Innovative strategies improve outcomes and prevent complications of stem cell transplants

"While stem cell transplant is one of the best treatment options we have available for many blood cancers, unfortunately, it can sometimes result in severe complications," said moderator of the press conference Armand Keating, MD, Director, Division of Hematology, and Professor of Medicine at the University of Toronto, Ontario, Canada. "The results of these studies are exciting because they highlight several new, innovative approaches we are taking that not only help reduce these life-threatening complications, but ultimately result in improved outcomes for our patients."

Adoptive Immunotherapy With Tregs Prevents Graft-Versus-Host Disease and Favors Immune Reconstitution After HLA Haploidentical Transplants for Hematological Malignancies [Abstract #4]

Bone marrow transplant is often recommended to patients with acute leukemia (a rapidly progressing disease that results in the accumulation of immature, functionless cells in the marrow and blood) who are at high risk for recurrence. A common complication of bone marrow transplantation is graft-versus-host disease, which occurs when donor's immune system reacts against the patient's body. When a patient and donor are mismatched (known as haploidentical transplants), high doses of stem cells can overcome rejection, a principle that has been successfully pioneered in animal models by study co-author Yair Reisner, MD. However, in order to prevent graft-versus-host disease, the donor stem cells must be extensively depleted of T cells, which play an important role in immune response. As a result of this extensive reduction in T-cells, the recovery of the patient's natural immune response against infectious agents is delayed, leading to a high incidence of infection-related deaths. Researchers from the University of Perugia in Italy and the Weizmann Institute of Science in Rehovot, Israel, have addressed this key challenge by infusing donor T cells in an effort to improve immune recovery without causing graft-versus-host disease.

For the first time in humans, researchers in this phase I/II clinical trial evaluated the impact on graft-versus-host disease prevention and immunologic reconstitution of an infusion of donor T-regulatory cells (CD4/CD25+), which are a type of T cell that suppresses the body's immune response and has been shown in several mouse studies to control graft-versus-host disease. T-regulatory cells were infused immediately after isolation from donors, three days before administering the stem cell graft, which consisted of donor mature T-cells and a megadose of hematopoietic stem cells CD34+.

Twenty-eight patients with leukemia or lymphoma enrolled in the study: 22 with acute myeloid leukemia, five with acute lymphoblastic leukemia, and one with high-grade relapsed non-Hodgkin lymphoma. All patients underwent a conditioning regimen that included total body irradiation (8Gy single fraction) and a chemotherapy regimen of thiotepa (4mg/kg x 2), fludarabine (40 mg/m² x 5), and cyclophosphamide (35 mg/kg x 2). Patients were then infused with CD4/CD25+ immune-selected T-regulatory cells (five patients received 4x10⁶/kg; 22 patients received a 2x10⁶/kg; one patient received a 1x10⁶/kg ). Three days later, patients received immune-selected CD34+ cells (median 8.2 cells, range 5.0-19.1) together with donor mature T-cells (five patients received 2x10⁶/kg; 17 patients received 1x10⁶/kg; four patients received 0.5x10⁶/kg; two patients did not receive donor mature T-cells because, for technical reasons, the T-regulatory cell infusion was contaminated with donor mature T cells).

Results revealed that long-term protection from graft-versus-host disease and robust immune system reconstitution can be achieved. For the first time, high doses of T cells were administered in patients who underwent a haploidentical transplant (stem cells from a relative who is a partial match only), which included freshly purified T-regulatory cells to prevent graft-versus-host disease. No graft-versus-host disease was observed in 25 of 26 patients who could be evaluated. Two patients developed self-limited (limiting own growth) acute cutaneous (skin) graft-versus-host disease, which was left untreated in accordance with current recommendations. One patient developed severe graft-versus-host disease.

In addition, the speed of immune recovery was enhanced. More specifically, researchers observed rapid and sustained immunological reconstitution in terms of CD4 and CD8 lymphocyte counts and high frequencies of specific CD4+ and CD8+ cells against microbial agents together with a significant reduction in post-transplant cytomegalovirus reactivation.

"This study demonstrates that T-regulatory cell-based therapy may be an innovative strategy to improve the outcome of patients who undergo bone marrow transplants," said Massimo F. Martelli, MD, Professor and Head of the Hematology and Clinical Immunology Section at the University of Perugia in Italy and senior author of this study. "We hope that this new method will reduce infection-related mortality and thus improve overall survival."

Defibrotide (DF) for the Prevention of Hepatic Veno-Occlusive Disease (VD) in Pediatric Stem Cell Transplantation: Results of a Prospective Phase ll/lll Randomized, Multicenter Study [Abstract #653]

The 100-day survival rates for pediatric patients who have received stem cell transplants has steadily increased. However, it is still associated with significiant mortality and morbidity including complications such as veno-occlusive disease, a disease in which the small vessles in the liver become obstructed. This life-threatening condition has a particularly high incidence in children undergoing allogeneic stem cell transplantation. In this study, researchers from the University of Ulm in Germany assessed the safety and efficacy of defibrotide, an investigational drug, for the prevention of this disease in the largest-ever, international, multicenter study of high-risk pediatric patients undergoing stem cell transplants. The study was co-sponsored by the European Group for Blood and Marrow Transplantion (EBMT).

A total of 360 high-risk patients with a median age of five years were enrolled in the study (24 percent infants, 52 percent children ages 2-11, and 23 percent adolescents ages 12-18). Sixty-eight percent of the patients underwent allogeneic stem cell transplant (a procedure in which a person receives blood-forming stem cells from a genetically similar, but not identical donor), and 31 percent received an autologous stem cell transplant (a procedure in which blood-forming stem cells are removed from a patient, stored, and then re-injected following high-dose chemotherapy to accelerate the "rescue" of blood formation). Patients were prospectively randomized prior to stem cell transplantation to receive either defibrotide or no preventive therapy for veno-occlusive disease. The patients who were randomized to the defibrotide arm received intravenous infusions (25 mg/kg/day) from the start of conditioning (the time before transplant when a patient is given chemotherapy to suppress the immune system, to make room for donor marrow cells to grow, or to destroy remaining cancer cells) until 30 days post stem cell transplant or discharge from the hospital, whichever came first. In the control arm, patients did not receive any preventive therapy. The primary endpoint of this study was to measure the incidence of veno-occlusive disease after 30 days, which was adjudicated by a blinded, independent review committee of three expert hematologists. Secondary endpoints of the study were to measure veno-occlusive disease-associated morbidity, mortality, and the incidence and severity of graft-versus-host disease.

According to the study results, preventive use of defibrotide resulted in a 40 percent reduction in the overall incidence of veno-occlusive disease in these pediatric patients. Consistent with the role of defibrotide in protecting endothelial cells (the thin layer of cells that line the inside of blood vessels), both the incidence of renal failure (1 percent with defibrotide versus 6 percent in control) and also the overall incidence and severity of acute graft-versus-host disease (32 percent in defibrotide versus 43 percent in control) were significantly lower in the defibrotide arm. In addition, the safety of defibrotide was confirmed by the lack of significant toxicity; the defibrotide and control arms had similar numbers of adverse events reported. Results from this study also confirm that the mortality at 100 days post-transplant in patients who developed veno-occlusive disease was four times higher than the mortality in patients who had not developed this disease.

"For pediatric stem cell transplant patients who develop veno-occlusive disease, we unfortunately have limited diagnostic tools, poor understanding of potential risk factors and mechanisms of the disease, and no established therapies to help prevent or treat this condition," said lead study author Selim Corbacioglu, MD, Assistant Professor of the Department of Hematology, Oncology, Immunology, and Stem Cell Transplantation at the University of Ulm in Germany. "Our study confirms that defibrotide is safe and effective for preventing veno-occlusive disease in this high-risk population."

HLA-Identified Sibling-Matched, CD34+ Selected, T-Cell Depleted Peripheral Blood Stem Cells Following Myeloablative Conditioning for First or Second Remission Acute Myeloid Leukemia (AML): Results of Blood and Marrow Transplant Clinical Trials Network (BMT CTN) Protocol 0303 [Abstract #655]

Acute myeloid leukemia (AML) is a type of blood cancer in which there is a rapid growth of abnormal white blood cells. While both children and adults of any age can develop AML, the incidence increases with age. Many patients who receive chemotherapy may enter complete remission, but in other patients, the disease returns (relapse). Allogeneic stem cell transplantation, a process in which a patient receives blood-forming stem cells from a genetically similar but not identical related or unrelated donor, is the most effective way to prevent the recurrence of AML. However, the patient's quality of life and overall survival are often affected by both acute (within the first 100 days after transplant) and chronic (later form) graft-versus-host disease, common complications of transplants.

Graft-versus-host disease is most effectively prevented by removing T cells (type of white blood cell that plays a central role in how the immune system responds to specific pathogens) from the donor's stem cells before they are transplanted into the patient. The T cells are removed because they may attack the patient's own cells. T-cell depletion, the process of removing T cells from the donor's stem cells, has not been used frequently because of logistical difficulties; lack of a U.S. Food and Drug Administration-approved method; and concerns regarding the potential risk of transplant rejection, post-transplant infections, and especially, leukemic relapse. Additionally, most reported T-cell depletion studies represent single centers, multiple disease types, and different processing methods with varying degrees of T-cell depletion, which are all factors that affect the overall outcome of patients.

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN), co-sponsored by the National Institutes of Health's National Heart, Lung, and Blood Institute and National Cancer Institute, designed BMT CTN 0303, a T-cell depletion trial using a single processing method that provides extensive T-cell depletion that did not require post-transplant graft-versus-host disease prevention in adult AML patients in first or second complete remission. The primary objective of this study was to achieve a six-month disease-free survival rate exceeding 75 percent following stem cell transplant. Secondary objectives included assessments of engraftment, transplant-related mortality, graft-versus-host disease, relapse, and the performance of a single T-cell depletion method at participating centers.

Researchers enrolled a total of 47 patients; 44 of these patients were then transplanted at eight different centers. Patients received a conditioning regimen that consisted of total body irradiation (1375 cGy in 11 fractions) with partial lung shielding, thiotepa (10 mg/kg), cyclophosphamide (120 mg/kg), and rabbit antithymocyte globulin (1.5 mg/kg). All stem cell donors were HLA-identical siblings and were given G-CSF (a cytokine that stimulates the production of white blood cells) to ensure a graft with a high CD34+ cell content. The majority of patients (84 percent) received the targeted CD34+ cell dose, and no patient received more than 1.0x10e5 CD3+ T-cells/kg (doses above this level can cause graft-versus-host disease). In addition, no further therapies were given for the prevention of graft-versus-host disease following transplant.

The study found that stem cell transplant following radiation and chemotherapy can be performed in a multicenter setting using a single T-cell depletion method without additional post-transplant graft-versus-host disease prevention methods, meeting the primary objective by producing an 81.3 percent disease-free survival rate at six months. Overall survival reached 74.3 percent at one year. While the most common way to prevent graft-versus-host disease is to give patients certain drugs to prevent it, the study shows encouraging results of low incidences of acute and chronic graft-versus-host disease without the use of these potentially toxic and less effective drugs. Additionally, there were no significant toxicities related to infusion of the CD34+ cells into the patients.

"By implementing a single method, we hope to make transplant procedures safer with less risk of graft-versus-host disease, ultimately leading to more patients benefiting from stem cell transplants," said lead author Steven M. Devine, MD, Associate Professor at the Ohio State University Comprehensive Cancer Center in Columbus. "As this study examined patients who had matched sibling donors, we will conduct further studies to see if this same approach will work for recipients of cells from unrelated volunteer donors."

Identification of Single Human Hematopoietic Stem Cells Capable of Long-Term Multilineage Engraftment and Self-Renewal [Abstract #816]

Stem cell scientists are continually challenged by the need to expand and grow pure stem cells, which have the ability to recreate all blood lineages, in order to gain a better understanding of the gene expression signatures (markers that make it easy to identify the specific cells) that define these stem cells. Researchers from the University of Toronto in Ontario, Canada, developed a laboratory test to measure the activity of individual human hematopoietic (blood-forming) stem cells by taking human stem cells from cord blood and transplanting these cells into immune-deficient mice.

Over the past 20 years, researchers have been able to purify mouse stem cells and prove the potential of a single mouse stem cell to become several mature cell types that will re-populate and re-grow blood in transplanted mice. However, such success with human cells has neither been achieved nor been considered feasible until now. There is a scientific need to develop the same level of knowledge about what makes up human hematopoietic stem cells. In this study, investigators looked at developing better markers in order to obtain pure stem cells. A series of cell surface markers (Lin-CD34+CD38-CD90+CD45RA-RholoCD49fhi) were added to blood cells from either cord blood or adult bone marrow to isolate individual human stem cells and then test their stem cell activity by transplanting them into mice. Of the 29 mice that were transplanted with single human stem cells, five gave rise to human cells, indicating that a pure population of cells was achieved and that these cells reconstituted myeloid, B-cell, and T-cell lineages for 18 weeks; this duration is considered long-term engraftment in mouse studies. Approximately 20 percent of all the cells in these five mice were human hematopoietic cells, which is considered to be a high engraftment level from a single, transplanted stem cell.

"For more than 40 years, the approach for stem cell research has been focused on the mouse because scientists haven't had the tools to try and conduct experiments in humans," said senior author John E. Dick, PhD, Senior Scientist of the Division of Cellular and Molecular Biology at Toronto General Research Institute in Ontario, Canada. "This study is a major step forward in bringing stem cell research into human studies and advancing our ability for developing stem cell therapies."