Long-Term Outcome Following Treatment With Allogeneic Mesenchymal Stem/Stromal Cells for Radiation-Induced Hyposalivation and Xerostomia

Background Adipose-derived mesenchymal stem/stromal cells (ASCs) are proposed as a new xerostomia treatment. The study evaluated the long-term safety and effectiveness of allogeneic ASCs in radiation-induced xerostomia among patients with previous oropharyngeal cancer.Methods This study constitutes 3-year follow-up on the original 10 patients who received allogeneic ASCs injections to the submandibular and parotid glands as part of the MESRIX-II trial. The MESRIX-II trial included the preliminary 4-month follow-up. The primary endpoint was long-term safety. Secondary endpoints were effectiveness evaluated by changes in salivary flow rate and patient-reported outcomes (PROs). Immune response was evaluated by assessing the development of donor-specific antibodies (DSA).Findings All 10 MESRIX-II patients completed the long-term follow-up (ie, no missing data). During the long-term follow-up, 2 patients encountered a significant adverse event, which was determined to be unrelated to the treatment. No DSAs were detectable at 3 years. The stimulated salivary flow rate increased significantly from an average of 0.66 mL/minute at baseline to 0.86 mL/minute at follow-up, corresponding to an increase of 0.20 [95% CI 0.08 to 0.30] mL/minute, or approximately 30%. Among the PROs, sticky saliva symptoms were reduced, with a -20.0 [95% CI -37.3 to -2.7] units.Interpretation In conclusion, this study is the first to present long-term follow-up outcomes of allogeneic ASC treatment as a therapeutic option for radiation-induced xerostomia. The study found that ASC treatment appears safe, and there were no indications of adverse immune responses at the 3-year follow-up. Further studies are warranted to evaluate the findings in larger settings. Graphical Abstract