Pre-Clinical Characterization of MAU868, a Novel Neutralizing Antibody Targeting BK Virus

Background: Reactivation of BK virus (BKV) can cause significant kidney and bladder disease in immunocompromised patients. There are currently no effective or BKV-specific therapies. MAU868 is a novel human monoclonal IgG1 that binds to the BKV major capsid protein VP1. Its binding affinity, antiviral activity, and resistance profile were investigated in vitro.

Methods: Binding affinity was determined using a solution equilibrium titration assay. Neutralization of BKV infection in primary renal proximal tubule epithelial (RPTE) cells was evaluated by quantitating TAg-expressing cells using an immunofluorescence-based high content imaging assay. The emergence of BKV resistance-associated variants (RAVs) with reduced susceptibility to MAU868 was investigated in two long-term selection studies with BKV genotypes I and IV in RPTE and HEK-293 cells. Crystallographic studies were conducted using the MAU868 single-chain variable fragment bound to VP1 pentamers.

Results: MAU868 had pM binding affinity and sub-nM neutralizing activity against the 4 major BKV genotypes, with EC₅₀ and EC₉₀ values ranging from 0.009 to 0.093 μg/ml (0.062 to 0.645 nM) and 0.102 to 4.160 μg/ml (0.708 to 28.865 nM). No cytotoxicity observed (highest concentration tested 500 μg/ml). MAU868 also potently neutralized BKV variants constructed to contain VP1 sequences from clinical isolates or highly prevalent VP1 polymorphisms, and JC virus, a related polyomavirus. No RAVs were identified following serial passage of BKV in the presence of MAU868 for up to 182 days. The crystal structure of MAU868 in complex with the VP1 pentamer at 2.66 Å resolution identified a conformational epitope including 3 contact residues in VP1 (Y169, R170, K172) that are strictly conserved across BKV isolates. BKV variants with double or triple alanine substitutions at residues Y169, R170, or K172 were non-viable.

Conclusions: The conserved key contact residues within the conformational epitope of VP1 may explain the broad-spectrum antiviral activity of MAU868 and its high in vitro barrier-to-resistance, ideal characteristics for a potential first-in-class therapeutic agent for the treatment or prevention of BKV disease.