Study On The Different Immune Responses Induced By RAd5and RAAV2/1Vaccine Expressing HIV-1Gag And Gp160/gp145

Since the first AIDS case was reported, the study of HIV vaccine has beingcarried on, but till now effective HIV vaccine is not available. We found thatcombined immunization with multiple vector-based vaccines could induce high andlong-lasting HIV-specific immune responses. To apply the combined immunizationstrategy more reasonably, it is necessary to understand the characteristics of thesevaccines used alone or in combined immunization strategy. Adenovirus andadeno-associated virus vectors are widely used in the field of vaccines and genetherapy research, the safty of these two vectors has been verified. This study wasdesigned to further investigate the difference of cellular and humoral immuneresponses induced by adenovirus and adeno-associated virus, which was observed inour preliminary study. It will provide experimental evidence for vaccine and genetherapy research.BALB/c mice were immunized with rAd5and rAAV2/1carring HIV-1gag gene，the titers of Gag-specific and vector-specific IgG in mice serum were detected byELISA, cellular immune responses were detectd by ELISPOT. The results showedthat mice immunized with rAd5-gag induced potent Gag-specific cellular immuneresponses and that were significantly higher than rAd5-specfic cellular responses,while rAAV2/1-gag elicited weak Gag-specific and rAAV2/1-specific cellularresponses. Both P24-specific and rAd5-specific IgG titers induced by rAd5-gag werehigh and in similar level. And the P24-specific IgG titers were higher than thevector-specific IgG titers in mice immunized with rAAV2/1. rAd5-gag inducedsimilar levels of vector-specific and exogenous gene-specific IgG. However inrAAV2/1-gag, the IgG titer induced by exogenous gene is higher than that induced byvector.Mice were immunized with rAd5and rAAV2/1carrying the luciferase reportergene through intramuscular way, the expression of luciferase reporter gene wasdetected using in vivo imaging methods at different time points. It showed that theexpression of luciferase reporter gene in rAd5vector reach peak immediately anddecline soon. However in rAAV2/1immunized mice the time that the expression ofexogenous gene reached peak was later compared with that in rAd5immunized mice,and the expression peak was long-lasting. When these two vaccines were used together, the trend of reporter gene expression was similar as that was observed whenthey were used alone. Adeno-associated virus vector significantly inhibited theexpression of exogenous gene after the second immunization of the same vector,while the inhibitory effect of adenovirus vector was very weak. rAAV2/1vector couldincompletely inhibit the expression of reporter gene in rAd5that was subsequentlyused.The BALB/c mice were immunized with rAd5-gp160and rAAV2/1-gp145vaccine alone or combined with rAd5or rAAV2/1carrying HIV-1gag,Gp120-specific binding antibody titers elicited by rAAV2/1-gp145alone were higherthan that of rAd5-gp160. When vectors expressing gp160/gp145were combined withvectors expressing Gag, Gp120-specific antibodies in immunized mice wereremarkably increased compared with using vector expressing Gp160/Gp145aloneirrespective with the type of vector. This enhancement is particularly evident in therAAV2/1vector. Env-specific cellular immune responses induced by rAd5vector ishigher than that of rAAV2/1vector, as it was observed in previous studies aboutvaccines encoding gag gene. But Env-specific cellular immune responses were notenhanced in gp160/gp145gene and gag gene combined immunization group.Gp41-specific binding antibody levels in mice immunized with vaccines encodinggp160were much higher than that of encoding gp145.To sum up, long term stable expression of luciferase reporter gene was found inrAAV2/1immunized mice, but exogenous gene expression of the second injectionwas completely inhibited. Short time expression of luciferase reporter gene was foundin rAd5immunized mice. rAAV2/1could induce strong target antigen-specifichumoral immune responses and weak cellular immune responses, while rAd5couldgenerate high level of target antigen-specific humoral and cellular responses. Whenvectors expressing Gp160/Gp145was combined with vectors expressing Gag,Gp120-specific antibodies in immunized mice were remarkably increased comparedwith using vector expressing Gp160/Gp145alone irrespective with the type of vector.It indicates that both vector and foreign gene may be important factors forimmunogenicity of vector-based vaccines. This study provided experimental evidence for applying these two vectors reasonably in vaccine design.