In defense of human-animal chimeras. In this week's State of the Union address, Bush made an odd appeal:

Tonight I ask you to pass legislation to prohibit the most egregious abuses of medical research, human cloning in all its forms, creating or implanting embryos for experiments, creating human-animal hybrids, and buying, selling or patenting human embryos.

To a biologist's ear, this statement is not too far removed from outright condemnation of our science. This is an affront to a field that has much to contribute to humanity. This work, after all, is undertaken in order to help people... so it's frustrating that biology tends to be the only science in which people conjur up so many "ethical dilemmas." So, in case you hear it from nobody else, allow me to say that mainstream biologists do not haphazardly muck with nature.

Bush doesn't know or doesn't care that molecular human-animal chimeras are an integral part of legitimate, mainstream research that saves lives. Human-mouse chimeric antibodies have been approved by the FDA and are currently on the market:

• Abciximab, approved for prevention of clotting during surgery;
  
• Rituximab, approved for treatment of non-Hodgkin's lymphoma;
  
• Basiliximab, approved for prevention of kidney rejection after transplant;
  
• Infliximab, approved for Crohn's disease and the treatment of rheumatoid arthritis;
  
• Trastuzumab (Herceptin), approved for the treatment of metastatic breat cancer.

Those are some of the older ones; there are more out there, and more in the pipeline. All of these treatments come from murine (mouse) hybridomas; these are tumor cells fused with B-cell lymphocytes to create hybrid cell lines that churn out monoclonal (identical) antibodies. Monoclonal antibody therapies have been fairly successful and have become somewhat of a Big Thing in the biotech industry. The first generation of treatments were chimeric antibodies: half-mouse, half-human. To limit allergic reactions in patients, second-generation treatments make use of genetically engineered mice whose antibodies have been "humanized"—in other words, the genes that code for the antibodies have been made even more similar to the human versions.

The antibodies and the cells from which they are derived could reasonably be called "human-animal hybrids." The cell lines have no potential for doing anything but making one type of antibody. Is our president really threatening to prohibit this type of research? Would he really prefer to outlaw chimeric cell lines at the expense of cures for cancer?

We cannot ignore the continuing importance of chimeras and hybridomas in biotechnology. If there's such an "ethical dilemma" about using chimeric cells, shouldn't we also be discussing the long-term benefits of this type of work? This is one area where public education about the benefits of modern biology would be extremely helpful.

UPDATE: Pharyngula highlights a better example of chimeric animal research, and participates in a must-read interview.

UPDATE: Jim Hu also responds to Bush's speech, but in a much less breathless tone.