Te-hui W. Chou

Enhanced Immunogenicity of gp120 Protein When Combined with Recombinant DNA Priming To Generate Antibodies That Neutralize the JR-FL Primary Isolate of Human Immunodeficiency Virus Type 1

ABSTRACT Strategies are needed for human immunodeficiency virus type 1 vaccine development that improves the neutralizing antibody response against primary isolates of the virus. Here we examined recombinant DNA priming followed by subunit protein boosting as a strategy to generate neutralizing antibodies. Both plasmid-based and recombinant protein envelope (Env) glycoprotein immunogens were derived from a primary viral isolate, JR-FL. Serum from rabbits immunized with either gp120 or gp140 DNA vaccines delivered by gene gun inoculation followed by recombinant gp120 protein boosting was capable of neutralizing JR-FL. Neither the DNA vaccines alone nor the gp120 protein alone generated a detectable neutralizing antibody response against this virus. Neutralizing antibody responses using gp120 DNA and gp140 DNA for priming were similar. The results suggest that Env DNA priming followed by gp120 protein boosting provides an advantage over either approach alone for generating a detectable neutralizing antibody response against primary isolates that are not easily neutralized.

Identification of Two Neutralizing Regions on the Severe Acute Respiratory Syndrome Coronavirus Spike Glycoprotein Produced from the Mammalian Expression System

ABSTRACT The Spike (S) protein of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) plays important roles in viral pathogenesis and potentially in the development of an effective vaccine against this virulent infectious disease. In this study, the codon-optimized S gene of SARS-CoV was synthesized to construct DNA vaccine plasmids expressing either the full-length or segments of the S protein. High titer S-specific immunoglobulin G antibody responses were elicited in rabbits immunized with DNA against various segments of the S protein. Two neutralizing domains were identified on the S protein, one at the N terminus (Ser12-Thr535) and the other near the C terminus (Arg797-Ile1192).

Immunogenicity and protection efficacy of monovalent and polyvalent poxvirus vaccines that include the D8 antigen

Abstract Recent studies have established the feasibility of subunit-based experimental vaccines to protect animals from lethal poxvirus infection. Individual outer membrane proteins from intracellular and extracellular virions of vaccinia virus, when delivered in the form of either DNA vaccines or recombinant protein vaccines produced from baculovirus-infected insect cells, were able to protect mice from the vaccinia virus challenge and rhesus macaques from the monkeypox virus challenge. The polyvalent formulations with various combinations of the four poxvirus antigens (A27, L1, B5 and A33) achieved better protection than the monovalent formulation using only one of these antigens. However, it is not clear whether any of the remaining outer membrane poxvirus proteins can further improve the efficacy of the current polyvalent formulations. In this study, we conducted detailed analysis on the immunogenicity of D8, a previously reported protective antigen from intracellular mature virions. Our results indicated that D8 induced strong protective antibody responses and was effective in improving the efficacy of previously reported polyvalent poxvirus vaccine formulations. Therefore, D8 is an excellent candidate antigen to be included in the final polyvalent subunit-based poxvirus vaccines.

Epitope mapping and biological function analysis of antibodies produced by immunization of mice with an inactivated Chinese isolate of severe acute respiratory syndrome-associated coronavirus (SARS-CoV)

Abstract Inactivated severe acute respiratory syndrome-associated coronavirus (SARS-CoV) has been tested as a candidate vaccine against the re-emergence of SARS. In order to understand the efficacy and safety of this approach, it is important to know the antibody specificities generated with inactivated SARS-CoV. In the current study, a panel of twelve monoclonal antibodies (mAbs) was established by immunizing Balb/c mice with the inactivated BJ01 strain of SARS-CoV isolated from the lung tissue of a SARS-infected Chinese patient. These mAbs could recognize SARS-CoV-infected cells by immunofluorescence analysis (IFA). Seven of them were mapped to the specific segments of recombinant spike (S) protein: six on S1 subunit (aa 12–798) and one on S2 subunit (aa 797–1192). High neutralizing titers against SARS-CoV were detected with two mAbs (1A5 and 2C5) targeting at a subdomain of S protein (aa 310–535), consistent with the previous report that this segment of S protein contains the major neutralizing domain. Some of these S-specific mAbs were able to recognize cleaved products of S protein in SARS-CoV-infected Vero E6 cells. None of the remaining five mAbs could recognize either of the recombinant S, N, M, or E antigens by ELISA. This study demonstrated that the inactivated SARS-CoV was able to preserve the immunogenicity of S protein including its major neutralizing domain. The relative ease with which these mAbs were generated against SARS-CoV virions further supports that subunit vaccination with S constructs may also be able to protect animals and perhaps humans. It is somewhat unexpected that no N-specific mAbs were identified albeit anti-N IgG was easily identified in SARS-CoV-infected patients. The availability of this panel of mAbs also provided potentially useful agents with applications in therapy, diagnosis, and basic research of SARS-CoV.

Assays for the assessment of neutralizing antibody activities against Severe Acute Respiratory Syndrome (SARS) associated coronavirus (SCV).

Abstract Accurate assessment of neutralizing antibody activities is important either for patients infected with Severe Acute Respiratory Syndrome (SARS) or for animals and volunteers immunized with the experimental vaccines against the SARS associated coronavirus (SCV). However, the current assay based on the cytopathic effect (CPE) which has been frequently cited in literature has several limitations. The CPE assay relies on the visual observation on the damage of SCV infected target cells under a microscope. It is subjected to observer variations and it is difficult to generate a quantitative determination of neutralizing activities based on the level of CPE. In the current study, we established the utility of two additional assays to measure the neutralizing activities against SCV: the plaque reduction (PR) and the neutral red staining (NRS) assays. The PR assay described in this study was modified from the traditional viral plaque reduction assay by using an improved crystal staining method to achieve better plague formation in SCV infected Vero E6 cells. The NRS neutralization assay was adopted from a similar system used for detecting neutralizing antibody responses against human immunodeficiency virus type 1 (HIV-1). In this assay, the protective effect of neutralizing antibodies was determined by the cell viability which is measured by the uptake of neutral red dye at A540. The neutralizing antibody titers can be easily determined with either of the two new assays. In this report, we described the utility of these two new neutralization assays in measuring the neutralizing activities against SCV infection from rabbit sera immunized with various forms of spike protein of SCV.