Study gives clues to how fetus is protected from HIV Mother's immune system may try to shield fetus.

MIAMI — MIAMI -- Researchers may have uncovered a reason for a puzzling phenomenon in AIDS transmission -- the mystery of why only 13 to 30 percent of babies with AIDS-infected mothers develop the disease.

The mothers' immune systems apparently block all but a few variants of the AIDS virus, researchers at the University of Miami say.


"Not all of the variants that we see in the mothers are being transmitted to the babies," said Dr. Cecelia Hutto, an associate professor of clinical pediatrics at UM.

The study was published yesterday in the journal Science by Dr. Hutto and scientists from Northwestern University, New York University and Los Alamos National Laboratory in New Mexico.


The study analyzed the types of human immunodeficiency virus (HIV) in the blood of three mother-infant pairs being treated at Jackson Memorial Hospital.

HIV taken from the mothers showed many variations in the virus' genetic code.

The variations are like typographical errors that occur when the code is "retyped" every time the virus replicates in a person. Sometimes the changes make it hard for the immune system to "see" that particular variant.

The mothers had many HIV variants. But the types found primarily in two of the babies occurred only rarely in their mothers.

The researchers suspect, but have not proved, that these are variants that the women's immune systems couldn't detect.

The findings indicate that strategies for protecting fetuses of infected women will require disabling multiple varieties of HIV, Dr. Hutto said.

But it will take much more research to determine why some varieties slip past the mother's immune system and some don't, she said.