-ESO-1 is internalized into the DCs via the calreticulin at the surface membrane [22]

Summary

Introduction

Experimental vaccines, which have been studied primarily in the context of advanced cancers, have not, to date, been as successful as expected. For complete T-cell activation and a productive immune response, cancer vaccines must be formulated with mature, antigen-pulsed DC(s), expressing the proper co-stimulatory molecules and bearing peptide-derived tumor protein on both MHC class I and class II molecules [4,5,6]. Apart from the conventional presentation of epitopes derived from exogenous antigens on MHC class II molecules, DCs can shuttle exogenous antigens to the MHC class I processing pathway for CD8+ Tcell activation in a special context [8,9]. This process, termed cross-presentation, plays a major role in immune defense against tumors. The challenge of defining the conditions and cellular context required for inducing a CD8+ T-cell response with antigen-pulsed dendritic cells has led to the design of a large number of vaccine strategies depending on peptide cross-presentation

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