The cationic liposome of  trehalose dimycolate (TDM) inducees antitumor immunity in bladder.
BCG therapy is the most effective immunotherapy for bladder cancer, but it sometimes causes serious adverse events because of infection with live BCG bacteria. To develop more effective and less toxic immunotherapeutic agents, we have developed formulations using BCG cell wall components. Trehalose dimycolate (TDM) is a predominant glycolipid that constitutes the cell wall of BCG, and reported to show activation of innate immunity and have adjuvant effect. We already established hydrophilic cationic liposomes incorporating TDM, and reported that local administration of the cationic liposome TDM (Lip-TDM) exerted antitumor effect to subcutaneously inoculated tumors by inducing activation of CD8+ T cells via dendritic cell maturation. In present study, we demonstrated that intraperitoneal administration of Lip-TDM exerted antitumor effects in orthotopic bladder carcinogenesis mouse model induced by N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN). In this model, intraperitoneal administration of Lip-TDM enhanced the systemic activation of dendric cells and macrophages, and increased infiltration of adaptive immune cells such as CD8+ T cells. Furthermore, Lip-TDM treatment induced Natural Killer (NK) cells to be cytotoxic NK cells in tumors and regulatory NK cells in lymphoid tissues. Lip-TDM treatment induced activation of DCs and cytotoxic CD8+ T cells and exerted antitumor effect in WT mice, but not in NK cell-depleted mice. These results indicate NK cells are essential for Lip-TDM to induce sufficient acquired immune response. Our findings elucidate the mechanism of the antitumor effect by Lip-TDM and suggest that Lip-TDM is a non-infectious agent which can be administered intraperitoneally and has potential to be an alternative to BCG. Overall design: RNA sequencing was performed using the bladders from the wild-type C57BL/6 mice treated with Lip-TDM or Lip-CON. Bladders were extracted from sacrificed animals at baseline and after 16 weeks of treatment.