Unexplored Territory

Suzanne Ildstad, M.D., compares looking inside the human immune system to an astronomer's quest to understand how physical forces like gravity affect stars, planets and galaxies.

"There are still so many things we don't understand about the human immune system," says Ildstad, who holds the Jewish Hospital Distinguished Chair in Transplantation Research at UofL. "We can't look at individual factors in isolation because there are numerous molecular processes that work in concert to regulate the body's defenses."

While Ildstad and her colleagues at the University of Louisville's Institute for Cellular Therapeutics (ICT) deal with the complexities of the immune system, a simple goal lies at the heart of the research: to make scientific discoveries that will improve patients' lives.

Their efforts recently got a boost through a $1.75 million award from the W.M. Keck Foundation to buy new laboratory equipment that will improve University of Louisville scientists' ability to see and analyze individual cells -- and to better understand cell interaction.

"The ability to see cells 'talk' to each other in real time will profoundly affect our ability to develop new therapies for more than 20 diseases or conditions with an immune component," Ildstad says.

Too many questions

Ildstad didn't start her career with the goal of leading a team of scientists into new frontiers. She grew up in Minnesota, where her mother and grandmother were nurses at the Mayo Clinic, and she graduated from the University of Minnesota. Ildstad then entered medical school at the Mayo Clinic, aiming to become a pediatric transplant surgeon.

"There was a time in my training when I said that research was a waste of time and money," she says. "When you are in clinical practice, however, you see firsthand the obstacles to successful organ transplantation, such as rejection, the side effects of anti-rejection drugs, infections and the shortage of donated organs."

Her observations in clinical training led her to start thinking about how the immune system works.

During her residency at Massachusetts General Hospital, where she was the seventh woman to train in the surgery program, Paul Russell, M.D., former chief of transplant, told her, "You ask too many questions. You should spend some time doing research." She followed the advice of her mentor, securing a medical staff fellowship at the National Institutes of Health (NIH).

There, she worked with noted transplantation biologist David Sachs, M.D., now director of Massachusetts General's Transplantation Biology Research Center.

It was at the NIH that Ildstad and Sachs made a seminal discovery: Mixed chimerism -- essentially the creation of a dual immune system -- induces tolerance to transplanted tissue.

Put simply, they discovered that the human immune system can be tricked into recognizing transplanted tissue as "self" by simultaneously transplanting bone marrow from the tissue donor.

The new bone marrow and the patient's original bone marrow co-exist, meaning that the patient can tolerate the transplanted tissue without rejection or immunosuppression therapy.

Laying the groundwork

Despite her focus on research, Ildstad never lost sight of the patients whose cases made her ask questions to begin with.

Richard Simmons, M.D., who chaired the department of surgery at the University of Pittsburgh where Ildstad was a faculty member, says she has "an amazing imagination linked to an unquenchable curiosity about how to harness biology to practical ends."

Today, Ildstad's early discoveries in the field of immunology and cellular therapeutics are showing enormous progress for practical applications.

In 1994, she received international acclaim for discovering a "facilitating" cell that allows bone marrow to be transplanted from one person to another without rejection.

The premise is that, if physician-scientists can make bone marrow transplants safe and routine, they open doors to curing a wide variety of diseases that are, wholly or in part, the result of a dysfunctional immune system.

Such a step also would mean that organ transplants could be performed without risk of rejection.

Ildstad brought her work and these discoveries to the University of Louisville in 1998 as one of the first faculty members recruited to fill an endowed chair matched by Kentucky's Research Challenge Trust Fund, commonly known as Bucks for Brains.

Since then, the team has made significant progress moving these new discoveries from the lab to the patient.

In current FDA-approved clinical trials using Ildstad's technique, doctors draw blood from the donor and treat it to isolate both bone marrow stem cells and facilitating cells.

When these cells are transplanted to the patient by IV transfusion, a state of "mixed chimerism" -- a twin immune system -- is induced. The immune systems of the donor and patient then co-exist within the patient's body, with the healthy donor's system regulating the patient's malfunctioning immune system.

Ildstad cautions that existing damage to the body cannot be reversed. However, the technique can halt a disease's progression, eliminating the need for expensive medications and hospitalizations.

Diseases potentially cured with this type of bone marrow transplant include type I diabetes, multiple sclerosis, rheumatoid arthritis, lupus, Crohn's disease and colitis, psoriasis and scleroderma, hemoglobinopathis like sickle cell disease and thalassemia, and immunodeficiencies like aplastic anemia.

The technique also opens the door to the use of mismatched donors for treating leukemia -- a key challenge for hematologists facing a shortage of bone marrow donors.

Safe bone marrow transplants also hold great promise for organ and limb transplantation.

In these cases, bone marrow is harvested from the donor at the time of donation, then treated and transfused into the recipient within a few hours of the transplant. The result is a combined immune system that recognizes the transplanted tissue as its own, eliminating the need for anti-rejection drugs.

"About 80 percent of heart transplant patients develop renal problems related to anti-rejection drugs, and there are significant complications for all patients on long-term immunosuppression, including cancers and susceptibility to infection," Ildstad says.

Her goal is to eliminate the need for these medications for all transplant patients.

Technology drives discovery

Ildstad is excited by the possibilities opened up by the $1.75 million award from the Keck Foundation. Her team has purchased several new pieces of equipment that will improve their ability to see and analyze individual cells and to better understand cell interaction in real time.

Two of these pieces of equipment, a FACSAria flow cytometer and a LSRII flow cytometric analyzer, triple the number of cell parameters that ICT scientists can measure at one time and allows them to collect data seven times faster, according to ICT faculty member Esma Yolcu, Ph.D.

Flow cytometry is a technique that analyzes cells and their components by detecting their light-absorbing or fluorescing properties while passing them in a narrow stream through a laser beam. Analysis of the profiles produced through this technique help scientists understand biological activity at a cellular level.

"This new equipment will allow us, for the first time, to obtain large numbers of facilitating cells," Yolcu explains. "We also will be better able to track the facilitating cells in bone marrow and view their interactions with stem cells."

According to Ildstad, this is the only system that allows scientists to take flow cytometry results -- which they had been looking at in isolation -- and actually track how cells behave in whole tissue.

The grant also allowed the ICT to purchase a laser-directed confocal microscope and a bioimager. The microscope offers cutting-edge technology that helps scientists get better contrast on images of cells and reconstruct three-dimensional models. The bioimager allows scientists to explore cells in real time and develop experiments and measurements more quickly, speeding the progress of their research.

"The equipment will sustain our competitive edge in the field of facilitating cell biology and regenerative medicine," Yolcu says.

"Our recent discoveries are timed perfectly with advances in cell imaging and sorting technology to allow us to definitively address critical questions concerning the mechanisms underlying the interaction between facilitating cells and human stem cells."

Allan Kirk, M.D., Ph.D., former chief of the transplantation branch at the NIH's National Institute for Diabetes & Digestive and Kidney Disease, echoes Ildstad's optimism about the impact of these new technologies on the development of new treatments.

"The relatively recent explosion in imaging techniques is allowing investigators to recognize the detail and complexity inherent in the immune system's function," says Kirk, who is now at Emory University in Atlanta. "Techniques like this definitely improve clinicians' ability to tailor therapies for patients, and at the same time humble investigators in recognizing how much more there is to know."

Ildstad believes that discoveries made with the new equipment will allow the ICT to make facilitating cell transplants even more potent and effective. In addition, ongoing studies to allow tissue repair with adult stem cells will move one step closer to clinical reality.

Future directions

Ildstad and her collaborators share a palpable excitement about the future of the institute's work and its potential for patients.

That work includes a newly approved clinical trial for multiple sclerosis patients, says Stephen Kirzinger, M.D., director of UofL's MS program and an assistant professor of neurology.

"We hope this study proves that this treatment is safe and does not have any negative impact on the progression of multiple sclerosis," says Kirzinger, who is working with Ildstad and UofL oncologist Roger Herzig, M.D., on the project.

"In the long term, the hope is that the grafted bone marrow cells will suppress a patient's dysfunctional immune system, replacing it with a normal immune system, halting the disease."

Kirzinger notes that current treatments for MS help modulate the disease but none of them completely stop its progress.

He also believes that Ildstad's approach has the potential to help doctors understand more about the role of the immune system in MS.

As progress accelerates, Ildstad continues to win praise from colleagues at UofL and elsewhere. In announcing the Keck Foundation funding, UofL President James Ramsey, Ph.D., said it offers the potential for "new hope for millions of patients and their families."

Emory University's Kirk concurs.

"Suzanne is a great example of a persistent, dedicated investigator and is a great asset to UofL."