Evaluation of the Safety and Efficacy of LB-DTK-BKV in Patients With BK Virus-Associated Hemorrhagic Cystitis Following Allogeneic Hematopoietic Stem Cell Transplantation

The goal of this clinical trial is to assess efficacy of BK virus specific T cells (LB-DTK-BKV) to treat pediatric, adolescent, and adult patients with BK virus-associated hemorrhagic cystitis after allogenic hematopoietic stem cell transplantation (allo-HSCT). It will also evaluate the safety of LB-DTK-BKV using treatment-emergent adverse events (TEAEs). The main questions it aims to answer are: * Does LB-DTK-BKV reduce the number of BKV virus viral load in allo-HSCT patients with hemorrhagic cystitis? * Do adverse events occur after the second dose? Researchers will compare LB-DTK-BKV to a placebo to see if LB-DTK-BKV works to treat hemorrhagic cystitis in allo-HSCT patients. Participants will: * Receive a single intravenous infusion of LB-DTK-BKV at the baseline visit (low dose: 1x10\^7/m\^2; high dose: 2x10\^7/m\^2). * Receive the second dose of LB-DTK-BKV intravenously at the same dose 14 days after the first dose. * Visit the clinic every week for follow-up for 6 months after the first dose.