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Biomedical subjects

F Lafay

Publications and source records attributed to F Lafay.

At least 19 recordsLinked to original sources
PubMed2006

[The stereotactic body radiation therapy: initiation and clinical program].

We fully describe an innovative radiotherapy technique called Stereotactic Body Radiation Therapy (SBRT), and explain how this technique is commonly used for clinical purpose at the anticancer center Léon-Bérard (Lyon, France). In this technique, a non-invasive stereotactic body frame is used to locate the tumor site with a great precision. This frame is combined with a system, which enables to track the respiratory motions (Active Breathing Control (ABC) or diaphragmatic compression (DC)) in order to reduce the treatment margins for organ motion due to breathing. Thus, the volume of normal tissues that will be irradiated is considerably reduced. The dosimetry is realized with 3 CT exams performed in treatment conditions. The 3D patient "repositioning" is done with a volume CT acquisition (kV) combined with orthogonal images (kV and MV). The SBRT requires a system to limit the organ motions. Although the ABC seems to be more fastidious for patient, it would enable to use smaller margins than with DC technique. Nevertheless, the ABC is not compatible with volume CT acquisitions, which considerably improve the patient repositioning. In conclusion, the quality of repositioning and the high level of conformation enable to deliver high equivalent doses (>100 Gy) in hypofractionated mode, without increasing the treatment toxicity. The SBRT employs the last technologic innovations in radiotherapy and is therefore considered as a new efficient tool for solid tumors treatment.

Equipment Design↗
PubMed2004

[Acute respiratory tract infections due to a human metapneumovirus in children: descriptive study and comparison with respiratory syncytial virus infections].

BACKGROUND: A new paramyxovirus, the human metapneumovirus was recently isolated. We report the first French cases collected between 2000 and 2002. MATERIAL AND METHODS: Samples were obtained from nasopharyngeal aspirates from children hospitalised for acute respiratory tract infection in hospitals of Caen and Flers in Basse-Normandie. Human metapneumovirus was studied by polymerase chain reaction on negative samples for respiratory syncytial virus, influenza A and B virus, parainfluenza (1, 2 and 3) virus, adenovirus, coronavirus and rhinovirus. Comparison between metapneumovirus virus and respiratory syncytial virus infections was done after matching sex, age and infection month. RESULTS: Twenty-six human metapneumovirus infections were identified. A comparative study of a matched group of children infected by respiratory syncytial virus found no significative difference for hospitalisation motive, clinical criteria and treatment. CONCLUSION: The human metapneumovirus is responsible for typical acute bronchiolitis in children.

Acute Disease↗
PubMed2003

[Rhinovirus and acute respiratory infections in hospitalized children. Retrospective study 1998-2000].

OBJECTIVES: Rhinoviruses are the most common aetiological agents of colds, but the frequency and the severity of other locations of the infection are not well known. This study describes the clinical aspects and the severity of rhinovirus infections in hospitalised children. METHODS: Isolation in culture and a RT-PCR were performed for the detection of rhinovirus in nasal aspirates from hospitalised children from September 1998 to October 2000. A group of 211 children found to be positive for rhinovirus was studied. RESULTS: Rhinovirus-infected children suffered from the following clinical syndromes: 60 (28.4%) upper airway infections, 81 (38.4%) bronchiolitis, 25 (11.9%) pneumonias and 12 (4.7%) acute attacks of asthma. Clinical symptoms were wheezing (32%), ronchi (37%) and 29% of children presented with acute distress respiratory syndrome; 40% of the available chest X-Ray were abnormal. Eight children were hospitalised in the intensive care unit and two children died. Twenty-five children (10.9%) had a nosocomial infection; a dual infection was observed in 19 cases (9%) with the following viruses: RSV (3), influenza (2) parainfluenza (8), adenovirus (2), enterovirus (4); 19 (9%) children had a secondary bacterial infection. Rhinoviruses were detected in nasal aspirates in 112 cases (53%) according to the culture and in the rhinovirus culture-negative samples in 99 cases (47%) according to the RT-PCR assay. CONCLUSION: After eliminating cases of bacterial or viral dual infections, the clinical aspects of rhinovirus infections in children are the following: upper respiratory tract infections (25.6%), bronchiolitis ou bronchitis (25.6%), pneumonia (6.2%), acute attack of asthma (5.7%). The virological diagnosis according to culture is mainly improved by molecular techniques.

Adolescent↗
PubMed2000

A study of dose delivery in small segments.

PURPOSE: Use of conformal therapy techniques increases the number of beams used in order to obtain better conformation of the treated volume to the planning target volume. As the number of beams increases, the number of monitor units (MU) for each beam decreases. In this work we have studied, the influence of low MU on dose and homogeneity. METHODS AND MATERIALS: To study the field symmetry and flatness, films were irradiated. The "dose" for each field was always 60 MU; but it was divided into different segment sizes: 2 segments of 30 MU, 3 segments of 20 MU, and so on up to 12 segments of 5 MU. After being developed, films were scanned and analyzed using a densitometer. The measurements were carried out for three X-ray energies: 6 MV, 10 MV, and 18 MV. RESULTS: Each measurement was repeated twice for each energy, and the results were equal. The means of the symmetry and flatness values obtained for each energy are lower than the commonly accepted limits. CONCLUSION: The dose delivered by adding small segments is equivalent to the dose delivered by a conventional segment with our Philips Linacs SL15 and SL20.

Phantoms, Imaging↗
PubMed2000

Impact of tissues heterogeneities on monitor units calculation and ICRU dose point: analysis of 30 cases of prostate cancer treated with 18-MV photons after three-dimensional planning.

PURPOSE: Analysis of dose specification of tissue heterogeneities. METHODS AND MATERIALS: Three-dimensional dose distribution analyses of 30 patients with localized prostate cancer were reviewed with and without tissue heterogeneity correction. The number of monitor units for each portal entrance (more than 300 different fields) was calculated and the impact of targeting and number of portal entrances was also integrated. RESULTS: The presence of gas in the rectum induces an overdosage of 0.6%, pubic bone induces an underdosage of -1.5%, and femoral heads are responsible for 6% underdosage. For the treatment as a whole, the underdosage is correlated with targeting techniques and weighting of each portal entrance (range, -0.5% to -3.2%). CONCLUSION: Dose calculation must take into account tissue heterogeneities and more precise guidelines for dose prescription are mandatory for further intercomparison.

Algorithms↗
PubMed2000

Neuronal pathways for the propagation of herpes simplex virus type 1 from one retina to the other in a murine model.

Herpetic retinitis in humans is characterized by a high frequency of bilateral localization. In order to determine the possible mechanisms leading to bilateral retinitis, we studied the pathways by which herpes simplex virus type 1 (HSV-1) is propagated from one retina to the other after intravitreal injection in mice. HSV-1 strain SC16 (90 p.f.u.) was injected into the vitreous body of the left eye of BALB/c mice. Animals were sacrificed 1, 2, 3, 4 and 5 days post-inoculation (p.i.). Histological sections were studied by immunochemical staining. Primary retinitis in the inoculated eye (beginning 1 day p.i.) was followed by contralateral retinitis (in the uninoculated eye) starting at 3 days p.i. Infected neurons of central visual pathway nuclei (lateral geniculate nuclei, suprachiasmatic nuclei and pretectal areas) were detected at 4 days p.i. Iris and ciliary body infection was minimal early on, but became extensive thereafter and was accompanied by the infection of connected sympathetic and parasympathetic pathways. The pattern of virus propagation over time suggests that the onset of contralateral retinitis was mediated by local (non-synaptic) transfer in the optic chiasm from infected to uninfected axons of the optic nerves. Later, retinopetal transneuronal propagation of the virus from visual pathways may have contributed to increase the severity of contralateral retinitis.

Animals↗
PubMed2000

Neuronal propagation of HSV1 from the oral mucosa to the eye.

PURPOSE: To identify possible neuronal pathways leading to herpetic ocular disease after primary oral infection in mice. METHODS: The SC16 strain of herpes simplex virus (HSV)-1 (10(6) plaque-forming units) was injected into the mucocutaneous border of the left upper lip. Animals were killed 2 to 10 days postinoculation (DPI). Spread of the virus in neural structures was studied by immunochemistry. RESULTS: HSV1 first replicated at the site of inoculation and then at the superior cervical ganglion (at 2 DPI). The trigeminal ganglion and the facial nerve fibers were infected by 4 DPI. Infection of the ciliary body and iris occurred at 6 DPI, together with several brain stem nuclei belonging to the autonomic or sensory pathways. Between 8 and 10 DPI, the neural infection gradually cleared up, except for the ipsilateral sympathetic ganglion, and ipsilateral keratitis appeared in some animals. CONCLUSIONS: The pattern of viral dissemination in this mouse model suggests that infection of iris and ciliary body results from transfer of virus in the superior cervical ganglion from sympathetic neurons innervating the lip to neighboring neurons innervating the anterior uvea. Later, zosteriform spread of virus from the trigeminal system may have contributed to the clinical and histologic findings.

Animals↗
PubMed1997

Phage-displayed and soluble mouse scFv fragments neutralize rabies virus.

A phage-display technology was used to produce a single-chain Fv antibody fragment (scFv) from the 30AA5 hybridoma secreting anti-glycoprotein monoclonal antibody (MAb) that neutralizes rabies virus. ScFv was constructed and then cloned for expression as a protein fusion with the g3p minor coat protein of filamentous phage. The display of antibody fragment on the phage surface allows its selection by affinity using an enzyme-linked immunosorbent assay (ELISA); the selected scFv fragment was produced in a soluble form secreted by E. coli. The DNA fragment was sequenced to define the germline gene family and the amino-acid subgroups of the heavy (VH) and light (VL) chain variable regions. The specificity characteristics and neutralization capacity of phage-displayed and soluble scFv fragments were found to be identical to those of the parental 30AA5 MAb directed against antigenic site II of rabies glycoprotein. Phage-display technology allows the production of new antibody molecule forms able to neutralize the rabies virus specifically. The next step could be to engineer and produce multivalent and multispecific neutralizing antibody fragments. A cocktail of multispecific neutralizing antibodies could contain monovalent, bivalent or tetravalent scFv fragments, for passive immunoglobulin therapy.

Amino Acid Sequence↗
PubMed1997

[Conformational radiotherapy with multi-leaf collimators: one year experience at the Leon-Berard Centre].

Taking advantage of the renewal of a linear accelerator, the Radiation Therapy Department of the Centre Léon Bérard implemented, in collaboration with Philips Systèmes Médicaux, a conformal therapy set-up procedure using CT-scan for 3D treatment planning and a multileaf collimator that allows achievement of numerous irregular-shaped beams via the multileaf preparation system. The various elements of this equipment make possible well defined and structured procedures for treatment planning with different steps and essential tools used by this technique. We describe the means used and indicate future improvements that will lead to automation in order to provide good quality assurance, better security and substantial time saving. During the first year, 115 patients were treated with this new technique. They presented with central nervous system tumors (32 patients), lung cancer (29 patients), prostate cancer (20 patients), paranasal sinus tumors (14 patients) and tumors located in other sites (13 patients with soft sarcoma, hepato-bilary tumor, etc).

Dose-Response Relationship, Radiation↗
PubMed1997

Mapping of monoclonal antibody epitopes of the rabies virus P protein.

Thirty-six monoclonal antibodies (MAbs) specific for the rabies virus P phosphoprotein were obtained from mice immunized with recombinant P (PV strain) produced in E. coli. All MAbs reacted against the corresponding rabies virus protein by ELISA and by Western blot analysis and revealed the presence of cytoplasmic inclusions in rabies virus infected cells. The epitopes of seven MAbs were mapped by testing their reactivity with protein fragments expressed from deletion mutants in transfected cells. Western blotting, immunoprecipitation and immunofluorescence assays were performed. These MAbs recognized epitopes in different domains of the P protein: 60% were directed against a region lying between residues 83-172 suggesting a major antigenic determinant of the rabies virus P protein in this region. Most of the antigenic sites appeared to be composed of linear epitopes. These MAbs will be useful as tools to dissect structural and functional properties of the rabies virus P protein.

Animals↗
PubMed1996

Immunodominant epitopes defined by a yeast-expressed library of random fragments of the rabies virus glycoprotein map outside major antigenic sites.

Nineteen yeast colonies secreting rabies virus glycoprotein (G) peptides immunoreactive with polyclonal anti-rabies virus sera were selected from a random expression library. The peptides, around 80 amino acids long, spanned amino acids 54-494 of the G protein. These peptides, together with two constructions including, respectively, immunodominant sites II and III, were analysed for their immunoreactivity with 40 anti-G protein monoclonal antibodies (MAbs) composed of 12 MAbs that reacted with SDS-treated protein in Western blot under reducing conditions (WB+) and 28 representative MAbs that did not react after denaturation (WB-). This last category represents 98% of anti-rabies virus G MAbs. None of the WB- MAbs bound peptides. Of the 12 WB+ MAbs, one bound two peptides situated before the transmembrane domain of the protein and six bound peptides overlapping a region situated between amino acids 223 and 276. These six MAbs define a new antigenic region that would be considered 'immunodominant' if the peptide strategy had been used to study the antigenicity of the protein; however, this region is only recognized by about 1% of our MAbs. Three of these WB+ MAbs had significant neutralizing activity; two were used for the selection of antigenic mutants (MAR mutants). Some mutants had a substitution within the region delimited by the peptides, confirming the pertinence of both the peptide and escape mutant approaches. However, a few mutants had a substitution outside the peptide-delimited region, suggesting that remote mutation(s) could affect epitope accessibility in the native protein.

Animals↗
PubMed1995

Monoclonal antibodies which recognize the acidic configuration of the rabies glycoprotein at the surface of the virion can be neutralizing.

Around 15% of our anti-glycoprotein monoclonal antibodies (MAbs) failed to neutralize the infectivity of the rabies virus during a 1-hr incubation at room temperature. In previous studies, we have demonstrated that it is possible to induce a massive conformational change of the glycoprotein population by incubating the virus at acidic pH. The conformational change is reversible and consequently viral infectivity is not affected by transient exposure at acidic pH. The proportion of glycoproteins in acidic or neutral configuration depends on the pH which means that even at neutral pH some glycoproteins transiently adopt the acidic configuration and vice versa. Here we report that some of our nonneutralizing MAbs recognize the acidic form of the glycoprotein at the virion surface. After incubation of the virus at pH 6.4, most glycoproteins are in the acidic configuration. Further 1-hr incubation with these MAbs at the same pH resulted in more immunoglobulins being attached to the virus and consequently neutralization was induced. It was also possible to induce neutralization with the same MAbs by incubation at neutral pH for a longer period or at a higher temperature. Mutants resistant to neutralization by these MAbs could be selected. Mutations confering resistance to neutralization were not localized in previously described antigenic sites and did not modify these sites at distance. They had no effect on the pathogenic power of the virus. Either they are situated in the epitope or they modify the epitope, so that it is no longer recognized by the antibody on the acidic configuration of the protein. Alternatively, these mutations may stabilize the protein in its neutral configuration. In addition, these experiments confirm our previous finding that neutralization requires the fixation of a large number of immunoglobulins on the virus, irrespective of the region of the protein recognized by the antibody.

Amino Acid Sequence↗
PubMed1994

Vaccination against rabies: construction and characterization of SAG2, a double avirulent derivative of SADBern.

A double avirulent mutant was isolated from the SADBern strain of rabies virus by two successive selection steps using neutralizing anti-glycoprotein monoclonal antibodies. Both mutations affect the triplet coding for amino acid 333 of the glycoprotein. The resulting virus, called SAG2, has a glutamate coded by GAA in position 333 instead of an arginine. This new codon differs by two nucleotides from all the arginine triplets. SAG2 is avirulent in adult mice by intracerebral and intramuscular routes and it protects mice against a challenge by the CVS strain. This double mutant is still avirulent after three successive passages in suckling mouse brain or after ten successive cycles of multiplication in cell culture. Because it is protective and genetically stable, SAG2 represents an improvement on SAG1 which is already used for oral vaccination of foxes in Switzerland and France. It could also be a candidate for oral vaccination of dogs against rabies.

Animals↗
PubMed1993

The CVS strain of rabies virus as transneuronal tracer in the olfactory system of mice.

The sequential distribution of transneuronally infected neurons was studied in the olfactory pathway of mice after unilateral inoculation of the challenge virus standard (CVS) strain in the nasal cavity. A first cycle of viral multiplication was observed in a subpopulation of receptor cells scattered in the main olfactory epithelium and in the septal organ. No viral spread from cell body to cell body was reported even in later stages of infection. The second round of viral replication which took place in the ipsilateral main olfactory bulb at 2 and 2.5 days post-inoculation (p.i.), involved second order neurons and periglomerular cells, known to be directly connected with the axon terminals of receptor cells. Also reported as a result of a second cycle of viral replication, was surprisingly the spread of CVS at 2 and 2.5 days p.i. in bulbar interneurons located in the internal plexiform layer and in the superficial granule cell layer, as well as that of 2 ipsilateral cerebral nuclei, the anterior olfactory nucleus and the horizontal limb of the diagonal band. From day 3, a rapid spread of CVS was suggested by detection of virus in all ipsilateral direct terminal regions of the second order neurons and in most tertiary olfactory projections. The locus coeruleus, a noradrenergic nucleus which sends direct afferents to the olfactory bulb, never appeared immunoreactive. In spite of a certain inability of CVS to infect some neuron types, the virus appears relevant to provide new information regarding the complex network of olfactory-related neurons into the CNS.

Afferent Pathways↗
PubMed1993

Avirulent mutants of rabies virus and their use as live vaccine.

Oral vaccination of foxes against rabies began in Switzerland some 20 years ago and was later extended to several European countries. The vaccine strains, which were derivatives of the SAD strain of rabies, retain a non-negligible pathogenicity for rodents and nontarget species. Antigenic mutants of the SAD Bern vaccine strain, which are avirulent for adult mice, foxes and dogs, have been isolated and are presently under trial.

Animals↗
PubMed1993

SAG-2 oral rabies vaccine.

The live modified rabies virus vaccine strain SAG-2 was selected from SADBerne in a two step process employing anti-rabies glycoprotein monoclonal antibodies. The first two nucleotides coding for the amino acid in position 333 of the rabies glycoprotein are mutated. Arginine at position 333, which is associated with rabies pathogenicity, was substituted first by lysine and then by glutamic acid. The two nucleotide differences at position 333 in SAG-2 to any of six possible arginine triplets translated into excellent genetic stability and apathogenicity for adult mice, foxes, cats and dogs. The vaccination of foxes and dogs by the oral route provided protection against a lethal challenge with rabies virus.

Animals↗