A human immunodeficiency virus prime-boost immunization regimen in humans induces antibodies that show interclade cross-reactivity and neutralize several X4-, R5-, and dualtropic clade B and C primary isolates.

A human immunodeficiency virus (HIV) vaccine that will be useful in diverse geographic regions will need to induce a broad immune response characterized by cross-clade immunity. To test whether a clade B-based HIV candidate vaccine could induce interclade humoral responses, including neutralizing activity against primary HIV-1 isolates, sera were tested from recipients of a vaccine consisting of recombinant canarypox virus vCP205 and recombinant gp120(SF2). Serum antibodies exhibited strong immunochemical cross-reactivity with V3 peptides from clades B, C, and F, with weaker activity for several V3 peptides from clades A, D, G, and H; essentially no reactivity could be demonstrated with V3 peptides from clades E and O. Extensive cross-clade reactivity was also documented by enzyme-linked immunosorbent assay with all nine recombinant HIV envelope glycoproteins tested from clades B, D, and E. In addition, vaccinees' sera displayed significant neutralizing activity against 5 of 14 primary isolates tested, including one X4 virus and two dualtropic viruses (from clade B) and two R5 viruses (from clades B and C). This is the first demonstration of the induction by a candidate HIV vaccine constructed from clade B laboratory strains of HIV of neutralizing activity against R5 and clade C primary isolates. The data suggest that, by virtue of their ability to induce cross-clade immune responses, appropriately formulated HIV vaccines based on a finite number of HIV isolates may ultimately be able to protect against the wide range of HIV isolates affecting the populations of many geographic regions.