Normal and Leukemic Hematopoiesis

Acute Myeloid Leukemia (AML) is a clonal myeloproliferative disease characterized by an uncontrolled proliferation and block in differentiation of myeloid committed blood cells in the bone marrow. Despite the lack of mature cells derived from the leukemic clone in the majority of AML patients, AML cells are heterogenous in phenotype and functional ability. AML progenitors capable of initiating the leukemia in immunocompromised mice and generating clonogenic cells after long-term culture in vitro are CD34+, CD38-, HLA-DR- and CD71-. This phenotype is similar to that of normal progenitors with these functional characteristics. In contrast to AML progenitors, normal progenitors express higher levels of CD117 and CD90. Cells with the primitive phenotype represent only a small minority of all AML blasts, but seem uniquely capable of propagating the leukemia, suggesting they are AML stem cells. Existing therapies to treat AML are largely directed against the bulk population of AML cells. The ability to phenotypically distinguish between AML and normal stem cells could be extremely useful to develop purging therapies for transplantation and AML stem cell specific therapies to target minimal residual disease. CD133 is a new stem cell antigen present on normal CD34+ and CD34- hematopoietic cells with in vivo repopulating ability. Although we found a close correlation between CD34 and CD133 expression on AML cells, CD133 is not useful to purify or purge AML stem cells. CD33 is a cell surface marker exclusively expressed on myeloid cells. Because CD33 is absent on normal hematopoietic stem cells, but is expressed on the majority of AML patient samples, CD33 appears to be useful for purging strategies and antibody-targeted therapy. We determined whether CD33 is expressed on AML progenitors with long-term proliferative ability in vitro and in vivo repopulating ability. We demonstrate that, although CD33 is expressed on the majority of AML samples it is absent on AML progenitors with long-term in vitro ability and is absent on some but not all repopulating cells of a substantial number of patients. Therefore, most AML stem cells will be spared by CD33 based therapies. Human somatic cells have a limited life span and telomeres and telomerase play an important role in the regulation of the lifespan and senescence of human cells. Telomerase is a DNA polymerase that maintains the telomeric ends of chromosomes. Most adult human cells have undetectable telomerase. However, 90% of human cancers including AML, express telomerase to maintain their telomere length. We introduced a dominant negative form of telomerase into a leukemic cell line and primary AML cells. This resulted in an inhibition of the proliferation of AML progenitors in vitro and in vivo suggesting that telomerase inhibition is a promising target to treat AML. Notch receptors influence the cell fates in progenitors of numerous cell types in a wide range of organisms. In humans, four Notch receptors have been identified, Notch1-4. In human hematopoiesis Notch activation results in the maintenance of stem cells and in a block in differentiation. We found higher Notch expression progenitor cells and overexpression of Notch4 results in stem cell maintenance and in a block in myeloid differentiation. In primary AML progenitors Notch receptors are not down-regulated upon differentiation. Notch activation through ligation with Jagged1 ligand resulted in an abnormal proliferation of long-term AML progenitor cells, suggesting that abnormal Notch expression or activation might play a role in AML

Training Deer to Avoid Sites Through Negative Reinforcement

Deer frequently visit areas where they may cause damage. Incidents along roadways and runways inflict numerous injuries to animals and humans, and cause considerable economic losses. Concerns are increasing that deer interactions with domestic animals may contribute to spread of disease. Deer foraging in residential areas, agricultural fields, or plant propagation sites can impede growth and possibly survival of desirable plants. We conducted a series of trials to determine whether mild electric shock would induce place avoidance in deer. Shock was delivered through a device attached to a collar. A noise cue was emitted as an animal approached a defined area if the animal failed to retreat a shock followed. Deer learned to avoid areas associated with shock. We concluded that place avoidance induced through negative reinforcement may be a feasible means to protect valuable resources from resident animals. However, the technological limitations of tested devices, costs to implement, and required training for individual deer reduced the practicality of this approach for highly mobile animals and as a means to protect resources with low economic significance