Priming a VRC01-like antibody response in human immunoglobulin locus transgenic mice
Devin Sok1,2,3, Bryan Briney1,2,3, Joseph Jardine1,2,3, Daniel W. Kulp1,2,3, Matthias Pauthner1,2,3, Andrew Wood4, Sara Chalk4, Khoa Le1,2,3, Alejandra Ramos1,2,3, Meaghan Jones1,2,3, Sergey Menis1,2,3, Glenn Friedrich4, Allan Bradley4, William R. Schief1,2,3,5, Dennis R. Burton1,2,3,5
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 VH1-2 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.