Abstract
Purpose :
Uveal melanoma (UM) is the most common primary intraocular tumor in adults and has a high mortality rate due to metastatic disease. Metastasis development is enabled by a tumour-induced immunosuppressive environment. Myeloid-derived Suppressor Cells (MDSCs), a heterogeneous population of immature myeloid cells which can mediate suppression of T-effector responses, have been recently implicated in cancer immunotolerance and failure of anti-tumor activity. MDSCs can be characterized based on their phenotypic features by displaying myeloid markers (CD33+ and CD11b) and further subcategorized into granulocytic or monocytic subsets, based on the presence of CD15+ and CD14+, respectively. Previous reports have showed the induction of canonical suppressive CD33+/CD11b+ MDSCs from human peripheral blood mononuclear cells (PBMCs) by co-culturing with several tumor cell lines, the most prominent being head and neck squamous cell carcinoma (SCCL-MT1). To the best of our knowledge, uveal melanoma cell lines have not been studied. We aim to evaluate the ability of a metastatic UM cell line to induce MDSCs from PBMCs.
Methods :
Human PBMCs were isolated from healthy donors and co-cultured with metastatic UM cell line OMM2.5 for 5 days. Myeloid CD33+/CD11b+ cells were phenotypically characterized by flow cytometry. Myeloid CD33+/CD11b+ cells cultured in the presence of SCCL-MT1 or in the absence of any tumour cells were used as positive and negative controls, respectively.
Results :
CD33+ cells induced from co-cultures with OMM2.5 showed a phenotype like the ones induced by SCCL-MT1 co-cultures. From all CD33+ cells, 23.5% showed a low expression of CD11b, positivity for CD14+ and low expression of HLA-DR. In contrast, CD33+ myeloid cells from PBMCs cultured in the absence of tumor cells were characterized by high levels of CD11b and HLA-DR (94.4%).
Conclusions :
Our study shows that PBMC co-cultured with OMM2.5 cells, produced CD33+ myeloid cells with a similar phenotype to CD33+ cells derived from co-cultures with SCCL-MT1, which have been previously reported as suppressive. This indicates the ability of metastatic uveal melanoma to induce MDSCs. MDSCs are a major obstacle for immunotherapy, therefore the study of immunotolerance in UM is relevant considering a potential target in adjunctive therapy.
This is a 2020 ARVO Annual Meeting abstract.