Hematologists have grappled for many years to understand the basic mechanisms underlying why some young patients with the inherited bleeding disorder hemophilia A develop inhibitory antibodies, also known as factor VIII (FVIII) inhibitors, to protein replacement therapy. The presence of FVIII inhibitors is a serious obstacle that makes it difficult and extremely expensive to treat their hemophilia, leads to complications such as joint disease, and increases mortality.
Such a major challenge requires major brain power. So the National Institutes of Health called on the scientific community to reframe the question: Why is FVIII so immunogenic?
Valder Arruda, MD, PhD, a researcher in the Division of Hematology at Children’s Hospital of Philadelphia and an associate professor of Pediatrics at the Perelman School of Medicine University of Pennsylvania, assembled a team of investigators at different stages of their careers and from a wide range of backgrounds — structural biology, immunology, genomics, and cancer immunotherapy — to put on their thinking hats. They developed a multi-pronged plan to test the problem from diverse perspectives and overlapping angles, and their synergistic approach won a five-year grant award from the National Heart, Lung, and Blood Institute. The funding will support CHOP’s establishment of one of three Centers for the Investigation of Factor VIII Immunogenicity.
“As a physician-scientist and the principal investigator, I was very excited to receive the U54 grant because I think it is important to bring people from completely different backgrounds to provide new insights and give them the freedom to see each other as scientific partners instead of competitors,” Dr. Arruda said. “This is a very fresh environment that the NIH has created. Together, we can finally overcome the serious challenge of the formation of FVIII inhibitors in patients with congenital hemophilia.”
Clinicians in the Hemophilia and Bleeding Disorders program at CHOP provide care for about 100 boys with hemophilia A, which is a lifelong disease. People with hemophilia lack the ability to stop bleeding because of the low levels, or complete absence, of specific proteins in their blood called “factors” that are necessary for clotting. Approximately 85 percent of hemophiliacs have type A disease, which is caused by a lack of the blood clotting factor VIII. In order to maintain clotting factor levels, they may receive factor replacement infusions; however, 20 percent to 30 percent of patients recognize infused FVIII as a foreign protein. They form inhibitory antibodies that prevent the protein replacement therapy from working.
“For many years, we’ve been trying to understand the basis of that, and we are a still quite puzzled,” Dr. Arruda said. “We can classify patients as high risk or low risk for inhibitor formation, but we cannot single out which patient will or will not form the antibody and the severity of inhibitor development. We have been trying to understand how we can overcome this antibody and provide the best clinical care for children who develop this complication, which is important. But it’s always better to find a way to prevent the damage.”
CHOP’s new FVIII Center has four projects under way that have the potential of predicting and preventing FVIII inhibitor development in patients and suggesting novel approaches for therapeutic intervention in hemophilia care.
In project one, Dr. Arruda is teaming up with Michael Milone, MD, PhD, who is a T cell biologist in the cancer immunology field and an associate professor of Pathology and Laboratory Medicine at Penn. Using new high definition technologies, they will identify which specific parts of the FVIII protein are more or less immunogenic. Once they define these regions, they will compare their findings in studies of a naturally occurring mutation of FVIII in dogs. The idea is to look at the disease in two different hosts, human and canine, and determine if they recognize the protein as foreign in the same way. Two junior faculty members, Benjamin Samelson-Jones, MD, PhD, and Vijay G. Bhoj, MD, PhD, from CHOP and Penn, respectively, also will participate in this work.
CHOP hematologist and hematology instructor Bhavya Doshi, MD, is joining the project to help pinpoint which is the main cytokine that is a mediator of the immune response to FVIII. Her work is focusing on a protein needed for B cell survival called B cell activating factor (BAFF), which is a member of the tumor necrosis factor superfamily. Dr. Doshi’spreliminary studies suggest that BAFF could be a new therapeutic target for hemophilia. Scientists already have developed an anti-BAFF monoclonal antibodythat the Food and Drug Administration has approved for the treatment of lupus, an autoimmune disease.
For the second project, Roland Herzog, PhD, a research scientist at Indiana University School of Medicine, will use in vivo visualization techniques to track where the immune response that triggers B and T cell activation against FVIII takes place. If scientists can see in real-time where most of the interaction occurs, then they could begin to identify ways to block the immune signaling.
With a longstanding clinical and research interest in hemophilia, David Lillicrap, MD, research chair in Molecular Hemostasis at Queen’s University in Kingston, Ontario, Canada, will pursue a novel line of investigation in the third project. He aims to reveal critical links between the gut microbiome and the immune response to FVIII, which could suggest that environmental factors may influence the development of inhibitory antibodies to FVIII.
The fourth project takes a biochemical and structural biological approach. Rodney Camire, PhD, CHOP’s endowed chair of Hematology research, and Sriram Krishnaswamy, PhD, a thrombosis researcher also in the Division of Hematology, are collaborating to better understand the molecular characterization and properties of the FVIII protein driving the immune response. A major hypothesis that they will pursue is that the binding interaction between FVIII and von Willebrand factor, a blood clotting protein, has a role as a modulator of inhibitor formation.Lindsey George, MD, a junior faculty member in the Division of Hematology at CHOP, will work with the PIs to explore new and exciting approaches to the immunogenicity of FVIII and compare their findings with the inhibitor formation to a similar, not identical, protein called factor V.
All four projects provide quite a different and broad perspective to reveal new mechanistic insights into the multiple facets of the immune response to FVIII, Dr. Arruda said. The investigators will share their progress and findings with the other two FVIII centers that the NIH designated at Emory University and Temple University so that they can exchange ideas and refine each other’s research questions related to FVIII immunogenicity.
Another innovative aspect of the new Centers is that they will incorporate a skills development core to support the next generation of interdisciplinary scientists interested in building expertise in hemophilia. In Dr. Arruda’s group, several promising early career investigators already have participated in the design of the integrated projects. He is eager to gather new ideas, from within the field of Hematology and beyond.
“We need friends and colleagues from other areas who might help us to train the younger generation with different eyes rather than using the same typical approaches that we already know,” Dr. Arruda said. “Maybe experts in other pediatric diseases are encountering the same type of problem with a replacement protein that is immunogenic. We can talk and think about better ways to deal with it. At CHOP, we have built a culture where the bridge between basic and clinical science is very big.”
Under the direction of the new FVIII Center, investigators’ stepwise approach on this bridge could lead to effective novel strategies to eliminate inhibitor formation in future therapies for hemophilia A.