PRP will be obtained with the following procedure: a 300-ml autologous venous blood sample will undergo 2 centrifugations (the first at 1480 rpm for 6 minutes to separate erythrocytes, and a second at 3400 rpm for 15 minutes to concentrate platelets) to produced 20 ml of leukocyte-rich PRP. In case of patients allocated to receive leukocyte-poor PRP, a special filter will be then used to separate leukocytes and obtain leukocyte-poor PRP.