Possible therapeutic effect of systemic (intravenous) transplantation of autologous mesenchymal stem cells was studied in experiments (C57Bl/6 mice) and pilot clinical trial. Clinical trial was performed on 11 patients with radiation-induced lung injuries developed after combined chemotherapy and radiation therapy for lymphogranulomatosis or breast cancer. The patients were subjected to single transplantation of mesenchymal stem cells and course of standard pharmacotherapy. The method for isolation of autologous mesenchymal stem cells was licensed. The transplantation of mesenchymal stem cells was followed by a decrease in the mortality rate of mice with radiation-induced lung injury. Clinical trial showed that cell therapy with autologous mesenchymal stem cells does not induce progression of the underlying oncological disease. Parameters of spirography, immune status, lung scintigraphy, and markers for inflammation and tissue hypoxia in the patients remained practically unchanged 1 year after the treatment. These clinical signs reflect stabilization of the radiation process.