Biol. Pharm. Bull. 29(1) 100—104 (2006)

totoxic T lymphocytes (CTLs) could control tumor growth and metastasis. The identification of T cell-recognizing tumor-associated antigens (TAAs) in human cancer, particularly in melanoma (i.e. MAGE, MART-1, gp100, tyrosinase, and TRP), facilitated the development of cancer immunotherapy based on TAA-vaccination with adjuvants to elicit tumor-specific CTLs. However, this immunological approach limits the application of this system only to certain cancer patients because TAAs are not yet identified for most of human cancers. Additionally, the expression levels of known TAAs that may be applicable for immunotherapy vary between tumor cells isolated from patients with cancer. Therefore, it is very difficult to predict which TAA would generate an effective anti-tumor immune response that would make it appropriate for use as a vaccine component for a specific patient. To overcome this limitation, several researchers have attempted to develop a vaccine strategy using tumor cell-lysate (TCL) as a possible source of TAA. The use of TCL prepared from surgically removed tumors is a promising approach to induce a broader T cell-immune response not only to defined TAAs but also to unknown TAAs. In TCL-based cancer immunotherapy, the development of both an antigendelivery system and an adjuvant that can efficiently prime and propagate CTLs specific for TAAs included in the TCL is required for achieving sufficient therapeutic effect. CTLs are activated by antigen-presenting cells (APCs), including dendritic cells (DCs), through the major histocompatibility complex (MHC) class I-restricted antigen presentation pathway. Peptides presented on MHC class I molecules are derived in most situations exclusively from endogenous antigens synthesized by cells. Antigens in the extracellular fluids fail to gain access to the MHC class I-pathway in most cells, although class I-presentation of endocytosed antigens also occurs in APCs under certain circumstances. Therefore, if we can introduce the TAA-containing TCL directly into the cytoplasm, the TAAs would be definitively delivered to the MHC class I-antigen presentation pathway, much like cytoplasmic proteins. Fusion active liposomes (fusogenic liposomes; FLs), which are composed of conventional liposomes (CLs) displaying Sendai virus-accessory proteins, retain membranefusion activity derived from Sendai-virus and efficiently introduce its contents into cytoplasm. We have previously reported that direct antigen loading into cytoplasm by FLs is an efficient approach for enhancing antigen-specific CTL induction in mice. In the present study, in order to evaluate the usefulness of FLs as antigen-delivery carriers for TCL-based cancer immunotherapy, we investigated anti-tumor efficacy of ex vivo vaccination using TCL-containing FLs (TCL/FLs)pulsed DCs and in vivo direct TCL/FLs-immunization in the murine B16BL6 melanoma model.