The yellow fever 17D vaccine virus: molecular basis of viral attenuation and its use as an expression vector.

The yellow fever (YF) virus is the prototype flavivirus. The use of molecular techniques has unraveled the basic mechanisms of viral genome structure and expression. Recent trends in flavivirus research include the use of infectious clone technology with which it is possible to recover virus from cloned cDNA. Using this technique, mutations can be introduced at any point of the viral genome and their resulting effect on virus phenotype can be assessed. This approach has opened new possibilities to study several biological viral features with special emphasis on the issue of virulence/attenuation of the YF virus. The feasibility of using YF virus 17D vaccine strain, for which infectious cDNA is available, as a vector for the expression of heterologous antigens is reviewed.

The yellow fever 17D vaccine virus: molecular basis of viral attennuation and it use as an expression vector

The yellow fever (YF) virus is the prototype flavivirus. The use of molecular techniques has unraveled the basic mechanisms of viral genome structure and expression. Recent trends in flavivirus research include the use of infectious clone technology with which it is possible to recover virus from cloned cDNA. Using this technique, mutations can be introduced at any point of the viral genome and their resulting effect on virus phenotype can be assessed. This approach has opened new possibilities to study several biological viral features with special emphasis on the issue of virulence/attenuation of the YF virus. The feasibility of using YF virus 17D vaccine strain, for which infectious cDNA is available, as a vector for the expression of heterologous antigens is reviewed.

Measles antibody prevalence after mass immunization campaign in Niterói, state of Rio de Janeiro, Brazil.

Three months after a mass vaccination campaign (coverage: 100%) against measles a random seroepidemiological survey was carried out in students aged 1 to 19 years old in the Municipality of Niterói, State of Rio de Janeiro. Blood samples were tested for measles antibodies by enzyme immunosorbent assay (EIA) and negative cases were tested again using hemagglutination inhibition (HI) and plaque reduction neutralization (PRN). Of the 798 samples tested by EIA, 718 (90.2%) were positive for measles antibodies. PRN test was more sensitive than EIA and HI in detecting measles specific antibodies. The total antibody prevalence increased from 90.2% to 93.2% when HI was employed in EIA negative specimens and to 98.9% when PRN was used. After the mass vaccination campaign a marked decrease in measles incidence was observed in the municipality studied, showing the effectiveness of the strategy used for measles control in developing countries.

Biological characterization of clones derived from the Edmonston strain of measles virus in comparison with Schwarz and CAM-70 vaccine strains.

Four virus clones were derived from the Edmonston strain of measles virus by repeated plaque purification. These clones were compared with the vaccine strains Schwarz and CAM-70 in terms of biological activities including plaque formation, hemagglutination, hemolysis and replication in Vero cells and chick embryo fibroblasts (CEF). Two clones of intermediate plaque yielded mixed plaque populations on subcultivation whereas the other two, showing small and large plaque sizes, showed stable plaque phenotypes. The vaccine strains showed consistent homogeneous plaque populations. All the Edmonston clones showed agglutination of monkey erythrocytes in isotonic solution while both vaccine strains hemagglutinated only in the presence of high salt concentrations. Variation in the hemolytic activity was observed among the four clones but no hemolytic activity was detected for the vaccine virus strains. Vaccine strains replicated efficiently both in Vero cells and CEF. All four clones showed efficient replication in Vero cells but different replication profiles in CEF. Two of them replicated efficiently, one was of intermediate efficiency and the other showed no replication in CEF. Two of the clones showed characteristics similar to vaccine strains. One in terms of size and homogeneity of plaques, the other for a low hemolytic activity and both for the efficiency of propagation in CEF.

Un nuevo sistema de cultivo por perfusión en estratos celulare: su aplicación para la producción de la vacuna vírica / Development of a new system for cell cultivation in perfused layered cultures: application to virus vaccine manufacture

En el presente artículo los autores describen con cierto detalle sus estudios con el recipiente de Mann de cultivo por perfusión. El mejoramiento con respecto al sistema de capas monocelulares fijas es muy notable. Por ejemplo, el recipiente de 5 metros cuadrados permite obtener una superficie de proliferación equivalente a 100 frascos de Povitsky; un recipiente de cultivo rinde el equivalente a 300-500 frascos de Povitsky, puesto que el cultivo es más denso (en una proporción de 3 a 5 veces mayor que en el método de frascos fijos). Para los casos en que se requiere más producción ya se dispone de recipientes hasta de 10 metros cuadrados y pueden utilizarse en cultivos paralelos para obtener un rendimiento prácticamente ilimitado. Cuando esta producción se traduce en la preparación de vacuna, los resultados son muy estimulantes. Si prosiguen debidamente las investigaciones con estos recipientes, se logrará un gran avance en lo que se refiere a la necesidad mundial de vacunas víricas preparadas en cultivo tisular (AU)

A perfusion culture system for virus vaccine manufacture in diploid cell cultures

Development of a new perfusion culture system for the production of attenuated poliomyelitis virus in cultures of diploid cells is described. The growth characteristics of the diploid cells (MRC-5) were found to be normal in the perfused system. Procedures for the routine production of cell cultures at twice the cell density of stationary bottle cultures were established. The yield of virus (Lsc 2ab) per cell and per unit of surface growth area were observed to be significantly higher in the perfused system than in parallel stationary bottle culture controls--by factors of three- and five-fold, respectively. The field was confirmed to be within the experimental range when small production-scale vessels were used. Subject to satisfactory results in the testing of the virus product, this system could be highly economic in large-scale vaccine manufacture (Au)