Engraftment of autologous bone marrow cells into the injured cranial cruciate ligament 3 in dogs 4 5

14 Current research indicates that exogenous stem cells may accelerate reparative 15 processes in joint disease. However, no previous studies have evaluated whether bone marrow 16 cells (BMCs) target the injured cranial cruciate ligament (CCL) in dogs. The objective of this 17 study was to investigate engraftment of BMCs following intra-articular injection in dogs with 18 spontaneous CCL injury. Autologous PKH26-labeled BMCs were injected into the stifle joint 19 of eight client-owned dogs with CCL rupture. The effects of PKH26 staining on cell viability 20 and PKH26 fluorescence intensity were analyzed in vitro using a MTT assay and flow 21 cytometry. Labelled BMCs in injured CCL tissue were identified using fluorescence 22 microscopy of biopsies harvested 3 and 13 days after intra-articular BMC injection. 23 24 The intensity of PKH26 fluorescence declines with cell division but was still 25 detectable after 16 days. Labelling with PKH26 had no detectable effect on cell viability or 26 proliferation. Only rare PKH26-positive cells were present in biopsies of the injured CCL in 27 3/7 dogs and in synovial fluid in 1/7 dogs. No differences in transforming growth factor-β1, 28 and interleukin-6 before and after BMC treatment were found and no clinical complications 29 were noted during a 1 year follow-up period. In conclusion, BMCs were shown to engraft to 30 the injured CCL in dogs when injected into the articular cavity. Intra-articular application of 31 PKH26-labeled cultured mesenchymal stem cells is likely to result in higher numbers of 32 engrafted cells that can be tracked using this method in a clinical setting. 33 34