Exploring Exosome-Mediated Stem Cell Engraftment for Hemoglobinopathies

By Barbara Drosey

Intent on pursuing a career in fetal surgery since age 11, Meghana V. Kashyap, MD, a general surgery resident at the University of Nebraska Medical Center, reached out to five prominent fetal surgery centers to determine where her two years of dedicated research, allowed by her training program, would best be spent.

“Every program I interviewed with had done their training under Dr. (Alan) Flake and his colleagues here at Children’s Hospital of Philadelphia,” Dr. Kashyap said. “I thought, why not train at the institution that produced these other surgeon-scientists?”

An ongoing in utero hematopoietic stem cell transplantation project in Alan Flake, MD, FACS, FAAP’s lab intrigued her with its scope — to take advantage of the immune-naïve state of the developing fetus to aid donor cell engraftment prior to hematopoiesis  — as well as the fact that it incorporated a microinjection technique she was familiar with from previous research. 

As a prerequisite to joining the lab last summer for her two-year fellowship, Dr. Kashyap submitted a grant application. Her proposal “Exosome-Mediated Enhancement of In Utero Hematopoietic Stem Cell Transplantation for the Treatment of Hemoglobinopathies” received a Ruth L. Kirschstein National Research Service Award Individual Postdoctoral Fellowship from the National Heart, Lung, and Blood Institute. She is investigating ways to lessen disease severity of hemoglobinopathies using cell-derived exosomes to increase hematopoietic stem cell repopulation in an animal model. 

Children born with hemoglobinopathies such as sickle cell disease, alpha thalassemia, and beta thalassemia face comorbidities and decreased quality of life. In their most severe and symptomatic forms, these inherited blood disorders require treatments such as blood transfusions and bone marrow transplant, leaving patients susceptible to graft versus host disease and side effects from immunosuppressive interventions.

“Our goal is to utilize the knowledge we have from prenatal diagnostics to provide a better quality of life for these children, and sometimes to even provide a live birth,” Dr. Kashyap said, noting that the most severe form of alpha thalassemia is incompatible with life. “Ideally, we would identify the risk factors for these conditions and provide an in utero intervention so these children can enjoy a better quality of life without constant transfusions, bone marrow transplants, and other painful, invasive treatments.” 

Path to Discovery

Previous investigations by Dr. Flake’s lab have utilized a drug that enhances the repopulation capacity of hematopoietic stem cells, which are the dysfunctional bone marrow cells in hemoglobinopathies. Following the delivery of this drug via synthetic nanoparticles, by direct conjugation to the donor hematopoietic stem cells, the injected cells were found to have a higher level of engraftment than untreated cells.

While considering what her contribution would be to advance that work, Dr. Kashyap reviewed studies in which exosomes were used as the drug-delivery vehicle. She hypothesized there might be a beneficial effect to using natural, cell-derived exosomes as the delivery vehicle instead of synthetic nanoparticles.

“In diseases like sickle cell disease and the thalassemias, the host cells are still occupying the bone marrow niche, even with dysfunctional hematopoiesis,” Dr. Kashyap said. “While low level engraftment can be achieved that is adequate for donor specific tolerance induction, levels of engraftment have not consistently been therapeutic; our lab is studying ways to impart a competitive advantage to the donor cells. This would avoid the need for a second, non-myeloablative transplant from the same donor into the tolerant recipient after birth.”

Building on evidence from previous work in Dr. Flake's and other labs demonstrating that mesenchymal stem cells (MSC) support hematopoietic stem cell engraftment, Dr. Kashyap is focusing on whether MSC-derived exosomes will provide an advantage of increased repopulation when cocultured with hematopoietic stem cells. Working with an animal model, she will inject those hematopoietic stem cells. Based on the results of the coculture, she will complete a postinjection comparison to the results of the nanoparticle drug delivery to determine the efficacy of this method to enhance repopulation. 

Aside from her work as a principal investigator, Dr. Kashyap is also contributing to multiple other projects, including a collaboration with the University of Pennsylvania using nanoparticles for mRNA delivery. The common thread through all her research is in utero injection, whether related to gene editing or hematopoietic stem cell transplantation.

Dr. Kashyap will return to Omaha in the summer of 2020, but CHOP won’t be far from her mind. When the time comes to apply and interview for her pediatric surgery fellowship, returning to Philadelphia is part of her plan.

“Not only is CHOP a top hospital with clinical research opportunities, the collaboration with University of Pennsylvania is awesome because as a researcher, any resource you need can be found within these two institutions,” she said.