Background Osteoporosis is a skeletal disease characterized by systemic bone loss with an increased risk to bone fractures, associated with high morbidity and mortality1. Mesenchymal stem cells (MSC) from bone marrow (BM) are ideal candidates for the treatment of osteoporosis because they are able to differentiate to osteoblasts although its osteotropism is low2. Ex vivo fucosylation (adding a fucose residue) in α1–3 position of the CD44 antigen by use of the enzyme fucosyltransferase VI (FTVI) yields Hematopoietic cell E and L-selectin ligand (HCELL) in MSC increasing the affinity for E-selectin and osteotropism.
Objectives To describe the safety and efficacy of human fucosylated MSC infused in an immunocompromised mice model (NOD/SCID).
Methods 31 NOD/SCID mice were randomized to by tail vein injection: 1x106 fucosylated MSC (n=13), 1x106 MSC (n=14) or saline (n=4). Toxicities were evaluated by a clinical score, weight and histological assessment (heart, lung, liver, spleen, kidney, gonads, brain, bone and BM). RT-PCR array-based evaluation of the expression of human β-actin and β2-microglobulin genes was performed to study biodistribution of MSC. The maintenance of genetic integrity was evaluated during in vitro culture by karyotype. Additional samples of tibia and calota were to immunostained with a polyclonal Rabbit anti-human osteocalcina to demonstrate efficacy. Osteocalcin-positive cells were identified by a dark-brown cytoplasmic precipitate.
Results There was no unexpected death and none of the mices had any acute toxicity. The histology of heart, liver, kidney, spleen, gonads, brain, bone and bone marrow was normal in all mice. There were localized areas of lung inflammation in 15%, 42% and 25% of mice infused with fucosylated MSC, MSC, and saline, respectively without significance differences (p=0.28). Biodistribution was normal with except one mice (infused with MSC non-fucosylated) showed an expression of human RNA β-actin and β2-microglobulin in the lung sample taken after 12 weeks of intravenous infusion. Osteoblasts were seen in 100% of mices infused with fucosylated MSC, in 62.5%% of animals infused with MSC alone, and none in saline group (p=0.01). NOD/SCID mice infused with fucosylated MSC presented a higher number of osteoblasts positive for osteocalcin in 10 high-power fields (400x) of tibia and calvarium sections that non-fucosylated (32 vs 5.5) (p=0.0082). Human osteoblasts were detected inside the bone from the fifth to the twelfth week after infusion.
Conclusions Intravenous infusion of human fucosylated MSC is safe and effective in guiding the cells to bone with a higher potential to ossification in NOD/SCID mices that non-fucosylated MSC. These results are allowing to start a human clinical trial with intravenous fucosylated MSC as treatment in patients with osteoporosis.
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Disclosure of Interest None declared