Plant-based strategies aimed at expressing HIV antigens and neutralizing antibodies at high levels. Nef as a case study

Abstract

The first evidence that plants represent a valid, safe and cost-effective alternative to traditional expression systems for large-scale production of antigens and antibodies was described more than 10 years ago. Since then, considerable improvements have been made to increase the yield of plant-produced proteins. These include the use of signal sequences to target proteins to different cellular compartments, plastid transformation to achieve high transgene dosage, codon usage optimization to boost gene expression, and protein fusions to improve recombinant protein stability and accumulation. Thus, several HIV/SIV antigens and neutralizing anti-HIV antibodies have recently been successfully expressed in plants by stable nuclear or plastid transformation, and by transient expression systems based on plant virus vectors or Agrobacterium-mediated infection. The current article gives an overview of plant expressed HIV antigens and antibodies and provides an account of the use of different strategies aimed at increasing the expression of the accessory multifunctional HIV-1 Nef protein in transgenic plants.

Boosting riboswitch efficiency by RNA amplification

“…For this purpose, we chose the Nef protein of HIV-1 ( 24 ; Figures 3 and 4A ). Nef is a non-structural HIV gene product regarded as a promising target for the development of a multi-component AIDS vaccine able to induce durable antiviral immunity ( 41 , 42 ). Previous attempts to express it from the chloroplast genome led to mutant plants that displayed a pigment-deficient phenotype and hardly grew photoautotrophically ( 24 ; Figure 4A ), presumably due to the propensity of the protein to associate with membranes and the resulting interference with thylakoid biogenesis.…”

Passive Immunization

“…High concentrations of neutralizing mAbs show promise for microbicide formulations but they are prohibitively expensive to produce in the amounts required. Consequently, the anti-HIV-neutralizing antibodies 2F5 and 2G12 have been expressed at high levels in plants and excellent results have been obtained in terms of production and neutralizing activity (Marusic et al, 2009;Rademacher et al, 2008;Ramessar et al, 2008).…”

High-level expression of the HIV entry inhibitor griffithsin from the plastid genome and retention of biological activity in dried tobacco leaves

“…Development of griffithsin as an affordable anti-HIV microbicide will require inexpensive mass production of the protein, ideally from a renewable source and not requiring expensive fermentation procedures. Plants represent a particularly cheap, readily scalable and safe production platform for biopharmaceuticals (Ma et al 2005 ; Daniell et al 2009 ; Rybicki 2010 ; Marusic et al 2009 ; Bock 2014 , 2015 ; Wong-Arce et al 2017 ). Therefore, extensive efforts have been made to develop technologies that enable high-level expression of recombinant proteins in plants, including antibodies, antigens for subunit vaccines and microbicides.…”