Altered Response Hierarchy and Increased T-Cell Breadth upon HIV-1 Conserved Element DNA Vaccination in Macaques

Abstract

HIV sequence diversity and potential decoy epitopes are hurdles in the development of an effective AIDS vaccine. A DNA vaccine candidate comprising of highly conserved p24gag elements (CE) induced robust immunity in all 10 vaccinated macaques, whereas full-length gag DNA vaccination elicited responses to these conserved elements in only 5 of 11 animals, targeting fewer CE per animal. Importantly, boosting CE-primed macaques with DNA expressing full-length p55gag increased both magnitude of CE responses and breadth of Gag immunity, demonstrating alteration of the hierarchy of epitope recognition in the presence of pre-existing CE-specific responses. Inclusion of a conserved element immunogen provides a novel and effective strategy to broaden responses against highly diverse pathogens by avoiding decoy epitopes, while focusing responses to critical viral elements for which few escape pathways exist.

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.…”

“…This vaccine strategy provides a novel approach to shift the immunodominance hierarchy and to induce robust immune responses to subdominant epitopes. 21 …”