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

Abstract

HIV sequence diversity and the propensity of eliciting immunodominant responses targeting variable regions of the HIV proteome are hurdles in the development of an effective AIDS vaccine. An HIV-derived conserved element (CE) p24gag plasmid DNA (pDNA) vaccine is able to redirect immunodominant responses to otherwise subdominant and often more vulnerable viral targets. By homology to the HIV immunogen, seven CE were identified in SIV p27Gag. Analysis of 31 rhesus macaques vaccinated with full-length SIV gag pDNA showed inefficient induction (58% response rate) of cellular responses targeting these CE. In contrast, all 14 macaques immunized with SIV p27CE pDNA developed robust T cell responses recognizing CE. Vaccination with p27CE pDNA was also critical for the efficient induction and increased the frequency of Ag-specific T cells with cytotoxic potential (granzyme B+ CD107a+) targeting subdominant CE epitopes, compared with the responses elicited by the p57gag pDNA vaccine. Following p27CE pDNA priming, two booster regimens, gag pDNA or codelivery of p27CE+gag pDNA, significantly increased the levels of CE-specific T cells. However, the CE+gag pDNA booster vaccination elicited significantly broader CE epitope recognition, and thus, a more profound alteration of the immunodominance hierarchy. Vaccination with HIV molecules showed that CE+gag pDNA booster regimen further expanded the breadth of HIV CE responses. Hence, SIV/HIV vaccine regimens comprising CE pDNA prime and CE+gag pDNA booster vaccination significantly increased cytotoxic T cell responses to subdominant highly conserved Gag epitopes and maximized response breadth.

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

“…After priming, the IM delivered vaccine induced robust Gag CE-specific (Figure 2A, top left panel) and Env CE-specific (Figure 2C, top left panel) T cell responses in all animals, as we previously reported, 76 , 77 reaching up to 1.2% of circulating total Gag and Env CE T lymphocytes in macaque T152. The ID delivered vaccine induced much lower CE-specific T cell responses and were detected in only 5 of the 8 animals (Figure 2A and 2C, top middle panels).…”

“…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.…”

“…Each of two p27CE proteins comprises 7 conserved elements CE that are 12–24 AA in length, differ by 6 AA (indicated by *) and are collinearly arranged, separated via 2–4 AA linkers. 76 The HIV Env CE DNA vaccine is a mixture of two plasmids expressing the Env CE1 and Env CE2 proteins. Each of two Env CE proteins comprises 12 CE distributed through gp120 and gp41, spanning 11–43 AA in length, differing by 24 AA (indicated by *), are collinearly arranged and separated via 3 AA linkers.…”

“…19 , 53 , 74 , 75 By positional analogy and sequence homology to the HIV p24CE, an SIV p27 Gag (p27CE) derived molecule was generated. 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.…”

“…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.…”