human variant, despite the non-human origin of some of its complementarity-determining region (CDR) segments responsible for the ability of the antibody to bind to its target antigen. Chimeric antibody names contain a -xi- stem. Examples of chimeric antibodies approved for human therapy include abciximab (ReoPro), basiliximab (Simulect), cetuximab (Erbitux), infliximab (Remicade) and rituximab (MabThera). There are also several examples of chimerics currently in clinical trials (e.g. bavituximab, see sortable list for additional examples). Humanizing via a chimeric intermediate The humanization process may also include the creation of a mouse-human chimera as an initial step. In this case, a mouse variable region is spliced to a human constant region. The chimera can then be further humanized by selectively altering the sequence of amino acids in the variable region of the molecule. The alteration process must be "selective" to retain the specificity for which the antibody was originally developed. That is, since the CDR portions of the variable region are essential to the ability of the antibody to bind to its intended target, the amino acids in these portions cannot be altered without the risk of undermining the purpose of the development. Aside from the CDR segments, the portions of the variable regions that differ from those in humans can be corrected by exchanging the appropriate individual amino acids. This is accomplished at the DNA level through mutagenesis. Naming of humanized chimeras includes the stem for both designations (-xi- + -zu-). Otelixizumab is an example of a humanized chimera currently in clinical trials for treatment of rheumatoid arthritis and diabetes mellitus. Humanization by insertion of relevant CDRs into human antibody "scaffold" It is possible to produce a humanized antibody without creating a chimeric intermediate. "Direct" creation of a humanized antibody can be accomplished by inserting the appropriate CDR coding segments (so-called 'donor', responsible for the desired binding properties) into a human antibody "scaffold" (so-called 'acceptor'). As discussed above, this is achieved through recombinant DNA methods using an appropriate vector and expression in mammalian cells. That is, after an antibody is developed to have the desired properties in a mouse (or other non-human), the DNA coding for that antibody can be isolated, cloned into a vector and sequenced. The DNA sequence corresponding to the antibody CDRs can then be determined. Once the precise sequence of the desired CDRs are known, a strategy can be devised for inserting these sequences appropriately into a construct