Induction of a mucosal cytotoxic T-lymphocyte response by intrarectal immunization 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 replication defect in most mammalian cells. Here we apply MVA to human immunodeficiency 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) immunity. 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 loop), homologous to that recognized by HIV MN loop-specific CTL and showed that HIV-1 MN-specific CTLs cross-reactively recognize the corresponding epitope from strain 89.6 presented by H-2Dd. Having defined the CTL specificity, we immunized BALB/c mice intrarectally with recombinant MVA 89.6. A single mucosal immunization with MVA 89.6 was able to elicit long-lasting antigen-specific mucosal (Peyer's patch and lamina propria) and systemic (spleen) CTL responses as effective as or more effective than those of a replication-competent vaccinia virus expressing 89.6 gp160. Immunization with MVA 89.6 led to (i) the loading of 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. These results indicate that nonreplicating recombinant MVA may be at least as effective for mucosal immunization as replicating recombinant vaccinia virus.