Humanized antibodies are antibodies from non-human species whose protein sequences have been modified to increase their similarity to antibody variants produced naturally in humans. The process of "humanization" is usually applied to monoclonal antibodies developed for administration to humans (for example, antibodies developed as anti-cancer drugs). Humanization can be necessary when the process of developing a specific antibody involves generation in a non-human immune system (such as that in mice). The protein sequences of antibodies produced in this way are partially distinct from homologous antibodies occurring naturally in humans, and are therefore potentially immunogenic when administered to human patients (see also Human anti-mouse antibody). The International Nonproprietary Names of humanized antibodies end in -zumab, as in omalizumab (see Nomenclature of monoclonal antibodies). Humanized antibodies are distinct from chimeric antibodies. The latter also have their protein sequences made more similar to human antibodies, but carry a larger stretch of non-human protein. There are other ways to develop monoclonal antibodies. This list covers many of the monoclonals developed for use in humans. Use of recombinant DNA in humanization process The humanization process takes advantage of the fact that production of monoclonal antibodies can be accomplished using recombinant DNA to create constructs capable of expression in mammalian cell culture. That is, gene segments capable of producing antibodies are isolated and cloned into cells that can be grown in a bioreactor such that antibody proteins produced from the DNA of the cloned genes can be harvested en masse. The step involving recombinant DNA provides an intervention point that can be readily exploited to alter the protein sequence of the expressed antibody. The alterations to antibody structure that are achieved in the humanization process are therefore all effectuated through techniques at the DNA level. Not all methods for deriving antibodies intended for human therapy require a humanization step (e.g. phage display) but essentially all are dependent on techniques that similarly allow the "insertion" or "swapping-out" of portions of the antibody molecule. Distinction from "chimeric antibody" Humanization is usually seen as distinct from the creation of a mouse-human antibody chimera. So, although the creation of an antibody chimera is normally undertaken to achieve a more human-like antibody (by replacing constant region of the mouse antibody with that from human) simple chimeras of this type are not usually referred to as humanized. Rather, the protein sequence of a humanized antibody is essentially identical to that of a