Rational design of rapidly translatable, highly antigenic and novel recombinant immunogens to address deficiencies of current snakebite treatments

Background: Snakebite envenomation (SBE) kills 138,000 and maims >400,000 people annually. Antivenom (antibodies purified from animals hyper-immunized with mixtures of venoms) is the only assured therapy for SBE, and is manufactured using expensive, century-old protocols of immunising horses/sheep with crude venoms. Current protocols make no attempt to account for variant venom protein immunogenicity or toxicity during antivenom design or manufacture.

Due to large venom diversity between different venomous snakes, this immunisation approach results in antivenoms which are snake species-specific, resulting in physicians having to make difficult diagnostic and antivenom-selection decisions when the offending snake species is unknown. Furthermore, the approach elicits toxin specific antibodies which often have poor toxin neutralising-potency, a problem further exacerbated when considering only 10-15% of the antibodies in antivenom are specific for venom components.

The remaining 85-90% of antibodies in antivenoms are specific to antigens (endemic pathogens, vaccines etc) which the manufacturing animals have encountered during their lifetime and are therefore of no use in treating envenoming. Consequently, antivenoms often have poor dose-efficacy, which results in the administration of large volumes (typically 200-400 ml in India) to neutralize pathology, often leading to severe adverse reactions and unaffordable costs for already impoverished victims.

There is therefore an urgent and compelling need to drastically improve the venom-neutralizing scope and potency of antivenom therapy.

Rationale: In the first four years of the FLF, we have identified regions, in multiple toxin families, that contain conserved features. We subsequently have engineered these conserved regions to be displayed on synthetic particles which enable focused and potent elicitation of anti-toxin antibodies when used in mice and rabbits. We now wish to apply the technology in full scale antivenom manufacturing in a good manufacturing practice environment.

Approach:

Objective 1 - producing experimental antivenoms with rationally designed immunogens Building on the success of the project to date, we will pilot the use of rationally designed antivenom antigens by employing them in antivenom production in a fully industrial scale. Working with an antivenom manufacturer, we will immunise horses for a period of 6 to 12 months with the developed antigens, while monitoring their development of anti-toxin antibodies before finally (in a manner that is not detrimental to the horses) producing fully formulated antivenom under good manufacturing conditions.

The full demonstration of the technology at this level will allow confidence and rapid uptake of the technology by manufacturers globally. Objective 2 - developing new antivenom bioprocessing methods to increase potency

Whilst the first approach is focused on antivenom upstream development of rationally designed antigens for immunisation, the downstream bioprocessing of antivenom has remained unchanged for many decades. The majority of (80-90%) of antibodies present in antivenoms are specific to venom toxins, but towards micro-organisms which manufacturing animals have encountered throughout their lifetime.

I have developed a method to selectively remove some of these redundant antibodies which results in an enrichment of the desired antivenom antibodies, thus increasing the toxin neutralising potency of the antivenom. In the FLF extension, I wish to further develop this bioprocessing technique to enable its use in full scale antivenom manufacturing.

Implications: This project represents the most substantial and advanced improvements to antivenom manufacturing since antivenoms were first conceived in the 1890s. The expected increases in potency and utility of the antivenom products developed we hope will assist in increasing the availability and treatment outcomes of snakebite victims globally.