Expression of complete SIV p27 Gag and HIV gp120 engineered outer domains targeted by broadly neutralizing antibodies in live rubella vectors

Abstract

Infection with HIV or SIV often elicits a potent immune response to viral antigens. This includes T cells and antibodies specific for Gag and Env antigens. In contrast, when given as a vaccine, the same antigens have been weak immunogens, unable to elicit antibodies with comparable titer, durability, or neutralizing activity. We have used the live attenuated rubella vaccine strain RA27/3 as a viral vector to express HIV and SIV antigens. By mimicking an HIV infection, these vectors could elicit stronger and more durable immunity to HIV antigens. The vectors are based on the licensed rubella vaccine strain, which has demonstrated safety and potency in millions of children. One or two doses protect for life against rubella infection. The question was whether rubella vectors could similarly enhance the immunogenicity of a foreign vaccine insert. We have previously reported that rubella vectors can express small protein antigens in vitro and in vivo, where they elicit a strong immune response to the vaccine insert. The vectors have now expressed larger vaccine inserts that include epitope-rich fragments of the Gag matrix and capsid proteins (aa 41-211) or the complete p27 capsid protein with p2 (aa 136-381). These vectors have elicited a robust and durable immune response to Gag in rhesus macaques. This size range also encompasses the engineered outer domain (eOD) of HIV envelope gp120 (172 amino acids). The rubella/eOD-GT6 and GT8 vectors stably expressed glycoproteins that bind germline precursors and mature forms of VRC01-class broadly neutralizing antibodies. These vectors potentially could be used as part of a sequential immunization strategy to initiate the production of broadly neutralizing antibodies.

Immunotherapy with DNA vaccine and live attenuated rubella/SIV gag vectors plus early ART can prevent SIVmac251 viral rebound in acutely infected rhesus macaques

“…This was followed by two doses of live rubella vectors expressing SIV gag, at weeks 15 and 22 post infection. The rubella/gag vectors were described previously [15,16]. One rubella vector expressed four predominant Gag T cell epitopes in tandem and was called BC-sGag2.…”

“…The rubella/gag vaccine consisted of two vectors based on the live attenuated rubella vaccine strain RA27/3, with gag inserts at the structural insertion site. One vector expressed SIV gag p27+p2 [16]. The other vector, called BC-sGag2, expressed four major gag T cell epitopes in tandem [15], including GY9, TE15, CM9 and ME11.…”

“…ART effect on rubella replication and protein expression was determined by measuring expression of rubella C and E1 structural proteins in Western blot of infected whole cell lysates treated with various concentrations of antiretroviral drugs. The Western blot procedure has been previously described [16]. Digital images were quantified using GeneSys (v.1.6.1.0) and GeneTools (v.4.3.8.0) software (Syngene/Synoptics Ltd., England).…”

“…Immunotherapy consisted of a DNA vaccine expressing SIV gag [13,14] followed by a boost with live attenuated rubella vectors expressing SIV gag [15,16]. The rubella vectors are based on the licensed vaccine strain RA27/3 [17], which has demonstrated its safety and potency in millions of children as part of the MMR vaccine.…”

“…It is even recommended for those HIV-positive children who can respond to it [18]. The vectors stably expressed SIV Gag antigens as small as a few T cell epitopes and as large as SIV p27 Gag protein [16]. The vectors grow well in rhesus macaques, and they are potent immunogens when used in tandem with DNA vaccines [19].…”