In HIV I infected individuals, CD4-bearing T cells (T helper), are functionally deficient early in the course of the infection and become numerically depleted in advanced stages of the disease. In devising a strategy for vaccinating HIV I infected individuals, we looked for means of stimulating their B cells to produce HIV I specific antibodies under conditions of limited T cell help. It was previously established in the murine and human systems that certain """"""""carriers"""""""" may convert an otherwise T-dependent antigen into a T-independent antigen. One such carrier is the inactivated bacterium Brucella abortus (Ba). Small haptens, when conjugated to Ba, can elicit strong antibody responses in vivo which are dominated by the IgGa+2b isotypes (which are most efficient in mediating Ab mediated cytotoxicity). Furthermore, in humans haptens-Ba can stimulate both adult and neonatal B cells to produce hapten specific Ab in the absence of T cells. Inactivated HIV I was conjugated to Ba, and the conjugate formed (HIV I-Ba) as well as unconjugated HIV I were tested for immunogenicity in normal Balb/c mice and CD4-depleted Balb/c (anti L3T4 treated mice). Mice immunized with HIV-Ba produced 2-3-fold higher titers of HIV I specific antibodies compared to HIV I immunized mice. The Ab generated were predominantly of the IgG2a in the HIV-BA immunized mice. The sera from both mouse groups reacted with all the major viral proteins on Western blots. Furthermore, in a syncytia assays, using the gpl6O-vaccinia vector infected CEM cells, the sera from HIV-BA immunized mice gave very strong inhibition. CD4-depleted mice did not respond at all to unconjugated HIV I, but did respond to the HIV-Ba conjugate. The ab produced were of the IgM and some IgG2a isotype. These sera also neutralized the syncytia assay. A similar approach is now used to test the immunogenicity of cloned gpl6O conjugated to Ba. We are also testing the ability of polymerized peptides to generate T independent IgG responses in athymic (nude) mice.
