BRUCELLA-ABORTUS CONJUGATED WITH A PEPTIDE DERIVED FROM THE V3 LOOP OF HUMAN-IMMUNODEFICIENCY-VIRUS (HIV) TYPE-1 INDUCES HIV-SPECIFIC CYTOTOXIC T-CELL RESPONSES IN NORMAL AND IN CD4(-DEPLETED BALB() CELL)C MICE/

We have previously shown that immunization of mice with human immunode ficiency virus (HIV)-derived proteins or peptides conjugated to inacti vated Brucella abortus induces the secretion of virus-neutralizing ant ibodies, predominantly of the immunoglobulin G2a (IgG2a) isotype, In a ddition, B, abortus activates human CD4(+) and CD8(+) cells to secrete gamma interferon. Since these are both characteristics of a Th1-type immune response, which is associated with the development of cell-medi ated immunity, it was important to determine if B. abortus conjugates would also act as a carrier to induce a cytotoxic T-lymphocyte (CTL) r esponse, To test this hypothesis, we conjugated an 18-amino-acid pepti de from the V3 loop of the MN strain of HIV-1 gp120 that contains both B- and cytotoxic T-cell epitopes to B, abortus (B. abortus-MN 18-mer) , A 10-amino-acid fragment of this peptide has been shown to be the mi nimal CTE determinant presented by murine H-2D(d), It was found that t wo in vivo immunizations with 10(8) organisms of B. abortus-MN 18-mer followed by in vitro stimulation with peptide induced a virus-specific CTL response, Conjugation to B. abortus was required for in vive prim ing, since there was no induction of memory CTLs when B. abortus was o nly mixed with peptide, Targets pulsed with peptide as well as those i nfected with a vaccinia virus encoding HIV gp160 were killed, demonstr ating recognition of naturally processed envelope, Also, major histoco mpatibility complex-incompatible L cells which were infected with vacc inia viruses that encoded H-2D(d) but not H-2k(d), and pulsed with pep tide were lysed, This demonstrated the appropriate major histocompatib ility complex class I restriction, Treatment of the mice with anti-L3T 4 prior to immunization caused a severe depletion of CD4(+) lymphocyte s, yet it did not decrease the CTL priming, Thus, inactivated B. abort us can induce non-CD4(+) cells to produce the cytokines required for C TL induction, We conclude that B, abortus stimulates a cellular as wel l as a humoral immune response, even in the relative absence of CD4(+) helper cells, It may be a particularly useful vaccine carrier in HIV- 1-infected individuals or others with impaired CD4(+) T-cell function.