Inclusion Criteria:

• * Age18 ≤ 75 years
• * Have BKV infection/viremia following kidney transplantation, where BKV viremia is defined as positive BKV qPCR (≥ 250 copies)
• * Have evidence of invasive BKV infection (BK Nephropathy)
• * Experience one of the following:
• * New, persistent and/or worsening BKV-related symptoms, signs and/or markers of end organ compromise despite being on lower immunosuppressive medication
• * Adverse effects of lower immunosuppressive medications (e.g., dnDSA, biopsy proven rejection)
• * Eligible Donor
• * Provide Written informed consent

Exclusion Criteria:

• * Non-kidney organ transplant recipient
• * Patient with acute rejection of the kidney allograft at time of T-cell transfer
• * Patient receiving steroids (\>0.5 mg/kg body weight (BW) prednisone equivalent) at the time of T-cell transfer
• * Patient treated with Thymoglobulin (ATG), Alemtuzumab or T-cell immunosuppressive monoclonal antibodies within 28 days prior to T-cell transfer
• * Extra renal tissue invasive BK infection
• * Concomitant enrollment in another clinical trial interfering with endpoints of this study
• * Any medical condition which could compromise participation in the study according to the investigator's assessment
• * Known HIV infection
• * Female patient who is pregnant or breast-feeding, or adult of reproductive potential not willing to use an effective method of birth control during study treatment Note: Women of childbearing potential must have a negative urine pregnancy test at study entry.
• * Patients unwilling or unable to comply with the protocol or unable to give informed consent
• Donor Eligibility
• * ≥ 18 years old
• * Available and capable of undergoing a single standard 2 blood volume leukapheresis
• * HLA Compatible (see Donor selection priority below):
• * Original kidney transplant donor
• * Fully HLA matched family member (6/6 HLA match considering HLA-A, HLA-B and HLA-DRB1 genes)
• * Partially matched family member (≥ 2/6 HLA match, considering HLA-A, HLA-B and HLA-DRB1 genes)
• * BK IgG seropositive
• * Meets the criteria for donor eligibility defined in the UW Program for Advanced Cell Therapy Standard Operating Policies and Procedures for Donor Evaluation and Eligibility Determination for the Donation of Viral Specific T Cells, which is in compliance with FACT standards for Immune Effector Cells, and 21 CFR 1271, subpart C.
• * Provide written informed consent
• Donor selection priority: The original kidney donor will be the first choice of donor peripheral mononuclear cells. If the original donor is not available or does not meet all donor eligibility criteria, alternative related donors will be selected, with preference for fully matched related donors (6/6 HLA match, considering HLA-A, -B, and -DRB1 genes) over related donors with partial HLA match (≥ 2/6 HLA match, considering HLA-A, -B, and -DRB1 genes).
• Note that if the selected donor is related, but not a biological parent or child of the recipient (i.e., at least haploidentical), then high resolution testing of HLA-A and HLA-B will be performed on donor and recipient (if high resolution HLA genotyping not already available in the medical record). If the degree of matching at high resolution reveals a less favorable match than an alternative donor, then prioritization of the alternative donor will occur.