Abstract: TH-PO1228
Patient BK Polyomavirus VP1 Genotyping Predicts Neutralizing Antibody Incompatibility and Provides Guardrails for VP1-Targeting Monoclonal Antibody Trial and Therapy
Session Information
- Late-Breaking Research Posters
November 06, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Transplantation
- 2102 Transplantation: Clinical
Authors
- Munawar, Ali, Orthogon Therapeutics LLC (affiliate of Pledge Therapeutics), Canton, Massachusetts, United States
- Akkermans, Onno, Pledge Tx B.V., Leuven, Belgium
- Úbeda Nicolau, Cristina, Pledge Tx B.V., Leuven, Belgium
- Bandara, Asanga, Pledge Therapeutics, LLC, Canton, Massachusetts, United States
- Correa Sierra, Consuelo Beatriz, Pledge Therapeutics, LLC, Canton, Massachusetts, United States
- Martins, Fernando H, Pledge Therapeutics, LLC, Canton, Massachusetts, United States
- De Graef, Steff, Pledge Tx B.V., Leuven, Belgium
- Deans, Erin E, Pledge Therapeutics, LLC, Canton, Massachusetts, United States
- Ross, Stephen, Pledge Therapeutics, LLC, Canton, Massachusetts, United States
- Sienaert, Senne, Pledge Tx B.V., Leuven, Belgium
- Galindo Cerrada, Miriam, Pledge Therapeutics, LLC, Canton, Massachusetts, United States
- Chitalia, Vipul C., Boston Medical Center, Boston, Massachusetts, United States
- Mani, Nagraj, Orthogon Therapeutics LLC (affiliate of Pledge Therapeutics), Canton, Massachusetts, United States
- Weeks, Stephen D, Pledge Tx B.V., Leuven, Belgium
Background
BK polyomavirus (BKPyV) reactivation affects up to 60% of kidney transplant recipients and threatens graft survival. No antivirals exist; reducing immunosuppression remains the standard but carries the risk of long-term graft dysfunction. Two VP1-targeting monoclonal antibodies (mAbs, MAU868 and Potravitug) failed to reduce viral load in Phase 2 trials. Due to their limited intrarenal access and epitope diversity, we hypothesize that sustained sub–curative exposure increases the likelihood of on–target VP1 escape mutants compromising the neutralizing capacity of Potravitug.
Methods
Structural analysis of VP1–mAb complexes was combined with >900 patient–derived VP1 sequences spanning major genotypes (I–IV) and subtypes (e.g., IV–a, II–b). Natural variations were mapped onto antibody epitopes to generate a 24–variant clinical panel. Resistance was assayed. A genotype–to–compatibility model was developed from the patient dataset.
Results
Our structural complexes and entry assays showed that Potravitug blocks viral entry by engaging the receptor cleft. Across >900 patient–derived VP1 sequences, extensive diversity at the receptor–cleft (BC–loop) footprint was observed with amino acid variations present in 53% of clinical isolates at contact residues of naturally elicited neutralizing antibodies and Potravitug. These substitutions markedly reduced Potravitug binding and neutralization, of which a single patient–observed E73K substitution reduced neutralization by >50,000–fold. In–cycle VP1 substitutions emerged within 16 weeks under antibody pressure. Our genotype–to–compatibility model distinctly separates compatible vs incompatible VP1 genotypes for VP1–mAbs.
Conclusion
Our study explains the suboptimal potency of therapeutic antibodies, increasing the risk for VP1 escape mutants. It demonstrates that the donor–recipient serology and BK VP1 genotype mismatch contributes to viral reactivation. Our model supports the following steps for Phase 2–4 design (i) baseline VP1 genotyping with compatibility stratification for study entry and clinical use; (ii) on–therapy VP1 sequencing (paired plasma/urine) to detect resistance.
Funding
- Commercial Support – Orthogon Therapeutics LLC (affiliate of Pledge Therapeutics), Canton, MA