Pelvic organ prolapse (POP) is common urogynecological disorder, with up to  19% of women having a lifetime risk of undergoing reconstructive surgery for POP [1], and a 30% risk of reoperation due to recurrent anatomical failure or adverse events associated with primary surgery [2]. There is a critical need to provide novel meshes for the treatment of POP that are safe, surgically efficacious, and congruent with host native tissue. Cellular therapy is an emerging field in clinical and personalised medicine that utilizes the clonogenic potential of adult mesenchymal stem/stromal cells to improve the biocompatibility of novel surgical constructs, which has potential applications in POP. Our discovery of endometrial stem/progenitor cells (eMSC) within unique perivascular niches of endometrial functionalis tissue has furthered the field of stem cell therapy, due to their improved clonogenicity and potential to modulate the foreign body responses triggered by meshes. In nature, cell behaviour and structural development is supported by the nanoscale arrangement of the extracellular matrix (ECM). In order to overcome the impediment posed by the tissue microenvironment, it is desirable to design biomaterials that mimic some mechanical and biochemical properties of the ECM of native tissues. Nanostructured poly-L-lactide-co-ε-caprolactone (PLCL) mesh is made from a biocompatible, elastic and flexible polymer that is well matched to the nanoarchitecture of vaginal tissue [3]. In a previous study on mice,  PLCL mesh blended with eMSC resulted in improved tissue integration, host cell recruitment, neovascularisation and ECM deposition, when compared with PLCL mesh alone [3]. 

Objective: This study aimed to assess the fate and effect of nanofiber PLCL mesh boosted with SUSD2+ eMSC in an ovine pre-clinical model of POP surgery (n=42). We hypothesised that when combined with eMSC, this degradable nanofiber construct strengthens the vaginal wall, whilst improving the host inflammatory response to reduce rates of mesh erosion and exposure, demonstrating a potential durable method of mesh augmentation at colporrhaphy.

eMSC were isolated from human endometrial tissue through fluorescent labelling and magnetic bead sorting with sushi domain-containing 2 (SUSD2) antigen. These cells were expanded in a serum-free media with transforming growth factor-beta receptor inhibitor, A83-01, which reduces cell apoptosis and senescence. Subsequently, PLCL polymer (10%w/w) was electrospun at 18kV to form uniform nanofibers and assessed for fiber diameter, pore size, hydrophilicity and biomechanical properties. PLCL meshes of diameter 3x2cm were sterilised and seeded with eMSCs with over 90% SUSD2+ expression at the density of 1 million cells/cm2, 72 hours prior to surgery. 

Multiparous ewes with demonstrated vaginal wall weakness were selected on the basis of abnormal modified POP-Q measurements. Following this, trained urogynecologists performed posterior vaginal repair (colporrhaphy) on a total of 42 sheep which were randomized into one of three groups; sham surgery (native tissue), PLCL mesh only, and PLCL mesh + eMSC. Post-operative POP-Q measurements were taken and vaginal tissue harvested at three post-mortem time points of 7, 30 and 90 days. Histology, immunohistochemistry, immunofluorescent microscopy, and scanning electron microscopy were used to assess for the survival of eMSC in explanted tissue, mesh integration, host foreign body response, angiogenesis and ECM formation.

We observed that eMSCs maintained the expression of SUSD2 over 90% even after attaching to PLCL meshes. H&E staining of histological sections from sheep vagina revealed that presence of eMSCs on PLCL meshes had a significant impact on foreign body response and giant cell formations. Nanomeshes with and without eMSCs could integrate well with vaginal tissues revealing formation of ECM and improved neovascularisation within  the  meshes. Scanning electron microscopy revealed that  there was swelling of individual fibers of mesh and new collagen fibrils were formed within the PLCL mesh (figure 1). Explanted PLCL mesh had a mean fibril diameter of 485.9nm. We are currently assessing macrophage polarization, inflammation, elastin metabolism as well as tensile properties of vaginal explants.

PLCL mesh seeded with SUSD2+ eMSC demonstrated promising biocompatibility, surgical efficacy and host tissue response when implanted vaginally in multiparous ewes. The presence of eMSC prevents rapid mesh degradation, improved neovascularization and induces a more favourable foreign body response.  Thus, nanofiber electrospun mesh combined with eMSC have demonstrated have demonstrated many great potential applications for the surgical management of POP.

Our study highlights that eMSCs modulate the  foreign body response and thus impact the fate of implants used for POP treatment. From a tissue engineering perspective, such bioengineered constructs have a significant potential as alternative autologous surgical constructs for the treatment of POP.

Smith, F. J., Holman, C. D., Moorin, R. E., & Tsokos, N. (2010). Lifetime risk of undergoing surgery for pelvic organ prolapse. Obstetrics and gynecology, 116(5), 1096–1100. https://doi.org/10.1097/AOG.0b013e3181f73729
Olsen, A. L., Smith, V. J., Bergstrom, J. O., Colling, J. C., & Clark, A. L. (1997). Epidemiology of surgically managed pelvic organ prolapse and urinary incontinence. Obstetrics and gynecology, 89(4), 501–506. https://doi.org/10.1016/S0029-7844(97)00058-6
Mukherjee, S., Darzi, S., Rosamilia, A., Kadam, V., Truong, Y., Werkmeister, J. A., & Gargett, C. E. (2019). Blended Nanostructured Degradable Mesh with Endometrial Mesenchymal Stem Cells Promotes Tissue Integration and Anti-Inflammatory Response in Vivo for Pelvic Floor Application. Biomacromolecules, 20(1), 454–468. https://doi.org/10.1021/acs.biomac.8b01661