Protection against streptococcal pharyngeal colonization with a vaccinia: M protein recombinant.

Phagocytosis of group A streptococci requires type-specific antibodies directed against the variable determinants of the bacterial surface M protein molecule. As a step toward developing a broadly protective anti-streptococcal vaccine, a vaccinia virus (VV) recombinant was constructed that expresses the conserved region of the structural gene encoding the M6 molecule (VV:M6'). Mice immunized intranasally with the VV:M6' virus showed markedly reduced pharyngeal colonization by streptococci after intranasal and oral challenge with these bacteria. M protein-specific serum immunoglobulin G was significantly elevated in vaccinated animals and absent in controls. A similar approach may prove useful for the identification of protective determinants present on other bacterial and viral pathogens.

Expression of streptococcal M protein in mammalian cells.

The M protein encoded by group A streptococci is a cell-wall polypeptide that has the property of enabling these organisms to evade the phagocytic cells of the human host. Therefore, the M protein plays a major role in the pathogenesis of streptococcal diseases. As an initial step toward the use of this protein as a target antigen for the production of protective anti-streptococcal immunity, a live vaccinia virus recombinant containing the M-protein gene has been constructed (VV:M6 delta). The bacterial M-protein DNA sequence is stable within this genetic context and is actively transcribed by viral RNA polymerase. Furthermore, high levels of immunoreactive M protein were detected in vivo when the VV:M6 delta recombinant was used to infect mammalian cells in culture. Thus, in addition to providing a powerful approach for dissecting the immunodominant domains of the M protein, the VV:M6 delta recombinant appears to be an excellent candidate vaccine for animal trials.

Cell-free translation of a chimeric eucaryotic-procaryotic message yields functional chloramphenicol acetyltransferase.

A vaccinia virus (VV) recombinant containing the DNA sequences encoding the bacterial chloramphenicol acetyltransferase (CAT) gene was constructed. The ability of the chimeric VV:CAT transcript to be translated in vitro into enzymatically active enzyme was assessed. Addition of mRNA isolated from the cytoplasm of VV:CAT infected cells to a mRNA-dependent reticulocyte lysate resulted in the synthesis of high levels of enzymatically active CAT. These results suggest that this assay may be used in concert with physical assays to study the expression and stability of chimeric transcripts in virus-infected cells.

Construction of recombinant vaccinia virus strains using single-stranded DNA insertion vectors.

The ability of single-stranded (ss) DNA, isolated from recombinant M13 bacteriophage, to direct the insertion of foreign genetic elements into the vaccinia virus (VV) genome was examined. An identical chimeric transcriptional unit [VV promoter/chloramphenicol acetyl transferase (CAT) gene embedded in DNA sequences encoding vaccinia virus thymidine kinase (TK)] was inserted into either the previously characterized plasmid insertion vector, pGS20, or into M13mp18. It was found that the ss vector (M13mp18:TK/CAT) was four times more efficient than the plasmid vector (pGS20:CAT) in catalyzing homologous recombination of the cat gene by marker transfer into the VV genome. Furthermore, Southern blot analyses and CAT enzymatic activity assays confirmed that the structure of the M13-derived recombinant genomes were as expected and that the chimeric genes were fully active. Although the precise mechanism responsible for the ss DNA-catalyzed insertion event is not known, these results are discussed with respect to the advantages of using M13-based vectors with which to manipulate and insert genetic information into infectious VV recombinants.