Boosting the potential of stem cells in cardialogy: an interview with Dr. Nicolas Noiseux

Figure 1 – Dr. Noiseux

In early March, I had the pleasure to discuss with Dr. Nicolas Noiseux about his work on stem cells at the CR-CHUM and his contribution to “The IMPACT-CABG trial: A multicenter, randomized clinical trial of CD133+ stem cell therapy during coronary artery bypass grafting for ischemic cardiomyopathy” (link below). Published in 2016, this study lays the foundation of a new protocol demonstrating the feasibility and security of an injection of stem cells in the heart during cardiac surgery to promote tissue regeneration after acute myocardial infarction.

Dr. Noiseux’s background is somewhat atypical. After a BSc in biochemistry followed by a MSc in cellular biology, he headed for medical studies where he developed an interest in regenerative medicine and molecular genetics. He went on to specialise in cardiac surgery for six years where he acquainted himself with medical research. He moved to Boston for a postdoctoral position in Harvard Medical School in the late 90s, which coincided with the discovery of stem cells. At Harvard, he developed several animal models to understand the mechanism of stem cells, and how their fusion to cardiac tissues worked. After the postdoc, he moved back to Montreal, where he spends half of his time as a surgeon, the other half in the lab.

 

The first step: developing the model

Dr Noiseux first explains that the main goal was to increase the therapeutic potential of stem cells for tissue regeneration. This process is still not completely defined and those years spent in Boston and Montreal lead to the establishment of a stem cell model that could described it precisely.

Dr Noiseux and colleagues have shown that more than 22 000 genes were directly involved in the tissue regeneration. Specific genes were expressed in cells injected in patients where the treatment was efficient, and these same genes remained quiet when the treatment turned out not to work. They identified an oncogene named Akt which protected cells in an inflammatory environment. Though normally expressed in cancer cells, leading to properties such as a fast cell proliferation and high resistance, the team found that the cells overexpressing Akt were much more effective at repairing the heart by secreting growth factors, angiogenic factor, and anti-apoptotic factors.

Meanwhile, the team highlighted a very interesting point: stem cells do not behave as we could actually think, integrating the tissue to regenerate it. Although stem cells have a rapid and persistent effect once injected, after a short period of time, the stem cells were no longer present. So, what explained the effect’s persistence? The team in Boston thus highlighted the paracrine effect which refers to a variety of secretions from a cell which act on neighboring tissues and cells. They found that regeneration derived more from the secretions than from the presence of cells in the organ.

In order to benefit from the Akt gene properties, the injected stem cell had to be treated. Since modifying the stem cells genetically is challenging to do in the clinic, using the paracrine effect to confer the cells these new properties is intended. The team had the idea to cultivate the stem cells in a specific medium, and remove the cells to keep only what they secreted (bioactive molecules, angiogenic molecules). Those active, pharmacological molecules, which are concentrated and implanted afterwards in the patient, would activate the Akt signaling pathways and would boost the regeneration. This process has been the subject of a number of patents and the creation of a company.  Choosing the best type of stem cells is the following step.

 

Figure 2 – Research method

 

Promising results with CD133+

The chosen stem cells are CD133+ whose markers are expressed only in the early, immature progenitor hematopoietic line. They are multipotent (can differentiate into more than one cell type) and are collected in the bone marrow. This type of stem cell tends to differentiate into epithelial cells, cardiomyocytes and have a great potential for retention in the myocardium.

The special feature of the surgery is that the stem cells are autologous (coming from the patient themselves) and collected in the morning preventing cell death. Thus the transplantation cannot be rejected since the cells are coming from the patient.  The CD133+ are isolated using a system of paramagnetic iron-dextran beads and antibodies, and then purified using flow cytometry.  Stem cells are then treated with boosting agents before injection (Figure 3) as described above.

 

Figure 3 – LVEF (Left ventricular ejection fraction)

 

Cardiac MRI (1.5 Tesla) was performed on the patient after the surgery using gadolinium-based contrast agent. Even though the main challenge of the study was to demonstrate the safety and feasibility of CD133+ stem cells in the patient’s heart, a secondary objective was to assess changes in left-ventricular (LV) end-systolic and end-diastolic volumes and left-ventricular ejection fraction (LVEF) (percentage of blood ejection contained in the left ventricular during a beat). MRI has several advantages: the precision is enhanced since magnetic resonance can be adjusted on the cardiac frequency, information on the composition of the tissue, etc.

It is estimated that a LVEF (Figure 2) between under 30% corresponds to a cardiac insufficiency. LVEF was increased by 6% on average : some patient saw a 40% recovery while some did not see anything. Dr Noiseux pointed out that clinically, this rise is a positive sign and quite hopeful, and the study worth it since the mortality decreases.

 

Figure 4 – Intramyocardial CD133+, CD34+ injection into infarct zone during surgery

 

Stem cell work is challenging because of uncertainties

The main challenge while working with stem cells is the cells themselves. As Dr. Noiseux explains, we do not know how stem cells will behave inside the body, especially since their behavior varies from one patient to another. Moreover, no one can be sure that stem cells will differentiate into cardiomyocytes once in the heart, nor is it known if differentiation is, in fact, needed. What is known is that stem cells tend to concentrate within the inflammatory region, thus attracting migratory cells.

Asked about the influence of the quantity of stem cells on the efficacy of the treatment, Dr. Noiseux says that the question continues to be debated. For humans, the percentage of viable cells in an injection is unknown and hard to estimate. In pharmacology, we often use the EC50 (the measure of the concentration of a drug when delivered at half of the maximum effect). To date, no one has been able to draw the dose-effect relationship, and the number of cells injected is restricted by Health Canada. The quantity of cells is in any case ridiculous compared to the amount of cells in the organ.

The loss of information while going from an animal model toward a human one is huge, admits Dr. Noiseux. Following the cells with fluorochromes is much more difficult in humans because of the toxicity. Studies are thus limited to external observations post-injection.

 

Beyond two generations of studies: next steps

As Dr Noiseux explains, studies involving stem cells developed through several generations. First, inoperable patients received injection of bone marrow, containing various kind of cells, whose a percent corresponded to stem cells. The second generation followed and tried to select more precisely stem cells from the bone marrow: “more characterized and established”. We are now at the third stage: cells are combined with matrix, gels, pharmacological molecules so as to boost the effects on targeted organs. The prospects are larger than we could think finally adds Dr Noiseux, and finding the best “recipe” (amount of cells, pharmaco-optimization of boosting molecules, delivery techniques) guaranteeing the best treatments is more than ever a challenge for the years to come.

 

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Références :

Noiseux N, Mansour S, Weisel R, Stevens LM, Der Sarkissian S, Tsang K, Crean AM, Larose E, Li SH, Wintersperger B, Vu MQ, Prieto I, Li RK, Roy DC, Yau TM. The IMPACT-CABG trial: A multicenter, randomized clinical trial of CD133(+) stem cell therapy during coronary artery bypass grafting for ischemic cardiomyopathy. J Thorac Cardiovasc Surg. 2016 Dec;152(6):1582-1588.e2. doi: 10.1016/j.jtcvs.2016.07.067. Epub 2016 Aug 13.

 

 

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