Expression and immunogenicity of an 18-residue epitope of HIV1 gp41 inserted in the flagellar protein of a Salmonella live vaccine.

A synthetic oligonucleotide specifying residues 735-752 of the product of the env gene of HIV1 IIIB was inserted by blunt-end ligation at restriction sites in the hypervariable, antigenically determinant region IV of two flagellin genes. Its integration, in frame and correct orientation, into gene fliC(d) in plasmid pLS408 allowed production of functional flagella when the plasmid was placed in a flagellin-negative aroA live-vaccine Salmonella dublin strain, SL5928. Bacteria thus made motile were immobilized and agglutinated by anti-(735-752 peptide) serum; expression was also shown by immunoelectron-microscopy and by Western blot of whole-cell lysates. Enzyme immunoassay (EIA) of sera of mice given three doses by intraperitoneal injection of the live-vaccine strain producing chimeric flagellin, or of concentrated flagella from it, showed production of antibody with affinity for the peptide, and in some sera, also for r-gp160. Pooled serum from mice given five i.p. doses of the live vaccine strain expressing the gp41 epitope at the surface of its flagellar filaments had higher titres of anti-peptide and anti-r-gp160 antibody and weak neutralizing activity on the IIIB isolate (90% neutralization at 1/100). The sera of nine mice given two doses of the live vaccine by the oral route had either no or only very low titres of antibody to flagellar antigen d; they were therefore not tested for anti-peptide activity.