Abstract

HIV-1 group M was transmitted to humans nearly one century ago. The virus has since diversified to form distinct clades, which spread to multiple regions worldwide. Of the different proteins encoded by HIV-1, the envelope glycoproteins (Envs) have diversified most rapidly in all infected populations. We compared the range of variants that emerged during the AIDS pandemic in diverse HIV-1 clades and distinct geographic regions. Our analyses focused on two components of Env that contain multiple epitopes of broadly-neutralizing antibodies: the glycan shield and apex domain. Interestingly, at each Env position, the amino acid in the inferred clade ancestor was replaced by a unique combination of emerging variants. Key antigenic sites and genetic signatures of vaccine protection have gradually evolved toward conserved frequency distributions (FDs) of all amino acids. FDs are specific for position and clade and are highly conserved in populations from different regions. Remarkably, founder effects of Env mutations in distinct clades and recently-infected regions were significantly reduced during the epidemic by evolution of each site toward the position-specific FD. These findings suggest that the selective pressures that guide evolution of Env are conserved in different populations. They are sufficiently strong to reduce founder effects at the clade and regional levels and have significantly altered the distribution of Env forms that circulate worldwide. Consequently, the intra-population diversity of the Env protein continues to increase whereas the inter-population diversity is gradually decreasing.\n\nImportanceThe Env protein of HIV-1 is the primary target in AIDS vaccine design. Due to frequent mutations, new Env variants continuously emerge in the population. The increasing number of Env forms and apparent randomness of the changes limit our ability to design broadly-effective vaccines. We examined the populations-level changes that occurred in Env during the AIDS epidemic. Each position of the molecule has evolved toward a specific combination of amino acids. Similar changes occurred in different HIV-1 subtypes and geographic regions toward the same sets of forms, often from distinct ancestral sequences. Such conserved patterns of evolution define a new framework for designing vaccines that are tailored to the unique combination of Env variants expected to circulate in each population.