Bruce R. Ksander

Immunity causing blindness: five different paths to herpes stromal keratitis

Herpes stromal keratitis (HSK) is a blinding infectious disease that results from an array of immunopathogenic processes, including herpes simplex virus 1 (HSV-1)-specific T helper 1 (Th1) and Th2 cells, cytotoxic T cells and antibodies. As discussed here by Wayne Streilein and colleagues, strategies designed to prevent and treat this syndrome must be aware of the fact that the disease is multifactorial in its cause and pathogenesis.

Hippo-independent activation of YAP by the GNAQ uveal melanoma oncogene through a trio-regulated rho GTPase signaling circuitry.

Mutually exclusive activating mutations in the GNAQ and GNA11 oncogenes, encoding heterotrimeric Gαq family members, have been identified in ∼ 83% and ∼ 6% of uveal and skin melanomas, respectively. However, the molecular events underlying these GNAQ-driven malignancies are not yet defined, thus limiting the ability to develop cancer-targeted therapies. Here, we focused on the transcriptional coactivator YAP, a critical component of the Hippo signaling pathway that controls organ size. We found that Gαq stimulates YAP through a Trio-Rho/Rac signaling circuitry promoting actin polymerization, independently of phospholipase Cβ and the canonical Hippo pathway. Furthermore, we show that Gαq promotes the YAP-dependent growth of uveal melanoma cells, thereby identifying YAP as a suitable therapeutic target in uveal melanoma, a GNAQ/GNA11-initiated human malignancy.

ABCB5 is a limbal stem cell gene required for corneal development and repair

Corneal epithelial homeostasis and regeneration are sustained by limbal stem cells (LSCs), and LSC deficiency is a major cause of blindness worldwide. Transplantation is often the only therapeutic option available to patients with LSC deficiency. However, while transplant success depends foremost on LSC frequency within grafts, a gene allowing for prospective LSC enrichment has not been identified so far. Here we show that ATP-binding cassette, sub-family B, member 5 (ABCB5) marks LSCs and is required for LSC maintenance, corneal development and repair. Furthermore, we demonstrate that prospectively isolated human or murine ABCB5-positive LSCs possess the exclusive capacity to fully restore the cornea upon grafting to LSC-deficient mice in xenogeneic or syngeneic transplantation models. ABCB5 is preferentially expressed on label-retaining LSCs in mice and p63α-positive LSCs in humans. Consistent with these findings, ABCB5-positive LSC frequency is reduced in LSC-deficient patients. Abcb5 loss of function in Abcb5 knockout mice causes depletion of quiescent LSCs due to enhanced proliferation and apoptosis, and results in defective corneal differentiation and wound healing. Our results from gene knockout studies, LSC tracing and transplantation models, as well as phenotypic and functional analyses of human biopsy specimens, provide converging lines of evidence that ABCB5 identifies mammalian LSCs. Identification and prospective isolation of molecularly defined LSCs with essential functions in corneal development and repair has important implications for the treatment of corneal disease, particularly corneal blindness due to LSC deficiency.

Lung cancer patients’ CD4+ T cells are activated in vitro by MHC II cell-based vaccines despite the presence of myeloid-derived suppressor cells

BackgroundAdvanced non-small cell lung cancer (NSCLC) remains an incurable disease. Immunotherapies that activate patients’ T cells against resident tumor cells are being developed; however, these approaches may not be effective in NSCLC patients due to tumor-induced immune suppression. A major cause of immune suppression is myeloid-derived suppressor cells (MDSC). Because of the strategic role of CD4+ T lymphocytes in the activation of cytotoxic CD8+ T cells and immune memory, we are developing cell-based vaccines that activate tumor-specific CD4+ T cells in the presence of MDSC. The vaccines are NSCLC cell lines transfected with costimulatory (CD80) plus major histocompatibility complex class II (MHC II) genes that are syngeneic to the recipient. The absence of invariant chain promotes the presentation of endogenously synthesized tumor antigens, and the activation of MHC II-restricted, tumor-antigen-specific CD4+ T cells.MethodsPotential vaccine efficacy was tested in vitro by priming and boosting peripheral blood mononuclear cells from ten NSCLC patients who had varying levels of MDSC. CD4+ T cell activation was quantified by measuring Type 1 and Type 2 cytokine release.ResultsThe vaccines activated CD4+ T cells from all ten patients, despite the presence of CD33+CD11b+ MDSC. Activated CD4+ T cells were specific for NSCLC and did not cross-react with tumor cells derived from non-lung tissue or normal lung fibroblasts.ConclusionsThe NSCLC vaccines activate tumor-specific CD4+ T cells in the presence of potent immune suppression, and may be useful for the treatment of patients with NSCLC.

By Altering Ocular Immune Privilege, Bone Marrow-derived Cells Pathogenically Contribute to DBA/2J Pigmentary Glaucoma.

Pigment dispersion syndrome causes iris pigment release and often progresses to elevated intraocular pressure and pigmentary glaucoma (PG). Because melanin pigment can have adjuvant like properties and because the Gpnmb gene, which contributes to pigment dispersion in DBA/2J (D2) mice, is expressed in dendritic cells, we tested the hypothesis that ocular immune abnormalities participate in PG phenotypes. Strikingly, we show that D2 eyes exhibit defects of the normally immunosuppressive ocular microenvironment including inability of aqueous humor to inhibit T cell activation, failure to support anterior chamber (AC)-associated immune deviation, and loss of ocular immune privilege. Histologic analysis demonstrates infiltration of inflammatory leukocytes into the AC and their accumulation within the iris, whereas clinical indications of inflammation are typically very mild to undetectable. Importantly, some of these abnormalities precede clinical indications of pigment dispersal, suggesting an early role in disease etiology. Using bone marrow chimeras, we show that lymphohematopoietic cell lineages largely dictate the progression of pigment dispersion, the ability of the eye to support induction of AC-associated immune deviation, and the integrity of the blood/ocular barrier. These results suggest previously unsuspected roles for bone marrow–derived cells and ocular immune privilege in the pathogenesis of PG.

Expression profiling reveals that methylation of TIMP3 is involved in uveal melanoma development

Uveal melanoma is associated with a high tumor‐related mortality due to the propensity to develop metastases. The mechanisms that are responsible for malignant dissemination are largely unknown and need to be explored to facilitate diagnosis and treatment of metastases. To identify molecules involved in dissemination, we used cell lines derived from a primary uveal melanoma and 2 liver metastases from the same patient as a model for tumor progression. Using a microarray representing 1,176 genes, we identified 63 differentially expressed genes. Forty genes showed a higher expression and 23 showed a lower expression in the primary cell line compared to the metastasis cell lines. These genes are involved in processes like angiogenesis, apoptosis, macrophage stimulation, and extracellular matrix regulation. In contrast, the 2 liver metastasis cell lines produced nearly identical expression profiles. Demethylation of the primary melanoma cell line by 5‐aza‐2′deoxycytidine treatment revealed that 19 genes were suppressed by hypermethylation. An important finding was the 5‐fold decreased expression of TIMP3 in the metastatic cell lines, a molecule involved in extracellular matrix degradation. We demonstrate in the cell lines that TIMP3 expression is regulated by methylation. These observations were confirmed in primary uveal melanoma and suggests a role for TIMP3 in uveal melanoma development.

MELANOMAS THAT DEVELOP WITHIN THE EYE INHIBIT LYMPHOCYTE PROLIFERATION

Experiments were performed to compare the ability of ocular and skin melanoma cells to stimulate T cells. Primary melanoma cell lines were obtained from a series of patients with either eye or skin melanoma. The ability of tumor cells to stimulate T cells in the absence of exogenous growth factors was assessed in mixed‐lymphocyte tumor cell cultures in which allogeneic lymphocytes were stimulated with irradiated ocular or skin melanoma cells. Expression of HLA class I and class II on tumor cells, in the presence or absence of IFN‐γ, was determined by flow cytometry. The ability of tumor cells to inhibit T‐cell proliferation was determined by adding various concentrations of irradiated tumor cells to standard mixed‐lymphocyte cultures. Our results indicate that primary skin melanoma cells induce vigorous proliferation of allo‐antigen‐specific T cells. By contrast, ocular melanoma cells failed to induce significant T‐cell proliferation. The failure of ocular melanoma cells to stimulate lymphocyte proliferation was not due to low levels of either class I or class II on tumor cells since tumor cells treated with IFN‐γ expressed high levels of class I and class II but still failed to induce lymphocyte proliferation. Ocular melanoma cells inhibited lymphocyte proliferation, as shown by experiments in which a small number of tumor cells prevented proliferation of T cells in mixed‐lymphocyte cultures. Inhibition of lymphocyte proliferation required cell‐to‐cell contact, and supernatants from tumor cell cultures did not prevent lymphocyte proliferation. Moreover, the ability of ocular melanoma cells to inhibit T‐cell proliferation was lost when tumor cells migrated from the eye and formed hepatic metastases. We conclude that there is a fundamental difference in the immunogenicity of ocular and skin melanoma cells. Ocular melanomas, but not primary skin melanomas, are poorly immunogenic tumors that inhibit T‐cell proliferation. Our results imply that the immunogenicity of melanoma cells is altered when they develop within the unique ocular micro‐environment. Int. J. Cancer 73:470–478, 1997.

Minor H, rather than MHC, alloantigens offer the greater barrier to successful orthotopic corneal transplantation in mice

Irrespective of HLA matching, a far higher proportion of human corneal allografts placed orthotopically in avascular corneal graft beds are accepted indefinitely, compared to other types of solid tissue allografts. However, many more corneal grafts are rejected if they are transplanted onto neovascularized recipient eyes. Using a murine model of orthotopic corneal transplantation in which grafts were placed in normal eyes, we have reported previously that grafts bearing minor H antigens alone are more likely to be rejected (approximately 50%) than are grafts displaying only MHC alloantigens (< 20%). Moreover, recipients of MHC plus minor H incompatible corneal grafts developed delayed hypersensitivity (DH) directed solely at minor H antigens. These studies have now been extended to include corneal grafts placed in neovascularized recipient eyes. Neovascularization was induced by placing sutures in the central cornea of one eye of BALB/c mice. Two weeks later corneas from C57BL/10 donors were grafted into these eyes. Rejection reactions were first apparent within 7 days and all grafts were destroyed by 14 days. Donor-specific DH responses were examined by injecting irradiated donor antigen-bearing spleen cells into the ear pinna. To distinguish DH directed at MHC versus minor antigens, some graft recipients were ear-challenged with BALB.B cells (donor MHC only), while other received B10.D2 cells (donor minor H only). Intense ear-swelling responses were evoked by B10.D2 cells, but not by BALB.B cells. These findings indicate that, for orthotopic corneal allografts, minor H antigens offer a more formidable barrier to graft acceptance than do MHC-encoded antigens. We speculate that this unexpected outcome may reflect a reduced level of MHC expression on corneal tissue. Moreover since the cornea lacks bone marrow derived dendritic cells, allorecognition by recipient T cells must occur via the indirect pathway, and in this situation minor H antigens may compete favorably with MHC antigens for processing and presentation by recipient antigen-presenting cells.

Membrane Fas Ligand Activates Innate Immunity and Terminates Ocular Immune Privilege

It has been proposed that the constitutive expression of Fas ligand (FasL) in the eye maintains immune privilege, in part through inducing apoptosis of infiltrating Fas+ T cells. However, the role of FasL in immune privilege remains controversial due to studies that indicate FasL is both pro- and anti-inflammatory. To elucidate the mechanism(s) by which FasL regulates immune privilege, we used an ocular tumor model and examined the individual roles of the membrane-bound and soluble form of FasL in regulating ocular inflammation. Following injection into the privileged eye, tumors expressing only soluble FasL failed to trigger inflammation and grew progressively. By contrast, tumors expressing only membrane FasL 1) initiated vigorous neutrophil-mediated inflammation, 2) terminated immune privilege, and 3) were completely rejected. Moreover, the rejection coincided with activation of both innate and adaptive immunity. Interestingly, a higher threshold level of membrane FasL on tumors is required to initiate inflammation within the immune privileged eye, as compared with nonprivileged sites. The higher threshold is due to the suppressive microenvironment found within aqueous humor that blocks membrane FasL activation of neutrophils. However, aqueous humor is unable to completely block the proinflammatory effects of tumor cells that express high levels of membrane FasL. In conclusion, our data indicate that the function of FasL on intraocular tumors is determined by the microenvironment in conjunction with the form and level of FasL expressed.

Characterization of complex chromosomal abnormalities in uveal melanoma by fluorescence in situ hybridization, spectral karyotyping, and comparative genomic hybridization

Several nonrandom recurrent chromosomal changes are observed in uveal melanoma. Some of these abnormalities, e.g., loss of chromosome 3, gain of the q arm of chromosome 8, and chromosome 6 abnormalities, are of prognostic value. Cytogenetic analysis and/or fluorescence in situ hybridization (FISH) are used to detect these changes. In some cases, however, detailed cytogenetic analysis is not possible due to the presence of complex abnormalities. To define more accurately these cytogenetic changes, we have applied comparative genomic hybridization (CGH) and/or spectral karyotyping (SKY) to two uveal melanoma cell lines and five primary uveal melanomas, with partially defined and/or complex abnormalities. SKY provided additional information on 34/39 partially defined aberrant chromosomes and revealed a new abnormality, a der(17)t(7;17)(?;q?), that had not been recognized by conventional cytogenetics. Additionally, using SKY, abnormalities involving chromosome 6 or 8 were found to be twice as common as observed with cytogenetic analysis. CGH was especially useful in assigning the abnormalities identified by SKY to specific chromosomal regions and, in addition, resulted in the detection of a small deletion of chromosome region 3q13∼21. We conclude that SKY and CGH, as methods complementary to cytogenetic and FISH analysis, provide more complete information on the chromosomal abnormalities occurring in uveal melanoma.