V-domain Ig suppressor of T cell activation (VISTA) is a novel negative checkpoint ligand that is homologous to PD-L1 and suppresses T cell activation. This study demonstrates the multiple mechanisms whereby VISTA relieves negative regulation by hematopoietic cells and enhances protective anti-tumor immunity. VISTA is highly expressed on myeloid cells and Foxp3+CD4+ regulatory cells, but not on tumor cells within the tumor microenvironment (TME). VISTA monoclonal antibody (mab) treatment increased the number of tumor-specific T cells in the periphery, and enhanced the infiltration, proliferation and effector function of tumor-reactive T cells within the TME. VISTA blockade altered the suppressive feature of the TME, by decreasing the presence of monocytic myeloid-derived suppressor cells and increasing the presence of activated DCs within the TME. In addition, VISTA blockade impaired the suppressive function and reduced the emergence of tumor-specific Foxp3+CD4+ regulatory T cells. Consequently, VISTA mab administration as a monotherapy significantly suppressed the growth of both transplantable and inducible melanoma. Initial studies explored a combinatorial regimen using VISTA blockade and a peptide-based cancer vaccine with TLR agonists as adjuvants. VISTA blockade synergized with the vaccine to effectively impair the growth of established tumors. Our study therefore establishes a foundation for designing VISTA-targeted approaches either as a monotherapy or in combination with additional immune-targeted strategies for cancer immunotherapy.

Evidence is accumulating that solid tumors contain a rare phenotypically distinct population of cells, termed cancer stem cells (CSC), which give rise to and maintain the bulk of the tumor. These CSC are thought to be resistant to current chemotherapeutic strategies due to their intrinsic stemlike properties and thus may provide the principal driving force behind recurrent tumor growth. Given the high frequency of recurrent metastasis associated with human ovarian cancer, we sought to determine whether primary human ovarian tumors contain populations of cells with enhanced tumor-initiating capacity, a characteristic of CSC. Using an in vivo serial transplantation model, we show that primary uncultured human ovarian tumors can be reliably propagated in NOD/SCID mice, generating heterogeneous tumors that maintain the histological integrity of the parental tumor. The observed frequency of tumor engraftment suggests only certain subpopulations of ovarian tumor cells have the capacity to recapitulate tumor growth. Further profiling of human ovarian tumors for expression of candidate CSC surface markers indicated consistent expression of CD133. To determine whether CD133 expression could define a tumor-initiating cell population in primary human ovarian tumors, fluorescence-activated cell sorting (FACS) methods were employed. Injection of sorted CD133 1 and CD133 2 cell populations into NOD/SCID mice established that tumor-derived CD133 1 cells have an increased tumorigenic capacity and are capable of recapitulating the original heterogeneous tumor. Our data indicate that CD133 expression defines a NOD/SCID tumor initiating subpopulation of cells in human ovarian cancer that may be an important target for new chemotherapeutic strategies aimed at eliminating ovarian cancer.

Currently available human tumour cell line panels consist of a small number of lines in each lineage that generally fail to retain the phenotype of the original patient tumour. Here we develop a cell culture medium that enables us to routinely establish cell lines from diverse subtypes of human ovarian cancers with >95% efficiency. Importantly, the 25 new ovarian tumour cell lines described here retain the genomic landscape, histopathology and molecular features of the original tumours. Furthermore, the molecular profile and drug response of these cell lines correlate with distinct groups of primary tumours with different outcomes. Thus, tumour cell lines derived using this methodology represent a significantly improved platform to study human tumour pathophysiology and response to therapy.

Recent data suggest that rare stem cell populations with the capacity to self renew and drive tumor formation are a feature of solid tumors. Several investigators have identified putative stem cells from solid tumors and cancer cell lines following isolation of a side population (SP) defined by dye exclusion. We investigated this parameter in our efforts to identify an endometrial cancer (EnCa) stem cell population. Multiple EnCa cell lines were assessed and verapamil sensitive SP and non-SP cells were isolated from two human EnCa cell lines. The functional significance of the SP and non-SP derived from AN3CA was evaluated in vitro and in vivo. SP cells proliferated at a significantly slower rate than the non-SP fraction, and a larger proportion of the SP cells were in the G 1 phase of the cell cycle as compared to the non-SP fraction. The SP fraction was more resistant to the chemotherapeutic agent paclitaxel. The SP comprised ~0.02% of the initial AN3CA cell population and this proportion of SP cells was maintained within the larger heterogeneous population following repeated passages of purified SP cells. These findings suggest that SP cells derived from the AN3CA cell line have the stem cell properties of low proliferative activity, chemoresistance and self-renewal. We also tested relative tumor formation activity of the SP and non-SP fractions. Only the SP fraction was tumorigenic. Additionally, we identified SP fractions in primary EnCa. Together these results are consistent with the hypothesis that EnCa contain a subpopulation of tumor initiating cells with stem like properties.

Objective The targeting of negative checkpoint regulators as a means of augmenting antitumor immune responses is now an increasingly used and remarkably effective approach to the treatment of several human malignancies. The negative checkpoint regulator VISTA (V-domain Ig–containing suppressor of T cell activation; also known as programmed death 1 homolog or as death domain 1α) suppresses T cell responses and regulates myeloid activities. We proposed that exploitation of the VISTA pathway is a novel strategy for the treatment of human autoimmune disease, and therefore we undertook this study to determine the impact of VISTA genetic deficiency on lupus development in a lupus-prone mouse strain. Methods To evaluate whether genetic deficiency of VISTA affects the development of lupus, we interbred VISTA-deficient mice with Sle1.Sle3 mice, a well-characterized model of systemic lupus erythematosus (SLE). Results We demonstrated that the development of proteinuria and glomerulonephritis in these mice, designated Sle1.Sle3 VISTA−/− mice, was greatly accelerated and more severe compared to that in Sle1.Sle3 and C57BL/6 VISTA−/− mice. Analysis of cells from Sle1.Sle3 VISTA−/− mice showed enhanced activation of splenic CD4+ T cells and myeloid cell populations. No increase in titers of autoantibodies was seen in Sle1.Sle3 VISTA−/− mice. Most striking was a significant increase in proinflammatory cytokines, chemokines, and interferon (IFN)–regulated genes associated with SLE, such as IFNα, IFNγ, tumor necrosis factor, interleukin-10, and CXCL10, in Sle1.Sle3 VISTA−/− mice. Conclusion This study demonstrates for the first time that loss of VISTA in murine SLE exacerbates disease due to enhanced myeloid and T cell activation and cytokine production, including a robust IFNα signature, and supports a strategy of enhancement of the immunosuppressive activity of VISTA for the treatment of human lupus.

BackgroundRecent data provide significant evidence to support the hypothesis that there are sub-populations of cells within solid tumors that have an increased tumor initiating potential relative to the total tumor population. CD133, a cell surface marker expressed on primitive cells of neural, hematopoietic, endothelial and epithelial lineages has been identified as a marker for tumor initiating cells in solid tumors of the brain, colon, pancreas, ovary and endometrium. Our objectives were to assess the relative level of CD133 expressing cells in primary human endometrial tumors, confirm their tumorigenic potential, and determine whether CD133 expression was epigenetically modified.MethodsWe assessed CD133 expression in primary human endometrial tumors by flow cytometry and analyzed the relative tumorigenicity of CD133+ and CD133- cells in an in vivo NOD/SCID mouse model. We assessed potential changes in CD133 expression over the course of serial transplantation by immunofluorescence and flow cytometry. We further examined CD133 promoter methylation and expression in normal endometrium and malignant tumors.ResultsAs determined by flow cytometric analysis, the percentage of CD133+ cells in primary human endometrial cancer samples ranged from 5.7% to 27.4%. In addition, we confirmed the tumor initiating potential of CD133+ and CD133- cell fractions in NOD/SCID mice. Interestingly, the percentage of CD133+ cells in human endometrial tumor xenografts, as evidenced by immunofluorescence, increased with serial transplantation although this trend was not consistently detected by flow cytometry. We also determined that the relative levels of CD133 increased in endometrial cancer cell lines following treatment with 5-aza-2'-deoxycytidine suggesting a role for methylation in the regulation of CD133. To support this finding, we demonstrated that regions of the CD133 promoter were hypomethylated in malignant endometrial tissue relative to benign control endometrial tissue. Lastly, we determined that methylation of the CD133 promoter decreases over serial transplantation of an endometrial tumor xenograft.ConclusionsThese findings support the hypotheses that CD133 expression in endometrial cancer may be epigenetically regulated and that cell fractions enriched for CD133+ cells may well contribute to endometrial cancer tumorigenicity, pathology and recurrence.

Ovarian cancer is the fifth leading cause of cancer death in women. Ovarian cancers display a high degree of complex genetic alterations involving many oncogenes and tumor suppressor genes. Analysis of the association between genetic alterations and clinical endpoints such as survival will lead to improved patient management via genetic stratification of patients into clinically relevant subgroups. In this study, we aim to define subgroups of high-grade serous ovarian carcinomas that differ with respect to prognosis and overall survival. Genome-wide DNA copy number alterations (CNAs) were measured in 72 clinically annotated, high-grade serous tumors using high-resolution oligonucleotide arrays. Two clinically annotated, independent cohorts were used for validation. Unsupervised hierarchical clustering of copy number data derived from the 72 patient cohort resulted in two clusters with significant difference in progression free survival (PFS) and a marginal difference in overall survival (OS). GISTIC analysis of the two clusters identified altered regions unique to each cluster. Supervised clustering of two independent large cohorts of high-grade serous tumors using the classification scheme derived from the two initial clusters validated our results and identified 8 genomic regions that are distinctly different among the subgroups. These 8 regions map to 8p21.3, 8p23.2, 12p12.1, 17p11.2, 17p12, 19q12, 20q11.21 and 20q13.12; and harbor potential oncogenes and tumor suppressor genes that are likely to be involved in the pathogenesis of ovarian carcinoma. We have identified a set of genetic alterations that could be used for stratification of high-grade serous tumors into clinically relevant treatment subgroups.

V-domain Ig suppressor of T-cell activation (VISTA) is a critical negative checkpoint molecule involved in regulating the immune response. Targeting the pathway with an antagonist anti-VISTA antibody designated 13F3 has been shown to enhance disease severity in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. To determine if VISTA plays a role in murine lupus, New Zealand Black × New Zealand White (BWF1) mice were treated with 13F3 or control hamster Ig and disease monitored. Onset of proteinuria was earlier and renal damage more profound in mice treated with 13F3. Cell subset analysis showed an increase of activated splenic T cells and inflammatory splenic myeloid cells, but no effect on B cells, in mice receiving 13F3. Examination of the kidney showed an increase in inflammatory myeloid cell infiltration with 13F3 treatment. This study along with previous EAE data, suggests that interventions that enhance VISTA regulatory activity may be effective for the treatment of autoimmune disease.