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

Reverse genetics has been developed for generating recombinant measles virus vectored vaccines encoding foreign antigens based on the Edmonston-Schwarz and AIK-C vaccine strain [15, 48] . The reverse genetic system described in this study was based on the EZ vaccine strain, which is used predominantly outside the US. The EZ strain might be immunogenic in population that has prior measles vaccine immunization [23] . The ectodomains of the RSV F and EBV gp350 glycoproteins instead of full length proteins were engineered to be expressed by EZ to avoid the incorporation of the foreign surface glycoproteins onto the measles virus envelope. The expression of heterologous membrane proteins on measles virus surface may alter the binding of measles to its natural receptors and thus change the tissue tropism of measles virus. We showed that both RSV F and EBV gp350 was expressed efficiently in vitro. However, rEZ vectored vaccines induced insert specific responses in cotton rats but poor responses in rhesus macaques although both cotton rats and rhesus macaques have previously been shown to be permissive to measles virus infection to various degrees [47, [49] [50] [51] . Titers of prevaccinated animals were under the limit of detection in all the assays. One of the important determinants for inducing a robust immune response in vivo is the amount of the expressed antigen level and antigen presentation. We have evaluated the effect of the gene insertion location and antigen expression level because transcription of nonsegmented negative strand RNA viruses is obligatorily sequential [52] . The genes located at proximal to the 3' promoter are produced more abundantly than the ones distal to the promoter [53] . Indeed, when RSV F was introduced 3' proximally to the N gene, it produced 10 times more secreted RSV F protein than when inserted between the P and M junction (data not shown). In comparison, insertion of the gp350 of EBV at the 1st position of EZ significantly affected virus replication. Insertion of the EBV gp350 gene between the P and M genes had less effect on virus growth, similar to that shown for Hepatitis B surface antigen (HBsAg) (14) . The gene insertion position affected immunogenicity of EZ vectored vaccines in cotton rats. rEZ encoding RSV F ectodomain induced antibody response against measles and RSV F. rEZ-sF3 induced MV specific antibody response comparable to rEZ and RSV specific Ab response comparable to those induced by intranasal RSV infection in cotton rats; it also induced cell mediated response as measured by IFN-ELISpot assay. Surprisingly, sF1 was inferior to sF3 in its ability to induce both RSV neutralizing antibody and RSV F-specific IFN-secreting T cell responses, suggesting that sF1 may be more attenuated than sF3 in vivo. Immune response is dependent on viral infectivity and the nature of the inserts. rEZ vectored EBV gp350 and gp350tr induced lower gp350 specific IgG Ab response and undetectable neutralizing antibody response in cotton rats.