Engineered bone tissue improves stem cell transplants

Bone marrow transplants are currently the only approved stem cell-based therapy in the United States. They involve replacing the hematopoietic, or blood-forming stem cells, found in the bone marrow with healthy stem cells to treat patients with cancers, immune diseases and blood disorders.

For bone marrow transplants to succeed, patients must undergo radiation therapy to wipe out their diseased bone marrow, which creates space for the donor stem cells to repopulate the blood system. Radiation can lead to complications including hair loss, nausea, fatigue and infertility.

Scientists at UC San Diego have a potential solution that could make current bone marrow transplants safer for patients. Their research, which was funded in part by a CIRM grant, was published yesterday in the journal PNAS.

Engineered bone with functional bone marrow in the center. (Varghese Lab)

Led by bioengineering professor Dr. Shyni Varghese, the team engineered artificial bone tissue that contains healthy donor blood stem cells. They implanted the engineered bone under the skin of normal mice and watched as the “accessory bone marrow” functioned like the real thing by creating new blood cells.

The implant lasted more than six months. During that time, the scientists observed that the cells within the engineered bone structure matured into bone tissue that housed the donor bone marrow stem cells and resembled how bones are structured in the human body. The artificial bones also formed connections with the mouse circulatory system, which allowed the host blood cells to populate the implanted bone tissue and the donor blood cells to expand into the host’s bloodstream.

Normal bone structure (left) and engineered bone (middle) are very similar. Bone tissue shown on top right and bone marrow cells on bottom right. (Varghese lab)

The team also implanted these artificial bones into mice that received radiation to mimic the procedures that patients typically undergo before bone marrow transplants. The engineered bone successfully repopulated the blood systems of the irradiated mice, similar to how blood stem cell functions in normal bone.

In a UC San Diego news release, Dr. Varghese explained how their technology could be translated into the clinic,

“We’ve made an accessory bone that can separately accommodate donor cells. This way, we can keep the host cells and bypass irradiation. We’re working on making this a platform to generate more bone marrow stem cells. That would have useful applications for cell transplantations in the clinic.”

The authors concluded that engineered bone tissue would specifically benefit patients who needed bone marrow transplants for non-cancerous bone marrow-related diseases such as sickle cell anemia or thalassemia where there isn’t a need to destroy cancer-causing cells.

Mixed Matches: How Your Heritage Can Save a Life

Today we bring you a guest blog from Athena Mari Asklipiadis. She’s the founder of Mixed Marrow, which is an organization dedicated to finding bone marrow and blood cell donors to patients of multiethnic descent. Athena helped produce a 2016 documentary film called Mixed Match that encourages mixed race and minority donors to register as adult donors.

Athena Asklipiadis

Due to the lack of diversity on the national and world bone marrow donor registries, Mixed Marrow was started in 2009 to increase the numbers of mixed race donors.

Prior to Mixed Marrow starting, other ethnic recruiters like Asians for Miracle Marrow Matches (A3M), based in Los Angeles, CA and Asian American Donor Program (AADP), based in Alameda, CA had been raising awareness in the Asian and minority communities for decades.  Closing the racial gap on the registry was something I was very much interested in helping them with so I began my outreach on the most familiar medium I knew—social media.

Because matching relies heavily on similar inherited genetic markers, I was particularly astonished seeing the less than 3% (back in 2009) sliver of the ethnic pie that mixed race donors made up.  Caucasians made up for about 70% at the time, with all minorities making up for the difference.  The ethnic breakdown made sense when comparing against actual population numbers, but a larger pool of minority donors was definitely something needed especially when multiracial people were being reported as the fastest growing demographic in the US.  Odds were just not in the favor of non-white searching patients.

Current Be The Match ethnic breakdown as of 2016.

After getting to know a local mixed race searching patient, Krissy Kobata, and hearing of her struggles finding a match, I knew I had to do my best to reach out to fellow multiracial people, most of which were young and likely online.  At the time, I was engaged with fellow hapas (half in Hawaiian Pidgin, referring mixed heritage) and mixed people via multiracial community Facebook groups and other internet forums.  One common thing I noticed, unlike topics like identity, food and culture– health was definitely not widely talked about. So with that lack of awareness, Mixed Marrow began as a facebook page and later as a website.  With the help of organizations like A3M supplying Be The Match testing kits, Mixed Marrow was able to also exist outside of the virtual world by hosting donor recruitment drives at different cultural and college events.

Athena Asklipiadis, Krissy Kobata and Mixed Match director, Jeff Chiba Stearns

After about a year of advocacy, in 2010, I connected with filmmaker Jeff Chiba Stearns to pitch an idea for a documentary on the patients I worked with.  Telling their stories in words and on flyers was not effective enough for me, I felt that more people would be inclined to register as a donor if they got to know the patients as well as I did.  Thus, the film Mixed Match was born.

Still from Mixed Match, Imani (center) and parents, Darrick and Tammy.

Still from Mixed Match, Imani mother, Tammy.

Over the course of the next 6 years, Jeff and I went on a journey across the US to gather not only patient stories, but input from pioneers in stem cell transplantation like Dr. Paul Terasaki and Dr. John E. Wagner.  It was so important to share these transplant tales while being as accurate and informed as possible.

Still from Mixed Match – Dr. Paul Teriyaki.

Our goal was to educate audiences and present a call-to-action where everyone can learn how they can save a life. Mixed Match not only highlights bone marrow and peripheral blood stem cell (PBSC) donation, but it also shares the possibilities of umbilical cord stem cells.

Mixed Match director, Jeff Chiba Stearns decided a great way to explain stem cell science and matching was through animation.  Stearns, with the help of animator, Kaho Yoshida, was able to reach across to non-medical expert audiences and create digestible and engaging imagery to teach what is usually very complex science.

Animation Still from Mixed Match.

At every screening we also make sure to host a bone marrow registry drive so audiences have the opportunity to sign up.  We have partnered with both the US national registry, Be The Match and Canadian Blood Services’ One Match registry.

Bone marrow drive at a Mixed Match screening in Toronto.

Nearly 8 years and about 40 cities later, Mixed Marrow has managed to spread advocacy for the need for more mixed race donors all over the US and even other countries like Canada, Japan, Korea and Austria all the while being completely volunteer-run.  It is our hope that through social media and film, Mixed Match, we can help share these important stories and save lives.

Further Information

Curing the Incurable through Definitive Medicine

“Curing the Incurable”. That was the theme for the first annual Center for Definitive and Curative Medicine (CDCM) Symposium held last week at Stanford University, in Palo Alto, California.

The CDCM is a joint initiative amongst Stanford Healthcare, Stanford Children’s Health and the Stanford School of Medicine. Its mission is to foster an environment that accelerates the development and translation of cell and gene therapies into clinical trials.

The research symposium focused on “the exciting first-in-human cell and gene therapies currently under development at Stanford in bone marrow, skin, cardiac, neural, pancreatic and neoplastic diseases.” These talks were organized into four different sessions: cell therapies for neurological disorders, stem cell-derived tissue replacement therapies, genome-edited cell therapies and anti-cancer cell-based therapies.

A few of the symposium speakers are CIRM-funded grantees, and we’ll briefly touch on their talks below.

Targeting cancer

The keynote speaker was Irv Weissman, who talked about hematopoietic or blood-forming stem cells and their value as a cell therapy for patients with blood disorders and cancer. One of the projects he discussed is a molecule called CD47 that is found on the surface of cancer cells. He explained that CD47 appears on all types of cancer cells more abundantly than on normal cells and is a promising therapeutic target for cancer.

Irv Weissman

Irv Weissman

“CD47 is the first gene whose overexpression is common to all cancer. We know it’s molecular mechanism from which we can develop targeted therapies. This would be impossible without collaborations between clinicians and scientists.”

 

At the end of his talk, Weissman acknowledged the importance of CIRM’s funding for advancing an antibody therapeutic targeting CD47 into a clinical trial for solid cancer tumors. He said CIRM’s existence is essential because it “funds [stem cell-based] research through the [financial] valley of death.” He further explained that CIRM is the only funding entity that takes basic stem cell research all the way through the clinical pipeline into a therapy.

Improving bone marrow transplants

judith shizuru

Judith Shizuru

Next, we heard a talk from Judith Shizuru on ways to improve current bone-marrow transplantation techniques. She explained how this form of stem cell transplant is “the most powerful form of cell therapy out there, for cancers or deficiencies in blood formation.” Inducing immune system tolerance, improving organ transplant outcomes in patients, and treating autoimmune diseases are all applications of bone marrow transplants. But this technique also carries with it toxic and potentially deadly side effects, including weakening of the immune system and graft vs host disease.

Shizuru talked about her team’s goal of improving the engraftment, or survival and integration, of bone marrow stem cells after transplantation. They are using an antibody against a molecule called CD117 which sits on the surface of blood stem cells and acts as an elimination signal. By blocking CD117 with an antibody, they improved the engraftment of bone marrow stem cells in mice and also removed the need for chemotherapy treatment, which is used to kill off bone marrow stem cells in the host. Shizuru is now testing her antibody therapy in a CIRM-funded clinical trial in humans and mentioned that this therapy has the potential to treat a wide variety of diseases such as sickle cell anemia, leukemias, and multiple sclerosis.

Tackling stroke and heart disease

img_1327We also heard from two CIRM-funded professors working on cell-based therapies for stroke and heart disease. Gary Steinberg’s team is using human neural progenitor cells, which develop into cells of the brain and spinal cord, to treat patients who’ve suffered from stroke. A stroke cuts off the blood supply to the brain, causing the death of brain cells and consequently the loss of function of different parts of the body.  He showed emotional videos of stroke patients whose function and speech dramatically improved following the stem cell transplant. One of these patients was Sonia Olea, a young woman in her 30’s who lost the ability to use most of her right side following her stroke. You can read about her inspiring recover post stem cell transplant in our Stories of Hope.

Dr. Joe Wu. (Image Source: Sean Culligan/OZY)

Dr. Joe Wu. (Image Source: Sean Culligan/OZY)

Joe Wu followed with a talk on adult stem cell therapies for heart disease. His work, which is funded by a CIRM disease team grant, involves making heart cells called cardiomyocytes from human embryonic stem cells and transplanting these cells into patient with end stage heart failure to improve heart function. His team’s work has advanced to the point where Wu said they are planning to file for an investigational new drug (IND) application with the US Food and Drug Administration (FDA) in six months. This is the crucial next step before a treatment can be tested in clinical trials. Joe ended his talk by making an important statement about expectations on how long it will take before stem cell treatments are available to patients.

He said, “Time changes everything. It [stem cell research] takes time. There is a lot of promise for the future of stem cell therapy.”

A single protein can boost blood stem cell regeneration

Today, CIRM-funded scientists from the UCLA Broad Stem Cell Research Center reported  in Nature Medicine that hematopoietic stem cells (HSCs) – blood stem cells that generate the cell in your blood and immune system – get a helping hand after injury from cells in the bone marrow called bone progenitor cells. By secreting a protein called dickkopf-1 (Dkk1), bone progenitor cells improve the recovery and survival of blood stem cells in a culture dish and in mice whose immune systems are suppressed by irradiation.

These findings build upon a related study published by the same UCLA team last month showing that deleting a single gene in HSCs boosts blood stem cell regeneration. We covered this initial story previously on the Stem Cellar, and you can refer to it for background on the importance of stimulating the regenerative capacity of HSCs in patients that need bone marrow transplants or have undergone radiation therapy for cancer.

Dkk1 boost blood stem cell regeneration

Senior author on the study, UCLA Professor Dr. John Chute, wanted to understand how the different cell types in the bone marrow environment, or niche, interact with HSCs to enhance their ability to recover from injury and regenerate the immune system. As mentioned earlier, he and his team found that bone progenitor cells secrete Dkk1 protein in response to injury caused by exposing mice to full body irradiation. Dkk1 promoted blood stem cell regeneration in the mice and increased their survival rates.

I inquired with Dr. Chute about this seemingly beneficial relationship between HSCs and cells in the bone marrow niche.

Dr. John Chute, UCLA

Dr. John Chute, UCLA

“The precise functions of bone cells, stromal cells and endothelial cells in regulating blood stem cell fate are not completely understood,” said Dr. Chute. “Our prior studies demonstrated that endothelial cells are necessary for blood stem cell regeneration after irradiation.  The current study suggests that bone progenitor cells are also necessary for normal blood stem cell regeneration after irradiation, and that this activity is mediated by secretion of Dkk1 by the bone progenitor cells.”

He further commented in a UCLA press release:

“The cellular niche is like the soil that surrounds the stem cell ‘seed’ and helps it grow and proliferate. Our hypothesis was that the bone progenitor cell in the niche may promote hematopoietic stem cell regeneration after injury.”

Not only did Dkk1 improve HSC regeneration in irradiated mice, it also boosted the regeneration of HSCs that were irradiated in a culture dish. On the other hand, when Dkk1 was deleted from HSCs in irradiated mice, the HSCs did not recover and regenerate. Diving in deeper, the team found that Dkk1 promotes blood stem cell regeneration by direct action on the stem cells and by indirectly increasing the secretion of the stem cell growth factor EGF by bone marrow blood vessels. Taken together, the team concluded that Dkk1 is necessary for blood stem cell recovery following injury/irradiation.

After radiation, blood cells (purple) regenerated in bone marrow when mice were given DKK1 intravenously (left), but not in those that received saline solution (right). (UCLA/Nature Medicine)

After radiation, blood cells (purple) regenerated in bone marrow when mice were given DKK1 (left), but not in those that received saline solution (right). (UCLA/Nature Medicine)

Future applications for blood stem cell regeneration

When I asked Dr. Chute how his current study on Dkk1 and HSCs relates to his previous study on boosting HSC regeneration by deleting a gene called Grb10, he explained:

“In this paper we discovered the role of a niche cell-derived protein, Dkk1, and how it promotes blood stem cell regeneration after myelosuppression in mice.  In the Cell Reports paper, we described our discovery of an adaptor protein, Grb10, which is expressed by blood stem cells and the inhibition of which also promotes blood stem cell regeneration after myelosuppression. So, these are two novel molecular mechanisms that regulate blood stem cell regeneration that could be therapeutically targeted.”

Both studies offer new strategies for promoting blood stem cell regeneration in patients who need to replenish their blood and immune systems following radiation treatments or bone marrow transplants.

Dr. Chute concluded:

“We are very interested in translating our observations into the clinic for the purpose of accelerating hematologic recovery in patients receiving chemotherapy or undergoing hematopoietic stem cell transplantation.”


Related Links:

Deleting a single gene can boost blood stem cell regeneration

A serious side effect that cancer patients undergoing chemotherapy experience is myelosuppression. That’s a big word for a process that involves the decreased production of the body’s immune cells from hematopoietic stem cells (HSCs) or blood stem cells in the bone marrow. Without these important cells that make up the immune system, patients are at risk for major infections and even death.

Human blood (red) and immune cells (green) are made from hematopoietic/blood stem cells. Photo credit: ZEISS Microscopy.

Human blood (red) and immune cells (green) are made from hematopoietic/blood stem cells. Photo credit: ZEISS Microscopy.

Scientists are trying to find ways to treat cancer patients that have undergone myelosuppressive therapies, as well as patients that need bone marrow transplants to replace their own bone marrow that’s been damaged or removed. One possible solution is boosting the regenerative capacity of HSCs. Transplanting HSCs that are specially primed to reproduce rapidly into cells of the immune system could improve the outcome of bone marrow transplants in patients.

Deleting Grb10 boost blood stem cell regeneration

A CIRM-funded team from the UCLA Broad Stem Cell Research Center and the Jonsson Comprehensive Cancer Center has identified a single gene that can be manipulated to boost HSC regeneration in mice. The study, which was published in Cell Reports, found that deleting or turning off expression of an imprinted gene called Grb10 in HSCs caused these blood stem cells to reproduce more robustly after being transplanted into mice that had their bone marrow removed.

I just used another big word in that last paragraph, so let me explain. An imprinted gene is a gene that is expressed or activated based on which parent it was inherited from. Typically, you receive one copy of a gene from your mother and one from your father and both are expressed – a process called Mendelian inheritance. But imprinted genes are different – they are marked with specific epigenetic tags that silence their expression in the sperm or egg cells of the parents. Thus if you inherited an imprinted gene from your mother, the other copy of that gene from your father would be expressed and vice versa.

Scientists have discovered that imprinted genes are important for human development and also for directing what cell types adult stem cells like HSCs develop into. The team from UCLA led by senior author Dr. John Chute, was interested in answering a different question: are imprinted genes involved in determining the function of HSCs? They compared two different populations of HSCs derived from mouse bone marrow: a normal, healthy population and HSCs exposed to total body irradiation (TBI), which destroys the immune system. They discovered that the expression of an imprinted gene called Grb10 was dramatically higher in HSCs exposed to TBI compared to healthy HSCs.

Cell Reports

Deleting Grb10  increases blood stem cell regeneration in the bone marrow of irradiated mice (bottom) compared to normal mice (top). Cell Reports

Because Grb10 is an imprinted gene, the scientists deleted either the paternal or maternal copy of that gene in mice. While deleting the paternal Grb10 gene had no effect on the function of HSCs, maternal deletion dramatically boosted the capacity of HSCs to divide and make more copies of themselves. Without the maternal copy of Grb10, HSCs were able to regenerate at a much faster scale than normal HSCs.

To further prove their point, the team transplanted normal HSCs and HSCs that lacked Grb10 into TBI or fully irradiated mice. HSCs that lacked Grb10 were able to regenerate themselves and produce other immune cells more robustly 20 weeks after transplantation compared to normal HSCs.

Potential applications and future studies

This study offers two important findings. First, they discovered that Grb10 plays an important role “in regulating HSC self-renewal following transplantation and HSC regeneration in response to injury.” Second, they found that inhibiting Grb10 function in HSCs could have potential therapeutic applications for boosting “hematopoietic regeneration in the setting of HSC transplantation or following myelosuppressive injury.” Patients in need of bone marrow transplants could potentially receive more benefit from transplants of HSCs that don’t express the Grb10 gene.

In my opinion, further studies should be done to further understand the role of Grb10 in regulating HSC self-renewal and regeneration. What is the benefit of having this gene expressed in HSCs if inhibiting its expression leads to an increased regenerative capacity? Is it to prevent cancer from forming? Additionally, the authors will need to address the potential long-term side effects of inhibiting Grb10 expression in HSCs. They did report that mice that lacked the Grb10 gene did not develop blood cancers at one year of age which is good news. They also suggested that instead of deleting Grb10, new drugs could be identified that inhibit Grb10 function in HSCs.

Gene Therapy Beats Half-Matched Stem Cell Transplant in Side-by-Side Comparison to Treat ‘Bubble Baby’ Disease

If you are born with Severe Combined Immunodeficiency (SCID), your childhood is anything but normal. You don’t get to play with other kids, or be held by your parents. You can’t even breathe the same air. And, without treatment, you probably won’t live past your first year.

The bubble boy.  Born in 1971 with SCID, David Vetter lived in a sterile bubble to avoid outside germs that could kill him. He died in 1984 at 12 due to complications from a bone marrow transplant. [Credit: Baylor College of Medicine Archives]

The bubble boy. Born in 1971 with SCID, David Vetter lived in a sterile bubble to avoid outside germs that could kill him. He died in 1984 at 12 due to complications from a bone marrow transplant. [Credit: Baylor College of Medicine Archives]

This is the reality of SCID, also called “Bubble Baby” disease, a term coined in the 1970s when the only way to manage the disease was isolating the child in a super clean environment to avoid exposure to germs. The only way to treat the disorder was with a fully matched stem cell transplant from a bone marrow donor, ideally from a sibling. But as you may have guessed, finding a match is extraordinarily rare. Until recently, the next best option was a ‘half-match’ transplant—usually from a parent. But now, scientists are exploring a third, potentially advantageous option: gene therapy. Late last year, we wrote about a promising clinical trial from UCLA researcher (and CIRM Grantee) Donald Kohn, whose team effectively ‘cured’ SCID in 18 children with the help of gene therapy. Experts still consider a fully matched stem cell transplant to be the gold standard of treatment for SCID. But are the second-tier contenders—gene therapy and half-matched transplant—both equally as effective? Until recently, no one had direct comparison. That all changes today, as scientists at the Necker Children’s Hospital in Paris compare in the journal Blood, for the first time, half-matched transplants and gene therapy—to see which approach comes out on top. The study’s lead author, Fabien Touzot, explained the importance of comparing these two methods:

“To ensure that we are providing the best alternative therapy possible, we wanted to compare outcomes among infants treated with gene therapy and infants receiving partial matched transplants.”

So the team monitored a group of 14 SCID children who had been treated with gene therapy, and compared them to another group of 13 who had received the half-matched transplant. And the differences were staggering. Children in the gene therapy group showed an immune system vastly improved compared to the half-matched transplant group. In fact, in the six months following treatment, T-cell counts (an indicator of overall immune system health) rose to almost normal levels in more than 75% of the gene therapy patients. In the transplant group, that number was just over 25%. The gene therapy patients also showed better resilience against infections and had far fewer infection-related hospitalizations—all indictors that gene therapy may in fact be superior to a half-matched transplant. This is encouraging news say researchers. Finding a fully matched stem cell donor is incredibly rare. Gene therapy could then give countless families of SCID patients hope that their children could lead comparatively normal, healthy lives. “Our analysis suggests that gene therapy can put these incredibly sick children on the road to defending themselves against infection faster than a half-matched transplant,” explained Touzot. “These results suggest that for patients without a fully matched stem cell donor, gene therapy is the next-best approach.” Hear more about how gene therapy could revolutionize treatment strategies for SCID in our recent interview with Donald Kohn:

Getting the right tools for the right job

Imagine a device that sits outside the body and works like a form of dialysis for a damaged liver, filtering out the toxins and giving the liver a chance to regenerate, and the patient a chance to avoid the need for a transplant.

Or imagine a method of enhancing the number of stem cells we can harvest or generate from umbilical cord blood, enabling us to use those stem cells and offer life-saving bone marrow transplants to all the patients who don’t have a matched donor.

Well, you may not have to imagine for too long. Yesterday, our governing Board approved almost $30 million in funding for our Tools and Technology Awards and two of the successful applications are for researchers hoping to turn those two ideas into reality.

The Tools n Tech awards may not have the glamor or cache of the big money awards that are developing treatments heading towards clinical trials, but they are nonetheless an essential part of what we do.

As our Board Chair Jonathan Thomas said in a news release they focus on developing new approaches or creating new ways of overcoming some of the biggest obstacles in stem cell research.

“Sometimes even the most promising therapy can be derailed by a tiny problem. These awards are designed to help find ways to overcome those problems, to bridge the gaps in our knowledge and ensure that the best research is able to keep progressing and move out of the lab and into clinical trials in patients.”

Altogether 20 awards were funded for a wide variety of different ideas and projects. Some focus on improving our ability to manufacture the kinds of cells we need for transplanting into patients. Another one plans to use a new class of genetic engineering tools to re-engineer the kind of stem cells found in bone marrow, making them resistant to HIV/AIDS. They also hope this method could ultimately be used to directly target the stem cells while they are inside the body, rather than taking the cells out and performing the same procedure in a lab and later transplanting them back.

Dr. Kent Leach, UC Davis School of Engineering

Dr. Kent Leach, UC Davis School of Engineering

One of the winners was Dr. Kent Leach from the University of California, Davis School of Engineering. He’s looking to make a new kind of imaging probe, one that uses light and sound to measure the strength and durability of bone and cartilage created by stem cells. This could eliminate the need for biopsies to make the same measurements, which is good news for patients and might also help reduce healthcare costs.

We featured Dr. Leach in one of our Spotlight videos where he talks about using stem cells to help repair broken bones that no longer respond to traditional methods.

In living color: new imaging technique tracks traveling stem cells

Before blood stem cells can mature, before they can grow and multiply into the red blood cells that feed our organs, or the white blood cells that protect us from pathogens, they must go on a journey.

A blood stem cell en route to taking root in a zebrafish. [Credit: Boston Children's Hospital]

A blood stem cell en route to taking root in a zebrafish. [Credit:
Boston Children’s Hospital]

This journey, which takes place in the developing embryo, moves blood stem cells from their place of origin to where they will take root to grow and mature. That this journey happened was well known to scientists, but precisely how it happened remained shrouded in darkness.

But now, for the first time, scientists at Boston Children’s Hospital have literally shone a light on the entire process. In so doing, they have opened the door to improving surgical procedures that also rely on the movement of blood cells—such as bone marrow transplants, which are in essence stem cell transplants.

Reporting in today’s issue of the journal Cell, Boston Children’s senior investigator Leonard Zon and his team developed a way to visually track the trip that blood stem cells take in the developing embryo. As described in today’s news release, the same process that guides blood stem cells to the right place also occurs during a bone marrow transplant. The similarities between the two, therefore, could lead to more successful bone marrow transplants. According to the study’s co-first author Owen Tamplin:

“Stem cell and bone marrow transplants are still very much a black box—cells are introduced into a patient and later on we can measure recovery of the blood system, but what happens in between can’t be seen. Now we have a system where we can actually watch that middle step.”

And in the following video, Zon describes exactly how they did it:

As outlined in the above video, Zon and his team developed a transparent version of the zebrafish, a tiny model organism that is often used by scientists to study embryonic development. They then labeled blood stem cells in this transparent fish with a special fluorescent dye, so that the cells glowed green. And finally, with the help of both confocal and electron microscopy, they sat back and watched the blood stem cell take root in what’s called its niche—in beautiful Technicolor.

“Nobody’s ever visualized live how a stem cell interacts with its niche,” explained Zon. “This is the first time we get a very high-resolution view of the process.”

Further experiments found that the process in zebrafish closely resembled the process in mice—an indication that the same basic system could exist for humans.

With that possibility in mind, Zon and his team already have a lead on a way to improve the success of human bone marrow transplants. In chemical screening experiments, the team identified a chemical compound called lycorine that boosts the interaction between the zebrafish blood stem cell and its niche—thus promoting the number of blood stem cells as the embryo matures.

Does the lycorine compound (or an equivalent) exist to boost blood stem cells in mice? Or even in humans? That remains to be seen. But with the help of the imaging technology used by Zon and the Boston Children’s team—they have a good chance of being able to see it.

No Fear of Rejection? Partial Stem Cell Transplant Reverses Sickle Cell Disease—even without Immunosuppressant Drugs

For those who suffer from the blood disorder sickle cell disease, there is really only one cure: a full bone marrow transplant followed by a lifetime of anti-rejection, immune-suppressing drugs. But now, researchers from the National Institutes of Health are testing an attractive alternative for the sickest patients.

Sickle cell disease gets its name from a single genetic change, or mutation, that alters the shape of one’s red blood cells.. Unlike the round cells that can pass easily through the body’s blood vessels, the sickle-shaped cells clump together, clogging up blood vessels. This leads to a lifetime of severe joint pain and, in many cases, organ damage and stroke. In this country it affects primarily African Americans.

Magnified blood sample of a patient with severe sickle cell disease.

Magnified blood sample of a patient with severe sickle cell disease.

The only cure is a bone marrow transplant, in which the patient’s own bone marrow is first depleted with chemotherapy, and replaced by the donor marrow. The patient then faces a lifetime of immunosuppressant, anti-rejection medication to prevent deadly rejection or graft-versus-host disease, a potentially fatal condition where the donor cells attack the recipient’s immune system.

But what if, instead of replacing the entirety of the patient’s bone marrow, doctors only replaced some of it? Would this mix of sickle and non-sickle-shaped cells be enough to reverse the symptoms? A clinical trial published today from the NIH research team in the Journal of the American Medical Association has some encouraging results.

As lead author Dr. Matthew Hsieh noted in today’s press release:

“Typically, stem-cell recipients must take immunosuppressants all their lives. That the patients who discontinued this medication were able to do so safely points to the stability of the partial transplant regimen.”

In this study, the researchers performed partial bone marrow transplantations on 30 adults with severe sickle cell disease. After one year, they took 15 patients off the standard regimen of immunosuppressant drugs. And more than three years later, those 15 patients remain free from rejection.

These results are promising, in that a lifetime of immunosuppressants comes with its own set of negative side effects for the patient. According to the paper’s senior author Dr. John Tinsdale:

“Side effects caused by immunosuppressants can endanger patients already weakened by years of organ damage from sickle cell disease. Not having to permanently rely on this medication…means that even older patients and those with severe sickle cell disease may be able to reverse their condition.”

Indeed, the research team found that even a partial transplant—which resulted in a stable mix of both red blood cell types from donor and recipient – was sufficient to reverse the disease’s debilitating symptoms.

The results from this trial open the door to treating patients whose immune systems are already too weak—and are unable to tolerate the negative effects of a full stem cell transplant.

But even this half transplant has the risks associated with donor marrow. That is why CIRM is funding a team using a patient’s own stem cells and genetically modifying them to produce the correct version of the mutated protein. These self-transplants would be safer and open up the therapy to all patients regardless of their ability to find an immunologically matching donor. We expect a clinical trial with this approach to begin soon.

Want to know more about how CIRM-funded scientists are working toward this goal? Check out our “Spotlight on Sickle Cell Disease.”