Effect Of Immune Route And Adjuvant On Immune Response In Mice

Respiratory syncytial virus(RSV)is a leading cause of lower respiratory illness,particularly in infants,the elderly,and immunocompromised adults.Considering the particular vulnerable population and the fact that formalin-inactivated RSV vaccine has caused enhanced respiratory diseases(ERD),the efficacy and safety have been the hot topic and focus in the development of RSV vaccine.Currently,there is still no licensed commercial vaccine against RSV.Among the eleven RSV-encoded proteins,fusion(F)protein has viral-host membrane fusion function.Antibodies against RSV-Fusion proteins can effectively inhibit virus invasion to the host.After fusion with the receptor on host cell membrane,the F protein forms a stable post-fusion conformation.Previous reports indicate that pre-fusion conformation F protein is more suitable as antigen than post-fusion conformation F protein,because it has rich effective epitopes and can induce a highly specific and protective immune response.However,similar to other subunit vaccine,RSV-F has low immunogenicity and usually leads to a Th2-biased immune response.In order to resolve the above problem,we used the recombinant pre-fusion conformation RSV-F protein as antigen and BALB/c mice as model,and investigated and compared the effect of inoculation routes and different adjuvants on the immune response in BALB/c mice.The inoculation routes include intramuscular and subcutaneous injections,two common routes used in preclinical and clinical studies.Adjuvants used in this study include Alhydrogel,MF59,AS03,AS02,and glycol chitosan.The first three have been used in many approved vaccines.We then compared adjuvant effect on immune responses,specifically assaying antigen-specific antibodies,antibody subtype,and neutralizing antibodies in BALB/c mice.Cytokine production and the blood transcriptome were also studied to illustrate the underlying mechanisms induced by the adjuvant vaccines.Moreover,virus challenge tests were performed to assess the protective effect of different adjuvant-assisted vaccines.The results show that intramuscular injection is more advantageous than subcutaneous injection in improving the immunogenicity of RSV-F subunit vaccine w/o adjuvants.Low-dose antigen delivered via intramuscular route showed comparable RSV-specific antibody level to that of 10-dose antigen via subcutaneous route,and no side effect was observed.All adjuvanted vaccines enhanced antigen-specific and neutralizing antibody titers.Compared with other adjuvants,AS02 elicited higher antibody level,which is followed by squalene-based emulsion adjuvants(AS03 and MF59).Alhydrogel and GCS showed relatively low efficacy in this way.In addition,the high antibody level induced by AS02 remaind until week 18 after the boost.Moreover,AS02 induced the original immune response into a balanced Th1/Th2 immune response.Mice in the AS02 group also showed faster recovery from viral attacks in challenge tests.Further transcriptome analysis revealed that AS02 regulates immune balance by activating TLR-4 and promotes Th1-type immune response.These results suggest that intramuscular route is an optimal choice for RSV-F vaccine and that AS02 may be an excellent candidate adjuvant for RSV-F subunit vaccine.This study provides valuable information regarding the development of RSV-F subunit vaccines.