Enhancement of mucosal immune responses by chimeric influenza HA/SHIV virus-like particles

To enhance mucosal immune responses using simian-human immunodeficiency virus-like particles (SHIV VLPs) as a mucosal HIV vaccine, we have produced phenotypically mixed, chimeric influenza HA/SHIV 89.6 VLPs and used them to immunize C57B/6J mice intranasally. Systemic and mucosal antibody responses, as well as cytotoxic T cell (CTL) responses, were compared in groups immunized with SHIV 89.6 VLPs or HA/SHIV 89.6 VLPs. Intranasal immunizations were given using VLPs either with or without the addition of the mucosal adjuvant cholera toxin. Total serum IgG, IgG1 and IgG2a, and IgA in saliva, vaginal lavage, lung wash, and fecal extracts were evaluated by enzyme-linked immunosorbent assay (ELISA). The level of serum IgG production to HIV Env was highest in the group immunized with chimeric HA/SHIV 89.6 VLPs. Similarly, mucosal IgA production was also enhanced in the mucosal HA/SHIV 89.6 VLP-immunized group. Analysis of the IgG1/IgG2a ratio indicated that a Th1-oriented immune response resulted from these VLP immunizations. High levels of serum IgG and mucosal IgA against influenza virus were also detected in mice immunized with HA/SHIV VLPs. HA/SHIV 89.6 VLP-immunized mice also showed significantly higher CTL responses than those observed in SHIV 89.6 VLP-immunized mice. Furthermore, a Major Histocompatibility Complex (MHC)-class-I-restricted T cell activation ELISPOT assay showed elevated interferon-gamma, interleukin-2, and interleukin-12 production in HA/SHIV 89.6 VLP-immunized mice, indicating that phenotypically mixed HA/SHIV 89.6 VLPs can enhance both humoral and cellular immune responses at multiple mucosal sites. Therefore, chimeric HA-containing VLPs represent a potential approach for mucosal immunization for prevention of HIV infection.