Abstract 2103: Immunophenotyping of extracellular vesicles isolated from lymphatic exudate identifies CD24 as a marker for lymph node metastases in oral cavity squamous cell carcinoma
Authors: Qu Xinyu , Leung Leanne Lee , Ng Cherrie Wing Kei , Chan Hiu Ching , Chen Zigui , Meehan Katie , Zeng Xianhai , Chan Jason Ying Kuen 
Published: June 2023

Background: Squamous cell carcinoma of the oral cavity (OSCC) is debilitating and fatal with a high risk of lymph node metastases. One of the key problems is that currently there is no robust molecular biomarker to determine whether the tumor has spread or is at risk of spreading to the regional lymph nodes, the first echelon that OSCC spreads to. Extracellular vesicles (EVs) are functional nanoparticles that are bound by natural protein-lipid bilayers. They are deliberately packaged and proactively secreted by all types of cells and serve as intercellular communication vehicles. Tumors release an excess of EVs which are loaded with the molecular and genetic cargo of the parental tumor cells.

Methods: Following ethical approval and written informed consent, pre-surgical plasma as well as matched post-surgical lymphatic drainage fluid were collected from 20 OSCC patients (nodal disease n=6, no node n=14), and control plasma was also collected from healthy donors. EVs were isolated by ultracentrifugation, quantified and characterized by nanoparticle tracking analysis, transmission electron microscopy, and western blot. Immune profiling of 37 EV surface markers was determined using flow cytometry with the MACSPlex Exosome kit.

Results: Lymphatic exudate was greatly enriched in EVs in comparison to plasma. Common EV tetraspanins, platelet markers, cancer-related proteins, as well as characteristic markers of immune cells were detected in both plasma and lymphatic exudate EVs based on normalized median fluorescence intensity (nMFI). The presence of OSCC led to an altered composition of blood cell-derived EVs. Elevated levels of CD3, CD25, and CD86, and cancer stem cell marker CD133 were observed in the plasma EVs. However, there were no significant changes in EV markers in plasma between patients with and without lymph node metastasis. Notably, EVs isolated from plasma and lymphatic exudate revealed completely divergent signatures of EV surface markers. Among them, cancer-related protein CD24 was found to be the most highly expressed EV marker in lymphatic exudate from patients with nodal disease (nMFI 1.28±0.50 versus 0.84±0.32, p&lt;0.05) and likewise correlated with advanced disease stages (nMFI 1.17±0.40 versus 0.70±0.27, p&lt;0.05).

Conclusions: Plasma-derived EVs are promising non-invasive biomarkers for cancer detection. This study shows that lymphatic exudate is a better source of EV biomarkers due to its high abundance of tumor-related factors directly from draining lymph nodes. In addition, CD24, as reported, is indicative of an immunosuppressive tumor microenvironment and it may serve as a predictor for lymph node metastases and progression of OSCC. These findings shed new light on the understanding of OSCC metastases and provide impetus for consideration of CD24-based liquid biopsy testing and possibly novel immunotherapy.

Citation Format: Xinyu Qu, Leanne Lee Leung, Cherrie Wing Kei Ng, Hiu Ching Chan, Zigui Chen, Katie Meehan, Xianhai Zeng, Jason Ying Kuen Chan. Immunophenotyping of extracellular vesicles isolated from lymphatic exudate identifies CD24 as a marker for lymph node metastases in oral cavity squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2103.