A Study to Evaluate the Efficacy and Safety of Autogene Cevumeran With Nivolumab Versus Nivolumab Alone in Participants With High-risk Muscle-invasive Urothelial Carcinoma (MIUC)

The main purpose of the study is to evaluate the efficacy of adjuvant treatment with autogene cevumeran plus nivolumab compared with nivolumab in participants with high risk MIUC. In this study participants will be enrolled in a safety run-in phase to receive autogene cevumeran + nivolumab. This phase will be conducted to monitor and ensure the safety of study participants. After all participants in the safety run-in have been enrolled to receive autogene cevumeran + nivolumab, further participants will be randomized in either autogene cevumeran + nivolumab or the saline + nivolumab arm.

Inclusion Criteria: * Participants must have the capacity to participate/enroll in the study and to provide informed consent * Histologically confirmed muscle-invasive UC (also termed transitional cell carcinoma \[TCC\]) of the bladder or upper urinary tract * Tumor-node-metastasis (TNM ) classification (Union for International Cancer Control \[UICC\]/American Joint Committee on Cancer \[AJCC\] 7th edition) at pathological examination of surgical resection specimen of (y)pT3-4 or (y)pN+ and M0 * Surgical resection of MIUC of the bladder or upper tract * Participants who have received neoadjuvant chemotherapy (NAC), including antibody drug-conjugate, either alone or in combination with a checkpoint inhibitor (CPI), are eligible * Participants who have not received any prior NAC are also eligible, provided they meet one of the following criteria, which would make them ineligible to receive adjuvant cisplatin-based therapy: participant refusal, cisplatin ineligibility or investigator decision * Tumor tissue must be provided for biomarker analysis * Absence of residual disease and absence of metastasis, as confirmed by a negative baseline computed tomography (CT) or magnetic resonance imaging (MRI) scan of the pelvis, abdomen, and chest no more than 28 days prior to randomization * Full recovery from cystectomy or nephroureterectomy within 120 days following surgery * Eastern cooperative oncology group (ECOG) performance status of 0 or 1 * Negative human immunodeficiency virus (HIV) test at screening * Negative hepatitis B surface antigen (HbsAg) test at screening * Positive hepatitis B surface antibody (HBsAb), or a negative HBsAb at screening accompanied by either of the following: negative total hepatitis B core antibody (HBcAb) or positive total HBcAb test followed by quantitative hepatitis B virus (HBV) deoxyribonucleic acid (DNA) \< 500 international units/milliliter (IU/mL) * Negative hepatitis C virus (HCV) antibody test at screening, or a positive HCV antibody test followed by a negative HCV ribonucleic acid (RNA) test at screening Exclusion Criteria: * Partial cystectomy in the setting of bladder cancer primary tumor or partial nephroureterectomy in the setting of renal pelvis primary tumor * Any approved anti-cancer therapy, including chemotherapy, or hormonal therapy within 3 weeks prior to initiation of study treatment * Adjuvant chemotherapy, immunotherapy, or radiation therapy for UC following surgical resection * Prior active malignancies within 3 years prior to randomization * Treatment with a live, attenuated vaccine within 4 weeks prior to initiation of study treatment