Helminthic therapy, an experimental type of immunotherapy, is the treatment of autoimmune illnesses and immunological disorders by means of purposeful infestation with a helminth or with the eggs of a helminth. Helminths are parasitic worms such as hookworms, whipworms, and threadworms that have evolved to dwell within a host creature on which they rely for nourishment. These worms are members of two phyla: nematodes, which are primarily used in human helminthic therapy, and flat worms.

Helminthic therapy consists of the inoculation of the patient with specific parasitic intestinal nematodes. A number of such organisms are currently being investigated for their use as treatment including: Trichuris suis ova, commonly known as pig whipworm eggs; Necator americanus, commonly known as hookworms; Trichuris trichiura ova, commonly referred to as human whipworm eggs; and Hymenolepis diminuta, commonly known as rat tapeworm cysticerci.

While the latter four species may be considered to be mutualists – providing benefit to their host without causing longterm harm – there are other helminth species that have demonstrated therapeutic effects but which also have a potential to cause less desirable or even harmful effects and therefore do not share the ideal characteristics for a therapeutic helminth. These include Ascaris lumbricoides, commonly known as human giant roundworm; Strongyloides stercoralis, commonly known as human roundworm; Enterobius vermicularis, commonly known as pinworm or threadworm; and Hymenolepis nana, also known as dwarf tapeworm.

Mechanisms of action

Experimental data support the hypothesis that clinically induced helminthic infections have the ability to alleviate or mitigate immune responses. Most autoimmune disorders are believed to involve hyperactive TH1 or TH17 immune responses that are down-regulated by the promotion of a TH2 response by helminths. Helminths secrete immune regulatory molecules that promote the induction of regulatory T cells while inhibiting the function of antigen presenting cells and other T cells. As such, helminthic therapy attempts to restore homeostasis by shifting a hyperactive TH1 pro-inflammatory response to a TH2 response with reduced inflammation.

Human and animal studies have provided evidence of decreased TH1 and TH17 immune responses with a shift to TH2 cytokine production resulting in significantly decreased levels of interleukin 12 and IFNy with simultaneous increases in the regulatory T cells, interleukin 4, interleukin 5 and interleukin 10 of test subjects. These observations indicate that helminth therapy can provide protection against autoimmune disease not only through prevention, since helminths can be present before autoimmune disease develops, but also after autoimmune responses are initiated. Furthermore, responses of type-2 T helper cells rarely kill the parasitic worms. Rather, the TH2 response limits the infection by reducing the viability and reproductive capacity of the parasite.

Potential side effects

Helminths are extremely successful parasites capable of establishing long-lasting infections within a host. During this time, helminths compete with the host organism's cells for nutrient resources and thus possess the potential to cause harm. However, the number of organisms hosted by individuals undergoing helminthic therapy is very small and any side effects are typically only encountered in the first three months of infection. In the long term, the vast majority of clinically infected individuals are asymptomatic, with no significant nutrient loss. If the side effects from helminthic therapy were to become unmanageable, they can be alleviated by the use of anti-helminthic medications.

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Immunotherapy: Open Access

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