Awoken from a persistent vegetative state: First successful treatment of paediatric cerebral palsy with autologous cord blood

The parents searched the literature for treatment options

At the end of November 2008, the child suffered from cardiac arrest with severe brain damage and was subsequently in a persistent vegetative state with his body paralysed. Up to now, there has been no treatment for the cause of what is known as infantile cerebral palsy. “In their desperate situation, the parents searched the literature for alternative therapies”, Arne Jensen explains. “They contacted us and asked about the possibilities of using their son’s cord blood, frozen at his birth.”

“Threatening, if not hopeless prognosis”

Nine weeks after the brain damage, on 27 January 2009, the doctors administered the prepared blood intravenously. They studied the progress of recovery at 2, 5, 12, 24, 30, and 40 months after the insult. Usually, the chances of survival after such a severe brain damage and more than 25 minutes duration of resuscitation are six per cent. Months after the severe brain damage, the surviving children usually only exhibit minimal signs of consciousness. “The prognosis for the little patient was threatening if not hopeless”, the Bochum medics say.

Rapid recovery after cord blood therapy

After the cord blood therapy, the patient, however, recovered relatively quickly. Within two months, the spasticity decreased significantly. He was able to see, sit, smile, and to speak simple words again. Forty months after treatment, the child was able to eat independently, walk with assistance, and form four-word sentences. “Of course, on the basis of these results, we cannot clearly say what the cause of the recovery is”, Jensen says. “It is, however, very difficult to explain these remarkable effects by purely symptomatic treatment during active rehabilitation.”

In animal studies, stem cells migrate to damaged brain tissue

In animal studies, scientists have been researching the therapeutic potential of cord blood for some time. In a previous study with rats, RUB researchers revealed that cord blood cells migrate to the damaged area of the brain in large numbers within 24 hours of administration. In March 2013, in a controlled study of one hundred children, Korean doctors reported for the first time that they had successfully treated cerebral palsy with allogeneic cord blood.

What are stem cells?

In a paper published in Cell yesterday, scientists from the US and Thailand have, for the first time, successfully produced embryonic stem cells from human skin cells.

That sounds interesting, but what are stem cells and where do they come from?

If you take a limb from a rose tree, and put it in soil, it will grow into a thriving bush.

But you might say: “Plants are special. This won’t work with animals.” Or will it? If you cut off a lizard’s tail, a new tail may grow. A lobster can grow back a lost claw.

There is a special type of flatworm that can be cut in half, again and again hundreds of times, and each half grows back into a full worm.

Similarly, if you cut out half a human liver, it will grow back. The story of Prometheus, whose liver was eaten away by eagles and regrew each day, suggests that the Greeks of ancient times knew about regeneration of organs.

This sort of regeneration is attributed to special cells called “stem cells”.

Reprogramming the workers

Most of our cells are like many professional workers – they are hardened in their ways and can’t manage career changes.

Blood cells carry oxygen or fight disease, muscle cells expand and contract to move us around, nerve cells carry signals, skin cells form a protective layer over our bodies, and structures made up of kidney cells filter our blood.

The cells of most organs or tissues are referred to as “terminally differentiated” cells. They have specialised, and many won’t divide again. If they are damaged or die they will disappear. This is very important.

Although we feel like we grow a lot after we are born, we really only double in size two or three times and most of our cells don’t divide much.

If they did we would be at great risk from cancer – the uncontrolled doubling of cells at the wrong time.

We have a lot of cells and it is important that none of them run out of control.

But some cells can double to renew themselves and can also differentiate and give rise to specialised progeny.

These are the stem cells. We need them to produce new skin to replace damaged skin cells. Similarly, we need them in our guts to replace damaged cells on the surface of our intestines.

Our blood cells also get worn out as they race around our bodies so we have blood stem cells that divide and replace themselves. They also differentiate to form the different types of white and red blood cells we need.

Australian researchers identified stem cells in the breast that can proliferate and form a complete functioning breast. There are also stem cells in the brain and in the heart.

While stem cells tend to be very rare, they exist in many of our organs.

Types of stem cells

The ultimate stem cells are embryonic stem cells.

These cells are found in the inner cell mass of the early embryo and are referred to as “totipotent” since they have the ability to form every cell that is needed in the growing embryo.

They can be extracted from the early embryo and grown in culture dishes.

They can also be genetically modified by the addition of DNA, then injected back into other embryos or into adult animals where find their way into localities that suit them and replace themselves by duplication or differentiate into other cell types that may be needed. For a long time this type of work had been done primarily in laboratory mice.

The techniques in yesterday’s Cell paper involved injecting the nucleus from a human skin cell into a human egg (the nucleus of which has been destroyed) then growing the resulting embryo until the inner cell mass cells could be harvested.

The method may still be controversial because it uses unfertilised eggs, but many people will regard it as preferable to using human embryos. And there are other interesting methods for making stem cells.

Somatic cells to stem cells

It is also possible to convert skin cells, and indeed many different terminally differentiated cells, back into what are called “induced pluripotent stem cells” or iPS cells.

One uses the “magic four” or “OKSM” set of DNA-binding proteins that govern normal stem cell biology:

• Octamer-binding transcription factor 4 (OCT4)
• Kruppel-like factor 4 (KLF4)
• SRY (sex determining region Y)-box 2 (SOX2)
• cellular myelocytomatosis virus-like gene (MYC)

In 2012 Shinya Yamanaka won the Nobel Prize for discovering how to convert normal cells into iPS cells using the OKSM regulators to turn on and off the right genes and convert skin cells into stem cells.

Researchers are continuing to investigate whether iPS cells have the same therapeutic potential as embryo derived stem cells.

It is hoped that stem cells may provide therapies for people suffering from degenerative diseases.

Skin cells could be taken from a patient, converted to stem cells, and then these could be injected back into the damaged organ.

Ideally, they would repopulate the damaged organ with new cells.

So why doesn’t this happen in normal biology? Why aren’t our own heart stem cells busy trying to repair broken hearts?

They may be but our natural supply of stem cells is limited and presumably insufficient to tackle severe disease.

So why don’t we just have more stem cells in our bodies?

The down side of having too many stem cells may be cancer.

Stem cells share a number of features with cancer cells – both are able to self-renew and double without limit.

One theory about cancer holds that the disease most often originates not from terminally differentiated cells but from one of the small number of stem cells in the relevant tissues.

The obvious concern about using stem cells for therapy is that injecting too many could increase the chances that some of these cells would proliferate beyond control, and ultimately give rise to cancer.

Stem cell therapy for regenerative medicine is an exciting idea.

Every day we are learning more about stem cells – how to purify or make them, and how to grow them in culture and direct them down particular pathways to repopulate different organs.

Future research will assess the risks and how effective they can be in experimental systems and ultimately in human patients.

Human stem cells successfully cloned for the first time

A working process for cloning stem cells from existing human cells has finally been discovered by a team at Oregon Health & Science University.

These stem cells were created by reprogramming healthy skin cells, a goal that has eluded researchers around the world for years. It’s the first key step in developing medical procedures for replacing dying or injured cells with new ones to stave off disease and age. That could mean growing a new liver, or kidney or heart, in the lab for an organ transplant, or even repairing the brains of those suffering with diseases like Parkinson’s.

The team was led by Shoukhrat Mitalipov from the reproductive and developmental sciences department of the Oregon National Primate Research Centre. He said: “A thorough examination of the stem cells derived through this technique demonstrated their ability to convert just like normal embryonic stem cells into several different cell types, including nerve cells, liver cells and heart cells. Furthermore, because these reprogrammed cells can be generated with nuclear genetic material from a patient, there is no concern of transplant rejection.”

"While there is much work to be done in developing safe and effective stem cell treatments, we believe this is a significant step forward in developing the cells that could be used in regenerative medicine."

The technique Mitalipov and his team used is called “somatic cell nuclear transfer” — as you can see in the video, it essentially involves sucking out the DNA from an adult cell and inserting it into the empty nucleus of a donor egg. This creates a clone of the original cell, and is in fact the first step in the cloning method used to create animal clones like Dolly the sheep.

However, in its therapeutic mode, the new cells can be grown as replacements for the original type of cell. That objective hasn’t been reached until now as human eggs are extremely fragile compared to many of the animals which we have cloned. That Mitalipov and team have succeeded is down to research on primates, and adapting primate stem cell research to humans.

As a cell divides after fertilisation, it undergoes several transformations as it prepares to split and multiply. The metaphase is the moment just before a cell splits, as the chromosomes align alongside each other in the very centre of the cell so that, when it splits, one goes one way as another goes the other, each taking the full copy of the genetic code. The researchers managed to stall the metaphase while the cell underwent nuclear transfer, effectively giving the new chromosomes time to get settled before the metaphase finished and cell division proceeded.

An added bonus is that the eggs used have not been fertilised, so there won’t be any debates over the ethics of embryonic stem cells as we have seen in the US in the past. While the researchers placed skin cell nuclei into the receptor egg cells, the method is conceivably similar for any other kind of cell.

And, while it may sounds like the first step towards a practical method for cloning humans, the Mitalipov has made it clear that’s not the aim. “Our research is directed toward generating stem cells for use in future treatments to combat disease. While nuclear transfer breakthroughs often lead to a public discussion about the ethics of human cloning, this is not our focus, nor do we believe our findings might be used by others to advance the possibility of human reproductive cloning.”

The research has been published in the journal Cell.

Same musicians: brand new tune

A small ensemble of musicians can produce an infinite number of melodies, harmonies and rhythms. So too, do a handful of workhorse signaling pathways that interact to construct multiple structures that comprise the vertebrate body. In fact, crosstalk between two of those pathways—those governed by proteins known as Notch and BMP (for Bone Morphogenetic Protein) receptors—occurs over and over in processes as diverse as forming a tooth, sculpting a heart valve and building a brain.

A new study by Stowers Institute for Medical Research Investigator Ting Xie, Ph.D., reveals yet another duet played by Notch and BMP signals, this time with Notch calling the tune. That work, published in this week’s online issue of PNAS, uses mouse genetics to demonstrate how one Notch family protein, Notch2, shapes an eye structure known as the ciliary body (CB), most likely by ensuring that BMP signals remain loud and clear.

In vertebrates, the CB encircles the lens and performs two tasks essential for normal vision. First, it contains a tiny muscle that reshapes the lens when you change focus, or “accommodate”. And it also secretes liquid aqueous humor into the front compartment of the eye where it likely maintains correct eye pressure. Understanding CB construction is critical, as excessive pressure is one risk factor for glaucoma.

Eye development is a relatively new field for Xie, a recognized leader in the study of adult stem cells in the fruit fly: only recently did he branch out into mouse studies. “A few years ago I was asked to participate in a think tank-type meeting to discuss the potential application of cell therapy to treat glaucoma,” he says.
“I became interested in using retinal progenitor cells to treat diseases like glaucoma or macular degeneration. But I realized that first we needed to understand eye disease at the molecular level.” The new study is an important step in that direction.

Previously, investigators knew that once cells that form the CB are established in an embryo, the BMP pathway drives their “morphogenesis”, the term used by developmental biologists to describe the process of expanding and then sculpting a committed population of cells into a unique structure. “The Notch2 receptor was previously shown to be expressed in the developing mouse eye,” explains Chris Tanzie, M.D., Ph.D., a former graduate student in the Xie lab and the study’s co-first author. “But its function was unknown, and no one connected how various signaling pathways direct CB morphogenesis.”

To determine what Notch2 was doing in the developing eye, the Stowers team constructed a conditional knockout mouse, meaning that the Notch2 gene is deleted from the genome only in eye cells that give rise to the CB. In normal newborn mice a series of cellular “folds” that characterize the CB emerges over the first 7 days of life. But the mutant knockout mice showed a complete absence of folds, dramatic evidence that Notch2 is required to elaborate a CB.

Furthermore, in normal mice a protein called Jagged-1, which activates Notch2, was expressed in cells adjacent to Notch2-expressing CB cells during the same developmental period. Strikingly, the team’s collaborators in Richard Libby’s laboratory at the University of Rochester Medical Center, were able to demonstrate that just like the Notch2 mutants, Jagged-1 conditional knockout mice showed almost total loss of CB fold structures, a major hint that Notch2 was switched on by Jagged1 to drive CB formation.

Biochemical and microarray analysis provided further explanation for defects observed after Notch2 loss. Comparison of normal and Notch2-mutant eye cells revealed that not only did cells of mutant mice lose BMP signaling but that expression of two proteins known to interfere with BMP increased in those cells.

“Up-regulation of BMP antagonists following Notch2 loss is an important observation,” says Xie. “In other systems people often observe that Notch and BMP cooperatively regulate common targets by transcription factor collaboration at the transcriptional level, but this is a unique mechanism. We find that Notch2 keeps BMP signaling active by inhibiting its inhibitors.”

The study’s second co-first author is Yi Zhou, a University of Kansas Medical Center graduate student earning his Ph.D. in Xie’s lab. “Our work reveals a novel link between Notch and BMP pathways potentially involved in the pathogenesis of glaucoma,” says Zhou, noting one more tantalizing implication of the paper. “In addition, mutations in Jagged-1 and Notch2 are thought to underlie the human genetic disease known as Alagille Syndrome. Our work may lead to a better understanding of both.”

Alagille Syndrome is an inherited childhood disorder causing defects in organ systems including liver, heart and the skeleton. Xie is equally intrigued by potential connections between his group’s observations in the mouse eye and Alagille outcomes in humans. Nonetheless, he remains focused on nailing down how perturbation of the Jagged1-Notch2-BMP axis might cause eye disease.

“We now know how to build better mouse mutants to study CB development. In this work we show that Notch regulates BMP signaling but have not yet determined whether alterations in CB structure actually change interocular pressure,” he says. “Answering that question is our future goal.”

Adult cells transformed into early-stage nerve cells, bypassing the pluripotent stem cell stage

A UW-Madison research group has converted skin cells from people and monkeys into a cell that can form a wide variety of nervous-system cells — without passing through the do-it-all stage called the induced pluripotent stem cell, or iPSC.

Bypassing the ultraflexible iPSC stage was a key advantage, says senior author Su-Chun Zhang, a professor of neuroscience and neurology. “IPSC cells can generate any cell type, which could be a problem for cell-based therapy to repair damage due to disease or injury in the nervous system.”

In particular, the absence of iPSC cells rules out the formation of tumors by pluripotent cells in the recipient, a major concern involving stem cell therapy.

A second advance comes from the virus that delivers genes to reprogram the adult skin cells into a different and more flexible form. Unlike other viruses used for this process, the Sendai virus does not become part of the cell’s genes.

Jianfeng Lu, Zhang’s postdoctoral research associate at the UW-Madison Waisman Center, removed skin cells from monkeys and people, and exposed them to Sendai virus for 24 hours. Lu then warmed the culture dish to kill the virus without harming the transforming cells. Thirteen days later, Lu was able to harvest a stem cell called an induced neural progenitor. After the progenitor was implanted into newborn mice, neural cells seemed to grow normally, without forming obvious defects or tumors, Zhang says.

Other researchers have bypassed the pluripotent stem cell stage while turning skin cells into neurons and other specialized cells, Zhang acknowledges, but the new research, just published in Cell Reports, had a different goal. “Our idea was to turn skin cells to neural progenitors, cells that can produce cells relating to the neural tissue. These progenitors can be propagated in large numbers.”

The research overcomes limitations of previous efforts, Zhang says. First, the Sendai virus, a kind of cold virus, is considered safe because it does not enter the cell’s DNA, and it is killed by heat within 24 hours. (This is quite similar to the fever that raises our temperature to remove cold virus.) Second, the neural progenitors have a greater ability to grow daughter cells for research or therapy. Third, the progenitor cells are already well along the path toward specialization, and cannot become, say, liver or muscle cells after implantation. Finally, the progenitors can produce many more specialized cells.

The neurons that grew from the progenitor had the markings of neurons found in the rear of the brain, and that specialization can also be helpful. “For therapeutic use, it is essential to use specific types of neural progenitors,” says Zhang. “We need region-specific and function-specific neuronal types for specific neurological diseases.”

Progenitor cells grown from the skin of ALS (Lou Gehrig’s disease) or spinal muscular atrophy patients can be transformed into various neural cells to model each disease and allow rapid drug screening, Zhang adds.

Eventually, the process could produce cells used to treat conditions like spinal cord injury and ALS.

"These transplantation experiments confirmed that the reprogrammed cells indeed belong to cells of the intended brain regions and the progenitors produced the three major classes of neural cells: neurons, astrocytes and oligodendrocytes," Zhang says. "This proof-of-principle study highlights the possibility to generate many specialized neural progenitors for specific neurological disorders."

After Brain Injury, New Astrocytes Play Unexpected Role in Healing

The production of a certain kind of brain cell that had been considered an impediment to healing may actually be needed to staunch bleeding and promote repair after a stroke or head trauma, researchers at Duke Medicine report.

These cells, known as astrocytes, can be produced from stem cells in the brain after injury. They migrate to the site of damage where they are much more effective in promoting recovery than previously thought. This insight from studies in mice, reported online April 24, 2013, in the journal Nature, may help researchers develop treatments that foster brain repair.

“The injury recovery process is complex,” said senior author Chay T. Kuo, M.D., PhD, George W. Brumley Assistant Professor of Cell Biology, Pediatrics and Neurobiology at Duke University. “There is a lot of interest in how new neurons can stimulate functional recovery, but if you make neurons without stopping the bleeding, the neurons don’t even get a chance. The brain somehow knows this, so we believe that’s why it produces these unique astrocytes in response to injury.”

Each year, more than 1.7 million people in the United States suffer a traumatic brain injury, according to the Centers for Disease Control and Prevention. Another 795,000 people a year suffer a stroke. Few therapies are available to treat the damage that often results from such injuries.

Kuo and colleagues at Duke are interested in replacing lost neurons after a brain injury as a way to restore function. Once damaged, mature neurons cannot multiply, so most research efforts have focused on inducing brain stem cells to produce more immature neurons to replace them.

This strategy has proved difficult, because in addition to making neurons, neural stem cells also produce astrocytes and oligodendrocytes, known as glial cells. Although glial cells are important for maintaining the normal function of neurons in the brain, the increased production of astrocytes from neural stem cell has been considered an unwanted byproduct, causing more harm than good. Proliferating astrocytes secrete proteins that can induce tissue inflammation and undergo gene mutations that can lead to aggressive brain tumors.

In their study of mice, the Duke team found an unexpected insight about the astrocytes produced from stem cells after injury. Stem cells live in a special area or “niche” in the postnatal/adult brain called the subventricular zone, and churn out neurons and glia in the right proportions based on cues from the surrounding tissue.

After an injury, however, the subventricular niche pumps out more astrocytes. Significantly, the Duke team found they are different from astrocytes produced in most other regions of the brain. These cells make their way to the injured area to help make an organized scar, which stops the bleeding and allows tissue recovery.

When the generation of these astrocytes in the subventricular niche was experimentally blocked after a brain injury, hemorrhaging occurred around the injured areas and the region did not heal.  Kuo said the finding was made possible by insights about astrocytes from Cagla Eroglu, PhD, whose laboratory next door to Kuo’s conducts research on astrocyte interactions with neurons.

“Cagla and I started at Duke together and have known each other since our postdoctoral days,” Kuo said. “To have these stem cell-made astrocytes express a unique protein that Cagla understands more than anyone else, it’s just a wonderful example of scientific serendipity and collaboration.”

Additionally, Kuo said first author Eric J. Benner, M.D., PhD, a former postdoctoral fellow who now has his own laboratory at Duke, provided key clinical correlations on brain injury as a physician-scientist and practicing neonatologist in the Jean and George Brumley Jr. Neonatal-Perinatal Research Institute.

“We are very excited about this innate flexibility in neural stem cell behavior to know just what to do to help the brain after injury,” Kuo said. “Since bleeding in the brain after injury is a common and serious problem for patients, further research into this area may lead to effective therapies for accelerated brain recovery after injury.”

Scientists Find Antibody that Transforms Bone Marrow Stem Cells Directly into Brain Cells

In a serendipitous discovery, scientists at The Scripps Research Institute (TSRI) have found a way to turn bone marrow stem cells directly into brain cells.

Current techniques for turning patients’ marrow cells into cells of some other desired type are relatively cumbersome, risky and effectively confined to the lab dish. The new finding points to the possibility of simpler and safer techniques. Cell therapies derived from patients’ own cells are widely expected to be useful in treating spinal cord injuries, strokes and other conditions throughout the body, with little or no risk of immune rejection.

“These results highlight the potential of antibodies as versatile manipulators of cellular functions,” said Richard A. Lerner, the Lita Annenberg Hazen Professor of Immunochemistry and institute professor in the Department of Cell and Molecular Biology at TSRI, and principal investigator for the new study. “This is a far cry from the way antibodies used to be thought of—as molecules that were selected simply for binding and not function.”

The researchers discovered the method, reported in the online Early Edition of the Proceedings of the National Academy of Sciences the week of April 22, 2013, while looking for lab-grown antibodies that can activate a growth-stimulating receptor on marrow cells. One antibody turned out to activate the receptor in a way that induces marrow stem cells—which normally develop into white blood cells—to become neural progenitor cells, a type of almost-mature brain cell.

Nature’s Toolkit

Natural antibodies are large, Y-shaped proteins produced by immune cells. Collectively, they are diverse enough to recognize about 100 billion distinct shapes on viruses, bacteria and other targets. Since the 1980s, molecular biologists have known how to produce antibodies in cell cultures in the laboratory. That has allowed them to start using this vast, target-gripping toolkit to make scientific probes, as well as diagnostics and therapies for cancer, arthritis, transplant rejection, viral infections and other diseases.

In the late 1980s, Lerner and his TSRI colleagues helped invent the first techniques for generating large “libraries” of distinct antibodies and swiftly determining which of these could bind to a desired target. The anti-inflammatory antibody Humira®, now one of the world’s top-selling drugs, was discovered with the benefit of this technology.

Last year, in a study spearheaded by TSRI Research Associate Hongkai Zhang, Lerner’s laboratory devised a new antibody-discovery technique—in which antibodies are produced in mammalian cells along with receptors or other target molecules of interest. The technique enables researchers to determine rapidly not just which antibodies in a library bind to a given receptor, for example, but also which ones activate the receptor and thereby alter cell function.

Lab Dish in a Cell

For the new study, Lerner laboratory Research Associate Jia Xie and colleagues modified the new technique so that antibody proteins produced in a given cell are physically anchored to the cell’s outer membrane, near its target receptors. “Confining an antibody’s activity to the cell in which it is produced effectively allows us to use larger antibody libraries and to screen these antibodies more quickly for a specific activity,” said Xie. With the improved technique, scientists can sift through a library of tens of millions of antibodies in a few days.

In an early test, Xie used the new method to screen for antibodies that could activate the GCSF receptor, a growth-factor receptor found on bone marrow cells and other cell types. GCSF-mimicking drugs were among the first biotech bestsellers because of their ability to stimulate white blood cell growth—which counteracts the marrow-suppressing side effect of cancer chemotherapy.

The team soon isolated one antibody type or “clone” that could activate the GCSF receptor and stimulate growth in test cells. The researchers then tested an unanchored, soluble version of this antibody on cultures of bone marrow stem cells from human volunteers. Whereas the GCSF protein, as expected, stimulated such stem cells to proliferate and start maturing towards adult white blood cells, the GCSF-mimicking antibody had a markedly different effect.

“The cells proliferated, but also started becoming long and thin and attaching to the bottom of the dish,” remembered Xie.

To Lerner, the cells were reminiscent of neural progenitor cells—which further tests for neural cell markers confirmed they were.

A New Direction

Changing cells of marrow lineage into cells of neural lineage—a direct identity switch termed “transdifferentiation”—just by activating a single receptor is a noteworthy achievement. Scientists do have methods for turning marrow stem cells into other adult cell types, but these methods typically require a radical and risky deprogramming of marrow cells to an embryonic-like stem-cell state, followed by a complex series of molecular nudges toward a given adult cell fate. Relatively few laboratories have reported direct transdifferentiation techniques.

“As far as I know, no one has ever achieved transdifferentiation by using a single protein—a protein that potentially could be used as a therapeutic,” said Lerner.

Current cell-therapy methods typically assume that a patient’s cells will be harvested, then reprogrammed and multiplied in a lab dish before being re-introduced into the patient. In principle, according to Lerner, an antibody such as the one they have discovered could be injected directly into the bloodstream of a sick patient. From the bloodstream it would find its way to the marrow, and, for example, convert some marrow stem cells into neural progenitor cells. “Those neural progenitors would infiltrate the brain, find areas of damage and help repair them,” he said.

While the researchers still aren’t sure why the new antibody has such an odd effect on the GCSF receptor, they suspect it binds the receptor for longer than the natural GCSF protein can achieve, and this lengthier interaction alters the receptor’s signaling pattern. Drug-development researchers are increasingly recognizing that subtle differences in the way a cell-surface receptor is bound and activated can result in very different biological effects. That adds complexity to their task, but in principle expands the scope of what they can achieve. “If you can use the same receptor in different ways, then the potential of the genome is bigger,” said Lerner.