Progenitor Cell Transplantation and Function following Myocardial Infarction

William O’Neill: I have a couple of questions for both of you. First, we are essentially talking about adult, autologous stem cells. As you all know, there is enormous controversy in the U.S. about the use of embryonic stem cells which we are currently prohibited from using. From a dispassionate, basic scientific approach, do you think there’s an advantage to using embryonic stem cells, or will adult stem cells be sufficient in terms of their ability to replicate and cause myogenesis? Peter Gonschior: After examining the data from experiences in other fields with vascular cells and their biological functions, I don’t think there is a need for embryonic stem cells. The bone marrow cells appear to be very robust; even the non-randomized European trial data show that with a not-so-profound approach, it is possible to obtain positive effects. Due to the political scenery in Europe, I don’t think it would be possible to conduct large clinical trials using embryonic stem cells. Sigrid Nikol: I think we should first try to optimize the strategies using autologous cells due to the ethical concerns. Due to these restrictions, there is not currently much proof available that embryonic stem cell therapy is that much better or even less risky. We know that these cells can differentiate, which means that they could differentiate into undesired cells as well. Thus, given the legal restrictions at present, we should stick with what we can do and try to make the best of it. William O’Neill: Another key issue that arises from a clinical standpoint is that of direct injection versus intra-arterial or intravenous infusion. Do we know yet which would be the most efficient way — if the appropriate cell were to be found — to deliver the cells for the most efficient myogenesis? Peter Gonschior: Sigrid and I have a lot of experience with local drug delivery. Efficiency of local drug delivery is in fact very low. It would be very smart to just inject the cells intravenously. But one critical issue with all of these data is that delivery efficiency, whether systemic or local, is very low. In fact, it turned out that endocardial delivery of these cells was the most efficient, resulting in the largest number of injected cells — up to about 30 million. William O’Neill: The problem I have is that the stem cells are very sensitive to hypoxia; they need an oxygenated environment in order to thrive. Thus, if these cells are injected into a core infarct area, it will likely be hypoperfused and the ambient oxygen tension in that area may not be sufficient to support those cells. Sigrid, your experience involved a permanent ligation, right? Sigrid Nikol: Actually, there were two sets of animals, but I only showed you those with the permanent ligation because there are currently more data on them. We also have a reperfusion model from 30 minutes after opening up the vessel. William O’Neill: Did you find in the reperfusion model that there was any more myogenesis efficiency? Sigrid Nikol: We perform stem cell therapy via bone marrow stimulation (not cell injection). At the moment, we do not have sufficient data on the reperfusion model. The problem is that when genes or cells are injected into the vessels, why should they pass the endothelium and migrate into the tissue where they are needed? It is very unlikely to happen, unless there is injured tissue. And with the venous application, there are the first-pass effects in the lungs and liver on top of it. These findings are not very convincing in my opinion, including the data from the Strauer group which lacked a truly randomized control group. The problem with intramyocardial injections into infarcted areas is a real one, as you stated, in that there is no blood/oxygen supply and potentially arrhythmogenic foci are created. Also, there may not be a homogeneous distribution of cells — an issue that has already been discussed with regard to gene therapy for the myocardium. Specifically, the question had been raised regarding how homogeneous gene therapy in the myocardium can be achieved without creating arrhythmias. With stem cells, this may be an even more important issue, as has been demonstrated in the work by Menasche et al. William O’Neill: It seems to me that a highway is needed to get the cells to the tissue, and that’s why we have been considering autoinfusion or direct intracoronary infusion of the agents, because in the reperfusion model, at least if there’s an intact vascular structure, then the environment will be ambient and oxygenated until the cells can engraft. But my question is: Why would those cells stay at that target site? Also, we are lacking basic scientific understanding of the signals that allow the stem cells to hone in on that particular tissue. Since stem cells could potentially be coming in from the systemic circulation, we need to come up with a honing material that could be injected into the infarcted area and would allow the stem cells to accumulate there. We are moving forward in this field. At the 2003 AHA meeting, data from the late-breaking BOOST trial were presented. It was, I think, a very well-conducted randomized trial involving 60 patients with placebo versus bone marrow infusion arms. The results showed a statistically significant increase in ejection fractions in the active treatment group compared with the placebo group. TOPCARE was a terrific study, but it was a sort of historical control study. Thus, we are beginning to accumulate data that suggest there is some merit to this approach. Let me turn this question over now to the other panelists. Matt Pollman, from Guidant Corporation, is on the panel. Matt, is there business potential in this field? Matt Pollman: That’s a great question, Bill. As a clinician and a scientist, this area is extremely provocative and intriguing, particularly the data from the BOOST and TOPCARE myocardial infarction trials. There is an aggressive movement to push these trials out into more randomized, controlled, multi-center arenas. The issue for a company such as Guidant is what we can bring to the table and whether there is business potential in this area. Confidentiality, of course, prevents me from saying too much here, but there certainly appear to be business opportunities for companies like ours. We believe that it will require a very safe delivery system that can be applied to a wide range of patients. The cells clearly need to be delivered at least very close to the target site in order to successfully do their job. In that light, an intracoronary infusion strategy raises questions about how to allow enough time for the cells to adhere, to transmigrate, enter the tissue and do their job. There is room for improvement in the delivery systems, and that’s what Guidant is looking into. The TOPCARE acute myocardial infarction study headed up by Andreas Zeiher in Frankfurt uses a simple syringe injection system loaded with 10 cc of bone marrow, 3 cc of which is applied to the coronary arteries. The patients are then allowed to be in an unreperfused state for 3 minutes to allow the cells to do their job. Often, the limiting factor is that the patients complain of chest pain during the unreperfused state. Thus, there are opportunities to improve the current infusion protocol. William O’Neill: We have been looking at it in a two-prong fashion, with a lot of interest in basic science on one end, and in clinical trials on the other end. As for the United States, if bone marrow is taken from a patient and then reinjected, the FDA considers it non-homologous use, even though it is not a drug or a commercial compound. The U.S. FDA regulations on stem cell use do not cover autologous use of these cells. Unfortunately, thus, this entire field has become embroiled in the embryonic stem cell and abortion debates. As a result, the FDA is incredibly cautious about allowing embryonic stem cell use. The FDA regulations state that if the stem cells are taken and not manipulated, and then reinjected, it falls outside of the FDA’s authority. At the 2003 TCT meeting, the FDA representative specifically stated that if any compound is taken from the body and reinjected (i.e., spinal fluid) into an area where it doesn’t normally need to be, then the FDA does have regulatory authority. Also, the FDA insists on receiving a significant amount of data — and rightfully so — on basic safety issues such as clotability and other matters surrounding the infusion of these cells into the coronary arteries. I think it will be another year or two in the U.S. before the basic science data are available to allow clinical trials to proceed. The bulk of the basic scientific studies will be carried out in South America and Europe. Having said that, we have a perfect opportunity right here to learn from our colleagues about where this field is headed internationally. I know that you, Alfredo, are very much in the midst of all of this research. Would you mind telling us what your group will be doing in terms of your randomized trial? Alfredo Rodriguez: Thank you, Bill. We are just starting a randomized trial that will follow the rules of the TOPCARE MI trial. Our trial involves 40 patients, 20 in each arm. One patient arm receives autologous bone marrow injections. These are acute myocardial infarction patients from 3 to 12 hours after symptom onset; all patients receive percutaneous coronary intervention and stenting. After reperfusion, we randomize the patients on day-4. On day-5, we puncture the patient’s iliac crest, and the next day, we infuse the drug in 10 ml of solution into the coronary arteries. The patient undergoes angiography immediately following the PCA procedure. Gobal and regional ejection fractions are measured. An acute and 4-month dobutamine stress echocardiogram is then done, followed by an MRI and SPECT imaging. Our institution has a very active bone marrow transplant team. The hematologists who serve on our trial’s executive committee told us that it was not necessary to place this trial under the Argentinian equivalent of the FDA, because autologous bone marrow is not a drug; it’s not foreign material to the body. Thus, our trial is approved by the local transplant agency. My concern involves legal problems that could arise. I would like to hear from Sigrid and the other European colleagues here if the ongoing clinical trials in Europe in this field are approved by their respective regulatory agencies, or if they are only approved as protocols by the local hospitals’ scientific committees, with the patients of course providing informed, written consent. Sigrid Nikol: According to the blood transfusion and federal drug laws, there are certain regulatory approvals needed, particularly if the doctor obtaining the cells is not the same doctor using them therapeutically. In this case, cells are considered a blood product and their use is regulated. Alfredo Rodriguez: I do know that the TOPCARE trial did not have local German regulatory approval. Richard Heuser: I assume that we’re talking here about a normal 10 cc bone marrow aspirant — no filtering — just administering it down the coronary arteries. Is that correct? And then the balloon is inflated for 3 minutes or so to allow the cells to disperse? And several injections are given? Alfredo Rodriguez: Yes, 3 or 4 injections are given. William O’Neill: This approach has generated controversy due to the fact that the bone marrow is unfiltered and thus contains fat, spicules, mesenchymal cells, and so on. Basically, the injection contains the “kitchen sink” and we hope that the right cells go to the right place and do the right thing. The other argument is that we know which cells we want, so we should just take them, filter them, grow them in media and replicate them, increase their efficiency, and then inject them. Those are the two schools of thought on the subject, but I can’t tell you which is the correct one, because we might not have the right cells. It may be that the CD34 positive cells are not the right ones. In the TOPCARE study, they actually took both the peripheral cells and the cells obtained through leukophoresis, then identified them, segregated them, and grew them in a culture medium to increase their numbers. In terms of FDA regulations, whenever you manipulate and produce cells, a commercial product results, and thus clearly falls under the FDA’s purview. A regulatory “gray” area still exists in the U.S. when it comes to simply taking cells, leukophoresing them, removing the stem cells, and reinfusing them. Richard Heuser: The first time I saw this technique presented by the group in Frankfurt, I was astonished at how simple it actually was. I am surprised that I didn’t get into regulatory trouble myself about 5 or 6 years ago when I treated a patient in the middle of the night who tore a coronary artery. At that time, I had our home-made covered stents and some JoMed stents, but the vessel was 2.3 mm, and the patient was in cardiogenic shock. I had administered ReoPro and t-PA to this 70-year-old female patient. I just took some clot, combined it with a little of the protamine, and it got to be enough of a slurry. I then put it down with a balloon, occluded the vessel, then re-opened it — and it was sealed. I then stented the vessel, and it was fine. But I find it hard to believe that if we administer these bone marrow cells to a patient with a huge infarct that we could get into trouble with the FDA. Some of these therapies make good sense for the individual patient, but more study data are needed. William O’Neill: Let me pose a question to Paul Overlie, who has had extensive experience treating acute myocardial infarction patients for the past 20 years. Is there a need for this, Paul? The CADILLAC and recent myocardial infarction studies showed a 2% mortality rate and an ejection fraction mean of about 50%. How often does the situation arise that would warrant going to the trouble of doing bone marrow aspirates and leukophoresis on these patients? Paul Overlie: The very high-risk, no-reflow patients might benefit from these therapies. Once these bone marrow cells are aspirated, is there some way to get the cytokines activated before injecting them, or concentrating them, so that the U.S. FDA would approve of the technique? William O’Neill: Now that more studies have been conducted since the last time — about a year-and-a-half ago —that the FDA was approached about this, it’s likely that the FDA will show more interest in allowing U.S. clinical trials to go forward. Phil, do you think there’s an application for the genetic or stem cell repair approaches in the general vasculature — the aorta or peripheral vasculature? Philip Walker: I am a peripheral vascular surgeon, so I am definitely interested in myocardial repair to get our patients fit for intervention or following infarcts after intervention. There are a number of emerging areas where the approach might be helpful. Peter mentioned the single-center study on stem cell use for peripheral revascularization which involves an area where patients are nonreconstructible, particularly diabetics with renal failure. I also wonder whether the no-reflow phenomenon — perhaps even in the setting of acute limb ischemia — might benefit from stem cell therapy. Stem cells may also be useful as an adjunct to tissue engineering. I work with a group who are developing a biological graft based on a peritoneal growth, which may be another useful area for the adjunctive use of stem cells. This therapy is being developed with the aim of improving the antithrombotic effects, which might also apply to prosthetic grafts that have been plagued by thrombotic problems when small diameters are involved. Aortic repair in patients who have not yet developed sizable aneurysmal disease may be yet another area for stem cell therapy, but we need to learn how to identify these patients. We also need to learn to identify patients with small aneurysms, as stem cell repair might be useful in repairing and inhibiting the process in these patients. Another viable area may be in the area of stroke and revascularization, as well as brain repair. This raises the issue of whether the mechanisms will be generic across all of those vascular beds, or whether differences exist, and whether the basic science needs to be worked out for the different areas. I would like to ask about the issue of toxicity, particularly in diabetic patients in whom there may be an acceleration of diabetic retinopathy, tumorigenesis in the elderly patients, as well as plaque instability. Are these issues relevant? William O’Neill: Perhaps because these bone marrow cells are pluripotential and have stimuli for differentiation, they will probably not be carcinogenic. And since they serve repair processes, it is unlikely that they will cause pathologic proliferation. Those are all critical questions that have plagued the field of gene therapy in which vectors were found that caused some cells to proliferate wildly. I think these cells will be safer, but we really won’t know until a large number of patients are treated. From our own acute myocardial infarction work, I presented a slide on the number of patients who present within 2 hours of symptom onset, and that number is about 5% of the U.S. acute myocardial infarction population — at least with the current standards. Perhaps with more novel, patient-directed approaches, this percentage could rise. After 2 hours, whether the patient is reperfused or not, there will be a substantial amount of necrotic tissue and a large permanent infarct zone. If stem cell therapy could be safely applied, I believe that many patients could benefit in terms of improved regional function, making an akinetic anterior wall hypokinetic, or improving or preventing aneurysm formation. Brian O’Murchu: Has the coronary sinus retrograde perfusion route been used for administration of these cells? William O’Neill: Not that I am aware. There is one company that makes a device for access to the coronary sinus, and then needle injection into the myocardium. I think there may be some interest in using that as an access site rather than performing ventricular puncture. Brian O’Murchu: I was just talking with my colleague, Alex Zapolanski, about whether the solution emerges from the ostia of the arterial coronaries during retrograde coronary perfusion, and of course it does. Thus, it would seem to provide the opportunity to “bathe” the myocardium through the use of a system that can be balloon-occluded, allowing perfusion to be maintained. William O’Neill: That has been discussed, but I am not aware of any ongoing trials on that topic.