Respiratory tract immunization of non-human primates with a Newcastle disease virus-vectored vaccine candidate against Ebola virus elicits a neutralizing antibody response

We previously developed a respiratory tract vaccine candidate against Ebola virus (EBOV) based on human parainfluenza virus type 3 (HPIV3), a respiratory paramyxovirus, expressing the EBOV GP envelope protein (HPIV3/GP) from an added gene. Two doses of this vaccine candidate delivered by the intranasal and intratracheal route protected monkeys against intraperitoneal challenge with EBOV; however, concerns exist that the vaccine candidate may have reduced immunogenicity in the adult human population due to pre-existing immunity against HPIV3. Here we developed a new vaccine candidate (NDV/GP) based on Newcastle disease virus (NDV), an avian paramyxovirus that is antigenically distinct from human viral pathogens and is highly attenuated in monkeys. Following one intranasal and intratracheal inoculation of Rhesus monkeys with NDV/GP, titers of EBOV-specific antibodies in respiratory tract secretions and serum samples determined by ELISA, as well as serum EBOV-neutralizing antibodies, were undetectable or low compared to those induced by HPIV3/GP. A second immunization resulted in a substantial boost in serum IgG ELISA titers, yet the titers remained lower than those induced by a second dose of HPIV3/GP. In contrast, the ELISA IgA titers in respiratory tract secretions and, more importantly, the serum EBOV-neutralizing antibody titers were equal to those induced after the second dose of HPIV3/GP. These data suggest that NDV/GP can be effective for immunization against EBOV alone, or in combination with either HPIV3/GP or another vaccine platform in a heterologous prime-boost regimen.