Induction of Plasmodium falciparum-Specific CD4+ T Cells and Memory B Cells in Gabonese Children Vaccinated with RTS,S/AS01E and RTS,S/AS02D

The recombinant circumsporozoite protein (CS) based vaccine, RTS,S, confers protection against Plasmodium falciparum infection in controlled challenge trials and in field studies. The RTS,S recombinant antigen has been formulated with two adjuvant systems, AS01 and AS02, which have both been shown to induce strong specific antibody responses and CD4 T cell responses in adults. As infants and young children are particularly susceptible to malaria infection and constitute the main target population for a malaria vaccine, we have evaluated the induction of adaptive immune responses in young children living in malaria endemic regions following vaccination with RTS,S/AS01(E) and RTS,S/AS02(D). Our data show that a CS-specific memory B cell response is induced one month after the second and third vaccine dose and that CS-specific antibodies and memory B cells persist up to 12 months after the last vaccine injection. Both formulations also induced low but significant amounts of CS-specific IL-2(+) CD4(+) T cells one month after the second and third vaccine dose, upon short-term in vitro stimulation of whole blood cells with peptides covering the entire CS derived sequence in RTS,S. These results provide evidence that both RTS,S/AS01(E) and RTS,S/AS02(D) induced adaptive immune responses including antibodies, circulating memory B cells and CD4(+) T cells directed against P. falciparum CS protein.ClinicalTrials.gov NCT00307021

T Cell Responses to the RTS,S/AS01E and RTS,S/AS02D Malaria Candidate Vaccines Administered According to Different Schedules to Ghanaian Children

BACKGROUND: The Plasmodium falciparum pre-erythrocytic stage candidate vaccine RTS,S is being developed for protection of young children against malaria in sub-Saharan Africa. RTS,S formulated with the liposome based adjuvant AS01(E) or the oil-in-water based adjuvant AS02(D) induces P. falciparum circumsporozoite (CSP) antigen-specific antibody and T cell responses which have been associated with protection in the experimental malaria challenge model in adults. METHODS: This study was designed to evaluate the safety and immunogenicity induced over a 19 month period by three vaccination schedules (0,1-, 0,1,2- and 0,1,7-month) of RTS,S/AS01(E) and RTS,S/AS02(D) in children aged 5-17 months in two research centers in Ghana. Control Rabies vaccine using the 0,1,2-month schedule was used in one of two study sites. RESULTS: Whole blood antigen stimulation followed by intra-cellular cytokine staining showed RTS,S/AS01(E) induced CSP specific CD4 T cells producing IL-2, TNF-α, and IFN-γ. Higher T cell responses were induced by a 0,1,7-month immunization schedule as compared with a 0,1- or 0,1,2-month schedule. RTS,S/AS01(E) induced higher CD4 T cell responses as compared to RTS,S/AS02(D) when given on a 0,1,7-month schedule. CONCLUSIONS: These findings support further Phase III evaluation of RTS,S/AS01(E). The role of immune effectors and immunization schedules on vaccine protection are currently under evaluation. TRIAL REGISTRATION: ClinicalTrials.gov NCT00360230

Préface

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Role of the vestibular commissure in gaze-holding in the cat: a pharmacological evaluation.

Recent theoretical studies have proposed that the vestibular commissure is a major component of the horizontal gaze-holding system. In order to test this hypothesis, we injected either bicuculline, a GABA receptor antagonist, or strychnine, a glycine receptor antagonist, into the medial vestibular nucleus of alert cats. The intervestibular connection is indeed inhibitory and mediated by GABA and glycine. As neither bicuculline nor strychnine caused serious deficit of the gaze-holding system, we conclude that the vestibular commissure is not essential for gaze-holding.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Gaze holding defect induced by injections of ketamine in the cat brainstem.

The signal responsible for horizontal gaze holding is known to be generated, at least in part, by the prepositus hypoglossi (PH) nucleus, whereas that responsible for vertical gaze holding is known to be generated by the interstitial nucleus of Cajal (INC). An intramuscular injection of ketamine was recently demonstrated to induce a gaze holding failure. The aim of the present study was to analyse if ketamine produced this effect by acting, at least in part, on the PH nucleus. We found that a unilateral injection of a small amount of ketamine in the PH nucleus could cause either bilateral horizontal gaze holding failure or a vertical gaze holding failure or both an horizontal and a vertical gaze holding failure.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Involvement of the N-methyl-D-aspartate receptors of the vestibular nucleus in the gaze-holding system of the cat.

Eye movements were recorded in alert cats after injections into one of the medial vestibular nuclei (MVN) either of a N-methyl-D-aspartate (NMDA) antagonist or of a non-NMDA antagonist. A gaze-holding failure was caused by the NMDA antagonist when it was injected into the central part of the MVN but not when it was injected into the rostral part of that nucleus. By contrast, injections of the non-NMDA-receptor antagonist into the MVN did not cause any sign of gaze-holding failure. We conclude that the NMDA receptors located in the central part of the MVN are involved in the gaze-holding system.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Effects of ketamine on ocular movements of the cat.

We studied the effects of ketamine, an antagonist of the N-methyl-D-aspartate receptors, on (1) the spontaneous saccades, (2) the vestibulo-ocular reflex (VOR), and (3) the optokinetic nystagmus (OKN) in 8 cats. Ketamine was given intramuscularly at four dosages (1, 2, 8, and 16 mg/kg). Eye movements were measured using the magnetic field-search coil technique. Ketamine did not prevent the occurrence of saccades, but each of them was followed by a centripetal postsaccadic drift. The time-constant of the drift induced by ketamine was 1.0 s when the given dosage was 1 mg/kg and 0.35 s when the given dosage was 16 mg/kg. Post-saccadic drift caused by a low dosage of ketamine may reflect only a mismatch between the pulse and the step commands that create saccades. The highest used dosages of ketamine aggravated the post-saccadic drift probably by disturbing the oculomotor neural integrator. To elicit the horizontal VOR, the head was submitted either to sinusoidal rotations (+/- 20 degrees; 0.05 to 1 Hz) or to a rotation at a constant velocity (100 degrees/s during 40 s). In darkness, the VOR step gain was reduced by ketamine in a dosage-dependent manner. VOR phase lead at 0.10 Hz oscillation in darkness increased from 4.0 degrees +/- 2.4 degrees to 51.6 degrees +/- 7.5 degrees after administration of ketamine at 16 mg/kg. This suggests that ketamine, at least at higher dosages, induces a failure of the neural integrator. Chemical blockade of the vestibular commissure by ketamine may also be responsible for the reduction of the VOR gain. Horizontal OKN was tested using a step stimulus (30 degrees/s during 40 s). When ketamine was given at 1 mg/kg, the average steady-state gain of the OKN diminished from 0.6 +/- 0.2 to 0.3 +/- 0.1. After administration of ketamine at 2 mg/kg, the OKN was abolished. The sensitivity of OKN to ketamine is explained at least partly by the fact that ketamine acts against the visual pathways in the retina, in the geniculate nucleus, and in the visual cortex. The time course of the optokinetic afternstagmus (OKAN) and that of the decrease of the prerotatory and postrotatory VOR were not reduced by ketamine administered at 1 or 2 mg/kg. This shows that ketamine does not affect the velocity-storage mechanism at these dosages.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

NMDA receptors are involved in temporal integration in the oculomotor system of the cat.

Spontaneous eye movements were recorded before and after a microinjection (0.1-0.2 microliter) of either APV (an NMDA receptor antagonist) or NBQX (a non-NMDA receptor antagonist) into the nucleus prepositus hypoglossi (NPH) of the alert cat. A unilateral injection of APV caused bilateral failure of the horizontal gaze-holding system: in the light, each saccade was followed by a post-saccadic drift. A unilateral injection of NBQX caused no sign of gaze-holding failure; in the light, spontaneous eye movements were unaffected; in complete darkness, a nystagmus with linear slow phases directed towards the injected side was observed. We conclude that NMDA receptors of the NPH neurones are involved in the gaze-holding system.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Ketamine induces failure of the oculomotor neural integrator in the cat.

We studied the effect of intramuscular injection of low dose of ketamine (1 mg/kg) on the spontaneous ocular movements of the cat. Ketamine is a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptors, which is used as an anesthetic agent in human surgery. We found that ketamine administration caused a failure of gaze holding: each saccade was followed by a centripetal post-saccadic drift. This defect was selective: the dynamics of the saccades was not altered (the amplitude/maximum velocity relationship was unaffected by ketamine at the dose of 1 mg/kg). We postulated that the observed effect was due to the fact that NMDA receptors were implicated in the network of the oculomotor neural integrator that converted activity related to the saccade (pulse signal) into activity responsible for gaze holding (step signal).Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Effect of muscimol microinjections into the prepositus hypoglossi and the medial vestibular nuclei on cat eye movements.

1. For horizontal eye movements, previous observations led to the hypothesis that the legendary neural integrator necessary for correct gaze holding, adequate vestibuloocular reflex (VOR), and optokinetic nystagmus, was located in the region of the complex formed by the nucleus prepositus hypoglossi (NPH) and the medial vestibular nucleus (MVN). 2. The aim of the present study was to test the respective contributions of the NPH, of the rostral part of the MVN, which contains most second-order vestibular neurons, and of the central part of the MVN to the horizontal integrator. 3. An injection of muscimol was used to inactivate each of these three zones in the cat's brain. Muscimol is a gamma-aminobutyric acid (GABA) agonist. By binding to GABAA receptors, it induces a hyperpolarization of the neurons that nullifies their activity. Muscimol was injected into the brain stem of the alert cat through a micropipette by an air pressure system. 4. The search coil technique was used to record spontaneous eye movements and the VOR induced by rotating a turntable at a constant velocity. VOR was analyzed by a new method: transient analysis of vestibular nystagmus. 5. A unilateral injection of muscimol into the NPH induced a bilateral gaze-holding failure: saccades were followed by a centripetal postsaccadic drift. A vestibular imbalance was also present but it was moderate and variable. The VOR responses were distorted drastically. Through transient analysis of vestibular nystagmus, that distortion was revealed to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator. The responses to a rotation either toward the injected side or in the opposite direction were asymmetrical. The direction of that asymmetry was variable. 6. A unilateral injection of muscimol into the rostral part of the MVN caused a vestibular imbalance: in complete darkness, a nystagmus appeared, whose linear slow phases were directed toward the side of injection. 7. A unilateral injection of muscimol into the central part of the MVN induced a syndrome where a severe bilateral gaze-holding failure was combined with a vestibular imbalance. In the light, saccades were followed by a bilateral centripetal postsaccadic drift. In complete darkness, a nystagmus was observed, whose curved slow phases were directed towards the side of injection. The VOR responses were distorted drastically. Here again, that distortion was revealed by our analysis to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator.(ABSTRACT TRUNCATED AT 400 WORDS)Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe