Augmented local immunity in the liver by a streptococcal preparation, OK432, related to antitumor activity of hepatic macrophages

Kupffer cells decrease metastasis of colon cancer cells to the liver in the early stage

Although Kupffer cells (KCs) play an important role in the liver's immune response, their role in colon cancer metastasis to the liver is unclear. We here analyzed the relationship between KCs and tumor cells (TCs) in colon cancer metastasis to the liver. Fischer 344 (F344) rats were divided into control group (KC+ group) and KC elimination group (KC‑ group), in which KC elimination was induced by Cl2MDP liposome injection. RCN‑H4 colon cancer cells were injected into the rats of both groups, and the relationship between the two types of cells was observed by intravital microscopy (IVM) for 6 h. Moreover, to investigate the effect of KCs on liver metastasis formation, KCs were eliminated at different time points before and after the TC injection. The number of metastatic nodules 2 weeks after the injection was evaluated. In the KC‑ group, IVM revealed that the number of adherent TCs had increased 1.5‑fold at 6 h after the TC injection as compared with in the KC+ group. Moreover, in the KC+ group, 74% of the TCs adhered to the KCs, and KC activation and KC phagocytosis of the TCs were observed. Two weeks after the injection, the number of metastatic nodules was significantly increased in rats in which the KCs had been eliminated before the injection, but not in rats in which the KCs had been eliminated after the injection. KC activation and KC phagocytosis of TCs decreased colon cancer cell metastasis to the liver.

Liposome-encapsulated OK-432 specifically and sustainedly induces hepatic natural killer cells and intermediate T cell receptor cells

BACKGROUND

OK-432 is a biological response modifier used in Japan to augment host immunity and is known to increase the host antitumour response. By using liposomes, which are vesicles made from phospholipids that have a structure resembling the cell membrane, we encapsulated OK-432.

METHODS AND RESULTS

Encapsulated OK-432 was injected into the tail veins of mice, and its effect was compared with that of unencapsulated OK-432 given intravenously. In mice that received either form of OK-432, both the number of natural killer (NK) and intermediate T cell receptor (intTCR) cells (intrahepatic T cells generated by extrathymic differentiation) increased markedly in the liver, with the peak level occurring 3 days after administration. Both forms of OK-432 also increased cytotoxic activity against Yac-1 cells. The increase in numbers of cells and in cytotoxic activity in the liver persisted for longer in mice that received encapsulated OK-432 than in animals that received unencapsulated OK-432.

CONCLUSIONS

Because it has been shown that both NK and intTCR cells play an important role in tumour immunity, an increase in the number of such cells can be considered likely to have an increased antitumour effect. Encapsulated OK-432 elicited liver-specific augmentation of cytotoxic activity and the effect was more persistent than that produced by OK-432 given in the conventional form; therefore, it may be useful for the treatment of tumours, particularly those arising in the liver.