Enhanced Mucosal Immune Responses to HIV Virus-Like Particles Containing a Membrane-Anchored Adjuvant

Previously, a modified HIV Env protein with a heterologous membrane anchor was found to be incorporated into HIV virus-like particles (VLPs) at 10-fold-higher levels than those of unmodified Env. To further improve the immunogenicity of such VLPs, membrane-anchored forms of bacterial flagellin (FliC) or a flagellin with a truncated variable region (tFliC) were constructed to be incorporated into the VLPs as adjuvants. HIV-specific immune responses induced by the resulting VLPs were determined in a guinea pig model. The VLPs induce enhanced systemic antibody responses by either systemic or mucosal vaccination and enhanced mucosal immunity by a mucosal immunization route, as demonstrated by high levels of HIV-specific serum IgG and mucosal IgG and IgA. The quality of the antibody responses was also improved, as shown by enhanced neutralization capacity. VLPs incorporating FliC were more effective in inducing systemic responses, while VLPs containing tFliC were more effective in inducing mucosal IgA responses. The IgG titers in sera were found to last for at least 5 months without a significant drop. These results indicate that HIV VLPs incorporating high levels of Env and a molecular adjuvant have excellent potential for further development as a prophylactic HIV vaccine.
IMPORTANCE A prophylactic vaccine is urgently needed to control the spread of HIV/AIDS. Antigens inducing strong systemic and mucosal immune responses are promising as vaccines for this mucosally transmitted disease. We found that novel HIV virus-like particles (VLPs) presenting a high level of Env in its native membrane-bound form and coincorporating an innate immune-signaling adjuvant in the same particles were effective in inducing enhanced systemic and mucosal immunity. As new HIV vaccine candidates, these VLPs bridge the gaps of the innate and adaptive, as well as systemic and mucosal, immune responses, providing a new approach for HIV vaccine development.