(601f) Cancer exosomes deliver extracellular mRNAs to suppress T lymphocyte function

The recent clinical success for cancer immunotherapy relies on two strategies: 1) immune checkpoint modulators to activate anti-tumor immunity and 2) adoptive cell transfer (ACT) that expands ex vivo a patient’s own immune cells by cytokine stimulation and re-injects cells. Both strategies aim to enhance anti-tumor immunity by increasing peripheral T lymphocytes, which would lead to increased retention and cytotoxic activity at the tumor sites. While a subset of patients responds remarkably well, a low response rate is a major criticism for cancer immunotherapy. Potent immunosuppressive mechanisms present within the tumor microenvironment are thought to limit the efficacy of cancer immunotherapies against melanoma. Nano-scaled membrane vesicles, called exosomes, are released by both normal and malignant cells and have emerged as an important mode of intercellular communications. Exosomes can transfer membrane-bound and cytosolic proteins, lipids, and coding and non-coding RNAs between cells. To better understand the immunosuppressive role that exosomes may play within the tumor microenvironment, we isolated exosomes from a variety of melanoma cell models, characterized their morphologies, and identified functional molecules including cytokine receptors and mRNAs. Using microarray analysis, we found that B16F0 exosomes contain coding mRNAs with a different enrichment pattern compared to donor cells. Functionally, pathway enrichment analysis suggested that these exosomal mRNAs impact a variety of immune signaling pathways. PTPN11 was the most common mRNAs present in the B16F0 exosomes among the enriched pathways. Exosomal PTPN11 mRNA was functionally active since we found that B16F0 melanoma but not melan-a melanocyte exosomes were able to dose-dependently increase PTPN11 protein in T lymphocytes. To determine the specific effects of such protein up-regulation in T cells, cDNA plasmids coding PTPN11 and other genes respectively were transferred into T cells and their specific effects to interleukin 2 and interleukin 12 cytokine signaling pathways were investigated. Our results suggest that B16F0 exosomes are able to deliver coding mRNA payload that can suppress the activity and function of tumor-infiltrating lymphocytes. This work is important due to the impact it will have on the T cell-based cancer immunotherapy and helping to unravel the specific immunosuppression mechanisms of tumor-derived exosomes.