Simultaneous administration of recombinant measles viruses expressing respiratory syncytial virus fusion (F) and nucleo (N) proteins induced humoral and cellular immune responses in cotton rats

We previously reported that recombinant measles virus expressing the respiratory syncytial virus (RSV) fusion protein (F), MVAIK/RSV/F, induced neutralizing antibodies against RSV, and those expressing RSV-NP (MVAIK/RSV/NP) and M2-1 (MVAIK/RSV/M2-1) induced RSV-specific CD8 ⁺ /IFN-γ ⁺ cells, but not neutralizing antibodies. In the present study, MVAIK/RSV/F and MVAIK/RSV/NP were simultaneously administered to cotton rats and immune responses and protective effects were compared with MVAIK/RSV/F alone. Sufficient neutralizing antibodies against RSV and RSV-specific CD8 ⁺ /IFN-γ ⁺ cells were observed after re-immunization with simultaneous administration. After the RSV challenge, CD8 ⁺ /IFN-γ ⁺ increased in spleen cells obtained from the simultaneous immunization group in response to F and NP peptides. Higher numbers of CD8 ⁺ /IFN-γ ⁺ and CD4 ⁺ /IFN-γ ⁺ cells were detected in lung tissues from the simultaneous immunization group after the RSV challenge. No detectable RSV was recovered from lung homogenates in the immunized groups. Mild inflammatory reactions with the thickening of broncho-epithelial cells and the infiltration of inflammatory cells were observed in lung tissues obtained from cotton rats immunized with MVAIK/RSV/F alone after the RSV challenge. No inflammatory responses were observed after the RSV challenge in the simultaneous immunization groups. The present results indicate that combined administration with MVAIK/RSV/F and MVAIK/RSV/NP induces humoral and cellular immune responses and shows effective protection against RSV, suggesting the importance of cellular immunity.