Membrane-bound SIV envelope trimers are immunogenic in ferrets after intranasal vaccination with a replication-competent canine distemper virus vector

Abstract

We are investigating canine distemper virus (CDV) as a vaccine vector for the delivery of HIV envelope (Env) that closely resembles the native trimeric spike. We selected CDV because it will promote vaccine delivery to lymphoid tissues, and because human exposure is infrequent, reducing potential effects of pre-existing immunity. Using SIV Env as a model, we tested a number of vector and gene insert designs. Vectors containing a gene inserted between the CDV H and L genes, which encoded Env lacking most of its cytoplasmic tail, propagated efficiently in Vero cells, expressed the immunogen on the cell surface, and incorporated the SIV glycoprotein into progeny virus particles. When ferrets were vaccinated intranasally, there were no signs of distress, vector replication was observed in the gut-associated lymphoid tissues, and the animals produced anti-SIV Env antibodies. These data show that live CDV-SIV Env vectors can safely induce anti-Env immune responses following intranasal vaccination.

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

“…Recombinant CDV is being investigated as a delivery vector for HIV vaccines because it has the potential to specifically deliver vaccine immunogens to lymphoid tissues that are susceptible to HIV infection Zhang et al, 2013). Previous studies showed that virulent CDV replicated in the ferret gut-associated lymphoid tissues (GALT) (Pillet et al, 2009;von Messling et al, 2006), and this work extends those results by showing that a recombinant vector based on an attenuated vaccine strain also targeted the GALT.…”

“…CDV was propagated in Vero cells and infectious virus was quantified by plaque assay. Recombinant CDV-SIVgag1 was constructed using procedures described in detail elsewhere (Zhang et al, 2013). Briefly, virus from a live attenuated vaccine based on the Onderstepoort strain was serially passaged in Vero cells after which a clonal isolate was derived by multiple rounds of plaque purification.…”

“…To rescue rCDV-SIVgag1, 293T cells were cotransfected with the CDV-SIVgag1 genomic plasmid DNA and 7 support plasmids (Witko et al, 2006) that express CDV structural proteins (N, P, M, F, H and L) and T7 DNA-dependent RNA polymerase using calcium-phosphate reagents obtained from a commercial supplier (Clontech, Mountain View, CA, USA). Structural protein expression was controlled by the human CMV promoter in pCI-Neo (Promega, Madison, WI, USA), which had been modified by deleting the T7 RNA polymerase promoter (Zhang et al, 2013). Clonal virus isolates then were derived by plaque purification and subsequent expansion on Vero cell monolayers.…”

“…Although MeV is an attractive vector candidate because of its long track record of use in humans, pre-existing neutralizing immunity against MeV might limit its use. Since recombinant CDV (rCDV) can express foreign proteins (Ludlow et al, 2012;Parks et al, 2002;von Messling et al, 2004;Wang et al, 2012), attenuated CDV vectors encoding SIV immunogens have been developed to evaluate whether they might provide a safe alternative to MeV for advancement of HIV vaccine candidates that are less subject to pre-existing anti-MeV antibodies (Zhang et al, 2013).…”

“…These assays enabled rapid, reliable, and sensitive detection of CDV N and SIV gag and were used to compile in vivo data on replication, distribution, and genetic stability of an early prototype rCDV-SIV-Gag vector. Importantly, by using the gRNA duplex assay to monitor the relative quantities of CDV N and SIV gag sequences in vector genomes over the course of infection, gag insert instability was detected in the vector prototype, providing valuable information for guiding vector and gene insert improvements that stabilized foreign genes in subsequent vaccine designs (Zhang et al, 2013).…”