Dr. Neema Mayor, Head of Immunogenetics Research at Anthony Nolan

Using ultrahigh resolution HLA typing to improve patient outcomes after a stem cell transplant

May 5, 2021
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In this blog post, Science Communications Manager Dr Jonathan Kay looks at Anthony Nolan’s research into ultrahigh resolution (UHR) DNA sequencing.

Following a study at our Research Institute in 2019, our HLA Informatics group led by Professor Steven Marsh, recently worked with the Center for International Blood and Bone Marrow Transplant Research (CIBMTR) to gain a more comprehensive answer on whether this process can help find better matches for our patients.

What did the initial research show?

Anthony Nolan’s researchers were the first to demonstrate the importance of using UHR DNA sequencing when matching transplant patients to potential stem cell donors. The improved resolution of this technique allows us to identify HLA mismatches that would not have been detected previously. Our initial research showed that harnessing this technique, as well as matching for a sixth HLA gene called DPB1 could improve patient survival and reduce post-transplant complications. In the UK and Europe, both are now widely used when the search for a new donor begins.

Why was further research necessary?

Our initial findings were achieved using samples from a relatively small collection of patients and donors from the UK. This means they still need to be validated further in a much larger group of patients that are independent of the first study.

Throughout the world, different countries carry out stem cell transplants according to different clinical guidelines. For instance, in the United States, it’s recommended that patients are matched to five HLA genes if possible, with some patients only matched to four. Similarly, donor cells are sometimes treated to reduce the number of T-cells present (depletion) in order to lower the risk of graft vs host disease (GvHD) developing.

Variations in practices like these highlight why it’s so important to demonstrate that UHR sequencing and HLA-DPB1 matching have a positive impact on patient outcomes in a second larger study. It should also give our researchers an indication of the clinical settings where UHR matching can have the biggest impact.

What did the recent study involve?

Anthony Nolan researchers collaborated with colleges at the CIBMTR in the US to study over 5,000 patient and donor DNA samples, originally assigned as 10/10 matches.

Initially, UHR was used to reanalyse all the samples and most of them remained at least a 10/10 match. However, the higher resolution of sequencing revealed previously unseen mismatches in 18% of patients. Most of these resulted in matches being downgraded to 9/10 matches and 1% to less than 9/10. When the HLA-DPB1 gene was also considered, just over 600 patients (12.3%) were shown to be complete matches for all six genes and given a 12/12 score.

What affect did this have on transplant outcomes?

One of the key questions of this study was: can UHR matching be used to make transplants more successful and ultimately improve patient survival? To answer this, a variety of clinical outcomes were considered once new matching scores had been assigned, based on the UHR sequencing data. This included the rate of disease relapse, transplant-related mortality and the incidence of both acute and chronic GvHD.

Unfortunately, the study was unable to demonstrate that UHR HLA matching improves patient survival. The patients with a 12/12 match did not have an improved chance of surviving compared to other patients, irrespective of whether they had a T-cell depleted transplant or not.

However, the study was able to show that the risk of acute graft vs host disease (aGvHD) increased for patients with at least one mismatch compared to the 12/12 matches. Patients who had a T-cell depleted transplant and at least one mismatch were also more likely to die from complications associated with their transplant including severe infections.

Why didn’t we see the results we were expecting?

Some of the study’s findings could be considered disappointing, but a deeper comparison between our original study and this one may shed some light on the results.

While every effort was made to account for differences between the patient groups in the two studies, there were fundamental differences that are known to influence transplant outcomes. For example, the US patients were generally older in age and had more advanced illnesses than their UK counterparts – and we know that the negative impact an HLA mismatch can have is lessened in cases of more advanced disease.

All UK transplants included in the study were performed before 2011, whereas the US patients had their transplants between 2008 and 2017. The continual improvement of medical practices during this time may have masked the effect of HLA mismatches in these more recent transplants.  

Finally, even though the same UHR sequencing technology was used in both studies, the original Anthony Nolan study considered larger regions of the HLA genes, including some untranslated regions. Although these areas are unlikely to influence the structure of the HLA proteins they code for, further studies that compare HLA genes to the same extent are needed to decide if these regions are clinically important.

But UHR HLA matching still provides many positives

As more clinicians and researchers switch to UHR sequencing platforms, the price and feasibility of the new system continues to improve. Compared to older systems, UHR HLA matching can characterise HLA genes far more accurately and in a timeframe that is suitable for clinical use.

Although there was no overall improvement in patient survival, the reduced risk of transplant related mortality, in certain settings, does provide partial validation of our original findings. This study also provides positive evidence that UHR 12/12 matches can improve patient outcomes by reducing the risk of aGvHD.

So, when there are a number of 10/10 donors, all equivalently matched and of a similar age, UHR typing should be considered to further improve the patient’s quality of life as they recover after their transplant. This could also possibly reduce NHS costs because less patients would need to have their GvHD monitored and treated.

The paper was published in the Journal of Clinical Oncology.

More information about the research Anthony Nolan is undertaking to improve every step of the stem cell transplant journey is available in the Our Research section.