Animal Experimental Studies On Sequential And Repeated Immunization With Multiple Vectors Based AIDS Vaccines

Acquired immunodeficiency syndrome?AIDS?,caused by human immunodeficiency virus?HIV?infection,has been prevalent worldwide for more than 30 years.There have been no safe and effective HIV vaccines available till now.In our previous study,the strategy of sequential and repeated immunization with multiple vectors based AIDS vaccines were proposed.The results of animal experiments showed that this strategy can induce high and long-lasting HIV specific immune response.Based on this immunization strategy,this study is designed to continue the work on sequential and repeated immunization with multiple HIV/SIV vaccines in mice and monkeys.The monkey immunodeficiency virus?SIV?is similar to HIV and can infect non-human primates to lead to Simian Acquired Immunodeficiency Syndrome?SAIDS?,it is often used as an alternative model for HIV studies.We first performed an immunogenicity experiment in mice with three vectors based SIV vaccines expressing SIV-gag/env which provided a basis for subsequent rhesus monkey experiments.Then we evaluated the preventive and therapeutic effect of the sequential and repeated immunization strategies in SIV-infected rhesus model with four SIVgag vaccines,including DNA vaccine,rAd5-SIVgag,rMVA-SIVgag and rAd5F35-SIVgag.Fifteen Chinese rhesus macaques were divided into prophylactic immunization group,therapeutic immunization group and control group.The macaques were immunized with the above four vaccines or PBS according to established procedure and challenged by 500 TCID50 SIVmac239 through intravenous route.The viral load,immune cells counts and SIV Gag-specific cellular responses in tested macaques were detected.The results showed that potent and long-lasting SIV Gag specific immune responses were induced by sequential and repeated immunization with four vector-based SIV vaccines.It also indicated that SIV Gag vaccine-induced specific T cell responses were associated with reduced plasma viral load.The protective immune responses were induced in 80%?4/5?of rhesus in preventive group after challenged with SIVmac239,the SIV infection was not blocked,but the peak viral load was significantly lower than that in the control group.It suggested that the viral load in acute phase was reduced by the protective effect which was induced by multiple vector vaccines.The specific immune responses in therapeutic group showed significant individual difference.Protective SIV Gag specific responses were induced in 40%?2/5?of rhesus in therapeutic group and the viral load was reducd by 2 log 10 copies/ml,was higher than the level of decline that in control group.It indicated that multiple vector vaccines have the ability to repair or reconstruct immune function which was damaged by SIV infection.The second roud of sequential immunization with four HIV vaccines was performed on rhesus monkeys which received the first round immunization in our previous study.The rAd5 vaccine was selected as the firstly immunized vaccine,and the immune responses in the four-vaccine group peaked very soon after the first inoculation and maintained the level above 850 SFCs/106 PMBCs for 52 weeks.Again the immune responses reached peak level at two weeks post the second inoculation and maintained the level above 500 SFCs/106 PMBCs for 69 weeks.The Results showed that sequential and repeated immunization with four vector-based HIV vaccines induced broad and long-lasting high level of specific immune responses.It might be a promising scheme for therapeutic HIV-1 vaccine.A novel method for HIV vaccine efficacy evaluating was estimated and the experimental conditions including the quantity of virus and incubation time were optimized.Then the novel method was applied to determine whether or not recombinant adenovirus type 5 AIDS therapeutic vaccines expressing Gag antigen?Ad5-HIVgag?could stimulate HIV-specific T cells responses.A total of 24 PBMCs samples from HIV-1 infected donors were assayed via the novel method.The level of IFN-y secreting lymphocytes stimulated with Ad5-HIVgag was in accordance with that of Gag peptide pool stimulated and significantly greater than Ad5-null stimulated which low level of IFN-y secreting lymphocytes were detected.It indicated that HIV-specific cellular immune responses were induced by Ad5-HIVgag vaccine.Comparison with other methods the in vitro stimulation method is safe,time saving and the result is more intuitive.At the same time,DNA vaccines?pVR-HIVAEgagi and pVR-HIVBCgagi?and recombinant MVA vaccines?rMVA-HIVAEgagi and rMVA-HIVBCgagi?expressing the gag gene of HIV-1 subtype CRF₀1AE and CRF₀7/08 were constructed successfully.The results of Western blot assay indicated that all the generated vaccines could express HIV Gag antigen efficiently in cells.