Description

Priming a VRC01-like antibody response in human immunoglobulin locus transgenic mice

Devin Sok^1,2,3, Bryan Briney^1,2,3, Joseph Jardine^1,2,3, Daniel W. Kulp^1,2,3, Matthias Pauthner^1,2,3, Andrew Wood⁴, Sara Chalk⁴, Khoa Le^1,2,3, Alejandra Ramos^1,2,3, Meaghan Jones^1,2,3, Sergey Menis^1,2,3, Glenn Friedrich⁴, Allan Bradley⁴, William R. Schief^1,2,3,5, Dennis R. Burton^1,2,3,5

­¹The Scripps Research Institute, USA; ²IAVI-NAC, USA; ³CHAVI-ID, TSRI, USA; ⁴Kymab Ltd., UK; ⁵Ragon Institute of MGH, MIT, and Harvard University, USA

BACKGROUND: An eOD-GT8 60mer nanoparticle was previously shown to successfully select VRC01-class precursors in a transgenic mouse model expressing the germline heavy chain gene. The ability of this immunogen to select for VRC01-class precursors in the context of competing antibody responses in a human antibody repertoire has yet to be determined.

METHODS: To determine if a germline-targeted immunogen can prime VRC01-class antibody (Ab) responses within a naïve human repertoire and to evaluate a human Ig locus transgenic mouse model for vaccine studies, we primed Kymab mice in Cambridge, UK with eOD-GT8 60mer nanoparticles and then performed sequence analysis of antigen-sorted memory B cells.

RESULTS: To define a baseline, we evaluated naïve Ab frequencies by next-generation sequencing. We found a V_H1-2 frequency of 4%, which is comparable to the human frequency, and a 5 AA CDRL3 frequency of 0.01–0.05%, which is >10-fold lower than the human frequency. We conclude that the frequency of VRC01-class precursor B cells in unimmunized Kymab mice is approximately 0 to 1 precursors per mouse. Mice were immunized once with 20 ug or 4 ug of eOD-GT8 60mer delivered in either Iscomatrix or Ribi adjuvant. A control group was immunized with 20 ug of a non-germline targeting eOD17 60mer in Iscomatrix. Following the prime, memory B cells were epitope-selected using eOD-GT8 and eOD17 by flow cytometry. 14 out of 39 immunized mice (36%) produced VRC01-class memory B cells compared to 0 out of 17 control mice (p = 0.02). Looking only at L chains, 19 out of 39 mice (49%) produced 5 AA CDRL3 memory B cells compared to 0 out of 17 control mice (p = 0.001).

CONCLUSIONS: The numbers described reflect a striking enrichment of VRC01-class memory responses relative to baseline in this humanized mouse model and indicate that eOD-GT8 60mers can function as designed when priming a human-like antibody repertoire.