A natural protein isolated from the marine mollusc keyhole limpet. Keyhole limpet hemocyanin is an immunogenic carrier protein that, in vivo, increases antigenic immune responses to haptens and other weak antigens such as idiotype proteins. Or A substance taken from a marine organism that may be linked to a specific antigen to boost the immune response to that antigen. Keyhole limpet hemocyanin is being studied as a way to increase the immune response to cancer vaccines. It is a type of immune modulator. Also called KLH.