Growth inhibition of virus-infected tumor cells by specific elimination of tumor infiltrating macrophages

Abstract

Subcutaneously injected, virus-infected Meth A tumor cells grow time-dependently to reach a peak on days 7-12, and are rejected around 3 weeks after injection. However, we reported recently that the rejection, but not the growth, phase was delayed after the specific elimination of macrophages by i.v. injections of dichloromethylene diphosphonate (DMDP)-liposomes. In the present study, we examined the effects of s.c. injections of DMDP-liposomes on the growth of s.c. injected, virus-infected Meth A tumor cells. Of particular interest, the tumor cells were rejected without growth after DMDP-liposome treatment, whereas s.c. injections of PBS-liposomes had no effect on the tumor growth and the rejection. These results suggest that at least two types of macrophages infiltrated into tumor. One infiltrated into tumor at early phase after tumor transplantation to stimulate the growth of virus-infected tumor cells; and the other infiltrated into tumor at late phase after the transplantation to reject the virus-infected tumor cells. [Jpn J Physiol 55 Suppl:S78 (2005)]