Immunogenicities of Env glycoproteins from circulating HIV-1 isolates in China focusing on the strategy of "DNA prime plus protein boost"

Department of HIV/AIDS Research, State Key Laboratory of Pathogen and Biosecurity, Institute of Microbiology and Epidemiology, Academy of Military Medical Sciences, Beijing 100071, China.
Chinese medical journal (Impact Factor: 1.05). 10/2009; 122(19):2339-45. DOI: 10.3760/cma.j.issn.0366-6999.2009.19.028
Source: PubMed


The adenovirus-based HIV-1 vaccine developed by Merck Company suffered from an unexpected failure in September 2007. This generated a big shift in the strategy of HIV vaccine development with renewed focus on the induction of neutralizing antibodies. A major challenge in developing an HIV-1 vaccine is to identify immunogens and adopt delivery methods that can elicit broadly neutralizing antibodies against primary isolates of different genetic subtypes.
Most circulating HIV-1 isolates in China are composed of clades Thai-B, CRF_BC and CRF01_AE. In order to construct DNA vaccines against these 3 HIV-1 subtypes, DNA vaccines carrying the gp120 regions from HIV-1 isolates of GX48(AE), GX79(AE), NX22(BC), GS22(BC), HN24(Thai-B) were constructed. Expression of gp120 from these DNA vaccines was detected by Western blotting in transiently transfected 293T cells. Pilot immunizations of New Zealand white rabbits were performed using the strategy of "DNA prime plus protein boost" and the neutralizing antibody response was detected in a Tzm-bl cell based assay against different HIV-1 strains.
Response of gp120-specific antibody was relatively low after DNA primes (mean titer = 10(4.72)); however, the titer of gp120-specific antibody went up with 2 protein boosts (mean titer = 10(6.81)). Above all, neutralizing antibody (Nab) titers induced by this combined approach were much better than those elicited by DNA or protein used alone (P < 0.01). Neutralizing activities of immunized rabbit sera against several pseudoviruses and laboratorial strains were evaluated, most rabbit sera primed with monovalent vaccine were capable of neutralizing only 1 of 5 viruses, however, sera primed with the polyvalent DNA vaccines were able to neutralize at least 2 of 5 viruses.
Polyvalent DNA prime plus protein boost is an effective immunization strategy to broaden the neutralization breadth and further research should be performed on the basis of this pilot study.

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    • "Moreover, we compared and contrasted the humoral immune responses elicited following DNA prime and protein boost immunisation regimens at different target mucosal surfaces. While a number of DNA prime protein boost vaccination strategies have been published using a range of HIV-1 antigen constructs, the majority involve the parenteral delivery of the DNA prime or viral vector component [24]–[27]. To our knowledge, few studies have directly compared the intranasal, vaginal and sublingual routes for their abilities to be immunologically primed by a gp140 expressing plasmid. "
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    • "A DNA vaccine (HN24) expressing CNHN24 gp120 was constructed and its expression by this DNA vaccine vector was confirmed by Western blot using supernatant that was transiently expressed in 293T cells (Fig 5-A). Rabbits were immunized with either a DNA prime-protein boost approach or protein immunization alone after receiving the mock immunization of empty DNA vector without HIV-1 Env antigen, as reported (Wang et al., 2009). Animal studies were conducted with the review and approval by the University of Massachusetts Medical School (UMMS) Institutional Animal Care and Use Committee (IACUC) according to accepted international animal welfare regulations. "
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