Abstract
Purpose :
Uveal melanoma (UM) occurs in an immune-privileged site that provides immune-escape for UM cells and systemic spreading. The presence of inflammatory cells in primary UM is associated with a pro-tumor immune response and poor prognosis. One proposed mechanism for immune evasion of cancer cells is through the induction of myeloid-derived suppressor cells (MDSCs). These immature cells are rare in healthy individuals but accumulate and acquire immunosuppressive functions in pathological conditions such as cancer. We determined whether co-culturing UM cells and healthy peripheral blood mononuclear cells (PBMCs) promoted an inflammatory response that contribute to the expansion and activation of MDSCs.
Methods :
UM cells (92.1, MEL270 and OMM2.5) were seeded onto a membrane insert with 0.4 μm pores, while PBMCs (from 3 healthy donors) were added on the bottom compartment, and co-cultured for 5 days. PBMCs or UM cells were cultured alone as controls. The purity, and number of MDSCs were determined by flow cytometry using specific antibodies (CD11b, CD33-PE, HLA-DR, CD14, CD15). Soluble factors known to promote the expansion (i.e., granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-6 (IL-6), and the immunosuppressive functions (i.e., Interferon gamma (IFNγ), IL-1β, and IL-10) of MDSCs were analyzed on supernatants of UM cells, PBMCs, or co-cultures. Experiments were repeated as triplicates. Data were analysed by an ANOVA followed by Tukey’s or Bonferroni multiple comparisons tests. A p< 0.05 was considered statistically significant.
Results :
Myeloid cells (purities > 95%), isolated from PBMCs/UM cells co-cultures, displayed phenotypic markers of human MDSCs. The levels of GM-CSF and IL-6PBMCs/UM cells co-cultures. In addition, the levels of IFNγ, IL-1β, and IL-10 were high in the supernatants of these co-cultures. In contrast, the level of the tumor necrosis factor alpha (TNFα) decreased.
Conclusions :
The crosstalk between UM cells and PBMCs induced release of soluble factors responsible for the expansion of MDSCs and induction of their immunosuppressive functions. This suggests that induction of MDSCs immunosuppressive phenotype underlay the immune escape of UM. Targeting these cells might represent a path to future immunotherapies.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.