A clinically relevant population of leukemic CD34(+)CD38(-) cells in acute myeloid leukemia.

Relapse of acute myeloid leukemia (AML) is thought to reflect the failure of current therapies to adequately target leukemia stem cells (LSCs), the rare, resistant cells presumed responsible for maintenance of the leukemia and typically enriched in the CD34(+)CD38(-) cell population. Despite the considerable research on LSCs over the past 2 decades, the clinical significance of these cells remains uncertain. However, if clinically relevant, it is expected that LSCs would be enriched in minimal residual disease and predictive of relapse. CD34(+) subpopulations from AML patients were analyzed by flow cytometry throughout treatment. Sorted cell populations were analyzed by fluorescence in situ hybridization for leukemia-specific cytogenetic abnormalities (when present) and by transplantation into immunodeficient mice to determine self-renewal capacity. Intermediate (int) levels of aldehyde dehydrogenase (ALDH) activity reliably distinguished leukemic CD34(+)CD38(-) cells capable of engrafting immunodeficient mice from residual normal hematopoietic stem cells that exhibited relatively higher ALDH activity. Minimal residual disease detected during complete remission was enriched for the CD34(+)CD38(-)ALDH(int) leukemic cells, and the presence of these cells after therapy highly correlated with subsequent clinical relapse. ALDH activity appears to distinguish normal from leukemic CD34(+)CD38(-) cells and identifies those AML cells associated with relapse.

Protection from fatal viral encephalomyelitis: AMPA receptor antagonists have a direct effect on the inflammatory response to infection.

Neuronal cell death during fatal acute viral encephalomyelitis can result from damage caused by virus replication, glutamate excitotoxicity, and the immune response. A neurovirulent strain of the alphavirus Sindbis virus (NSV) causes fatal encephalomyelitis associated with motor neuron death in adult C57BL/6 mice that can be prevented by treatment with the prototypic noncompetitive alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptor antagonist GYKI 52466 [Nargi-Aizenman J, et al. (2004) Ann Neurol 55:541-549]. To determine the mechanism of protection, NSV-infected mice were treated with 7-acetyl-5-(4-aminophenyl)-8(R)-methyl-8,9-dihydro-7H-1,3-dioxolo-(4,5-h)-benzodiazepine (talampanel), a potent, orally available member of the 2,3 benzodiazepine class of noncompetitive AMPA glutamate receptor antagonists. Talampanel-treated mice were protected from NSV-induced paralysis and death. Examination of the brain during infection showed significantly less mononuclear cell infiltration and no increase in astrocyte expression of glial fibrillary acidic protein in treated mice compared with untreated mice. Lack of CNS inflammation was attributable to failure of treated mice to induce activation and proliferation of lymphocytes in secondary lymphoid tissue in response to infection. Antibody responses to NSV were also suppressed by talampanel treatment, and virus clearance was delayed. These studies reveal a previously unrecognized effect of AMPA receptor antagonists on the immune response and suggest that prevention of immune-mediated damage, in addition to inhibition of excitotoxicity, is a mechanism by which these drugs protect from death of motor neurons caused by viral infection.