Respiratory syncytial virus (RSV) remains a major cause of morbidity and mortality in infants and the elderly and is a continuing challenge for vaccine development. A murine T helper cell (Th) type 2 response associates with enhanced lung pathology, which has been observed in past infant trials using formalin-inactivated RSV vaccine. In this study, we have engineered an optimized plasmid DNA vector expressing the RSV fusion (F) protein (DNA-F). DNA-F was as effective as live RSV in mice at inducing neutralizing antibody and cytotoxic T lymphocyte responses, protection against infection, and high mRNA expression of lung interferon γ after viral challenge. Furthermore, a DNA-F boost could switch a preestablished anti-RSV Th2 response towards a Th1 response. Critical elements for the optimization of the plasmid constructs included expression of a secretory form of the F protein and the presence of the rabbit β-globin intron II sequence upstream of the F-encoding sequence. In addition, anti-F systemic immune response profile could be modulated by the route of DNA-F delivery: intramuscular immunization resulted in balanced responses, whereas intradermal immunization resulted in a Th2 type of response. Thus, DNA-F immunization may provide a novel and promising RSV vaccination strategy.

Respiratory syncytial virus (RSV) remains a major cause of severe respiratory diseases in infants, young children, and the elderly. However, development of a RSV vaccine has been hampered by the outcome of the infant trials in the 1960s with a formalin-inactivated RSV preparation. Enhanced lung disease was induced by the vaccination post-RSV exposure. Previous studies in mice primed with RSV G protein either formulated in adjuvants or delivered by recombinant vaccinia viruses have indicated that enhanced lung pathology resulted from a Th2-type host immune response against the viral G protein. However, in the present report, we have demonstrated that vaccination with plasmid vectors encoding either a full-length or a secreted G protein (DNA-G) clearly elicited balanced systemic and pulmonary Th1/Th2 cytokine responses in mice and did not induce an atypical pulmonary inflammatory reaction post-RSV challenge in cotton rats. DNA-G immunization also induced marked virus neutralizing antibody responses and protection against RSV infection of the lower respiratory tract of both mice and cotton rats. So far, only genetic immunization has been able to induce a balanced Th1/Th2 response with the RSV G protein, reminiscent of that induced by live RSV. Therefore, DNA-G is a promising immunogen for inclusion in a nucleic acid RSV vaccine.

We have previously described a myoblast cell surface glycoprotein of the molecular mass 46,000 (gp46), which is associated with myoblast differentiation. In this report we demonstrate that gp46 binds specifically to gelatin-Sepharose and in this respect is similar to a glycoprotein of the molecular mass 47,000, which has earlier been described as a cell surface localized protein in mouse parietal endoderm cells and in chick embryo fibroblasts. To ascertain the relationship of gp46 to myoblast differentiation, wild-type L6 myoblasts, as well as two concanavalin A (ConA) resistant, differentiation-negative, myoblast mutants (D-1 and C-8), were examined for gp46 expression. In the mutant designated D-1, which has a defect in dolichol mannosyl transferase, both mannose incorporation into gp46 and ConA binding to gp46 was reduced compared with L6, without markedly affecting the gelatin adhesion properties of gp46. Western blotting with a monoclonal antibody against gp46 was used to show that the expression of gp46 was normal in D-1 but was reduced in mutant C-8 compared with L6. Reduction occurred both in the plasma membrane and endoplasmic reticulum fractions of C-8 compared with wild-type L6. In L6 myoblasts, the expression of gp46 remained constant during myoblast replication and fusion but decreased markedly postfusion. In the nonfusing myoblast mutants D-1 and C-8 and in wild-type L6 cells that were prevented from fusing by treatment with 5-bromo-2'-deoxyuridine, the expression of gp46 remained invariant. We suggest that collagen interactions, mediated by gp46, are important for normal rat skeletal muscle differentiation.

1. Surface labelling of plasma-membrane proteins with 125I, catalysed by lactoperoxidase, and radioactive l-fucose incorporation into glycoprotein were used as plasma-membrane markers for skeletal-muscle cells in culture. 2. Plasma membranes were prepared at various stages of myogenesis in vitro and rates of synthesis and accumulation of proteins in the membranes were compared. 3. Increased synthesis and accumulation of a protein of apparent mol.wt. 70000 occurred in the plasma-membrane fraction concomitant with the onset of myoblast fusion. 4. In cultures in which fusion of myoblasts was inhibited by 5'-bromo-2-deoxyuridine, synthesis and accumulation of the protein of apparent mol.wt. 70000 was selectively inhibited. 5. It is suggested the protein of apparent mol.wt. 70000 may be involved in the process of myoblast fusion.

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