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Nanobodies (aka single domain antibodies or VHH antibodies) are antibody fragments consisting of a single monomeric variable antibody domain. They are derived from heavy chain antibodies from camelids some of which only consist of two antibody heavy chains. With a molecular weight of only 12-15 kDa nanobodies are much smaller than traditional IgG antibodies (150-160 kDa) which are conglomerates of two heavy protein chains and two light chains, intricately folded and garnished with elaborate sugars.[1] Nanobodies are being researched for multiple pharmaceutical applications and have potential for use in cancer and Alzheimer's Disease treatments.

Traditional therapeutic monoclonal antibodies (MAbs) must be stored at near freezing temperatures to prevent their destruction. Antibodies are not suited for oral administration because they are digested quickly in the gut, and are not usually useful for treating diseases of the brain because they do not easily permeate the blood-brain barrier. Additionally, therapeutic antibodies are not well suited to target large tumors because they are held to the periphery of solid tumors. Many illnesses are thus unreachable by monoclonals, and patients who use MAb therapies must receive them by injection or infusion at a clinic. For certain conditions in which the traditional MAbs do not work well, and even for some in which they currently do, simpler, smaller proteins like nanobodies might perform better, be easier to make, easier to handle, easier to administer, and be more affordable. (2)

In 1989 a group of biologists led by Raymond Hamers at the Free University (Brussels, Belgium) investigated an odd observation handed in as part of a student project on parasite immunodefense in dromedary camels (the one-humped Arabian variety) and water buffalo. One of the tests for antibodies in the dromedary blood seemed to show an error: in addition to normal four-chain antibodies it indicated the presence of simpler antibodies composed solely of a pair of heavy chains.

After several years of investigation, Hamers and his colleagues published their discovery in Nature in 1993.[2] In dromedaries — and also in two-humped Asian camels and South American llamas — about half the antibodies circulating in the blood lack a light chain. Equally surprising, they found that these "incomplete" antibodies are able to grasp their targets just as firmly as normal antibodies do, with affinities for their targets virtually equal to a full antibody 10 times their size.

These shortened proteins were also more chemically agile, able to engage targets — including the active sites of enzymes and clefts in cell membranes — too small to admit an antibody.

Because nanobodies are so much smaller than antibodies and are not hydrophobes (as are standard human antibodies), they are more resistant to heat and pH, and may retain their activity as they pass through the gastrointestinal tract, raising the prospect of oral nanobody pills to treat inflammatory bowel disease, colon cancer and other disorders of the gut. (2)

References

  1. ^ Harmsen MM, De Haard HJ (November 2007). "Properties, production, and applications of camelid single-domain antibody fragments". Appl. Microbiol. Biotechnol. 77 (1): 13–22. doi:10.1007/s00253-007-1142-2. PMID 17704915.  
  2. ^ Hamers-Casterman C, Atarhouch T, Muyldermans S, Robinson G, Hamers C, Songa EB, Bendahman N, Hamers R., Naturally occurring antibodies devoid of light chains, Nature. 1993 Jun 3;363(6428):446-8

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