Characterization of V3 loop-Pseudomonas exotoxin chimeras: Candidate vaccines for human immunodeficiency virus-1

To develop a candidate vaccine for human immunodeficiency virus, type 1 (HIV-1), chimeric proteins were constructed by inserting sequences derived from the V3 loop of gp120 into a nontoxic form of Pseudomonas exotoxin (PE). Inserts of 14 or 26 amino acids, constrained by a disulfide bond, were introduced between domains II and III of PE. V3 loop-toxin proteins expressed in Escherichia coil and corresponding to either MN (subtype B) or Thai (subtype E) strains, were recognized by strain-specific monoclonal anti- gp120 antibodies. When loop sequences were in introduced into an enzymatically active form of the toxin, there was no loss of toxin-mediated cell killing, suggesting that these sequences were co-transported to the cytosol. Sera from rabbits injected with nontoxic PE-V3 loop chimeras were reactive for strain-specific gp120s in Western blots, immunocapture assays, enzyme-linked immunosorbent assays, and neutralized HIV-I infectivity. Since toxin vectors were designed to receive oligonucleotide duplexes encoding any V3 loop sequence, this approach should allow for the production of V3 loop- toxin chimeras corresponding to multiple HIV isolates.