RECOMBINATION IN AIDS VIRUSES

Recombination contributes to the generation of genetic diversity in hu man immunodeficiency viruses (HIV) but can only occur between viruses replicating within the same cell. Since individuals have not been foun d to be simultaneously coinfected with multiple divergent strains of H IV-1 or HIV-2, recombination events have been thought to be restricted to the rather closely related members of the quasispecies that evolve s during the course of HIV infection. Here we describe examples of bot h HIV-1 and HIV-2 genomes that appear to be hybrids of genetically qui te divergent viruses. Phylogenetic analyses were used to examine the e volutionary relationships among multiple HIV strains. Evolutionary tre es derived from different genomic regions were consistent with respect to most of the viruses investigated. However, some strains of HIV-1 a nd HIV-2 exhibited significantly discordant branching orders indicativ e of genetic exchanges during their evolutionary histories. The crosso ver points of these putative recombination events were mapped by exami ning the distribution of phylogenetically informative sites supporting alternative tree topologies. A similar example of a recombinant simia n immunodeficiency virus identified in West African green monkeys has also been described recently. These results indicate that coinfection with highly divergent viral strains can occur in HIV-infected humans a nd SIV-infected primates and could lead to the generation of hybrid ge nomes with significantly altered biological properties. Thus, future c haracterization of primate lentiviruses should include careful phyloge netic investigation of possible genomic mosaicism.