Abstract B045: EV-mediated immune modulation of CD8+ T cells in renal cell carcinoma

Introduction: Treatment regimens for advanced renal cell carcinoma (RCC) involve immune checkpoint inhibition targeting the PD-(L)1 pathway. PD-L1 is often overexpressed on tumor cells in advanced disease and plays a crucial role in regulating tumor-directed immune responses. It can also be expressed on tumor-secreted extracellular vesicles (EVs), which are an essential part of intercellular communication. PD-L1 carrying EVs have been shown to have immunomodulatory effects in several tumor entities, however their role in RCC is still unknown. The aim of this study was the evaluation of putative immunomodulatory effects of RCC-derived small EVs on CD8+ T cells. Materials and Methods: EVs of 5 untreated as well as interferon γ (IFNγ)-treated RCC cell lines were isolated through serial ultracentrifugation. Quality and quantity of the EVs were verified using Western Blotting (WB), Nano Particle Tracking Analysis and Transmission Electron microscopy, their PD-L1 expression was analyzed semi quantitatively through WB. CD8+ T cells were isolated from the blood of healthy donors, activated and subsequently co-cultured with RCC-derived EVs for a duration of 3 days. Proliferation and PD-1 expression of the T cells was assessed using flow cytometry. ELISAs were performed to analyze cyto- and chemokine secretion. Results: All RCC cell lines expressed PD-L1, albeit at varying low levels. Four out of 5 treated cell lines responded to IFNγ treatment with an upregulation of PD-L1 expression on both cells and secreted EVs. Co-cultures of CD8+ T cells and RCC-derived EVs, particularly PD-L1+ EVs isolated from IFNγ-stimulated cells, lead to a reduction in T cell PD-1 expression. Additionally, PD-L1-expressing EVs of RCC cell line RCC53 had an antiproliferative effect on CD8+ T cells. EVs also increased the secretion of IL-2, IL-10, CXCL10 and CCL5 by the CD8+ T cells. Conclusions: PD-L1 is expressed at low levels in RCC cell lines. However, repetitive IFNγ stimulation can lead to upregulation of PD-L1 on both cells and EVs enabling us to use this model to further investigate EV-mediated, PD-L1 dependent effects. In co-cultures, RCC-derived EVs impede early T cell activation and proliferation patterns of CD8+ T cells. Furthermore, early results indicate a shift towards a more pro-inflammatory cyto- and chemokine production by the T cells induced by RCC-derived EVs. The results support the hypothesis of a tumor-EV-mediated immune modulation in RCC. Citation Format: Greta Jasch