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Camelid Antibodies

Don't feel bad, Kuzco. You'll see that llamas have their benefits!
Emperor's New Groove, Disney.
The "Y" shape is iconic in the field of immunology. When it's drawn floating around a cell, you instinctively know it's an antibody. Well, each part of that Y is important, representing two heavy chains, joined by disulfide bonds, and two light chains, each joined to a heavy chain by a disulfide bond. The "tips" of the Y are particularly key, as they contain the variable region of the antibody, including the antigen-binding site which gives the antibody specificity for particular antigens. You can learn more about antibodies, including their structure and function, on our Making Antibodies page. But, what if an antibody didn't look like that? If it was missing the top half of that Y, would you expect it to perform just as well as a normal antibody? Well, antibodies that look like that exist, and will be the subject of this blog.
Do antibodies have to look like this? Image from Univ. of British Columbia.
In 1989, Raymond Hamers' lab at Vrije Universiteit Brussel discovered something incredibly unique while investigating the immune system of dromedaries (a type of camel). As the story goes, a couple of undergrads in the lab were bored of the simple experiments assigned to them and wanted something different to investigate. Dr. Hamers had reserved some camel blood for a study on sleeping sickness, and asked the students if they were interested in trying to purify antibodies from an aliquot1. The students did just that, and found that among the conventional antibodies, there was also a smaller type present. Upon reviewing his students' data, Dr. Hamers thought their results were a mistake and was worried that these smaller antibodies were just fragments of normal antibodies or products of degradation from storing the blood so long. So they flew in fresh camel blood from Kenya and verified their results, which were eventually published in Nature in 19932.

Camelids make heavy-chain antibodies and aren't afraid who knows it. Image from
Dr. Hamers' group had discovered heavy-chain antibodies, a type of antibody that is found in all members of the Camelidae family, including llamas, alpacas, and camels. These antibodies lack light chains, and consist of two heavy chains attached to variable domains (variable heavy homodimers, VHH). Because of this, heavy-chain antibodies are much smaller, about 95 kDa (while a typical IgG can range from 150-160 kDa). The VHH alone, which is 15 kDa, is considered the smallest naturally derived antigen-binding fragment3. The patent for these VHH fragments was transferred to Ablynx in 2001, who engineered single-domain antibodies based on their design, calling them "Nanobodies®".
A Nanobody is small, indeed.3

Though smaller, Nanobodies are just as specific as conventional antibodies.
But how well does it work? Does it recognize its target as specifically and with as high affinity as a conventional antibody? Well, most evidence is saying yes, these 15 kDa Nanobodies perform just as well as classical mammalian antibodies with respect to target recognition and binding affinity4. Thus, the potential benefits of using Nanobodies for both therapeutic and research applications are endless:

  • Faster accumulation as a therapeutic or imaging agent in tissue.
  • Higher stability due to its smaller size.
  • Lower toxicity due to more rapid clearance of unbound antibodies.
  • Additional routes of administration.
  • Increased manufacturing production efficiency and potentially lower costs.
Thus, the question becomes, if these were discovered so long ago, why haven't they revolutionized the study of immunology or immunotherapy? A breakthrough is increasingly urgent as the patent expiry of general use of these antibodies creeps closer (it has been 20 years, after all!). As it turns out, small size can be a double-edged sword, creating a number of limitations for Nanobodies, such as:
  • High clearance in imaging applications can make it more difficult to obtain images.
  • High clearance in immunotherapy, though it lowers toxicity, can also lower efficacy (particularly in cancer) of a single dose due to shorter half-life.
  • Fluorophore conjugation, which does not drastically alter the binding properties of conventional antibodies, can do so with Nanobodies (imagine sticking 240 kDa PE on a 15 kDa Nanobody!).
Thus, while there is a lot of potential regarding the future of Nanobodies, it does seem like more work needs to be done. There is increasing interest in developing single-domain antibodies for therapeutic and research use, particularly because it will be coming off patent soon, reducing the costs of procuring them. Hopefully this will lead to advancements in single-domain antibodies as more and more researchers begin to work with them! Feel free to look below for more information, and contact us if you have any comments:

  1. The camel factor: Nanobody revolution,
  2. Naturally occurring antibodies devoid of light chains, Nature
  3. Nanobody: The "Magic Bullet" for Molecular Imaging? Theranostics
  4. Camel heavy-chain antibodies: diverse germline VHH and specific mechanisms enlarge the antigen-binding repertoire, EMBO Journal
  5. Understanding Nanobodies, Ablynx
Contributed by Ed Chen, Ph.D.

Nanobody® is a registered trademark of Ablynx NV
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