Early disappearance of tumor antigen-reactive T cells from peripheral blood correlates with superior clinical outcomes in melanoma under anti-PD-1 therapy

Background

Anti-programmed cell death protein 1 (PD-1) antibodies are now routinely administered for metastatic melanoma and for increasing numbers of other cancers, but still only a fraction of patients respond. Better understanding of the modes of action and predictive biomarkers for clinical outcome is urgently required. Cancer rejection is mostly T cell-mediated. We previously showed that the presence of NY-ESO-1-reactive and/or Melan-A-reactive T cells in the blood correlated with prolonged overall survival (OS) of patients with melanoma with a heterogeneous treatment background. Here, we investigated whether such reactive T cells can also be informative for clinical outcomes in metastatic melanoma under PD-1 immune-checkpoint blockade (ICB).

Methods

Peripheral blood T cell stimulation by NY-ESO-1 and Melan-A overlapping peptide libraries was assessed before and during ICB in two independent cohorts of a total of 111 patients with stage IV melanoma. In certain cases, tumor-infiltrating lymphocytes could also be assessed for such responses. These were characterized using intracellular cytokine staining for interferon gamma (IFN-γ), tumor negrosis factor (TNF) and CD107a. Digital pathology analysis was performed to quantify NY-ESO-1 and Melan-A expression by tumors. Endpoints were OS and progression-free survival (PFS).

Results

The initial presence in the circulation of NY-ESO-1- or Melan-A-reactive T cells which became no longer detectable during ICB correlated with validated, prolonged PFS (HR:0.1; p>0.0001) and OS (HR:0.2; p=0.021). An evaluation of melanoma tissue from selected cases suggested a correlation between tumor-resident NY-ESO-1- and Melan-A-reactive T cells and disease control, supporting the notion of a therapy-associated sequestration of cells from the periphery to the tumor predominantly in those patients benefitting from ICB.

Conclusions

Our findings suggest a PD-1 blockade-dependent infiltration of melanoma-reactive T cells from the periphery into the tumor and imply that this seminally contributes to effective treatment.

Abstract 653: Ovarian cancer persister cells: 2D and 3D in-depth characterization and analysis

Ovarian cancer is one of the five cancer types with highest incidence of death in women. Due to a lack of diagnostic options, timely detection of ovarian cancer is difficult and 75% of patients are diagnosed at a late stage. The standard therapy for ovarian cancer is resection of the affected tissue, followed by chemotherapy. However, patients frequently suffer from relapse of the disease, as some tumor cells persist chemotherapy and grow into a new, more aggressive tumor. To offer therapeutic approaches that prevent relapse by eradicating persister cells we aimed to identify the molecular mechanisms and determinants that are characteristic for persister cells. As initial cellular model system OVCAR-3 cells were used to select ovarian cancer persister cells. Selection was performed analogously to serum levels of chemotherapy patients, i.e. OVCAR-3 cells were incubated twice in the presence of 13 µM Cisplatin for 4 hours. Cisplatin-selection identified clones were collected and in further analyses compared to randomly collected untreated control clones. In order to account the native tumor microenvironment and heterogeneity within the tumor and among patients we cultured precision-cut tissue slices from primary ovarian tumor tissue with 280 µm thickness. Tumor tissue slices were cultured either under control conditions or exposed to 13 µM Cisplatin. Slices were further processed and cultured in Matrigel producing tumor-derived organoids, i.e. tumoroids. In contrast to OVCAR-3 control clones, the Cisplatin-selected OVCAR-3 persister cells showed filopodia-like structures. A scratch assay demonstrated enhanced motility of OVCAR-3-persister cells. Interestingly, cell death analysis (Annexin V) of Cisplatin exposed control and persister clonal cell lines showed the presence of surviving cells in both, persister and control groups. To identify the molecular determinants specific for persister cells we performed RNA sequencing. Data showed that, in line with initial results, the motility associated genes Snail and Vimentin are up regulated in persister clones. We successfully generated tumoroids from patient-derived ovarian cancer tissue slices. Tumoroids were cultured for more than two months and displayed a high viability. After exposure to Cisplatin less tumoroids generated from tumor slices were found. OVCAR-3-derived persister clones show morphological alterations (filopodia-like structures), enhanced motility and expression of motility associated genes. We expect the identification of genetic determinants for persister cell characteristics from comparison of RNAseq results of OVCAR-3 persister clones and tumor-derived organoids. The identification of genetic determinants will direct the development of therapeutics approaches targeting persister cells in ovarian cancer to prevent recurrence of tumors.

Citation Format: Kathrin Boepple, Meng Dong, Andrea Gaissler, Bernd Winkler, Markus Kleih, Frank Essmann, Walter E. Aulitzky. Ovarian cancer persister cells: 2D and 3D in-depth characterization and analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 653.