Inclusion Criteria:

          -  Histologically documented advanced or metastatic solid tumors.

          -  Phase I-Ib part (including dose ranging part): Patients with advanced/metastatic solid
             tumors, with measurable or non-measurable disease as determined by RECIST v1.1, who
             have progressed despite standard therapy or are intolerant of standard therapy, or for
             whom no standard therapy exists and who did not receive prior anti-PD-1/PD-L1
             treatment.

          -  Phase II part (MBG453 single agent): Patients with advanced/metastatic solid tumors in
             the indication in which at least one confirmed PR or CR was seen during the dose
             escalation phase I part. Patients must have measurable disease as determined by RECIST
             v1.1, have progressed despite standard therapy or be intolerant to standard therapy.

          -  Phase II part (MBG453 in combination PDR001): Patients with advanced/metastatic tumors
             in the below selected indications, with at least one measurable lesion as determined
             by RECIST v1.1, who have received standard therapy and are intolerant of standard
             therapy or have progressed following their last prior therapy.:

               -  Melanoma (anti-PD-1/PD-L1 therapy naïve or pre-treated)

               -  Non small cell lung cancer (anti-PD-1/PD-L1 therapy naïve or pre-treated)

               -  Renal Cell Carcinoma (anti-PD-1/PD-L1 therapy naïve or pre-treated)

          -  Must have a site of disease amenable to biopsy, and be a candidate for tumor biopsy
             according to the treating institution's guidelines. Patient must be willing to undergo
             a new tumor biopsy at screening/baseline, and during therapy on the study.

          -  For MBG453 in combination with decitabine: anti-PD-1/PD-L1 therapy naïve SCLC patients
             who have failed no more than two lines of standard chemotherapy including topotecan

        Exclusion Criteria:

          -  Presence of symptomatic central nervous system metastases.

          -  History of severe hypersensitivity reactions to other monoclonal antibodies.

          -  Human Immunodeficiency Virus, Hepatitis B Virus or Hepatitis C Virus infection.

          -  Active autoimmune disease or a documented history of autoimmune disease, including
             ulcerative colitis and Crohn's disease or any condition that requires systemic
             steroids.

          -  Systemic steroid therapy or any immunosuppressive therapy (≥10mg/day prednisone or
             equivalent).

          -  Use of any vaccines against infectious diseases (e.g. varicella, pneumococcus) within
             4 weeks of initiation of study treatment.

          -  Pre-treatment with anti-CTLA4 antibodies in combination with any other antibody or
             drug specifically targeting T-cell co-stimulation or checkpoint pathway.

          -  Participation in an interventional, investigational non-immunotherapy study within 2
             weeks of the first dose of study treatment.

          -  Prior participation in an interventional, investigational cancer vaccine or
             immunotherapy study except for an anti-PD-1/PD-L1 study.

          -  For MBG453 in combination with decitabine: Hypersensitivity to decitabine or to any of
             the excipients, listed in decitabine country specific label

        Other inclusion/exclusion criteria may apply.