Mutations in BRAF are present in the majority of patients with melanoma, rendering these tumors sensitive to targeted therapy with BRAF and MEK inhibitors. Unfortunately, resistance almost invariably develops. Recently, a phenomenon called "phenotype switching" has been identified as an escape route. By switching from a proliferative to an invasive state, melanoma cells can acquire resistance to these targeted therapeutics. Interestingly, phenotype switching bears a striking resemblance to the epithelial-to-mesenchymal-like transition that has been described to occur in cancer stem cells in other tumor types. We propose that these changes are manifestations of one and the same underlying feature, namely a dynamic and reversible phenotypic tumor cell plasticity that renders a proportion of cells both more invasive and resistant to therapy. At the same time, the specific characteristics of these tumor cell populations offer potential for being explored as target for therapeutic intervention. Cancer Res; 74(21); 5937-41. Ó2014 AACR.

Mesothelioma has been regarded as a nonimmunogenic tumor, which is also shown by the low response rates to treatments targeting the PD-1/PD-L1 axis. Previously, we demonstrated that autologous tumor lysate-pulsed dendritic cell (DC) immunotherapy increased T-cell response toward malignant mesothelioma. However, the use of autologous tumor material hampers implementation in large clinical trials, which might be overcome by using allogeneic tumor cell lines as tumor antigen source. The purpose of this study was to investigate whether allogeneic lysate-pulsed DC immunotherapy is effective in mice and safe in humans. First, in two murine mesothelioma models, mice were treated with autologous DCs pulsed with either autologous or allogeneic tumor lysate or injected with PBS (negative control). Survival and tumor-directed T-cell responses of these mice were monitored. Results were taken forward in a first-in-human clinical trial, in which 9 patients were treated with 10, 25, or 50 million DCs per vaccination. DC vaccination consisted of autologous monocyte-derived DCs pulsed with tumor lysate from five mesothelioma cell lines. In mice, allogeneic lysate-pulsed DC immunotherapy induced tumor-specific T cells and led to an increased survival, to a similar extent as DC immunotherapy with autologous tumor lysate. In the first-in-human clinical trial, no dose-limiting toxicities were established and radiographic responses were observed. Median PFS was 8.8 months [95% confidence interval (CI), 4.1-20.3] and median OS not reached (median follow-up = 22.8 months). DC immunotherapy with allogeneic tumor lysate is effective in mice and safe and feasible in humans. .

Myeloid-derived suppressor cells (MDSCs) play an important role in immune suppression and accumulate under pathologic conditions such as cancer and chronic inflammation. They comprise a heterogeneous population of immature myeloid cells that exert their immunosuppressive function via a variety of mechanisms. Immunoglobulin-like transcript 3 (ILT3) is a receptor containing immunoreceptor tyrosine-based inhibition motifs (ITIMs) that can be expressed on antigen-presenting cells and is an important regulator of dendritic cell tolerance. ILT3 exists in a membrane-bound and a soluble form and can interact with a yet unidentified ligand on T cells and thereby induce T-cell anergy, regulatory T cells, or T suppressor cells. In this study, we analyzed freshly isolated peripheral blood mononuclear cells (PBMCs) of 105 patients with non-small cell lung cancer and 20 healthy controls and demonstrated for the first time that ILT3 is expressed on MDSCs. We show that increased levels of circulating MDSCs correlate with reduced survival. On the basis of ILT3 cell surface expression, an ILT3 low and ILT3 high population of polymorphonuclear (PMN)-MDSCs could be distinguished. Interestingly, in line with the immunosuppressive function of ILT3 on dendritic cells, patients with an increased proportion of PMN-MDSCs and an increased fraction of the ILT3 high subset had a shorter median survival than patients with elevated PMN-MDSC and a smaller ILT3 high fraction. No correlation between the ILT3 high subset and other immune variables was found. ILT3 expressed on MDSCs might reflect a previously unknown mechanism by which this cell population induces immune suppression and could therefore be an attractive target for immune intervention.

Purpose: Chemotherapy has long been the standard treatment for advanced stage non-small cell lung cancer (NSCLC), but checkpoint inhibitors are now approved for use in several patient groups and combinations. To design optimal combination strategies, a better understanding of the immunemodulatory capacities of conventional treatments is needed. Therefore, we investigated the immune-modulatory effects of paclitaxel/carboplatin/bevacizumab (PCB), focusing on the immune populations associated with the response to checkpoint inhibitors in peripheral blood.Experimental Design: A total of 223 patients with stage IV NSCLC, enrolled in the NVALT12 study, received PCB, with or without nitroglycerin patch. Peripheral blood was collected at baseline and after the first and second treatment cycle, proportions of T cells, B cells, and monocytes were determined by flow cytometry. Furthermore, several subsets of T cells and the expression of Ki67 and coinhibitory receptors on these subsets were determined.Results: Although proliferation of CD4 T cells remained stable following treatment, proliferation of peripheral blood CD8 T cells was significantly increased, particularly in the effector memory and CD45RA þ effector subsets. The proliferating CD8 T cells more highly expressed programmed death receptor (PD)-1 and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) compared with nonproliferating CD8 T cells. Immunologic responders (iR; >2 fold increased proliferation after treatment) did not show an improved progression-free (PFS) or overall survival (OS).Conclusions: Paclitaxel/carboplatin/bevacizumab induces proliferation of CD8 T cells, consisting of effector cells expressing coinhibitory checkpoint molecules. Induction of proliferation was not correlated to clinical outcome in the current clinical setting. Our findings provide a rationale for combining PCB with checkpoint inhibition in lung cancer.