Safety, Tolerability and Efficacy of AntiBKV as Treatment of BKV Infection in Kidney Transplant Recipients

The purpose of this study is to evaluate the safety, tolerability, and efficacy of AntiBKV in reducing BKV DNAemia and progression to biopsy-confirmed BKVAN in kidney transplant recipients. This study has an operationally seamless phase II/III design. The phase II part will evaluate the safety of AntiBKV in kidney transplant recipients and establish antiviral proof of concept. The phase II part includes a dose-comparison part to generate additional PK and PD data of AntiBKV. The phase III part will assess the efficacy of AntiBKV in kidney transplant recipients. For both the phase II and phase III parts, participants will be randomized to receive either four doses of AntiBKV or four doses of placebo (every four weeks). In phase II, 60 participants will be first randomized (1:1) to receive either four doses of 1,000 mg of AntiBKV or placebo. In an additional dose-comparison extension, another 30 participants will be enrolled and randomized (1:1:1) to receive either four doses of 1,000 mg AntiBKV, four doses of 500 mg AntiBKV, or placebo. Based on a Day 141 analysis after phase II the sample size for the phase III part of the trial will be defined. Both the phase II and phase III parts will follow identical study assessments and schedules for participants. Eligible participants will receive an intravenous infusion of the investigational medicinal product (IMP) that will be administered four times at a four-week interval. For the first ten participants enrolled in the study, the infusion time will be at least 60 minutes. Provided there are no safety concerns observed with the first ten participants the duration of subsequent infusions will be at least 30 minutes. After administration of the final dose, participants will return as out participants for periodic safety, BKV DNAemia, and PK follow-up assessments until the end of the trial visits, 26 weeks post last IMP application. Regular kidney biopsies will be performed at baseline (prior to infusion) and on Day 141 (8