Dynamic Observation: Immune-Privileged Microenvironment Limited the Effectiveness of Immunotherapy in an Intraocular Metastasis Mouse Model.

INTRODUCTION: Intraocular metastasis (IM) occurred in approximately 8-10% of patients with metastatic malignancy, for whom oncological immunotherapies showed poor visual potential. However, the mechanism for that inefficiency remains unclear and requires further exploration. METHODS: We established a novel mouse model of IM by intracarotid injection of cutaneous melanoma cells. We investigated disease progression using ophthalmic and histological examinations. We used combined anti-PD-1 and anti-CTLA4 antibodies for immunotherapy and evaluated the therapeutic effects in the mouse model. In addition, we characterized the immune microenvironment of tumor-infiltrating CD8+ T by fluorescence staining and assessed their cytotoxicity by flow cytometry. RESULTS: All mice presented IM in the left eye, while the right eye was healthy. Uveal tissues with rich vascularity (e.g., the iris, ciliary body, and choroid) initiated IM at an early stage, and IM development resulted in several secondary changes, including corneal swelling, retinal detachment, and intratumoral hemorrhage. Immunotherapy could inhibit IM and prolong the time to eye rupture but did not prevent rupture ending. This inefficiency might be attributed to ocular tissues specificities that inhibited CD8+ T-cell infiltration via PD-L1 expression. PD-L1low corneal tissue resisted tumor invasion with high levels of CD8+ T-cell infiltration, whereas CD8+ T cells were deficient in PD-L1high uveal metastasis. Furthermore, we found a significantly increased PD-1+/- CD4+ and PD-1+/- CD8+ T cells infiltrating the intratumoral hemorrhage area. Although these CD8+ T cells in the IM were not exhausted and had a higher capacity of cytotoxicity (higher interferon-γ ratio) than CD8+ T cells in the blood, FasL+ PD-L1+ ocular tissue can strongly inhibit these IM-infiltrating T cells. CONCLUSIONS: Immunotherapy can inhibit the disease progression of IM. Enhancing the effects of tumor-infiltrating CD8+ T cells should be one of the highest potentials to improve the visual potential.