The Pace of Progress in Heart Regeneration

By Lisa Willemse

ONTARIO

Dr. Michael Laflamme is mixing old and new technologies to piece together the right combination of stem cells needed to repair the damaged heart.

Heart repair has long been a challenge of modern medicine. Comprised primarily of muscle, the heart is somewhat unique among our organs in that its resident population of stem cells are not terribly active once they’ve finished the job of building the organ prior to birth.

As a result, these lazy (the scientific term is quiescent) stem cells don’t jump to action after injury, as is the case in a heart attack. Instead, scar tissue develops from the dead and dying cells, which can place undue strain on other areas of the heart and lead to heart failure and other associated illnesses in the long term.

Over the years, two main approaches to dealing with this problem have emerged: the first seeks ways to encourage the resident population of heart stem cells to wake up and repair the tissue, and the second uses heart stem cells grown in the lab that can then be transplanted into the patient. It’s in this second approach that Dr. Michael Laflamme, principal investigator at the McEwen Centre for Regenerative Medicine, has directed his focus. Dr. Laflamme is leading a Disease Team project, funded by the Ontario Institute for Regenerative Medicine (OIRM) that seeks to convert scar tissue left behind after heart attack into new replacement muscle.

The replacement muscle comes in the form of new cardiac cells, grown from stem cells in the lab and then transplanted into the injured heart. Much like a puzzle, each piece requires a certain amount of specialized work, from the uniform type of heart muscle cells required for transplant, to the ability to efficiently scale these cells up into large numbers, and to the use of a new electrical mapping technology to determine what effect the transplanted cells have on the natural rhythm of the recipient heart.

To find this level of expertise and infrastructure, Dr. Laflamme, had to pick up his lab and move from America’s west coast to Toronto. He is unequivocal about the wisdom of his move.

“Many of the missing pieces for our work in Seattle were already in place here,” said Dr. Laflamme, who is also a member of the Toronto General Research Institute’s Cardiac Pathology team in the University Health Network. “Toronto has world class experts in stem cell biology; people that are working in the same area and are kindred spirits. I’m an applied sort of guy. I want to see these cells put to use fixing injured hearts, and I think we can do it better here than any other place in the world.”

In Toronto, Dr. Laflamme has already built on his earlier research conducted at the University of Washington, that, while successful in growing and grafting new heart tissue, showed less than optimal results. The research animals tended to develop arrhythmias (irregular heart rhythm), which Dr. Laflamme speculated was a result of the transplant having contained a mix of different types of heart cells, including pacemaker cells, which began working on their own rhythm rather than that of the host’s heart.

“This is where the imaging capabilities will be very helpful. We can record the electrocardiogram to see if the animal experiences arrhythmias, but we can even go further and we can actually map the electrical activity. ” — Dr. Michael Laflamme

After a heart attack, scar tissue can severely limit heart function and lead to heart failure and other associated illnesses. In Toronto, a team led by Dr. Michael Laflamme is testing how cultivated stem cells, injected into the damaged heart, can form new, healthy tissue.

STAGE 1 DAMAGED HEART

VERSION 1 STAGE 2

VERSION 2

A mixture of pacemaker, ventricular and atrial cells.

bioreactor

A purified selection of ventricular cells.

Two different populations of heart cells, each grown from stem cells, are cultured in bioreactors.

The two different cell populations are transplanted into damaged hearts. Each transplant will grow new tissue and the two are compared.

Imaging technologies measure heart function to assess the success of the transplants and to determine which cell population is better.

The better of the two cell populations will be refined and tested, in preparation for clinical trials in humans.

STAGE 3

STAGE 4

STAGE 5

This research project is funded in part through a Disease Team grant from the Ontario Institute for Regenerative Medicine. www.oirm.ca

ONTARIO

Enter Dr. Gordon Keller, director of the McEwen Centre and an expert in the growth and applications of embryonic stem cells. Like Dr. Laflamme, Dr. Keller had long been interested in optimizing cardiac and vascular cells from embryonic stem cells for cardiovascular repair. “The key piece of technology that Keller’s group had,” explained Dr. Laflamme, “was a more precise way to grow the particular cell type that we need for replacing the heart muscle cells lost during a heart attack. We were already able to make human embryonic stem cells into heart muscle cells—cardiomyocytes—but his group had figured out how to take them one step further into ventricular cardiomyocytes.” Thus Keller could provide access to a population of pure cells, better suited to the purpose at hand.

Since the goal is ultimately to test the heart cells as part of a human clinical trial (the current OIRM Disease Team project will work with a pig model in preparation for this), Dr. Laflamme’s next challenge was finding a way to grow the large numbers of cells needed and ensure they were at a standard high enough for clinical use. Once again, Toronto had the answer, in the form of the bioreactors housed in the Centre for Commercialization of Regenerative Medicine’s (CCRM) facilities, conveniently located a short walk down the street.

“In Seattle, we were able to grow up the requisite number of cells [about 1 billion cardiomyocytes for each transplant] for large animal studies, but we were doing it by brute force, growing many dozens of flasks of cells,” recalled Dr. Laflamme. “But of course that’s not scalable, it’s not economic and it’s hard to imagine how you’d be able to convert that process into something that is clinical grade. CCRM can do this in a single bioreactor, so they’re obviously one of the key players on our disease team.”

The final piece of the puzzle is the expertise that Dr. Laflamme himself brings—a keen understanding of the electrical properties of the engrafted heart that, up until now, had been missing from Toronto.

Since the problem in earlier studies had been the development of arrhythmias in the recipient animals—a problem that is electrical at its core and that could potentially be remedied with the more appropriate cells produced in uniform batches, the last remaining question will be to determine if it works.

To answer this question, Dr. Laflamme found it necessary to back up all the way to his early career, when he was studying the electrical properties of cardiomyocytes at the single cell level. “I certainly wasn’t expecting to revisit these techniques,” he said. “But, in 2002, when I began working with cardiomyocytes grown from human embryonic stem cells, we didn’t really understand their electrical properties. So I dusted off those old techniques and applied them to these new cells. I kind of came full circle.”

In Toronto, Dr. Laflamme will be applying these dusted-off skills as well as a new imaging technique that will allow his team to visualize the electrical activity in both the newly-formed heart muscle and the recipient heart. By combining this approach with EKG (electrocardiogram) recordings and catheter-based electrical measurements used in clinical practice, they will be able to better understand the electrical behavior of the engrafted hearts. He’ll be testing both the cocktail of imprecise cardiac cells used in the earlier studies and the more refined ventricular cardiomyocytes grown in the large-batch bioreactor, and looking for new heart muscle that’s firing and contracting in synchrony with the host muscle.