Stories about: Regenerative medicine

Intestine chip models gut function, in disease and in health

villus-like projections growing in gut chip
Villus-like extensions formed by small intestinal cells from patient biopsies, protruding into the Intestine Chip’s luminal channel. (Credit: Wyss Institute at Harvard University)

The small intestine is much more than a digestive organ. It’s a major home to our microbiome, it’s a key site where mucosal immunity develops and it provides a protective barrier against a variety of infections. Animal models don’t do justice to the human intestine in all its complexity.

Attempts to better model human intestinal function began with intestinal “organoids,” created from intestinal stem cells. The cells, from human biopsy samples, form hollowed balls or “mini-intestines” bearing all the cell types of the intestinal lining, or epithelium. Recently, intestinal organoids helped reveal how Clostridium difficile causes such devastating gastrointestinal infections.

But while organoids have all the right cells, they don’t fully replicate the environment of a real small intestine. Real intestines are awash in bacteria and nutrients, are fed by blood vessels and are stretched and compressed by peristalsis, the intestines’ cyclical muscular contractions that push nutrients forward.

Efforts to recreate that environment led to the Intestine Chip. An early version, created by the Wyss Institute for Biologically Inspired Engineering, cultured cells from a human intestinal tumor cell line.

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More surprises about blood development — and a possible lead for making lymphocytes

blood development chart
Blood development in the embryo begins with cells that make myeloid and erythroid cells – but not lymphoid cells. Why? A partial answer is in today’s Nature.

Hematopoietic stem cells (HSCs) have long been regarded as the granddaddy of all blood cells. After we’re born, these multipotent cells give rise to all our cell lineages: lymphoid, myeloid and erythroid cells. Hematologists have long focused on capturing HSCs’ emergence in the embryo, hoping to recreate the process in the lab to provide a source of therapeutic blood cells.

But in the embryo, oddly enough, blood development unfolds differently. The first blood cells to show up are already partly differentiated. These so-called “committed progenitors” give rise only to erythroid and myeloid cells — not lymphoid cells like the immune system’s B and T lymphocytes.

Researchers in the lab of George Q. Daley, MD, PhD, part of Boston Children’s Hospital’s Stem Cell Research program, wanted to know why. Does nature deliberately suppress blood cell multipotency in early embryonic development? And could this offer clues about how to reinstate multipotency and more readily generate different blood cell types?

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‘Pull’ from an implanted robot could help grow stunted organs

Surgeons at Boston Children’s Hospital have long sought a better solution for long-gap esophageal atresia, a rare birth defect in which part of the esophagus is missing. The current state-of-the art operation, called the Foker process, uses sutures anchored to children’s backs to gradually pull the unjoined ends of esophagus until they’re long enough to be stitched together. To keep the esophagus from tearing, children must be paralyzed in a medically induced coma, on mechanical ventilation, for one to four weeks. The lengthy ICU care means high costs, and the long period of immobilization can cause complications like bone fractures and blood clots.

Now, a Boston Children’s Hospital team has created an implantable robot that could lengthen the esophagus — and potentially other tubular organs like the intestine — while the child remains awake and mobile. As described today in Science Roboticsthe device is attached only to the tissue being lengthened, so wouldn’t impede a child’s movement.

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News Note: Cell ‘barcodes’ trace the natural development of blood

in situ blood development
(Credit: Stem Cell Program, Boston Children’s Hospital)

Genetic labels, or “barcodes,” are shedding new light on the natural process of blood development and immune-cell production, finds a study published in Nature this week. It was led by Fernando Camargo, PhD, and first author Alejo Rodriguez Fraticelli, PhD, at Boston Children’s Hospital’s Stem Cell Research Program, the Harvard Department of Stem Cell and Regenerative Biology and the Harvard Stem Cell Institute.

Most of what we know about blood production is through observing what happens when blood stem and progenitor cells are transplanted into an animal. To observe what happens “in the wild,” researchers went in and tagged the blood stem and progenitor cells of mice, using genetic elements called transposons. This allowed them to track how the cells differentiated into five kinds of blood cells (above: megakaryocytes, erythroid cells, granulocytes, monocytes and B-cell progenitors).

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Delivered through amniotic fluid, stem cells could treat a range of birth defects

Transamniotic stem cell therapy, or TRASCET, is like amniocentesis is reverse.
Amniotic fluid is routinely withdrawn for prenatal testing. It could also be a delivery route for fetal cell therapy to treat congenital anomalies, with broader applications than once thought.

The amniotic fluid surrounding babies in the womb contains fetal mesenchymal stem cells (MSCs) that can differentiate into many cell types and tissues. More than a decade ago, Dario Fauza, MD, PhD, a surgeon and researcher at Boston Children’s Hospital, proposed using these cells therapeutically. His lab has been exploring these cells’ healing properties ever since.

Replicated in great quantity in the lab and then reinfused into the amniotic fluid in animal models — a reverse amniocentesis if you will — MSCs derived from amniotic fluid have been shown to repair or mitigate congenital defects before birth. In spina bifida, they have induced skin to grow over the exposed spinal cord; in gastroschisis, they have reduced damage to the exposed bowel. Fauza calls this approach Trans-Amniotic Stem Cell Therapy, or TRASCET.

New research findings, reported this month in the Journal of Pediatric Surgery, could expand TRASCET’s therapeutic potential.

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3D organoids and RNA sequencing reveal the crosstalk driving lung cell formation

lung disease
A healthy lung must maintain two key cell populations: airway cells (left), and alveolar epithelial cells (right). (Joo-Hyeon Lee)

To stay healthy, our lungs have to maintain two key populations of cells: the alveolar epithelial cells, which make up the little sacs where gas exchange takes place, and bronchiolar epithelial cells (also known as airway cells) that are lined with smooth muscle.

“We asked, how does a stem cell know whether it wants to make an airway or an alveolar cell?” says Carla Kim, PhD, of the Stem Cell Research Program at Boston Children’s Hospital.

Figuring this out could help in developing new treatments for such lung disorders as asthma and emphysema, manipulating the natural system for treatment purposes.

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Novel therapeutic cocktail could restore fine motor skills after spinal cord injury and stroke

CST axons sprout from intact to injured side
Therapeutic mixture induces sprouting of axons from healthy (L) into the injured (R) side of the spinal cord.

Neuron cells have long finger-like structures, called axons, that extend outward to conduct impulses and transmit information to other neurons and muscle fibers. After spinal cord injury or stroke, axons originating in the brain’s cortex and along the spinal cord become damaged, disrupting motor skills. Now, reported today in Neuron, a team of scientists at Boston Children’s Hospital has developed a method to promote axon regrowth after injury.

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Optic nerve regeneration: One approach doesn’t fit all

alpha retinal ganglion cells optic nerve regeneration
Alpha-type retinal ganglion cells (RGCs) in part of an intact mouse retina. The cell axons lead to the optic nerve head (top right) and then exit into the optic nerve. The alpha RGCs are killed by the transcription factor SOX11 despite its pro-regenerative effect on other types of RGCs. (Fengfeng Bei)

Getting a damaged optic nerve to regenerate is vital to restoring vision in people blinded through nerve trauma or disease. A variety of growth-promoting factors have been shown to help the optic nerve’s retinal ganglion cells regenerate their axons, but we are still far from restoring vision. A new study published yesterday in Neuron underscores the complexity of the problem.

A research team led by Fengfeng Bei, PhD, of Brigham and Women’s Hospital, Zhigang He, PhD, and Michael Norsworthy, PhD, of Boston Children’s Hospital, and Giovanni Coppola, MD, of UCLA conducted a screen for transcription factors that regulate the early differentiation of RGCs, when axon growth is initiated. While one factor, SOX11, appeared to be critical in helping certain kinds of RGCs regenerate their axons, it simultaneously killed another type — alpha-RGCS (above)— when tested in a mouse model.

At least 30 types of retinal ganglion cell message the brain via the optic nerve. “The goal will be to regenerate as many subtypes of neurons as possible,” says Bei. “Our results here suggest that different subtypes of neurons may respond differently to the same factors.”

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Helping tissue grafts build a blood supply: Less is more

blood vessels in vivo

For a tissue graft to survive in the body — whether it’s a surgical graft or bioengineered tissue — it needs to be nourished by blood vessels, and these vessels must connect with the recipient’s circulation. While scientists know how to generate blood vessels for engineered tissue, efforts to get them to connect with the recipient’s vessels have mostly failed.

“Surgeons will tell you that when putting tissue in a new location in the body, the small blood vessels don’t connect at the new site,” says Juan Melero-Martin, PhD, a researcher in Cardiac Surgery in Boston Children’s Hospital. “If you want to engineer a tissue replacement, you’d better understand how the vessels get connected, because if the vessels go, the graft goes.”

Melero-Martin and colleagues have uncovered several strategies to help these connections form, as they describe online today in Nature Biomedical Engineering. The strategies could help improve the success of such procedures as heart patching, bone grafting, fat transplants and islet transplantation.

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Medical milestone: Making blood stem cells in the lab

blood stem cells
The gradation of pink-to-blue cells illustrates the transition from hemogenic endothelial cells to blood progenitor cells during normal embryonic blood development. Daley, Sugimura and colleagues recreated this process in the lab, then added genetic factors to produce a mix of blood stem and progenitor cells. (O’Reilly Science Art)

Pluripotent stem cells can make virtually every cell type in the body.  But until now, one type has remained elusive: blood stem cells, the source of our entire complement of blood cells.

Since human embryonic stem cells (ES cells) were isolated in 1998, scientists have tried to get them to make blood stem cells. In 2007, the first induced pluripotent stem (iPS) cells were made from human skin cells, and have since been used to generate multiple cell types, such as neurons and heart cells.

But no one has been able to make blood stem cells. A few have have been isolated, but they’re rare and can’t be made in enough numbers to be useful.

Now, the lab of George Daley, MD, PhD, part of Boston Children’s Stem Cell Research program as finally hit upon a way to create blood stem cells in quantity, reported today in Nature.

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