Laws of nature, natural phenomena, and abstract ideas are unpatentable subject matters, which is known as exclusionary principle under U.S. patent law for subject matter patentability. The question is: how to interpret this principle in specific cases? Too broad an interpretation will eviscerate patent law, for all inventions at some level embody, use, reflect, rest upon, or apply laws of nature, natural phenomena, or abstract ideas. If the principle is interpreted too narrowly, any step beyond mere exposition of laws of nature, natural phenomena or abstract ideas will become a patentable subject matter. This paper intends to analyze and summarize, in light of the recent case of Mayo as an example, application of the exclusionary principle for patentable subject matter in a specific case, by taking an insight look at American patent legislation and judicial practice.

I. Exclusionary principle of patentable subject matter

(i) The exclusionary principle

According to precedents established by the U.S. Supreme Court, there are three exceptions for patentable subject matter under U.S. Patent Act Section 101, namely, the laws of nature, natural phenomena, and abstract ideas. These three exceptions are not found in the US patent statute, but have long been held by the U.S. Supreme Court as an important exception implied in Section. This has been known as patentable subject matter exclusionary principle under the American patent law.

(ii) Legal basis for exclusionary principle of patentable subject matter

The U.S. Supreme Court made an interpretation in Diamond v.Chakrabarty that, “a new mineral discovered in the earth or a new plant found in the wild is not patentable subject matter. Likewise, Einstein could not patent his celebrated E=mc2; nor could Newton have patented the law of gravity. Such discoveries are manifestations of nature, free to all men and reserved exclusively to none.” It also made an essentially same interpretation in Funk Brothers Seed Co. v. Kalo Inoculant Co. that laws of nature, natural phenomena, and abstract ideas were the source of human knowledge and naturally belong to the whole human kind and therefore reserved exclusively to none.

In O’Reilly v. Morse, 56 How. 62 (1854), the Court ruled that the claims of Samuel Morse were non-patentable because it was too broad. U.S. Supreme Court interpreted that “since the claim of the patent involved in the case covers new method in the future, inventor in the future could not use such new method, nor the public have the benefit of it without the permission of this patentee.” It also expressed its concern in its trial of other cases. In Parker v. Flook, 437 U.S. 584 (1978), the Court ruled that the claimed method of the patent involved in the case was just “a formula to calculate the updated alarm limit” and its claims covered “post-solution applications of such a formula in a broad extent.” It held that the claims of the patent involved in Gottschalk v. Benson, 409 U.S. 63 (1972) was “so abstract and sweeping as to cover both known and unknown uses of such mathematical formula” and that “phenomena of nature, though just discovered, mental processes, and abstract intellectual concepts are not patentable, as they are the basic tools of scientific and technological work.” U.S. Supreme Court stated in Bilski v.Kappos that “allowing petitioners to patent risk hedging would preempt use of this approach in all fields, and would effectively grant a monopoly over an abstract idea.”

It can be seen from the above that although it may encourage people to continue to engage in the discovery of the laws of nature by way of granting patent to the laws of nature and others alike, it may also result in a risk that the patent granted to the laws of nature will limit the application of such laws and inhibit the future innovation based on such laws because such laws and principles are generally “basic tools of scientific and technological work.” Some scholars have made an analysis of patentable subject matter exclusionary principle from a perspective of economics. W. Landes and R. Posner make an explanation in their book, The Economic Structure of Intellectual Property Law, that the exclusion of basic truths from patent law reflects “both the enormous potential for rent seeking that would be created if property rights could be obtained in them and the enormous transaction costs that would be imposed on would-be users of those truths.”

In short, if patent were granted to the laws of nature, natural phenomena, and abstract ideas, these basic tools of scientific and technological work would be monopolized, and the possibility of their hindrance to innovation would be much higher than that of their furtherance. Therefore, in accordance with the purpose of patent law, the laws of nature, physical phenomena, abstract ideas and mathematic formula and laws and others alike should be excluded from the scope of patentable subject matter.

II. The Introduction of Mayo v. Prometheus

(i) The patents involved in the case

The patents involved in the case of Mayo were mainly related to the use of thiopurine drugs in the treatment of autoimmune diseases, such as Crohn’s disease and ulcerative colitis. When a patient ingests a thiopurine compound, his body metabolizes the drug, causing metabolites to form in his bloodstream. Because the way in which people metabolize thiopurine compounds varies, the same dose of thiopurine drug affects different people differently, and it has been difficult for doctors to determine whether for a particular patient a given dose is too high, risking harmful side effect, or too low, and so likely ineffective.

At the time the discoveries embodied in the patents were made, scientists have already understood that the levels in a patient’s blood of certain metabolites, including, in particular, 6-thioguanine and its nucleotides (6–TG) and 6-methyl-mercaptopurine(6–MMP), were correlated with the likelihood that a particular dosage of a thiopurine drug could cause harm or prove ineffective. But those in the field had not known the precise correlations between metabolite levels and likely harm or ineffectiveness. The patent claims at issue here set forth processes embodying researchers’ findings that identified these correlations with some precision.

More specifically, the patents—U.S. Patent No. 6,355,623 (623patent) and U.S. Patent No. 6,680,302(302patent)— embodied findings that concentrations in a patient’s blood of 6–TG or of 6–MMP metabolite beyond a certain level (400 and 7000 picomoles per 8x108 red blood cells, respectively) indicated that the dosage was likely too high for the patient, while concentrations in the blood of 6–TG metabolite lower than a certain level (about 230 picomoles per 8x108 red blood cells) indicated that the dosage was likely too low to be effective.

The patent claims sought to embody this research in a set of processes. Both U.S. Court of Appeals for the Federal Circuit and the U.S. Supreme Court took the claim 1 of the 623 Patent as a typical claim to analyze, which describes one of the claimed processes as follows: “A method of optimizing therapeutic efficacy for treatment of an immunemediated gastrointestinal disorder, comprising: (a) administering a drug providing 6-thioguanine to a subject having said immune-mediated gastrointestinal disorder; and (b) determining the level of 6-thioguanine in said subject having said immune-mediated gastrointestinal disorder, “wherein the level of 6-thioguanine less than 230 pmol per 8x108 red blood cells indicates a need to increase the amount of said drug subsequently administered to said subject and wherein the level of 6-thioguanine greater than 400 pmol per 8x108 red blood cells indicates a need to decrease the amount of said drug subsequently administered to said subject.”

(ii) The procedural posture

Prometheus Laboratories, Inc. (Prometheus), is the sole and exclusive licensee of U.S. Patent No. 6,355,623 (the ’623 patent) and U.S. Patent No. 6,680,302 (the ’302 patent). It sold diagnostic tests that embodied the processes the patents described. For some time, Mayo Clinic Rochester and Mayo Collaborative Services (Mayo), bought and used those tests. But in 2004 Mayo announced that it intended to begin using and selling its own test — a test using somewhat higher metabolite levels to determine toxicity (450 pmol per 8x108 for 6–TG and 5700 pmol per 8x108 for 6–MMP). Prometheus then brought this action claiming patent infringement.

The District Court found that Mayo’s test infringed claim 7 of the ’623 patent. In interpreting the claim, the court accepted Prometheus’ view that the toxicity-risk level numbers in Mayo’s test and the claim were too similar to render the tests significantly different. The court ruled that the number Mayo used (450) was too close to the number the claim used (400) to matter given appropriate margins of error. The District Court also accepted Prometheus’ view that a doctor using Mayo’s test could violate the patent even if he did not actually alter his treatment decision in the light of the test. In doing so, the court construed the claim’s language, “indicates a need to decrease” (or “to increase”), as not limited to instances in which the doctor actually decreases (or increases) the dosage level where the test results suggest that such an adjustment is advisable. Nonetheless the District Court ultimately granted summary judgment in Mayo’s favor. The court reasoned that the patents effectively claim natural laws or natural phenomena — namely the correlations between thiopurine metabolite levels and the toxicity and efficacy of thiopurine drug dosages — therefore are not patentable. Prometheus appealed to U.S. Court of Appeals for the Federal Circuit which reversed the judgment rendered by the District Court. The Appeal Court pointed out that in addition to these natural correlations, the claimed processes specify the steps of “administering a (thiopurine) drug” to a patient and “determining the resulting metabolite level.” These steps, it explained, involved the transformation of the human body or of blood taken from the body. Thus, the patents satisfied the standard of “machine or transformation test” set forth by U.S. Court of Appeals for the Federal Circuit in the past, which the court thought sufficient to “confine the patent monopoly within rather definite bounds,” thereby bringing the claims into compliance with §101 of U.S. Patent Act.

Mayo filed a petition to the U.S. Supreme Court for certiorari, which was granted. The Court vacated the judgment, and remanded the case for reconsideration in light of Bilski, which clarified that the “machine or transformation test” is not a definitive test of patent eligibility, but merely an important and useful clue. On remand, the Federal Circuit reaffirmed its earlier conclusion. It ruled that even if the “machine-or-transformation test” is understood merely as an important and useful clue, it can still lead to the “clear and compelling conclusion that the claims do not encompass laws of nature or preempt natural correlations.” Mayo again filed a petition for certiorari, which U.S. Supreme Court granted.

III. Detailed analysis of the claims of Mayo case