Immunogenicity Of A Chimeric Adenovirus Type 5 Vector With Type 35 Fiber Containing HIV-1 Gag

The global Human Immunodeficiency Virus(HIV) epidemic continues to expand, exceeding previous predictions and causing tremendous suffering. It has been the leading cause of death in Africa. The Joint United Nations Programme on HIV/AIDS and World Health Organization "2006 AIDS Epidemic Update," which indicates that the global epidemic continued to grow in 2006, with more than four million new infections and nearly three million deaths. This report clearly shows that national and global efforts have led to vital progress in the fight against the HIV/AIDS pandemic. But that progress is still too slow and too limited. At the same time, a rapid increase of HIV infection was also found in China in recent years. Therefore, developing HIV vaccines targeting the prevalent strains in China is one of the most important tasks of Chinese HIV/AIDS control and prevention.Prophylactic vaccines are not able to induce persistent immunity against HIV, our objectives are to develop therapeutic vaccines and vaccinate individuals under HAART to restore and broaden HIV specific cellular immunity, contral viral replication and delay viral rebound.In this study, we compared the expression of wild-type gag and codon-modified gag. In transient expression in vitro, the expressing level of mod.gag was considerably increased compared with that of wt.gag. Then the expression of HIV Gag protein was determined using Western Blot and indirect immuno-fluorescent staining. To compare the immunogenicity of rAd5/F35,DNA, rAd5 and rAAV2/1 vaccines expressing Gag, BALB/c mice were inoculated with these vaccines 2 times with 3-week interval either in single vaccine or combination vaccines. The IgG antibody was detected by ELISA and CTL response was detected by intracellular cytokine stain assay. The Results showed that the rAd5/F35-mod.gag vector could express HIV Gag protein in 293 cells in vitro and generate strong HIV-specific immune responses either in single vaccine or combination vaccines in vivo. The best CTL response was found when the rAd5/F35-mod.gag vaccine was used alone. The percentage of IFN-γproducing CD8+ T cells over all CD8+ cells was 8.828±1.554% which was higher than that of the DNA vaccine was used as a primer, followed by the rAd5/F35 virus vaccine as a booster, the frequency of CTL responses in this group was 3.62±2.03%. Anti-P24 IgG antibodies in serum of immunized mice were detected by ELISA, the highest level was also found in the group immunized with rAd5/F35-mod.gag alone. The antibody titer was 1:12800 at week 4.Recombinant adenovirus serotype 5 (rAd5) vector-based vaccines have been shown to elicit high frequency cellular immune responses in animal models. Candidate rAd5 vaccines for HIV-1 and other pathogens are therefore being advanced into large-scale clinical trials. A major limitation of this approach, however, is that the majority of the human population has pre-existing immunity to the Ad5 vector as a result of natural exposure. Such pre-existing antivector immunity may substantially reduce the immunogenicity and clinical utility of rAd5 vaccines. In fact, anti-Ad5 immunity has already been demonstrated to suppress the immunogenicity of rAd5 vaccines in studies in mice, rhesus monkeys, and humans in early phase 1 clinical trials. So our laboratory has examined the immunogenicity of a replication-defective chimeric Ad5 vector with Ad type 35 fiber (rAd5/F35) (Ad35 virus was classified as subgroup B). Anti-Ad5 immunity typically found dramatically blunted the immunogenicity of rAd5-mod.gag. In contrast, rAd5/F35-mod.gag showed lower level of Gag specific CTL and antibody response than without pre-existing adenovirus type 5 immunity. The exchange of fiber can partially reduce inhibition of the pre-existing immunity against the parent adenovirus.All together, it is evident that rAd5/F35 vector can induce strong HIV-specific immune responses in BALB/c mice and efficiently transfer human dendritic cells ex vivo. Based on these observations, rAd5/F35 vectors can be used as a valuable tool for the studies of immunotherapy and vaccination.