BKV Infection

The goal of this prospective clinical study is to evaluate the safety and efficacy of Multi-Virus Specific T cells (LB-DTK-MV) in pediatric patients with systemic viral infection, including CMV, EBV, and BKV, after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The main questions it aims to answer are: * What is the maximum tolerated dose of LB-DTK-MV based on dose-limiting toxicity? * What treatment emergent adverse events occur within 14 days after the second infusion? * Is there a clinically significant reduction in CMV, EBV, and BKV viral loads within 14 days following the second infusion? * Is there a clinically significant improvement in clinical symptoms within 14 days following the second infusion? Participants will: * Receive a single intravenous infusion of LB-DTK-MV during the baseline visit (low dose: 1x10\^7/m\^2; high dose: 2x10\^7/m\^2). * Receive the second infusion of LB-DTK-MV intravenously at the same dose 14 days after the first infusion. * Attend weekly follow-up visits at the clinic for 6 months after the first infusion.

The goal of this clinical trial is to evaluate the efficacy and safety of Multi-Virus Specific T cells (LB-DTK-MV) to treat patients diagnosed with antiviral-resistant CMV, BKV, or EBV infection or associated diseases after anticancer therapy or allogeneic hematopoietic stem cell transplantation (allo-HSCT). The main questions it aims to answer are: * What is the maximum tolerated dose of LB-DTK-MV based on dose-limiting toxicity? * Does the number of CMV, BKV, or EBV virus viral load decrease within 7 or 14 days after the second infusion of LB-DTK-MV? * Do treatment emergent adverse events occur after the second infusion? Participants will: * Receive a single intravenous infusion of LB-DTK-MV during the baseline visit (low dose: 1x10\^7/m\^2; high dose: 2x10\^7/m\^2). * Receive the second infusion of LB-DTK-MV intravenously at the same dose 14 days after the first infusion. * Attend weekly follow-up visits at the clinic for 6 months after the first dose.

Epstein Barr Virus (EBV) or Cytomegalovirus (CMV) infection results in significant morbidity and mortality in hematopoietic stem cell transplantation (HSCT) patients. HSCT patients often face opportunistic infections due to the immunosuppressive state during transplantation. Antimicrobial drugs are usually used for prophylactic purposes and for treatment after early detectable infections. Unfortunately, some patients develop resistance to such drug treatment. In addition to HSCT patient, immune compromised patient may also be victim to opportunistic infections. Many infections can be effectively managed by functional immune recovery. In this study, the safety and efficacy of microbial-specific cytotoxic T lymphocytes (CTLs) will be investigated.