BK cytotoxic T cells (CTLs) manufactured with the Miltenyi CliniMACS Prodigy Cytokine Capture System will be safe and effective in decreasing specific viral load in children, adolescents and young adults (CAYA) with refractory BK infection post Allogeneic Hematopoietic Stem Cell Transplantation (AlloHSCT) or with primary immunodeficiencies (PID).

Inclusion Criteria:

.1.1 Patients with refractory BK infection post allogeneic HSCT, post solid organ transplantation or with primary immunodeficiencies with either

• Increasing urine and/or plasma BK RT-PCR DNA (by 1 log) after 7 days or persistent quantitative qRT-PCR DNA copies after 14 days despite two weeks of appropriate anti-viral therapy AND/OR

• Medical intolerance to anti-viral therapies including:

  • 2 renal toxicity with cidofovir or other > grade 2 toxicities secondary to cidofovir And/or

• known resistance to cidofovir 1.2. Consent: Written informed consent given (by patient or legal representative) prior to any study-related procedures.

1.3 Performance Status > 30% (Lansky < 16 yrs and Karnofsky > 16 yrs) 1.4 Age: 0.1 to 79.99 years 1.5 Females of childbearing potential with a negative urine pregnancy test

Exclusion:

1. Patient with acute GVHD > grade 2 or extensive chronic GVHD at the time of BK CTL infusion
2. Patient receiving steroids (>0.5 mg/kg prednisone equivalent) at the time of BK CTL infusion
3. Patient treated with donor lymphocyte infusion (DLI) within 4 weeks prior to BK CTL infusion
4. Thymoglobulin (ATG) or Alemtuzumab within 30 days
5. Patient with poor performance status determined by Karnofsky (patients >16 years) or Lansky (patients ≤16 years) score ≤30%
6. Concomitant enrollment in another experimental clinical trial investigating the treatment of refractory BK infection.
7. Any medical condition which could compromise participation in the study according to the investigator's assessment
8. Known HIV infection
9. Female patient of childbearing age who is pregnant or breast-feeding or not willing to use an effective method of birth control during study treatment.
10. Known hypersensitivity to iron dextran
11. Patients unwilling or unable to comply with the protocol or unable to give informed consent.
12. Known human anti-mouse antibodies