Equine Fetal, Adult, and Embryonic Stem Cell-Derived Tenocytes Are All Immune Privileged but Exhibit Different Immune Suppressive Properties In Vitro

Abstract

In horses and humans, tendon injuries are a significant problem. Not only can they occur in both athletes and nonathletes, they require lengthy periods of recuperation and undergo poor natural regeneration, which leads to high reinjury rates. Embryonic stem cells (ESCs) may provide a renewable source of allogeneic cells to use in clinical applications to aid tissue regeneration. Equine ESCs can undergo tenocyte differentiation in vivo and in vitro, but the immune properties of tenocytes isolated from either ESCs or tissues have not previously been characterized. Here, we demonstrate that equine tenocytes derived from fetal and adult tendon tissue and ESCs express robust levels of major histocompatibility complex (MHC) I but no MHC II in response to inflammatory cytokine interferon gamma (IFNg). However, MHC expression does not affect their allorecognition by peripheral blood mononuclear cells in vitro. Adult and fetal tenocytes remain immune privileged and strongly immune suppressive in both the presence and absence of exogenously applied IFNg. In contrast, ESC-derived tenocytes are immune privileged even in the presence of IFNg, but they are only weakly immune suppressive in the presence but not in the absence of exogenously applied IFNg. This is despite ESC-tenocytes expressing a number of genes involved in immune modulation at significantly higher levels than those expressed by adult and fetal tenocytes when in standard, nonstimulated monolayer culture. Together, this work suggests that, similar to other fibroblasts, tenocytes have immune modulatory properties, and that culture-expanded tenocytes derived from primary tissues or ESCs may be safe to use in clinical transplantations to injured tendons of unrelated animals.

Cyclical strain improves artificial equine tendon constructs in vitro

“…However, adult tenocytes do have a limited self‐renewal in vitro, which would limit their numbers for clinical application , and in vivo, they generate reparative scar tissue rather than healthy tendon tissue (Tang et al, 2014). Therefore, future work is required to examine the effects of force on cells that may aid tendon regeneration, for example mesenchymal stromal cells (Godwin, Young, Dudhia, Beamish, & Smith, 2012) and embryonic stem cells (Barsby et al, 2014; McClellan, Evans, et al, 2019; McClellan, Paterson, Paillot, & Guest, 2019).…”

Genome-wide transcriptome analysis reveals equine embryonic stem cell-derived tenocytes resemble fetal, not adult tenocytes

“…Three lines of fetal, adult and ESC-tenocytes cultured in 3D and adult and fetal tenocytes cultured in 2D were used in the RNA-sequencing experiments. The 2D samples, although processed in parallel, are available through NCBI GEO, (https://www.ncbi.nlm.nih.gov/geo/) under accession number GSE132358 [39]. Tenocytes were used between passages (P) 3 and P8.…”

“…Embryonic stem cells (ESCs) present another potential therapeutic option as they can differentiate into derivatives of all three germ layers, be propagated extensively in culture with manual passaging whilst maintaining a stable karyotype [34][35][36] and have a degree of immune privilege [32,[37][38][39]. We have previously isolated and characterised equine ESCs and demonstrated that when injected into the injured horse tendon, they exhibit a high survival rate, express tendon-associated markers and do not illicit an immune response within a 90-day study period [29,[40][41][42].…”

Tissue-Engineered Decellularized Allografts for Anterior Cruciate Ligament Reconstruction

“…The risk of bone expansion is also present resulting in failures in ACL reconstruction with allografts . Decellularization can reduce the immunogenicity of allografts and studies report that stem cells can reduce the body’s immune response to many biomaterials. , In this study, IgE and IL-1β secretion were significantly lower in the TEDA group at the early stage of implantation, indicating a reduced immune response. Proper inflammatory responses are likely to be necessary for tissue regeneration, which may be impaired by the high levels of proinflammatory cytokines .…”