Research Highlights

Match making donors

Published online 19 June 2013

Aisha El-Awady

The human leukocyte antigen (HLA) system is composed of many genes that play a major role in how the body recognizes its own cells as self – and therefore protect them from attack by the immune cells. A HLA mismatch is the major reason transplanted organs are rejected, either by the organ recipient's immune system targeting the organ as foreign, or the immune factors from the organ attacking the host tissue, known as 'graft-versus host' disease.

A person inherits one set of HLA genes from each parent. When the two combinations of HLA genes from both parents are identical, the person is said to be HLA homozygous, whereas HLA heterozygous if not. The more alike individuals are in their HLA, the more likely an organ transplant between them would succeed.

An international team of researchers, led by Carolyn Hurley from Georgetown University in Washington, DC, and including Mahmoud Aljurf from King Faisal Specialist Hospital in Riyadh, studied the outcome of bone marrow transplants in mismatched HLA individuals when either donor or recipient was homozygous while the other was heterozygous.

The researchers compared 2,687 unrelated adult donors organized into four groups: one group with heterozygous donors and recipients (bi-directional mismatch); another group with homozygous recipients (host versus graft mismatch); a group with homozygous donors (graft versus host mismatch); and a final control group where donors and recipients had matched HLA.

They found that the group with HLA homozygous recipients receiving transplants from HLA heterozygous donors were the least likely to develop acute graft-versus-host disease. The researchers found no significant difference in other transplant-related complications among the three groups. These findings suggest that the pool of potential donors can be expanded for HLA homozygous recipients.


  1. Hurley, C. et al. The impact of HLA unidirectional mismatches on the outcome of myeloablative hematopoietic stem cell transplantation with unrelated donors. Blood (2013) doi:10.1182/blood-2013-01-480343