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Example 3
Investigation of Virus Infectivity as a Factor that Determines Plaque Size.
With the revelation that plaque formation is strongly influenced by the immunogenicity of the virus, the possibility that infectivity of the virus could be another factor that determines plaque sizes was investigated. The uptake of viruses into cells in vitro was determined by measuring the amounts of specific viral RNA sequences through real-time PCR.
To measure total viral RNA, total cellular RNA was extracted using the RNEasy Mini kit (Qiagen), and complementary DNA synthesized using the iScript cDNA Synthesis kit (Bio-Rad). To measure total viral RNA, quantitative real-time PCR was done using a primer pair targeting a highly conserved region of the 3′ UTR common to all four serotypes of dengue; inter-sample normalization was done using GAPDH as a control. Primer sequences are listed in Table 5. Pronase (Roche) was used at a concentration of 1 mg/mL and incubated with infected cells for five minutes on ice, before washing with ice cold PBS. Total cellular RNA was then extracted from the cell pellets in the manner described above.
The proportion of infected cells was assessed by flow cytometry. Cells were fixed and permeabilised with 3% paraformaldehyde and 0.1% saponin, respectively. DENV envelope (E) protein was stained with mouse monoclonal 4G2 antibody (ATCC) and AlexaFluor488 anti-mouse secondary antibody. Flow cytometry analysis was done on a BD FACS Canto II (BD Bioscience).
Unexpectedly, despite DENV-2 PDK53 inducing stronger antiviral immune responses, it had higher rates of uptake by HuH-7 cells compared to DENV-2 16681 (
Results above demonstrate that the DENV-2 PDK53 and DENV-3 PGMK30 are polarized in their properties that influence plaque morphologies. While both attenuated strains were selected for their formation of smaller plaques compared to their parental strains, the factors leading to this outcome are different between the two.
Accordingly, this study has demonstrated that successfully attenuated vaccines, as exemplified by DENV-2 PDK53 in this study, form smaller plaques due to induction of strong innate immune responses, which is triggered by fast viral uptake and spread of infection. In contrast, DENV-3 PGMK30 form smaller plaques due to its slower uptake and growth in host cells, which inadvertently causes lower up-regulation of the innate immune response.
Based on the results presented in the foregoing Examples, the present invention provides a new strategy to prepare a LAV, which expedites the production process and ensures the generation of effectively attenuated viruses fit for vaccine use.
Example 4
To determine where 2F2-grafted “humanized” antibodies and antibody variants are delivered upon internalization into the cell, colocalization studies of the anti-CD79b antibodies internalized into B-cell lines may be assessed in Ramos cell lines. LAMP-1 is a marker for late endosomes and lysosomes (Kleijmeer et al., Journal of Cell Biology, 139(3): 639-649 (1997); Hunziker et al., Bioessays, 18:379-389 (1996); Mellman et al., Annu. Rev. Dev. Biology, 12:575-625 (1996)), including MHC class II compartments (MIICs), which is a late endosome/lysosome-like compartment. HLA-DM is a marker for MIICs.
Ramos cells are incubated for 3 hours at 37° C. with 1 μg/ml 2F2-grafted “humanized” antibodies and antibody variants, FcR block (Miltenyi) and 25 μg/ml Alexa647-Transferrin (Molecular Probes) in complete carbonate-free medium (Gibco) with the presence of 10 μg/ml leupeptin (Roche) and 5 μM pepstatin (Roche) to inhibit lysosomal degradation. Cells are then washed twice, fixed with 3% paraformaldehyde (Electron Microscopy Sciences) for 20 minutes at room temperature, quenched with 50 mM NH4Cl (Sigma), permeabilized with 0.4% Saponin/2% FBS/1% BSA for 20 minutes and then incubated with 1 μg/ml Cy3 anti-mouse (Jackson Immunoresearch) for 20 minutes. The reaction is then blocked for 20 minutes with mouse IgG (Molecular Probes), followed by a 30 minute incubation with Image-iT FX Signal Enhancer (Molecular Probes). Cells are finally incubated with Zenon Alexa488-labeled mouse anti-LAMP1 (BD Pharmingen), a marker for both lysosomes and MIIC (a lysosome-like compartment that is part of the MHC class II pathway), for 20 minutes, and post-fixed with 3% PFA. Cells are resuspended in 20 μl saponin buffer and allowed to adhere to poly-lysine (Sigma) coated slides prior to mounting a coverglass with DAPI-containing VectaShield (Vector Laboratories). For immunofluorescence of the MIIC or lysosomes, cells are fixed, permeabilized and enhanced as above, then co-stained with Zenon labeled Alexa555-HLA-DM (BD Pharmingen) and Alexa488-Lamp1 in the presence of excess mouse IgG as per the manufacturer's instructions (Molecular Probes).
Accordingly, colocalization of 2F2-grafted “humanized” antibodies or antibody variants with MIIC or lysosomes of B-cell lines as assessed by immunofluorescence may indicate the molecules as excellent agents for therapy of tumors in mammals, including B-cell associated cancers, such as lymphomas (i.e. Non-Hodgkin's Lymphoma), leukemias (i.e. chronic lymphocytic leukemia), and other cancers of hematopoietic cells.