Verbesserung der immunstimulatorischen Wirkung von Tumorantigenen durch liposomale Vektoren

Abstract

Introduction: Immunodominant epitopes from tumor associated antigens (TAA) are currently used as soluble peptides (SP) in clinical trials in spite of an acknowledged low immunogenicity. We asked whether encapsulation into liposomes (LP) could improve their immunogenic capacity. Materials and Methods: The HLA-A2 restricted melanoma associated epitope Mart_26–35 was synthesized and included into sterically stabilized liposomes, characterized by prolonged bio-availability in biological fluids in comparison with conventional reagents. Proliferation, cytokine production and cytotoxicity induced by either LP or SP in Mart_26-35 specific CTL clones were evaluated by 3H-thymidine incorporation, ELISA and ⁵¹Cr release assays. To assess the induction of specific CTL, peripheral blood mononuclear cells (PBMC) from healthy donors were stimulated with autologous antigen presenting cells and LP or SP. Cytotoxic activity was evaluated by ⁵¹Cr release. Results: Proliferation of CTL clones could be comparably stimulated by saturating doses (> 100 ng/ml) of either SP or LP. At limiting concentrations (< 50 ng/ml), however, only LP were effective. IFN-γ production by specific CTL was also enhanced by LP as compared to SP stimulation. Furthermore, LP displayed a significantly higher capacity of sensitizing target cells to the cytotoxic effects of specific CTL clones as compared to SP. Most importantly, LP were able to induce specific cytotoxic activity in healthy donors PBMC, following a limited number of restimulation courses (n = 2). In the same conditions SP was totally ineffective. Conclusion: These data indicate that the specific immunostimulatory capacity of Mart_26-35 melanoma associated epitope can be significantly improved by encapsulation into sterically stabilized liposomes.