Hybrid Hearts: Stem Cell Transplants 2.0

“Can we use stem cells to make a new heart/eye/lung/liver etc?”

This is the predictable and perennial question that comes up from at least one student when we are looking at stem cells, genetic engineering, cell differentiation and transplanting. Until now, the answer has (perhaps in an oversimplified way) been ‘no’.

We can use stem cell transplants to treat lymphoma. Recently a young woman had a trachea transplant based on stem cell technology. Skin grafts from a patient’s own cultured cells are also possible, as are stem cell-based bladders. However, these are all rather simple technologies.

To treat lymphoma, bone marrow cells are replaced, and are all the same. The trachea transplant was a pre-existing trachea simply coated in the patient’s stem cells to prevent immune rejection. Skin transplants are basically sheets of epidermis that cover a wound, yet do not have the intricate functions of original skin: temperature regulation, secretion, senses. The bladder is a bag.

The challenge with using stem cells to transplant a more complex organ, such as a heart, is that it is not a simple sheet made of one type of cell. It is complex 3D structure, with a range of cells performing specific tasks within the organ. These cells have differentiated to perform their functions: cardiomyocytes (beating cells), vascular endothelial cells (smooth internal surfaces) and smooth muscle cells (blood vessel walls).

How can we get the stem cells to become the right type of cell, in the right position?

The answer to this question could be the key to opening up new doors in the search for viable transplantable organs in medicine, and bears much in common with the trachea case. It also marks a return to form for the NewScientist YouTube channel, who have this short clip of the new hearts in action:

A full article to accompany the footage is here.

In a nutshell:

Decellularised pig heart: the scaffold (NewScientist)

1. Find a suitable transplant organ, such as a pig’s heart.

2. Strip of all cells and DNA, using a detergent. Only the collagen ‘scaffold’ remains, as in the image of the decellularised heart to the right.

3. Coat the scaffold with the recipient’s stem cells.

4. Ensure that the blood supply is adequate and will provide the right signals for differentiation.

What is amazing in this case is how the cells ‘knew’ what specialised cells to become. The leader of the research group, Dr. Doris Taylor, puts it down to the mechanical stimulus of the pressure of the blood in the vessels and chambers and chemical signals from growth factors and peptides that remained on the stripped heart structure.

They even went as far as replacing a healthy rat’s heart with one of these new hybrid hearts. The rat survived for the trial, but she says they need to focus on producing more muscular hearts in order to ensure long-term survival of transplant recipients.

Food for thought:

Read the whole article and some of the links within it. Discuss these questions:

1. What are the potential uses for this kind of transplant technology?

2. What are the current limitations of this method and how might they be overcome?

3. What are the ethical issues related to using hybrid (pig-human) organs in medical transplants? How would you feel if you were the patient?

4. Who are the various stakeholders in this technology and what are their viewpoints?

Useful Sources:

Dr Doris Taylor’s research page from the University of Minnesota

NewScientist Article: Hybrid hearts could solve transplant problem

BioAlive stem cells links and resources

Can stem cells repair a damaged heart? from the NIH

Research reveals how stem cells build a heart, from Harvard news.