Study to Evaluate Viralym-M (ALVR105) for the Treatment of Virus-Associated Hemorrhagic Cystitis (HC)

Key Inclusion Criteria Participants must meet all of the following criteria in order to be eligible to participate in the study: * Male or female ≥1 year of age. * Had an allogeneic hematopoietic cell transplant (HCT) performed ≥21 days and ≤1 year prior to randomization. * Myeloid engraftment confirmed, defined as an absolute neutrophil count ≥500/mm³ for 3 consecutive laboratory values obtained on different days, and platelet count \>10,000/mm³ at the time of randomization. * Diagnosed with HC based on the following criteria (all 3 criteria must be met): 1. Clinical signs and/or symptoms of cystitis. 2. Grade ≥3 hematuria, defined as macroscopic hematuria with visible clots. 3. Viruria with ≥1 target virus (ie, BKV, JCV, AdV, CMV, EBV, and/or HHV-6). * At least 1 identified, suitably matched posoleucel (ALVR105) cell line for infusion is available. Key Exclusion Criteria Participants who meet any of the following criteria will be excluded from participation in the study: * Ongoing therapy with high-dose systemic corticosteroids (ie, prednisone dose \>0.5 mg/kg/day or equivalent). * Therapy with antithymocyte globulin, alemtuzumab (Campath-1H), or other immunosuppressive T cell-targeted monoclonal antibodies ≤28 days before randomization. * Evidence of active Grade \>2 acute graft versus host disease (GVHD). * Uncontrolled or progressive bacterial or fungal infections. * Uncontrolled or progressive viral infections not targeted by posoleucel (ALVR105). * Uncontrolled or progressive EBV-associated post-transplant lymphoproliferative disorder. * Known or presumed pneumonia secondary to any organism that is not considered to be well-controlled by antimicrobial therapy. * Pregnant or lactating or planning to become pregnant. Note: Other protocol defined Inclusion/Exclusion criteria may apply.