Keyhole Limpet Hemocyanin (KLH) is a large, oxygen-carrying, multisubunit metalloprotein derived from the hemolymph of the Giant Keyhole Limpet, Megathura crenulata. KLH is highly immunogenic in mammals, including humans, strongly stimulating an immune response. KLH is a huge protein complex with a high molecular weight. Its structure consists of multiple subunits, making it highly suitable for conjugation. KLH is a potent immune stimulant, capable of eliciting a strong humoral response that results in antibody production and cellular T-cell-based immune responses. KLH contains numerous primary amines from lysine residues, making it an excellent candidate for chemically linking or conjugating other molecules to it.

How-to-prepare-peptide-protein-conjugates-for-immunization

KLH-peptide-antigen

Protein-bioconjugation

Small molecules, called haptens, such as peptides, small proteins, or drug molecules, are generally not immunogenic on their own. When conjugated to KLH, the hapten becomes more visible to the immune system, leading to the production of specific antibodies against the hapten, crucial for generating antibodies for research and diagnostics, as well as for the development of various laboratory assays, including ELISA, Western blot, and immunohistochemistry, and for the development of therapeutic antibodies. Additionally, KLH is being investigated and used as a component in cancer vaccines. In this context, specific tumor-associated antigens or haptens are conjugated to KLH. The KLH acts as a carrier to boost the immune response against these tumor antigens, aiming to stimulate the body's immune system to destroy cancer cells. It has shown promise in trials for various cancers, including bladder cancer (where it's clinically approved in some countries for recurrence prevention), melanoma, breast cancer, and non-Hodgkin lymphoma.

KLH can help assess the immune status and function in individuals, particularly in clinical studies evaluating the effects of new drug candidates on the immune system, such as in immunotoxicity testing. KLH can stimulate innate immune responses, activating pathways involved in inflammation. KLH can also be used as a vaccine adjuvant, enhancing the immune response to other antigens in a vaccine.

Safety and Side Effects: KLH is generally considered unlikely to cause harmful effects. Studies have shown that a single injected dose can result in a robust immune response. While the antibody profiles generated in humans can be highly variable, KLH itself is well-tolerated.

The sole natural source of KLH is the Giant Keyhole Limpet (Megathura crenulata), which exists in wild populations. Due to increasing demand from the pharmaceutical industry, there has been a focus on sustainable aquaculture practices to ensure a consistent and ethical supply of KLH.

References

4BED: Keyhole limpet hemocyanin (KLH): 9A cryoEM structure and molecular model of the KLH1 didecamer reveal the interfaces and intricate topology of the 160 functional units. Structure

Gatsogiannis C, Markl J. Keyhole limpet hemocyanin: 9-A CryoEM structure and molecular model of the KLH1 didecamer reveal the interfaces and intricate topology of the 160 functional units. J Mol Biol. 2009 Jan 23;385(3):963-83. [PubMed].

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