Abstract 3642: Phenotypic biomarkers of aqueous humor extracellular vesicles from retinoblastoma eyes
Authors: Amacker Anne , Peng Chen-Ching , Reiser Bibiana J. , Berry Jesse L. , Xu Liya 
Published: March 2024

Abstract
Purpose: Retinoblastoma (RB) is the most common pediatric intraocular cancer, yet tumor biopsies are contraindicated. This challenge emphasizes the need for investigation of non-tissue biomarkers. Extracellular vesicles (EVs), which are secretory vesicles containing bioactive molecules, have emerged as promising biomarker candidates due to their ability to be phenotyped using known tetraspanin markers. Aqueous humor (AH) provides an exciting liquid biopsy source for intraocular tumor information, with EVs having recently been identified in AH. Our laboratory has previously proposed that CD63/81+EVs are associated with retinoblastoma, but specific tumor-derived markers have not been linked to AH EVs using traditional tetraspanin assays. In this study, we employed MACSPlex, a high-dimensional magnetic bead-based immunoassay, to further explore RB-EV.
Methods: 7 AH samples consisting of two congenital glaucoma (GLC) samples and five RB samples taken at the time of primary enucleation were analyzed. We utilized Macsplex, a multiplex bead-based flow cytometry assay, to analyze the expression profiles of surface markers found on EVs. With 39 capture beads coated with monoclonal antibodies for 37 different EV surface antigens and two negative controls, the mean fluorescence intensity (MFI) of APC conjugated antibody cocktail from three tetrapanins (CD9, CD63 and CD81) on EVs captured by each surface antigen could be measured by flow cytometry. Enrichment ratios were then calculated by normalizing the fluorescence of each signal to the mean fluorescence of CD9, CD63, and C81.
Results: Macsplex analysis of the 2 GLC AH samples demonstrated a strong CD63 dominance compared with RB AH. The mean CD63 enrichment ratio for GLC samples was 2.6 (S.D. = 0.34), and 1.3 (S.D. = 0.27) in RB samples, with a p-value of 0.069. In comparison to the GLC patients, the analysis of EVs in the AH of the 5 RB samples exhibited a greater co-dominance of CD63/CD81 positivity consistent with past research on RB EVs. The mean CD81 enrichment ratio for the 5 RB samples was 1.5 (S.D. = 0.26), in contrast to 0.3 (S.D. = 0.24) in GLC AH, with a p-value of 0.03. Interestingly, 4 out of the 5 RB AH samples demonstrated very strong CD133 signals, which is a known cancer marker. Deeper investigation into one RB AH sample utilizing single tetraspanin detection revealed higher coexpression of CD63 and CD81 with CD133 than seen with CD9. The CD133 enrichment ratio for the CD81, CD63, and CD9 single channel experiments were 6.6, 3.4, and 1.5 respectively.
Conclusions: Comparison between this study and previous work done by our group demonstrate a high concordance between results utilizing Macsplex and Exoview. However, this is the first study identifying the expression of CD133, a cancer stem cell marker, on retinoblastoma-derived EVs in AH. Macsplex technology illustrates an incredible clinical potential of AH EVs for characterizing retinoblastoma phenotype in vivo.
Citation Format: Anne Amacker, Chen-Ching Peng, Bibiana J. Reiser, Jesse L. Berry, Liya Xu. Phenotypic biomarkers of aqueous humor extracellular vesicles from retinoblastoma eyes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3642.