Do an online search for “autism stem cells” and you quickly come up with numerous websites offering stem cell therapies for autism. They offer encouraging phrases like “new and effective approach” and “a real, lasting treatment.” They even include dense scientific videos featuring people like Dr. Arnold Caplan, a professor at Case Western Reserve University who is known as the “father of the mesenchymal stem” (it would be interesting to know if Dr. Caplan knows he is being used as a marketing tool?)
The problem with these sites is that they are offering “therapies” that have never been proven to be safe, let alone effective. They are also very expensive and are not covered by insurance. Essentially they are preying on hope, the hope that any parent of a child with autism spectrum disorder (ASD) will do anything and everything they can to help their child.
But there is encouraging news about stem cells and autism, about their genuine potential to help children with ASD. That’s why we are holding a special Facebook Live “Ask the Stem Cell Team” about Autism on Thursday, March 19th at noon (PDT).
The event features Dr. Alysson Muotri from UC San Diego. We have written about his work with stem cells for autism in the past. And CIRM’s own Associate Director for Discovery and Translation, Dr. Kelly Shephard.
We’ll take a look at Dr. Muotri’s work and also discuss the work of other researchers in the field, such as Dr. Joanne Kurtzberg’s work at Duke University.
But we also want you to be a part of this as well. So, join us online for the event. You can post comments and questions during the event, and we’ll do our best to answer them. Or you can send us in questions ahead of time to firstname.lastname@example.org.
By Kelly Shepard, PhD., CIRM’s Associate Director, Discovery & Translation
CIRM has previously blogged about advances in treating certain forms of “bubble baby” disease”, where a person is born with a defect in their blood forming stem cells that results in a deficient immune system, rendering them vulnerable to lethal infections by all manner of bacteria, virus or germ.
If a suitable donor can be found, or if the patient’s own defective cells can be corrected through gene therapy approaches, it is now possible to treat or cure such disorders through a bone marrow transplant. In this procedure, healthy blood stem cells are infused into the patient, taking up residence in his or her bone marrow and dividing to give rise to functioning immune cells such as T cells and B cells.
Unfortunately, there is another type of “bubble baby” disease that cannot be treated by providing healthy blood stem cells, because the defective immune system is caused by a different culprit altogether- a missing or dysfunctional thymus.
T Cells Go to School
What is a thymus? Most of us give little thought to this leaf-shaped organ, which is large and important in our early childhoods, but becomes small and inconspicuous as we age. This transformation belies the critical role a thymus plays in the development of our adaptive immune systems, which takes place in our youth: to prepare our bodies to fight infections for the rest of our lives.
One might think of the thymus as a “school”, where immature T cells go to “learn” how to recognize and attack foreign antigens (surface markers), such as those found on microorganisms or tissues from other individuals. The thymus also “teaches” our immune system to distinguish “self” from “other” by eliminating any T cells that attack our own tissues. Without this critical function, our immune system could inadvertently turn against us, causing serious autoimmune disorders such as ulcerative colitis and myasthenia gravis.
Many children with a severely deficient or absent thymus, referred to as athymia, have inherited a chromosome that is missing a key stretch of genes on a region called 22q11. Doctors believe perhaps 1/2000-1/4000 babies are born with some type of deletion in this region, which leads to a variable spectrum of disorders called 22q11 syndrome that can affect just about any part of the body, and can even cause learning disabilities and mental illness.
Individuals with one form of 22q11, called DiGeorge Syndrome, are particularly affected in the heart, thymus, and parathyroid glands. In the United States, about 20 infants are born per year with the “complete” and most severe form of DiGeorge Syndrome, who lack a thymus altogether, and have severely depressed numbers of T cells for fighting infections. Without medical intervention, this condition is usually fatal by 24 months of age.
Optimism and Setback
Although there are no therapies approved by the Food and Drug Administration (FDA) for pediatric athymia, Dr. Mary Louise Markert at Duke University and Enzyvant, Inc. have been pioneering an experimental approach to treat children with complete DiGeorge syndrome.
In this procedure, discarded thymic tissues are collected from infants undergoing cardiac surgery, where some of the thymus needs to be removed in order for the surgeon to gain access to the heart. These tissues are processed to remove potentially harmful donor T cells and then transplanted into the thigh of an athymic DiGeorge patient.
Results from early clinical trials seemed promising, with more than 70% of patients surviving, including several who are now ten years post-transplant. Based on those results, in June of 2019 Enzyvant applied to the FDA for a Biologics License Application (BLA), which is needed to be able to sell the therapy in the US. Unfortunately, only a few months later, Enzyvant announced that the FDA had declined to approve the BLA due to manufacturing concerns.
While it may be possible to address these issues in time, the need to step back to the drawing board was a devastating blow to the DiGeorge Community, who have waited decades for a promising treatment to emerge on the horizon.
Despite the setback, there is reason to hope. In early 2019, CIRM granted a “Quest” Award to team of investigators at Stanford University to develop a novel stem cell based approach for treating thymic deficiency. Co-led by Katja Weinacht, a pediatric hematologist/oncologist, and Vittorio Sebastiano, a stem cell expert and developmental biologist, the team’s strategy is to coax induced pluripotent stem cells (iPS) in the laboratory to differentiate into thymic tissue, which could then be transplanted into patients using the route pioneered by Duke and Enzyvant.
The beauty of this new approach is that pluripotent stem cells are essentially immortal in culture, providing an inexhaustible supply of fresh thymic cells for transplant, thereby allowing greater control over the quality and consistency of donor tissues. A second major advantage is the possibility of using pluripotent cells from the patient him/herself as the source, which should be perfectly immune-matched and alleviate the risk of rejection and autoimmunity that comes with use of donated tissues.
Sounds easy, so what are the challenges? As with many regenerative medicine approaches, the key is getting a pluripotent stem cell to differentiate into the right type of cells in the lab, which is a very different environment than what cells experience naturally when they develop in the context of an embryo and womb, where many cells are interacting and providing complex, instructive cues to one another. The precise factors and timing all need to be worked out and in most cases, this is done with an incomplete knowledge of human development.
A second challenge relates to using cells from DiGeorge patients to produce thymic tissue, which are missing several genes on their 22nd chromosome and will likely require sophisticated genetic engineering to restore this ability.
Fortunately, Drs. Weinacht and Sebastiano are up to the challenge, and have already made progress in differentiating human induced pluripotent stem cells (iPS) into thymic lineage intermediates that appear to be expressing the right proteins at the right time. They plan to combine these cells with engineered materials to create a three-dimensional (3D) tissue that more closely resembles an authentic organ, and which can be tested for functionality in athymic mice.
There is more work to be done, but these advances, along with continued technological improvements and renewed efforts from Enzyvant, could forge a path to the clinic and lead to a brighter future for patients suffering from congenital athymia and other forms of thymic dysfunction.
One hundred billion nerve cells working together empowering us to see, walk, think, speak, remember: the human brain is a stunning machine. Even more stunning is its formation in the growing fetus. It starts with a set of neural, or brain, stem cells in the early embryo. Then with each cell division, more and more cells emerge and specialize to perform various brain functions. All the while, some of those “daughter” cells remain uncommitted, staying in their neural stem cell form in order to keep a steady cell supply to build the brain. With all these 100,000,000,000 cells needing to be assembled in a precise way, it’s amazing that our brains work at all.
MRIs of a healthy individual (left) and a patient with microcephaly (right). Credit: PLoS Biol 2(5): e134
Suffer the children
Well, sometimes they don’t. For about 25,000 babies born in the U.S. each year, the brain doesn’t grow the way it should, leading to microcephaly, a disorder characterized by an abnormally small head (micro=small; cephaly=head). These babies have a range of symptoms including speech delays, seizures, mental retardation and balance difficulties. Preventing microcephaly first requires understanding why this devastating condition leads to a smaller brain size. On Thursday, a Duke research team reported in Neuron that they have the answer: stem cells dividing too slowly.
In 2010, the team, led by Debra Silver, an assistant professor of molecular genetics and microbiology at the Duke University School of Medicine, found that mice lacking one of two copies of the Magoh gene showed a reduced brain size much like what’s seen in human microcephaly. Their study showed that the genetic defect upset the normal ratio of neural stem cells to neurons (nerve cells) in the brain. But how?
Slowly dividing neural stem cells generate aberrant stem cells and neurons. Credit: Louis-Jan Pilaz, Duke University
That’s where this new data comes into play. They found that many neural stem cells in mice lacking one copy of the Magoh gene divided at a slower rate, taking up to three times longer than cells with both copies of Magoh. Using specialized microscopes, the team observed the cells in real time and noticed that the slowly dividing cells were more likely to specialize into neurons rather remain in a stem cell state. On top of that, these neurons died off more readily. Silver described the results of this double-whammy of defects in a Duke University press release:
“It’s really a combination that helps explain the microcephaly. On one hand, you’re really not making enough new stem cells, and if you don’t have enough stem cells you can’t make enough neurons in the brain. On the other hand, some neurons do get made, but a lot of them die.”
Proving their point To back up this claim, the team treated healthy mice with drugs that lengthen the time it takes for a cell to divide. Sure enough, an unusually high number of neural stem cells from those mice specialized into neurons and then succumbed to an early death.
From Silver’s perspective, this discovery doesn’t just provide a foothold in understanding (and maybe in even one day treating) microcephaly, it could be a fundamental insight for human developmental disorders in general:
This study shows that the time it takes for a stem cell to divide matters during brain development, But beyond microcephaly, I think it’s going to be relevant for thinking about how stem cell dysfunction can change the repertoire of other cells in the body.