HIV has been responsible for more than 32 million deaths, and infects an estimated 1.7 million people per year, mainly in Eastern and Southern Africa(1). Despite enormous effort, there is no cure and no vaccine(2). The current treatment is anti-retroviral therapy (ART), which must be taken according to a strict regimen, otherwise the patient could relapse(3). Not only is consistent access therefore essential, the treatment is very expensive (~$10,000/year)(4). The global spread of resistance to ART means more treatments are urgently needed(5, 6).
Monoclonal antibodies (mAbs) that neutralise HIV have been of widespread interest for almost 30 years(7–11). Antibodies’ most obvious advantage over ART is that they can direct antibody-dependent cellular cytotoxicity (ADCC), so that in addition to blocking infection, they can also trigger the immune system to kill infected cells. As well as this, antibodies have a longer half-life than ARTs, which means the treatment can be administered less frequently(12). mAbs are widely used in other medical areas, such as cancer and chronic disease(13–15) but are yet to make an impact in HIV for several reasons. Importantly, mAbs remain costly using conventional manufacturing technologies. Immunotherapy has been estimated to cost $96,731 per year, compared to $10,000 for ARTs(16),(4). Another important barrier is the diversity of HIV strains, and the virus’s propensity for mutation and escape, necessitating the use of cocktails of multiple mAbs, which would significantly increase the cost with every additional mAb added.
The discovery of broadly neutralising antibodies (bNAbs) in a small group of patients, so-called ‘elite controllers’(17, 18), took the prospect of using mAbs against HIV a major step closer. Several anti-HIV bNAbs are currently in clinical trials(19). Current bNAbs are significantly more potent than the early neutralising mAbs. Examples such as VRC01 and 3BNC117, which mimic CD4-gp120 binding, are able to neutralise 91% and 82% of HIV-1 virus strains respectively(20),(21). Recently, bNAb ‘N6’ with almost pan-neutralisation was discovered in an elite controller patient(22). N6 binds to more conserved regions of gp120, and tolerates changes in HIV envelope such as glycans attaching to V5, which is a common mechanism for resistance to other bNAbs(22). The vast neutralisation breadth of N6 has never been reported in any other bNAb and provides the possibility that far fewer mAbs would need to be combined to make a useful and durable anti-HIV product.
A low-cost production platform would be necessary for this treatment to be feasible, however. One such platform, which is gaining traction, is the use of plant biotechnology to turn plants like tobacco into living bioreactors. This approach is simple, scalable, low-tech, and requires a smaller initial investment than traditional drug production platforms(23–26). One plant-expressed anti-HIV bNAb, 2G12, successfully completed its phase I clinical trial as of 2015(27). Producing N6 in tobacco plants could offer LMICs, many of which already have tobacco-growing expertise, the opportunity to produce their own anti-HIV therapeutic production platform for their whole region, given that the plant production system can quickly produce bulk quantities(28),(29).
In this study, the feasibility of producing bNAb N6 in plants was investigated. A glyco-engineered line of Nicotiana benthamiana (ΔXF)(30) was used to overcome potential issues with effector function and blood clearance activity(31). The purified protein was characterised and compared to the same antibody produced by a conventional mammalian cell expression system, in terms of antigen binding, binding kinetics and breadth of viral neutralisation, as well as glycosylation and FcγRIIIa and ADCC activity. Our results suggest that plants can be developed as a scalable, low-cost production platform for N6. Their use could help offset the prohibitive expense of mAb therapies, and the low upstream costs for plant manufacturing could allow the most affected regions to take ownership of their own treatment development programmes.