Cytomegalovirus (CMV) is the leading infectious cause of birth defects, and until now scientists had no effective way of developing a preventative vaccine.
According to the Centers for Disease Control and Prevention
(CDC), pregnant women can transmit CMV through the placenta to their fetus when the mother is infected during pregnancy. Although birth defects only occur in some babies who receive a CMV infection from their mothers, at least a quarter of these infants will
develop neurological impairment either at birth or later in infancy or childhood. One-third of pregnant women are exposed to CMV, and 5000 children per year are born with or develop birth defects due to a CMV infection.
Although CMV is treatable, the treatment is not safe for pregnant women. Scientists have struggled to develop a vaccine without a proper mammal model. Scientists needed to know what kind of immune response was necessary to protect mothers and their babies from CMV, but until now, guinea pigs were the only mammals known to also transmit CMV from mother to fetus via the placenta. The dissimilarities between humans and guinea pigs were too large for them to be useful as models of disease.
Fortunately, Duke Medicine discovered and published in Proceedings of the National Academy Of Sciences
this week that Rhesus macaque monkey mothers also transmit CMV to their fetuses, and now they can be used as animal models for developing a CMV vaccine for pregnant women. Senior author Sallie R. Permar, M.D., Ph.D., of the Duke Human Vaccine Institute, is excited now that scientists can "manipulate each arm of the immune system" by studying these monkeys.
The Duke scientists made this discovery through a series of three experiments.
- CD4 helper T cell population was depleted in monkeys bred free of CMV. When pregnant mothers were infected with CMV, the virus passed through the placenta and caused miscarriages.
- CMV-negative mothers were infected with CMV but their immune systems were not disrupted. Babies were infected with CMV from their mothers but were otherwise healthy (no miscarriages).
- Control group of pregnant mothers with natural CMV infections and depleted CD4 helper T cells did not transmit CMV to their fetuses.
"This told us not only that the virus could be transmitted through the placenta, but that the mother's immune system was playing an important role in the severity of the infection," Permar adds.
The next step for Duke Medicine is to determine what kind of vaccine would work best to defend monkeys (and humans) from passing CMV to their children. The scientists are considering neutralizing antibody vaccines and T cell vaccines. Only time will tell which option will successfully provide immunity from CMV.
Watch the following video to hear from mothers affected by CMV.
Source: Science Daily and Duke University