By: Noam Sade with Prof. Lior Gepstein
Head of the Laboratory of Cardiac Research, Rappaport Faculty of Medicine, Technion
Senior physician, Clinical Electrophysiology unit, Rambam Medical Center

“Do you want to see them?” Prof. Gepstein finally asked. It was a rhetorical question. He opened the door of the incubator, which contained small round laboratory dishes, selected one and placed it under the microscope. “Here they are, there in the center … our beating cells.”
Through the microscope eyepiece could clearly be seen a collection of tiny grayish cells, beating regularly, contracting and expanding, contracting and expanding, exactly like a tiny cardiac muscle. Even without thinking about the broad scientific context - there was something exciting and unexplained about it.

“The beaters” - that’s what they’re called in Prof. Gepstein’s laboratory, as if they were living creatures. About six years ago (in 2001), they were first exposed in a scientific publication, which brought to the world exciting news about researchers from the Rappaport Faculty of Medicine at the Technion, who succeeded in creating beating cardiac tissue from human embryonic stem cells.
“That was a significant breakthrough,” says Prof. Gepstein, “the first publicized work in the world which was performed in my lab by Dr. Izhak Kehat in collaboration with the laboratory of Prof. Joseph Itzkowitz-Eldor, showing that human cardiac cells, possessing all the features of the natural cardiomyocytes, can be produced in a laboratory.”

Cardiac cells are the only cells in our body which beat spontaneously and constantly. Skeletal muscles, for example, have to receive a nerve impulse in order to contract. However, the regeneration capacity of cardiac cells is very limited - they don’t know how to divide and multiply. Thus, any loss of cardiac cells is in fact irreversible. During myocardial infarction, for example, a certain region of the heart does not receive its blood supply due to a sudden occlusion of a coronary blood vessel. If blood supply to the tissue is not renewed within several hours, the cells in the affected area die, and the muscle turns into scar tissue and no longer contracts. As a result, the functioning of the heart as a pump deteriorates. If the loss of cardiac cells is very significant (more than a quarter of cardiomyocytes), and the heart function deteriorates below a certain level, a “cardiac insufficiency” syndrome develops. This syndrome accounts for more hospitalizations than all cancer cases together. Despite significant improvements in drug therapy and other therapies for treating this syndrome, the number of patients suffering from it, as well as the rates of mortality associated with it, continue to increase. In the most severe cases of cardiac insufficiency, the only solution is heart transplantation. Due to the constant lack of organs for transplant, this is a limited solution.

Prof. Gepstein is familiar with this problem at first hand. He is a cardiologist by profession, specializing in the field of cardiac electrophysiology. “It is unique to the research physician,” Gepstein explains, “that he encounters clinical problems and attempts to resolve them in the research lab, as opposed to a researcher who is only a researcher, or a physician who is only a physician. That’s how the idea of trying to grow cardiac cells in the lab developed: instead of transplanting an entire heart, why not replace only the damaged scar tissue with new cardiac tissue?”
The choice of embryonic stem cells was quite clear: in contrast to mature stem cells, embryonic stem cells are easy to grow in the lab. They can divide and create huge numbers of cells, and they also have the ability to differentiate into any type of body tissue.

In the first stage, embryonic stem cells are grown undifferentiated. Later, they are transferred to a solution, in which differentiation into a variety of tissues begins. At this stage, certain factors are added, with the aim of pushing them towards a specific direction of differentiation, so that part of the resulting cells will be cardiac cells. However, the fact that beating cells were formed was still not sufficient to establish with certainty that these were indeed cardiac cells. “We ran them through a variety of tests,” Prof. Gepstein recalls. “ We saw that they express genes and proteins unique to cardiac cells, and that their structure is unique to cardiac cells. In addition, we found that the cells possess the functional properties of human cardiac cells. It was possible to record their electrical activity, similarly to an ECG. They also responded to various hormones, so that if they’re administered adrenaline, for example, they start beating faster.”

“The next question we asked ourselves was: are these cells connected together and do they act in synchronization, as a single functional tissue? For this purpose, we used a set of electrodes to record the electrical activity of the beating cells, and we saw that, indeed, these were not just single cardiac cells, but that a tissue of cardiac cells had been created, that beat in synchronization.”

Prof. Gepstein’s stem cell laboratory, situated on the 10th floor of the Rappaport building near Rambam, is a little misleading at first glance. One room, not particularly large, with a few shelves loaded with test tubes and jars, and three more small rooms adjacent to it. Somehow, that’s not how one imagines one of the leading centers in the world in the field of tissue engineering, where science fiction is turned into reality. But right here, Israeli scientists succeeded in doing what so many other scientists around the world attempted to do, without success.

The tissue of beating cells was a huge step forward in the development process. It enabled the researchers to begin performing experiments on a complete tissue of cardiac cells, which till now had only been a dream. Now, the discovery could be used, for example, to test the effects of various new drugs on cardiac tissue. This is an application that could save millions of dollars to drug-developing companies just on human cardiac tissue.
However, the primary/initial goal of the development - transplantation of “the beaters” into scar tissue of a human heart to treat cardiac insufficiency - is still a long way away.

Prof. Gepstein: “There are still many problems to be solved: during the process of differentiation, several types of cells are produced, and only a minority of the stem cells turn into cardiac cells. We are trying to develop a system to enhance cardiac differentiation. Later, we will need to develop methods for singling out only the cardiac cells. Another significant problem is quantity. In the future, we will need to develop industrial methods in order to produce billions of such cells, because today, in the lab, we are able to produce only millions of cardiac cells. And, we haven’t yet talked about the problem of immune rejection of the cells, and will the transplanted cells survive in the hostile environment within the scar…? There is still a lot of hard work, and a lot of blood, sweat and tears.
“Now, we are dealing with the question of how we are going to implant the cells into the patient’s heart. There are three options, and we’re working on all of them. The first option is to implant the cells directly into the scar tissue during surgery. The second option is to inject the cells into the scar tissue during catheterization. The third option is based on tissue engineering technology, which we are working on in collaboration with several groups in the Technion and around the world. For example, we are involved in a joint project with Dr. Shulamit Levenberg from the Technion, who succeeded in inducing differentiation of embryonic stem cells into endothelial cells (cells lining the inner surfaces of blood vessels). Just at the beginning of this year, a paper by Dr. Oren Caspi from my lab and Ayelet Lasman, an M.Sc. student from Dr. Levenberg’s lab, was published: They succeeded in combining the resulting human cardiac cells with the endothelial cells to create engineered human cardiac tissue, containing cardiac cells and blood vessels, beating as one unit. The tissue obtained by methods of tissue engineering is already beginning to slightly resemble a more complex structure of an organ.”

- How far are you from creating an organ, a complete beating heart?

Prof. Gepstein: “We are trying to imitate, in a simplistic fashion, what happens naturally and amazingly in every embryo and newborn baby. It is very hard to do this. We have indeed succeeded in creating beating heart tissue, but a whole organ is a complex structure containing a variety of tissues of different types, combined together in a way which cannot yet be reproduced in a laboratory. This process teaches you to be very, very humble talking about what man is capable of doing.”

And, what about the future? “Perhaps you’ll come ten years from now to interview me again, and none of the ideas we mentioned in this interview will have attained clinical application. But this is how research processes begin. And, meanwhile, it looks promising. Only the future will tell where it will all lead.”