The promise of stem cell therapies is growing ever closer to becoming realized in the medical setting. In a recent study, a team from the Hopkins School of Medicine used imaging technology to watch adult cardiac stem cells as they colonized the injured heart of a rat.
A major stepping stone before stem cell therapies that can be routinely used in human subjects is the ability to observe the progression of the stem cells repairing the tissue of interest.
A physician must know exactly what type of cell they are using on a patient, where this cell is being injected and also what this cell's behavior is upon transplantation.
The members of the Hopkins team, led by multiple researchers from the cardiology and radiology departments, collaborated to image cardiac stem cells growing on the hearts of rats that had undergone a simulated heart attack.
The researchers isolated cardiac stem cells - the adult stem cells that maintain the heart - and then labeled these cells with a novel protein that allows them to image the cell while they are inside the animal. This protein is known as NIS, for sodium (Na)-iodide symporter, and is normally expressed in the thyroid.
Cancer researchers take advantage of its selective uptake of iodine, which allows targeting of cancerous thyroid cells through their radioactive iodine uptake and, consequently, killing of those cancer cells specifically. A symporter is a type of protein that can import multiple small molecules into the cell, in this case sodium and iodine.
The researchers then created cardiac stem cells that express NIS on their surface, allowing these cells to selectively take in iodine from their surroundings. The transgenic expression of NIS was necessary for the CT imaging once the cells were injected.
The promising aspect of this method is that uptake of the specific iodine used in this study is non-toxic to cells, and it can be visualized by cameras which pick up the energy released by the iodine.
This special camera is the same type used in computer tomography (CT) scans. These scans are traditionally used in medicine to diagnose diseases such as cancer or a ruptured aorta. CT scans take two-dimensional pictures and then paste these pictures together to create a three-dimensional image.
They do this non-invasively, which means there is no need for surgery or any other procedure to view the object inside of the body.
The researchers isolated the cardiac stem cells, had the cells express the NIS protein, simulated a heart attack in a rat and then injected the hearts of the rats with these stem cells.
To image the stem cells, the team injected the rats with specifically labeled iodine that is taken in by the cardiac stem cells. Then, using CT scans, they could image where the stem cells were located and where they grew in the heart muscle over time.
However, as this is the first of many studies to come from the researchers, they have not tested whether the cardiac stem cells are actually repairing the heart.
This study was a proof of principle that stem cells could be imaged non-invasively using current medical technologies. The second step will be to show that the stem cells used in this study actually repair the heart muscle, although this has been shown in other studies.
From here, it is important to prove these cells are repairing the heart and also have the ability to be imaged in humans. This is a major step towards creating better and more effective stem cell therapies, with the hope of using them in humans as soon as that is safely possible.
