A TWIST in mesenchymal stem cell trials: protein predicts therapy’s potential

Mesenchymal stem cells are adult stem cells with the potential to specialize into a somewhat limited number of cell types – those responsible for making fat, bone and cartilage. But MSCs are also known for their anti-inflammatory properties which are carried out via the release of protein factors.  This ability to dampen the immune system makes the MSC an extremely attractive source material for cell therapies. In fact, there are over 500  mesenchymal stem cell-based clinical trials testing treatments for diseases that target a wide range of tissues including spinal cord injury, diabetes, multiple sclerosis, respiratory disorders and graft versus host disease, just to name a few.

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Human mesenchymal stem cells grown in a single layer on the bottom of a flask; 4x magnification Image source: EuroStemCell

 MSCs and the Variability Problem
While some MSC-based human trials have had promising results in patients, other studies haven’t been as successful. A key culprit of these mixed results is the lack of standardization on what exactly is a MSC. It’s well documented that preparations of MSC vary significantly from one patient to the next. Even the composition of MSCs from one patient is far from a pure population of cells. And few of the cell surface markers used to define MSCs provide a measure of the cells’ function. This is a real problem for demonstrating the effectiveness and the marketability of MSC-based cell therapies which rely on the delivery of cell product with a consistent, well-defined composition and functional activity.

Help is now on the way based on research reported this week in EBioMedicine by a research team led by Professor Donald Phinney at the Florida campus of The Scripps Research Institute. In the study, the team found that the amount of TWIST1, a protein that regulates gene activity, in a given batch of MSCs could reliably predict the therapeutic effectiveness of those cells.

Meet TWIST1: predictor of a MSC therapy’s potential
They set their sights on TWIST1 because previous research described its important role in driving a MSC fate during human development. The team examined the natural variability of TWIST1 levels in human MSCs from several donors. They showed that lower levels of TWIST1 correlated to MSCs with stronger anti-inflammatory properties. Higher levels of TWIST1, on the other hand, were consistent with MSCs that induced angiogenesis, or blood vessel growth, another known ability of this versatile cell type. In another set of experiments, TWIST1 production was silenced using genetic tools. As predicted by the earlier results, these MSCs showed increased anti-inflammatory properties.

Move over Ritcher, Say Hello to the CLIP Scale

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The Clinical Indication Prediction (CLIP) scale. Image: Boregowda et al. EBioMedicine, Volume 4 , 62-73

Putting this data together, the team devised a scale they call Clinical Indication Prediction, or CLIP for short. The scale gives a clinical researcher an indication of the therapeutic potential of a given batch of donor MSCs based on the TWIST1 protein levels. This information could have a major impact on a clinical trial’s fate. Depending on the goal of a MSC-based cell therapy, a clinical team could set themselves up for failure before the trial even gets underway if they don’t take TWIST1 levels into account. First author Siddaraju V. Boregowda explains this scenario in a press release:

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Siddaraju V. Boregowda

“There are a number of clinical trials testing mesenchymal stem cells to treat arthritis. Since angiogenesis is a key part of the disease process, stem cells with high levels of TWIST1 (indicating they are more angiogenic) would not be beneficial. These cells might be helpful instead for indications such as peripheral vascular disease where new vascularization is beneficial. The proposed CLIP scale accurately predicts these indications and contra-indications.”

We’ll be keeping our eye on this exciting discovery to see if CLIP becomes an integral step in developing MSC-based cell therapies. If it pans out, the CLIP scale could help accelerate the development of new therapies by providing scientists with more clarity and confidence around classifying the identity of a MSC cell product. Stay tuned!

Cell survival strategy gives mesenchymal stem cells their “paramedic” properties

Electron micrograph of a human mesenchymal stem cells (Credit: Robert M. Hunt)

Electron micrograph of a human mesenchymal stem cells (Image credit: Robert M. Hunt)

A cell for all therapies
Type “mesenchymal stem cells” into the federal online database of registered clinical trials, and you’ll get a sprawling list of 527 trials testing treatments for diabetes, multiple sclerosis as well as diseases of the kidney, lung, and heart, to name just a few. Mesenchymal stem cells (MSCs) have the capacity to specialize into bone, cartilage, muscle and fat cells but their popularity as a therapeutic agent mostly comes from their ability to reduce inflammation and to help repair tissues.

MSCs may be great tools for scientists to fight disease, but what is it about their natural function that make MSCs – as UC Davis researcher Jan Nolta likes to calls them – the body’s “paramedics”? A fascinating study reported yesterday in Nature Communications by scientists at the Florida campus of The Scripps Research Institute (TSRI) and the University of Pittsburgh suggest that it’s a trait the cells gain as a result of their complex cell survival mechanisms.

The TSRI team came to this conclusion by studying how MSCs respond to oxygen-related stress. MSCs reside in the bone marrow where they help maintain and regulate blood stem cells. The bone marrow is naturally a hypoxic, or low oxygen, environment. Growing MSCs in the lab at oxygen levels found in the air we breathe are much higher than what is found in the marrow. This creates oxidative stress in which the excess oxygen leads to unwanted chemical reactions which disrupt a cell’s molecules.

One cell’s trash is another’s treasure
One result of this oxidative stress is damage to the MSCs’ mitochondria, structures responsible for generating the energy needs of a cell. The team found that MSCs package the faulty mitochondria into sacs, or vesicles, which travel to the cell surface to be dumped out of the cell. At this point, another resident of the bone marrow comes into the picture: the macrophage. Previous research has shown that macrophages and MSCs work closely together to maintain the health of the blood stem cells in the bone marrow.

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White arrow shows vesicles (red) carrying mitochondra (green) to the surface of the MSC  and being ingested by a macrophage (round shape in lower half) – (From Fig 2 Nat Commun. 2015 Oct 7;6:8472)

In a high oxygen stress environment, the team observed that MSCs can recruit macrophages to engulf the damaged mitochondria-containing vesicles and repurpose them for their own use. In fact, the researchers measured improved energy production in the macrophages after ingesting the MSCs’ mitochondria. Blocking the transfer of the damaged mitochondria from MSCs to macrophages caused the MSCs to die, confirming that this off-loading of mitochondria to macrophages is critical for MSC survival.

Evolving tricks for cell survival
Macrophages (macro=big; phages=eaters), key players of the immune system and the inflammation response, also rid the body of invading bacteria or damaged cells by devouring them. To avoid being swallowed up by the macrophage while donating its mitochondria, the stressed MSCs have another trick up their sleeve. The research team identified the release of other vesicles from the MSCs that contain molecules called microRNAs which stimulate anti-inflammatory properties in the macrophages. This prevented the macrophages from attacking and eating the MSCs.

And there you have it: as a result of relying on macrophages to survive stressful environments, MSCs appear to have evolved anti-inflammatory activities that turn out to be a handy tool for numerous ongoing and future cell therapy trials.

In a TSRI press release picked up by Newswise, professor Donald Phinney co-leader of study points out the groundbreaking aspect of the study:

Donald G. Phinney

Donald Phinney (photo: TSRI)

“This is the first time anyone has shown how mesenchymal stem cells provide for their own survival by recruiting and then suppressing normal macrophage activity.”