Correlation of Baseline Tumor Burden with Clinical Outcome in Melanoma Patients Treated with Ipilimumab.

INTRODUCTION: Tumor burden is a frequently mentioned parameter; however, a commonly accepted definition is still lacking. METHODS: In this double-center prospective and retrospective study, 76 patients with unresectable stage III or stage IV melanoma treated with ipilimumab were included. We defined the baseline tumor burden (BTB) as the global sum of all metastases' longest diameters before treatment started and correlated the calculated BTB with disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and with the baseline levels of LDH, S100B, and sULPB2. RESULTS: BTB correlated significantly with DCR (p = 0.009), PFS (p = 0.002), OS (p = 0.032), and the occurrence of NRAS mutation (p = 0.006). BTB was also correlated to baseline serum levels of LDH (p = 0.011), S100B (p = 0.027), and SULBP (p < 0.0001). Multivariate analysis revealed that BPB and LDH were independently correlated with PFS and OS. With increasing BTB, disease control was less likely; no patient with a BTB >200 mm achieved disease control. For patients with brain metastasis, no correlation of BTB with DCR (p = 0.251), PFS (p = 0.059), or OS (p = 0.981) was observed. CONCLUSION: Calculated BTB is an independent prognostic factor for patients with metastatic melanoma treated with ipilimumab. Using calculated BTB as a definition of tumor burden may help increase comparability of outcome of therapies in future studies.

Prognostic role of gamma-glutamyl transferase in metastatic melanoma patients treated with immune checkpoint inhibitors.

BACKGROUND: Hepatic immune-related adverse events (irAE) including elevated liver function tests (transaminases) occur in 1.4-22.3% of melanoma patients receiving immune checkpoint inhibitors (ICPI) and constitute a potentially serious toxicity that is challenging to treat. In contrast to the liver transaminases alanine aminotransferase (ALT) and aspartate aminotransferase (AST), only little is known about the frequency and impact of gamma-glutamyl transferase (GGT) elevations. METHODS: GGT determined prior to and during therapy of metastatic melanoma patients treated with ICPI were retrospectively assessed in two independent cohorts (PD-1: n = 218, Ipi + Nivo: n = 148). Overall survival (OS) and best objective response were analyzed according to baseline and immune-related GGT (irGGT) elevations during treatment. RESULTS: In multivariate analysis, OS was reduced in patients with elevated baseline GGT (PD-1 group: hazard ratio [HR] 1.76, p = .0073; Ipi + Nivo group: HR 1.77, p = .032). Immune-related GGT elevation was recorded in 17% (PD-1 group) and 38.5% (Ipi + Nivo group). Of these patients, the majority (81 and 68%, respectively) had normal ALT and AST and showed no clinical signs of hepatotoxicity. Patients who experienced irGGT elevation had superior response (PD-1 group: odds ratio [OR] 3.57, p = .00072; Ipi + Nivo group: OR 1.74, p = .12) and OS (PD-1 group: HR 0.37, p = .0016; Ipi + Nivo group: HR 0.33, p = .00050). CONCLUSIONS: The frequency of hepatic irAE is currently underestimated. The addition of the sensitive enzyme GGT to the laboratory panel before and during therapy with ICPI allows to detect two to three times more patients developing hepatic or hepatobiliary toxicity than known so far. Immune-related GGT elevations correlate with response and favorable survival. Precis for use in the Table of Contents The frequency of hepatotoxicity under immune checkpoint blockade is currently underestimated. We suggest the addition of gamma-glutamyl transferase to the laboratory panel in checkpoint inhibitor patients for the detection of hepatobiliary toxicity.

Dermatofluoroscopy diagnostics in different pigmented skin lesions: Strengths and weaknesses.

BACKGROUND: The melanin fluorescence of skin lesions is measurable with two-photon excitation, a process termed dermatofluoroscopy, which has shown a shift from the green spectra in benign melanocytic lesions to the red spectra in melanoma. This study addressed the question as to which kind of pigmented lesions can be correctly diagnosed as melanin-bearing malignant tumors. METHODS: 476 pigmented lesions including 101 cutaneous melanomas were analyzed with dermatofluoroscopy, measuring the melanin fluorescence in a grid-like fashion with a separation of measurement points of 0.2 mm. The results of the dermatofluoroscopy are presented as a diagnostic score with a cut-off score of ≥ 28 for the diagnosis of melanin-bearing malignant tumors, and were compared to the gold standard of histopathology. RESULTS: A highly significant difference (p < 0.0001) between the diagnostic scores of different skin tumors was found. Dermatofluoroscopy scores showed the highest sensitivity for melanomas (92.1 %). Interestingly, most pigmented basal cell carcinomas (BCCs, 88.9 %) were diagnosed as melanin-bearing malignant tumors. A higher sensitivity for the correct diagnosis was observed in older patients (≥ 53 years, p = 0.003), in patients with skin tanning (p = 0.025), and in patients with freckles during childhood (p = 0.046). CONCLUSIONS: Two-photon fluorescence is an innovative technique for the diagnosis of pigmented skin lesions, and shows a high sensitivity for detection of melanomas and pigmented BCCs.

A phase II study of the L19IL2 immunocytokine in combination with dacarbazine in advanced metastatic melanoma patients.

Engineered cytokine products represent promising agents for the treatment of immunogenic tumors, such as malignant melanoma, in addition to immune checkpoint inhibitors. Here we describe the results of a controlled, randomized phase II clinical trial, aimed at assessing the therapeutic potential of L19IL2, a fully human fusion protein consisting of the L19 antibody specific to the alternatively spliced extra-domain B of fibronectin, fused to human interleukin-2 in advanced metastatic melanoma. In one arm, patients received dacarbazine (DTIC; 1000 mg/m2 of body surface on day 1 of 21-day cycles) as single agent, while in two other arms L19IL2 (22.5 million international units of IL2 equivalents) was added, based on two different schedules of administration. In total, 69 patients with stage IV melanoma were enrolled (24 in the dacarbazine arm, 23 and 22 in the other combination arms, respectively) and 67 received treatment. Analyses of efficacy results show a statistically significant benefit in terms of overall response rate and median progression-free survival for patients receiving L19IL2 in combination with DTIC, compared to DTIC as single agent. In light of these results, further clinical investigations with L19IL2 (alone or in combination with other agents) are warranted.

First-line therapy-stratified survival in BRAF-mutant melanoma: a retrospective multicenter analysis.

BACKGROUND: Inhibition of the mitogen-activated protein kinase (MAPK) pathway as well as programmed death 1 receptor (PD-1) blockade was shown to prolong overall survival (OS) in patients with advanced B-Raf proto-oncogene (BRAF)-mutant melanoma. However, due to the lack of head-to-head trials, it remains unclear if one of these therapeutic approaches should be preferred in first-line therapy. Here, we present a retrospective analysis comparing anti-PD-1 monotherapy with BRAF/MAPK/ERK kinase (MEK) combined inhibition used as first-line agents in a real-world clinical setting. PATIENTS AND METHODS: Clinical data, routine blood counts and lactate dehydrogenase (LDH) levels of 301 patients with unresectable or metastatic melanoma harboring an activating mutation in BRAF (V600E/K) were included. Of these, 106 received anti-PD-1 antibodies, while 195 patients were treated with a selective BRAF inhibitor combined with an MEK inhibitor as palliative first-line therapy. Patients were sub-grouped according to previously described predictive and prognostic markers. RESULTS: OS was significantly longer in patients receiving anti-PD-1 monotherapy compared to patients receiving combined MAPK inhibitors. Subsequent therapies were comparable among these groups. The difference in OS was less pronounced in patients with high LDH levels and visceral metastatic spread. CONCLUSION: First-line treatment with a PD-1 blocking antibody might be associated with longer OS than first-line inhibition of the MAPK pathway in patients with advanced melanoma harboring mutant BRAF. These hypothesis-generating data need to be confirmed or rejected in prospective, randomized trials.

Establishing High Dimensional Immune Signatures from Peripheral Blood via Mass Cytometry in a Discovery Cohort of Stage IV Melanoma Patients.

The identification of blood-borne biomarkers correlating with melanoma patient survival remains elusive. Novel techniques such as mass cytometry could help to identify melanoma biomarkers, allowing simultaneous detection of up to 100 parameters. However, the evaluation of multiparametric data generated via time-of-flight mass cytometry requires novel analytical techniques because the application of conventional gating strategies currently used in polychromatic flow cytometry is not feasible. In this study, we have employed 38-channel time-of-flight mass cytometry analysis to generate comprehensive immune cell signatures using matrix boolean analysis in a cohort of 28 stage IV melanoma patients and 17 controls. Clusters of parameters were constructed from the abundance of cellular phenotypes significantly different between patients and controls. This approach identified patient-specific combinatorial immune signatures consisting of high-resolution subsets of the T cell, NK cell, B cell, and myeloid compartments. An association with superior survival was characterized by a balanced distribution of myeloid-derived suppressor cell-like and APC-like myeloid phenotypes and differentiated NK cells. The results of this study in a discovery cohort of melanoma patients suggest that multifactorial immune signatures have the potential to allow more accurate prediction of individual patient outcome. Further investigation of the identified immune signatures in a validation cohort is now warranted.

Accurate quantification of T-cells expressing PD-1 in patients on anti-PD-1 immunotherapy.

Increasing numbers of trials employing anti-PD-1 immunotherapy emphasize the requirement for predictive biomarkers of clinical response. Many studies examine the cell surface expression of PD-1 and other key regulators of T-cell activation and inhibition. Here, we compared common commercially available anti-PD-1 diagnostic antibodies and tested whether they can bind the PD-1 receptor in the presence of the therapeutic antagonists pembrolizumab and nivolumab. We observed that currently no antibodies are available that can reliably stain all PD-1 receptors on T-cells from patients treated with anti-PD-1 antibodies. Furthermore, none of the diagnostic antibodies detected the entire population of PD-1+ T-cells relative to indirect staining using the therapeutic antibodies themselves. To overcome this problem, here we present a reliable method for quantifying PD-1 expression on immune cells from treated patients which can be included in any conventional flow or mass cytometry antibody panel used for patient monitoring.

Ipilimumab-dependent cell-mediated cytotoxicity of regulatory T cells ex vivo by nonclassical monocytes in melanoma patients.

Enhancing immune responses with immune-modulatory monoclonal antibodies directed to inhibitory immune receptors is a promising modality in cancer therapy. Clinical efficacy has been demonstrated with antibodies blocking inhibitory immune checkpoints such as cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) or PD-1/PD-L1. Treatment with ipilimumab, a fully human CTLA-4-specific mAb, showed durable clinical efficacy in metastatic melanoma; its mechanism of action is, however, only partially understood. This is a study of 29 patients with advanced cutaneous melanoma treated with ipilimumab. We analyzed peripheral blood mononuclear cells (PBMCs) and matched melanoma metastases from 15 patients responding and 14 not responding to ipilimumab by multicolor flow cytometry, antibody-dependent cell-mediated cytotoxicity (ADCC) assay, and immunohistochemistry. PBMCs and matched tumor biopsies were collected 24 h before (i.e., baseline) and up to 4 wk after ipilimumab. Our findings show, to our knowledge for the first time, that ipilimumab can engage ex vivo FcγRIIIA (CD16)-expressing, nonclassical monocytes resulting in ADCC-mediated lysis of regulatory T cells (Tregs). In contrast, classical CD14(++)CD16(-) monocytes are unable to do so. Moreover, we show that patients responding to ipilimumab display significantly higher baseline peripheral frequencies of nonclassical monocytes compared with nonresponder patients. In the tumor microenvironment, responders have higher CD68(+)/CD163(+) macrophage ratios at baseline and show decreased Treg infiltration after treatment. Together, our results suggest that anti-CTLA-4 therapy may target Tregs in vivo. Larger translational studies are, however, warranted to substantiate this mechanism of action of ipilimumab in patients.

The Generation of CAR-Transfected Natural Killer T Cells for the Immunotherapy of Melanoma.

Natural killer T (NKT) cells represent a cell subpopulation that combines characteristics of natural killer (NK) cells and T cells. Through their endogenous T-cell receptors (TCRs), they reveal a pronounced intrinsic anti-tumor activity. Thus, a NKT cell transfected with a chimeric antigen receptor (CAR), which recognizes a tumor-specific surface antigen, could attack tumor cells antigen-specifically via the CAR and additionally through its endogenous TCR. NKT cells were isolated from peripheral blood mononuclear cells (PBMCs), expanded, and electroporated with mRNA encoding a chondroitin sulfate proteoglycan 4 (CSPG4)-specific CAR. The CAR expression on NKT cells and their in vitro functionality were analyzed. A transfection efficiency of more than 80% was achieved. Upon stimulation with melanoma cells, CAR-NKT cells produced cytokines antigen-specifically. Compared with conventional CAR-T cells, cytokine secretion of CAR-NKT cells was generally lower. Specific cytotoxicity, however, was similar with CAR-NKT cells showing a trend towards improved cytotoxicity. Additionally, CAR-NKT cells could kill target cells through their endogenous TCRs. In summary, it is feasible to generate CAR-NKT cells by using mRNA electroporation. Their CAR-mediated cytotoxicity is at least equal to that of conventional CAR-T cells, while their intrinsic cytotoxic activity is maintained. Thus, CAR-NKT cells may represent a valuable alternative to conventional CAR-T cells for cancer immunotherapy.

Intralesional treatment of metastatic melanoma: a review of therapeutic options.

Intralesional therapy of melanoma patients with locally advanced metastatic disease is attracting increasing interest, not least due to its ability to lead to both direct tumor cell killing and the stimulation of both a local and a systemic immune response. An obvious pre-requisite for this type of approach is the presence of accessible metastases that are amenable to direct injection with the therapeutic agent of interest. Patients who present with these characteristics belong to stages IIIB/C or IV of the disease. Surgical resection with intention to cure is the standard of care for patients with limited tumor burden and confined spread of disease (resectable patients). However, this category of patients is at a high risk of further recurrences until the disease becomes inoperable (unresectable) or progresses to a more advanced stage with visceral organ involvement, after which the prognosis is particularly grim. Most of the intralesional treatments tested so far, including the recently approved oncolytic virus talimogene laherparepvec, target the subpopulation of patients with unresectable disease, but the possibility to use the intralesional treatment in a neoadjuvant setting for fully resectable patients is attracting considerable interest. The present article reviews approved products and advanced stage pharmaceutical agents in development for the intralesional treatment of melanoma patients.

Combined treatment with ipilimumab and intratumoral interleukin-2 in pretreated patients with stage IV melanoma-safety and efficacy in a phase II study.

Treatment of advanced melanoma patients with ipilimumab results in improved survival. However, only about 20% of treated patients experience long-term benefit. Combining treatment of ipilimumab with other drugs may improve immune activation and potentially enhance clinical efficacy. The aims of the phase II clinical trial reported here were to investigate tolerability and efficacy of a combined immunotherapeutic strategy comprising standard systemic ipilimumab at 3 mg/kg four times at 3-week intervals and intratumorally injected IL-2 at 9 MIU daily twice weekly for four weeks in pretreated melanoma patients with distant metastasis. The primary endpoint was the disease control rate according to immune-related response criteria at week 12; tolerability according to Common Terminology Criteria for Adverse Events criteria was secondary endpoint. No objective responses were observed in the 15 enrolled patients. Three patients had stable disease 12 weeks after starting treatment, yielding a disease control rate of 20%. Tolerability of this combination treatment was acceptable. Observed adverse events were those expected from the respective monotherapies. Autoimmune colitis was observed in two patients. Grade III/IV adverse events were observed in 40% of patients, and no treatment-related deaths occurred. Thus, this combined immunotherapy is associated with adverse events similar to those associated with the respective monotherapies. However, this study does not provide any evidence of improved efficacy of the combination over ipilimumab alone.

High-sensitivity HLA class I peptidome analysis enables a precise definition of peptide motifs and the identification of peptides from cell lines and patients' sera.

The characterization of peptides bound to human leukocyte antigen (HLA) class I is of fundamental importance for understanding CD8+ T cell-driven immunological processes and for the development of immunomodulatory therapeutic strategies. However, until now, the mass spectrometric analysis of HLA-bound peptides has typically required billions of cells, still resulting in relatively few high-confidence peptide identifications. Capitalizing on the recent developments in mass spectrometry and bioinformatics, we have implemented a methodology for the efficient recovery of acid-eluted HLA peptides after purification with the pan-reactive antibody W6/32 and have identified a total of 27 862 unique peptides with high confidence (1% false discovery rate) from five human cancer cell lines. More than 93% of the identified peptides were eight to 11 amino acids in length and contained signatures that were in excellent agreement with published HLA binding motifs. Furthermore, by purifying soluble HLA class I complexes (sHLA) from sera of melanoma patients, up to 972 high-confidence peptides could be identified, including melanoma-associated antigens already described in the literature. Knowledge of the HLA class I peptidome should facilitate multiplex tetramer technology-based characterization of T cells, and allow the development of patient selection, stratification and immunomodulatory therapeutic strategies.

Phenotypic characterization and prognostic impact of circulating γδ and αß T-cells in metastatic malignant melanoma.

Human T cells carrying γδ T-cell receptors (TCRs) represent a minor population relative to those with αß TCRs. There has been much interest recently in the possibility of using these γδ T-cells in cancer therapy because they can kill tumor cells in vitro in an MHC-unrestricted manner, and possess potential regulatory capability and antigen-presenting capacity. The presence of γδ T-cells in late-stage melanoma patients and their relationship with survival has not been extensively explored, although relatively lower percentages of total γδ T-cells and Vδ2+ cells have been reported. Here, we present a detailed analysis of associations of γδ T-cell subsets and differentiation stages with survival in Stage IV patients, compared with CD4+ and CD8+ αß T-cells. We found an increased Vδ1:Vδ2-ratio and a decreased CD4:CD8-ratio in patients compared to healthy controls, on the basis both of relative frequencies and absolute cell counts per µL blood. Nonetheless, Kaplan-Meier analyses showed that a higher than median frequency of Vδ1+ cells was negatively associated with survival, whereas there were no positive or negative associations with frequencies of Vδ2+ cells. Correlations of cell differentiation status with survival revealed a negative association of early-differentiated Vδ1+ T cells with survival, both on the basis of relative frequencies and absolute counts. There was also a positive correlation between the frequencies of early-differentiated CD8+ αß T-cells and survival. Our findings suggest peripheral blood frequencies of Vδ1+ T-cells as a potential prognostic marker in melanoma. The mechanisms by which higher abundance of Vδ1+ cells are associated with poorer survival require determination.

Diminished levels of the soluble form of RAGE are related to poor survival in malignant melanoma.

RAGE is a central driver of tumorigenesis by sustaining an inflammatory tumor microenvironment. This study links the soluble forms of RAGE (sRAGE and esRAGE) with clinical outcome of melanoma patients. Moreover, tissue expression of RAGE was analyzed using immunohistochemistry on two independent tissue microarrays (TMA) containing 35 or 257 primary melanomas, and 41 or 22 benign nevi, respectively. Serum concentrations of sRAGE and esRAGE were measured in 229 Stage III-IV patients using ELISA and plasma concentrations of sRAGE were analyzed in an independent second cohort with 173 samples of Stage I-IV patients. In this cohort, three well-described SNPs in the RAGE gene were analyzed. RAGE protein expression was highly upregulated in primary melanomas compared to benign nevi in the two TMA (p < 0.001 and p = 0.005) as well as in sun-exposed melanomas (p = 0.046). sRAGE and esRAGE were identified as prognostic markers for survival as diminished sRAGE (p = 0.034) and esRAGE (p = 0.012) serum levels correlated with poor overall survival (OS). Multivariate Cox regression analysis showed that diminished serum sRAGE was independently associated with poor survival (p = 0.009). Moreover, diminished sRAGE was strongly associated with impaired OS in the second cohort (p < 0.001). Multivariate Cox regression analysis including the investigated SNPs revealed an independent correlation of the two interacting promoter SNPs with impaired OS. In conclusion, the soluble forms of RAGE and variants in its genetic locus are prognostic markers for survival in melanoma patients with high risk for progression.

Increased CCL17 serum levels are associated with improved survival in advanced melanoma.

BACKGROUND: Prognostic factors of melanoma patients with distant metastases remain poorly established. This study aimed to compare the prognostic impact of putative serum biomarkers, namely S100B, YKL-40 or CCL17, in stage IV melanoma patients. PATIENTS AND METHODS: Serum concentrations were analyzed by ELISA. Disease-specific survival of 80 patients according to S100B, YKL-40 or CCL17 and clinical factors were calculated by univariate Kaplan-Meier survival and multivariate analysis. RESULTS: Low serum levels of S100B, high concentrations of CCL17 and female gender correlated with improved survival. A trend for favorable prognosis was observed for the M categories M1a/b versus M1c according to the AJCC classification. No correlation with survival was evident for YKL-40 serum levels and age. In multivariate analysis, S100B (HR 2.1; p = 0.005) and CCL17 (HR 1.8; p = 0.029) had independent prognostic impact. Patients with a combination of normal S100B and high CCL17 had a high chance for long-term survival, which was 43 % after 3 years. CONCLUSION: Serum levels of CCL17 and S100B represent independent prognostic markers for melanoma patients with distant metastases. These biomarkers were more powerful than the M category according to the AJCC classification to indicate overall survival. CCL17 represents a promising biomarker upon immune checkpoint blockade in melanoma.

Sentinel Lymph Node Dissection in Head and Neck Melanoma has Prognostic Impact on Disease-Free and Overall Survival.

BACKGROUND: Sentinel lymph node biopsy (SLNB) plays an important role in the prognostic classification of melanoma and is now a standard staging procedure. However, due to the complex drainage pattern and the risk of site associated morbidity, the potential survival benefit of SLNB is controversial in head and neck (H&N) melanoma. METHODS: Patients with primary H&N melanoma with a tumor thickness ≥1.00 mm diagnosed in the Department of Dermatology, University of Tuebingen, Germany between 1991 and 2010 were included in this study. Regarding patterns of metastases, disease-free, and overall-survival, 259 patients with SLNB were compared retrospectively to 218 patients without SLNB. RESULTS: The detection of micrometastasis in SLN proved to be a significant prognostic factor in H&N patients [hazard ratio (HR) 3.69, p < 0.0001]. A significant improvement of recurrence-free survival (RFS, p = 0.011), regional lymph node metastasis-free survival (LFS, p = 0.007), and distant metastasis-free survival (DMSF, p = 0.015) was observed for patients with SLNB versus non-SLNB. Furthermore, a trend towards better overall survival (OS) was found (p = 0.053) for the SLNB group. CONCLUSIONS: SLNB improved prognostic outcome in H&N melanoma in terms of disease-free and distant metastases survival, reduced subsequent regional lymph node metastases, and showed a trend towards a better OS.

Vemurafenib reverses immunosuppression by myeloid derived suppressor cells.

Myeloid derived suppressor cells (MDSCs) suppress innate and adaptive immunity, thereby limiting anti-tumor immune responses in cancer patients. In patients with advanced melanoma, the phenotype and function of MDSCs remains controversial. In our study, we further explored two distinct subpopulations of MDSCs and investigated the impact of Vemurafenib on these cells. Flow cytometry analysis revealed that in comparison to healthy donors and patients with localized disease, PBMCs from patients with metastatic melanoma showed an increased frequency of CD14(+) HLA-DR(-/low) monocytic MDSCs (moMDSCs) and of a previously unrecognized population of CD14(-) CD66b(+) Arginase1(+) granulocytic MDSCs (grMDSCs). In vitro, both populations suppressed autologous T-cell proliferation, which was tested in CFSE-based proliferation assays. Vemurafenib treatment of melanoma patients reduced the frequency of both moMDSCs and grMDSCs. According to our in vivo finding, conditioned medium (CM) from Vemurafenib treated melanoma cells was less active in inducing moMDSCs in vitro than CM from untreated melanoma cells. In conclusion, patients with advanced melanoma show increased levels of moMDSCs, and of a population of CD14(-) CD66b(+) Arginase1(+) grMDSCs. Both MDSCs are distinct populations capable of suppressing autologous T-cell responses independently of each other. In vitro as well as in vivo, Vemurafenib inhibits the generation of human moMDSCs. Thus, Vemurafenib decreases immunosuppression in patients with advanced melanoma, indicating its potential as part of future immunotherapies.

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.

Early decrease of blood myeloid-derived suppressor cells during checkpoint inhibition is a favorable biomarker in metastatic melanoma.

BACKGROUND: The need for reliable clinical biomarkers to predict which patients with melanoma will benefit from immune checkpoint blockade (ICB) remains unmet. Several different parameters have been considered in the past, including routine differential blood counts, T cell subset distribution patterns and quantification of peripheral myeloid-derived suppressor cells (MDSC), but none has yet achieved sufficient accuracy for clinical utility. METHODS: Here, we investigated potential cellular biomarkers from clinical routine blood counts as well as several myeloid and T cell subsets, using flow cytometry, in two independent cohorts of a total of 141 patients with stage IV M1c melanoma before and during ICB. RESULTS: Elevated baseline frequencies of monocytic MDSCs (M-MDSC) in the blood were confirmed to predict shorter overall survival (OS) (HR 2.086, p=0.030) and progression-free survival (HR 2.425, p=0.001) in the whole patient cohort. However, we identified a subgroup of patients with highly elevated baseline M-MDSC frequencies that fell below a defined cut-off during therapy and found that these patients had a longer OS that was similar to that of patients with low baseline M-MDSC frequencies. Importantly, patients with high M-MDSC frequencies exhibited a skewed baseline distribution of certain other immune cells but these did not influence patient survival, illustrating the paramount utility of MDSC assessment. CONCLUSION: We confirmed that in general, highly elevated frequencies of peripheral M-MDSC are associated with poorer outcomes of ICB in metastatic melanoma. However, one reason for an imperfect correlation between high baseline MDSCs and outcome for individual patients may be the subgroup of patients identified here, with rapidly decreasing M-MDSCs on therapy, in whom the negative effect of high M-MDSC frequencies was lost. These findings might contribute to developing more reliable predictors of late-stage melanoma response to ICB at the individual patient level. A multifactorial model seeking such markers yielded only MDSC behavior and serum lactate dehydrogenase as predictors of treatment outcome.