Mothers May Pass on Mutant HIV to Infants

By Merritt McKinney

NEW YORK (Reuters Health) - New research suggests that mothers infected with HIV , the virus that causes AIDS , sometimes pass on to their infants versions of the virus that are more difficult for the immune system to battle.

Over time, mother-to-child transmission of mutant HIV could have serious implications on the course of the disease as well as on the effectiveness of potential vaccines that protect against HIV, researchers report.

HLA molecules are substances that help direct immune-system cells called ``killer'' T-cells towards viruses and other outside invaders. These proteins vary from person to person, and some of them, including one called HLA-B27, have been shown to protect against AIDS progression.

But a team led by Dr. Bruce D. Walker of Harvard Medical School in Boston, Massachusetts, identified four African children with HLA-B27, a normally protective version of HLA, who were infected with a mutant form of HIV.

All four of the children had been infected by their mothers, so Walker's team analyzed the HLA of the mothers. In three of the mother-child pairs, the mother had HLA-B27. In the case of the women, the virus had mutated to counter the protection of HLA-B27.

This mutation, which occurred only after HIV had time to adapt to the attacks of the women's immune systems, appears to have been transmitted directly to the children, according to the report in the July 19th issue of the journal Nature. The authors note that the infected infants are not able to control HIV infection as well as adults who carry HLA-B27.

The research shows that ``HIV is able to learn how to avoid the immune system while it is in one person, and then retain this knowledge when it infects the next person,'' Walker told Reuters Health.

The Harvard researcher explained that the children's genes are programmed to zero in on the same region of HIV that their mothers' immune systems target. ``Since the virus has already 'learned' how to avoid this attack in the mother, the child is already at a disadvantage. This we think, in part, explains why children do worse than their mothers,'' he said.

The findings are troubling, according to Walker's team, because they suggest that mutations that allow HIV to weaken the body's natural defenses more rapidly may become more common as the AIDS epidemic continues. The investigators also discovered evidence that the altered versions of HIV can be transmitted sexually.

Based on research in animals, people infected with the mutant forms of the virus may not be able to fight off the devastating effects of HIV as long, the report indicates.

A concern for vaccine development, according to Walker, is that the virus is likely to accumulate mutations that help it to avoid major responses of the immune system. ``Our concern is that HIV may be like influenza, changing to a degree that new vaccines need to be made on a regular basis,'' he said.

Right now, the goal is to develop a vaccine that is at least partially protective, Walker explained. ``Our data apply to fine-tuning of a vaccine once we get one that seems to work so that it will stay effective against the viruses that are circulating in the population,'' he said.

SOURCE: Nature 2001;412:334-338.