Using TGS technology to make the perfect match even better for stem cell transplant recipients

Mar 4 2019

At Anthony Nolan we save the lives of people with blood cancers and blood disorders that need a stem cell transplant. Every day we use our register to match individuals willing to donate their stem cells to people who need lifesaving transplants.

We match potential donors to patients by looking at their human leukocyte antigen (HLA) tissue type. It’s part of our genetic characteristic that makes us all unique individuals. We look at five HLA genes (called HLA-A, -B, -C, DQb1 and DRB1), each of which has two versions inherited from your mother and father, making 10 in total. When it comes to finding a match, the higher the number of matching alleles the better, but sometimes a perfect match isn’t successful and sometimes other matches are.

It’s clear we don’t know everything just yet, but we are continually expanding our knowledge about what makes the perfect match. Anthony Nolan’s ultra high-resolution sequencing technique, that we call Third Generation Sequencing (TGS), has revolutionized how we analyze HLA genes. It’s also been used to confirm the importance of other genes, including a sixth HLA gene called DPB1.

What is TGS?

TGS technology allows DNA to be analyzed in more detail than ever before. We have previously only been able to focus on the parts of HLA genes that were the most variable and thought to be the most important when finding a match. However, with the improved resolution of TGS and its ability to read much longer DNA strands we are beginning to discover the importance of other regions in these genes too. This means we can be more confident at identifying the key mismatches between patients and potential donors.

Now Anthony Nolan scientists have shown, for the first time, that using TGS to match patients and donors improves transplant outcome. The research has been published in the journal Biology of blood and marrow transplantation.

What did the study look at?

Over the past 20 years Anthony Nolan has collected paired DNA samples from over 2,500 stem cell recipients and their matched donors. Clinical data from these patients has also been collected during this time to see which matches were more successful and those that caused complications such as Graft vs Host Disease (GvHD) and relapse.

Nearly 900 of these donor and recipient paired samples have been re-analyzed using TGS to see if the new technology provides better insight into why some matches were more successful.

What has the latest study revealed?

Overall, the matching score of nearly a quarter of patients changed because sequences could be viewed in more detail, which revealed previously unseen mismatches.

The study focused on patients that were originally given a perfect match – a 12/12 score for all six HLA genes, including DPB1. However, after TGS analysis, those patients that still had a perfect score were roughly twice as likely to be alive after 5 years compared to those that were 10/10 but had certain mismatches in DPB1. The study confirmed previous findings that some DPB1 mismatches can have a better outcome than others. Similarly, 12/12 patients were less likely to experience transplant related complications in the 12 months post-transplant. Patients with mismatches in DPB1 were also twice as likely to develop acute GvHD after their transplant.

Importantly, this new TGS data was combined with other factors that also influence transplant success. This included matching patients and donors for cytomegalovirus (CMV) status – a common virus that causes few complications in healthy individuals. This improved the chance of transplant success threefold, when compared to patients with a 10/10 score and CMV mismatch.

What does it mean for the future?

This study demonstrates the essential need for all stem cell recipients and potential donors to be HLA typed using ultra high-resolution sequencing techniques. It improves on the current gold standard 10/10 matches that were thought to be the best possible. The improved sequencing accuracy will mean more patients have a successful transplant and reduce the chance of them developing GvHD afterwards.

Dr Neema Mayor, Senior Post-Doctoral Research Scientist at Anthony Nolan, said:

We are very excited about the potential benefits of this DNA sequencing technology in being able to provide us with unparalleled information about the tissue types of our patients and donors.

The clinical impact of achieving this level of resolution HLA typing data is considerable, particularly because in organ and blood stem cell transplantation matching donors and recipients for their HLA is of utmost importance.

This level of matching can reduce the risk of complications such as graft-versus-host disease and, consequently, the risk of mortality – potentially saving more lives."

Professor Steven Marsh, Director of Bioinformatics at Anthony Nolan, added:

Anthony Nolan was the world’s first stem cell registry when it was founded more than 40 years ago. Our work with this new high-resolution sequencing shows that, even after four decades of saving lives, we remain a pioneering organization.

By investing in what we believe to be the gold standard of tissue typing, we have once again shown our commitment to improving the lives of people with blood cancer. We look forward to a bright future for Anthony Nolan and for stem cell transplant patients and we firmly believe this new TGS will be an important part of that goal."