Identification of a clade A HIV envelope immunogen from Protocol G that elicits neutralizing antibodies to tier 2 viruses

Background Broadly neutralizing antibodies PG9 and PG16 have been isolated from the B cells of one clade A-infected individual from IAVI Protocol G. PG16 is relatively trimer-specific whereas PG9 binds trimer preferentially, but can bind monomeric gp120 from several viral isolates. Both antibodies are potent neutralizers that recognize greater than 70% of tier 2 pseudovirues in the TZM-bl assay. We sought to begin immunogen design efforts based on sequences from the Protocol G donor, however all viruses isolated from the donor were resistant to neutralization by PG9 and PG16. We used a bioinformatics approach to infer the most recent common ancestor (MRCA) sequence for the viral envelope (Env) to identify closely related viruses sensitive to PG9/16.