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Human embryonic stem (hES) cells are defined by their extensive self-renewal capacity and their potential to differentiate into any cell type of the human body. The challenge in using hES cells for developmental biology and regenerative medicine has been to direct the wide differentiation potential toward the derivation of a specific cell fate. Within the nervous system, hES cells have been shown to differentiate in vitro into neural progenitor cells, neurons, and astrocytes. However, to our knowledge, the selective derivation of any given neuron subtype has not yet been demonstrated. Here, we describe conditions to direct hES cells into neurons of midbrain dopaminergic identity. Neuroectodermal differentiation was triggered on stromal feeder cells followed by regional specification by means of the sequential application of defined patterning molecules that direct in vivo midbrain development. Progression toward a midbrain dopamine (DA) neuron fate was monitored by the sequential expression of key transcription factors, including Pax2, Pax5, and engrailed-1 (En1), measurements of DA release, the presence of tetrodotoxin-sensitive action potentials, and the electron-microscopic visualization of tyrosinehydroxylase-positive synaptic terminals. High-yield DA neuron derivation was confirmed from three independent hES and two monkey embryonic stem cell lines. The availability of unlimited numbers of midbrain DA neurons is a first step toward exploring the potential of hES cells in preclinical models of Parkinson's disease. This experimental system also provides a powerful tool to probe the molecular mechanisms that control the development and function of human midbrain DA neurons.

Dendritic antigen-presenting cells derived from epidermis (Langerhans cells), bone marrow, and peripheral blood can present a wide variety of antigens, including tumor-associated antigens, for various immune responses. The development and function of dendritic cells is dependent upon a number of cytokines including granulocyte–macrophage-colony-stimulating factor. For example, Langerhans cells can present tumor-associated antigens for the induction of substantial in vivo anti-tumor immunity but only after activation in vitro by granulocyte–macrophage-colony-stimulating factor. Thus, we reasoned that insertion of a cDNA for granulocyte–macrophage-colony-stimulating factor into dendritic antigen-presenting cells may allow for autocrine stimulation and increased antigen-presenting capability. To test this possibility, we utilized an adenovirus vector to insert a cDNA for murine granulocyte–macrophage-colony-stimulating factor into the dendritic cell lines XS52–4D and XS106 (derived from neonatal mouse epidermis), bone marrow-derived dendritic cells, and epidermal cells that contain Langerhans cells. Infection of each of these cell types resulted in release of abundant quantities of granulocyte–macrophage-colony-stimulating factor. XS52–4D and XS106 cells infected with adenovirus granulocyte–macrophage-colony-stimulating factor exhibited prolonged dendrites and greater expression of major histocompatibility complex class II molecules and CD86 compared with cells infected with a null vector. Granulocyte–macrophage-colony-stimulating factor cDNA-containing XS cells, bone marrow-derived dendritic cells, and epidermal cells had more potent alloantigen presenting capability than cells infected with a null vector. Most importantly, granulocyte–macrophage-colony-stimulating factor gene-transferred epidermal cells were able to present tumor-associated antigens for in vivo anti-tumor immunity against challenge with the S1509a spindle-cell tumor whereas null vector-infected cells were unable to prime for immunity. These results suggest that introduction of a cDNA for granulocyte–macrophage-colony-stimulating factor into dendritic cells may be an effective means to augment their antigen-presenting capability and that granulocyte–macrophage-colony-stimulating factor gene-transfer- red epidermal cells may be useful in tumor vaccination strategies.

Volatile anesthetics and alcohols enhance transmission mediated by gamma-aminobutyric acid type A receptors (GABA(A)Rs) in the central nervous system, an effect that may underlie some of the behavioral actions of these agents. Substituting a critical serine residue within the GABA(A)R alpha(1) subunit at position 270 with the larger residue histidine eliminated receptor modulation by isoflurane, but it also affected receptor gating (increased GABA sensitivity). To correct the shift in GABA sensitivity of this mutant, we mutated a second residue, leucine at position 277 to alanine. The double mutant alpha(1)(S270H,L277A)beta(2)gamma(2S) GABA(A)R was expressed in Xenopus laevis oocytes and human embryonic kidney (HEK)293 cells, and it had near-normal GABA sensitivity. However, rapid application of a brief GABA pulse to receptors expressed in HEK293 cells revealed that the deactivation was faster in double mutant than in wild-type receptors. In all heterologous systems, the enhancing effect of isoflurane and ethanol was greatly decreased in the double mutant receptor. Homozygous knockin mice harboring the double mutation were viable and presented no overt abnormality, except hyperactivity. This knockin mouse line should be useful in determining which behavioral actions of volatile anesthetics and ethanol are mediated by the GABA(A)Rs containing the alpha(1) subunit.

Propofol (2,6-diisopropylphenol) is a widely used intravenous general anesthetic, which has been reported to produce bradycardia in patients at concentrations associated with profound sedation and loss of consciousness. Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels conduct a monovalent cationic current I(h) (also known as I(q) or I(f)) that contributes to autorhythmicity in both the brain and heart. Here we studied the effects of propofol on recombinant HCN1, HCN2, and HCN4 channels and found that the drug inhibits and slows activation of all three channels at clinically relevant concentrations. In oocyte expression studies, HCN1 channel activation was most sensitive to slowing by propofol (EC(50) values of 5.6 +/- 1.0 microM for fast component and 31.5 +/- 7.5 microM for slow component). HCN1 channels also showed a marked propofol-induced hyperpolarizing shift in the voltage dependence of activation (EC(50) of 6.7 +/- 1.0 microM) and accelerated deactivation (EC(50) of 4.5 +/- 0.9 microM). Furthermore, propofol reduced heart rate in an isolated guinea pig heart preparation over the same range of concentrations. These data suggest that propofol modulation of HCN channel gating is an important molecular mechanism that can contribute to the depression of central nervous system function and also lead to bradyarrhythmias in patients receiving propofol during surgical anesthesia.