Mesenchymal stromal cell therapy is a long-term regenerative approach for chronic radiation cystitis, involving coordinated modulation of the urothelial, immune, vascular, and fibrotic pathways.

Chronic radiation cystitis (CRC) is a disabling late adverse effect of pelvic irradiation, characterized by urothelial barrier loss, persistent inflammation, vascular alteration, and progressive fibrosis. No curative treatment exists. Mesenchymal stromal cells (MSCs) are investigated for their regenerative potential, however their long-term mechanisms of action in CRC remain incompletely elucidated. CRC was induced in rats by localized bladder irradiation (40 Gy). Animals were randomized into unirradiated controls, irradiated controls, and irradiated MSC-treated groups. The treated group received three intravenous injections of adipose-derived MSCs at 4.5, 5.0, and 5.5 months post-irradiation, during the pre-chronic phase. Bladders were analyzed up to 18 months post-irradiation by immunostaining and RT-qPCR for urothelial differentiation (Upk1a, Upk1b, Upk2, Upk3a, Upk3b), epithelial proliferation (CK14⁺/PCNA⁺) and fibrosis (collagen I and III). Immune activation (CD45⁺ leukocytes, neutrophils, mast cells, Gata3, Th1, Th2) was analyzed by flow cytometry and vascular integrity by cystoscopy and Cspg4, VegfA expression. At 18 months post-irradiation, irradiated bladders showed a 90% loss of UPK3 staining and hyperplasia (urothelium thickening) greater than 300 μm result of basal cell hyperproliferation, a ninefold increase compared to controls. MSC treatment reduced hyperplasia by 66% compared to irradiated rats, restored gene expression of Upk1a and Upk3a to 80-90% unirradiated control levels and decreased proliferative CK14⁺/PCNA⁺ progenitors by 93%). Immune response was attenuated, with a 49% reduction in Th2-associated cell infiltration and downregulation of Gata3 expression (p < 0.05) relative to irradiated rats. A decrease in mast cell degranulation (61%) was observed at neurovascular interfaces. Vascular architecture was preserved, with VegfA expression normalization and reduction of cystoscopic vascular lesions. Fibrotic remodeling was limited, with less accumulation of collagen 1 and a maintained physiological collagen 1/3 balance in the detrusor. MSC treatment had durable, multi-compartment effects in CRC. It limited basal hyperplasia, restored urothelial lineage differentiation, selectively modulated adaptive immune activation and mast cell activity, and constrained collagen 1-driven fibrosis. Vascular architecture was partially preserved, which together supported urothelial homeostasis in CRC. These findings provide strong preclinical evidence supporting MSCs as a targeted long-term regenerative strategy for CRC.