Controlling the Potency of T Cell Activation Using an Optically Tunable Chimeric Antigen Receptor

The ability of biological systems to convert inputs from their environment into information to guide future decisions is central to life and a matter of great importance. While we know the components of many of the signaling networks that make these decisions, our understanding of the dynamic flow of information between these parts remains far more limited. T cells are an essential white blood cell type of an adaptive immune response and can discriminate between healthy and infected cells with remarkable sensitivity. This chapter describes the use of a synthetic T-cell receptor (OptoCAR) that is optically tunable within cell conjugates, providing control over the duration, and intensity of intracellular T-cell signaling dynamics. Optical control can also provide control over signaling with high spatial precision, and the OptoCAR is likely to find application more generally when modulating T-cell function with imaging approaches.

Pre-T cell receptor localization and trafficking are independent of its signaling

Expression of the pre-T cell receptor (preTCR) is an important checkpoint during the development of T cells, an essential cell type of our adaptive immune system. The preTCR complex is only transiently expressed and rapidly internalized in developing T cells and is thought to signal in a ligand-independent manner. However, identifying a mechanistic basis for these unique features of the preTCR compared with the final TCR complex has been confounded by the concomitant signaling that is normally present. Thus, we have reconstituted preTCR expression in non-immune cells to uncouple receptor trafficking dynamics from its associated signaling. We find that all the defining features of the preTCR are intrinsic properties of the receptor itself, driven by exposure of an extracellular hydrophobic region, and are not the consequence of receptor activation. Finally, we show that transitory preTCR cell surface expression can sustain tonic signaling in the absence of ligand binding, suggesting how the preTCR can nonetheless drive αβTCR lineage commitment.

CD33 BiTE® molecule-mediated immune synapse formation and subsequent T-cell activation is determined by the expression profile of activating and inhibitory checkpoint molecules on AML cells

Bispecific T-cell engager (BiTE^®) molecules recruit T cells to cancer cells through CD3ε binding, independently of T-cell receptor (TCR) specificity. Whereas physiological T-cell activation is dependent on signal 1 (TCR engagement) and signal 2 (co-stimulation), BiTE molecule-mediated T-cell activation occurs without additional co-stimulation. As co-stimulatory and inhibitory molecules modulate the strength and nature of T-cell responses, we studied the impact of the expression profile of those molecules on target cells for BiTE molecule-mediated T-cell activation in the context of acute myeloid leukemia (AML). Accordingly, we created a novel in vitro model system using murine Ba/F3 cells transduced with human CD33 ± CD86 ± PD-L1. T-cell fitness was assessed by T-cell function assays in co-cultures and immune synapse formation by applying a CD33 BiTE molecule (AMG 330). Using our cell-based model platform, we found that the expression of positive co-stimulatory molecules on target cells markedly enhanced BiTE molecule-mediated T-cell activation. The initiation and stability of the immune synapse between T cells and target cells were significantly increased through the expression of CD86 on target cells. By contrast, the co-inhibitory molecule PD-L1 impaired the stability of BiTE molecule-induced immune synapses and subsequent T-cell responses. We validated our findings in primary T-cell-AML co-cultures, demonstrating a PD-L1-mediated reduction in redirected T-cell activation. The addition of the immunomodulatory drug (IMiD) lenalidomide to co-cultures led to stabilization of immune synapses and improved subsequent T-cell responses. We conclude that target cells modulate CD33 BiTE molecule-dependent T-cell activation and hence, combinatorial strategies might contribute to enhanced efficacy.

Quantifying persistence in the T-cell signaling network using an optically controllable antigen receptor

T cells discriminate between healthy and infected cells with remarkable sensitivity when mounting an immune response, which is hypothesized to depend on T cells combining stimuli from multiple antigen-presenting cell interactions into a more potent response. To quantify the capacity for T cells to accomplish this, we have developed an antigen receptor that is optically tunable within cell conjugates, providing control over the duration, and intensity of intracellular T-cell signaling. We observe limited persistence within the T-cell intracellular network on disruption of receptor input, with signals dissipating entirely in ~15 min, and directly show sustained proximal receptor signaling is required to maintain gene transcription. T cells thus primarily accumulate the outputs of gene expression rather than integrate discrete intracellular signals. Engineering optical control in a clinically relevant chimeric antigen receptor (CAR), we show that this limited signal persistence can be exploited to increase CAR-T cell activation threefold using pulsatile stimulation. Our results are likely to apply more generally to the signaling dynamics of other cellular networks.

Peptide gels of fully-defined composition and mechanics for probing cell-cell and cell-matrix interactions in vitro

Current materials used for in vitro 3D cell culture are often limited by their poor similarity to human tissue, batch-to-batch variability and complexity of composition and manufacture. Here, we present a "blank slate" culture environment based on a self-assembling peptide gel free from matrix motifs. The gel can be customised by incorporating matrix components selected to match the target tissue, with independent control of mechanical properties. Therefore the matrix components are restricted to those specifically added, or those synthesised by encapsulated cells. The flexible 3D culture platform provides full control over biochemical and physical properties, allowing the impact of biochemical composition and tissue mechanics to be separately evaluated in vitro. Here, we demonstrate that the peptide gels support the growth of a range of cells including human induced pluripotent stem cells and human cancer cell lines. Furthermore, we present proof-of-concept that the peptide gels can be used to build disease-relevant models. Controlling the peptide gelator concentration allows peptide gel stiffness to be matched to normal breast (<1 kPa) or breast tumour tissue (>1 kPa), with higher stiffness favouring the viability of breast cancer cells over normal breast cells. In parallel, the peptide gels may be modified with matrix components relevant to human breast, such as collagen I and hyaluronan. The choice and concentration of these additions affect the size, shape and organisation of breast epithelial cell structures formed in co-culture with fibroblasts. This system therefore provides a means of unravelling the individual influences of matrix, mechanical properties and cell-cell interactions in cancer and other diseases.

Human interleukin-2 receptor β mutations associated with defects in immunity and peripheral tolerance

Zhang et al. identify human IL-2Rβ deficiency as a cause of severe immune dysregulation. The hypomorphic gene mutations reveal variable IL-2Rβ expression and function between different lymphocyte subsets as a means of selectively modulating immune responses.

Interleukin-2, which conveys essential signals for immunity, operates through a heterotrimeric receptor. Here we identify human interleukin-2 receptor (IL-2R) β chain (IL2RB) gene defects as a cause of life-threatening immune dysregulation. We report three homozygous mutations in the IL2RB gene of eight individuals from four consanguineous families that cause disease by distinct mechanisms. Nearly all patients presented with autoantibodies, hypergammaglobulinemia, bowel inflammation, dermatological abnormalities, lymphadenopathy, and cytomegalovirus disease. Patient T lymphocytes lacked surface expression of IL-2Rβ and were unable to respond to IL-2 stimulation. By contrast, natural killer cells retained partial IL-2Rβ expression and function. IL-2Rβ loss of function was recapitulated in a recombinant system in which IL2RB mutations caused reduced surface expression and IL-2 binding. Stem cell transplant ameliorated clinical symptoms in one patient; forced expression of wild-type IL-2Rβ also increased the IL-2 responsiveness of patient T lymphocytes in vitro. Insights from these patients can inform the development of IL-2–based therapeutics for immunological diseases and cancer.

Tuning ITAM multiplicity on T cell receptors can control potency and selectivity to ligand density

The T cell antigen receptor (TCR) recognizes peptides from pathogenic proteins bound in the major histocompatibility complex (MHC). To convert this binding event into downstream signaling, the TCR complex contains immunoreceptor tyrosine-based activation motifs (ITAMs) that act as docking sites for the cytoplasmic tyrosine kinase ZAP-70. Unique among antigen receptors, the TCR complex uses 10 ITAMs to transduce peptide-MHC binding to the cell interior. Using synthetic, drug-inducible receptor-ligand pairs, it was found that greater ITAM multiplicity primarily enhanced the efficiency with which ligand binding was converted into an intracellular signal. This manifested as an increase in the fraction of cells that became activated in response to antigen, and a more synchronous initiation of TCR-proximal signaling, rather than direct amplification of the intracellular signals. Exploiting these findings, the potency and selectivity of chimeric antigen receptors targeted against cancer were substantially enhanced by modulating the number of encoded ITAMs.

Encoding optical control in LCK kinase to quantitatively investigate its activity in live cells

LCK is a tyrosine kinase essential for initiating T-cell antigen receptor (TCR) signaling. A complete understanding of LCK function is constrained by a paucity of methods to quantitatively study its function within live cells. To address this limitation, we generated LCK*, in which a key active site lysine is replaced by a photo-caged equivalent, using genetic code expansion. This enabled fine temporal and spatial control over kinase activity, allowing us to quantify phosphorylation kinetics in situ using biochemical and imaging approaches. We find that auto-phosphorylation of the LCK active site loop is indispensable for its catalytic activity and that LCK can stimulate its own activation by adopting a more open conformation, which can be modulated by point mutations. We then show that CD4 and CD8, the T cell coreceptors, can enhance LCK activity, helping to explain their effect in physiological TCR signaling. Our approach also provides general insights into SRC-family kinase dynamics.

Membrane-Proximal Epitope Facilitates Efficient T Cell Synapse Formation by Anti-FcRH5/CD3 and Is a Requirement for Myeloma Cell Killing

The anti-FcRH5/CD3 T cell-dependent bispecific antibody (TDB) targets the B cell lineage marker FcRH5 expressed in multiple myeloma (MM) tumor cells. We demonstrate that TDBs trigger T cell receptor activation by inducing target clustering and exclusion of CD45 phosphatase from the synapse. The dimensions of the target molecule play a key role in the efficiency of the synapse formation. The anti-FcRH5/CD3 TDB kills human plasma cells and patient-derived myeloma cells at picomolar concentrations and results in complete depletion of B cells and bone marrow plasma cells in cynomolgus monkeys. These data demonstrate the potential for the anti-FcRH5/CD3 TDB, alone or in combination with inhibition of PD-1/PD-L1 signaling, in the treatment of MM and other B cell malignancies.

Selective, rapid and optically switchable regulation of protein function in live mammalian cells

The rapid and selective regulation of a target protein within living cells that contain closely related family members is an outstanding challenge. Here we introduce genetically directed bioorthogonal ligand tethering (BOLT) and demonstrate selective inhibition (iBOLT) of protein function. In iBOLT, inhibitor-conjugate/target protein pairs are created where the target protein contains a genetically encoded unnatural amino acid with bioorthogonal reactivity and the inhibitor conjugate contains a complementary bioorthogonal group. iBOLT enables the first rapid and specific inhibition of MEK isozymes, and introducing photoisomerizable linkers in the inhibitor conjugate enables reversible, optical regulation of protein activity (photo-BOLT) in live mammalian cells. We demonstrate that a pan kinase inhibitor conjugate allows selective and rapid inhibition of the lymphocyte specific kinase, indicating the modularity and scalability of BOLT. We anticipate that BOLT will enable the rapid and selective regulation of diverse proteins for which no selective small-molecule ligands exist.

The T cell receptor triggering apparatus is composed of monovalent or monomeric proteins

Understanding the component stoichiometry of the T cell antigen receptor (TCR) triggering apparatus is essential for building realistic models of signal initiation. Recent studies suggesting that the TCR and other signaling-associated proteins are preclustered on resting T cells relied on measurements of the behavior of membrane proteins at interfaces with functionalized glass surfaces. Using fluorescence recovery after photobleaching, we show that, compared with the apical surface, the mobility of TCRs is significantly reduced at Jurkat T cell/glass interfaces, in a signaling-sensitive manner. Using two biophysical approaches that mitigate these effects, bioluminescence resonance energy transfer and two-color coincidence detection microscopy, we show that, within the uncertainty of the methods, the membrane components of the TCR triggering apparatus, i.e. the TCR complex, MHC molecules, CD4/Lck and CD45, are exclusively monovalent or monomeric in human T cell lines, implying that TCR triggering depends only on the kinetics of TCR/pMHC interactions. These analyses also showed that constraining proteins to two dimensions at the cell surface greatly enhances random interactions versus those between the membrane and the cytoplasm. Simulations of TCR-pMHC complex formation based on these findings suggest how unclustered TCR triggering-associated proteins might nevertheless be capable of generating complex signaling outputs via the differential recruitment of cytosolic effectors to the cell membrane.

A new pathway of CD5 glycoprotein-mediated T cell inhibition dependent on inhibitory phosphorylation of Fyn kinase

Triggering of the T cell receptor initiates a signaling cascade resulting in the activation of the T cell. These signals are integrated alongside those resulting from the triggering of other receptors whose function is to modulate the overall response. CD5 is an immunotyrosine-based inhibition motif-bearing receptor that antagonizes the overt T cell receptor activation response by recruiting inhibitory intracellular mediators such as SHP-1, RasGAP, or Cbl. We now propose that the inhibitory effects of CD5 are also mediated by a parallel pathway that functions at the level of inhibition of Fyn, a kinase generally associated with T cell receptor-mediated activation. After CD5 ligation, phosphorylation of the negative regulatory tyrosine (Tyr(531)) of Fyn increases, and this correlates with a substantial reduction in the kinase activity of Fyn and a profound inhibition of ZAP-70 activation. The effect requires the last 23 amino acids of the cytoplasmic domain of the receptor, strongly implying the involvement of a new CD5-interacting signaling or adaptor protein. Furthermore, we show that upon CD5 ligation there is a profound shift in its distribution from the bulk fluid phase to the lipid raft environment, where it associates with Fyn, Lck, and PAG. We suggest that the relocation of CD5, which we also show is capable of forming homodimers, to the proximity of raft-resident molecules enables CD5 to inhibit membrane proximal signaling by controlling the phosphorylation and activity of Fyn, possibly by interfering with the disassembly of C-terminal Src kinase (Csk)-PAG-Fyn complexes during T cell activation.

In vivo nicotine exposure in the zebra finch: a promising innovative animal model to use in neurodegenerative disorders related research

Nicotine improves cognitive enhancement and there are indications that neurodegenerative (age-related) cognitive disorders could be treated with nicotine-based drugs. The zebra finch is a well-recognized model to study cognitive functioning; hence this model could be used to study the effects of nicotine in neurodegenerative cognitive disorders. However, nicotine's in vivo physiological and behavioral effects have never been studied in the zebra finch. Here we present the first in vivo nicotine study in zebra finches. We evaluated the dose-response effects of nicotine on locomotor activity, song production, food intake and body weight. A liquid chromatography tandem mass spectrometry method was developed and validated for quantification of nicotine and cotinine in feces. The subcutaneous nicotine drug regiment (0.054-0.54mg/kg) induced physiologically significant values of nicotine and cotinine. The mid (0.18mg/kg) and high (0.54mg/kg) dose of nicotine promoted the development and expression of a sensitized response of song production and locomotor activity. Food intake and body weight were not affected following nicotine exposure. In conclusion, the zebra finch can be used as an innovative animal model not only in nicotine-related research studying cognitive functioning, but also in studies examining nicotine dependence and addictive mechanisms.

The platelet receptor CLEC-2 is active as a dimer

The platelet receptor CLEC-2 binds to the snake venom toxin rhodocytin and the tumor cell surface protein podoplanin. Binding of either of these ligands promotes phosphorylation of a single tyrosine residue in the YXXL motif in the intracellular domain of CLEC-2. Phosphorylation of this tyrosine initiates binding of spleen tyrosine kinase (Syk) and triggers further downstream signaling events and ultimately potent platelet activation and aggregation. However, it is unclear how a single YXXL motif can interact efficiently with Syk, which usually recognizes two tandem YXXL repeats presented as an immunoreceptor tyrosine-based activation motif (ITAM). Using bioluminescence resonance energy transfer, coimmunopreciptitation, recombinant protein expression and analytical gel filtration chromatography, surface plasmon resonance, Western blotting, multiangle light scattering (MALS), and analytical ultracentrifugation, we show that CLEC-2 exists as a non-disulfide-linked homodimer which could allow each Syk molecule to interact with two YXXL motifs, one from each CLEC-2 monomer.

Distinctive properties of the hyaluronan-binding domain in the lymphatic endothelial receptor Lyve-1 and their implications for receptor function

The lymphatic endothelial hyaluronan (HA) receptor Lyve-1 is a member of the Link protein superfamily most similar to the leukocyte HA receptor CD44. However, the structure of Lyve-1 and the nature of its interaction with ligand are obscure. Here we present new evidence that Lyve-1 is functionally distinct from CD44. Using truncation mutagenesis we confirm that Lyve-1 in common with CD44 contains an extended HA-binding unit, comprising elements flanking the N and C termini of the consensus lectin-like Link module, bridged by a third conserved disulfide linkage that is critical for HA binding. In addition, we identify six essential residues Tyr-87, Ile-97, Arg-99, Asn-103, Lys-105, and Lys-108 that define a compact HA-binding surface on Lyve-1, encompassing the epitope for an adhesion-blocking monoclonal antibody 3A, in an analogous position to the HA-binding surface in CD44. The overtly electrostatic character of HA binding in Lyve-1 and its sensitivity to ionic strength (IC(50) of 150 mm NaCl) contrast markedly with CD44 (IC(50) > 2 m NaCl) in which HA binding is mediated by hydrogen bonding and hydrophobic interactions. In addition, unlike the extended Link module in CD44, which binds HA efficiently when expressed as a soluble monomer (K(d) = 65.7 mum), that of Lyve-1 requires artificial dimerization, although the full ectodomain is active as a monomer (K(d) = 35.6 mum). Finally, full-length Lyve-1 did not form stable dimers in binding-competent 293T transfectants when assessed using bioluminescent resonance energy transfer. These results reveal that elements additional to the extended Link module are required to stabilize HA binding in Lyve-1 and indicate important structural and functional differences with CD44.

DySCo: quantitating associations of membrane proteins using two-color single-molecule tracking

We present a general method called dynamic single-molecule colocalization for quantitating the associations of single cell surface molecules labeled with distinct autofluorescent proteins. The chief advantages of the new quantitative approach are that, in addition to stable interactions, it is capable of measuring nonconstitutive associations, such as those induced by the cytoskeleton, and it is applicable to situations where the number of molecules is small.

Ferroportin: lack of evidence for multimers

Ferroportin is a multi-transmembrane glycoprotein that mediates iron export from cells. Mutations in ferroportin are linked to type IV hemochromatosis, a dominantly inherited disorder of iron metabolism. Multimers of ferroportin, whose existence may relate to the dominant inheritance pattern of disease, have been detected in some studies but not others. We looked for evidence of multimerization in several different types of experiment. We assayed the maturation of mutant and wild-type ferroportin and found that loss-of-function mutants had a reduced half-life but did not alter the stability of coexpressed wild-type. Using bioluminescence resonance energy transfer analysis, we tested how mature wild-type ferroportin behaved in intact live cell membranes. Ferroportin-ferroportin interactions gave the very low acceptor/donor ratio-independent energy transfer levels characteristic of random protein-protein interactions, consistent with ferroportin behaving as a monomer. Consistent with these experiments, we were unable to detect a dominant negative functional effect of mutant ferroportin on wild-type, even when expression of wild-type protein was titrated to low levels. These data suggest that dominantly inherited ferroportin disease does not result from the direct action of a mutated protein inhibiting a wild-type protein within multimers. We propose other possible mechanisms of disease.

Cellular nicotinic receptor desensitization correlates with nicotine-induced acute behavioral tolerance in rats

RATIONALE

Individuals vary in their susceptibility to nicotine addiction. However, there is little evidence that behavioral sensitivity to nicotine is dependent upon the functional state of nicotinic cholinergic receptors (nAChRs).

OBJECTIVE

This study aims to determine the relationship between in vivo behavioral desensitization and in vitro desensitization of nAChR function.

METHODS

Male Sprague-Dawley rats trained to discriminate nicotine were tested for development of acute behavioral tolerance. The rats were injected with nicotine (0.4 mg/kg free base, s.c.), tested for nicotine discrimination for 2 min, then injected with the same dose of nicotine 90, 180, and 270 min after the first injection and tested for nicotine discrimination after each injection. Susceptibility of nAChRs of individual rats to desensitization was assessed by use of the (86)Rb(+) efflux assay using synaptosomes prepared from the "thalamus," which included the hypothalamus and midbrain as well as the thalamic nuclei. To desensitize nAChRs, synaptsosomes were superfused with low concentrations of nicotine (5, 10, 20, and 30 nM) before stimulation of (86)Rb(+) efflux with nicotine (10 muM).

RESULTS

The slopes of the behavioral desensitization were plotted as a function of the decline of nicotine-stimulated (86)Rb(+) efflux after in vitro desensitization. A significant correlation was observed between the in vitro desensitization of thalamic (86)Rb(+) efflux and the extent of behavioral desensitization of individual rats.

CONCLUSIONS

These findings are consistent with the idea that production of acute behavioral tolerance by nicotine is related to its ability to induce nAChR desensitization at the cellular level.

Glycoprotein VI oligomerization in cell lines and platelets

BACKGROUND

Glycoprotein VI (GPVI) is a physiologic receptor for collagen expressed at the surface of platelets and megakaryocytes. Constitutive dimerization of GPVI has been proposed as being necessary for the interaction with collagen, although direct evidence of dimerization has not been reported in cell lines or platelets.

OBJECTIVES

To investigate oligomerization of GPVI in transfected cell lines and in platelets under non-stimulated conditions.

METHODS AND RESULTS

By using a combination of molecular and biochemical techniques, we demonstrate that GPVI association occurs at the surface of transfected 293T cells under basal conditions, through an interaction at the extracellular domain of the receptor. Bioluminescence resonance energy transfer was used to confirm oligomerization of GPVI under these conditions. A chemical crosslinker was used to detect constitutive oligomeric forms of GPVI at the surface of platelets, which contain the Fc receptor (FcR) gamma-chain.

CONCLUSIONS

The present results directly demonstrate GPVI-FcR gamma-chain oligomerization at the surface of the platelet, and thereby add to the growing evidence that oligomerization of GPVI may be a prerequisite for binding of the receptor to collagen, and therefore for proper functioning of platelets upon vascular damage.

A rigorous experimental framework for detecting protein oligomerization using bioluminescence resonance energy transfer

Bioluminescence resonance energy transfer (BRET), which relies on nonradiative energy transfer between luciferase-coupled donors and GFP-coupled acceptors, is emerging as a useful tool for analyzing the quaternary structures of cell-surface molecules. Conventional BRET analyses are generally done at maximal expression levels and single acceptor/donor ratios. We show that under these conditions substantial energy transfer arises from random interactions within the membrane. The dependence of BRET efficiency on acceptor/donor ratio at fixed surface density, or expression level at a defined acceptor/donor ratio, can nevertheless be used to correctly distinguish between well-characterized monomeric and oligomeric proteins, including a very weak dimer. The pitfalls associated with the nonrigorous treatment of BRET data are illustrated for the case of G protein-coupled receptors (GPCRs) proposed to form homophilic and/or mixed oligomers on the basis of previous, conventional BRET experiments.

Neurochemical and behavioral effects of bupropion and mecamylamine in the presence of nicotine

The primary mechanism of action of bupropion, a smoking cessation drug, is commonly believed to involve the dopaminergic system although evidence exists that bupropion also has effects at nicotinic acetylcholine receptors (nAChRs). This study evaluated the disruptive effects of nicotine on response rates in the presence of bupropion and the nAChR antagonist, mecamylamine, as well as the ability of these drugs to alter nicotine-stimulated nAChR function in various brain areas. Rats were trained to respond on a single lever under a variable interval 15 (VI15) schedule for food reinforcement. Initially, dose effect curves were generated for nicotine, bupropion and mecamylamine. Upon determining the dose of nicotine (1.2 mg/kg) effective in completely disrupting rates of responding, it was established that both mecamylamine and bupropion block nicotine's rate-reducing effects. This result suggests that bupropion shares behavioral effects with mecamylamine when administered in the presence of nicotine. To explore this relationship further, the effect of in vivo administration of bupropion or mecamylamine on nicotine-stimulated (86)Rb(+) efflux was studied in synaptosomes prepared from the frontal cortex, hippocampus, striatum and thalamus. Nicotine-stimulated (86)Rb(+) efflux from all brain regions was significantly reduced in rats administered 3.0 mg/kg mecamylamine (s.c.) 15 min prior to dissection compared to control rats. In contrast, a significant increase in nicotine-stimulated (86)Rb(+) efflux was observed in all brain regions from rats administered 30.0 mg/kg bupropion (s.c.) 15 min prior to dissection compared to control rats. Taken together these results demonstrate that when administered in the presence of nicotine, bupropion elicits unique pharmacological differences such that it exhibits both nAChR agonist- and antagonistic-like effects.

Nicotinic receptor inactivation after acute and repeated in vivo nicotine exposures in rats

Nicotine tolerance is often accompanied by an upregulation of brain area nicotinic acetylcholine receptors (nAChRs) in both animal and human subjects. This upregulation has been hypothesized to result from repeated or prolonged exposures of these receptors to nicotine. To explore this further, this study examined the level of nAChR desensitization following acute and repeated nicotine administration in the male Lewis rat. Nicotine-stimulated (86)Rb(+) efflux was measured in synaptosomes prepared from the frontal cortex, hippocampus, striatum, and thalamus. Analysis of receptor functionality was achieved by calculating area-under-the-curve (AUC) for nicotine-induced fractional (86)Rb(+) efflux. Nicotine-stimulated (86)Rb(+) efflux from all brain regions was significantly less in rats that received an acute injection of 0.4 mg/kg nicotine (s.c.) 15 min prior to dissection compared to control rats. This decrease in nAChR functional status was also observed in rats treated with 1 day or 14 days of twice-daily nicotine administration. These results are consistent with the concept that acute exposure to nicotine induces rapid desensitization of nAChRs. In addition, following repeated exposure to nicotine, nAChRs did not become tolerant to the loss in receptor function that occurs after an initial nicotine administration. Overall, these data suggest that neuronal adaptations underlying nicotine tolerance may begin upon initial exposure then persist following repeated exposures.

Evidence of cellular nicotinic receptor desensitization in rats exhibiting nicotine-induced acute tolerance

RATIONALE

Individuals vary in their susceptibility to nicotine addiction. However, there is little evidence that behavioral sensitivity to nicotine is dependent upon the functional state of nicotinic cholinergic receptors (nAChRs).

OBJECTIVE

To determine the relationship between in vivo pharmacological desensitization (in other words, acute tolerance) and brain regional nAChR function.

METHODS

Male Sprague-Dawley rats, trained to discriminate nicotine (0.4 mg/kg free base) from saline in a two-lever drug discrimination task, were tested for the development of acute tolerance. Rats were injected with 0.4 mg/kg nicotine, tested for nicotine discrimination for 2 min, then injected with the same dose of nicotine 90 min, 180 min, and 270 min after the first injection and tested for nicotine discrimination after each injection. These subjects were separated into two groups, desensitizers (DZ) and nondesensitizers (NDZ), based upon performance in the repetitive dosing drug discrimination paradigm. The sensitivity of nAChRs in specific brain regions of these two groups was assessed by the use of an 86Rb+ efflux assay using synaptosomes prepared from the frontal cortex, hippocampus, striatum, and "thalamus," which included the midbrain and hypothalamus as well as the thalamus.

RESULTS

The nicotine-induced increase in 86Rb+ efflux was significantly greater in NDZ as compared to DZ in the "thalamus." There was no statistically significant difference in the effects of nicotine in the frontal cortex, hippocampus, and striatum of these two groups. A significant correlation was observed between thalamic 86Rb+ efflux and the rate of behavioral desensitization of individual rats.

CONCLUSION

These findings are consistent with the concept that the production of acute tolerance by nicotine in vivo correlates directly with its ability to induce nAChR desensitization at the cellular level.

Withdrawal from chronic nicotine administration impairs contextual fear conditioning in C57BL/6 mice

The effects of acute nicotine administration (0.09 mg/kg nicotine), chronic nicotine administration (6.3 mg/kg/d nicotine for 14 d), and withdrawal from chronic nicotine administration on fear conditioning in C57BL/6 mice were examined. Mice were trained using two coterminating conditioned stimulus (30 s; 85 dB white noise)--unconditioned stimulus (2 s; 0.57 mA foot shock) pairings and tested 24 h later for contextual and cued fear conditioning. Acute nicotine administration enhanced contextual fear conditioning, chronic nicotine administration had no effect on contextual fear conditioning, and withdrawal from chronic nicotine administration impaired contextual fear conditioning. Plasma nicotine concentrations were similar after acute and chronic treatment and were within the range reported for smokers. During withdrawal, concentrations of nicotine were undetectable. An acute dose of nicotine (0.09 mg/kg) during withdrawal from chronic nicotine treatment reversed withdrawal-associated deficits in contextual fear conditioning. The results suggest that tolerance to the effects of nicotine on contextual fear conditioning develops with chronic nicotine treatment at a physiologically relevant dose, and withdrawal from this chronic nicotine treatment is associated with impairments in contextual fear conditioning. These findings provide a model of how the effects of nicotine on learning may contribute to the development and maintenance of nicotine addiction.

Crystal structure of a soluble CD28-Fab complex

Naive T cell activation requires signaling by the T cell receptor and by nonclonotypic cell surface receptors. The most important costimulatory protein is the monovalent homodimer CD28, which interacts with CD80 and CD86 expressed on antigen-presenting cells. Here we present the crystal structure of a soluble form of CD28 in complex with the Fab fragment of a mitogenic antibody. Structural comparisons redefine the evolutionary relationships of CD28-related proteins, antigen receptors and adhesion molecules and account for the distinct ligand-binding and stoichiometric properties of CD28 and the related, inhibitory homodimer CTLA-4. Cryo-electron microscopy-based comparisons of complexes of CD28 with mitogenic and nonmitogenic antibodies place new constraints on models of antibody-induced receptor triggering. This work completes the initial structural characterization of the CD28-CTLA-4-CD80-CD86 signaling system.

Differential behavioral responses to nicotine in Lewis and Fischer-344 rats

Individual and strain variability in the effects of nicotine suggests the involvement of a genetic component in nicotinic cholinergic receptor (nAChR) function, which may help explain nicotine's variable behavioral and pharmacological effects in different individuals. The present study evaluated differential responses to the discriminative stimulus (DS) and rewarding properties of nicotine in Lewis (LEW) and Fischer-344 (F-344) rats. Drug discrimination (DD) data suggest that the LEW rat is more sensitive to nicotine as LEW rats acquired the nicotine discrimination at a dose of 0.4 mg/kg, whereas F-344 rats acquired the dose of 0.9 mg/kg (all nicotine doses expressed as free base). Similarly, LEW rats exhibited nicotine-conditioned place preference (CPP) at 0.6 mg/kg, whereas the F-344 rats did not. Subsequent testing with a higher dose (0.9 mg/kg) failed to maintain the nicotine-CPP in the LEW rats. Conversely, nicotine-place preference in the F-344 rats was not changed at the higher dose. Taken together, these results suggest potential differences of sensitivities in LEW and F-344 rats to the rewarding and discriminative stimulus (DS) properties of nicotine. These findings support previous research by demonstrating that the F-344 rat is less sensitive to nicotine compared to the LEW rat.

Individual variability of dopamine release from nucleus accumbens induced by nicotine

Effects of subcutaneous administration of vehicle, amphetamine (1 mg/kg) or nicotine (0.4 mg/kg, injected twice, 90 min apart) on extracellular dopamine (DA) concentration in the nucleus accumbens (ACC) and ventral tegmental area (VTA) of the Sprague-Dawley rat were studied using microdialysis. Experiments were conducted at least 10 days following implantation of guide cannulae, and at least 2 h following insertion of microdialysis probes into the guides on the morning of each experiment. Probes were perfused at 2.5 microl/min and several fractions were collected every 10 min before and after the two test injections. Samples were analyzed by high-performance liquid chromatography with electrochemical detection for the major neurotransmitters and their metabolites. Significant DA release following nicotine administration was observed in ACC but not in VTA. By classifying ACC DA responses of individual rats, three major subgroups were identified which exhibited more robust responses. Nicotine appeared to be acting as a modulator of ACC DA, increasing DA output if baseline was <5 nM, but slowing release when the baseline exceeded 5 nM. These data are consistent with previous reports of modulation of arousal level by nicotine via DA.

Discriminative stimulus (DS) properties of nicotine in the C57BL/6 mouse

Previous research conducted in this and other laboratories has examined the role of genetic factors in determining sensitivity to (-)-nicotine in a variety of behavioral and physiological measures in the rat. More recent research further indicates that genetic factors can also influence the level of sensitivity to (-)-nicotine when serving as a discriminative stimulus (DS) in different rat strains. However, there has been little work examining the influence of genotype on the discriminative stimulus (DS) properties of (-)-nicotine in mice, a species that has played a major role in understanding the relationship between genetics and (-)-nicotine pharmacological effects. To further our understanding of the role of genetics and the ability of (-)-nicotine to exert DS control of behavior in the mouse, a group of C57BL/6 mice was trained to discriminate 0.4 mg/kg (-)-nicotine from saline using a two-lever operant procedure. (-)-Nicotine's discriminative stimulus in C57BL/6 mice appears to be similar to that generated in the rat. Results from behavioral tests with other drugs indicated that d-amphetamine exhibited a partial generalization, while (+)-nicotine fully generalized with nicotine. Tests of antagonism with mecamylamine and scopolamine further showed the cholinergic specificity of the (-)-nicotine DS in the mouse; mecamylamine but not scopolamine completely antagonized the (-)-nicotine DS. This work lays the groundwork for future comparisons of different mouse strain's sensitivities to (-)-nicotine's discriminative stimulus as well as using this behavioral model to search for new nicotinic receptor agonists and antagonists.

Pharmacological investigation of (+)- and (-)-cis-2,3,3a,4,5,9b-hexahydro-1-methyl-1H-pyrrolo-[3,2-h]isoq uinoline, a bridged-nicotine analog

We recently synthesized a bridged-nicotine (BN) analog and its enantiomers. They failed to compete for [3H]nicotine binding in rat brain homogenates, yet they produced nicotine-like effects by decreasing locomotor activity and producing antinociception in the tail-flick, hot-plate and PPQ tests in mice. Therefore, additional in vivo and in vitro studies were undertaken to determine whether these compounds are indeed acting independently of the nicotinic system. Although these analogs did not produce nicotine-like responding when evaluated in rat drug discrimination, the racemate augmented the cue when administered in conjunction with nicotine. Moreover, the antinociceptive measured in the different tests and hypothermic effects of (+)-BN, the more potent enantiomer, were not blocked by the nicotinic antagonists mecamylamine and dihydro-beta-erythroidine. Acute tolerance developed to (+)-BN-induced antinociception but not to hypothermia after subcutaneous administration. In addition, no cross-tolerance was observed between (+)-BN and nicotine in the different tests. The absence of generalization in the discrimination test suggests that the BN analogs do not possess nicotine-like activity. In addition, the failure of mecamylamine and dihydro-beta-erythroidine to antagonize the antinociceptive and hypothermic effects of (+)-BN, on one hand, and the inability of the bridge analogs to stimulate 86Rb+ efflux in brain synaptosomes, on the other hand, provide further evidence that BN analog agonist effects are not mediated by the alpha-4, beta-2 receptor subunit combination. It is unlikely that alpha-7 subunits mediate the agonists effects of BN analogs because their affinity to neuronal [125I]alpha-bungarotoxin binding sites is in the higher micromolar range. Other nicotinic receptor subtypes remain possible candidates because (+/-)-BN augments the generalization of nicotine in drug discrimination and produces some nicotine-like pharmacological effects. BN analogs could represent a novel class of nicotinic analgesics because naloxone and atropine failed to alter the antinociceptive effects of (+)-BN. Alternatively, their actions may be entirely independent of the nicotinic system.

Genetic and environmental aspects of the role of nicotinic receptors in neurodegenerative disorders: emphasis on Alzheimer's disease and Parkinson's disease

As neurodegenerative disorders are better characterized, the importance of genetic and environmental interactions is becoming more evident. Among the neurodegenerative disorders, Alzheimer's disease and Parkinson's disease are both characterized by large losses of nicotinic binding sites in brain. In addition, losses in nicotinic receptors occur during normal aging. Chronic administration of nicotine in man or experimental animals increases the number of nicotinic receptors in brain. Nicotine has been shown to possess some neuroprotective properties for both cholinergic and dopaminergic neurons. These neuroprotective properties, when better understood, may provide important information on normal aging and neurodegenerative disorder related neuronal cell death. Understanding the functional aspects of neuronal nicotinic receptor subtypes may lead to successful therapeutic treatments or disease preventative strategies for neurodegenerative disorders.

Restructuring the CNS role for a managed care environment

The CNS role in a large northeast teaching hospital was the focus of a major organizational change process in response to a tightening fiscal environment. CNSs worked with the nurse executive team to restructure their role from expert consultant to case manager, nurse manager partner, and resource and consultant to the Department of Nursing. Development needs of the CNSs were assessed before and after role revision to evaluate the process and provide evidence of learning and change. The change and learning process evidenced in this article exemplifies the CNSs' ability to adapt and respond to the rapidly changing needs of today's managed care setting.

Evidence that nicotine can acutely desensitize central nicotinic acetylcholinergic receptors

Current concepts concerning nicotine's CNS mechanism(s) of action suggest that this drug produces its effects via an interaction at nicotinic-cholinergic receptors (nAChRs) sensitive to acetylcholine. In vitro research further suggests that, following its initial agonist effect, this cholinergic drug may also induce a rapid desensitization of the nAChR similar to that of acetylcholine, resulting in termination of its pharmacological effect. Research described in this paper provides evidence of this secondary desensitization process in vivo by demonstrating nicotine's ability to induce acute tolerance in a Discriminative Stimulus (DS) paradigm. The ability of nicotine (400 micrograms/kg, SC) to elicit DS control of behavior in a two-lever operant procedure was significantly reduced via a challenge dose (800 micrograms/kg, SC) of nicotine administered 15-180 min before the training dose. Twenty-three of 52 rats demonstrated this phenomenon. The time to develop acute tolerance varied, providing additional evidence that these effects may be contingent upon individual rat variability. In addition, physostigmine was also observed to induce a similar desensitization in a random population of desensitizing rats. Lastly, there were no differences between desensitizers and non-desensitizers in relation to the ability of mecamylamine (1000 micrograms/kg, SC) to antagonize the DS, while in both populations of rats scopolamine (100 micrograms/kg, SC) failed to antagonize the DS.

Development needs of advance practice nurses in a managed care environment

The authors describe an organizational change process driven by a critical cost containment effort in a teaching hospital in the northeastern United States. This process resulted in a major shift in the role of the clinical nurse specialist. Development priorities of clinical nurse specialists before and after redesign of the role are described.

Withdrawal from chronic nicotine fails to produce a conditioned taste aversion to saccharin in rats

Sprague-Dawley rats were maintained on a daily regimen of nicotine, morphine or saline administration for 28 days. Following the discontinuation of the daily drug regimen, rats were given a choice of tap water or a saccharin-water solution. The rats previously receiving morphine drank significantly less saccharin-water solution than did the rats receiving nicotine or saline injections. The failure of the nicotine rats to display a conditioned aversion to the novel saccharin flavor suggests that nicotine did not produce a physiological withdrawal syndrome analogous to morphine withdrawal in this paradigm.

Osteopenia in extremely low birthweight infants

Fifteen extremely low birthweight (ELBW) white infants (those weighing 1000 g or less) were observed at birth, within eight weeks of birth and near 40 weeks postconception. On the second and third occasions, weight, crown-heel length, and bone mineral content of their forearms were measured. Fifteen infants born at full term on whom similar measurements were made soon after birth acted as controls. Between 32 and 39 weeks the median weight of ELBW infants increased from 970 g to 1850 g and crown-heel length from 35.7 cm to 41.0 cm. There was no evidence, however, of bone mineral accretion in the measurement region; initial and final median measurements of bone mineral content were 76 mg/cm and 86 mg/cm, the median individual difference being only 4 mg/cm with an interquartile range of 25 mg/cm. Median weight, crown-heel length, and bone mineral content of the control group were 3270 g, 50.6 cm, and 196 mg/cm, respectively. Compared with the controls, ELBW infants at 39 weeks were a median (interquartile range) of 1420 (525) g lighter, 9.9 (3.9) cm shorter, and had a bone mineral content deficit of 108 (32) mg/cm. In terms of weight and crown-heel length ELBW infants at 39 weeks were comparable with infants born and observed at 32 weeks' gestation; compared with these infants the bone mineral content deficit in the ELBW group was about 33%.

Bone mineral content in bronchopulmonary dysplasia

Fourteen preterm infants who developed bronchopulmonary dysplasia diagnosed radiologically were compared with a group of similar infants who did not. The two groups were of comparable maturity and birth weight. The clinical histories indicated that those infants with bronchopulmonary dysplasia had had longer periods of supplemental oxygen, more frequent treatment with dexamethasone, and a higher mean total dosage of frusemide. Bone mineral content in the mid-forearm was measured by photon absorptiometry at or near the postconceptional age of 40 weeks in all cases; no significant difference was found between the two groups, although both were severely undermineralised when compared with infants born at full term. In both groups mean daily calcium intake (about 70 mg/kg/day) was about half the daily intrauterine accretion of calcium.

Osteopenia of prematurity

Bone mineral content of the forearm was measured by photon absorptiometry in 17 preterm infants at a postconceptional age of 40 weeks. Radiographs of the forearm were assessed by Koo's method and plasma alkaline phosphatase activity was also measured at this time. Bone mineral content was significantly but weakly correlated with Koo score and was not significantly correlated with alkaline phosphatase activity. Neither of these two commonly used investigations accurately predicts the presence of underlying bone disease. Compared with 15 full term infants the preterm infants had significantly lower values of bone mineral content, palpated ulnar length, and crown-heel length. After adjusting for weight and ulnar length the preterm group still had a significantly lower mean value of bone mineral content than the full term group. Accurate diagnosis of osteopenia of prematurity requires photon absorptiometry, with bone mineral content assessed relative to body weight or ulnar length.

Measurement of bone mineral content in the human fetus by photon absorptiometry

A photon absorptiometer designed to measure the bone mineral content (BMC) of the radius and ulna in premature or term babies was used to examine 34 forearm specimens obtained from 25 male and 9 female babies dying before or up to 13 weeks after birth. Gestational age, foot and crown-heel lengths and birth weight were recorded. Radiographic measurements showed that the midshaft of the radius can be located with a positioning error of +/- 1.28 mm (+/- 2 S.E.E.) from the distance between the distal ulnar styloid process and proximal tip of the olecranon, both of which can be palpated in vivo. Scanning at 5 sites showed that effects of positioning errors on BMC measurements are least at the midshaft site. Subsequent measurements of the ash weight of sections of the radius and ulna, centred on the midshaft of the radius, showed that ash weight/unit length can be estimated with a standard error 2.99 mg/cm from scan data.

Field penetration of arrays of compact applicators in localized hyperthermia

The three-dimensional analysis of a range of new compact applicators indicates that there is an optimum operating frequency for maximum depth of field penetration and a given applicator size. The prospect of obtaining increased penetration depth by deploying more than one applicator is considered and assessed for an equi-phase array of compact applicators arranged symmetrically around a cylindrical shaped volume of uniform muscle phantom material; field penetration curves enable the maximum cross-section that can be heated to be assessed. Experiments at 200 MHz and results from a three-dimensional analysis demonstrate the usefulness of the assessment and establish that in multi-applicator configurations the field penetration decreases markedly for cross-sectional diameters in excess of 10 cm. However, the three-dimensional analysis for four applicators also shows that more uniform fields are obtained in the muscle phantom when it is surrounded by a low loss bolus region. In conclusion the clinical implications of the investigations are briefly discussed.