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

ABSTRACT 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 vacci-nation and enhancedmucosal immunity by a mucosal immunization route, as demonstrated by high levels of HIV-specific se-rum IgG andmucosal IgG and IgA. The quality of the antibody responses was also improved, as shown by enhanced neutraliza-tion 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 signifi-cant drop. These results indicate that HIV VLPs incorporating high levels of Env and amolecular adjuvant have excellent poten-tial 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 andmucosal 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 andmucosal immunity. As ne