In vitro magnetic cell retention

In vitro magnetic retention assays were carried out under flow conditions in a modified channel slide (μ-Slide I Luer, 0.4-mm height, ibidi) using a two-magnet system as previously described (43 (link)). The neodymium iron boron (NdFeB) permanent magnets (Supermagnete) used in this study were the following: an 5 × 14-mm magnet with 1.35 T of remanent magnetization (Br) (magnet A) and an 8 × 6-mm magnet with 1.45 T of remanent magnetization (Br) (magnet B). Briefly, either murine NK cells expanded in vitro in the presence of IL-2 or the human NK-92MI cell line (10⁷ cells/ml) were treated with MNPs (150 μg Fe/ml) or not for 2 h in standard conditions, and then washed and stained with calcein-AM. An Olympus Inverted Microscope (model IX71) coupled to a Cell^∧R imaging station under standard culture conditions was used in this assay. Shear stress was fixed at 0.5 dyne/cm² and events were recorded every 1 s. After 60 s, the two-magnet system was applied for the next 2 min. Imaris software (Bitplane) was used to analyse displacement along the Y-axes (in the direction of the magnetic field).