CHALLENGE OF CHIMPANZEES IMMUNIZED WITH A RECOMBINANT CANARYPOX-HIV-1 VIRUS

Abstract To evaluate the potential protective efficacy of a live recombinant human immunodeficiency virus type 1 (HIV-1) canarypox vaccine candidate, two chimpanzees were immunized five times with ALVAC-HIV-1 vCP250, a recombinant canarypox virus that expresses the HIV-1 IIIB(LAI) gp120/TM, gag, and protease gene products. One month after the last booster inoculation, the animals were challenged by intravenous injection of cell-associated virus in the form of peripheral blood mononuclear cells from an HIV-1 IIIB(LAI) -infected chimpanzee. One chimpanzee with a neutralizing antibody titer to HIV-1 IIIB(LAI) of 128 at the time of challenge was protected, whereas both the second animal, with a neutralizing antibody titer of 32, and a naive control animal became infected. At 5 months after challenge, the protected chimpanzee and a third animal, previously immunized with various HIV-1 MN antigens, were given a booster inoculation. The two animals were challenged intravenously 5 weeks later with twenty 50% tissue culture infectious doses of cell-free HIV-1 DH12 , a heterologous subtype B isolate. Neither chimpanzee had neutralizing antibodies to HIV-1 DH12 , and neither one was protected from infection with this isolate. The immune responses elicited by vaccination against HIV-1 IIIB(LAI) or HIV-1 MN did not, therefore, protect the animals from challenge with the heterologous cell-free HIV-1 DH12 .