Intravenous Bone Marrow For Stroke: Clinical Trial


Akihiko Taguchi from the Institute of Biomedical Research and Innovation in Kobe, Japan, in collaboration with a whole host of colleagues from various places treated stroke with their own bone marrow. This is a Phase 1/2 clinical trial but it is a very small trial that was neither blinded not placebo-controlled. Therefore, while this trial is useful, the results are of limited value.

In this clinical trial, 12 stroke patients were divided into two groups, one of which received 25 milliliters and the other of which received 50 milliliters of bone marrow cells 7-10 days after their strokes. The bone marrow cells were administered intravenously. To isolate bone marrow cells, the so-called “mononuclear fraction” was isolated from whole bone marrow samples that came from bone marrow aspirations. Patients were evaluated by means of brain imaging to measure blood flow in their brains, and a series of neurological tests. The National Institute of Health Stroke Scale or NIHSS scores were used to grade the neurological capabilities of each patient. Patients were examined 1 month and then 6 months after treatment.

All treated patients were compared with the records of other stroke patients in the past who were not treated with bone marrow cells. These comparisons showed that the bone marrow-treated patients showed a trend towards improved neurological outcomes. Statistically, the bone marrow-treated patients had significantly better blood flow and oxygen consumption in their brains 6 months after treatment compared to the historic controls. Also, the NIHSS scores of the bone marrow-treated patients were also significantly better than those of the historic controls. Patients who received the higher doses of bone marrow cells did better than those who received the lower doses.

There were also no apparent adverse effects to administering the bone marrow cells. One patient experienced pneumonia and sepsis 3 months after cell therapy, but data monitoring largely eliminated the cell therapy as being a contributing factor to this issue. Another patient experienced a seconded stroke that was detected the day after the cell therapy. Because the patient had shown signs of a stroke the day before treatment, the association between the cell therapy and the recurrent stroke is rather unclear. None of the other patients showed any worsening of their present strokes, seizures, or other complications.

All in aloe, it seems as though this procedure is safe, and there is a trend towards increased metabolic and neurological recovery. However, this is a very small study and these trends may not hold in a larger study. Secondly, these patients must be followed for an extended period of time in order to determine if these improvements are durable or transient. Finally, these improvements must be compared with a placebo if there are going to convince the FDA.

Bone marrow cells contain a variety of stem cells and other types of cells that may release cocktails of healing molecules that help cells survive, make new blood vessels, and tamp down inflammation. Additionally, bone marrow cells might stimulate resident populations of stem cells to proliferate and make new neurons and glial cells. Until these positive results can be reproduced in larger, better controlled studies, these results will remain interesting and hopeful, but ultimately inconclusive.

These results were published in Stem Cells and Development 2015 DOI: 10.1089/scd.2015.0160.

Mouse Blood Cells Reprogrammed into Blood Cell Stem Cells


Boston Children’s Hospital researchers have directly reprogrammed mature blood cells from mice into blood-forming hematopoietic stem cells by using a cocktail of eight different transcription factors.

These reprogrammed cells have been called induced hematopoietic stem stem cells or iHSCs. These cells have all the hallmarks of mature mouse HSCs and they have the capacity to self-renew and differentiate into all the blood cells that circulate throughout the body.

These findings are highly significant from a clinical perspective because they indicate that it might be entirely possible to directly reprogram a patient’s existing, mature blood cells into a hematopoietic stem cell for transplantation purposes. Such a procedure, known as hematopoietic stem cells transplantation or HSCT, is a common treatment for patients whose bone marrow has suffered irreparable damage due to environmental causes (heavy metals, chloramphenicol, etc) or disease (cancer). The problem with HSCT is finding a proper match for the patient and then procuring clinically significant quantities of high-quality bone marrow for HSCT.

Derrick J. Rossi, an investigator in the Program in Cellular and Molecular Medicine at Boston Children’s Hospital and Assistant Professor in the Department of Stem Cell & Regenerative Biology, explained: “HSCs comprise only about one in every 20,000 cells in the bone marrow. If we could generate autologous (a patient’s own) HSCs from other cells, it could be transformative for transplant medicine and for our ability to model diseases of blood development.”

Rossi and his collaborators have screened genes that are expressed in 40 different types of blood progenitor cells in mice. This screen identified 36 different genes that control the expression of the other genes. These 36 genes encode so-called “transcription factors,” which are proteins that bind to DNA and turn gene express on or shut it off.

Blood cell production tends to go from the stem cells to progeny cells called progenitor cells that can still divide to some limited extent, and to effector cells that are completely mature and, in most cases, do not divide (the exception is lymphocytes, which expand when activated by specific foreign substances called antigens).

Further work by Rossi and others identified six transcription factors (Hlf, Runx1t1, Pbx1, Lmo2, Zfp37, and Prdm5) of these 36 genes, plus two others that were not part of their original screen (N-Myc and Meis1) that could robustly reprogram myeloid progenitor cells or pro/pre B lymphocytes into iHSCs.

Print

To put these genes into these blood cells, Rossi and others uses souped-up viruses that introduced all either genes under the control of sequences that only allowed expression of these eight genes in the presence of the antibiotic doxycycline. Once these transfected cells were transplanted into mice, the recipient mice were treated with doxycycline, and the implanted cells formed HSCs.

When this experiment utilized mice that were unable to make their own blood cells, because their bone marrow had been wiped out, the implanted iHSCs reconstituted the bone marrow and blood cells of the recipient mice.

To further show that this reconstituted bone marrow was normal, high-quality bone marrow, Rossi and others used these recipient mice as bone marrow donors for sibling mice whose bone marrow had been wiped out. This experiment showed that the mice that had received the iHSCs had bone marrow that completely reconstituted the bone marrow of their siblings. This established that the iHSCs could completely reestablish the bone marrow of another mouse.

Thus Rossi and others had established that iHSCs could in fact created HSCs from progenitor cells, but could they do the same thing with mature blood cells that were not progenitor cells? Make that another yes. When Rossi and others transfected their eight-gene cocktail into mature myeloid cells, these mature cells also made high-quality iHSCs.

Rossi noted that no one has been able to culture HSCs in the laboratory for long periods of time. A few laboratories have managed expand HSCs in culture, but only on a limited basis for short periods of time (see Aggarwal R1, Lu J, Pompili VJ, Das H. Curr Mol Med. 2012 Jan;12(1):34-49).  In these experiments, Rossi used his laboratory mice as living culture systems to expand his HSCs, which overcomes the problems associated with growing these fussy stem cells in culture.

Gene expression studies of his iHSCs established that, from a gene expression perspective, the iHSCs were remarkably similar to HSCs isolated from adult mice.

This is certainly an exciting advance in regenerative medicine, but it is far from being translated into the clinic.  Can human blood progenitor cells also be directly reprogrammed using the same cocktail?  Can mature myeloid cells be successfully reprogrammed?  Will some non-blood cell be a better starting cell for iHSC production in humans?  As you can see there are many questions that have to be satisfactorily answered before this procedure can come to the clinic.

Nevertheless, Rossi and his team has succeeded where others have failed and the results are remarkable.  HSCs can be generated and transplanted with the use of only a few genes.  This is certainly the start of what will hopefully be a fruitful regenerative clinical strategy.

On a personal note, my mother passed about almost a decade ago after a long battle with myelodysplastic syndrome, which is a pre-leukemic condition in which the bone marrow fails to make mature red blood cells.  Instead the bone marrow fills up with immature red blood cells and the patient has to survive on blood transfusions.

The reason for this condition almost certainly stems from defective HSCs that do not make normal progeny.  Therefore the possibility of using a patient’s own cells to make new HSCs that can repopulate the bone marrow is a joyful discovery for me to read about, even though it is some ways from the clinic at this point.

A Patient’s Own Bone Marrow Stem Cells Defeat Drug-Resistant Tuberculosis


People infected with multidrug-resistant forms of tuberculosis could, potentially, be treated with stem cells from their own bone marrow. Even though this treatment is in the early stage of its development, the results of an early-stage trial of the technique show immense promise.

British and Swedish scientists have tested this procedure, which could introduce a new treatment strategy for the estimated 450,000 people worldwide who have multi drug-resistant (MDR) or extensively drug-resistant (XDR) TB.

This study, which was published in the medical journal, The Lancet, showed that over half of 30 drug-resistant TB patients treated with a transfusion of their own bone marrow stem cells were cured of the disease after six months.

“The results … show that the current challenges and difficulties of treating MDR-TB are not insurmountable, and they bring a unique opportunity with a fresh solution to treat hundreds of thousands of people who die unnecessarily,” said TB expert Alimuddin Zumla at University College London, who co-led the study.

TB initially infects the lungs but can rapidly spread from one person to another through coughing and sneezing. Despite its modern-day resurgence, TB is often regarded as a disease of the past. However, recently, drug-resistant strains of Mycobacterium tuberculosis, the microorganism that causes TB, have spread globally, rendering standard anti-TB drug treatments obsolete.

The World Health Organisation (WHO) estimates that in Eastern Europe, Asia and South Africa 450,000 people have MDR-TB, and close to half of these cases will fail to respond to existing treatments.

Mycobacterium tuberculosis, otherwise known as the “tubercle bacillus, trigger a characteristic inflammatory response (granulomatous response) in the surrounding lung tissue that elicits tissue damage (caseation necrosis).

Bone-marrow stem cells are known to migrate to areas of lung injury and inflammation. Upon arrival, they initiate the repair of damaged tissues. Since bone marrow stem cells also they also modify the body’s immune response, they can augment the clearance of tubercle bacilli from the body. Therefore, Zumla and his colleague, Markus Maeurer from Stockholm’s Karolinska University Hospital, wanted to test bone marrow stem cell infusions in patients with MDR-TB.

In a phase 1 trial, 30 patients with either MDR or XDR TB aged between 21 and 65 who were receiving standard TB antibiotic treatment were also given an infusion of around 10 million of their own bone marrow-derived stem cells.

The cells were obtained from the patient’s own bone marrow by means of a bone marrow aspiration, and then grown into large numbers in the laboratory before being re-transfused into the same patient.

During six months of follow-up, Zumla and his team found that the infusion treatment was generally safe and well tolerated, and no serious side effects were observed. The most common non-serious side effects were high cholesterol levels, nausea, low white blood cell counts and diarrhea.

Although a phase 1 trial is primarily designed only to test a treatment’s safety, the scientists said further analyses of the results showed that 16 patients treated with stem cells were deemed cured at 18 months compared with only five of 30 TB patients not treated with their own stem cells.

Maeurer stressed that further trials with more patients and longer follow-up were needed to better establish how safe and effective the stem cell treatment was.

But if future tests were successful, he said, this could become a viable extra new treatment for patients with MDR-TB who do not respond to conventional drug treatment or for those patients with severe lung damage.

Priming Cocktail for Cardiac Stem Cell Grafts


Approximately 700,000 Americans suffer a heart attack every year and stem cells have the potential to heal the damage wrought by a heart attack. Stem cells therapy has tried to take stem cells cultured in the laboratory and apply them to damaged tissues.

In the case of the heart, transplanted stem cells do not always integrate into the heart tissue. In the words of Jeffrey Spees, Associate Professor of Medicine at the University of Vermont, “many grafts simply didn’t take. The cells would stick or would die.”

To solve this problem, Spees and his colleagues examined ways to increase the efficiency of stem cell engraftment. In his experiments, Spees and others used mesenchymal stem cells from bone marrow. Mesenchymal stem cells are also called stromal cells because they help compose the spider web-like filigree within the bone marrow known as “stroma.” Even though the stroma does not make blood cells, it supports the hematopoietic stem cells that do make all blood cells.  Here is a picture of bone marrow stroma to give you an idea of what it looks like:

Immunohistochemistry-Paraffin: Bone marrow stromal cell antigen 1 Antibody [NBP2-14363] Staining of human smooth muscle shows moderate cytoplasmic positivity in smooth muscle cells.
Immunohistochemistry-Paraffin: Bone marrow stromal cell antigen 1 Antibody [NBP2-14363] Staining of human smooth muscle shows moderate cytoplasmic positivity in smooth muscle cells.
Stromal cells are known to secrete a host of molecules that protect injured tissue, promote tissue repair, and support the growth and proliferation of stem cells.

Spees suspected that some of the molecules made by bone marrow stromal cells could enhance the engraftment of stem cells patches in the heart. To test this idea, Spees and others isolated proteins from the culture medium of bone marrow stem cells grown in the laboratory and tested their ability to improve the survival and tissue integration of stem cell patches in the heart.

Spees tenacity paid off when he and his team discovered that a protein called “Connective tissue growth factor” or CTGF plus the hormone insulin were in the culture medium of these stem cells. Furthermore, when this culture medium was injected into the heart prior to treating them with stem cells, the stem cell patches engrafted at a higher rate.

“We broke the record for engraftment,” said Spees. Spees and his co-workers called their culture medium from the bone marrow stem cells “Cell-Kro.” Cell-Kro significantly increases cell adhesion, proliferation, survival, and migration.

Spees is convinced that the presence of CTGF and insulin in Cell-Kro have something to do with its ability to enhance stem cell engraftment. “Both CTGF and insulin are protective,” said Spees. “Together they have a synergistic effect.”

Spees is continuing to examine Cell-Kro in rats, but he wants to take his work into human trials next. His goal is to use cardiac stem cells (CSCs) from humans, which already have a documented ability to heal the heart after a heart attack. See here, here, and here.

“There are about 650,000 bypass surgeries annually,” said Spees. “These patients could have cells harvested at their first surgery and banked for future application. If they return for another procedure, they could then receive a graft of their own cardiac progenitor cells, primed in Cell-Kro, and potentially re-build part of their injured heart.”

Stem Cell Treatments to Improve Blood Flow in Angina Patients


Angina pectoris is defined as chest pain or discomfort that results from poor blood flow through the blood vessels in the heart and is usually activated by activity or stress.

In Los Angeles, California, physicians have initiated a double-blind, multicenter Phase III clinical trial that uses a patient’s own blood-derived stem cells to restore circulation to the heart of angina patients.

This procedure utilizes state-of-the-art imaging technology to map the heart and generate a three-dimensional image of the heart. These sophisticated images will guide the physicians as they inject stem cells into targeted sites in the heart.

This is a double-blinded study, which means that neither the patients nor the researcher will know who is receiving stem-cell injections and who is receiving the placebo.

The institution at which this study is being conducted, University of Los Angeles (UCLA), is attempting to establish evidence for a stem cell treatment that might be approved by the US Food and Drug Administration for patients with refractory angina. The subjects in this study had received the standard types of care but did not receive relief. Therefore by enrolling in this trial, these patients had nothing to lose.

Dr. Ali Nasir, assistant professor of cardiology at the David Geffen School of Medicine and co-principal investigator of this study, said: “We’re hoping to offer patients who have no other options a treatment that will alleviate their severe chest pain and improve their quality of life.”

Before injecting the stem cells or the placebo, the team examined the three-dimensional image of the heart and ascertained the health of the heart muscle and voltage it generated. Damaged areas of the heart fail to produce adequate quantities of voltage and show low levels of energy.

Jonathan Tobis, clinical professor of cardiology and director of interventional cardiology research at Geffen School of Medicine, said: “We are able to tell by the voltage levels and motion which area of the [heart] muscle is scarred or abnormal and not getting enough blood and oxygen. We then targeted the injections to the areas just adjacent to the scarred and abnormal heart muscle to try to restore some of the blood flow.”

What did they inject? The UCLA team extracted bone marrow from the pelvic bones and isolated CD34+ cells. CD34 refers to a cell surface protein that is found on bone marrow stem cells and mediates the adhesion of bone marrow stem cells to the bone marrow matrix. It is found on the surfaces of hematopoietic stem cells, placental cells, a subset of mesenchymal stem cells, endothelial progenitor cells, and endothelial cells of blood vessels. These are not the only cells that express this cell surface protein, but it does list the important cells for our purposes. Once the CD34+ cells were isolated, the were injected into the heart through a catheter that was inserted into a vein in the groin.

CD34

The team hopes that these cells (a mixture of mesenchymal stem cells, hematopoietic stem cells, and endothelial progenitor cells) will stimulate the growth of new blood vessels (angiogenesis) in the heart, and improve blood flow and oxygen delivery to the heart muscle.

“We will be tracking patients to see how they’re doing,” said William Suh MD, assistant clinical professor of medicine in the division of cardiology at Geffen School of Medicine.

The goal of this study is to enroll 444 patients nation-wide, of which 222 will receive the stem cell treatment, 111 will receive the placebo, and 111 who will be given standard heart care.

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.

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.

The Nooks and Crannies in Bone Marrow that Nurture Stem Cells


Stems cells in our bodies often require a specific environment to maximize their survival and efficiency. These specialized locations that nurture stem cells is called a stem cell niche. Finding the right niche for a stem cell population can go a long way toward growing more stem cells in culture and increasing their potency.

To that end, a recent discovery has identified the distinct niches that exist in bone marrow for hematopoietic stem cells (HSCs), which form the blood cells in our bodies.

A research team from Washington university School of Medicine in St. Louis has shown that stem niches in bone marrow can be targeted, which may potentially improve bone marrow transplants and cancer chemotherapy. Drugs that support particular niches could encourage stem cells to establish themselves in the bone marrow, which would greatly increase the success rate of bone marrow transplants. Alternatively, tumor cells are known to hide in stem cell niches, and if drugs could disrupt such niches, then the tumor cells would be driven from the niches and become more susceptible to chemotherapeutic agents.

Daniel Link, the Alan A. and Edith L. Wolff Professor of Medicine at Washington University, said, “Our results offer hope for targeting these niches to treat specific cancers or to impress the success of stem cell transplants. Already, we and others are leading clinical trials to evaluate whether it is possible to disrupt these niches in patients with leukemia or multiple myeloma.”

Working in mice, Link and his colleagues deleted a gene called CXCL12, only in “candidate niche stromal cell populations.” CXCL12 which encodes a receptor protein known to be crucial for maintaining HSC function, including retaining HSCs in the bone marrow, controlling  HSCs activity, and repopulating the bone marrow with HSCs after injury.

CXCL12 crystal structure
CXCL12 crystal structure

CXCL12 signaling pathways

In bone marrow, HSCs are surrounded by a whole host of cells, and it is difficult to precisely identify which type of cells serve as the niche cells. These bone marrow cells are known collectively as “stroma,” but there are several different types of cells in stroma. Cells that have been implicated in the HSC niche include endosteal osteoblasts (osteoblasts are bone-making cells and the endosteum in the layer of connective tissue that lines the inner cavity of the bone), perivascular stromal cells (cells that hang out around blood vessels), CXCL12-abundant reticular cells, leptin-receptor-positive stromal cells, and nestin–positive mesenchymal progenitors. Basically, there are a lot of cells in the stroma and figuring out which one is the HSC niche is a big deal.

bone marrow stromal cells

When HSCs divide, they form two cells, one of which replaces the HSC that just divided and a new cells called a hematopoietic progenitor cell (HPC), which can divide and differentiate into either a lymphoid progenitor or a myeloid progenitor. The lymphoid progenitor differentiates into either a B or T lymphocyte and the myeloid progenitor differentiates into a red blood cell, or other types of white blood cells (neutrophil, basophil, macrophage, platelet or eosinophil). As the cells become more differentiated, they lose their capacity to divide.

HSC differentiation

Deleting CXCL12 from mineralizing osteoblasts (bone making cells) did nothing to the HSCs or those cells that form lymphocytes (lymphoid progenitors). Deletion of Cxcl12 from osterix-expressing stromal cells, which include CXCL12-abundant reticular cells and osteoblasts, causes mobilization of hematopoietic progenitor cells (HPCs) from the bone marrow into the bloodstream, and loss of B-lymphoid progenitors, but HSC function is normal. Cxcl12 deletion from blood vessel cells causes a modest loss of long-term repopulating activity. Deletion of Cxcl12 from nestin-negative mesenchymal progenitors causes a marked loss of HSCs, long-term repopulating activity, and lymphoid progenitors. All of these data suggest that osterix-expressing stromal cells comprise a distinct niche that supports B-lymphoid progenitors and retains HPCs in the bone marrow. Also, the expression of CXCL12 from stromal cells in the perivascular region, including endothelial cells and mesenchymal progenitors, supports HSCs.

Link summarized his results this way: “What we found was rather surprising. There’s not just one niche for developing blood cells in the bone marrow. There’s a distinct niche for stem cells, which have the ability to become any blood cell in the body, and a separate niche for infection-fighting cells that are destined to become T cells and B cells.”

These data provide the foundation for future investigations whether disrupting these niches can improve the effectiveness of cancer chemotherapy.

In a phase 2 study at Washington University, led by oncologist Geoffrey Uy, assistant professor of medicine, Link and his team are evaluating whether the drug G-CSF (granulocyte colony stimulating growth factor) can alter the stem cell niche in patients with acute lymphoblastic leukemia and whose disease is resistant to chemotherapy or has recurred. The FDA approved this drug more than 20 years ago to stimulate the production of white blood cells in patients undergoing chemotherapy, who have often weakened immune systems and are prone to infections.

Uy and his colleagues want to evaluate G-CSF if it is given prior to chemotherapy. Patients enrolled at the Siteman Cancer Center will receive G-CSF for five days before starting chemotherapy, and the investigators will determine whether it can disrupt the protective environment of the bone marrow and make cancer cells more sensitive to chemotherapy.

This trial is ongoing, and the results are not yet in, but Link’s work has received a welcome corroboration of his work. A companion paper was published in the same issue of Nature by Sean Morrison, the director of the Children’s Medical Center Research Institute at the University of Texas Southwestern Medical Center in Dallas. Morrison and his team used similar methods as Link and his colleagues and came to very similar conclusions.

Link said, “There’s a lot of interest right now in trying to understand these niches. Both of these studies add new information that will be important as we move forward. Next, we hope to understand how stem cells niches can be manipulated to help patients undergoing stem cell transplants.”

Mesenchymal Stem Cell Web Site Publishes A Review Article Written By the Author of This Web Site


The mesenchymal stem cell web site has published my review that compares mesenchymal stem cells from different sources. The article is entitled “Comparisons of Mesenchymal Stem Cells from Bone Marrow and Other Sources,” It can be found at this link.