Improving ability of RSV microneutralization assay to detect G-specific and cross-reactive neutralizing antibodies through immortalized cell line selection.

Respiratory syncytial virus (RSV) is a significant cause of bronchiolitis and pneumonia. Protection against RSV is associated with neutralizing antibodies against the fusion (F) and attachment (G) glycoproteins. Several RSV vaccine candidates are in development, but their immunogenicity is hard to compare due to the little-understood differences between multiple RSV neutralizing antibody assays used. Existing assays utilize primarily Vero or HEp-2 cells, but their ability to detect G-neutralizing antibodies or antibodies against specific RSV strains is unclear. In this work, we developed an RSV microneutralization assay (MNA) using unmodified RSV and immortalized cell line derived from human airway epithelial cells (A549). Performance of A549-, HEp-2- and Vero-based MNA was compared under the same assay conditions (fixed amount of virus and cells) with regards to detection of neutralizing antibodies against RSV A or B viruses, G-reactive neutralizing antibodies, and effect of complement. Our results indicate that A549 cells yield the highest MNA titers, particularly in the RSV A/A2 MNA, are least susceptible to complement-enhancing effect of neutralizing titer readout and are superior to Vero or HEp-2 MNA at recognizing G-reactive neutralizing antibodies when no complement is used. Vero cells, however, can be more consistent at recognizing neutralizing antibodies against multiple RSV strains. The choice of substrate cells thus affects the outcome of MNA, as some immortalized cells better support detection of broader range of neutralizing antibodies, while others facilitate detection of G-targeting neutralizing antibodies, a long-thought prerogative of primary airway epithelial cells.

Cotton rat model for testing vaccines and antivirals against respiratory syncytial virus.

Respiratory syncytial virus is the leading cause of pneumonia and bronchiolitis in infants and is a serious health risk for elderly and immunocompromised individuals. No vaccine has yet been approved to prevent respiratory syncytial virus infection and the only available treatment is immunoprophylaxis of severe respiratory syncytial virus disease in high-risk infants with Palivizumab (Synagis®). The development of respiratory syncytial virus vaccine has been hampered by the phenomenon of enhanced respiratory syncytial virus disease observed during trials of a formalin-inactivated respiratory syncytial virus in 1960s. A search for effective respiratory syncytial virus therapeutics has been complicated by the fact that some of the most advanced respiratory syncytial virus antivirals, while highly effective in a prophylactic setting, had not demonstrated clinical efficacy when given after infection. A number of respiratory syncytial virus vaccines and antivirals are currently under development, including several vaccines proposed for maternal immunization. The cotton rat Sigmodon hispidus is an animal model of respiratory syncytial virus infection with demonstrated translational value. Special cohort scenarios, such as infection under conditions of immunosuppression and maternal immunization have been modeled in the cotton rat and are summarized here. In this review, we focus on the recent use of the cotton rat model for testing respiratory syncytial virus vaccine and therapeutic candidates in preclinical setting, including the use of special cohort models. An overview of published studies spanning the period of the last three years is provided. The emphasis, where possible, is made on candidates in the latest stages of preclinical development or currently in clinical trials.

Treatment with novel RSV Ig RI-002 controls viral replication and reduces pulmonary damage in immunocompromised Sigmodon hispidus.

Respiratory syncytial virus (RSV) is a significant cause of bronchiolitis and pneumonia in several high health risk populations, including infants, elderly and immunocompromised individuals. Mortality in hematopoietic stem cell transplant recipients with lower respiratory tract RSV infection can exceed 80%. It has been shown that RSV replication in immunosuppressed individuals is significantly prolonged, but the contribution of pulmonary damage, if any, to the pathogenesis of RSV disease in this susceptible population is not known. In this work, we tested RI-002, a novel standardized Ig formulation containing a high level of RSV-neutralizing Ab, for its ability to control RSV infection in immunocompromised cotton rats Sigmodon hispidus. Animals immunosuppressed by repeat cyclophosphamide injections were infected with RSV and treated with RI-002. Prolonged RSV replication, characteristic of immunosuppressed cotton rats, was inhibited by RI-002 administration. Ab treatment reduced detection of systemic dissemination of viral RNA. Importantly, pulmonary interstitial inflammation and epithelial hyperplasia that were significantly elevated in immunosuppressed animals were reduced by RI-002 administration. These results indicate the potential of RI-002 to improve outcome of RSV infection in immunocompromised subjects not only by controlling viral replication, but also by reducing damage to lung parenchyma and epithelial airway lining, but further studies are needed.

Active site mutations in CheA, the signal-transducing protein kinase of the chemotaxis system in Escherichia coli.

We investigated the functional roles of putative active site residues in Escherichia coli CheA by generating nine site-directed mutants, purifying the mutant proteins, and quantifying the effects of those mutations on autokinase activity and binding affinity for ATP. We designed these mutations to alter key positions in sequence motifs conserved in the protein histidine kinase family, including the N box (H376 and N380), the G1 box (D420 and G422), the F box (F455 and F459), the G2 box (G470, G472, and G474), and the "GT block" (T499), a motif identified by comparison of CheA to members of the GHL family of ATPases. Four of the mutant CheA proteins exhibited no detectable autokinase activity (Kin(-)). Of these, three (N380D, D420N, and G422A) exhibited moderate decreases in their affinities for ATP in the presence or absence of Mg(2+). The other Kin(-) mutant (G470A/G472A/G474A) exhibited wild-type affinity for ATP in the absence of Mg(2+), but reduced affinity (relative to that of wild-type CheA) in the presence of Mg(2+). The other five mutants (Kin(+)) autophosphorylated at rates slower than that exhibited by wild-type CheA. Of these, three mutants (H376Q, D420E, and F455Y/F459Y) exhibited severely reduced k(cat) values, but preserved K(M)(ATP) and K(d)(ATP) values close to those of wild-type CheA. Two mutants (T499S and T499A) exhibited only small effects on k(cat) and K(M)(ATP). Overall, these results suggest that conserved residues in the N box, G1 box, G2 box, and F box contribute to the ATP binding site and autokinase active site in CheA, while the GT block makes little, if any, contribution. We discuss the effects of specific mutations in relation to the three-dimensional structure of CheA and to binding interactions that contribute to the stability of the complex between CheA and Mg(2+)-bound ATP in both the ground state and the transition state for the CheA autophosphorylation reaction.

Establishment and characterization of conditionally immortalized organ of corti cell lines.

A culture of cells was isolated from the organ of Corti of 2-week-old H-2Kb-tsA58 (Immortomouse) transgenic mice. All cells of these mice harbor a mutant of the simian virus 40 A-gene, encoding a thermolabile large T-antigen (Tag) protein. At 33 degrees C the Tag protein is functional and induces cell proliferation, but at 39 degrees C it is rapidly denatured and inactivated. Isolated organ of Corti cells growing at 33 degrees C were predominantly small, rounded or fusiform and proliferated rapidly. When moved to 39 degrees C, the cells reduced their rate of proliferation and differentiated into specific morphological phenotypes. Four cell lines were cloned by limiting dilution and characterized by immunofluorescence microscopy and Western blot. The cell lines, named OC-k1, OC-k2, OC-k3 and OC-k4, have been passaged at least 50 times with retention of a stable phenotype. These cell lines were all positive for the neuroepithelial precursor cell marker nestin and for the inner ear cell marker OCP2. In addition, the cells showed reactivity to epithelial and neuronal cell markers, but with a pattern of protein expression different for each clone and different between cells of the same clone growing at 33 degrees C or 39 degrees C. Some of the clones exhibited asymmetric cell division which is a characteristic commonly ascribed to stem cells. These cell lines can be used advantageously to study mechanisms and signals involved in the control of cell differentiation and morphogenesis of the mammalian inner ear and to isolate inner ear specific proteins.