Synthetic stem cells repair damaged hearts

Researchers in the US and China have developed a durable 'synthetic stem cell' that can repair tissue damaged by a heart attack.

Stem cell therapy carries risks, notably that the cells can divide out of control and form tumours, or that the body's immune system can reject the cells as foreign bodies. They are also complex and costly to produce and store. The scientists hope that their synthetic cells can bypass these risks, while offering comparable benefits to natural stem cells.

'We are hoping that this may be a first step toward a truly off-the-shelf stem cell product that would enable people to receive beneficial stem cell therapies when they're needed, without costly delays,' said Dr Ke Cheng of North Carolina State University, and a lead author of the study.

Stem cell therapies can regenerate organs and tissues by releasing of 'paracrine growth factors' – proteins and other substances which cause healing responses in the surrounding cells.

In the study, published in Nature Communications, the team made microparticles out of a biodegradable polymer and loaded them with growth factors secreted by cardiac stem cells. They then 'cloaked' these particles by coating them with membrane fragments taken from cardiac stem cells. The resulting synthetic stem cells are known as cell-mimicking microparticles (CMMPs).

The scientists added these CMMPs to lab-grown cultures of developing rat heart muscle cells. The CMMPs were able to bind to the developing cells, and increased both the production of heart cells and their ability to contract.

The researchers also injected the CMMPs into the hearts of mice that had undergone a simulated heart attack. Most of the CMMPs were retained in the heart, and after seven days the protective effects of the microparticles could be seen. The hearts pumped more blood, and the muscle cells had improved. Cell death and damage caused by the heart attack were also reduced.

These improvements were similar to those achieved by injecting cardiac stem cells, but did not provoke as much of an immune reaction. Furthermore, the CMMPs cannot replicate like natural stem cells or cause tumours.

'The synthetic cells operate much the same way a deactivated vaccine works,' said Dr Cheng. 'Their membranes allow them to bypass the immune response, bind to cardiac tissue, release the growth factors and generate repair, but they cannot amplify by themselves. So you get the benefits of stem cell therapy without risks.'

The particles are much more durable than stem cells, and can be frozen and thawed without damage. They also avoid the need to find an embryonic or patient source. The researchers hope that the same approach could be used to manufacture other types of stem cell.