Development of a vaccine based on bacteria‐mimicking tumor cells coated with novel engineered toll‐like receptor 2 ligands

For a successful tumor vaccine, it is necessary to develop effective immuno‐adjuvants and identify specific tumor antigens. Tumor cells obtained from surgical or biopsy tissues are a good source of tumor antigens but, unlike bacteria, they do not induce strong immune responses. Here, we designed 2 novel lipopeptides that coat tumor cell surfaces and mimic bacterial components. Tumor cells coated with these lipopeptides (called bacteria‐mimicking tumor cells [ BMTC ]) were prepared and their efficacy as a tumor vaccine examined. Natural bacterial lipopeptides act as ligands for toll‐like receptor 2 ( TLR 2) and activate dendritic cells ( DC ). To increase the affinity of the developed lipopeptides for the negatively charged plasma membrane, a cationic polypeptide was connected to Pam2Cys (P2C), which is the basic structure of the TLR 2 ligand. This increased the non‐specific binding affinity of the peptides for the cell surface. Two such lipopeptides, P2 CSK 11 (containing 1 serine and 11 lysine residues) and P2 CSR 11 (containing 1 serine and 11 arginine residues) bound to irradiated tumor cells via the long cationic polypeptides more efficiently than the natural lipopeptide MALP 2 (P2C‐ GNNDESNISFKEK ) or a synthetic lipopeptide P2 CSK 4 (a short cationic polypeptide containing 1 serine and 4 lysines). BMTC coated with P2 CSR 11 or P2 CSK 11 were efficiently phagocytosed by DC and induced antigen cross‐presentation in vitro. They also induced effective tumor‐specific cytotoxic T cell responses and inhibited tumor growth in in vivo mouse models. P2 CSR 11 activated DC but induced less inflammation‐inducing cytokines/interferons than other lipopeptides. Thus, P2 CSR 11 is a strong candidate antigen‐specific immuno‐adjuvant, with few adverse effects.