2.1. Cell culture

All the reagents for cell culture were purchased from Gibco (Thermo Fisher Scientific, Waltham, MA, USA). The human embryonic kidney (HEK) 293 cell line was purchased from China Center for Type Culture Collection (CCTCC). 293 cells were maintained in high glucose Dulbecco's Modified Eagle Medium (DMEM) containing 10% heat inactivated fetal bovine serum and 1× antibiotic‐antimycotic. The BM‐MSCsof Balb/c mice were purchased from Cyageeen Biosciences (Suzhou, China) and were maintained in low glucose DMEM medium, supplemented with 20% fetal bovine serum, 2 mmol/L L‐glutamine and 1 × Antibiotic‐Antimycotic.