Macrophages are vital in spontaneous intraocular tumor eradication.

PURPOSE: Injection of tumor cells transformed by the early region 1 of human adenovirus type 5 (Ad5E1) in the anterior chamber (AC) of C57BL/6 mice leads to intraocular tumor formation. This tumor disappears spontaneously 3 to 4 weeks after tumor inoculation without damaging the neighboring ocular tissues. Previous studies have shown that CD4+ T cells, IFNgamma, and TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) play a role in the spontaneous eradication of this particular intraocular tumor. This study was conducted to determine whether macrophages are involved in the natural elimination of this intraocular tumor.

METHODS: Ad5E1-expressing tumor cells were inoculated into the AC of syngeneic C57BL/6 mice. Macrophage depletion was obtained by subconjunctival (scj), subcutaneous (sc), or intravenous (iv) injection of clodronate liposomes 2, 8, and 14 days after tumor inoculation. Control C57BL/6 mice received PBS liposomes at similar time points after tumor injection or were left untreated. The presence of macrophages in the AC tumor was determined with the macrophage marker F4/80.

RESULTS: Progressive tumor growth was observed in mice that were subconjunctivally depleted of macrophages, whereas spontaneous tumor eradication occurred in all other groups. F4/80 staining was negative in the AC tumors of mice treated scj with clodronate liposomes in contrast to the positive F4/80 staining in the tumors of the other groups. Ad5E1 tumor antigen still reached the tumor-draining lymph nodes (DLNs) of mice locally depleted for macrophages.

CONCLUSIONS: Local macrophages in the eye are involved in the process of spontaneous AC tumor eradication in mice. However, it is not conclusive from these data exactly how tumor-specific CD4+ T cells and macrophages interact with each other to eliminate the Ad5E1-AC tumor without any collateral eye damage.