Splenectomy Promotes Indirect Elimination of Intraocular Tumors by CD8+ T Cells That Is Associated with IFNγ- and Fas/FasL-Dependent Activation of Intratumoral Macrophages

Abstract

Ocular immune privilege (IP) limits immune surveillance of intraocular tumors as certain immunogenic tumor cell lines (P815, E.G7-OVA) that are rejected when transplanted in the skin grow progressively when placed in the anterior chamber (a.c.) of the eye. As splenectomy (SPLNX) is known to terminate ocular IP, we characterized immune mechanisms responsible for rejection of intraocular tumors in SPLNX mice as a first step toward identifying how to restore tumoricidal activity within the eye. CD8+ T cells, IFNγ, and FasL, but not perforin, or TNFα were required for elimination of intraocular E.G7-OVA tumors that culminated in destruction of the eye (ocular phthisis). IFNγ and FasL did not target tumor cells directly as the majority of SPLNX IFNγR1−/− mice and Fas defective lpr mice failed to eliminate intraocular E.G7-OVA tumors that expressed Fas and IFNγR1. Bone marrow chimeras revealed that IFNγR1 and Fas expression on immune cells was most critical for rejection and SPLNX increased the frequency of activated macrophages (Mϕ) within intraocular tumors in an IFNγ-and-Fas/FasL-dependent manner suggesting an immune cell target of IFNγ and Fas. As depletion of Mϕs limited CD8 T cell-mediated rejection of intraocular tumors in SPLNX mice, our data support a model in which IFNγ-and-Fas/FasL-dependent activation of intratumoral Mϕs by CD8+ T cells promotes severe intraocular inflammation that indirectly eliminates intraocular tumors by inducing phthisis, and suggests that immunosuppressive mechanisms which maintain ocular IP interfere with the interaction between CD8+ T cells and Mϕs to limit immunosurveillance of intraocular tumors.

Beyond the tumour microenvironment

“…Importantly, these observations suggest that the distant environment (the spleen in this case) can represent a useful therapeutic target to affect primary tumour progression. Similar findings were reported in other cancer types . Along these lines, increased risk of malignancies has been observed in follow‐up studies of patients subjected to splenectomy .…”

“…Similar findings were reported in other cancer types. 29,30 Along these lines, increased risk of malignancies has been observed in follow-up studies of patients subjected to splenectomy. 31,32 Of note, in some reports, a tumour-promoting effects of splenectomy has been observed, associated with increased number of FoxP3 + regulatory T cells at the metastatic sites.…”

Splenectomy restores tumoricidal activity to promote elimination of intraocular tumors

“…4 However, we demonstrated that CD4 C T cells were not required for rejection of intraocular tumors; 2 rather, CD8 C T cells were indispensable. 2 The simplest explanation for how the spleen limits immunosurveillance of intraocular tumors is that CD8 C T-cell tolerance to tumor antigens arises in the spleen, which is supported by our previous study indicating that introduction of soluble antigens into the anterior chamber induced expansion but functional inactivation of antigen-specific CD8 C T cells. 5 However, we and others have shown that intraocular tumor growth does not induce systemic CD8 C T-cell tolerance.…”

“…1) but not perforin or TNFa. 2 IFNg and FasL did not target tumor cells directly as SPLNX IFNgR1 ¡/¡ and Fas-defective lpr mice failed to eliminate intraocular tumors that expressed IFNgR1 and Fas. 2 Bone marrow chimeric mice indicated that rejection of intraocular tumors in SPLNX mice required IFNgR1 and Fas expression on immune cells, and SPLNX increased the frequency of activated macrophages within intraocular tumors in an IFNg and Fas/FasL-dependent manner suggesting a cellular target for IFNg and FasL.…”

“…2 IFNg and FasL did not target tumor cells directly as SPLNX IFNgR1 ¡/¡ and Fas-defective lpr mice failed to eliminate intraocular tumors that expressed IFNgR1 and Fas. 2 Bone marrow chimeric mice indicated that rejection of intraocular tumors in SPLNX mice required IFNgR1 and Fas expression on immune cells, and SPLNX increased the frequency of activated macrophages within intraocular tumors in an IFNg and Fas/FasL-dependent manner suggesting a cellular target for IFNg and FasL. Intratumoral macrophages were necessary at the effector stage as the elimination of intraocular tumors in SPLNX mice deficient for CD8 C T cells given ACT therapy with activated OT-I CD8 C T-cell effectors was abrogated if intratumoral macrophages were eliminated by local administration of clodronate liposomes.…”