History of Envenoming Therapy and Current Perspectives

Abstract

Each year, millions of humans fall victim to animal envenomings, which may either be deadly or cause permanent disability to the effected individuals. The Nobel Prize-winning discovery of serum therapy for the treatment of bacterial infections (tetanus and diphtheria) paved the way for the introduction of antivenom therapies for envenomings caused by venomous animals. These antivenoms are based on polyclonal antibodies derived from the plasma of hyperimmunized animals and remain the only specific treatment against animal envenomings. Following the initial development of serum therapy for snakebite envenoming by French scientists in 1894, other countries with high incidences of animal envenomings, including Brazil, Australia, South Africa, Costa Rica, and Mexico, started taking up antivenom production against local venomous animals over the course of the twentieth century. These undertakings revolutionized envenoming therapy and have saved innumerous patients worldwide during the last 100 years. This review describes in detail the above-mentioned historical events surrounding the discovery and the application of serum therapy for envenomings, as well as it provides an overview of important developments and scientific breakthroughs that were of importance for antibody-based therapies in general. This begins with discoveries concerning the characterization of antibodies, including the events leading up to the elucidation of the antibody structure. These discoveries further paved the way for other milestones in antibody-based therapies, such as the introduction of hybridoma technology in 1975. Hybridoma technology enabled the expression and isolation of monoclonal antibodies, which in turn formed the basis for the development of phage display technology and transgenic mice, which can be harnessed to directly obtain fully human monoclonal antibodies. These developments were driven by the ultimate goal of producing potent neutralizing monoclonal antibodies with optimal pharmacokinetic properties and low immunogenicity. This review then provides an outline of the most recent achievements in antivenom research, which include the application of new biotechnologies, the development of the first human monoclonal antibodies that can neutralize animal toxins, and efforts toward creating fully recombinant antivenoms. Lastly, future perspectives in the field of envenoming therapies are discussed, including rational engineering of antibody cross-reactivity and the use of oligoclonal antibody mixtures.

Keywords: antibodies; antiserum; antivenom; antivenom history; envenoming therapy; hybridoma technology; phage display; recombinant antivenom.

Figure 1

Antivenom history timeline. The timeline presents the most important discoveries related to antivenom research and development, including groundbreaking discoveries within immunology (years in purple) and molecular biology (years in green). The discoveries awarded with the Nobel Prize are indicated with the Alfred Nobel medal, but does not mean that all the researchers involved were laureated with the prize. *Gene modification discovery in mice was awarded with the Nobel Prize, and not the generation of fully human antibodies in transgenic mice.

Figure 2

Serum therapy discovery: Experimental generation of immunity against (A) tetanus and (B) diphtheria. The experiments involved (1) immunizing rabbits against an inactivated bacteria culture; (2) collecting the blood from the immunized rabbits; (3) injecting the blood (before coagulation) into the abdominal cavity of another animal (mouse or guinea pig); (4) and inoculating the virulent culture in the same group of animals.

Figure 3

Schematic representation of important antibody discovery theories. (A) Ehrlich's side chain theory: Immune cells present a vast array of receptors or side chains (1); when a toxin interacts with a specific side chain (2), the immune cell is activated and thereafter produces more side chains (3); then, the receptors are released into the bloodstream as soluble side chains or magic bullets (4). (B) Linus Pauling's instructional model: Six different postulated stages of antibody formation as the result of interaction with an antigen. An antigen is held in place at the site of antibody production, and the antibody is generated around the antigen molecule (1). The ends of the antibody coil into a configuration complementary to groups on the antigen and attach to these complementary groups (2). The center of the chain is freed from the site of synthesis, causing one of two things to happen. If the forces between the ends of the chain are sufficiently strong, both ends will continue to be attached to the antigen, and the antibody will never be completed (3). If the forces between the ends of the chain and the antigen are weak, one end will dissociate from the antigen (4). Assuming one end of the chain dissociates from the antigen, the center of the chain coils into its most stable configuration, making a complete antibody (5). Eventually, the antibody will dissociate from the antigen and float away (6). There is also shown (lower) an antigen molecule surrounded by attached antibody molecules (saturation). (C) Burnet's clonal selection theory: A hematopoietic stem cell (1) undergoes differentiation and genetic rearrangement to produce immature lymphocytes with many different antigen receptors (2); the cells that bind to antigens from the body's own tissues (self-antigens) are destroyed (3), while the rest mature into inactive lymphocytes (4); cells that are activated by a foreign antigen (5) can produce many clones of themselves (6). This figure was based on the original diagrams prepared by the respective scientist.