Selection of maternal human immunodeficiency virus type 1 variants in human placenta

To determine the mechanisms by which human immunodeficiency virus type 1 (H IV-1) crosses the placenta into the fetal blood, 12 matched samples of seri al maternal blood, term placentas, and infant blood obtained from a cohort of pregnant women in Cameroon identified as predominantly infected by subty pe A viruses were studied. HIV-1 env sequences were detected by polymerase chain reaction (PCR) in both chorionic villi and enriched trophoblastic cel ls of all 12 placentas but at variable rates of detection. Heteroduplex mob ility assay analysis showed the presence of multiple HIV-1 env quasispecies in sequential maternal peripheral blood mononuclear cell samples, but only a small number of env variants were found in chorionic villi and enriched trophoblastic cells. These data indicate that HIV-1 env sequences are alway s present in term placentas of seropositive women, contrasting with the low frequency at which infection is diagnosed by PCR in neonates with tat, gag , and env primers. Maternal HIV-1 variants appear to undergo a strong negat ive selection by different cell populations within the placental villi.