Altering an Artificial Gagpolnef Polyprotein and Mode of ENV Co-Administration Affects the Immunogenicity of a Clade C HIV DNA Vaccine

Abstract

HIV-1 candidate vaccines expressing an artificial polyprotein comprising Gag, Pol and Nef (GPN) and a secreted envelope protein (Env) were shown in recent Phase I/II clinical trials to induce high levels of polyfunctional T cell responses; however, Env-specific responses clearly exceeded those against Gag. Here, we assess the impact of the GPN immunogen design and variations in the formulation and vaccination regimen of a combined GPN/Env DNA vaccine on the T cell responses against the various HIV proteins. Subtle modifications were introduced into the GPN gene to increase Gag expression, modify the expression ratio of Gag to PolNef and support budding of virus-like particles. I.m. administration of the various DNA constructs into BALB/c mice resulted in an up to 10-fold increase in Gag- and Pol-specific IFNγ + CD8 + T cells compared to GPN. Co-administering Env with Gag or GPN derivatives largely abrogated Gag-specific responses. Alterations in the molar ratio of the DNA vaccines and spatially or temporally separated administration induced more balanced T cell responses. Whereas forced co-expression of Gag and Env from one plasmid induced predominantly Env-specific T cells responses, deletion of the only H-2 d T cell epitope in Env allowed increased levels of Gag-specific T cells, suggesting competition at an epitope level. Our data demonstrate that the biochemical properties of an artificial polyprotein clearly influence the levels of antigen-specific T cells, and variations in formulation and schedule can overcome competition for the induction of these responses. These results are guiding the design of ongoing pre-clinical and clinical trials.

Potential To Streamline Heterologous DNA Prime and NYVAC/Protein Boost HIV Vaccine Regimens in Rhesus Macaques by Employing Improved Antigens

“…Most likely, this is a consequence of the improved antigen configuration, i.e., splitting of Gag, PolNef, and gp140 in the context of the DNA vaccine or using Gag FS PolNef in the context of NYVAC. This outcome was predicted by previous mouse immunogenicity studies of our redesigned antigens and is likely related to the increased expression levels, especially of Gag (27,32). Similar observations were made in cynomolgus monkeys and humans after splitting of a differently designed Gag-Pol-Nef fusion protein into three parts which were subsequently delivered as a mixture of three plasmids rather than one (16,28,29).…”

“…Moreover, a gp140 form was used instead of gp120 to more closely resemble the native trimeric envelope structure (26) and was included in a third DNA vector. Immunogenicity analyses in mice clearly showed superiority of this three-plasmid configuration over the parental EuroVacc vaccines regarding both the magnitude of antigen-specific T cells and the balance toward the different antigens (27). Improved responses after splitting of a different Gag-Pol-Nef antigen into separate parts were also observed in humans in clinical phase I trials (16,28).…”

Evaluation of humoral, mucosal, and cellular immune responses following co-immunization of HIV-1 Gag and Env proteins expressed by Newcastle disease virus

“…The gp160 mediated suppression of CD4C and CD8C T cell responses against Gag could be due to various reasons as reported in various findings reported previously (1) competition of expression resulting in immunodominance of Env over Gag; 36 (2) suppression of expression via type1 IFN; 37 (3) Env-mediated suppression of dendritic cell activation and maturation; 38 and (4) epitope competition for H-2 d MHC class I presentation especially in case of CD8C T cell suppression. 39,40 Further, inclusion of rLasota/optGag with rLaSota/gp160, rLaSota/gp140L and rLaSota/gp140S enhanced Env-specific IFN-g-producing CD4C and CD8C T cells compared to the Env expressing rNDVs inoculated alone in our previous study. 32 These findings are unexpected and this phenomenon might be explained by higher level of activation due to increased cytokine production and proliferation in the doubly immunized mice.…”

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

“…The HIV vaccine was included in this study to evaluate its immunogenicity and to interrogate possible interference of the two types of CE DNA vaccine regimens, since we and others previously reported potent inhibition of Gag T cell responses by FL Env vaccines. 78–81 The 31 Indian rhesus macaques enrolled in this study are described in Table 1. Two groups of animals received the same CE DNA vaccine but differed in the delivery routes (Figure 1B), intramuscular (IM) followed by electroporation (EP) using CELLECTRA® 5P (CE IM group) versus intradermal (ID) followed by EP using CELLECTRA®3P (CE ID group).…”

“…To evaluate the potential interference between Env and Gag epitopes that has been reported previously in mice, macaques and humans, 78–81 , 87 macaques immunized with the SIV Gag CE and FL gag DNA also received the HIV Env CE and FL env DNA vaccine. Importantly, and in contrast to previous observations using only full-length immunogens, we did not find any interference or negative effects from the Env CE DNA immunogen on the cellular responses targeting Gag CE.…”