Stephen E. Ullrich

Immune suppression and skin cancer development: regulation by NKT cells.

Ultraviolet (UV) radiation is carcinogenic and immunosuppressive. UV-induced immune suppression is mediated by antigen-specific T cells, which can transfer suppression to normal recipients. These cells are essential for controlling skin cancer development in the UV-irradiated host and in suppressing other immune responses, such as delayed-type hypersensitivity. Despite their importance in skin cancer development, their exact identity has remained elusive. We show here that natural killer T cells from UV-irradiated donor mice function as suppressor T cells and play a critical role in regulating the growth of UV-induced skin cancers and suppressing adaptive immune responses in vivo.

The role of IL-4, IL-10, and TNF-α in the immune suppression induced by ultraviolet radiation

Cytokines produced by keratinocytes play an essential role in the induction of immune suppression following ultraviolet (UV) exposure. Using antibodies specific for either interleukin‐10 (IL‐10) or tumor necrosis factor α (TNF‐α), we present evidence indicating that IL‐10 suppresses delayed‐type hypersensitivity (DTH) but not contact hypersensitivity (CHS), whereas TNF‐α suppresses CHS but not DTH following UV exposure. UV exposure also activates antigen‐specific suppressor T cells. To determine whether the antigen‐specific CD4+ T cells that transfer suppression in this system mediate their suppressive effect by releasing IL‐4 or IL‐10, we transferred UV Ts into normal mice that were then injected with either anti‐IL‐4 or anti‐IL‐10 antibody. Both anti‐ IL‐4 and anti‐IL‐10 blocked the ability of UV Ts cells to suppress DTH in the recipient animals. When UV Ts that suppress CHS were transferred into normal recipients, however, neither antibody was able to block the UV Ts activity. These findings suggest that UV Ts suppress DTH by secreting IL‐4 and IL‐10 and appear to act like Th2 cells. Because anti‐IL‐4 and anti‐IL‐10 did not block the activity of the UV Ts that regulate contact hypersensitivity, their effects appear to be mediated by a different mechanism. J. Leukoc. Biol. 56: 769–775; 1994.

Metastasis is regulated via microRNA-200/ZEB1 axis control of tumour cell PD-L1 expression and intratumoral immunosuppression

Immunosuppression of tumor-infiltrating lymphocytes (TIL) is a common feature of advanced cancer, but its biological basis has remained obscure. We demonstrate here a molecular link between epithelial-to-mesenchymal transition (EMT) and CD8+ TIL immunosuppression, two key drivers of cancer progression. We show that microRNA-200 (miR-200), a cell-autonomous suppressor of EMT and metastasis, targets PD-L1. Moreover, ZEB1, an EMT activator and transcriptional repressor of miR-200, relieves miR-200 repression of PD-L1 on tumor cells, leading to CD8+ T cell immunosuppression and metastasis. These findings are supported by robust correlations between the EMT score, miR-200 levels and PD-L1 expression in multiple human lung cancer datasets. In addition to revealing a link between EMT and T cell dysfunction, these findings also show that ZEB1 promotes metastasis through a heretofore unappreciated cell non-autonomous mechanism, and suggest that subgroups of patients in whom malignant progression is driven by EMT activators may respond to treatment with PD-L1 antagonists.

Platelet-activating factor, a molecular sensor for cellular damage, activates systemic immune suppression.

Ultraviolet (UV) radiation plays a critical role in the induction of nonmelanoma skin cancer. UV radiation is also immune suppressive, and the immune suppression induced by UV irradiation has been identified as a major risk factor for skin cancer induction. Previously, we showed that UV exposure activates a cytokine cascade involving prostaglandin (PG)E2, interleukin (IL)-4, and IL-10 that induces immune suppression. However, the earliest molecular events that occur immediately after UV exposure, especially those upstream of PGE2, are not well defined. UV-irradiated keratinocytes secrete the inflammatory phospholipid mediator, platelet-activating factor (PAF). Because PAF upregulates the production of immunomodulatory compounds, including PGE2, we tested the hypothesis that UV-induced PAF activates cytokine production and initiates UV-induced immune suppression. Both UV and PAF activated cyclooxygenase (COX)-2 and IL-10 reporter gene construct transcription. PAF mimicked the effects of UV in vivo and suppressed delayed-type hypersensitivity (DTH). Furthermore, immune suppression was blocked when UV-irradiated mice were injected with PAF receptor antagonists. In addition to the well-known role of PAF as a proinflammatory lipid mediator, we propose that the PAF receptor senses cellular damage through the recognition of PAF and/or PAF-like molecules, such as oxidized phosphatidylcholine, which activates cytokine transcription and induces systemic immune suppression.

Regulation of tumor growth and metastasis by interleukin- 10: The melanoma experience

Because interleukin-10 (IL-10) has potent immunosuppressive and anti-inflammatory properties and is produced by some cancers, including melanoma, we hypothesized that its production by tumor cells may contribute to the escape from immune surveillance. To test this hypothesis, we transfected human A375P melanoma cells that do not express IL-10 with the murine IL-10 gene and subsequently analyzed for changes in tumor growth and metastasis in nude mice. Surprisingly, IL-10 gene transfer resulted in a loss of metastasis and significant inhibition of tumor growth. In addition, the growth of other murine or human melanoma cells was also inhibited when they were admixed with IL-10-transfected cells before injection into nude mice. We provide evidence that IL-10 exerts its antitumor and antimetastatic activity by inhibiting angiogenesis in vivo. The in vivo decrease in neovascularization found in IL-10-secreting tumors is most likely due to the ability of IL-10 to downregulate the synthesis of vascular endothelial growth factor (VEGF), interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-6, and matrix metalloproteinase-9 (MMP-9) in tumor-associated macrophages. Other studies have shown that IL-10 inhibits tumor metastasis through a natural killer (NK) cell-dependent mechanism. The inhibitory effects of IL-10 on tumor growth and metastasis were also demonstrated in other tumor models, including breast cancers. Furthermore, administration of rIL-10 into mice resulted in inhibition of tumor metastasis. Because IL-10 has little toxicity when given systemically to human volunteers, its efficacy as an antimetastatic agent should be further explored, both as an independent and in combination with other inhibitors of neovascularization.

Temporal Events in Skin Injury and the Early Adaptive Responses in Ultraviolet-Irradiated Mouse Skin

We examined the effects of ultraviolet (UV) radiation on the time course for induction of sunburn (apoptotic) cells and expression of proteins known to be associated with growth arrest and apoptosis in SKH-hr1 mouse skin. Mice were irradiated with a single dose (2.5 kJ/m(2)) of UV from Kodacel-filtered (290-400 nm) FS40 sunlamps and the skin tissues were analyzed at various times after irradiation for the presence of apoptotic cells and expression of p53, p21(Waf-1/Cip1), bcl-2, bax, and proliferating cell nuclear antigen. The results indicated that p53 expression was induced early in the epidermis, reaching maximum levels 12 hours after irradiaton, and p21(Waf-1/Cip1) expression in the epidermis peaked at 24 hours after irradiation. In contrast, UV radiation induced high levels of bax at 24 to 72 hours after irradiation with a concomitant decrease in bcl-2 expression. Coinciding with these changes, apoptotic cells began to appear 6 hours after irradiation and reached a maximum at 24 hours after irradiation. Interestingly, proliferating cell nuclear antigen expression, which was initially confined to the basal layer, became dispersed throughout the basal and suprabasal layers of the skin at 48 hours and paralleled marked hyperplasia. These results suggest that UV irradiation of mouse skin induces apoptosis mediated by the p53/p21/bax/bcl-2 pathway and that the dead cells are replaced by hyperproliferative cells, leading to epidermal hyperplasia. This implies that UV-induced apoptosis and hyperplasia are closely linked and tightly regulated and that dysregulation of these two events may lead to skin cancer development.

THE ROLE OF EPIDERMAL CYTOKINES IN THE GENERATION OF CUTANEOUS IMMUNE REACTIONS and ULTRAVIOLET RADIATION‐INDUCED IMMUNE SUPPRESSION

For most of the past century scientists and physicians have recognized that UV rays present in sunlight have the potential to affect human health and well being adversely. Ultraviolet radiation is the primary cause of non-melanoma skin cancer. Exposure to UV induces sunburn and erythema, promotes premature aging of the skin and causes ocular damage, including cataract formation. In addition, exposure to UV radiation impairs the function of the immune system. In a pioneering set of experiments carried out by Kripke in the mid1970s, the association between the immunosuppressive effects of UV radiation and its carcinogenic potential was first recognized. Unlike the vast majority of murine tumors, a large proportion of skin tumors induced by UV exposure failed to grow progressively when transplanted to normal syngeneic immune-competent hosts. These “regressor” tumors would only grow progressively upon transfer to immune-compromised individuals. The explanation for this observation is that the UV-induced tumors are highly antigenic, they are recognized as foreign by the immune system of the host animal and are rejected. Thus, one observes tumor rejection when transplanted into immune-competent animals but progressive tumor growth in mice whose immune system is suppressed. How then did these regressor tumors grow progressively in the primary UV-irradiated host? In addition to inducing skin cancer, UV is also immune suppressive. Exposure to subcarcinogenic doses of UV suppresses the immune system of the autochthonous host, thus allowing the antigenic tumors to grow progressively. Subsequent studies by Kripke and coworkers and Daynes and colleagues demonstrated that exposure to subcarcinogenic doses of UV radiation suppressed the generation of cell-mediated immune reactions, in part by the induction of antigenic-specific suppressor T cells. These cells control both the development of the primary tumor in the UV-irradiated host and can transfer the tumor-susceptible state from UV-irradiated mice to normal age-matched syngeneic controls. Thus, these early studies in experimental animals established a link between the ability of UV to suppress the immune response and induce skin cancer.’J More recently a similar conclusion has been arrived at from studies with human volunteers. Ultraviolet exposure suppresses the induction of a contact hypersensitivity (CHS)* reaction in a proportion (40-50%) of normal human volunteer^^,^; however, in almost 100% of biopsyproven skin cancer patients, UV exposure suppresses the induction of an immune r e a ~ t i o n . ~ This finding suggests that the immune suppression generated by UV exposure is a major risk factor for skin cancer induction in both experimental animals and skin cancer patients. This observation has fueled the efforts of many to understand the mechanisms involved in the immune suppression induced by exposure to UV radiation. The focus of this report will be to review some of the more recent findings in the field, concentrating on the role of epidermal cytokines in both the enhancement and suppression of cutaneous immune reactions.

Mast Cell Migration from the Skin to the Draining Lymph Nodes upon Ultraviolet Irradiation Represents a Key Step in the Induction of Immune Suppression

The UV radiation in sunlight is the primary cause of skin cancer. UV is also immunosuppressive and numerous studies have shown that UV-induced immune suppression is a major risk factor for skin cancer induction. Previous studies demonstrated that dermal mast cells play a critical role in the induction of immune suppression. Mast cell-deficient mice are resistant to the immunosuppressive effects of UV radiation, and UV-induced immune suppression can be restored by injecting bone marrow-derived mast cells into the skin of mast cell- deficient mice. The exact process however, by which mast cells contribute to immune suppression, is not known. In this study, we show that one of the first steps in the induction of immune suppression is mast cell migration from the skin to the draining lymph nodes. UV exposure, in a dose-dependent manner, causes a significant increase in lymph node mast cell numbers. When GFP+ skin was grafted onto mast cell-deficient mice, we found that GFP+ mast cells preferentially migrated into the lymph nodes draining the skin. The mast cells migrated primarily to the B cell areas of the draining nodes. Mast cells express CXCR4+ and UV exposure up-regulated the expression of its ligand CXCL12 by lymph node B cells. Treating UV-irradiated mice with a CXCR4 antagonist blocked mast cell migration and abrogated UV-induced immune suppression. Our findings indicate that UV-induced mast cell migration to draining lymph nodes, mediated by CXCR4 interacting with CXCL12, represents a key early step in UV-induced immune suppression.

Cis-urocanic acid, a sunlight-induced immunosuppressive factor, activates immune suppression via the 5-HT2A receptor.

Exposure to UV radiation induces skin cancer and suppresses the immune response. To induce immune suppression, the electromagnetic energy of UV radiation must be absorbed by an epidermal photoreceptor and converted into a biologically recognizable signal. Two photoreceptors have been recognized: DNA and trans-urocanic acid (UCA). Trans-UCA is normally found in the outermost layer of skin and isomerizes to the cis isomer upon exposure to UV radiation. Although UCA was identified as a UV photoreceptor years ago, and many have documented its ability to induce immune suppression, its exact mode of action remains elusive. Particularly vexing has been the identity of the molecular pathway by which cis-UCA mediates immune suppression. Here we provide evidence that cis-UCA binds to the serotonin [5-hydroxytryptamine (5-HT)] receptor with relatively high affinity (Kd = 4.6 nM). Anti-cis-UCA antibody precipitates radiolabeled 5-HT, and the binding is inhibited by excess 5-HT and/or excess cis-UCA. Similarly, anti-5-HT antibody precipitates radiolabeled cis-UCA, and the binding is inhibited by excess 5-HT or excess cis-UCA. Calcium mobilization was activated when a mouse fibroblast line, stably transfected with the human 5-HT2A receptor, was treated with cis-UCA. Cis-UCA-induced calcium mobilization was blocked with a selective 5-HT2A receptor antagonist. UV- and cis-UCA-induced immune suppression was blocked by antiserotonin antibodies or by treating the mice with 5-HT2A receptor antagonists. Our findings identify cis-UCA as a serotonin receptor ligand and indicate that the immunosuppressive effects of cis-UCA and UV radiation are mediated by activation of the 5-HT2A receptor.

Dendritic cells require T cells for functional maturation in vivo

We examined dendritic cell (DC) status in SCID and RAG2 -/- mice to assess the influence of T cells on DC development and function in vivo. These mice have reduced numbers of DC in the epidermis and lymph nodes draining hapten-sensitized skin. Epidermal DC in these mice were defective in presenting antigen in vivo to adoptively transferred, hapten-sensitized T cells from normal mice. Likewise, draining lymph node DC were deficient in their capacity to stimulate naive T cells in vitro and in vivo. DC numbers as well as the impaired ability to present antigen in vivo, were corrected by reconstituting these animals with normal T lymphocytes, suggesting that T cells are crucial for normal DC maturation and function in vivo.