Versiti Blood Research Institute (VBRI) Associate Investigator Phillip Doerfler, PhD, studies the genetics behind hemoglobin switching, with a goal of developing therapies that permanently reactivate fetal hemoglobin. “My work is focused on studying naturally occurring genetic variants that keep fetal hemoglobin on and reverse the hemoglobin switch,” he said. “There are a number of ways to do that. Some of them involve recreating these naturally occurring genetic variants. We know where they are, and we have a pretty good idea of how they work. We can accomplish that with genome editing.”

What is genome editing?

Genome editing involves making intentional, targeted changes to a patient’s DNA. Dr. Doerfler uses the CRISPR-Cas9 system, a laboratory tool that allows scientists to break a strand of DNA, and base editing, a derivative of Cas9 that changes a single DNA base without cutting the entire strand. This allows for precise changes and is less likely to introduce unintended cell mutations or off-target effects.

“For the most part, it’s very specific. One mismatch in different spots and it’s not going to make the cut. But if that mismatch is somewhere there’s a bit more ambiguity, where it’s like, ‘Close enough,’ it will cut,” Dr. Doerfler said. “Having a lot of genetic variability in the population can mean that the genome editing machinery goes somewhere it is not supposed to. More and more research has been dedicated to better understanding how to account for these things, and the way in which people accomplish this is through de-risking.”

De-risking involves identifying off-target sites where Cas9 made cuts and understanding whether or not they could be detrimental. “We try to determine if the cut is happening somewhere safe or not,” Dr. Doerfler said. “If it’s in the middle of nowhere next to nothing in terms of a coding gene or a region we know is important for regulating other genes, then we can say it is de-risked. There will always be some amount of risk, and we will hopefully be able to identify these sites and evaluate them quickly.”

Making the cut

Dr. Doerfler’s research focuses on what happens when Cas9 makes the cut where it is supposed to and what happens when these cells naturally divide. “Every time a cell divides, it needs to copy the genetic material completely without any issues,” he said. “Sometimes, what can happen is pieces of DNA get lost. Errors in cell division can potentially lead to malignancies and can be cancer-driving events.”

Understanding what happens during genome editing can help mitigate this. “We’re using genome editing to see how these cells respond to intentional DNA damage,” Dr. Doerfler said. “We want to understand whether or not we’re doing things that could be potentially dangerous, even though the application is for a therapeutic purpose.”

Despite these challenges, Dr. Doerfler is confident that clinical genome editing is the future of disease treatment. “I am trying to understand what the cell product that we use does in response to DNA damage so that we have a better idea of the safety of genetic therapies,” he said. “I love genetic therapies, and I don’t think they’re going away.”

The future of genetic therapies

Some genetic therapies for treatment of SCD are already approved by the FDA, and approximately 100 patients have benefited so far.

“The key is getting the FDA to approve these therapies more broadly. So far, each time you design a therapy like this, you are starting over. All of the parts remain the same—it just recognizes a different part of the genome,” Dr. Doerfler said. “Patients who received it in the clinical trial are already seeing the benefits; they are less prone to stroke, they have better lung function, they’re not having kidney failure anymore. But they still get pain, albeit at a reduced frequency, they still have pre-existing complications associated with sickle cell disease. There simply is no reason to continue to delay the development of these products when people are dying.”

One barrier to rolling out genetic therapies to the SCD community is its cost. “The availability of gene therapy to most of the people with sickle cell disease is currently an impossibility,” Dr. Doerfler said, citing its hefty $2.3 million price tag. “It’s too expensive, it requires too many specialists, it requires dedicated facilities that can do this kind of thing.”

But he is quick to note that Versiti Blood Research Institute is well positioned to move the needle. “We can do this here,” Dr. Doerfler said. “We are doing genome editing as a therapy for sickle cell disease on campus. Dr. Amanda Brandow, Dr. Josh Field and everyone associated with the Pediatric and Adult Sickle Cell Clinic at Children’s Wisconsin and Froedtert Hospital are doing this. I am working with an outstanding team of scientists and physicians who are dedicated to studying how these therapies are working, if they’re not, and if we’re seeing anything that should be cause for concern.”

“Versiti Blood Research Institute is equipped to do this kind of work,” he added. “We have access to patient samples in Milwaukee that can inform the next phase of this type of therapy, and we are building a program to do some very comprehensive studies on basic, translational and clinical sickle cell research here at VBRI.”

About the expert: Phillip Doerfler, PhD, is an associate investigator at Versiti Blood Research Institute.