Evaluation of Measles Vaccine Virus as a Vector to Deliver Respiratory Syncytial Virus Fusion Protein or Epstein-Barr Virus Glycoprotein gp350

Mok, Hoyin; Cheng, Xing; Xu, Qi; Zengel, James R; Parhy, Bandita; Zhao, Jackie; Wang, C. Kathy; Jin, Hong

Rhesus macaques are fully permissive to measles virus infection and have been used for evaluation of measles vaccine and measles virus pathogenesis studies [45] [46] [47] . The ability of rEZ vectored RSV F and EBV gp350 to induce measles virus specific or F or gp350 specific immune responses was examined in this more permissive animal model. Since sF3 demonstrated better immunogenicity than sF1 in cotton rats, only sF3 was evaluated in measles virus seropositive (MV+) rhesus macaques that had prior measles vaccination and measles virus seronegative (MV-) rhesus macaques. No abnormal clinical signs were observed and serum chemistries were within the normal range in all monkeys throughout the study (data not shown). sF3 or gp350 vaccinated monkeys induced a similar level of MV neutralizing antibody in both MV-and MV+ monkeys. A second dose of vaccination with sF3 or gp350 increased MV neutralizing Ab titers by about 4-fold in all groups ( Table 2) . The Ab titer differences between the groups were not statistically significant. Fig. (4) . Reduction of titers of RSV in the lungs of cotton rats vaccinated with measles-vectored RSV F after challenge. Naïve cotton rats were immunized with 10 5 PFU of sF1 or sF3 on day 0 and 28. Cotton rats were then challenged with 10 6 PFU of RSV A2 on day 56. Lungs were harvested on day 60 and RSV titers were determined in the lung homogenates by standard plaque assay. Each experimental group represents 5 individual animals except in UVinactivated sF3 group (n=3). Antibody responses to the inserted genes, however, were relatively low. sF3 inoculated animals had RSV F-specific IgG titer higher than the pre-vaccination level (titers were under the detection limit). F specific IgG Ab titers were 9.3 log 2 and 8.8 log 2 in MV+ and MV-groups after dose 1, respectively. After a second dose, three out of 4 animals in MV+ group had more than 4-fold increase in RSV F-specific IgG Ab titer but none of the animals in MV-group had 4-fold increase in Ab response (Fig. 5A) . After two doses of vaccination, RSV neutralizing Ab titers in all groups were very low in both MV+ and MV-groups. Seven out of 8 animals had a detectable level of RSV neutralizing Ab. The RSV Nt Ab titers were not statistically different between the two groups (5.0 log 2 for MV+ versus 4.5 log 2 for MV-groups) ( Table 2) . Ab responses to EBV gp350 in the gp350 vaccinated monkeys were not detected at all time points. Similar to antibody responses, IFN-secreting cells in PBMC to measles viral antigens were significantly higher (~10fold) than the responses to either RSV F or EBV gp350 (Fig. 5B) while PBMC, when stimulated with measles viral antigens, RSV F or EBV gp350, did not secrete any IL-4. Thus, compared to the cotton rat studies, rEZ vectored viruses were poorly immunogenic in the primate model.