A Study of Multiple Immunotherapy-Based Treatment Combinations in Patients With Locally Advanced Unresectable or Metastatic Gastric or Gastroesophageal Junction Cancer (G/GEJ) (Morpheus-Gastric Cancer)

Inclusion Criteria:

- Age >/= 18 years;

- Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1;

- Life expectancy >/= 3 months, as determined by the investigator;

- Histologically or cytologically confirmed locally advanced unresectable or metastatic
adenocarcinoma of gastric or gastroesophageal junction; (for the 1L Cohort: no prior
systemic therapy for the locally advanced or metastatic disease; for the 2L Cohort:
disease progression during or following a first-line platinum-containing or
fluoropyrimidine-containing chemotherapy regimen);

- Only for the 1L Cohort: human epidermal growth factor receptor 2 (HER2)-negative
tumors;

- Measurable disease (at least one target lesion) according to Response Evaluation
Criteria in Solid Tumors, Version 1.1 (RECIST v1.1);

- Adequate hematologic and end organ function based on laboratory results obtained
within 14 days prior to initiation of study treatment;

- For women of childbearing potential: agreement to remain abstinent (refrain from
heterosexual intercourse) or use contraceptive measures as outlined for each specific
treatment arm;

- For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use
contraceptive measures, and agreement to refrain from donating sperm, as outlined for
each specific treatment arm.

Exclusion Criteria:

Exclusion criteria for the 2L Cohort:

- Urinary protein is > 1 + on dipstick and the required following 24-hour urine
collection shows urinary protein > 2000 mg;

- Serious or non-healing wound, peptic ulcer, or bone fracture within 28 days prior to
initiation of study treatment;

- History of gastrointestinal perforation and/or fistulae within 6 months prior to
initiation of study treatment;

- Presence of a bowel obstruction, history or presence of inflammatory enteropathy, or
extensive intestinal resection, Crohn disease, ulcerative colitis, or chronic
diarrhea;

- Uncontrolled arterial hypertension >/= 150/ >/= 90 millimeter of mercury (mmHg)
despite standard medical management;

- Chronic therapy with non-steroidal anti-inflammatory agents or other anti-platelet
agents.

Exclusion Criteria:

- Uncontrolled hypercalcemia or symptomatic hypercalcemia requiring continued use of
bisphosphonate therapy;

- Symptomatic, untreated, or actively progressing central nervous system (CNS)
metastases;

- History of leptomeningeal disease;

- Active or history of autoimmune disease or immune deficiency;

- History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis
obliterans), drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of
active pneumonitis on screening chest computed tomography (CT) scan;

- Positive test for human immunodeficiency virus (HIV) at screening;

- Active hepatitis B virus (HBV) or hepatitis C (HCV) infection;

- Severe infection within 4 weeks prior to initiation of study treatment;

- Significant cardiovascular disease;

- Significant bleeding disorder;

- Prior allogeneic stem cell or solid organ transplantation;

- Major surgical procedure, other than for diagnosis, within 4 weeks prior to initiation
of study treatment, or anticipation of need for a major surgical procedure during the
study;

- Treatment with anticoagulation with warfarin, low-molecular-weight heparin, or similar
agents for therapeutic purposes;

- History of malignancy other than gastric or gastroesophageal junction carcinoma within
2 years prior to screening, with the exception of those with a negligible risk of
metastasis or death;

- Known allergy or hypersensitivity to any of the study drugs or their excipients.