Virosome vaccines and their application in cancer immunotherapy

Background: An increasing number of tumor associated antigens (TAA) capable of inducing immune responses have been identified in the last two decades. Unfortunately, they are weak immunogens and require potent adjuvants to promote their immunogenicity. Virosomes, nano-lipid vesicles containing viral protein spikes, have been proven amenable for transferring antigen (Ag) to the major histocompatibility complex (MHC) class I processing pathway with the aim to prime cytotoxic T-ymphocytes (CTL) responses. Objective: This mini-review outlines the virosomes platform, ranging from virosomal preparation, their intracellular trafficking and mechanism of action. Methods: The review is directed toward an application of virosomes as a novel and potential vaccine adjuvant in active cancer immunotherapy. Results and conclusion: Virosomes have been proven to be a suitable TAA delivery carrier. Ag encapsulated inside the lumen of virosomes could be prevented from serum- and cell-associated peptidases. Virosomes also facilitated the intracellular trafficking of encapsulated Ag, in which Ag could reach the cytosol and be presented by the MHC-Class I machinery. In addition, virosomes with TAA encapsulated are amenable to be a novel tumor immunotherapeutic strategy.

Identification of predicted epitopes of HLA-A*0201-restricted cytotoxic T lymphocytes derived from human papillomavirus type 11 E7 antigen / 中华微生物学和免疫学杂志

Objective To screen and identify the predicted epitopes of synthesized HLA-A*0201restricted CTL derived from HPVll E7 antigen.Methods Five HPVll E7 CTL epitope peptides and terramers consisting of HLA-A*0201 were selected by way of computer and synthesized by Sanquin company,including HPVllE7 7-15(TLKDIVLDL),15-23(LQPPDPVGL),47-55(PLTQHYQIL),81-89(DLLLGTLNI)and 82-90(LLLGTLNIV).These peptides binding to human peripheral blood-derived DCs were tested for their ability to activate T cells isolated from peripheral blood lymphocytes of HLA-A*0201 healthy individuals.the number of specific tetramer+CD8+T cells by flow cytometry,the level of the section of IFN-γ by ELISA,and the ability of the CTL to kill the target cells were observed.Results The immature DCs could be fully activated by all the five HPV11 E7 peptides.Peptide-loaded mature DCs were able to stimulate the epitope-specific T cells responses in vitro.An increased frequency(P<0.05)of T ceils specific for the E7 7-15 epitope compared to other epitopes of HPV11E7.The epitope-specific CTL of E7 7-15 induced by the activated DCs specifically killed HPV11E7 expressing 293 cell line,and in a ratio of 50:1,the specific cytolytic activity was the strongest than the others(P<0.05).Conclusion DCs loaded with HPV11 E7 7-15(TLKDIVLDL)peptide can induce highly effective and specific ectogenic processed epitopespecific CTL responses in vitro.This peptide may be the candidate for development of CTL based vaccine in the treatment of HPV infeetions.

IL-12 Production and Subsequent Natural Killer Cell Activation by Necrotic Tumor Cell-loaded Dendritic Cells in Therapeutic Vaccinations

BACKGROUND: Immunization of dendritic cells (DCs) pulsed with tumor antigen can activate tumor-specific cytotoxic T lymphocytes (CTL) that are responsible for protection and regression. In this study, we examined whether the uptake of necrotic tumor cells could modulate DC phenotypes and whether the immunization of necrotic tumor cell-loaded DCs could elicit efficient tumor specific immune responses followed by a regression of established tumor burdens. METHODS: We prepared necrotic tumor cell-pulsed DCs for the therapeutic vaccination and investigated their phenotypic characteristics, the immune responses induced by these DCs, and therapeutic vaccine efficacy against colon carcinoma in vivo. Several parameters including phagocytosis of tumor cells, surface antigen expression, chemokine receptor expression, IL-12 production, and NK as well as CTL activation were assessed to characterize the immune response. RESULTS: DCs derived from mouse bone marrow efficiently phagocytosed necrotic tumor cells and after the uptake, they produced remarkably increased levels of IL-12. A decreased CCR1 and increased CCR7 expression on DCs was also observed after the tumor uptake, suggesting that antigen uptake could induce DC maturation. Furthermore, co-culturing of DCs with NK cells in vitro enhanced IL-12 production in DCs and IFN-gamma production in NK cells, which was significantly dependent on IL-12 production and cell-to-cell contact. Immunization of necrotic tumor cell-loaded DCs induced cytotoxic T lymphocytes as well as NK activation, and protected mice against subsequent tumor challenge. In addition, intratumoral or contra-lateral immunization of these DCs not only inhibited the growth of established tumors, but also eradicated tumors in more than 60% of tumor-bearing mice. CONCLUSION: Our data indicate that production of IL-12, chemokine receptor expression and NK as well as CTL activation may serve as major parameters in assessing the effect of tumor cell-pulsed DC vaccine. Therefore, DCs loaded with necrotic tumor cells offer a rational strategy to treat tumors and eventually lead to prolonged survival.

Induction of CEA-specific Cytotoxic T Lymphocytes by Murine Dendritic Cells Expressing CEA

BACKGROUND: Carcinoembryonic antigen (CEA) is well-known soluble tumor marker frequently detectable in peripheral blood of carcinoma patients and considered as good target for antigen-specific immunotherapy. In this study, we used a replication-deficient adenovirus containing CEA to study CTL induction in vitro after adenovirus-mediated gene transfer into DC. METHODS: DC were obtained from mouse bone marrow and cultured with IL-4 and GM-CSF. For measuring CTL activity, splenocytes were harvested from the mice, which were immunized with DC that had been infected AdV-CEA or pulsed with CEA peptide. Untreated DC was used as a control. Splenocytes were re-stimulated in vitro with DC pulsed with CEA peptide for 7 days and CTL activity with CEA peptide-pulsed EL-4 cells were assessed in a standard 51Cr-release assay. The frequencies of antigen-specific cytokine-secreting T cell were determined with mIFN-gamma ELISPOT. RESULTS: DC infected with recombinant adenovirus expressing CEA induced CEA-specific CTL responses in vivo. Splenocyte induced from mice immunized with AdV-CEA-infected DC increase in the number of IFN-gamma secreting T cells compared with those from mice immunized with CEA peptide-pulsed DC. CONCLUSION: These results suggested that DC infected with recombinant adenovirus has advantages over other forms of vaccination and could provide an alternative approach vaccination therapies.