Liposomes containing interferon-gamma as adjuvant in tumor cell vaccines

Abstract

Purpose. Liposomal systems may be useful as a cytokine supplement in tumor cell vaccines by providing a cytokine reservoir at the antigen presentation site. Here, we examined the effect of liposome incorporation of mIFNγ on its potency as adjuvant in an established tumor cell vaccination protocol in the murine B16 melanoma model. Adjuvanticity of the mIFN-γ- liposomes was compared to that achieved by mIFNγ-gene transfection of the B16 tumor cells. Furthermore, we studied whether liposomal incorporation of mIFNγ indeed increases the residence time of the cytokine at the vaccination site. Methods. C57B1/6 mice were immunized with i) irradiated IFNγ-gene transfected B16 melanoma cells or ii) irradiated wild type B16 cells supplemented with (liposomal) mIFNγ, followed by a challenge with viable B16 cells. The residence time of the (liposomal) cytokine at the subcutaneous (s.c.) vaccination site was monitored using radiolabeled mIFNγ and liposomes. Results. Immunization with irradiated tumor cells admixed with liposomal mIFNγ generated comparable protection against B16 challenge as immunization with mIFNγ-gene modified tumor cells. Irradiated tumor cells admixed with soluble mIFNγ did not generate any protective responses. Radiolabeling studies indicated that free mIFNγ rapidly cleared from the s.c. injection site. Association of [125I]-mIFNγ with liposomes increased the local residence time substantially: liposomal association of mIFNγ resulted in a prolonged local residence time of the cytokine as reflected by a 4-fold increase of the area under the curve. The amount of released cytokine in the optimal dose range corresponds to the amount released by the gene-transfected cells. Moderate but significant CTL-activity against B16 cells was found for mice immunized with irradiated cells supplemented with mIFNγ-liposomes compared to untreated control animals. Conclusions. Prolonged presence of mIFNγ at the site of antigen presentation is crucial for the generation of systemic immune responses in the B16 melanoma model. These studies show that liposomal encapsulation of cytokines is an attractive strategy for paracrine cytokine delivery in tumor vaccine development.