A Novel, Live-Attenuated Vesicular Stomatitis Virus Vector Displaying Conformationally Intact, Functional HIV-1 Envelope Trimers That Elicits Potent Cellular and Humoral Responses in Mice

Abstract

Though vaccination with live-attenuated SIV provides the greatest protection from progressive disease caused by SIV challenge in rhesus macaques, attenuated HIV presents safety concerns as a vaccine; therefore, live viral vectors carrying HIV immunogens must be considered. We have designed a replication-competent vesicular stomatitis virus (VSV) displaying immunogenic HIV-1 Env trimers and attenuating quantities of the native surface glycoprotein (G). The clade B Env immunogen is an Env-VSV G hybrid (EnvG) in which the transmembrane and cytoplasmic tail regions are derived from G. Relocation of the G gene to the 5′terminus of the genome and insertion of EnvG into the natural G position induced a ∼1 log reduction in surface G, significant growth attenuation compared to wild-type, and incorporation of abundant EnvG. Western blot analysis indicated that ∼75% of incorporated EnvG was a mature proteolytically processed form. Flow cytometry showed that surface EnvG bound various conformationally- and trimer-specific antibodies (Abs), and in-vitro growth assays on CD4+CCR5+ cells demonstrated EnvG functionality. Neither intranasal (IN) or intramuscular (IM) administration in mice induced any observable pathology and all regimens tested generated potent Env-specific ELISA titers of 104–105, with an IM VSV prime/IN VSV boost regimen eliciting the highest binding and neutralizing Ab titers. Significant quantities of Env-specific CD4+ T cells were also detected, which were augmented as much as 70-fold by priming with IM electroporated plasmids encoding EnvG and IL-12. These data suggest that our novel vector can achieve balanced safety and immunogenicity and should be considered as an HIV vaccine platform.

Vaccine-induced immune responses against both Gag and Env improve control of simian immunodeficiency virus replication in rectally challenged rhesus macaques

“…Six rVSV vectors expressing SIVmac239 inserts were used in this experiment. Five were based on a VSV Indiana vector in which the G gene was repositioned to the 5’ terminus of the genome [ 78 ]. By placing the G gene in the most distal gene position relative to the promoter (6 th position), its expression was modestly downregulated.…”

“…The five VSV constructs based on this vector included: 1) rVSV-EnvΔct 4 -G nj6 encoded SIV Env protein with a cytoplasmic tail that was truncated by 159 aa at its carboxyl terminus. This modification increased Env surface expression and genetic stability of rVSV-Env4-G nj6 -infected cells in vivo [ 78 , 79 ]. The envΔct 4 gene was inserted into the 4 th position relative to the 3’ end of the VSV genome.…”

Bacterially expressed HIV-1 gp120 outer-domain fragment immunogens with improved stability and affinity for CD4-binding site neutralizing antibodies

“…odomain and membrane-proximal external region joined to the vesicular stomatitis virus G transmembrane and cytoplasmic domains on its surface (34). V1cycP gp120 molecule is a trimeric cyclic permutant of gp120, made by introducing new N and C termini at the V1 loop (at amino acids 144 -142) while connecting the original N and C termini with a short linker.…”

Development of a duplex real-time RT-qPCR assay to monitor genome replication, gene expression and gene insert stability during in vivo replication of a prototype live attenuated canine distemper virus vector encoding SIV gag

“…The deleted sequences included the target RT-qPCR amplicon used to detect gag in the gRNA assay, which explained reduction in signal compared to the N amplicon. This result also demonstrated that the duplex qPCR assay and gene quantity ratios could be used to effectively monitor gene insert stability in vivo, which provided valuable practical data for guiding future vector development by specifically showing that for some foreign genes alternative gene optimization approaches were needed to generate genetically stable negative-strand RNA virus vectors (Rabinovich et al, 2014).…”