Mucosal Immunization with Newcastle Disease Virus Vector Coexpressing HIV-1 Env and Gag Proteins Elicits Potent Serum, Mucosal, and Cellular Immune Responses That Protect against Vaccinia Virus Env and Gag Challenges

Newcastle disease virus (NDV) avirulent strain LaSota was used to coexpress gp160 Env and p55 Gag from a single vector to enhance both Env-specific and Gag-specific immune responses. The optimal transcription position for both Env and Gag genes in the NDV genome was determined by generating recombinant NDV (rNDV)-Env-Gag (gp160 located between the P and M genes and Gag between the HN and L genes), rNDV-Gag-Env (Gag located between the P and M genes and gp160 between the HN and L genes), rNDV-Env/Gag (gp160 followed by Gag located between the P and M genes), and rNDV-Gag/Env (Gag followed by gp160 located between the P and M genes). All the recombinant viruses replicated at levels similar to those seen with parental NDV in embryonated chicken eggs and in chicken fibroblast cells. Both gp160 and Gag proteins were expressed at high levels in cell culture, with gp160 found to be incorporated into the envelope of NDV. The Gag and Env proteins expressed by all the recombinants except rNDV-Env-Gag self-assembled into human immunodeficiency virus type 1 (HIV-1) virus-like particles (VLPs). Immunization of guinea pigs by the intranasal route with these rNDVs produced long-lasting Env- and Gag-specific humoral immune responses. The Env-specific humoral and mucosal immune responses and Gag-specific humoral immune responses were higher in rNDV-Gag/Env and rNDV-Env/Gag than in the other recombinants. rNDV-Gag/Env and rNDV-Env/Gag were also more efficient in inducing cellular as well as protective immune responses to challenge with vaccinia viruses expressing HIV-1 Env and Gag in mice. These results suggest that vaccination with a single rNDV coexpressing Env and Gag represents a promising strategy to enhance immunogenicity and protective efficacy against HIV. IMPORTANCE A safe and effective vaccine that can induce both systemic and mucosal immune responses is needed to control HIV-1. In this study, we showed that coexpression of Env and Gag proteins of HIV-1 performed using a single Newcastle disease virus (NDV) vector led to the formation of HIV-1 virus-like particles (VLPs). Immunization of guinea pigs with recombinant NDVs (rNDVs) elicited potent long-lasting systemic and mucosal immune responses to HIV. Additionally, the rNDVs were efficient in inducing cellular immune responses to HIV and protective immunity to challenge with vaccinia viruses expressing HIV Env and Gag in mice. These results suggest that the use of a single NDV expressing Env and Gag proteins simultaneously is a novel strategy to develop a safe and effective vaccine against HIV.