By David N. Leff
Old MacDonald would never recognize his farm today.
Biotech pharmers are raising transgenic cows, sheep and goats, all designed to give milk spiked with pharmaceutical proteins. Like Dolly, they¿ve all won blue ribbons for the ingenuity of their cloning strategies, but so far no milk-made product has come near commercialization.
Described as edging closest to market is human recombinant antithrombin III (hrAT III) produced by goats that express the anticoagulant molecule in their mammary glands.
A progress report in the forthcoming May 1999 issue of Nature Biotechnology bears the title: ¿Production of goats by somatic cell nuclear transfer.¿ Its senior author is molecular embryologist Yann Echelard, director of embryology at Genzyme Transgenics Corp. (GTC) in Framingham, Mass.
Putting that title in its place, Echelard told BioWorld Today: ¿The whole thing about this technique of nuclear transfer is fairly arcane, and a very small picture. That¿s not the big point of our paper. The big point of interest to biotech is that we actually made protein in milk, using these cloned animals.
¿The cloning part has been reported before,¿ he observed. ¿You can clone sheep and you can clone cows, so cloning goats is not totally surprising. For us what¿s more important is to report that these animals are producing this protein in milk in a very similar fashion to our earlier technique, microinjection. There¿s no difference in the product.¿
The three GTC-created caprine does reported in the paper came into the world last fall. The first, named Mira, was born in October; the other two ¿ twins Veda and Vesta ¿ in November. All three carried the gene for human recombinant antithrombin III, programmed for expression in the kids¿ mammary glands.
So at 8 weeks of age, Mira started giving the high-value milk, thanks to lactation induction that fooled her ovulatory system and milk glands into behaving as if she were a full-grown doe with newborn hungry kids of her own.
The Art Of Precocious Lactation
¿It¿s done hormonally,¿ Echelard explained, ¿like a pseudo-ovulation. There is some art there, as well as science, and in fact we have a paper coming out on that. We give them a steroid that induces hormones. It doesn¿t affect the animal¿s health when we stop the ovular induction and start the hormonal treatment. Then when we begin milking, we don¿t need to give them any more hormone. We just keep milking till we dry them off.
¿Veda, the first twin, has now been lactated,¿ he went on. ¿And Vesta is either on course of being lactated or will be pushed a little bit later. The reason we do that is because we also want to look at the influence of age on induction. We have two identical November animals. One induced at two months, the other to follow soon.¿
GTC started creating hrAT III-transgenic goats seven years ago, by microinjection, to meet an emerging market. ¿We used those animals,¿ Echelard recounted, ¿to derive a herd that has been the progenitor and production source for the material we¿re using right now in Phase III trials of the anticoagulant protein.¿
The company¿s vice president of business development, Suzanne Groet, told BioWorld Today that these pivotal clinical trials are under way ¿in both the U.S. and Europe, at over 20 different clinical sites. Patient enrollment began in May of 1998,¿ she added, ¿and our expectation is that we should complete it in 1999. These patients are all undergoing coronary bypass surgery, and they are resistant to heparin. So the initial antithrombin indication is for the restoration of their heparin sensitivity.
¿Human recombinant antithrombin is used today,¿ she added, ¿for a whole host of acquired deficiencies of the drug, so this would be our initial indication.¿
Groet noted that ¿the current market for antithrombin worldwide is close to $200 million. Most of that market is in Europe and Asia,¿ she observed. ¿In the U.S. today it¿s relatively small because the drug has only been approved here for hereditary antithrombin deficiency.¿
¿These are people,¿ Echelard explained, ¿who don¿t make enough AT to lead a normal life. They need it principally when they get an operation. An AT-deficient woman who becomes pregnant may suffer very bad circulation problems, especially deep-vein thrombosis.
¿In Europe and Japan,¿ he continued, ¿the larger market, AT is used mainly in septic shock and organ failures. There¿s a condition called disseminated intravascular coagulation, which is a hallmark of these life-threatening disorders. ATP is used to treat that.¿
Proteins, Antibodies Due From Transgenic Goats
But it¿s only the first of many goat-made Genzyme Transgenics drugs under active development.
¿In our pipeline besides antithrombin III,¿ Groet pointed out, ¿we actually have a very large number of different proteins. For example, we¿re developing human serum albumin and a protein that¿s unidentified, with Eli Lilly. And we¿re working on a malaria vaccine. Also, a product called GAD ¿ glutamic acid decarboxylase, which is potentially useful in early-stage diabetes.
¿Then,¿ she continued, ¿we¿re working on a whole host of monoclonal antibodies for a number of different companies. I would characterize those as among the key products we¿re developing.¿
Echelard counted the ways in which caprine bioreactors outpoint transgenic bovines and ovines. ¿We find goats are excellent for the purpose we have, which is the milk production of therapeutic proteins. That¿s where the big picture is for us. One advantage of goats in that respect is that their reproductive timing is quite quick ¿ five months¿ gestation and seven months to maturity. For cows it¿s nine and up to 15 months, respectively.
¿If you use goats as adults to produce proteins in milk,¿ he went on, ¿then you can get mature lactation in a year and a half. In cows it would be more than three years. That¿s another benefit.
¿However, there are more advantages to goats over sheep. Both species have about the same gestational timing, but sheep produce less than half the amount of milk that goats do. Also, goats are very insensitive to scrapie, which is linked to mad cow disease.¿
Echelard noted that the U.S. Department of Agriculture recorded only seven cases of scrapie in goats through 1998, but 1,117 in sheep through 1992. n