Image provided by Dr. Ann Dahlberg
Blood stem cell transplantation is used to treat patients with blood disorders. While transplants can be lifesaving, a large number of people in need of a transplant lack a suitably matched donor. Blood stem cells derived from umbilical cord blood are more tolerant of mismatches versus donor cells derived from bone marrow or peripheral blood, making them a particularly important stem cell source for patients who do not otherwise have a matched donor. Before receiving a transplant, patients must first undergo conditioning regimens to remove diseased bone marrow and blood cells and to allow engraftment of donor stem cells and reconstitution of a normal blood system. Cord blood transplant recipients are particularly susceptible to delayed blood and immune system recovery due to the low stem cell numbers available in the cord blood graft. In order to decrease this risk, cord blood stem cells have been cultured and expanded in the laboratory to be given along with a standard cord blood unit in order to provide sufficient numbers of cells for transplant. Unfortunately, both the cost and the ability to maintain the stemness of these cells limit their widespread application. As a step forward to improving the efficiency and reducing the cost of culture conditions, lead author Dr. Ann Dahlberg in the Clinical Research Division reports in the journal Leukemia that alteration of two important signaling pathways expands stem and progenitor cells in cultured cord blood. These conditions maintain the stemness of cells to improve transplant in a preclinical model.
In order to expand cord blood stem cells in culture, conditions must maximize proliferation and limit their differentiation to mature white blood cells. Breakthrough studies led by Drs. Colleen Delaney and Irv Bernstein in the Clinical Research Division demonstrated that cord blood stem and progenitor cells could be expanded by treating cells with specific cytokines and inducing Notch signaling (Delaney et al., 2010). The ligand Delta1 activates Notch signaling in cord blood stem cells, and improved transplant success in preclinical models. This method is currently in human clinical trials to improve cord blood stem cell transplant. More recently, another research group reported an alternate method to expand stem cells and improve transplant using StemRegenin1 (SR1), an antagonist of the transcription factor aryl hydrocarbon receptor (Boitano et al., 2010).
In order to improve on these conditions, Dr. Dahlberg and colleagues tested whether a combination of Delta1 and SR1 generated greater numbers of stem and progenitor cells from the same original starting material. The researchers added SR1, Delta1 or both reagents with a cocktail of cytokines known to maintain stem cell renewal (IL-6, TPO, SCF, and Flt-3 ligand) and cultured cord blood cells for 14 to 16 days. The combination of both Delta1 and SR1 increased progenitor numbers and decreased the differentiation of cells to more mature myeloid cells compared to SR1 alone.
The researchers then addressed the mechanism underlying this boost in stem and progenitor cell numbers by combining Delta1 and SR1. Treatment with Delta1 increased expression of the Notch-controlled gene HES1, suggesting this induction was in part responsible for maintaining the stemness of cells and increasing cell numbers. HES1 had been previously shown to block the differentiation of stem cells to myeloid progeny, and indeed the researchers were able to boost stem and progenitor cell numbers in cultured cord blood by overexpressing HES1 in combination with SR1 treatment 25-fold, recapitulating the effect seen with Delta1.
The researchers then addressed whether cord blood stem cells cultured with the combination of Delta1 and SR1 increased the repopulating capability of the cells transplanted into mice. Significantly enhanced rapid reconstitution of myeloid cells was observed in animals transplanted with cells cultured with both reagents versus SR1 or Delta1 alone. By transplanting limited dilutions of cells, the researchers found that culture with the combination of Delta1 and SR1 increased the number of rapidly repopulating cells by 3-fold over either treatment alone. In addition to myeloid cells, the researchers found SR1 alone improved B-cell repopulation better than Delta1 alone or the combination of Delta1 and SR1. The authors suggested this was due in part to a combination of Notch blocking the formation of lymphoid progenitor cells and SR1 promoting B cell development.
Dr. Dahlberg states this study is one step closer to achieving the ultimate goal "to develop an economically feasible and widely available cellular therapy able to mitigate the risks associated with delayed myeloid recovery following cord blood transplant or intensive myelo-suppressive chemotherapy."
Dahlberg A, Brashem-Stein C, Delaney C, Bernstein ID. 2014. Enhanced generation of cord blood hematopoietic stem and progenitor cells by culture with StemRegenin1 and Delta1. Leukemia Epub ahead of print, doi: 10.1038/leu.2014.181.
See also: Delaney C, Heimfeld S, Brashem-Stein C, Voorhies H, Manger RL, and Bernstein ID. 2010. Notch-mediated expansion of human cord blood progenitor cells capable of rapid myeloid reconstitution. Nature Medicine 16: 232-236.
Boitano AE, Wang J, Romeo R, Bouchez LC, Parker AE, Sutton SE, Walker JR, Flaveny CA, Perdew GH, Denison MS, Schultz PG, Cooke MP. 2010. Aryl hydrocarbon receptor antagonists promote the expansion of human hematopoietic stem cells. Science 329: 1345-1348.