['myelodysplastic syndromes']
['atezolizumab', 'azacitidine']

        Inclusion Criteria:

          -  Diagnosis of MDS (participants with therapy-related MDS are eligible)

          -  Eastern Cooperative Oncology Group (ECOG) performance status score less than or equal
             to (</=) 2

          -  Adequate end-organ function, as determined by laboratory tests obtained within 28 days
             prior to the first dose of study drug

          -  Willing and able to undergo a pre-treatment bone marrow biopsy and subsequent
             on-treatment bone marrow biopsies

          -  Women who are not postmenopausal or surgically sterile must have a negative serum
             pregnancy test result within 28 days prior to initiation of study drug

          -  For women of childbearing potential and men: agreement to remain abstinent (refrain
             from heterosexual intercourse) or use highly effective contraceptive measures

        For participants in Cohorts A, A2, B, and B2:

          -  Progression at any time after initiation of azacitidine or decitabine treatment OR

          -  Failure to achieve complete or partial response or hematological improvement after at
             least six 4-week cycles of azacitidine or either four 4-week or four 6-week cycles of
             decitabine OR

          -  Relapse after initial complete or partial response or hematological improvement after
             six 4-week cycles of azacitidine or either four 4-week or four 6-week cycles of
             decitabine administered within the past 2 years

        For participants in Cohorts C1 and C2:

          -  Must not have received prior treatment for MDS with any hypomethylating agent

          -  IPSS-R risk category of Intermediate, High, or Very High assessed at screening

        Exclusion Criteria:

          -  Participants with a diagnosis of MDS secondary to paroxysmal nocturnal hemoglobinuria
             (PNH), aplastic anemia, or another inherited bone marrow failure disorder

          -  Prior allogeneic stem cell transplant or solid organ transplant

          -  Pregnant or lactating, or intending to become pregnant during the study

          -  Investigational therapy within 28 days prior to initiation of study treatment

          -  Immunosuppressive therapy within 6 weeks of Cycle 1, Day 1

          -  Prior treatment with immune checkpoint blockade therapies (anti-cytotoxic
             T-lymphocyte-associated protein 4 [CTLA-4], anti-programmed death-1 [PD-1] or
             anti-PD-L1) or immune agonists (anti-cluster of differentiation [CD] 137, anti-CD40,
             anti-OX40)

          -  Any other therapy or serious medical condition, as specified in the protocol, or
             abnormality in clinical laboratory tests that, in the investigator's judgement,
             precludes the participant's safe participation in and completion of the study

          -  Left ventricular ejection fraction (LVEF) </= 40 percent (%) at screening

          -  Planned major surgery during the study or within 4 weeks of Cycle 1, Day 1

          -  History of idiopathic pulmonary fibrosis, organizing pneumonitis, drug-induced
             pneumonitis, or idiopathic pneumonitis or evidence of active pneumonitis on screening
             chest computed tomography (CT) scan. History of radiation pneumonitis in the radiation
             field (fibrosis) is permitted.
      