IMPROVED HUMORAL AND CELLULAR IMMUNE-RESPONSES AGAINST THE GP120 V3 LOOP OF HIV-1 FOLLOWING GENETIC IMMUNIZATION WITH A CHIMERIC DNA VACCINE ENCODING THE V3 INSERTED INTO THE HEPATITIS-B SURFACE-ANTIGEN

The gp120-derived V3 loop of HIV-1 is involved in co-receptor interact ion, it guides cell tropism, and contains an epitope for antibody neut ralization. Thus, HIV-1 V3 is an attractive vaccine candidate. The V3 of the MN strain (MN V3) contains both B- and T-cell epitopes, includi ng a known mouse H-2(d)-restricted cytotoxic T lymphocyte (CTL) epitop e. In an attempt to improve the immunogenicity of V3 in DNA vaccines, a plasmid expressing MN V3 as a fusion protein with the highly immunog enic middle (pre-S2 + S) surface antigen of hepatitis B virus (KBsAg) was constructed. Epidermal inoculation by gene gun was used for geneti c immunization in a mouse model. Antibody and CTL responses to MN V3 a nd HBsAg were measured and compared with the immune responses obtained after Vaccination with plasmids encoding the complete HIV-1 MN gp160 and HBsAg (pre-S2 + S), respectively. DNA vaccination with the HIV MN gp160 envelope plasmid induced a slow and low titred anti-MN V3 antibo dy response at 12 weeks post-inoculation (p.i.) and a late appearing ( 7 weeks), weak and variable CTL response. In contrast, DNA vaccination with the HBsAg-encoding plasmid induced a rapid and high titred anti- HBsAg antibody response and a uniform strong anti-HBs CTL response alr eady 1 week p.i. in all mice. DNA vaccination with the chimeric MN V3/ HBsAg plasmid elicited humoral responses against both viruses within 3 -6 weeks which peaked at 6-12 weeks and remained stable for at least 2 5 weeks. In addition, specific CTL responses were induced in all mice against both MN V3 and HBsAg already within the first 3 weeks, lasting at least ii weeks. Thus, HBsAg acts as a 'genetic vaccine adjuvant' a ugmenting and accelerating the cellular and humoral immune response ag ainst the inserted MN V3 loop. Such chimeric HIV-HBsAg plasmid constru cts may be useful in DNA immunizations as a 'carrier' of protein regio ns or minimal epitopes which are less exposed or poorly immunogenic.