Breaking Boundaries in Organ Transplantation with 21st-Century Glycomics
- GlycoNet investigators have developed a new diagnostic test that will advance organ transplantation and enable more transplants across blood type barriers, saving more lives.
The ABO blood group system is critical in transplantation, but donor-recipient compatibility relies on more than just blood groups. Blood groups—A, B, AB, and O—are determined by specific sugar molecules or glycans (called antigens) present on the surface of red blood cells and other tissues and organs; antibodies are normally produced to the ABO sugars we don’t express. These antibodies and sugars influence immune responses and whether patients can safely accept ABO mismatched organ transplants. As a result, we need precise tools to determine donor-recipient ABO compatibility and reduce the risk of organ rejection.
The current standard for assessing donor-recipient ABO compatibility is an agglutination test that involves mixing a patient’s serum with donor red blood cells to see if agglutination (red cell clumping) occurs, indicating the presence of antibodies reactive to the donor cells. This method, dating back to the early 1900s, lacks reproducibility and precision where organ transplantation is concerned, as the types of glycans or sugars on red blood cells are not the same as those on tissue and organs that we transplant.
“The antibodies reactive to glycans that are present on a red blood cell might be completely irrelevant to the organ,” explains GlycoNet investigator Dr. Anne Halpin, Assistant Professor at the University of Alberta. “For example, in heart transplantation, there are subtypes of glycans present on a red blood cell that are not actually on the heart. So the agglutination test could be detecting an antibody that’s not donor-specific for that heart.”
As a result, some people are being deemed ineligible for transplants when they should be considered eligible. The agglutination test contributes to unnecessary barriers, particularly for people with blood group ABO-O or -B, who have smaller pools of potential ABO-compatible donors than ABO-A or -AB patients.
“It’s sort of a disconnect that we have in transplantation right now that we make these very challenging and very important decisions based on a technology that is old—it’s still robust in some ways, for example in red blood cell transfusion, but not meeting clinical need to support transplantation.”
Halpin, who is also a clinical laboratory doctoral scientist at Alberta Precision Laboratories, has been working with GlycoNet investigator Dr. Lori West, a pediatric transplant cardiologist and Professor at the University of Alberta, to create a more precise test for assessing donor-recipient compatibility.
They developed a bead-based ABO antibody assay that detects antibodies to specific glycan subtypes relevant to organs and tissues. A trial involving nine laboratories across North America and Europe also demonstrated that the assay results were consistent and reproducible.
Creating the assay was a collaborative effort, acknowledges Halpin. “We worked with GlycoNet Integrated Services and carbohydrate chemists who are also GlycoNet investigators to manufacture or synthesize the glycans present in different cells and tissues.”
The synthesized glycans are then coupled onto microscopic beads. Patient serum is incubated with the beads; if antibodies are present, they will stick to the glycans on the beads. The beads are then acquired using a LuminexÒ machine to detect the antibodies on the beads. The colour intensities of the beads separate which glycan was coupled as well as indicate whether patient antibodies have attached to the beads. The higher the level of antibody present, the more the fluorescence intensity is detected. This fluorescence output helps determine whether a donor and recipient are compatible.
“We’re really excited to see the potential applications of this assay in a clinical setting, with the goal of allowing more patients the opportunity to be transplanted,” says Halpin.
Halpin and West are now founding a company together and working to make the bead-based assay widely available as soon as possible.
“GlycoNet has been our biggest supporter of this work, not just because of the readily available expertise and funding support but also because of the shared enthusiasm of our goal and assistance in moving this work forward to facilitate more compatible transplants.”
Translating research into application
Halpin was a doctoral student under West’s mentorship when she first became involved in the project. At the time, West had been working with other GlycoNet collaborators on an earlier version of the assay, utilizing a different platform for studying glycan interactions with antibodies, called a glycan microarray. Halpin recognized that integrating the glycan microarray, an instrument not yet in use in the clinical setting, could potentially pose a challenge to widespread use of this assay.
“One of the barriers to implementing new technology in a clinical laboratory is whether the equipment already exists and the expertise is already there,” explains Halpin, “which wasn’t the case for the microarray.”
Halpin was taking a graduate grant writing course at the time when she reflected on whether the microarray test could be modified for more seamless integration into a clinical lab setting. She and West decided to explore this avenue as part of a GlycoNet grant application. That grant was successful and led to the development of the bead-based ABO antibody assay based on the LuminexÒ platform—an instrument that is already used in clinical histocompatibility laboratories around the world—reducing potential equipment costs and training for staff.
“I think that’s helped to advance this new test more quickly because it’s not an unfamiliar technology in the clinical laboratory setting and to transplant professionals,” says Halpin.
This innovative assay is a critical step to enable more ABO-incompatible transplants, offering hope to many patients waiting for organ transplants.
Honouring both donors and recipients
As a living kidney donor herself, Halpin notes that her personal experience has made her think not only about the transplant recipients but also about how we honour organ donors and their decisions to help others in need.
“Transplantation is an interesting space because you’re not just honouring the patients, you’re really honouring a donor as well. When we use this donor gift in the best possible way and use the best possible technology to assess the immune risk of a donor/recipient pair, then we’re actually honouring both those sides.”
Original source here.