NEW YORK, Mar 02 (Reuters Health) - A powerful blocker of HIV produced in the placenta--the organ that connects the mother with the developing fetus by way of the umbilical cord--may one day be used to prevent mother-to-child transmission of the AIDS-causing virus, scientists report.

The molecule, called leukemia inhibitory factor, plays a key role in maintaining pregnancy, but its potential for inhibiting HIV had not been noted before now, according to Dr. Bruce K. Patterson from Children's Memorial Hospital in Chicago, Illinois, and associates.

The researchers looked at levels of leukemia inhibitory factor in the placentas of HIV-positive women who had transmitted the virus to their infants and other HIV-positive women who did not pass the infection.

The level of leukemia inhibitory factor was significantly higher in the placentas of women who did not pass the virus to their babies than in women whose infants contracted the infection, the authors report in the February Journal of Clinical Investigation.

In experiments, leukemia inhibitory factor potently prevented the growth of several strains of HIV without impairing the growth of normal cells or causing direct cell damage, the researchers note.

Patterson and colleagues call leukemia inhibitory factor "a potent inhibitor" of HIV.

"We are currently working on ways to upregulate leukemia inhibitory factor expression naturally in those with HIV infection," Patterson told Reuters Health. The researchers are also investigating the properties of the molecule for potential future treatments, he said.

"The identification by Patterson and colleagues of another innate substance that inhibits HIV-1 replication opens an additional line of attack for inhibiting mother-to-infant transmission of HIV-1," Dr. Stephen A. Spector from University of California-San Diego in La Jolla, writes in a related commentary.

"The application of these novel approaches may further increase the ability to efficiently and safely interrupt transmission of HIV-1 from an infected mother to her infant," he adds.

But doctors need not give women leukemia inhibitory factor directly to have similar effects.

The hormone progesterone, which is produced by the placenta to prevent rejection of the fetus from the uterus, indirectly boosts leukemia inhibitory factor levels, Patterson explains. So progesterone could be used to help "prevent maternal-fetal transmission in women already infected," he told Reuters Health.

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