In a special edition of our weekly roundup, here are some highlights from just the first two days of the four-day annual meeting of the International Society for Stem Cell Research
Seeing stem cells from both sides now. As the biggest gathering of stem cell researchers each year, the annual meeting of the International Society for Stem Cell Research offers a chance to catch up on progress across the complete spectrum of research, from fundamental exploration in the lab to clinical trials. This year’s meeting in San Francisco offers more advances toward the clinic than ever before, but it also shows a cadre of basic researchers struggling to understand what is really going on at the genetic and molecular level with some of the biggest breakthroughs of the past few years. It is a bit like the opening verse of Joni Mitchell’s song “Both Sides Now” in which she laments that even after seeing clouds as beautiful patterns and as blocks to the sun she does not really know clouds at all.
Nothing captured that spirit better than the opening talk on the second day by Nobel Prize winner Shinya Yamanaka who maintains labs at Kyoto University in Japan and at the Gladstone institutes here in San Francisco, about a mile from the site of the meeting. This year marks the 10th anniversary of his Nobel-winning discovery that you can use genetic factors to reprogram adult cells into embryonic-like stem cells called iPS cells. Even as his institute is supplying the cells for the first ever clinical trial using iPS, in this case in the blinding disease called macular degeneration, he spent much of his talk discussing his ongoing basic research trying to understand what really goes on in that reprogramming process, and why so many cells are refractory to reprogramming with only a few percent in most experiments becoming stem cells.
Before launching into his ongoing basic research—some of it from a research thread he began to unravel as a postdoc at the Gladstone—he told an enlightening tale of how he had been reprogrammed as a scientist. He said that he went from a a basic researcher just working in his lab to someone who spent much of their time talking to government officials, bankers and donors. But he noted that like our cells, part of him was refractory to reprogramming and he still liked getting into the lab to do the basic research needed to understand the creation of iPS cells and make it it faster and more efficient, which is critical to any future role for the cells at the other end of the research pipeline—treating patients in need.
It takes a neighborhood. As usual much of the basic science revolved around the lab recipes needed to keep stem cells in the stem cell state in the lab, or how to efficiently direct them to become a specific type of adult tissue. On the latter there was also considerable work presented on how to get around the fact that too often the adult cells created from stem cells are not fully mature and function more like those tissues would in the fetus than they should in an adult patient.
Fiona Watt of Kings College London presented her work on studying the one “organ” that is easier to study in humans than mice: the skin hair follicle. In the furry critters the hair follicles are too close together to easily isolate individual ones. With our sparser covering it is easy to study single hair follicles, which serve as the niche that houses skin stem cells until they are needed to replenish or repair our outer barrier. In recent years, when trying to understand how stem cells stay stem cells or decide to mature into specific tissue, researchers have increasingly turned their attention to the niches all over the body that stem cells call home. They are finding that there are many facets to these homes—physical, chemical and genetic—that like any neighborhood, impact how a stem cell grows up.
Watt opened by paying tribute to a pioneer in the field who died this past year, Harvard Med School’s Howard Green, who was always a treat to interview when I was there, and who pioneered single cell analysis in skin four decades ago. Watt’s work tries to break down the various components of the skin stem cell niche in the lab to see how each contributes to cell fate. She looked at the extracellular matrix, the scaffold that holds cells in place, and found a link between the size of the hole in the scaffold and cells remaining stem cells. She also found difference between soft and hard scaffolds. She noted other factors such as the type of cell that lives next door and the oxygen level all impact the cell decisions.
She suggested that these determinants of cell fate are likely consistent across stem cell niches throughout the body and will be critical to more efficiently producing replacement tissues to help patients.
Jumping from A to C, skipping B. Two researchers followed Watt who are trying to develop ways to skip the step of turning adult cells in to iPS-type stem cells and instead convert them directly into the desired tissue needed for repair. Stanford’s Marius Wernig, who cited funding from CIRM and the New York Stem Cell Foundation, reported on his work trying to improve his breakthrough from a few years ago in which he converted skin into nerve with just one genetic factor. He is investigating the underlying structures of our DNA to try to understand why only 20 percent of cells make the desired conversion. He is finding some answers but has more to ferret out.
Then Malin Parmar of Sweden’s Lund University went into more detail on the fetal cell and stem cell transplant trials she is working with in Parkinson’s disease that she described at our public symposium earlier in the week. But she closed with work that she thinks could be the ultimate best solution to the disease. Finding genetic factors that can convert other nerve cells directly into the dopamine-producing nerve cells lost in patients with the disease. She started with Wernig’s recipe and added a genetic factor known to drive cells to become dopamine nerves. She succeeded in turning brain cells called glial cells into dopamine nerves inside the brains of mice and showed they made the needed connections to other brain cells. But the work is still some years from getting to patients.
The complexities of the heart. Yesterday afternoon five researchers presented different ways to figure out how to use stem cells to repair or replace a very complex organ, the heart. Shen Ding from Gladstone, who has pioneered the concept of using chemical instead of genetic factors to reprogram cells, presented his latest work in which he used that technique to grow partially mature heart cells in the lab, transplanted them into mice and saw them mature into tissue that improved heart function in a model of heart attack. He said his next experiments will involve finding a way to deliver the chemicals directly into the damaged heart to try to get the reprogramming done in the living animal.
Stephanie Protze, of the McEwen Centre for Regenerative Medicine in Toronto, presented work on another component of the heart, the pace maker cells that ensure any new muscle cell beats at the right speed. She described a recipe to drive stem cells to become pace maker cells, but there was a glitch. They beat at 150 beats per minute, which is the fetal rate not the adult rate. So, once again the field ran into the block of creating only partially mature tissue.
Tamer Mohamed, also of the Gladstone, presented work using chemicals to convert heart scar tissue to functional heart muscle. His work tweaked an earlier recipe that resulted in fewer than one percent of cells converting to a procedure that resulted in 30 percent. In the mouse model he saw improved heart function and reduced scarring.
University of Pittsburgh’s Lei Yang presented work on a very big, long-term goal for the field: producing a complete replacement heart. Like several other teams, his group started with a mouse donor heart and used detergents to wash away the cells so that all that was left was the scaffold of that extracellular matrix mentioned above. He then seeded the scaffold with heart cells derived from iPS cells and let them mature. The work resulted in what he called “beating heart constructs.” Some of the cells beat with needed synchronicity and some did not.
All in all, the meeting exudes measured confidence. The field is clearly making rapid strides toward understanding stem cells well enough to create meaningful therapies. However, it is ripe for what is called “reverse translation,” which is taking the findings of early clinical trials that don’t perform quite as well as desired, and going back to the lab to figure out how to make them better.