A Study to Understand How a New, Unlicensed Drug Works, Compared With a Placebo, Against BK Virus in Patients Who Have Had a Kidney Transplant.

Inclusion Criteria: 1. Male or female aged 18 years or older 2. Kidney transplantation within 12 months prior to randomization 3. First episode of detectable BKV DNA in plasma since last kidney transplantation. As defined by either: 1. positive BKV DNA test of one time \>104 IU/mL and \<106 IU/mL, within 30 days prior to randomization, or 2. \>103 IU/mL and ≤104 IU/mL sustained for at least 2 weeks (confirmed by at least 2 consecutive measurements), with the most recent measurement within 14 days prior to randomization. 4. Female participants (if of childbearing potential) must agree to remain abstinent (refrain from heterosexual intercourse) or use at least one highly effective contraceptive method that result in a failure rate of \<1% per year until the end of the trial. Male participants must agree to refrain from donating sperm, and to remain abstinent (refrain from heterosexual intercourse) or use a condom with a female partner of childbearing potential until the end of the trial. 5. Negative serum β-HCG (beta-human chorionic gonadotropin) test for women of child-bearing potential at Screening and a negative urine pregnancy test prior to randomization on Day 1. 6. Able and willing to provide written informed consent and comply with trial protocol. Exclusion Criteria: 1. Known hypersensitivity to any component of the IMP 2. Estimated glomerular filtration rate (\[e\]GFR) \<30 mL/minute/1.73 m2 at screening 3. Alanine transaminase (ALT) \>2×upper limit of normal (ULN) or direct bilirubin \>1.1×ULN (except Gilbert's Disease) at screening 4. Uncontrolled participants who are treated or planned to be treated with an mTOR inhibitor or belatacept as part of their immunosuppression regimen post-transplantation at the time of enrollment and during the trial period 5. Participants who have received a multi-organ transplant involving a kidney (e.g. kidney-pancreas, kidney-liver, kidney-heart) 6. Participants who are treated or planned to be treated during trial participation with leflunomide, cidofovir, or medicinal products potentially active against BKV at the time of randomization and during the trial period until end of treatment. 7. Participants who received antibody-depletion therapy within 3 months prior to randomization, or in the opinion of the Investigator are likely to require antibody-depletion therapy during trial participation. Antibody-depletion therapies include but are not necessarily limited to plasmapheresis, immunoadsorption, and intravenous immunoglobulins (IVIg) 8. Participants with active kidney transplant rejection or those considered at high-risk of recurrence of native kidney disease (e.g. primary focal segmental glomerulosclerosis \[FSGS\], C3 glomerulopathy) 9. Participants with known donor-specific antibodies (\[DSA\], de novo, or pre-transplantation). Kidney transplant recipients with low-level pretransplant DSAs (\<1,000 mean fluorescence intensity \[MFI\]) can be included if no impact on the trial assessments is expected by the discretion of the Investigator. 10. Pregnant or nursing (lactating) women 11. Uncontrolled acute or chronic infections such as hepatitis B (HBV), hepatitis C (HCV), human immunodeficiency virus (HIV), cytomegalovirus (CMV), or Epstein-Barr virus (EBV) 12. History of malignancy within the past 5 years, except completely excised basal cell or squamous cell carcinoma of the skin, or cervical carcinoma in situ at least 2 years prior to screening 13. Documented evidence of the use of another Investigational Medicinal Product (IMP) within 30 days or 5 half-lives of randomization, or until the expected PD effect has returned to baseline (whichever is longer) 14. Known current alcoholism or drug addiction 15. Any other condition or laboratory abnormality, that in the opinion of the Investigator, would interfere with the evaluation of the IMP or interpretation of the participant safety data or trial results.