A Phase I/II, Randomized, Multi-site Trial to Investigate the Efficacy and Safety of BNT314 in Combination With BNT327 and Chemotherapy in Participants With Metastatic Colorectal Cancer

Key Inclusion Criteria: * Have unresectable histologically confirmed adenocarcinoma of the colon or rectum. * Have confirmed non-microsatellite instability-high (non-MSI-H)/pMMR mCRC per Food and Drug Administration (FDA)/European Commission (EC) approved test or based on local testing. * Have measurable disease defined by RECIST v1.1. * Must provide a tumor tissue sample (formalin-fixed, paraffin-embedded or tissue slides) collected before C1D1 for enrollment. A newly obtained tumor sample is preferred. If it is not feasible to obtain a recent tumor sample, participants can provide archival tumor tissue (less than 2 years prior treatment). * Have Eastern Cooperative Oncology Group Performance Status of 0 or 1. * Have a life expectancy of ≥12 weeks. * Have an adequate organ and bone marrow function within ≤7 days of Day 1 as defined in the protocol. * Have had an adequate previous treatment washout period before randomization/enrollment as defined in the protocol. Inclusion criteria applicable to only protocol-specific cohorts: * Have received at least two previous lines of therapy for metastatic disease. * Have progressed following first-line chemotherapy as specified in the protocol. * Have not received prior systemic therapy for MSS/pMMR mCRC. Participants who received chemotherapy, radiotherapy, or chemoradiotherapy with curative intent for non-metastatic disease in the neoadjuvant or adjuvant setting are eligible for the study if therapy was completed at least 6 months prior to initiation of study treatment. Other cohort-specific inclusion criteria apply. Key Exclusion Criteria: * Confirmed MSI-H/deficient mismatch repair mCRC (per FDA/CE approved test or based on local testing). * Prior treatment with epithelial cell-adhesion molecule or 4-1BB targeted or immunotherapy. * Prior treatment with immune checkpoint inhibitors or programmed death-ligand 1 (PD\[L\]-1)/vascular endothelial growth factor bispecific antibody. * Is a candidate to locoregional treatment (including surgical resection, stereotactic radiation therapy or tumor ablation) with potential to induce complete or near complete response and prolonged tumor control (sometimes described as "radical" intent), per investigator's assessment. * Have uncontrolled or significant cardiovascular disease as specified in the protocol. * Have left ventricular ejection fraction \<50% by echocardiogram within 28 days before randomization/enrollment. * Have clinically uncontrolled pleural effusion, ascites or pericardial effusion requiring drainage, peritoneal shunt, or cell-free concentrated ascites reinfusion therapy within 2 weeks prior to randomization/enrollment. * Have clinically active central nervous system metastases, defined as untreated and symptomatic, or requiring therapy with corticosteroids or anticonvulsants to control associated symptoms. Participants with treated brain metastases that are no longer symptomatic and who require no treatment with corticosteroids or anticonvulsants may be included in the study if they have recovered from the acute toxic effect of radiotherapy. Participants with untreated, asymptomatic brain metastasis for whom local therapy is not indicated per SoC may be eligible if neurologically stable and (if deemed necessary by the investigator). Participants at imminent risk for spinal cord compression or leptomeningeal disease are not eligible. * Have unresolved toxicities from previous anticancer therapy, defined as toxicities (other than alopecia) not yet resolved to Grade ≤1 or baseline toxicities that have resolved with sequelae (e.g., tracheostomy, chronic use of feeding tube, replacement hormones) are allowed, if not associated with increased risk of complications per investigator's assessment. * Participants in Part B or C who fulfill one of the conditions: * Prior treatment with anticancer therapies (as defined in the protocol) with unusual toxicity, or * Known dihydropyrimidine dehydrogenase (DPD) deficiency, testing performed according to the local guidelines. If not tested, lack of DPD activity must be tested for the participants who have not received anticancer therapies (as defined in the protocol) in the prior lines of treatment; testing should be performed according to the local guidelines. * Have a history of another primary malignancy within 2 years, except adequately resected non-melanoma skin cancer, curatively treated in-situ disease, or other solid tumors curatively treated (adjuvant hormone therapy for malignancies at low risk of relapse is allowed) or have a known additional malignancy that is progressing or requires treatment. * Have a history of small bowel obstruction requiring hospitalization within the past 3 months prior to the first dose of IMP. * Have 24-h urine protein excretion ≥1 g. If qualitative urine protein is ≤1+, a 24-h urine protein quantitative test is not required. * Have history of autoimmune disease (myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, psoriatic arthritis, inflammatory bowel disease, vasculitis, antiphospholipid antibody syndrome, Wegener granulomatosis, Sjögren's syndrome, Guillain-Barré syndrome, or multiple sclerosis) with a risk of exacerbation following PD-L1 inhibition or have an immune deficiency (allogeneic hematopoietic stem cell transplantation or organ transplantation). Participants with protocol-specified conditions may be eligible. * Have serious non-healing wounds, ulcers, or bone fractures. This includes history of abdominal fistula, gastrointestinal perforation, or intra abdominal abscess or esophageal and gastric varices, acute gastrointestinal bleeding for which an interval of 6 months must pass before enrollment into this study. In addition, the participant must have undergone correction (or spontaneous healing) of the perforation/fistula and/or the underlying process causing the fistula/perforation. * Have evidence of major coagulation disorders or other significant risks of hemorrhage. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.