Putative Cancer Stem Cell Markers are Frequently Expressed by Melanoma Cells in Vitro and in Situ but are also Present in Benign Differentiated Cells.

BACKGROUND: Currently, there remains an incomplete view of cancer stem cells (CSCs) in solid tumours. METHODS: We studied a panel of putative CSC surface markers (ALDH1A1, ABCG2, CD44v7/8, CD44v10, CD133, CD271, and Nestin) in 40 established melanoma cell lines and four early-passage melanoma strains by flow cytometry. We additionally examined 40 formalin-fixed paraffin-embedded melanoma tissues using immunofluorescence microscopy. This was compared with their expression in healthy skin, normal differentiated melanocytes and fibroblasts. RESULTS: Most of the putative CSC markers were expressed by both melanoma cell lines and tissues. When present, these proteins were expressed by the majority of cells in the population. However, the expression of these markers by cells in healthy skin sections, normal differentiated melanocytes, and fibroblasts revealed that differentiated non-malignant cells also expressed CSC markers indicating that they lack of specificity for CSCs. Culturing cell lines under conditions more characteristic of the tumour microenvironment upregulated CSC marker expressions in a proportion of cell lines, which correlated with improved cell growth and viability. CONCLUSIONS: The testing of melanoma cell lines (n = 40), early-passage cell strains (n = 4), and melanoma tissues (n = 40) showed that several putative CSC markers (ALDH1A1, ABCG2, CD44v7/8, CD44v10, CD133, CD271, and Nestin) are commonly present in a large proportion of melanoma cells in vitro and in situ. Further, we showed that these putative markers lack specificity for CSCs because they are also expressed in differentiated non-malignant cell types (melanocytes, fibroblasts, and skin), which could limit their use as therapeutic targets. These data are consistent with the emerging notion of CSC plasticity and phenotype switching within cancer cell populations.

Frequency of Immune Cell Subtypes in Peripheral Blood Correlates With Outcome for Patients With Metastatic Breast Cancer Treated With High-Dose Chemotherapy.

BACKGROUND: The frequency of circulating leukocytes has been shown to be a prognostic factor in patients being treated for different types of cancer. In breast cancer, tumor-infiltrating leukocytes may predict patient outcome, but few studies have investigated such associations for circulating leukocytes. PATIENTS AND METHODS: Multiparametric flow cytometry was used to examine the immunophenotypes of circulating peripheral blood mononuclear cells for 88 patients with metastatic breast cancer, which was then correlated to breast cancer-specific survival. Patients had been treated either with high-dose cyclophosphamide-containing regimens (group 1, n = 51 patients) or high-dose paclitaxel-containing regimens (group 2, n = 37 patients). RESULTS: The frequency of peripheral blood CD14+ monocytes indicated prognosis for patients in group 1 (but not group 2), while higher levels of CD11c+ dendritic cells indicated a better prognosis for patients in group 2 (but not group 1). The frequency of a number of different CD4+ or CD8+ T cell subtypes also predicted prognosis for patients in group 2. For example, patients in group 2 with a higher frequency of circulating CD4+ or CD8+ naive T cells (CD45RA+CD95-CD27+CD28+) showed a poorer prognosis. In contrast, T cells were not associated with prognosis for patients in group 1. CONCLUSION: Circulating leukocytes can predict clinical outcome for patients with breast cancer. Prediction of clinical outcome in this cohort of metastatic breast cancer patients was specific to the type of chemotherapy, and this finding is likely to apply to other therapies.

Low levels of intra-tumoural T cells in breast cancer identify clinically frail patients with shorter disease-specific survival.

OBJECTIVES: The global health status of older patients with cancer influences their clinical course, but little is known regarding the influence of the immune system on the global health of older patients with cancer. The goal of this study was to assess the relationships between patient fitness/frailty status and survival, and the local tumour immune environment of older patients with breast cancer. MATERIALS AND METHODS: In a cohort of 58 older patients with breast cancer (over 70 years of age), fluorescence microscopy was used to investigate whether levels of intra-tumoural T cells (CD3+) and granulocytic cells (CD15+) could predict clinical outcome, and/or whether they correlated with patient physical and mental performance as evaluated by comprehensive geriatric assessment. RESULTS: We observed that patients with higher levels of intra-tumoural T cells were fitter according to a number of clinical health measures including G8 (p = 0.006), Karnofsky Index (p = 0.0372), and Leuven Oncology Frailty Score (LOFS) (p = 0.0187). In contrast, high relative levels of granulocytic cells were found in patients with poorer clinical health (LOFS, p = 0.0474). Furthermore, high levels of T cells but not granulocytic cells were associated with longer breast cancer-specific survival (p = 0.0444). CONCLUSIONS: This is the first study to show that low relative levels of intra-tumoural T cells are associated with inferior patient fitness. In contrast to T cells, we observed that intra-tumoural granulocytic cells displayed an inverse relationship with patient performance. Further research is needed to determine whether boosting the level of intra-tumoural T cells in older non-fit patients can result in improved outcome.

Inhibiting HSP90 prevents the induction of myeloid-derived suppressor cells by melanoma cells.

Metastatic melanoma is the most dangerous form of skin cancer, with an ever-increasing incidence worldwide. Despite encouraging results with immunotherapeutic approaches, long-term survival is still poor. This is likely partly due to tumour-induced immune suppression mediated by myeloid-derived suppressor cells (MDSCs), which were shown to be associated with response to therapy and survival. Thus, identifying pathways responsible for MDSC differentiation may provide new therapeutic targets and improve efficacy of existing immunotherapies. Therefore, we've analysed mechanisms by which tumour cells contribute to the induction of MDSCs. Established melanoma cell lines were pre-treated with inhibitors of different pathways and tested for their capacity to alleviate T cell suppression via MDSC differentiation in vitro. Targeting HSP70/90 in melanoma cells resulted in reduced induction of immune suppressive cells on a phenotypic and functional basis, for which a more potent effect was observed when HSP90 was inhibited under hypoxic conditions. This initial study suggests a novel mechanism in tumour cells responsible for the induction of MDSC in melanoma.

CD14+ HLA-DR-/low MDSCs are elevated in the periphery of early-stage breast cancer patients and suppress autologous T cell proliferation.

PURPOSE: Despite the recent expansion in the use of immunotherapy for many cancer types, it is still not a standard treatment for breast cancer. Identifying differences in the immune systems of breast cancer patients compared to healthy women might provide insight into potential targets for immunotherapy and thus may assist its clinical implementation. METHODS: Multi-colour flow cytometry was used to investigate myeloid and lymphoid populations in the peripheral blood of breast cancer patients (n = 40) and in the blood of healthy age-matched women (n = 25). We additionally performed functional testing to identify immune suppressive mechanisms used by circulating CD14+ myeloid cells from breast cancer patients. RESULTS: Our results show that breast cancer patients have significantly elevated frequencies of cells with the monocytic myeloid-derived suppressor cell (mMDSC) phenotype CD14+ HLA-DR-/low compared with healthy women (p < 0.01). We also observed higher levels of earlier differentiated T cells and correspondingly lower levels of T cells in later stages of differentiation (p < 0.05). These disease-associated differences could already be detected in early-stage breast cancer patients in stages 1 and 2 (n = 33 of 40) (p < 0.05). Levels of circulating T cells correlated with certain clinical features and with patient age (p < 0.05). Functional tests showed that CD14+ myeloid cells from breast cancer patients more potently suppressed autologous T cell proliferation than CD14+ cells from healthy women (p < 0.01). Subsequent investigation determined that suppression was mediated in part by reactive oxygen species, because inhibiting this pathway partially restored T cell proliferation (p < 0.01). CONCLUSION: Our results highlight the potential importance of cells with mMDSC phenotypes in breast cancer, identifiable already at early stages of disease. This may provide a basis for identifying possible new therapeutic targets to enhance anti-cancer immunity.

Peripheral T cell responses to tumour antigens are associated with molecular, immunogenetic and cellular features of breast cancer patients.

PURPOSE: Breast cancer is a leading cause of cancer deaths in women, but despite steady improvements in therapies, treatment is still suboptimal. Immunotherapy holds promise as a more effective therapy for breast cancer; supporting this, our prior study showed that patients possessing HER2-reactive CD8+ T cells in blood experience survival superior to patients without these cells. Here, we define a composite set of biomarkers that identify patients with T cell responses to tumour antigens. METHODS: We assessed T cell responses following in vitro stimulation with the HER2, MUC1 and SUR tumour-associated antigens (TAA) by flow cytometry and intracellular cytokine staining in 50 breast cancer patients. We also measured HLA type, serum cytokines, tumour-infiltrating leukocytes and blood leukocyte populations. RESULTS: We found few correlations between TAA-reactive T cells and HLA type, serum cytokines and tumour-infiltrating leukocytes, whereas blood leukocyte phenotypes broadly correlated with TAA responses. This showed monocytes, natural killer cells, dendritic cells and T cells to be inversely associated with both CD4+ and CD8+ T cells reactive to tumour antigens. Moreover, combining multiple parameters improved the accuracy in predicting patients with TAA-responsive T cells. CONCLUSION: This study therefore defines composite immune profiles that identify patients responding to TAAs which may allow better personalisation of cancer therapies.

A clinical and biological perspective of human myeloid-derived suppressor cells in cancer.

Considering the large number of studies focused on myeloid-derived suppressor cells (MDSCs) to date, only a handful of well-defined relationships in human cancer have been established. The difficulty of assessing the impact of MDSCs in human cancer is partly due to the relatively small number of studies performed in humans. This is compounded in the literature by a common lack of clear indication of which species is being referred to for each characteristic described. These aspects may result in inappropriate extrapolation of animal studies to those in the human setting. This is especially the case for studies focused on investigating therapies which can be used to target MDSCs or those aimed at understanding their mechanism. Here, we attempt to rectify this by reviewing only studies on MDSC performed in humans. We survey studies which explore (1) whether MDSC levels are altered in cancer patients and if this is correlated with patient survival, (2) the so far identified mechanisms employed by MDSC to exert immune suppression, and (3) whether therapeutic agents can be used to target MDSCs by either altering their level, influencing their differentiation or inhibiting their suppressive function. Despite the fact that these studies clearly show that MDSCs are important in human cancer, the clinical employment of agents intended to target them has not yet been accomplished. We identify factors which have contributed to this and propose steps which may facilitate the translation of these therapies to the clinic in future.