Study On Immune Strategy Of Three Vector-based Therapeautic Vaccines Expressing HIV-1and SIV Genes

Academician Yi Zeng and his colleagues from National Institute for ViralDisease Prevention and Control, China CDC focus on the study of therapeutic AIDSvaccines. Previous studies indicated that the strategy of sequential and repeatedimmunization with vector-based AIDS vaccines could induce high level andlong-lasting HIV-specific cellular immune responses in mice and rhesus macaques.And now DNA and rMVA vaccines are being tested in phaseâ… clinical trials inHIV-infected individuals. Application of rAd5as a therapeutic vaccine for Phaseâ… clinical trial has been submitted. In this study the strategy of combined immunizationwith above three vector-based AIDS vaccines were further investigated to provide theexperimental basis for application of clinical trial. On one hand, different immunedoses, orders of vaccines and intrervals between administration of the three vaccineswere compared to choose a suitable immunization strategy; Meanwhile, full-lengthenv genes were cloned from PBMCs of CRF01_AE HIV-1infected patients,vector-based vaccines expressing the consensus env gene were constructed in order toinduce more broadly immune responses by combination of different subtype-specificvaccines.On the other hand, DNA, rMVA and rAd5vaccines expressing SIV gag andenv genes were constructed. The immune responses in mice immunized with thesethree vaccines by the optimized strategy were observed, which laid the foundation forfurther evaluating the therapeutic effect of this strategy in SIV infected monkeys.In mice immunized with DNA, rMVA or rAd5expressing HIV-1genes alone, thecellular immune responses peaked at2weeks post immunization. Cellular immuneresponses induced by DNA （immunized once or twice） or rMVA vaccines （threedifferent doses） were weak, and there is no significant difference between thesegroups. Three different doses of rAd5vaccine could induce high level of specificcell-mediated immunity. So middle-dose was chosen for rMVA and rAd5vaccine, andDNA vaccine was immunized twice as a prime vaccine. When mice were immunizedwith two vaccines, DNA prime/rAd5boost induced higher level of responses than thatof DNA prime/rMVA boost. And the group with4-week interval is better than that of3-week interval in DNA prime/rAd5boost strategy, while there is no differencebetween the groups with4-week and3-week intervals in DNA prime/rMVA booststrategy. The immune responses in all test groups declined with time. When threevaccines were administered in combination, the mice were primed with DNA vaccinetwice at2-week interval, then boosted with rMVA or rAd5at4-week interval, at lastboosted with rAd5or rMVA at6-week or4-week interval. The results showed thathigh level of persistent Gag-specific immune responses was elicited in all test groups after the last immunization. They still maintained high level even at12weeks post lastvaccination. In summary, the suitable immune strategy is as follow: primed with DNAvaccine twice at2-week interval, boosted with rAd5at4-week interval, boosted withrMVA at6-week interval.The above DNA and rMVA vaccines encoded subtype B/C HIV-1genes andrAd5vaccine expressed subtype B′HIV-1gene. In recent years, HIV-1CRF01_AEspread rapidly in China and has become dominant strains. So it is necessary to designvaccines based on CRF01_AE strains. It may induce more broadly immune responsesby combining HIV vaccines targeting different subtypes. In this study, env genes werecloned from HIV-1CRF01_AE infected patients. The codons of the consensusCRF01_AE env sequence were modified according to mammalian codon usage andplasmid DNA vaccine expressing this consensus CRF01_AE Env protein wasconstructed. It could induce specific cellular immune responses in mice. The geneticproperties of the cloned env genes were also analyzed. The V1, V2, V4, and V5regions exhibited substantial length variations, whereas the V3regions were relativelyconserved. There was no drastic alteration in the numbers of N-linked glycosylationsites in V3, C3, C4, and V5region of gp120. A large majority of gp41glycosylationsites were located in the ectodomain outside the transmembrane. Pseudoviruses basedon these env genes were packaged, and8strains with high titers were obtained. All the8strains used co-receptor CCR5. They were sensitive to neutralization by VRC₀1,PG9, PG16and NIH45-46, but insensitive to2G12. And the pseudoviruses were moresensitive to neutralization by plasma from subtype CRF01_AE and CRF07/08_BCHIV-1infected donors compared with subtype B’.At the same time in order to evaluate the therapeutic effect of this strategy inmonkey models，plasmid DNA, recombinant MVA and Ad5vaccines expressing SIVgag and env were constructed successfully. All the generated vaccines could expressSIV antigen efficiently and induce strong Gag/Env-specific cellular immuneresponses. It laid the foundation for evaluating the therapeutic effect of combinedvaccines in SIV infected macaque models.