VACCINATION OF RABBITS WITH RECOMBINANT VACCINIA VIRUS CARRYING THE ENVELOPE GENE OF HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-I

Two groups of 3 rabbits each were immunized with either recombinant va ccinia virus, WR-SFB5env, carrying the human T-cell lymphotropic virus type 1 (HTLV-1) env gene at the site of the hemagglutinin gene of the WR strain, or control vaccinia virus, HA-WR, lacking the functional h emagglutinin gene. All 6 rabbits responded with anti-vaccinia virus an tibodies. WR-SFB5env elicited anti-HTLV-1 env antibodies but no vesicu lar stomatitis virus (HTLV-1) pseudotype neutralizing antibodies in al l 3 rabbits. After 10 weeks, the animals were challenged by transfusio n of blood from an HTLV-1-infected rabbit. Two of the 3 vaccinated rab bits and all 3 control rabbies became infected with HTLV-1, as indicat ed by seroconversion and detection of HTLV-1 proviral sequences by pol ymerase chain reaction. The rabbit that had been protected from initia l challenge became infected with HTLV-1 upon rechallenge 12 weeks afte r the first challenge. In view of the proven prophylactic effect of pa ssive immunization against HTLV-1, our vaccine trial failed because WR -SFB5env was incapable of inducing neutralizing antibodies against HTL V-1 in the immunized animals. It remains to be studied whether cell-me diated immunity such as antibody-dependent cellular cytotoxicity was i nvolved in the temporary protection of 1 vaccinated rabbit. (C) 1995 W iley-Liss, Inc.