Clinically Relevant Mesenchymal Stem/Stromal Cell Sheet Transplantation Method for Kidney Disease.

Chronic kidney disease (CKD) is the irreversible loss of nephron function, leading to a build-up of toxins, prolonged inflammation, and ultimately fibrosis. Currently, no effective therapies exist to treat CKD due to its complex pathophysiology. Mesenchymal stem/stromal cell (MSC) transplantation is a promising strategy to treat kidney diseases, and multiple clinical trials are currently ongoing. We previously demonstrated that rat bone marrow-derived MSC (BMSC) sheets transplanted onto surgically decapsulated kidney exert therapeutic effects that suppressed renal fibrosis progression based on enhanced vascularization. However, there are clinical concerns about kidney decapsulation such as impaired glomerular filtration rate and Na⁺ ion and H₂O excretion, leading to kidney dysfunction. Therefore, for transitioning from basic research to translational research using cell sheet therapy for kidney disease, it is essential to develop a new cell sheet transplantation strategy without kidney decapsulation. Significantly, we employed cell sheets engineered from clinical-grade human clonal BMSC (cBMSC) and transplanted these onto intact renal capsule to evaluate their therapeutic ability in the rat ischemia-reperfusion injury (IRI) model. Histological analysis 1-day postsurgery showed that cBMSC sheets engrafted well onto intact renal capsule. Interestingly, some grafted cBMSCs migrated into the renal parenchyma. At 1-3 days postsurgery (acute stage), grafted cBMSC sheets prevented tubular epithelial cell injury. At 28 days postsurgery (chronic phase), we observed that grafted cBMSC sheets suppressed renal fibrosis in the rat IRI model. Taken together, engineered cBMSC sheet transplantation onto intact renal capsule suppresses tubular epithelial cell injury and renal fibrosis, supporting further development as a possible clinically relevant strategy. Impact statement Chronic kidney disease (CKD) produces irreversible loss of nephron function, leading to toxemia, prolonged inflammation, and ultimately kidney fibrosis. Currently, no therapies exist to effectively treat CKD due to its complex pathophysiology. Mesenchymal stem/stromal cells (MSCs) are widely known to secret therapeutic paracrine factors, which is expected to provide a new effective therapy for unmet medical needs. However, unsatisfied MSC quality and administration methods to patients limit their therapeutic effects. In this study, we engineered clonal bone marrow-derived MSC sheets and established clinically relevant cell sheet transplantation strategy to treat renal fibrosis, which would improve MSC treatment for kidney disease.