IL-17-dependent, IFN-gamma-independent tumor rejection is mediated by cytotoxic T lymphocytes and occurs at extraocular sites, but is excluded from the eye

The Costimulatory Receptor OX40 Inhibits Interleukin-17 Expression through Activation of Repressive Chromatin Remodeling Pathways

T helper 17 (Th17) cells are prominently featured in multiple autoimmune diseases, but the regulatory mechanisms that control Th17 cell responses are poorly defined. Here we found that stimulation of OX40 triggered a robust chromatin remodeling response and produced a "closed" chromatin structure at interleukin-17 (IL-17) locus to inhibit Th17 cell function. OX40 activated the NF-κB family member RelB, and RelB recruited the histone methyltransferases G9a and SETDB1 to the Il17 locus to deposit "repressive" chromatin marks at H3K9 sites, and consequently repressing IL-17 expression. Unlike its transcriptional activities, RelB acted independently of both p52 and p50 in the suppression of IL-17. In an experimental autoimmune encephalomyelitis (EAE) disease model, we found that OX40 stimulation inhibited IL-17 and reduced EAE. Conversely, RelB-deficient CD4(+) T cells showed enhanced IL-17 induction and exacerbated the disease. Our data uncover a mechanism in the control of Th17 cells that might have important clinic implications.

Role of interferon-γ and cytotoxic T lymphocytes in intraocular tumor rejection

The eye is normally an immunosuppressive environment. This condition is better known as immune privilege and protects the eye from immune-mediated inflammation of tissues that cannot regenerate. However, immune privilege creates a dilemma for the eye when intraocular neoplasms arise. In some cases, immune privilege is suspended, resulting in the immune rejection of intraocular tumors. This study employed a mouse model in which interferon-γ-dependent intraocular tumor rejection occurs. We tested the hypothesis that this rejection requires interferon-γ for the generation and functional capacity of cytotoxic T lymphocyte-mediated rejection of intraocular tumors. Tumors grew progressively in the eyes of interferon-γ knockout mice, even though the mice generated tumor-specific cytotoxic T lymphocyte responses in the periphery. However, interferon-γ knockout mice rejected tumors that were introduced into extraocular sites. Subcutaneous tumor immunization before intraocular challenge led to tumor rejection and preservation of the eye in wild-type mice. By contrast, tumors grew progressively in the eyes of interferon-γ knockout mice despite their ability to generate peripheral tumor-specific cytotoxic T lymphocytes as well as the capacity of CD8(+) T cells to enter the eye as shown by the presence of CD8 and perforin message and CD3(+)CD8(+) leukocytes within the tumor-bearing eye. We found that cytotoxic T lymphocytes generated in wild-type mice and adoptively transferred into interferon-γ knockout mice mediated the rejection of intraocular tumors in interferon-γ knockout hosts. The results indicate that interferon-γ is critical for the initial priming and differentiation of cytotoxic T lymphocytes residing in the periphery to produce the most effect antitumor function within the eye.

IFN-γ-independent intraocular tumor rejection is mediated by a macrophage-dependent process that leaves the eye intact

Intraocular tumors reside in an immune-privileged site, yet in certain circumstances, they can undergo immune rejection. Ocular tumor rejection can follow one of two pathways. One pathway is CD4(+) T cell-dependent and culminates in ischemic necrosis of the tumor and phthisis (atrophy) of the eye. A second pathway is also CD4(+) T cell-dependent but does not inflict collateral injury to ocular tissues, and the eye is preserved. We isolated two clones of a murine tumor, Ad5E1 that undergo profoundly different forms of immune rejection in the eye. Clone 2.1 tumors undergo an ischemic necrotizing form of rejection that requires IFN-γ, T cells, and ocular macrophages and culminates in destruction of the eye. By contrast, the second clone of Ad5E1, clone 4, undergoes rejection that also requires T cells and ocular macrophages, but leaves the eye in pristine condition (nonphthisical rejection). Here, we demonstrate that nonphthisical tumor rejection of clone 4 tumors is IFN-γ-independent but requires an ocular macrophage population that contains M1 and M2 macrophages. Clone 4 tumor-bearing eyes displayed ten- and 15-fold increases in M2- and M1-associated markers Arg1 and NO2, respectively. This is in sharp contrast to previous results with clone 2.1 tumor rejection, in which M2 markers were undetectable, and the eye was destroyed. These results suggest that the presence of M2 macrophages tempers the immune rejection of intraocular tumors and promotes immune effectors that inflict minimal injury to innocent bystander cells and thereby preserve the integrity and function of the eye.