In the U.S., patent ownership vests with inventors, and each inventor can exploit their rights without accounting to the other. Neglecting to identify the true inventors of a claimed invention, and obtain assignments of their rights, can create chaos. This is what happened in Dana-Farber Cancer Institute, Inc. v. Ono Pharmaceutical (Fed. Circ., 2020), where the Court found that persons who significantly contributed to the invention were inventors, even though their contributions were not explicitly recited in the claims. The consequence was that Dana-Farber became a co-owner of the Ono patents.

The patents at issue relate to the discovery that an immune system T cell is inhibited when a ligand binds its PD-1 receptor. Certain cancer cells present PD-1 ligands, like healthy cells, to evade destruction. The inventive method of treating cancer relies on disrupting this lock-and-key interaction between PD-1 and PD ligands that masks cancer cells from T cells. Claim 1 of US Patent No. 8,728,474 (“the ’474 patent”) is illustrative, and narrowly recites the use of an anti-PD-1 antibody for the treatment of a patient:

Claim 1. A method for treatment of a tumor in a patient, comprising administering to the patient a pharmaceutically effective amount of an anti-PD-1 monoclonal antibody. (Emphasis added.)

The ’474 patent names Dr. Honjo (of Kyoto University and assignor to Ono), his post-doc, Dr. Iwai, and a colleague, Dr. Minato as inventors. Dr. Honjo and his colleagues discovered PD-1 and that it bound cancer cells, but not the ligand to which it binds. Dr. Honjo and his colleagues also did not appreciate that a ligand binding to PD-1 inhibited an antitumor immune response by T cells. They collaborated with Dr. Freeman (whose rights Dana-Farber acquired) and Dr. Wood, who jointly disclosed PD-1 ligands and discovered that PD-1/PD-L1 binding inhibits an antitumor immune response. The court found that the work of Drs. Freeman and Wood was a sufficient and significant contribution demonstrating co-inventorship.

How it Happened

Before their collaboration ended, Drs. Freeman and Wood filed a provisional patent application disclosing modulation of the immune response via activating or blocking the PD-1/PD-L1 pathway, but did not list Dr. Honjo as an inventor. Dr. Honjo contested his exclusion but took no official legal action. Instead, in 2002, Dr. Honjo filed his own patent application which did not list Drs. Freeman and Woods as inventors and which became the priority application for the patents in this case.

Ono argued that Drs. Freeman and Wood were not inventors because their contributions were too far removed from the conception of the invention, noting that Dr. Wood merely speculated that PD-1 could be a candidate for antibody therapy and did not test this in vivo. Ono further argued that the invention was independently conceived based on Drs. Honjo and Iwai’s knockout mice experiments and discussions with Dr. Minato. Ono also argued that Drs. Freeman and Wood did not contribute to conception of the invention because their alleged contribution—that PD-L1 was also expressed in cancers and that some tumors may use PD-L1 to inhibit an antitumor immune response—published before Dr. Honjo filed.

Dana-Farber argued that accepting Ono’s position would require each joint inventor to individually have conceived the complete invention and have participated in a particular moment of conception, which is inconsistent with law.

The Court noted that all joint inventors don’t need to conceive of the complete invention or even a substantial portion of it, nor must they work together or at one particular moment. The bar is much lower. The Court explained that a joint invention is simply the product of a collaboration between two or more persons working together. As provided in the statue, a joint inventor must:

(1) contribute in some significant manner to the conception or reduction to practice of the invention … and (3) do more than merely explain … well-known concepts and/or the current state of the art. 35 USC §116(a)

Even minimal contributions matter. There is no “explicit lower limit on the quantum or quality of inventive contribution required for a person to qualify as a joint inventor.”[1] Moreover, joint inventors do not need to “…physically work on the invention together or at the same time, …[nor] make the same type or amount of contribution.”[2]

Based on this law, the Court found that Drs. Freeman and Wood were inventors despite lacking in vivo confirmation. An inventor “need not know… that an invention will work for its intended purpose in order for conception to be complete….”[3] The in vivo experiments, which confirmed that PD-1 inhibits the immune response, did not negate Drs. Freeman and Wood’s contribution to the conception of the invention.

The Court further noted that joint inventorship is an independent inquiry apart from other patentability requirements. It was therefore irrelevant that Ono patents issued over Drs. Freeman and Wood’s 1999 provisional patent application. Novelty and nonobviousness “are not probative of whether the collaborative research efforts of Drs. Honjo, Freeman, and Wood led to the inventions claimed here or whether each researcher’s contributions were significant to their conception.”[4] The Court further explained that inventorship may depend on partial contributions to conception over time, and there is no principled reason to discount genuine contributions because portions were published prior to conception. Even though Drs. Freeman and Wood published that PD-L1 might be used to inhibit an antitumor immune response before Dr. Honjo filed, this didn’t mean that Drs. Freeman and Wood had not contributed to the conception of the invention in Dr. Honjo’s patent up until the time of publication.

Drs. Freeman and Wood’s contribution were not explicitly claimed. But as the Court noted, “Unless one also knows that the PD-1 receptor binds to at least one ligand that inhibits the immune response, such as PD-L1, there would be no reason to use anti-PD-1 antibodies to treat tumors.” As such, the Court found that the contributions of Freeman and Wood demonstrated they were inventors.


While inventorship can be corrected in most situations,[5] it is not to be ignored. If there is a nexus between significant contributions and the claimed invention, even if that contribution is not recited in the claims, the contributions may indicate co-inventorship.

[1] Eli Lilly & Co. v. Aradigm Corp., 376 F.3d 1352, 1358 (Fed. Cir. 2004) (quoting Fina Oil & Chemical Co. v. Ewen, 123 F.3d 1466, 1473 (Fed. Cir. 1997)).

[2] Burroughs Wellcome Co. v. Barr Labs., Inc, 40 F.3d 1223, 1227 (Fed. Cir. 1994) (citing 35 U.S.C. § 116).

[3] Applegate v. Scherer, 332 F.2d 571, 573 (CCPA 1964); Oka v. Youssefyeh, 849 F.2d 581, 584 n.1 (Fed. Cir. 1988).

[4] Dana-Farber Cancer Institute, Inc. v. Ono Pharmaceutical (Fed. Circ., 2020) slip. opinion, at p. 12.

[5] 37 CFR 1.48; 35 USC 256.