`Pharming' is the production of human pharmaceuticals in farm animals that is currently in the developmental stage with possible commercialisation by the year 2000. It has been gaining application among biotechnologists since the development of transgenic "super mice" in 1982 and the development of the first mice to produce a human drug, TPA (tissue plasminogen activator to treat blood clots), in 1987.

Transgenic organisms have been modified by genetic engineering to contain DNA from an external source. The first drugs produced by this approach are about to enter clinical trials as part of the USA's Federal Drug Administration (FDA) review process.

These transgenic animals will likely be raised by the pharmaceutical companies and will certainly be kept separate from the food supply.During the 1970s, advances in DNA manipulation techniques provided a significant, economical alternative source for many drugs made of protein.

Previously, these protein drugs were available in extremely limited supplies; for example, human cadavers were the source for human growth hormone, and insulin to treat diabetes was collected from slaughtered pigs.

By genetic engineering, the DNA gene for a protein drug of interest can be transferred into another organism that will produce large amounts of the drug. This technique can be used to impart new production characteristics to an organism, as well as to trigger the production of a protein drug.

The first successful products of the genetic engineering process were protein drugs like insulin and growth hormone. These drugs do not have to be produced by mammals to be active in mammals. An inexpensive, easy-to-grow culture of genetically engineered bacteria like the common E. coli can manufacture these protein drugs.

Other human drugs, such as tPA for blood clots, erythropoietin for anemia, and blood clotting factors VIII and IX for hemophilia, require modifications that only cells of higher organisms like mammals can provide. The higher costs of maintaining mammalian cell cultures that produce only small amounts of the drugs have been an enormous barrier to the commercial development of this type of cell culture production method.

By genetic engineering, the DNA gene for a protein drug of interest can be transferred into another organism for production. Which organism to us for production is a technical and economic decision. The commercial application of this technology is being done by Pharming Group NV from the Netherlands.

To generate the transgenic calves, the desired gene is introduced into cultured female bovine cells of fetal origin. The cells that take up the transgene are isolated, and their nuclei fused to cow oocytes (eggs) from which the nucleus has been removed. The resulting transgenic embryos are then implanted in the wombs of foster mothers, and carried to term.

In the past, micro-injection, an area pioneered by Pharming, was the method of choice for the generation of transgenic cattle. Essentially, it is now possible to generate only female transgenic calves, which are directly suitable for the production of the biopharmaceutical product.

For certain protein drugs that require complex modifications or are needed in large supply, production in transgenic animals seems most efficient. The farm animal becomes a production facility with many advantages-it is reproducible, has a flexible production capacity through the number of animals bred, and maintains its own fuel supply. Best of all, in most animal drug production, the drug is delivered from the animal in a very convenient form-along with the milk!

A transgenic animal for pharmaceutical production should (1) produce the desired drug at high levels without endangering its own health and (2) pass its ability to produce the drug at high levels to its offspring.

The current strategy to achieve these objectives is to couple the DNA gene for the protein drug with a DNA signal directing production in the mammary gland. The new gene, while present in every cell of the animal, functions only in the mammary gland so the protein drug is made only in the milk.

Since the mammary gland and milk are essentially "outside" the main life support systems of the animal, there is virtually no danger of disease or harm to the animal in making the "foreign" protein drug.

Success in creating a transgenic animal that can produce the drug is far from guaranteed. About 10-30 percent of mouse embryos produce transgenics, but less than 5 percent of goats, sheep, or cows do. Production of the drug is measured during lactation after the animal is raised to maturity and bred. Because of the long time periods involved and low success rates, developing transgenic animals is currently very expensive. Although most protein drugs are made in milk, a notable exception is human hemoglobin that is being made in swine blood to provide a blood substitute for human transfusions. Because hemoglobin is naturally a blood protein, it is likely to be one of few exceptions to the usual method of production in milk.

Furthermore, the economics of blood production are less favourable, because to recover human hemoglobin, the animal producing it must be slaughtered. Notice that pharming is expected to increase the value of animals dramatically.

In general, animal pharming is considered to be 5 to 10 times more economical on a continuing basis and 2 to 3 times cheaper in startup costs than cell culture production methods.

* Current market price of the drug and supply produced by one animal Production of human pharmaceuticals in farm animals has many technical barriers to overcome, although most technologists agree that these technical difficulties will be easily resolved in the 1990s.

As a production method, animal pharming is entirely unprecedented and is likely to undergo significant evaluation by the Food and Drug Administration (FDA). Human drugs purified from animal milk or blood are likely to require exceptional levels of safety testing before animal and human health concerns are addressed to the satisfaction of consumers.

At a more fundamental level, many people are genuinely concerned about animal welfare and biotechnology's redefinition of the relationship between humans and animals. Genetic engineering and transgenic animal research are essentially human endeavours to improve the availability, quality, and safety of drugs; to enhance human health; and to improve animal health.

Animal breeding has gone on for centuries, but the ability to change the DNA of the animal brings breeding to a revolutionary new level.The authors are associated with Biotechnology Resource Centre, Mumbai.

STEPS IN PHARMING