Posted on June 24, 2004 at 5:30 p.m.

BIRMINGHAM, AL — New findings by researchers at UAB (University of Alabama at Birmingham) may explain why some individuals are at increased risk for HIV infection. Details of the study, led by Dr. Richard Kaslow, professor of epidemiology with UAB’s School of Public Health, are published in the June 26 issue of the Lancet.

The study found among cohabitating couples in Zambia where one partner was HIV-positive that couples with matching alleles (variants) of the HLA-B gene — one of the human leukocyte antigen (HLA) genes involved in determining how the body recognizes and responds to infection — transmitted HIV more quickly than couples with non-matching HLA-B alleles.

“For each of the several HLA genes, individuals inherit one allele from their mother and the other from their father, so HLA makeup differs considerably among individuals,” Kaslow said.

Researchers studied 229 of the more than 1300 couples participating in the Zambia UAB HIV Research Project, a voluntary counseling and testing program, from 1994 to 2000. “Health care workers provided free condoms and outpatient medical care as well as appropriate counseling for partners who became infected,” Kaslow said.

Despite ongoing counseling and efforts to prevent HIV transmission, new infections among couples occurred. “Of participating couples, we compared information obtained from 125 transmitting couples and 104 non-transmitting couples,” Kaslow said. “The median transmission time was 185 days for the three couples who shared both B alleles, 395 days for 33 couples who shared one, and 638 days for 89 couples who shared none.”

The reason for the increased risk among partners with matching HLA-B alleles is unclear, but researchers offer one plausible explanation. “Because the infected partner’s virus has already adapted to or escaped the immune response, it may already be partly primed to infect the susceptible partner who has a matching B allele,” Kaslow said.

While this evidence may seem to support routine genetic typing for prediction and prevention of HIV transmission, investigators caution more research is needed. “There have been few similar studies and none exactly like this one,” Kaslow said. “Over time there will be more, but it’s unclear whether findings identical to ours will be reproduced elsewhere soon. Also, before genetic typing is used widely as a predictive tool, it would need to be proven of benefit to patients beyond the information we already provide about how to avoid HIV infection.”

In the meantime, the study provides “strong, persuasive observations” with implications for better understanding disease transmission. “And it may be that results are applicable to infectious diseases other than HIV,” Kaslow said.