Heterologous immunization strategy developed broadly reactive human monoclonal antibodies against the BK virus
BK polyomavirus (BKV) causes polyomavirus-associated nephropathy (BKV-nephropathy) and polyomavirus-associated hemorrhagic cystitis (BKV-HC) following kidney transplantation and allogeneic hematopoietic stem cell transplantation (HSCT). BKV strains consist of four distinct genotypes (BKV-I, - II, -III, and -IV) with more than 80% of individuals seropositive for the BKV-I genotype, and lower prevalences of infection or co-infection with the other genotypes. BKV-nephropathy occurs widely in immunosuppressed transplant recipients, with the recommended treatment including reduction of immunosuppressive drugs. High serum titers of BKV-neutralizing antibodies and treatment with BKV-neutralizing intravenous immunoglobulin (IVIG) are associated with reduced levels of BKV-DNAemia in kidney transplant recipients, suggesting anti-BKV antibodies can limit viral load. Thus, we set out to generate broadly neutralizing human monoclonal antibodies (mAbs) against the viral protein 1 (VP1) major capsid protein of BKV genotypes I-IV using VelocImmune(R) transgenic mice that encode for human immunoglobulins. Hybridoma clones from VelocImmune(R) mice immunized with combinations of BKV I-IV VP1 and respective genotypes of BKV pseudoviruses (BK-PsV) were screened using a high-throughput binding assay against BKV-I VP1 expressed in HEK-293 cells. The VP1-binding hybridoma clones were then assessed for neutralization with BK-PsV consisting of respective VP1 proteins from BKV-I, -II, -III, or -IV on the virion surface. Overall, thirty-six broadly cross-neutralizing mAbs against BKV-I, -II, -III, and -IV -were identified. Twenty of the cross-reactive immunoglobulins were subjected to nucleotide sequencing resulting in six clonotype families with fourteen genetically distinct immunoglobulins. Several of the most effective mAbs were fully humanized with the IgG1 Fc domain and broad neutralization of BK-PsV-I, II, III, and IV genotypes with IC50s ranging from [~]7-200 pM. Thus, these cross-neutralizing mAbs represent potential biologics to developed into BKV therapeutics.