1.1. Type 2 diabetes mellitus 1.2. Duration of T2DM between 3 and 15 years inclusively 1.3. HbA1c up to 7.5% inclusively 1.4. Treated with LANTUS+MET (Group LANTUS+MET) or SU+MET (Group SU+MET) or DPP-4+MET (Group DPP-4+MET) respectively during the past 6 months before entering the study 1.5. Treated on a stable antidiabetic dosage during the past 3 months before entering the study