Assessing TMV as an immunogenic particle : the expression of HIV-1 subtype C V3 loop neutralizing antibody epitopes on the surface of TMV virions

In an attempt to establish a plant-based Human immunodeficiency virus-1 (HIV-1) subtype C neutralizing antibody stimulating vaccine, a Tobacco mosaic virus (TMV) derived vector was used to express recognized HIV neutralizing antibody epitopes. These epitopes were expressed on the surface of the TMV coat protein, which served as an ideal means of antigen display. This model antigen display system was capable of assembling into multivalent, highly repetitive structures thereby displaying many copies of the attached epitope in the assembled virion. Three TMV-based vectors were acquired, which were essentially identical, differing only in the position at which they could accommodate a foreign protein fusion. These vectors allowed the display of a foreign peptide at the N-terminus, Cterminus or 60S-loop regions of the TMV coat protein. all of which protrude on the surface of the assembled virion. The HIV V3 loop is recognized as the principal neutralizing domain, and was the neutralizing epitopes displayed by the vectors. The epitope sequences used were derived from a cohort of infected individuals in Durban, South Africa, who displayed broad cross-neutralizing V3-specific activity towards heterologous viral strains. The recombinant viral vectors were shown to efficiently infect the host Nicotiana benthamiana plants and assemble into multivalent recombinant virion structures as observed by transmission electron microscopy. However, the level of coat protein expression was significantly dependent on the position of the coat protein fusion as either the levels of V3 epitope expressed or TMV coat protein was found to vary between the different vector types, confirmed by means of immunoblotting and enzyme-linked immunosorbent assays. Immunogenicity analysis using a guinea pig model was used to assess the ability of the recombinant vectors to firstly establish a V3-specific immune response, and secondly to stimulate a virus-specific neutralization antibody response. As a result of time constraints only the C-terminal coat protein fusions were assessed in the guinea pig model. Inoculated guinea pigs displayed distinct and gradually increasing V3-specific immune responses after 2 boosts. Serum samples that displayed the strongest V3 peptide responses were then analyzed for their ability to neutralize HIV infection in HIV pseudovirion neutralization assays. Results for selected serum samples showed no HIV neutralizing activity above what could be recognized as background activity. Thus the candidate vaccine, although establishing a path for the assembly of a multivalent vaccine, failed in its attempt to stimulate a neutralizing antibody response. This study has nevertheless paved a direct path to the development of variations of this type of vaccine possibly using different and perhaps more effective epitopes for candidate vaccine purposes.

Grantor dc:publisher.institution

Department of Molecular and Cell Biology

Year dc:date.issued

2005

Author dc:creator

• Valley-Omar, Ziyaad

Advisors dc:contributor.advisor

• Rybicki, Ed
• Jaffray, Ann

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/4344

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/4344