HIV-1 p24gag Derived Conserved Element DNA Vaccine Increases the Breadth of Immune Response in Mice

Abstract

Viral diversity is considered a major impediment to the development of an effective HIV-1 vaccine. Despite this diversity, certain protein segments are nearly invariant across the known HIV-1 Group M sequences. We developed immunogens based on the highly conserved elements from the p24gag region according to two principles: the immunogen must (i) include strictly conserved elements of the virus that cannot mutate readily, and (ii) exclude both HIV regions capable of mutating without limiting virus viability, and also immunodominant epitopes located in variable regions. We engineered two HIV-1 p24gag DNA immunogens that express 7 highly Conserved Elements (CE) of 12–24 amino acids in length and differ by only 1 amino acid in each CE (‘toggle site’), together covering >99% of the HIV-1 Group M sequences. Altering intracellular trafficking of the immunogens changed protein localization, stability, and also the nature of elicited immune responses. Immunization of C57BL/6 mice with p55gag DNA induced poor, CD4+ mediated cellular responses, to only 2 of the 7 CE; in contrast, vaccination with p24CE DNA induced cross-clade reactive, robust T cell responses to 4 of the 7 CE. The responses were multifunctional and composed of both CD4+ and CD8+ T cells with mature cytotoxic phenotype. These findings provide a method to increase immune response to universally conserved Gag epitopes, using the p24CE immunogen. p24CE DNA vaccination induced humoral immune responses similar in magnitude to those induced by p55gag, which recognize the virus encoded p24gag protein. The inclusion of DNA immunogens composed of conserved elements is a promising vaccine strategy to induce broader immunity by CD4+ and CD8+ T cells to additional regions of Gag compared to vaccination with p55gag DNA, achieving maximal cross-clade reactive cellular and humoral responses.

Gag and env conserved element CE DNA vaccines elicit broad cytotoxic T cell responses targeting subdominant epitopes of HIV and SIV Able to recognize virus-infected cells in macaques

“…In agreement with previous results, 20 , 21 , 76 , 77 priming with CE DNA was more efficient at inducing CE-specific T cell responses in the blood than immunization with the FL vaccine, for both Gag and Env. Gag CE-specific responses were also found in rectal mucosa lymphocytes (Env responses were not evaluated in the rectal mucosa due to sample limitations).…”

“…We previously reported the generation of two DNA vaccines targeting the highly conserved sequences in HIV Gag 20 , 21 , 73 (and its homolog SIV p27CE) 76 and in HIV Env (Env CE) 77 ( Figure 1 A) and demonstrated induction of robust CE-specific T cell responses in cohorts of vaccinated macaques. The CE selection included analysis of MHC binding prediction to address immunogenicity in humans, and we found that epitopes from all MHC class I known supertypes were represented in Gag CE.…”

“…76 Using a similar approach based on sequence conservation, association with virologic control, and CTL escape resulting in a loss in viral fitness, we generated HIV Env CE molecules 77 comprising 12 highly conserved regions of Env, spanning 11 to 43 AA in length. In proof-of-concept studies in mice 20 and outbred macaques, 21 , 73 , 76 we demonstrated that immunization with HIV p24CE DNA and SIV p27CE elicited robust cellular and humoral immune responses against CE and that HIV Env CE DNA vaccine regimen induced robust T cell responses yet low antibody responses in macaques, 77 whereas induction of CE-specific responses was poor with DNA vaccines expressing only full-length (FL) Gag and Env. 21 , 76 , 77 Importantly, however, priming with CE DNA and boosting with CE+FL gag or env DNA is a vaccine regimen that maximizes the magnitude of both cellular 21 , 76 , 77 and humoral 73 , 77 immune responses in macaques.…”

“…20 , 21 , 73 Seven CE, spanning 12 to 24 AA in length, were selected based on their stringent conservation across all known HIV sequences, broad HLA-coverage, and association with HIV control. 19 , 53 , 74 , 75 By positional analogy and sequence homology to the HIV p24CE, an SIV p27 Gag (p27CE) derived molecule was generated.…”

DNA Prime-Boost Vaccine Regimen To Increase Breadth, Magnitude, and Cytotoxicity of the Cellular Immune Responses to Subdominant Gag Epitopes of Simian Immunodeficiency Virus and HIV

“…To address the problem of viral variability, many approaches have been tested including strategies that use consensus, center-of-tree or ancestral sequences, multiple strains or mosaic immunogens, immunogens consisting of known epitopes, and chimeric molecules expressing a selection of the most conserved epitopes from different clades of HIV . In our approach (20)(21)(22), we designed a plasmid DNA (pDNA) vaccine to focus the immune response to conserved elements (CE) of the HIV-1 proteome based on stringent conservation, broad HLA-coverage, and association with HIV control (19,(23)(24)(25). The p24…”