Tuesday, February 21, 2006

Look! Manimals!

Mr. BROWNBACK introduced the following bill; which was read twice and referred to the Committee on the Judiciary: S. 1373:

301. Definitions
In this chapter the following definitions apply:
(1) HUMAN CHIMERA.--The term `human chimera' means--
(A) a human embryo into which a non-human cell or cells (or the component parts thereof) have been introduced to render its membership in the species Homo sapiens uncertain through germline or other changes;
(B) a hybrid human/animal embryo produced by fertilizing a human egg with non-human sperm;
(C) a hybrid human/animal embryo produced by fertilizing a non-human egg with human sperm;
(D) an embryo produced by introducing a non-human nucleus into a human egg;
(E) an embryo produced by introducing a human nucleus into a non-human egg;
(F) an embryo containing haploid sets of chromosomes from both a human and a non-human life form;
(G) a non-human life form engineered such that human gametes develop within the body of a non-human life form; or
(H) a non-human life form engineered such that it contains a human brain or a brain derived wholly or predominantly from human neural tissues.
(2) HUMAN EMBRYO.--The term `human embryo' means an organism of the species Homo sapiens during the earliest stages of development, from 1 cell up to 8 weeks.

302. Prohibition on human chimeras
(a) IN GENERAL.--It shall be unlawful for any person to knowingly, in or otherwise affecting interstate commerce--
(1) create or attempt to create a human chimera;
(2) transfer or attempt to transfer a human embryo into a non-human womb;
(3) transfer or attempt to transfer a non-human embryo into a human womb; or
(4) transport or receive for any purpose a human chimera.
(1) IN GENERAL.--Whoever violates subsection (a) shall be fined under this title, imprisoned not more than 10 years, or both.
This definition seems to exclude simple things like the bacteria that produce insulin, a live-saving form of manimal. It also probably doesn't cover the mice Dr. Myers and I talked about when the President took on the Manimal Threat, since they don't have a full haploid set from humans, just one chromosome, and the brain isn't human (though human genes are an essential part of the brain in a mouse model of Down's syndrome).

What this covers is two very different things. One thing going on in the Manimal Bill is banning of certain sorts of transgenics. I'll skip that, since they aren't properly chimeras.

Properly speaking, a chimera is a mixture of cells from two sources. CSI fans will remember a case in which a man had two genetically distinct sets of cells in his body, so a DNA test wrongly excluded him as a suspect. That's a naturally forming human-human chimera (strictly a mosaic, but let's not get too caught up in terminology). For research purposes, one can put cells from one species (say a sheep) into the embryo of another (say a goat). The product will look like the little cutey right here, a so-called "geep."

Scientists use these chimeras to study the development of mammals, improving our understanding of our own growth and development, as well as that of commercially important species.

Chimeras involving putting part of a developing quail brain into a chicken embryo have revealed new insights into the genes controlling brain development. The quail cells can be identified in sections, making it easy to tell which parts of the developing brain become what parts of the adult brain.

A Chinese group managed to grow human stem cells in a mouse, potentially illustrating an easy way to mass-produce stem cells. A professor at Stanford is working toward growing a mouse embryo with human neurons, to better study human brain development. At this point, this research is not applied. Professor Weissman explained "if we … have mouse brains that have genetic diseases then we can ask whether the human cells we put in have a chance of curing them." His group is close to a treatment of a disease called Batten's disease.

Recent research has shown that cancer may all (or mostly) result from problems in stem cells. Curing cancer may depend on understanding how these stem cells go wrong. This insight may lead to new treatments that target only the stem cells, not the resulting cancer. Turning these inklings into treatments requires chimeras and the sort of basic research Sam Brownback wants to ban.

Finding a treatment that will work in humans will require having a distinct cell line with mutations associated with cancer growing in a living model. Since it's grossly unethical to cause cancer in humans, introducing those stem cells into a mouse is the best path to understanding human cancers (if this insight is correct). That might well include a mouse with a brain consisting mostly of human neurons, which will in turn develop cancer.

Nicholas Wade explains that:

Pharmaceutical companies are "waiting for more academic research before they take a clear view on how to proceed," Dr. Weinberg said. "Our knowledge base is still rather fragmentary, and we need another year or two of research before we can say to pharmaceutical companies you should do this or that."

On the other hand, maybe Senator Brownback is just worried about the great American Chickenhawk.