Characterization of a novel simian immunodeficiency virus (SIV) from L'Hoest monkeys (Cercopithecus l'hoesti): Implications for the origins of SIVmndand other primate lentiviruses

The human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) appear to have originated by cross-species transmission of simian immunodeficiency vi rus (SN) from asymptomatically infected African primates. Few of the SIVs c haracterized to date efficiently infect human primary lymphocytes. Interest ing, two of the three identified to infect such cultures (SIVsm and SIVcpz) have appeared in human populations as genetically related HIVs. In the pre sent study, we characterized a novel SIV isolate from an East African monke y of the Cercopithecus genus, the l'hoest monkey (C. l'hoesti), which we de signated SIVlhoest. This SN isolate efficiently infected both human and mac aque lymphocytes and resulted in a persistent infection of macaques, charac terized by high primary virus load and a progressive decline in circulating CD4 lymphocytes, consistent with progression to AIDS. Phylogenetic analyse s showed that SIVIhoest is genetically distinct from other previously chara cterized primate lentiviruses but clusters in the same major lineage as SIV from mandrills (SIVmnd), a West African primate species. Given the geograp hic distance between the ranges of l'hoest monkeys and mandrills, this may indicate that SIVmnd arose through cross-species transmission from close re latives of l'hoest monkeys that are sympatric with mandrills. These observa tions lend support to the hypothesis that the primate lentiviruses originat ed and coevolved within monkeys of the Cercopithecus genus. Regarded in thi s light, lentivirus infections of primates not belonging to the Cercopithec us genus may have resulted from cross-species transmission in the not-too-d istant past.