PURPOSE OF THE STUDY Rotator cuff tears are one of the most frequent shoulder disorders which are often associated with pain and interfere with proper arm function. In order to evaluate the safety and effectiveness of using cultured human autologous mesenchymal stem cells (MSC) applied to the suture site during arthroscopic repair of a rotator cuff tear, a prospective clinical study was designed and started recently at the authors' department. Its primary goal was to evaluate the safety of using cultured human MSCs, the secondary goal then was to study a therapeutic effect of their application. Preliminary results of the study on a limited number of patients are presented here. MATERIAL AND METHODS Ten patients who met the indication criteria for arthroscopic repair of a rotator cuff tear were included in the study. In addition, they also had to meet inclusion and lack exclusion criteria. According to the protocol, their bone marrow was harvested at 3 to 4 weeks before surgery. Subsequently, an arthroscopic repair of the rotator cuff tear was performed and an suspension of cultured MSCs was applied to the suture site at the end of the procedure. The isolation of MSCs from bone marrow and their cultivation was carried out by the company Bioinova, Ltd. The patients were followed up at 6 weeks and 3 and 6 months post-operatively. Their clinical assessment included physical examination of the shoulder, pain intensity evaluation according to the visual analogue scale (VAS), and subjective questionnaires for Constant and University of California (UCLA) scores. All patients underwent MRI examination at 6 post-operative months to evaluate the quality of rotator cuff reconstruction. The findings were compared with the pre-operative results. RESULTS A final evaluation was made in eight patients of 10. Two patients were excluded from the study because their exclusion criteria were fulfilled. The evaluated patients showed significantly better clinical outcomes as early as 6 weeks after surgery; also all pre-operative scores were improved at 3 and 6 months. The average values at 6 months post-operatively were: 0 points for the VAS score, 32 for the UCLA score and 84 for the Constant score. The MRI findings at 6 months after surgery showed fully healed and well-integrated tissue of the rotator cuff tendon attachment in all eight patients. No adverse effects of therapy were recorded during the follow-up period. DISCUSSION The use of autologous stem cells and growth factors in the treatment of tendons, muscles and cartilage is currently the topic of many experimental studies on animal models. Its utilisation in human clinical trials has been reported only marginally; the relevant studies have so far used only suspensions of non-cultured mononuclear cells. Our study, although on a smallsize patient group, provides evidence that human cultured autologous MSCs can safely be used for tissue repair in the indications mentioned above. CONCLUSIONS Our preliminary short-term results show that using human cultured autologous MSCs in the treatment of rotator cuff tears is safe. However, further research is needed, particularly with regard to the effectiveness of the method. Key words: rotator cuff tear, arthroscopic repair, mesenchymal stem cells, tendon, cell therapy.