CD4+ T Cells, IFN and Macrophages Play an Important Role in the Spontaneous Eradication of an Intraocular Tumor

Abstract

Abstract: : Purpose: The Ad5E1-expressing tumor in the anterior chamber (AC) disappears spontaneously 3 to 4 weeks after tumor inoculation without damage in the neighboring ocular tissues. This is a CD4⁺ T cell mediated process. We whished to investigate which immunological cells besides CD4⁺ T cells are involved in the spontaneous eradication of these intraocular tumors. Methods: The Ad5E1-expressing tumor was inoculated into the AC of syngeneic C57BL/6 mice and IFNγ KO mice. Macrophages were depleted either locally or systemically by treating the mice with clodronate-containing liposomes 2, 4 and 8 days post-tumor inoculation. Control mice received PBS-containing liposomes either subconjunctivally (scj.), subcutaneously (s.c.) in the neck area or intravenously (i.v.) at similar time points post tumor injection. Tumor growth in the AC was determined macroscopically, histologically and immuno-histochemically. Additionally, antigen presentation in several lymphoid organs was investigated by adoptively transferring CFSE labeled E1A-specific CD8⁺ T cells from TCR-transgenic C57BL/6 into macrophage-depleted and non-depleted mice, which were analyzed for clonal expansion and activation by flow cytometry. Results: Progressive tumor growth was observed in mice locally depleted (scj.) for macrophages and in IFNγ KO mice. Spontaneous tumor eradication still occurred in all mice injected i.v. with clodronate-containing liposomes and in half the mice which received s.c. clodronate-liposomes injections in the neck area and in all the control mice. Immuno-histochemistry of treated AC tumors showed no macrophage-staining in contrast to the eyes of control-treated animals. Activated tumor-specific CD8⁺ T cells were still observed in the tumor-draining submandibular lymph nodes in mice locally depleted (scj and sc) for macrophages. Conclusions: Our results show that both macrophages and IFNγ, besides CD4⁺ T cells, are involved in the process of spontaneous AC tumor eradication. Macrophages are effector cells rather than antigen presenting cells, since antigen was still presented in the tumor draining lymph nodes in depleted mice. Thus, our observations show that multiple cell types as well as effector molecules are involved in tumor eradication, which might act in an orchestral fashion or independently.

Keywords: immunomodulation/immunoregulation • tumors • anterior chamber