Choroidal neovascularization (CNV) is the most severe form of age-related macular degeneration (AMD), which causes rapid visual loss. Transplantation of cultured retinal pigment epithelium (RPE) cell sheet by tissue engineering is a possible approach to the treatment of CNV. In the present study, we investigated the possibility of using magnetite nanoparticles and magnetic force to construct and deliver RPE cell sheets in vitro. When magnetite cationic liposomes (MCLs), having a positive charge at the surface, were added to ARPE-19 human RPE cells at a concentration of 25 or 50 pg of magnetite per cell, the cells took up 40 to 55% of the MCLs. The magnetically labeled ARPE-19 cells (8 x 10(3) cells/mm(2), which corresponds to 10-fold the confluent concentration against the culture area [4 mm(2)]) were seeded into an ultra-low-attachment plate and a magnet (4000 G) was placed under the well. The magnetically labeled ARPE-19 cells formed an approximately 15-layered cell sheet after a 24 h of culture. When the magnet was removed, the sheets were detached from the bottom of the plate and then harvested and transferred to a tissue culture dish, using a magnet. Subsequently, the cell sheets were attached onto the dish, and the cells growing on the sheets were observed. This novel methodology, termed "magnetic force-based tissue engineering" (Mag-TE), is a possible approach for CNV treatment.

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Recently, there has been an accumulation of evidence indicating that human mesenchymal stem cells (MSCs, multipotent cells resident in the bone marrow) are useful for autologous cell transplantation. However, only small numbers of MSCs have been obtained in bone marrow aspirates. We have developed a novel methodology for enriching and proliferating MSCs from bone marrow aspirates using antibody-conjugated magnetoliposomes (AMLs). The AMLs are liposomes conjugated to anti-CD105 antibody (immunoliposomes) and contain magnetite nanoparticles (diameter 10 nm). In the present study, the AMLs were added to a small volume (1 mL) of human bone marrow aspirate. After a 1-h incubation period, the bone marrow aspirates containing AMLs were seeded into 10-cm tissue culture dishes, and a disk-shaped magnet (diameter 2.2 cm; height 1 cm; 4000 Gauss) was positioned under the dish to enrich MSCs by magnetic force. The MSCs proliferated, forming colonies at the site where the magnet was positioned. In contrast, no colonies and very few viable cells were observed in ordinary culture based on plastic-adherent tendencies of cells without use of AMLs. These results suggest that this AML culture method can rapidly and efficiently expand a small number of MSCs into numbers suitable for clinical application.

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