Mar. 20, 2013 The promise of repairing damaged hearts through regenerative medicine -- infusing stem cells into the heart in the hope that these cells will replace worn out or damaged tissue -- has yet to meet with clinical success. But a highly sensitive visualization technique developed by Stanford University School of Medicine scientists may help speed that promise's realization.

The technique is described in a study published March 20 in Science Translational Medicine. Testing the new imaging method in humans is probably three to five years off.

Human and animal trials in which stem cells were injected into cardiac tissue to treat severe heart attacks or substantial heart failure have largely yielded poor results, said Sam Gambhir, PhD, MD, senior author of the study and professor and chair of radiology. "We're arguing that the failure is at least partly due to faulty initial placement," he said. "You can use ultrasound to visualize the needle through which you deliver stem cells to the heart. But once those cells leave the needle, you've lost track of them."

As a result, key questions go unanswered: Did the cells actually get to the heart wall? If they did, did they stay there, or did they diffuse away from the heart? If they got there and remained there, for how long did they stay alive? Did they replicate and develop into heart tissue?

"All stem cell researchers want to get the cells to the target site, but up until now they've had to shoot blindly," said Gambhir, who is also the Virginia and D.K. Ludwig Professor in Cancer Research and director of the Molecular Imaging Program at Stanford. "With this new technology, they wouldn't have to. For the first time, they would be able to observe in real time exactly where the stem cells they've injected are going and monitor them afterward. If you inject stem cells into a person and don't see improvement, this technique could help you figure out why and tweak your approach to make the therapy better."

Therapeutic stem cells' vague initial positioning is just part of the problem. No "signature" distinguishes these cells from other cells in the patient's body, so once released from the needle tip they can't be tracked afterward. If, in the weeks following stem cells' infusion into the heart, its beating rhythm or pumping prowess has failed to improve -- so far, more often the case than not -- you don't know why. That ambiguity, perpetuated by the absence of decent imaging tools, stifles researchers' ability to optimize their therapeutic approach.

The new technique employs a trick that marks stem cells so they can be tracked by standard ultrasound as they're squeezed out of the needle, allowing their more precise guidance to the spot they're intended to go, and then monitored by magnetic-resonance imaging for weeks afterward.

To make this possible, the Gambhir lab designed and produced a specialized imaging agent in the form of nanoparticles whose diameters clustered in the vicinity of just below one-third of a micron -- less than one-three-thousandth the width of a human hair, or one-thirtieth the diameter of a red blood cell. The acoustical characteristics of the nanoparticles' chief constituent, silica, allowed them to be visualized by ultrasound; they were also doped with the rare-earth element gadolinium, an MRI contrast agent.

The Stanford group showed that mesenchymal stem cells -- a class of cells often used in heart-regeneration research -- were able to ingest and store the nanoparticles without losing any of their ability to survive, replicate and differentiate into living heart cells. The nanoparticles were impregnated with a fluorescent material, so Gambhir's team could determine which mesenchymal stem cells gobbled them up. (Mesenchymal stem cells, which are able to differentiate into beating heart cells, can sometimes be harvested from the very patients about to undergo a procedure. This could, in principle, alleviate concerns about the cells being rejected by a patient's immune system.)

Upon infusing the imaging-agent-loaded stem cells from mice, pigs or humans into the hearts of healthy mice, the scientists could watch the cells via ultrasound after they left the needle tip and, therefore, better direct them to the targeted area of the heart wall. Two weeks later, the team could still get a strong MRI signal from the cells. (Eventually, the continued division of the healthy infused stem cells diluted the signal to below the MRI detection limit.)

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Stem cells entering heart can be tracked with nano-hitchhikers

Mar. 21, 2013 More than 50,000 stem cell transplants are performed each year worldwide. A research team led by Weill Cornell Medical College investigators may have solved a major issue of expanding adult hematopoietic stem cells (HSCs) outside the human body for clinical use in bone marrow transplantation -- a critical step towards producing a large supply of blood stem cells needed to restore a healthy blood system.

In the journal Blood, Weill Cornell researchers and collaborators from Memorial-Sloan Kettering Cancer Center describe how they engineered a protein to amplify adult HSCs once they were extracted from the bone marrow of a donor. The engineered protein maintains the expanded HSCs in a stem-like state -- meaning, they will not differentiate into specialized blood cell types before they are transplanted in the recipient's bone marrow.

Finding a bone marrow donor match is challenging and the number of bone marrow cells from a single harvest procedure are often not sufficient for a transplant. Additional rounds of bone marrow harvest and clinical applications to mobilize blood stem cells are often required.

However, an expansion of healthy HSCs in the lab would mean that fewer stem cells need to be retrieved from donors. It also suggests that adult blood stem cells could be frozen and banked for future expansion and use -- which is not currently possible.

"Our work demonstrates that we can overcome a major technical hurdle in the expansion of adult blood stem cells, making it possible, for the first time, to produce them on an industrial scale," says the study's senior investigator, Dr. Pengbo Zhou, professor of pathology and laboratory medicine at Weill Cornell.

If the technology by Weill Cornell passes future testing hurdles, Dr. Zhou believes bone marrow banks could take a place alongside blood banks.

"The immediate goal is for us to see if we can take fewer blood stem cells from a donor and expand them for transplant. That way more people may be more likely to donate," Dr. Zhou says. "If many people donate, then we can type the cells before we freeze and bank them, so that we will know all the immune characteristics. The hope is that when a patient needs a bone marrow transplant to treat cancer or another disease, we can find the cells that match, expand them and use them."

Eventually, individuals may choose to bank their own marrow for potential future use, Dr. Zhou says. "Not only are a person's own blood stem cells the best therapy for many blood cancers, but they may also be useful for other purposes, such as to slow aging."

A Scrambled Destruction Signal

Bone marrow is the home of HSCs that produce all blood cells, including all types of immune cells. One treatment for patients with blood cancers produced by abnormal blood cells is to remove the unhealthy marrow and transplant healthy blood stem cells from a donor. Patients with some cancers may also need a bone marrow transplant when anticancer treatments damage the blood. Bone marrow transplantation can also be used to treat other disorders, such as immune deficiency disorders.

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New method developed to expand blood stem cells for bone marrow transplant

Public release date: 21-Mar-2013 [ | E-mail | Share ]

Contact: Krista Conger kristac@stanford.edu 650-725-5371 Stanford University Medical Center

STANFORD, Calif. Cells in the body need to be acutely aware of their surroundings. A signal from one direction may cause a cell to react in a very different way than if it had come from another direction. Unfortunately for researchers, such vital directional cues are lost when cells are removed from their natural environment to grow in an artificial broth of nutrients and growth factors.

Now, researchers at the Stanford University School of Medicine and the Howard Hughes Medical Institute have devised a way to mimic in the laboratory the spatially oriented signaling that cells normally experience.

Using the technique, they've found that the location of a "divide now" signal on the membrane of a human embryonic stem cell governs where in that cell the plane of division occurs. It also determines which of two daughter cells remains a stem cell and which will become a progenitor cell to replace or repair damaged tissue.

The research offers an unprecedented, real-time glimpse into the intimate world of a single stem cell as it decides when and how to divide, and what its daughter cells should become. But the implications stretch beyond stem cells.

"In the body, it is likely that every cell grows and differentiates in some kind of orientation," said Roeland Nusse, PhD, professor of developmental biology. "Without this guidance, specialized cells would end up in the wrong place. Now, we can study the division of single mammalian cells in real time and see them dividing and differentiating in an oriented way."

Understanding this process of self-renewal and specialization (or differentiation) is critical to learning how to truly harness the power of stem cells for future therapies. But polarity, or the ability of a cell to distinguish its top from bottom or left from right, is also vital to many other biological processes. For example, hair grows out of, rather than into, the body, and tissues develop with orderly layers of specific cell types.

Nusse is the senior author of the work, which will be published March 23 in Science. He is also a member of the Stanford Cancer Institute, the Stanford Institute for Stem Cell Biology and Regenerative Medicine and HHMI investigator. Shukry Habib, PhD, a research associate and Siebel Scholar, is the lead author of the work. The study was funded in part by a grant from the California Institute of Regenerative Medicine.

Stem cells are unique in their ability to both self-renew and to generate progenitor cells that can become many cell types. A single stem cell can divide to make two new stem cells or, in a process called asymmetric division, give rise to one stem cell and one progenitor cell. Because the original parent cell is replaced by the two new daughter cells, this approach ensures that stem cells will not be depleted during periods of development or healing.

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Stem cells use signal orientation to guide division, Stanford study shows

Mar. 21, 2013 Cells in the body need to be acutely aware of their surroundings. A signal from one direction may cause a cell to react in a very different way than if it had come from another direction. Unfortunately for researchers, such vital directional cues are lost when cells are removed from their natural environment to grow in an artificial broth of nutrients and growth factors.

Now, researchers at the Stanford University School of Medicine and the Howard Hughes Medical Institute have devised a way to mimic in the laboratory the spatially oriented signaling that cells normally experience.

Using the technique, they've found that the location of a "divide now" signal on the membrane of a human embryonic stem cell governs where in that cell the plane of division occurs. It also determines which of two daughter cells remains a stem cell and which will become a progenitor cell to replace or repair damaged tissue.

The research offers an unprecedented, real-time glimpse into the intimate world of a single stem cell as it decides when and how to divide, and what its daughter cells should become. But the implications stretch beyond stem cells.

"In the body, it is likely that every cell grows and differentiates in some kind of orientation," said Roeland Nusse, PhD, professor of developmental biology. "Without this guidance, specialized cells would end up in the wrong place. Now, we can study the division of single mammalian cells in real time and see them dividing and differentiating in an oriented way."

Understanding this process of self-renewal and specialization (or differentiation) is critical to learning how to truly harness the power of stem cells for future therapies. But polarity, or the ability of a cell to distinguish its top from bottom or left from right, is also vital to many other biological processes. For example, hair grows out of, rather than into, the body, and tissues develop with orderly layers of specific cell types.

Nusse is the senior author of the work, published March 23 in Science. He is also a member of the Stanford Cancer Institute, the Stanford Institute for Stem Cell Biology and Regenerative Medicine and HHMI investigator. Shukry Habib, PhD, a research associate and Siebel Scholar, is the lead author of the work. The study was funded in part by a grant from the California Institute of Regenerative Medicine.

Stem cells are unique in their ability to both self-renew and to generate progenitor cells that can become many cell types. A single stem cell can divide to make two new stem cells or, in a process called asymmetric division, give rise to one stem cell and one progenitor cell. Because the original parent cell is replaced by the two new daughter cells, this approach ensures that stem cells will not be depleted during periods of development or healing.

Things change when these cells are grown in the laboratory, however. Researchers usually choose growth conditions that favor specific outcomes: self-renewal or differentiation into specialized cell types. These growth or differentiation signals affect all parts of the cell equally, and it's not been possible under these conditions to ascertain whether and how the location of these signals may affect the outcome.

In the current study, Habib tested the effect on human embryonic stem cells of a protein called Wnt3a, which is known to play a critical role in embryonic development and in the growth and maintenance of stem cells. The stem cells have many receptors for Wnt proteins on their surfaces, and Wnt3a has been shown to promote self-renewal over differentiation in several types of stem cells.

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Stem cells use signal orientation to guide division, study shows