INDUCTION OF A MUCOSAL CYTOTOXIC T-LYMPHOCYTE RESPONSE BY INTRARECTALIMMUNIZATION WITH A REPLICATION-DEFICIENT RECOMBINANT VACCINIA VIRUS EXPRESSING HUMAN-IMMUNODEFICIENCY-VIRUS-89.6 ENVELOPE PROTEIN

To improve the safety of recombinant vaccinia virus vaccines, modified vaccinia virus Ankara (MVA) has been employed, because it has a repli cation defect in most mammalian cells. Here we apply MVA to human immu nodeficiency virus type 1 (HIV-1) vaccine development by incorporating the envelope protein gp160 of HIV-1 primary isolate strain 89.6 (MVA 89.6) and use it to induce mucosal cytotoxic-T-lymphocyte (CTL) immuni ty. In initial studies to define a dominant CTL epitope for HIV-1 89.6 gp160, we mapped the epitope to a sequence, IGPGRAFYAR (from the V3 l oop), homologous to that recognized by HIV MN loop-specific CTL and sh owed that HIV-1 MN-specific CTLs cross-reactively recognize the corres ponding epitope from strain 89.6 presented by H-2D(d). Having defined the CTL specificity, we immunized BALB/c mice intrarectally with recom binant MVA 89.6. A single mucosal immunization with MVA 89.6 was able to elicit long-lasting antigen-specific mucosal (Peyer's patch and lam ina propria) and systemic (spleen) CTL responses as effective as or mo re effective than those of a replication-competent vaccinia virus expr essing 89.6 gp160. Immunization with MVA 89.6 led to (i) the loading o f antigen-presenting cells in vivo, as measured by the ex vivo active presentation of the P18-89.6 peptide to an antigen-specific CTL line, and (ii) the significant production of the proinflammatory cytokines ( interleukin-6 and tumor necrosis factor alpha) in the mucosal sites. T hese results indicate that nonreplicating recombinant MVA may be at le ast as effective for mucosal immunization as replicating recombinant v accinia virus.