Elevated interferon-alpha in maternal and umbilical cord blood and in the placental trophoblast suggests natural protection against vertical transmission of HIV-1 in a Kenyan cohort [letter]

An analysis of sera and placental specimens collected at Pumwani Maternity Hospital in Nairobi Kenya in 1992 indicated that elevated interferon (IFN)-alpha protects against transplacental HIV-1 transmission. Enrolled in the study were 152 HIV-positive but asymptomatic pregnant women and 117 randomly selected HIV-negative pregnant women. Blood samples were obtained from mothers prior to delivery and cord blood was withdrawn. IFN-alpha was present in the cord blood and simultaneously in the placentas in 5 (3.3%) of the HIV-positive mothers. In 4 of these mothers the elevation was also seen in the matched maternal blood. No viral RNA was detected in the cord blood samples from mothers with elevated IFN-alpha; however in a control group of maternal-infant pairs negative for IFN-alpha HIV-1 RNA was detected in 3 of 6 cord blood samples analyzed. A potent inhibitory effect of IFN-alpha on HIV-1 replication in vitro has been demonstrated in T lymphocytes and monocytic cells as well as in placenta-derived cells. In addition IFN has been shown to suppress simian immunodeficiency virus replication in vitro in macaque trophoblasts. Collaboration of the apparent protective effect of IFN-alpha during pregnancy is being sought through an ongoing study based in Malawi.