BIOM-45. ON THE DEVELOPMENT OF A CLINICALLY FEASIBLE PROTOCOL FOR LABELING MESENCHYMAL STEM CELLS WITH IRON OXIDE PARTICLES AND ONCOLYTIC VIRUS: A PILOT STUDY

Abstract INTRODUCTION Detecting oncolytic virus-loaded mesenchymal steml cells (MSCs) is critical for optimizing cancer immunotherapy’s safety, efficacy, and precision. Labeling stem cells with iron oxide particles (IOP) and using magnetic resonance imaging (MRI) enables in vivo tracking. This study investigates a dual labeling protocol for simultaneously loading MegaPro IOP and the Delta-24-RGD oncolytic virus into MSCs and evaluates labeled MSC functionality. MRI sensitivity to detect IOP-labeled cells was also investigated. METHODS Using an in-house developed dual-label protocol, the MSCs were loaded either with IOPs or IOP+oncolytic virus. Cell viability, Prussian blue iron staining, Hexon virus staining, cellular iron quantification, and invasion were assessed for labeled cells, and an additional differentiation assay was performed for IOP-labeled cells. Seven 100 µl phantoms were created with varying counts of iron-labeled MSCs (1.5x105 to 9x103 cells). R2-, R2*-, and R1-weighted MRI images were acquired, and parametric maps were fitted for the phantom data. ROI analysis was conducted on the 1-mm-thick slices (1/5 of the total phantom volume) covering the central slice of the MSC layer for each phantom. RESULTS In vitro studies show similar IOP loading in IOP-labeled and IOP+virus-labeled MSCs, with iron content of 6 and 5 pg iron/cell, respectively. 86% Cell viability was achieved for IOP+virus-labeled MSCs. The invasion and differentiation into osteogenic and chondrogenic lineages were preserved in IOP-labeled MSCs. The MRI relaxation rates R2*, R2, and R1 for the 1.5x105 iron-labeled MSC were approximately 8, 2.5, and 1.5 times higher compared to the agarose cell phantom. R2* and both R2 and R1 detection sensitivities were about 2x10³ and 6x10³ MSC cells in a 20 µl volume slice, respectively. CONCLUSION In vitro studies indicate excellent functionality of labeled MSCs and IOP loading into the cells. Phantom studies indicate that as low as 2X103 IOP-labeled cells can be detected by MRI.