Stem-Cell Gene Therapy for Sickle Cell Disease


Donald Kohn, a professor of pediatrics and microbiology, immunology and molecular genetics in the UCLA College of Letters and Science, and his colleagues, have successfully established the means to cure sickle-cell disease. This strategy uses hematopoietic (blood-producing) stem cells from the bone marrow of patients with sickle-cell disease in order to treat the disease itself.

This approach provides a revolutionary alternative to current treatments, since it creates self-renewing, normal blood cells by inserting a gene that abrogates the sickling properties into hematopoietic stem cells. With this technique, there is no need to identify a matched donor, and therefore, patients avoid the risk of their bodies rejecting donor cells.

During the clinical trial, the anti-sickling hematopoietic stem cells will be transplanted back into patients’ bone marrow to increase the population of “corrected” cells that make red blood cells that don’t sickle. Kohn will hopefully begin enrolling patients in the trial within three months. The first subject will be enrolled and observed for safety for six months. The second subject will then be enrolled and observed for safety for three months. If evaluations show that no problems have arisen, the study will continue with two more subjects and another evaluation, until a total of six subjects have been enrolled.

Sickle cell disease, which affects more than 90,000 individuals in the U.S., is seen primarily in people of sub-Saharan African descent. It is caused by an inherited mutation in the beta-globin gene that transforms normal-shaped red blood cells, which are round and pliable, into rigid, sickle-shaped cells. Normal red blood cells are able to pass easily through the tiniest blood vessels (capillaries) and carry oxygen to organs like the lungs, liver and kidneys. However, sickled cells get stuck in the capillaries, depriving the organs of oxygen, which can lead to organ dysfunction and failure.

Current treatments include transplanting patients with hematopoietic stem cells from a donor. This is a potential cure for the disease, but due to the serious risks of rejection, only a small number of patients have undergone this procedure, and it is usually restricted to children with severe symptoms.

“Patients with sickle-cell disease have had few therapeutic options,” Kohn said. “With this award, we will initiate a clinical trial that we hope will become a treatment for patients with this devastating disease.”

Finding for this work comes from new grants to researchers at UCLA’s Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, which total nearly $21 million.  These grants were announced Dec. 12 at a meeting of the California Institute of Regenerative Medicine (CIRM) Citizen’s Oversight Committee.  They are apart of the state agency’s Disease Team Therapy Development III initiative.

Radio Interview About my New Book


I was interviewed by the campus radio station (89.3 The Message) about my recently published book, The Stem Cell Epistles,

Stem Cell Epistles

It has been archived here. Enjoy.

A Link Between Stem Cells, Atherosclerosis, and Cholesterol


Researchers at the University of Buffalo have discovered that stem cells are involved in the inflammation that promotes atherosclerosis.

Atherosclerosis or hardening of the arteries occurs when fat, cholesterol, and other substances build up in the walls of arteries and form hard structures called plaques. With the passage of time, these plaques can grow and block the arteries, depriving tissues of oxygen and nutrition.

High serum cholesterol levels have been unequivocally linked to an increased risk of arteriosclerosis. However, the deposition of cholesterol and other molecules underneath the inner layer (intima) of arteries requires a phenomenon known as inflammation. Inflammation occurs in response to tissue damage and it involves the dilation of blood vessels, increased blood flow the damaged area, the recruitment of white blood cells to the area, and increased heart, volume, and pain at the area in question. Increased inflammation within blood vessels damages the intimal layer and allows the deposition of cholesterol and other molecules underneath it to form an atheroma or a plaque.

The stem cell link to atherosclerosis is that the bone marrow-based stem cells that make our blood cells (hematopoietic stem/progenitor cells or HSPCs) ramp up their production of white blood cells in response to increased serum cholesterol levels.

Thomas Cimato, assistant professor in the Department of Medicine in the UB School of Medicine and Biomedical Sciences, said of his publication, “Our research opens up a potential new approach to preventing heart attack and stroke, by focusing on interactions between cholesterol and the HSPCs. Cimto also suggested that these findings could lead to the development of a useful therapy in combination with statins, or a treatment in place of statins for those who cannot tolerate statins.

In Cimato’s study, high cholesterol levels were shown to cause increases in the levels of interleukin -17 (IL-17). IL-17 is a cytokine that recruits monocytes and neutrophils to the site of inflammation. IL-17 boosts levels of granulocyte colony stimulating factor (GCSF), which is a factor that induces the release of HSPCs from the bone marrow to the peripheral circulation.

Cimato also found that statin drugs reduce the number of HSPCs in circulation, but not all patients responded similarly to statins. “We’ve extrapolated to humans what other scientists previously found in mice about the interactions between LDL, cholesterol, and these HSPCs,” said Cimato.

In order to transport cholesterol through the bloodstream, cells must construct a vehicle into which the cholesterol is packaged. Cholesterol does not readily dissolve in water. Therefore, packaging cholesterol into lipoprotein particles allows for its transport around the cell. Cell use cholesterol to vary the fluidity of their membranes, and to synthesize steroid hormones. Once cholesterol is absorbed from the diet, the cells of the small intestine package cholesterol and fat into a particle known as a chylomicron.

chylomicron

Chylomicrons are released by the small intestinal cells and they travel to the liver. In the liver, chylomicrons are disassembled and the cholesterol is packaged into a particle known as a very-low density lipoprotein particle (VLDL). After its release and sojourning through the bloodstream, the VLDL looses some surface proteins and is depleted of its fat and becomes known as a low-density lipoprotein or LDL particle.  While these particles sojourn through the bloodstream, they release fat for tissues to use as an energy source.

LDL

LDL particles are gradually removed from circulation. If they build up to high concentrations, they can be taken up by a wandering white blood cell known as a macrophage. If these macrophages take up too much LDL, they can become a foam cell.  Foams cells can become lodged underneath the intimal layer of blood vessels when inflammation occurs inside blood vessels, and this is the cause of atherosclerosis.

Increased LDL levels in mice have been shown to stimulate the release of HSPCs from bone marrow and accelerate the differentiation of these cells into white blood cells (neutrophils and monocytes) that participate in inflammation.

Mice do not regulate their cholesterol levels in the same way humans do.  Cimato commented, “mice used for atherosclerosis studies have very low total cholesterol levels at baseline.  We feed then very high fat diets in order to study high cholesterol but it isn’t easy to interpret what the levels in mice will mean in humans and you don’t know if extrapolating to humans will be valid.”

Therefore, in order to properly model cholesterol regulation in their human subjects, Cimato had them take statins for a two-week period followed by one-month intervals when they were off the drugs.  “We modeled the mechanism of how LDL cholesterol affects stem cell mobilization in humans,” said Cimato.

The experiments showed that increased LDL levels tightly correlated with IL-17 levels.

IL-17 and cholesterol levels

Secondly, blood LDL levels also correlated with GCSF levels.

LDL levels and GCSF levels

Finally, increasing GCSF levels led to higher levels of circulating HSPCs.

CD34 cells and G-CSF levels

These circulating HSPCs increase the numbers of neutrophils, monocytes, and macrophages that are involved in the formation of plaque and atherosclerosis.

The next step is to determine if HSPCs, like LDL cholesterol levels are connected to stroke, cardiovascular disease and heart attacks.

Increasing Engraftment Rates of Umbilical Cord Blood Transplantations


Harvard Stem Cell Institute (HSCI) researchers have published initial results of a Phase Ib human clinical trial of a therapeutic that has the potential to improve the success of blood stem cell transplantation. This publication marks a success for the HSCI and their ability to carry a discovery from the lab bench to the clinic. This was actually the mandate for the HSCI when it was founded.

This Phase 1b safety study was published in the journal Blood, and it included 12 adult patients who underwent umbilical cord blood transplantation for leukemia or lymphoma at the Dana Farber Cancer Institute and Massachusetts General Hospital. Each patient received two umbilical cord blood units; one of which was untreated and another that was treated with a small molecule called 16,16 dimethyl prostaglandin E2 (dmPGE2). The immune systems of all 12 patients were successfully reconstituted and their bone marrow tissues were able to make blood cells. However, 10 of the 12 patients had blood formation that was solely derived from those umbilical cord blood cells that had been treated with dmPGE2.

This clinical test is now entering Phase II, during which the HSCI scientists will determine the efficacy of this treatment in 60 patients at 8 different medical centers. They expect results from this trial within 18-24 months.

The success of the HSCI depended on collaborations with scientists at different Harvard-affiliated institutions. These collaborations included 1) Leonard Zon, chair of the HSCI Executive Committee and Professor of Stem Cell and Regenerative Biology at Harvard, and his colleagues, 2) Dana-Farber Cancer Institute and Massachusetts General Hospital, led by hematologic oncologist and HSCI Affiliated Faculty member Corey Cutler, and 3) Fate Therapeutics, Inc., a San Diego-based biopharmaceutical company of which Zon is a founder, sponsored the Investigational New Drug application, under which the clinical program was conducted, and translated the research findings from the laboratory into the clinical setting.

“The exciting part of this was the laboratory, industry, and clinical collaboration, because one would not expect that much close interplay in a very exploratory trial,” Cutler said. “The fact that we were able to translate someone’s scientific discovery from down the hall into a patient just a few hundred yards away is the beauty of working here.”

Gastroenterologists have been interested in dmPGE2 for decades, because it has the ability to protect the intestinal lining from stress. However, its ability to amplify stem cell populations was identified in 2005 during a chemical screen exposing 5,000 known drugs to zebrafish embryos. Wolfram Goessling, MD, PhD, and Trista North, PhD former Zon postdoctoral fellows, were involved in that work.

“We were interested in finding a chemical that could amplify blood stem cells and we realized looking at zebrafish embryos that you could actually see blood stem cells budding from the animal’s aorta,” Zon said. “So, we elected to add chemicals to the water of fish embryos, and when we took them out and stained the aortas for blood stem cells, there was one of the chemicals, which is this 16,16 dimethyl prostaglandin E2, that gave an incredible expansion of stem cells—about a 300 to 400 percent increase.”

The dramatic effects of this molecule on blood stem cells causes Zon, who practices as a pediatric hematologist, consider how this prostaglandin could be applied to bone marrow transplantation. Bone marrow transplantations are often used to treat blood cancers, including leukemia and lymphoma. Bone marrow contains the body’s most plentiful reservoir of blood stem cells, and so patients with these conditions may be given bone marrow transplants to reconstitute their immune systems after their cancer-ravaged bone marrow has been wiped out with chemotherapy and radiation.

Zon designed a preclinical experiment, similar to the one later done with cord blood patients, in which mice undergoing bone marrow transplants received two sets of competing bone marrow stem cells, one set treated with dmPGE2 and a second untreated set.

“What we found was the bone marrow stem cells that were treated with prostaglandin, even for just two hours, had a four times better chance of engrafting in the recipient’s marrow after transplant,” he said. “I was very excited to move this into the clinic because I knew it was an interesting molecule.”

Zon and his team’s then visited the Dana Farber Cancer Institute (DFCI). There, they presented the mouse research at bone marrow transplant rounds and found physicians interested in giving the prostaglandin to patients.

“We basically sat down in a room and we brainstormed a clinical trial based on their scientific discovery, right then and there,” said Farber oncologist Corey Cutler. “They knew that it was something they could bring to the clinic, but they just didn’t know where it would fit. We said, if this molecule does what you say it does, significant utility would lie in umbilical cord blood transplants.”

A cord blood transplant is similar to a bone marrow transplant, but the blood stem cells are not from an adult donor but from the umbilical cord blood of a newborn. The degree of tissue matching is less in an umbilical cord blood transplant than in a bone marrow transplant. The umbilical cord stem cells are young and incipient and the immune system simply does not recognize them as readily as adult cells. Therefore, potentially fatal graft-versus-host disease is less common with umbilical cord blood transplants. About 10-20 percent of stem cell transplantation procedures now use umbilical cord blood. However the main disadvantage of umbilical cord blood transplantations is that the cord blood contains uses smaller amounts of cells, which makes engraftment is more difficult.

Umbilical cord blood transplants fail about 10 percent of the time. Therefore, increasing the procedure’s success would significantly help patients who do not have adult bone marrow donors, including a disproportionate number of non-Caucasian patients in North America. Increasing the engraftment rate would also allow the use of smaller umbilical cord blood units that are potentially better matches to their recipients, increasing the number of donations that go on to help patients.

Fate Therapeutics received the first green light from the US Food and Drug Administration, and the DFCI Institutional Review Board for this clinical trial. Umbilical cord blood processing was done by Dana-Farber’s Cell Manipulation Core Facility, directed by HSCI Executive Committee member Jerome Ritz, MD. There was a stumbling block in that once the human trial was underway with the first nine patients in that the protocol in use, which was developed in mice, did not translate to improved engraftment in humans.

“The initial results were very disappointing,” Cutler said. “We went back to the drawing board and tried to figure out why, and it turned out some of the laboratory-based conditions were simply not optimized, and that was largely because when you do something in the lab, the conditions are a little bit different than when you do it in a human.”

Fate Therapeutics discovered that the human cord blood was being handled at temperatures that were too cold (4-degrees Celsius) for the prostaglandin to biologically activate the stem cells. Therefore even after prostaglandin treatment, the umbilical cord blood did not show enhanced engraftment rates. Fate further demonstrated that performing the incubation of the hematopoietic stem cells at 37-degrees Celsius and increasing the incubation time from 1 hour to 2 hours elicited a much stronger gene and protein expression response that correlated with improved engraftment in animal models.

In running a second cohort of the Phase Ib trial, which included 12 patients, dmPGE2 appeared to enhance the engraftment properties of the blood stem cells in humans and was deemed safe to continue into Phase II. “It’s probably the most exciting thing I’ve ever done,” Zon said. “Basically, to watch something come from your laboratory and then go all the way to a clinical trial is quite remarkable and very satisfying.”

Producing blood cells from stem cells could yield a purer, safer cell therapy


The journal Stem Cells Translational Medicine has published a new protocol for reprogramming induced pluripotent stem cells (iPSCs) into mature blood cells. This protocol uses only a small amount of the patient’s own blood and a readily available cell type. This novel method skips the generally accepted process of mixing iPSCs with either mouse or human stromal cells. Therefore, is ensures that no outside viruses or exogenous DNA contaminates the reprogrammed cells. Such a protocol could lead to a purer, safer therapeutic grade of stem cells for use in regenerative medicine.

The potential for the field of regenerative medicine has been greatly advanced by the discovery of iPSCs. These cells allow for the production of patient-specific iPSCs from the individual for potential autologous treatment, or treatment that uses the patient’s own cells. Such a strategy avoids the possibility of rejection and numerous other harmful side effects.

CD34+ cells are found in bone marrow and are involved with the production of new red and white blood cells. However, collecting enough CD34+ cells from a patient to produce enough blood for therapeutic purposes usually requires a large volume of blood from the patient. However, a new study outlined But scientists found a way around this, as outlined by Yuet Wai Kan, M.D., FRS, and Lin Ye, Ph.D. from the Department of Medicine and Institute for Human Genetic, University of California-San Francisco has devised a way around this impasse.

“We used Sendai viral vectors to generate iPSCs efficiently from adult mobilized CD34+ and peripheral blood mononuclear cells (MNCs),” Dr. Kan explained. “Sendai virus is an RNA virus that carries no risk of altering the host genome, so is considered an efficient solution for generating safe iPSC.”

“Just 2 milliliters of blood yielded iPS cells from which hematopoietic stem and progenitor cells could be generated. These cells could contain up to 40 percent CD34+ cells, of which approximately 25 percent were the type of precursors that could be differentiated into mature blood cells. These interesting findings reveal a protocol for the generation iPSCs using a readily available cell type,” Dr. Ye added. “We also found that MNCs can be efficiently reprogrammed into iPSCs as readily as CD34+ cells. Furthermore, these MNCs derived iPSCs can be terminally differentiated into mature blood cells.”

“This method, which uses only a small blood sample, may represent an option for generating iPSCs that maintains their genomic integrity,” said Anthony Atala, MD, Editor of STEM CELLS Translational Medicine and director of the Wake Forest Institute for Regenerative Medicine. “The fact that these cells were differentiated into mature blood cells suggests their use in blood diseases.”

Using Sleeping Stem Cells to Treat Aggressive Leukemias


British scientists have discovered that aggressive forms of leukemia (blood cancers) do not displace normal stem cells from the bone marrow, but instead, put them to sleep. If the normal stem cells are asleep, it implies that they can be awakened. This offers a new treatment strategy for acute myeloid leukemia or AML.

This work comes from researchers at Queen Mary, University of London with the support of Cancer Research UK’s London Research Institute.

In the United Kingdom, approximately 2,500 people are diagnosed with AML each year. The disease strikes young and old patients and the majority of patients die from AML.

In healthy patients, the bone marrow contains hematopoietic stem cells (HSCs) that divide to form either a common myeloid precursor (CMP) or a common lymphoid precursor (CLP) that differentiate into various kinds of white blood cells or red blood cells or lymphocytes. Individuals afflicted with AML, however, have bone marrow invaded by leukemic myeloid blood cells. Since red blood cells are derived from the myeloid lineage, AML causes red blood cell deficiencies (anemia), and the patient becomes tired, and is at risk for excessive bleeding. AML patients are also more vulnerable to infection those white blood cells that fight infections are not properly formed.

HSC differentiation2

David Taussig from the Barts Center Institute at Queen Mary, University of London said that the widely accepted explanation for these symptoms is that the cancerous stem cells displace or destroy the normal HSCs.

However, Taussig and his colleagues have found in bone marrow samples from mice and humans with AML contain plenty of normal HSCs. Thus, AML is not destroying or displacing the HSCs. Instead, the cancerous stem cells appear to be turning them off so that they cannot form HSCs. If Taussig and his coworkers and collaborators had determine how these leukemic myeloid blood cells are shutting off the normal HSCs, they might be able to design treatments to turn them back on.

Such a treatment strategy would increase the survival of AML patients. Only 40% of younger patients are cured of AML, and the cure rate for older patients in much lower. Current treatments that include chemotherapy and bone marrow transplants are not terribly successful with older patients.

Taussig’s group examined the levels of HSCs in the bone marrow of mice that had been transplanted with human leukemic myeloid cells from AML patients. They discovered that the numbers of HSCs stayed the same, but these same HSCs failed to transition through the developmental stages that result in the formation of new blood cells. When Taussig and his group examined bone marrow from 16 human AML patients, they discovered a very similar result.

Even though AML treatment has come a long way in the last ten years, there is still an urgent need for more effective treatments to improve long-term survival. This present study greatly advances our understanding of what’s going on in the bone marrow of AML patients. The future challenge is to turn this knowledge into treatments.

Under normal circumstances, stress on the body will boost HSC activity. For example, when the patient hemorrhages, the HSCs kick into action to produce more red blood cells that were lost during the bleed. However, the cancer cells in the bone marrow are somehow over-riding this compensatory mechanism and the next phase of this research will determine exactly how they do it.

Stem Cell Gene Therapy For An Inherited Neurological Disease


Scientists at the University of Manchester in the United Kingdom have used stem cell gene therapy to treat a fatal genetic brain disease in mice. Sanfilippo is a fatal, inherited condition that causes progressive dementia in children. This particular treatment strategy could also be used to treat other types of neurological, inherited diseases. The Manchester team hopes to bring this strategy to a clinical trial within two years.

Sanfilippo afects one in 89,000 children in the United Kingdom and is an untreatable “mucopolysaccharide disease ” or MPS disease. MPS diseases involve an abnormal storage of mucopolysaccharides. This abnormal storage results from the absence of a specific enzyme. Without the enzyme, the breakdown process of mucopolysaccharides is incomplete. Partially broken down mucopolysaccharides accumulate in the body’s cells causing progressive damage. The storage process can affect appearance, development, and the function of various organs of the body. Each MPS disease is caused by the deficiency of a specific enzyme.

Patients with Sanfilippo are unable to degrade heparan sulfate. There are four different types of Sanfilippo, which is also called MPS type III. MPS type IIIA results from a deficiency in the enzyme N-sulfoglucosamine sulfohydrolase, MPS type IIIB lacks N-Acetylglucosaminidase, MPS type IIIC has an absence in Acetyl-CoA:alpha-glucosaminide-acetyltransferase, and MPS type IIID lacks N-acetylglucosamine 6-sulphatase. In all four forms of MPS III, excessive heparan sulphate storage occurs in the brain, leading to its progressive deterioration; the amount of heparan sulphate storage in other tissues influences the extent of physical symptoms. Children eventually lose the ability to walk and swallow.

Brian Bigger from the University of Manchester’s Institute of Human Development led this research into therapies for MPS type IIIA. According to Bigger, bone marrow transplants have been used to treat similar diseases (e.g., Hurler syndrome). In this case, gene therapy was used to introduce the missing enzyme into the transplanted cells. Unfortunately, this did not work terribly well because the white blood cells from the bone marrow did not make enough of the enzyme to treat the disease.

A fraction of the white blood cells made bone marrow are called monocytes, and some of the monocytes traffic to the brain to become microglia. Since microglia are made by hematopoietic stem cells (HSCs) in the bone marrow, genetic engineering of cultured HSCs should increase expression of the missing enzyme in microglia. In previous experiments, HSCs were engineered with viruses to express the missing enzyme, but this expression was poor in microglia.

To fix this problem, Bigger and his team increased enzyme expression in the engineered HSCs in bone marrow. They used a gene control region from the “pyruvate kinase” gene, which is a very highly expressed gene. This increased expression of the missing enzyme to five times the normal levels and to 11% of normal levels in the microglia cells in the brain. The enzyme

This type of treatment corrects the inflammation in the brain and completely corrects the hyperactivity behavior in mice with Sanfilippo. Bigger adds, “We now hope to work to a clinical trial in Manchester in 2015.”

Bigger and his colleagues are manufacturing a viral vector to deliver genetic material into cells for use in humans and they hope to use this in a clinical trial with patients at Central Manchester University Hospital NHS Foundation Trust by 2015.

This stem cell gene therapy approach was recently shown by Italian scientists to improve conditions in patients with a similar disease that affects the brain called metachromatic leukodystrophy. Bigger refined the vector used bythe Italian group.

According to Bigger, this approach might have the potential to treat several neurological genetic diseases.

Using Human Induced Pluripotent Stem Cells to Study Diamond Blackfan Anemia


Diamond-Blackfan Anemia or DBA results from mutations in a gene on chromosome 19 (in most cases). Mutations in the ribosomal protein S19 affects the ability of blood cells to make protein and causes low numbers of red blood cells. DBA patients are dependent on blood transfusions, but some are cured, to some extent at least, by bone marrow transplants. Unfortunately, some DBA patients have severe side effects from bone marrow transplants, which means that bone marrow transplants are not a panacea for all DBA patients.

Fortunately, Michell J. Weiss and his colleagues at the Children’s Hospital of the Philadelphia (CHOP) have used human induced pluripotent stem cells (iPSCs) to study DBA at the molecular level and even develop the beginnings of a cure for DBA patients. Weiss collaborated with Monica Bessler, Philip Mason, and Deborah French, all of whom work at CHOP.

Remember that red blood cells are made inside the bone marrow of the patient by hematopoietic stem cells (HSCs). HSCs divide to renew themselves, and to produce a daughter cell that will differentiate into one of several different types of blood cells. As a kind of gee-wiz number, a healthy adult person will produce approximately 10[11]–10[12] (100 billion to 1 trillion) new blood cells are produced daily in order to maintain steady state levels in the peripheral circulation.

In DBA patients, the bone marrow is empty of red blood cells. In order to get a better idea why, Weiss and his team isolated fibroblasts from the skin of DBA patients, and used genetic engineering techniques to convert them into iPSCs. When Weiss and his group tried to differentiate these iPSCs derived from DBA patients into red blood cells, they were not able to make normal red blood cells. However, Weiss and his colleagues used different genetic engineering techniques to fix the mutation in these iPSCs. After fixing the mutation, these cells could be differentiated into red blood cells. This experiment showed that it is possible to repair a patient’s defective cells.

This is a proof-of-principle experiment and there are many hurdles to overcome before this type of experiment can be done in the clinic to DBA patients. However, these iPSCs can play a vital role in deciphering some of the mysteries surrounding this disease. For example, two family members may have exactly the same mutation, but only one of them shows the disease whereas the other does not. Since iPSCs are specific to the patient from whom they were made, Weiss and his group hope to compare the molecular differences between them and understand the difference in expression of this disease.

Also, these cells offer a long-lasting model system for testing new drugs or gene modifications that may offer new treatments that are personalized to individual patients.

Weiss and his research group used this same technology to test drugs for the often aggressive childhood leukemia, JMML or Juvenile Myelomonocytic Leukemia. Once again, iPSCs were made from JMML patients and differentiated into myeloid cells, which divided uncontrollably just as the original myeloid cells from JMML patients.

Weiss and his colleagues used these cells to test two drugs, both of which are active against JMML. One of them is an inhibitor of the MEK kinase that was quite active against these cells. This illustrates how iPSCs can be used to test personalized treatment regimes for patients.

The stem cell core facility at CHOP is also in the process of making iPCS lines for several inherited diseases: dyskeratosis congenita, congenital dyserythropoietic anemia, thrombocytopenia absent radii, Glanzmann’s thrombasthenia, and Hermansku-Pudlak syndrome.

The even longer term goal is the use these lines to specifically study the behavior of such cells in culture and under certain conditions, test various drugs on them, and to develop treatment strategies on them as well.

Stem Cell Gene Therapy for Sickle Cell Disease Moves Toward Clinical Trials


UCLA stem cell researchers and “gene jockeys” have successfully proven the efficacy of using genetically engineered hematopoietic (blood cell-making) stem cells from a patient’s own bone marrow to treat sickle-cell disease (SCD).

In a study led by Donald Kohn, professor of pediatrics and microbiology at the UCLA Eli & Edythe Broad Center of Regenerative Medicine & Stem Cell Research, an “anti-sickling” gene was introduced into the hematopoietic stem cells (HSCs) from patients with SCD. Because the HSCs divide continuously throughout the life of the individual, all the blood cells they make will possess the anti-sickling gene and will therefore no sickle. This breakthrough gene therapy technique is scheduled to begin clinical trials by early 2014.

SCD results from a specific mutation in the beta-globin gene. Beta-globin is one of the two proteins that makes the multisubunit protein hemoglobin. Hemoglobin is a four-subunit protein that ferries oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. It is tightly packed into each red blood cell.

The structure of hemoglobin, each subunit is in a different color.
The structure of hemoglobin, each subunit is in a different color.

Hemoglobin has a very high affinity for oxygen when oxygen concentrations are high, but a low affinity for oxygen when oxygen concentrations are low. Therefore, hemoglobin does a very good job of binding oxygen when it is in the lungs, where oxygen is plentiful, and a very good job of releasing oxygen in the tissues, where oxygen is not nearly as plentiful. This adaptive ability displayed by hemoglobin is the result of cooperativity between the four polypeptide chains that compose hemoglobin. Two of these polypeptide chains are alpha-globin proteins and the other two a beta globin proteins. Hemoglobin acts as though it is an alpha-beta dimer, or as though it is composed of two copies of an alpha-globin.beta-globin pair. The interactions between these polypeptide chains and the movement of the hemoglobin subunits relative to each other creates the biochemical properties of hemoglobin that are so remarkable.

A mutation in the beta-globin gene that substitutes a valine residue where there should be a glutamic acid residue (position number 6), creates a surface on the outside of the beta-globin subunit that does not like water, and when oxygen concentrations drops, the mutant hemoglobin molecule changes shape and this new water-hating surface becomes a site for protein polymerization.

Sickle cell hemoglobin

The mutant hemoglobin molecules for long, stiff chains that deform the red blood cells into a quarter moon-shaped structure that clogs capillaries.

Sickle cell RBCs

 

This new therapy seeks to correct the genetic mutation by inserting into the genome of the HSC that makes the abnormal red blood cells a gene for beta-globin that encodes a normal version of beta globin rather than a version of it that causes sickle-cell disease.  By introducing those engineered HSCs back into the bone marrow of the SCD patient, the engineered HSCs will make normal red blood cells that do not undergo sickling under conditions of low oxygen concentration.

Dr. Kohn noted that the results from his research group “demonstrate that our technique of lentiviral transduction is capable of efficient transfer and consistent expression of an effective anti-sickling beta-globnin gene in human SCD bone marrow progenitor cells, which improved the physiologic parameters of the resulting red blood cells.” Dr. Kohn’s statement may lead the reader to believe that this was done in a human patient, but that is not the case.  All this work was done in culture and in laboratory animals.

Kohn and his co-workers showed that in laboratory experiments, genetically engineered HSCs from SCD patients produced new non-sickled blood cells at a rate that would effectively allow SCD patients to show significant clinical improvement.  These new red blood cells also survived longer than those made by the nonengineered SCD HSCs.  The in vitro success of this technique has convinced the US Food and Drug Administration to grant Kohn the right to conduct clinical trials in SCD patients by early next year.

SCD affects more than 90,000 patients in the US, but it most affects people of sub-saharan African descent.  As stated before, the mutation that causes SCD produces red blood cells that are stiff, long, and get stuck in the tiny blood vessels known as capillaries that feed organs.  SCD causes multi-organ dysfunction and failure and can lead to death.

Sickle_cell_01

Treatment of SCD include bone marrow transplants, but immunological rejection of such transplants remains a perennial problem.   The success rate of bone marrow transplants is low and it is typically restricted to those patients with very severe disease who are on the verge of dying.

If Kohn’s clinical trials are successful, this stem cell-based treatment will hopefully become the gold standard for treatment of patients with SCD.  One potential problem with this technique is the use of lentiviral vectors to introduce a new gene into the HSCs.  Because lentiviruses are retroviruses, they insert their DNA into the genome of the host cells.  Such insertions can produce mutations, and it will be incumbent on Kohn and his colleagues to carefully screen each transformed HSC line to ensure that the insertion is not problematic and that the transformed cells are not sick or potentially tumorous.  However, such a vector is necessary in order to ensure permanent residence of the newly-introduced gene.

Even with these caveats, Kohn’s SCD treatment should go forward, and we wish all the best to Dr. Kohn, his team, and to the patients treated in this trial.

Directly Programming Skin Cells to Become Blood-Making Stem Cells


Within our bones lies a spongy, ribbon-like material called bone marrow.  Bone marrow is home to several different populations of stem cells, but the star of the stem cell show in the bone marrow are the hematopoietic stem cells or blood-making stem cells.   When a patient receives a bone marrow transplant these are the stem cells that are transferred, take up residence in the new bone marrow, and begin making new red and white blood cells for the patient.  Because bone marrow is such a precious commodity from a clinical standpoint, finding a way to make more of it is essential.

Hematopoiesis from Pluripotent Stem Cell

A new report from scientists at Mt Sinai Hospital in New York suggest that the transfer of specific genes into skin fibroblasts can reprogram mature, adult cells into hematopoietic stem cells that look and function exactly like the ones normally found within our bone marrow.

A research team at the Icahn School of Medicine at Mount Sinai led by Kateri Moore screen a panel of 18 different genes for their ability to induce blood-forming activity when transfected into fibroblasts. Kateri and others discovered that a combination four different genes (GATA2, GFI1B, cFOS, and ETV6) is sufficient to generate blood vessel precursors with the subsequent appearance of hematopoietic stem cells. These cells expressed several known hematopoietic stem cell surface proteins (CD34, Sca1 and Prominin1/CD133).

Reprogramming of fibroblasts to HSCs

“The cells that we grew in a Petri dish are identical in gene expression to those found in the mouse embryo and could eventually generate colonies of mature blood cells,” said Carlos Filipe Pereira, first author of this paper and a postdoctoral research fellow in Moore’s laboratory.

The combination of gene factors that we used was not composed of the most obvious or expected proteins,” said Ihor Lemischka, a colleague of Dr. Moore at Mt. Sinai Hospital.  “Many investigators have been trying to grow hematopoietic stem cells from embryonic stem cells, but this process has been problematic.  Instead, we used mature mouse fibroblasts, pick the right combination of proteins, and it worked.”

According to Pereira, there is a rather critical shortage of suitable donors for blood stem cells transplants.  Bone marrow donors are currently necessary to meet the needs of patients suffering from blood diseases such as leukemia, aplastic anemia, lymphomas, multiple myeloma and immune deficiency disorders.  “Programming of hematopoietic stem cells represents an exciting alternative,” said Pereira.

“Dr. Lemischka and I have been working together for over 20 years in the fields of hematopoiesis and stem cell biology,” said Kateri Moore.  “It is truly exciting to be able to grow these blood forming cells in a culture dish and learn so much from them.  We have already started applying this new approach to human cells and anticipate similar success.”

Stem Cells to Make Red Blood Cells and Platelets in Culture


A collaborative study between Boston University School of Public Health and researchers at Boston Medical Center has used induced pluripotent stem cells to make unlimited numbers of human red blood cells and platelets in culture.

This finding could potentially reduce the need for blood donations to treat patients who require blood transfusions. Such research could also help researchers examine fresh and new therapeutic targets in order to treat blood diseases such a sickle-cell anemia.

The lead scientist on this project was George Murphy, assistant professor of medicine at Boston University School of Medicine and co-director of the Center for Regenerative Medicine at Boston University. Murphy’s main collaborator was David Sherr, professor of environmental health at Boston University School of Medicine and the Boston University School of Public Health.

Induced pluripotent stem cells or iPSCs are made from adult cells by applying genetic engineering technology to the adult cells that introduces genes into them. The introduction of four specific genes de-differentiates the adult cells into pluripotent stem cells that can, potentially, differentiate into any adult cell type. This makes iPSCs powerful tools for research and potential therapeutic agents for regenerative medicine.

In this study, Murphy and others used iPSCs from the CreM iPS Cell Bank and exposed them to a battery of different growth factors in order to push them to differentiate into different adult cell types. They were looking for the precise cocktail to differentiate iPSCs into red blood cells, since they wanted to further study red blood cell development in detail.

One group of compounds given to the set of iPSCs were molecules that activate “aryl hydrocarbon” receptors. Aryl hydrocarbon receptors (AHRs) play important roles in the expansion of hematopoietic stem cells, which make blood cells, since antagonism of AHRs promotes expansion of hematopoietic stem cells (see AE Boitano et al.,Science 10 September 2010: Vol. 329 no. 5997 pp. 1345-1348). In this case, however, Murphy and his colleagues observed a dramatic increase in the production of functional red blood cells and platelets in a short period of time. THis suggests that the ARH is important for normal blood cell development.

Aryl Hydrocarbon Receptor
Aryl Hydrocarbon Receptor

“This finding has enabled us to overcome a major hurdle in terms of being able to produce enough of these cells to have a potential therapeutic impact both in the lab and, down the line, in patients,” said Murphy. “Additionally, our work suggests that AHR has a very important biological function in how blood cells form in the body.”

“Patient-specific red blood cells and platelets derived from iPSC cells, which would solve problems related to immunogenicity and contamination, could potentially be used therapeutically and decrease the anticipated shortage and the need for blood donation,” added Murphy.

iPS-derived cells have tremendous potential as model systems in which scientists can test and develop new treatments for disease, given that such diseases can be constructed in the laboratory. These iPSC-derived red blood cells could be used by malaria researchers, and IPSC-derived platelets could be used to explore cardiovascular disease and treatments for blood clotting disorders.

Because my mother died from myelodysplasia, this finding has some personal interest to me. Mom had a difficult blood type to match, since she had the Bombay blood type (H). Finding blood for her was a major tour de force, and as she received blood that was less and less well matched to her body, she suffered the ravages of poorly matched blood. A treatment of red blood cells made from IPSCs derived from her own cells might have extended her life and even improved her quality of life in her later years.

I look forward to this research eventually culminating in clinical trials.

RNA Molecule Protects Stem Cells During Inflammation


During inflammation and infection, bone marrow stem cells that make blood cells (so-called hematopoietic stem cells or HSCs) and progenitor cells are stimulated to proliferate and differentiate into mature immune cells. This especially the case for cells of the so-called “myeloid lineage.

Hematopoietic Stem Cells (HSCs) are able to differentiate into cells of two primary lineages, lymphoid and myeloid. Cells of the myeloid lineage develop during the process of myelopoiesis and include Granulocytes, Monocytes, Megakaryocytes, and Dendritic Cells. Circulating Erythrocytes and Platelets also develop from myeloid progenitor cells.

Hematopoiesis from Multipotent Stem Cell

Repeated infections and inflammation can deplete these cell populations, which leads to serious blood conditions and increased incidence of cancer.

A research team from the California Institute of Technology, led by Nobel Prize winner, David Baltimore, has discovered a small RNA molecule called microRNA-146a (miR-146a) that acts as a safety valve to protect HSCs during chronic inflammation. These findings also suggest that deficiencies for miR-146a might contribute to blood cancers and bone marrow failure.

Baltimore and his colleagues bred mice that lacked miR146a. MicroRNAs are very short RNA molecules (around 22 base pairs long) that regulate the activities of other genes. They control the expression of genes at the transcriptional and post-transcriptional level. In the case of miR146a(-) mice, whenever these mice were subjected to chronic inflammation, the total number and quality of their HSCs declined steadily. In contrast, miR-146a(+) mice were better able to maintain their levels of HSCs despite long-term inflammation.

The lead author of this work, Jimmy Zhao, said, “This mouse with genetic deletion of miR146a is a wonderful model with which to understand chronic inflammation-driven tumor formation and hematopoietic stem cell biology during chronic inflammation.”

Zhao also noted the surprising result that the deletion of one microRNA could cause such a profound and dramatic pathology. This underscores the critical and indispensable function of miR-146a in protecting the quality and longevity of HSCs. This work also establishes the connection between chronic inflammation and bone marrow failure and diseases of the blood.

Even more exciting is the prospect of synthesizing anti-inflammatory drugs that could treat blood disorders. In fact, it is possible that artificially synthesized miR146a might be an effective treatment if small RNAs can be effectively delivered to specific cells.

Zhao also noted the close resemblance that this mouse model has to the blood disorder human myelodysplastic syndrome or MDS. MDS is a form of pre-leukemia that causes severe anemia and a dependence on blood transfusions. MDS usually leads to acute myeloid leukemia. Further study of Zhao and Baltimore’s miR146a(-) mouse might lead to a better understanding of MDS and potential new treatments for MDS.

David Baltimore, senior author of this paper, said, “This study speaks of the importance of keeping chronic inflammation in check and provides a good rationale for broad use of safer and more effective anti-inflammatory molecules. If we can understand what cell types and proteins are critically important in chronic-inflammation-driven tumor formation and stem cell exhaustion, we can potentially design better and safer drugs to intervene.”

See Jimmy L Zhao, Dinesh S Rao, Ryan M O’Connell, Yvette Garcia-Flores, David Baltimore. MicroRNA-146a acts as a guardian of the quality and longevity of hematopoietic stem cells in mice.  DOI: http://dx.doi.org/10.7554/eLife.00537Published May 21, 2013.  Cite as eLife 2013;2:e00537.

Postscript: This paper is especially meaningful to me because my mother died of MDS. The fact that a better model system for MDS has been established is an essential first step in finding a treatment for this killer disease.

Discarded White Blood Cells Induce Relocation of Blood Stem Cells


Researchers at the Fundación Centro Nacional de Investigaciones Cardiovasculares or CNIC in Madrid, Spain have discovered that the clearance of the white blood cells called neutrophils induces the release of blood cell making stem cells into the bloodstream.

Our blood consists of a liquid component known as plasma and cells collectively known as “formed elements.” Formed elements include red blood cells and a whole encore of white blood cells. Red blood cells contain hemoglobin that ferry oxygen from the lungs to the tissues. White blood cells come in two flavors: granulocytes, which contain granules, and agranulocytes, which are devoid of granules.

Granulocytes are a subgroup of white blood cells characterized by the presence of cytoplasmic granules. Granulocytes are formed in the bone marrow and can be classified as basophils, eosinophils, or neutrophils. These particular cell types are named according to their distinct staining characteristics using hematoxylin and eosin (H&E) histological preparations. Granules in basophils stain dark blue, eosinophilic components stain bright red, and neutrophilic components stain a neutral pink.

Granulocytes

The most abundant white blood cells is known as a neutrophil. Neutrophils comprise 50-70% of all white blood cells and are a critical component of the immune system. When immature, neutrophils have a distinct band-shaped nucleus that changes into a segmented nucleus following maturation. Neutrophils are normally in circulating blood, but they migrate to sites of infection via chemotaxis under the direction of molecules such as Leukotriene B4. The main function of neutrophils is to destroy microorganisms and foreign particles by phagocytosis.

Granulocytes-blood smear

Because neutrophils are packed with granules that are toxic to microorganisms and our own cells, damaged neutrophils can spill a plethora of pernicious chemicals into our bodies. To prevent neutrophils from aging and becoming a problem, they live hard and die young. in the vicinity of 1011 neutrophils are eliminated every day. They are rapidly replaced, however, and the means of replacement includes stem cell mobilization from the bone marrow to the bloodstream.

Workers in the laboratory of Andrés Hidalgo have discovered what happens to the discarded neutrophils. Earlier work in mice showed that injections of dead or dying neutrophils increase the number of circulating blood cell-making stem cells. Therefore, something about dead neutrophils causes the hematopoietic stem cells to move from the bone marrow to the bloodstream. By following marked, dying neutrophils, Hidalgo and his coworkers showed that the neutrophils went to the bone marrow to die. While in the bone marrow, the dying neutrophils were phagocytosed (gobbled up) by special cells called macrophages.

Once these bone marrow-located macrophages phagocytose aged neutrophils, they begin to signal to hematopoietic stem cells in the bone marrow, and these signals drive them to move from the bone marrow to the bloodstream to replenish the neutrophil population.

Hidalgo admits that even though his research has produced some unique answers to age-old questions, it also poses almost as many questions as it answers. For example, Hidalgo and his colleagues showed that neutrophils follow a circadian or day/night rhythm and this has implications for diseases. For instance, the vast majority of heart attacks are in the morning. Does this have something to do with neutrophil aging cycles?

“Our study shows that stem cells are affected by day/night cycles thanks to this cell recycling . It is possible that the malign stem cells that cause cancer use this mechanism to relocate, for example, during metastasis,” said Hidalgo.

Daily changes in neutrophil function could be part of the reason that acute cardiovascular and inflammatory events such as heart attack, sepsis or stroke tend to occur during particular times of the day.

“Given that this new discovery describes fundamental processes in the body that were unknown before, it will now be possible to interpret the alterations to certain physiological patterns that occur in many diseases,” Hidalgo said.

See Cell 2013; 153(5): 1025 DOI:10.1016/j.cell.2013.04.040.

The Surprising Ability of Blood Stem Cells to Respond to Emergencies


A research team from Marseille, France has revealed an unexpected role for hematopoietic stem cells (the cells that make blood cells): not only do these cells continuously renew our blood cells, but in emergencies these cells can make white blood cells on demand. that help the body deal with inflammation and infection. This stem cell-based activity could be utilized to protect against infection in patients who are undergoing a bone marrow transplant.

The research team that discovered this previously unknown property of hematopoietic stem cells were from INSERM, CNRS and MDC led by Michael Sieweke of the Centre d’Immunologie de Marseille Luminy and the Max Delbruck Centre for Molecular Medicine, Berlin-Buch.

Cells in our blood feed, clean, and defend our tissues, but their lifespan is limited. The life expectancy of a red blood cell rarely exceeds three months, our platelets die after ten days and the vast majority of our white blood cells survive only a few days.

Therefore, our bodies must produce replacements for these dying cells in a timely manner and in the right quantities and proportions. Blood cells replacement is the domain of the hematopoietic stem cells, which are nested in the bone marrow; that soft tissue inside long bones of the chest, spine, pelvis, upper leg and shoulder. Bone marrow produces and releases billions of new cells into out blood every day. To do this, hematopoietic stem cells must not only divide but their progeny must also differentiate into specialized cells, such as white blood cells, red blood cells, platelets, and so on.

For several years, researchers have been interested in how the process of differentiation and specialization is triggered in stem cell progeny. Sieweke and his colleagues discovered in previous work that hematopoietic stem cell progeny are not preprogrammed to assume a particular cell fate, but respond to environmental cues that direct them to become one cell type or another.

Nevertheless, it is still unclear how stem cells respond during emergencies? How are hematopoietic stem cells able to meet the demand for white blood cells during an infection? Recently, the answer was considered clear: the stem cells neither sensed nor responded to the signals sent to induce their progeny to differentiate into particular cell types. They merely proliferated and their progeny responded to the available signals and differentiated into the necessary cell fates. However, Sieweke’s research team has found that rather than being insensitive to these inductive signals meant for their progeny, hematopoietic stem cells perceive these environmental signals and, in response to them, manufacture the cells that are most appropriate for the danger faced by the individual.

Dr. Sandrine Sarrazin, INSERM researcher and co-author of the publication, said, “We have discovered that a biological molecule produced in large quantities by the body during infection or inflammation directly shows stem cells the path to take.”

Sieweke added, “Now that we have identified this signal, it may be possible in the future to accelerate the production of these cells in patients facing the risk of acute infection.” He continued: “This is the case for 50,000 patients worldwide each year who are totally defenseless against infections just after bone marrow transplantation. Thanks to M-CSF [monocyte-colony stimulating factor], it may be possible to stimulate the production of useful cells while avoiding to produce those that can inadvertently attack the body of these patients. They could therefore protect against infections while their immune system is being reconstituted.”

To reach their conclusions the team had to measure the change of state in each cell. This was a terrifically difficult challenge since the stem cells in question are very rare in the bone marrow: only one cell in 10,000 in the bone marrow of a mouse. Furthermore, the hematopoietic stem cells are, by appearance, indistinguishable from their progeny, the hematopoietic progenitor cells. Therefore, this experiment was tedious and difficult, but it proved that M-CSF could instruct single hematopoietic stem cells to differentiate into the monocyte lineage.

The clinical use of M-CSF will hopefully follow in the near future, but for now, this is certainly an exciting finding that may lead to clinical trials and applications in the future.

Rejuvenating the Blood of Older People With New Stem Cells


Like it or not, the blood of young people and older people is different. Can the blood of an older person be rejuvenated and made young again?

In an article published recently by the scientific journal Blood, a research group at Lund University in Sweden details a series of experiments in which they rejuvenated the blood of mice by reversing, or re-programming, the blood cell-making stem cells.

Stem cell populations throughout the body form and replace cells in the body and help repair organs. Stem cells have the capability to divide an unlimited number of times, and when they divide, one cell remains a stem cell and the other matures into another cell type needed by the body.

Martin Wahlestedt, a doctoral student in stem cell biology at the Faculty of Medicine at Lund University, and principal author of the article explained, “Our ageing process is a consequence of changes in our stem cells over time.” Wahlestedt continued, “Some of the changes are irreversible, for example damage to the stem cells’ DNA, and some could be gradual changes, known as epigenetic changes, that are not necessarily irreversible, even if they are maintained through multiple cell divisions. When the stem cells are re-programmed, as we have done, the epigenetic changes are cancelled.”

Shinya Yamanaka was awarded the Nobel Prize in Medicine last year for this very discovery.

Blood composition changes as we age. For example, blood from a young person contains a certain mix of B- and T-lymphocytes and myeloid cells, but in older people, according to Wahlestedt, “In older people, the number of B- and T-lymphocytes falls, while the number of myeloid cells increases.” Therefore, when an elderly person is affected by leukemia, the cancer usually originates in the myeloid cells, since the elderly have more myeloid cells. Being able to refurbish the blood, as Martin and his colleagues have done in their mouse studies, therefore, presents interesting possibilities for future treatment.

“There is a lot of focus on how stem cells could be used in different treatments, but all that they are routinely used for in clinical work today is bone marrow transplants for diseases where the blood and immune systems have to be regenerated”, said Martin Wahlestedt, continuing:  “A critical factor that gives an indication of whether the procedure is going to work or not is the age of the bone marrow donor. By reversing the development of the stem cells in the bone marrow, it may be possible to avoid negative age-related changes.”

Even if the composition of the blood in old and young mice is remarkably like that in young and elderly people, Martin Wahlestedt stressed that at this stage; the technology is only at the basic research stage and is far from a functioning treatment. The research group is pleased with the results, because they indicate that it may not primarily be damage to DNA that causes blood to age, but rather the reversible epigenetic changes.

Transplantable Hematopoietic Stem Cells Made From Induced Pluripotent Stem Cells


Induced pluripotent stem cells (iPSCs) are made from adult cells by genetic manipulation. In short, four different genes, all of which encode DNA-binding proteins that direct gene expression, are introduced into adult cells. The four proteins direct a gene expression program that dedifferentiates a small proportion of the cells to become stem cells that greatly resemble embryonic stem cells.

These iPSCs have the capacity to differentiate into any cell type in the adult body, but there are particular cell types that have proven difficult for iPSCs to make. One of these is the blood cell-making stem cell that normally resides in bone marrow. This stem cells, the hematopoietic stem cell or HSC. Several different types of blood cells have been made from iPSCs, but, again, making HSCs from iPSCs has proven elusive.

A paper from the laboratories of Leslie Silberstein and Daniel Tenen at the Harvard Stem Cell Institute and Harvard Medical School has used a new approach to make HSCs from iPSCs. In this paper, Giovanni Amabile and colleagues injected undifferentiated HSCs into mice whose immune systems were compromised to prevent them from rejecting the implanted cells. The iPSCs formed tumors known as teratomas that contained a wide variety of cells types that included HSCs. Isolation of these HSCs from the teratomas produced pure cultures of HSCs that could be used to reconstitute the immune system of mice.

Isolation of HSCs from teratomas is actually rather easy, since very high-affinity antibodies can bind to the surfaces of HSCs and facilitate their isolation. Once isolated, Amabile and others used them to reconstitute the immune system of imunodeficient mice. This demonstrates that HSCs isolated in this manner are transplantable.

Embryonic stem cells can be converted to HSCs by co-culturing them with OP9 cells, a special mouse bone marrow-derived cell line. If iPSCs were injected into mice with OP9 cells, the number of HSCs they made in culture greatly increased.

OP9 cells
OP9 cells

The cells produced by the HSCs were evaluated for functionality, and the white blood cells made all the right molecules, ate bacteria like they should and also moved like white blood cells. Antibody making cells all made antibodies and T cells responded just as they should and made all the right molecules in response to stimulation. Thus, these HSCs were normal HSCs and produced blood cells that were completely normal from a functional perspective.

This technique could provide a way to make HSCs for human antibody production, drug screening, and, possibly, transplanation. Unfortunately, if these cells have been passed through an animal, there is no way they can be used for human treatments, since they might have picked up animal viruses and animal sugars on their surfaces. If these procedure could be refined to eliminate passing the iPSCs through an animal , then this technique could certainly be used to make transplantable HSCs for the treatment of human diseases of the blood.

See Amabile et al., Blood 121(8):1255-1264.