Mesenchymal stem cells can be specifically transplanted into the femur: a Magic result by Magnetism-induced cell target transplantation (MagiC-TT) in dual transgenic mice model
Authors: Jiang Qianli , Huang Hao , Mai Qiusui , Wang Jia peng , Lu Yuncong , Liu Li , Yuan Yifang , Zhao Peiran , Yuan Lezhong , Ye Yanyan , Zhou Yongjun , Sun Jing 
Published: October 2019

Abstract
BACKGROUND: Mesenchymal stem cells (MSCs), like non-hematopoietic multipotent stem cells, are considered as the most promising stem cells for clinical use, such as treatment of aplastic anemia, graft-versus-host-disease after allogeneic hematopoietic stem cell (HSC) transplantation, as well as tissue engineering, etc. But the fate of MSC in vivo remains almost unknown, including its homing, proliferation and the interaction between MSC and surrounding cells. Target transplantation has been a dream of researchers for many years, especially for such important cells as MSC or HSC, and now it can be made possible by our self-established novel Magnetism-induced cell target transplantation (MagiC-TT).
OBJECTIVE: To explore the distribution and survival of donor MSCs transplanted by Magnetism-induced cell target transplantation (MagiC-TT) in vivo, with dual fluorescent protein transgenic mice model.
Methods and results: 1) Magnetized cells: the C57BL/6 RFP-MSCs were bought from Cyagen Biosciences Inc. (China) and were magnetized by self-made Au@Fe nano-particle, positive cells were sorted by MACS column. 2) Cell biology: Both magnetized and wild type (wt) cells were stained by Wright Giemsa and HE staining, as well as Prussian blue, there were no differences in cell morphology, while the particles of Au@Fe exist within or on the surface of magnetized cells. CCK8 method did not find any statistical significances in cell proliferation (P=0.802), cell cycle and cell viability. 3) In vitro study: In order to study the influence of magnetism to magnetized cells, cells' migration to magnetism and proliferation curve, transwell migration and matrigel migration assays were carried out. Within the magnetic field, magnetized cells can migrate through matrigel and transwell membrane much more efficiently, 174±22 vs. 2±1 per 200X microscopic vision (P<0.0001); they also can migrate horizontally towards magnetism in matrigel (showed in Fig.1A); magnetized cells even grow well on the roof of 24-plate (grows against gravity) in the culture medium. 4) In Vivo study: Twenty C57BL/6 female GFP transgenic mice were divided into magnetized cell group and non-magnetized cell group (10 in each), magnetized and wt cells were injected into the femur cavity of the mice in both groups respectively. All the mice in both groups had magnetic field (which is of the same magnitude as the one used in vitro) on its femur for 24h. At different time points, 1h, 24h, 72h and 3m after RFP-MSCs injection, bioluminescence by Xenogen IVIS Imaging System (Lumina), FACS analysis of peripheral blood, bone marrow, liver, spleen and thymus; fluorescence and confocal microscopy, together with real-time PCR for GFP and RFP cells in different tissue after mice total body perfusion fixation were performed. Femurs and humeri of recipients were decalcified with self-made semi-solid decalcification (SSD, 2010 ASH poster, no.2625) to clarify the distribution of RFP-MSCs, traditional methods were used as control. At 1h, most MSCs stayed in lung in non-magnetized cell group while few in magnetized cell group. 24h later, confocal microscopy showed that lots of RFP-MSCs exit within femur and knee joint in magnetized cells group (Fig. 1B) while few in control group, thus, demonstrating the success of MSCs target transplantation. At 72h (2d post withdrawal of magnetic field), microscopy and bioluminescence showed the presence of few MSC in the lung of non-magnetized cell group, while many MSCs presented in lung and femur in magnetized cell group, MSCs also appeared in spleen, kidney, gut and other organs, showing the slow release of target transplanted MSCs from femur. By real-time PCR and frozen sections, MSCs were found to survive for 3m in the bone, lung, liver, spleen, etc. in both groups.
Discussion: This study shows that magnetized MSCs have extra potential of moving under magnetism and comparable biology with wild-type cells. MagIC-TT can help MSCs' homing to bone marrow effectively, withdrawal of magnetic field permits MSCs to migrate into many tissues such as lungs, liver and spleen etc. Donor MSCs can survive for at least 3m in vivo.
CONCLUSION: This dual transgenic mice model demonstrated that target cell transplantation can be achieved by MagIC-TT technology, and that it is useful in studying MSC and its mechanism in vivo. MagIC-TT also can be used in other cell therapy, by helping cells migrate to target tissues and organs in the future.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.