Abstract
Cancer is the second leading cause of death in the United States, and over half amillion cancer-related deaths are expected to occur in our country this year alone. While cancer prognosis has generally improved over the past 20 years, there are still certain kinds of cancer, such as head and neck squamous cell carcinoma (HNSCC), that are far behind in terms of improved treatment outcomes, recurrence rates, and overall mortality statistics. HNSCC is the 6th most common malignancy globally, and the five-year survival rate for stage III and IV patients is only 50%. Additionally, HNSCC patients who relapse have a mean survival rate of less than one year. Therefore, understanding the mechanism of local recurrences and the development of second primary tumors is imperative for improving disease outcomes for stage III and IV HNSCC patients. Cancer stem cells (CSCs) are a subpopulation of cells within a tumor that possessself-renewing properties that have been linked to tumor initiation, neoplastic maintenance, and recurrence post treatment. CSCs have been shown to be resistant to both chemotherapeutics and radiotherapy. Consequently, residual CSCs not completely eliminated by surgical resection, or chemoradiation, are thought to mediate recurrence in many patients. A key feature of CSCs and their ability to induce recurrence is their immunoregulatory properties that allow them to evade immunosurveillance and elimination. Several studies have established that CSCs secrete canonical secretoryproteins with immunoregulatory properties such as transforming growth factor beta (TGFb), Interleukin 4 (IL-4), and cluster of differentiation 200 (CD200). However, it remains unclear what role, if any, exosomes play in CSCs immunomodulatory properties, as little is currently known about the physiology or function of CSC-derived exosomes (CSC-EV).
Therefore, here we propose to investigate the immunomodulatory contents and functional properties of CSC-EV. To address the current gap in knowledge surrounding the immunoregulatoryproperties of CSCs and CSC-EV, we conducted studies to elucidate the mechanisms associated with CSC and CSC-EV’s ability to regulate the immune system. We designed
experiments that 1) directly analyzed the expression patterns of immunoregulatory factors in CSCs and CSC-EV and that 2) targeted the immunomodulatory properties of CSC and
CSC-EV in vitro. To characterize the immunoregulatory properties of CSC-EV, we used a canonical macrophage polarization assay that employs CD14+ macrophage progenitor cells known as monocytes, which were isolated from peripheral blood mononuclear cells (PBMCs). After the successful implementation of these assays, our results indicate that CSC-EV induce M2-like, cancer promoting, macrophage polarization, and that this polarization is in part mediated by the presentation of sialic acid residues. These results are expected to have a positive impact because they will provide a strong evidence-based proof of principle for further development of novel therapies for the future treatment of cancer. With such a large subset of the population affected by this disease, understanding theunderlying mechanisms of tumorigenesis, metastasis, and immune escape is imperative to improving the disease outcomes for affected patients worldwide.