A human fetus can survive 9 months of gestation in a mother carrying a virus such as herpes or HIV, but the baby may still contract the disease during birth or afterward by drinking infected milk. Antiviral drugs or a caesarian section can reduce the risk of transmission, but never completely eliminate it. Now, experimental work with lambs has shown promise for vaccination while still in the womb.
The researchers--led by Philip Griebel of the University of Saskatchewan in Saskatoon, Canada--gave four fetal lambs a DNA vaccine for bovine herpesvirus 1. After making an incision in the mother sheep's abdomen during the last trimester of pregnancy, the researchers located the mouth of the fetus--where infection would be most likely to occur--and injected the vaccine straight in.
Several days prior to birth, Griebel and his colleagues collected blood and lymph node samples from the fetuses and analyzed the antibodies they found. All four of the lamb fetuses had responded to the herpesvirus vaccine, he reports in the August issue of Nature Medicine. (Previous studies of fetal immunization against hepatitis B in baboons have had less success, with five of eight fetuses producing antibodies.) Not only were antibodies against bovine herpesvirus found in the blood of the four lamb fetuses, but also in the lymph nodes that drain the mouth and nose. "With protection right at the site of virus entry, you get much better protection from the disease," Griebel says.
The findings should "stir up a lot of interest," predicts Ron Kennedy, a microbiologist at the University of Oklahoma Health Sciences Center in Oklahoma City. But to prove that the vaccine is effective, Kennedy notes, the researchers must still expose the newborn lambs to the virus and make sure the immune system can handle it. Griebel is confident his vaccine is effective, and if he's right, "there'll be the impetus to take it forward with primates, then humans," he says.