• Incidence of adverse events (AEs), serious adverse events (SAEs), and dose limiting toxicities (DLTs) [ Time Frame: Initiation of study treatment through 100 days post-last dose (up to approximately 27 months) ]
• Objective Response Rate (ORR) in Phase 2 using RECIST v1.1 [ Time Frame: Initiation of study treatment until disease progression (up to approximately 27 months) ]
• Identify the recommended Phase 2 dose (RP2D) of GRT-C903 and GRT-R904 [ Time Frame: Up to approximately 6 months ]

• Measure the immune response to the neoantigens encoded by GRT-C903 and GRT-R904 [ Time Frame: Baseline to end of treatment (up to approximately 12 months) ]
• Objective Response Rate (ORR) in Phase 1 using RECIST v1.1 [ Time Frame: Initiation of study treatment until disease progression (up to approximately 27 months) ]
• Duration of response (DOR) using RECIST v1.1 [ Time Frame: Initiation of study treatment until disease progression (up to approximately 27 months) ]
• Clinical benefit rate (CBR) using RECIST v1.1 [ Time Frame: Initiation of study treatment until disease progression (up to approximately 27 months) ]
• Progression-free survival (PFS) [ Time Frame: Up to approximately 4 years ]
• Overall survival (OS) [ Time Frame: Up to approximately 4 years ]

• Non Small Cell Lung Cancer
• Colorectal Cancer
• Pancreatic Cancer
• Solid Tumor
• Shared Neoantigen-Positive Solid Tumors

• Biological: GRT-C903
  a shared neoantigen cancer vaccine prime
• Biological: GRT-R904
  a shared neoantigen cancer vaccine boost
• Biological: nivolumab
  anti-PD-1 monoclonal antibody
• Biological: ipilimumab
  anti-CTLA-4 monoclonal antibody

• Experimental: Phase 1
  • GRT-C903
  • GRT-R904
  • nivolumab
  • ipilimumab
  Interventions:

  • Biological: GRT-C903
  • Biological: GRT-R904
  • Biological: nivolumab
  • Biological: ipilimumab
• Experimental: Phase 2
  • GRT-C903
  • GRT-R904
  • nivolumab
  • ipilimumab
  Interventions:

  • Biological: GRT-C903
  • Biological: GRT-R904
  • Biological: nivolumab
  • Biological: ipilimumab

Inclusion Criteria:

• Provide a signed and dated informed consent form prior to initiation of study-specific procedures.

• Patients with the indicated advanced or metastatic solid tumor as follows:

  1. Microsatellite-stable colorectal cancer (MSS-CRC) who are currently receiving systemic treatment with a fluoropyrimidine and oxaliplatin and/or irinotecan that may include a VEGF or EGFR targeting therapy as their 1L therapy for metastatic disease OR who have experienced disease progression following treatment with a fluoropyrimidine, oxaliplatin, and irinotecan that may include a VEGF or EGFR targeting therapy and have not received additional lines of systemic therapy in the metastatic setting.
  2. Non-small cell lung cancer (NSCLC) who are currently receiving systemic treatment with an anti-PD-(L)1 antibody in combination with cytotoxic, platinum-based chemotherapy OR who have experienced disease progression following treatment with an anti-PD-(L)1 antibody in combination with cytotoxic, platinum-based chemotherapy (or anti-PD-(L)1 alone if patient refuses platinum-based chemotherapy), and have not received additional lines of systemic therapy in the metastatic setting.
  3. Pancreatic ductal adenocarcinoma (PDA) who are currently receiving systemic cytotoxic chemotherapy as their 1L therapy for metastatic disease OR who have experienced disease progression on 1L systemic cytotoxic chemotherapy and have received no more than 1 prior line of therapy in the metastatic setting.
  4. Any solid tumor histology where the patient has experienced disease progression with all available therapies known to confer clinical benefit
• Patient's tumor possesses one of the mutations listed below, and is determined to express a HLA allele for antigen presentation of the identified tumor mutation:

BRAF_G466V // CTNNB1_S37F // CTNNB1_S45F // CTNNB1_S45P // CTNNB1_T41A // ERBB2_Y772_A775dup // KRAS_G12C or NRAS_G12C // KRAS_G12D or NRAS_G12D // KRAS_G12V // KRAS_G13D // KRAS_Q61H or NRAS_Q61H // KRAS_Q61K or NRAS_Q61K // KRAS_Q61L or NRAS_Q61L // KRAS_Q61R or NRAS_Q61R // TP53_K132E // TP53_K132N // TP53_R213L // TP53_R249M // TP53_S127Y

• ECOG Performance Status 0 or 1
• Measurable disease according to RECIST v1.1
• Adequate organ function, as measured by laboratory values (criteria listed in protocol)

Exclusion Criteria:

• Tumors with genetic characteristics as follows:

  1. For NSCLC, patients with a known genetic driver alteration in EGFR, ALK, ROS1, RET, or TRK
  2. Patients with known MSI-high disease based on institutional standard
• Known exposure to chimpanzee adenovirus or any history of anaphylaxis in reaction to a vaccination
• Bleeding disorder (eg., factor deficiency, coagulopathy) or history of significant bruising or bleeding following IM injections or blood draws
• History of allogenic/solid organ transplant
• Active, known, or suspected autoimmune disease
• Active tuberculosis or recent (<2 week) clinically significant infection, or evidence of active hepatitis B or hepatitis C
• Known history of positive test for human immunodeficiency (HIV) or known acquired immunodeficiency syndrome (AIDS)

Complete inclusion and exclusion criteria are listed in the clinical study protocol.