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.”

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 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.”

Treating a Rare Immune Disorder with Mesenchymal Stem Cells


In the journal Stem Cells and Development, there is a case report from the University Hospital at Karolinska Institutet in Stockholm, Sweden of a 21-year-old man who suffered from a rare immune disorder and was treated with an infusion of mesenchymal stem cells (MSCs) from a donor.

This patient was seen in October, 2010 and had been suffering from a fever for 2 months. He had had a previous gastrointestinal infection that had resolved, but the inflammation that resulted from the infection refused to go away. He was diagnosed with hemophagic lymphohistiocytosis (HLH). This is a mouthful, but it is a relatively rare immune disorder that results in pronounced systemic hyperinflammation. This hyperinflammation essentially results from some sort of infection that causes inflammation, but the inflammation does not turn off when the infection resolves. The condition causes the spleen to enlarge and the number of blood cells to decrease to abnormally low levels and the patient has a constant, burning fever.

The medical team that treated this poor soul used steroids, and that worked from about a week. Then they tried the HLH-94 treatment protocol, which involves treating the patient with a combination of powerful immunosuppressive drugs; etoposide, (VP-16), corticosteroids, CyclosporinA, and, in some patients, intrathecal methotrexate, before the patient is given a bone marrow transplant. The HLH-94 protocol returned the patient to normal – for about 2 months, and then the patient was back to square one.

At this point, the medical team needed a Hail Mary, if you will. Therefore, they decided to use MSCs from a healthy donor. The patient was given a total of 124 million bone marrow-derived MSCs, and within 24 hours, the patient’s fever was gone and his blood work normalized.

Unfortunately, the poor chap contracted a nasty fungal infection that, in his weakened state, spread throughout his whole body and killed him. However, postmortem examinations showed that the MSCs had mobilized a whole gaggle of special white blood cells called macrophages, and these MSC-recruited macrophages suppressed the over-active immune response of this HLH patient. The fungal infection was contracted before the administration of the MSCs, therefore, the stem cell treatment had no causal relationship to the fungal infection.

However, this case study suggests that MSCs have a future in the treatment of immune disorders. Furthermore, the use of MSCs from donors can also provide therapeutic material for the treatment of immune disorders.

HIV Drug Maraviroc Reduces Graft-Versus-Host Disease In Stem Cell Transplant Patients


A drug called maraviroc is normally used to treat Human Immunodeficiency Virus (HIV) infections, but work at the University of Pennsylvania suggests that maraviroc redirects the trafficking of immune cells. The significance of these results are profound for transplant patients, since a drug like maraviroc can potentially reduce the incidence of graft-versus-host disease in cancer patients who have received allogeneic (from someone else) stem cell transplantation (ASCT). This research, which was conducted at the Perelman School of Medicine at the University of Pennsylvania, was presented at the 53rd American Society of Hematology Annual Meeting.

Graft-versus-host disease or GvHD occurs as complication after a stem cell or bone marrow transplant. During GvHD, the newly transplanted cells recognize the recipient’s body as foreign and mount an attack against it. Acute cases of GvHD usually occur within the first 3 months after the transplant. Chronic GvHD usually starts more than 3 months after the transplant. GvHD rates vary from 30 – 40% among related bone marrow or stem cells donors and from 60 – 80% between unrelated donors and recipients. The greater the degree of immunological mismatches between the donor and the recipient, the greater the risk of GvHD. After a transplant, the recipient usually takes a battery of drugs that suppress the immune system. These drug treatments help reduce the chances or severity of GvHD.

Standard treatments for GvHD suppress the immune system. Commonly used medicines include methotrexate, cyclosporine, tacrolimus, sirolimus, ATG (Antithymocyte globulin), and alemtuzumab either alone or in combination. High-dose corticosteroids are the most effective treatment for acute GVHD. Antibodies to T cells and other medicines are given to patients who do not respond to steroids. Chronic GvHD treatments include prednisone, (a steroid) with or without cyclosporine. Other treatments include mycophenolate mofetil (CellCept), sirolimus (Rapamycin), and tacrolimus (Prograf). These treatments, if given during the course of the stem cell or bone marrow transplant, reduce but do not eliminate the risk of developing GvHD.

In the current trial, treatment with maraviroc dramatically reduced the incidence of GvHD in organs where it is most dangerous (liver, GI tract, lung, skin — without compromising the immune system and leaving patients more vulnerable to severe infections.

Assistant professor in the division of Hematology-Oncology and a member of the Hematologic Malignancies Research Program at Penn’s Abramson Cancer Center, Ran Reshef, commented: “There hasn’t been a change to the standard of care for GvHD since the late 1980s, so we’re very excited about these results, which exceeded our expectations. Until now, we thought that only extreme suppression of the immune system can get rid of GvHD, but in this approach we are not killing immune cells or suppressing their activity, we are just preventing them from moving into certain sensitive organs that they could harm.”

Reshef and colleagues presented results showing that maraviroc is safe and feasible in stem cell transplant patients who have received stem cells from a healthy donor. A brief course of the drug led to a 73% reduction in severe GvHD in the first six months after transplant, compared with a matched control group treated at Penn during the same time period (6% who received maraviroc developed severe GvHD vs. 22% of other patients receiving standard drug regimens).

Reshef explained, “Just like in real estate, immune responses are all about location, location, location. Cells of the immune system don’t move around the body in a random way. There is a very distinct and well-orchestrated process whereby cells express particular receptors on their surface that allows them to respond to small proteins called chemokines. The chemokines direct the immune cells to specific organs, where they are needed, or in the case of GvHD, to where they cause damage.”

Thirty-eight patients with blood cancers, including acute myeloid leukemia, myelodysplastic syndrome, lymphoma, myelofibrosis, and others, enrolled in the phase I/II trial. All patients received the standard GvHD prevention drugs tacrolimus and methotrexate, plus a 33-day course of maraviroc that began two days before transplant. In the first 100 days after transplant, none of the patients treated with maraviroc developed GvHD in the gut or liver. By contrast, 12.5% of patients in the control group developed GvHD in the gut and 8.3 percent developed it in the liver within 100 days of their transplant.

The differential impact of maraviroc on those organs indicates that the drug is working as expected, by limiting the movement of T lymphocytes to specific organs in the body. Maraviroc works by blocking the CCR5 receptor on the surfaces of lymphocytes. This prevents the lymphocytes from trafficking to certain organs. Maraviroc did not affect GvHD rates in the skin, which might mean that the CCR5 receptor is more important for sending lymphocytes into the liver and the gut than the skin.

After 180 days, the benefit of maraviroc appeared to be partially sustained in patients and the cumulative incidence of gut GvHD rose to 8.8% and the rates of liver GvHD rose only to 2.9%. The cumulative incidence of GvHD in the control group, however, remained higher, at 28.4% for gut and 14.8% for liver GvHD. Based on these data, the research team plans to try a longer treatment regimen with maraviroc to see if longer exposures to maraviroc can its protective effect.

Additionally, maraviroc treatment appeared to neither increase treatment-related toxicities nor alter the relapse rate of their underlying disease. Clearly this drug shows promise for limiting the devastating effects of GvHD in stem transplant patients.