Addressing the issue of obviousness of a patent directed toward a method of killing antibiotic-resistant bacteria using only visible light with no photosensitizer, the US Court of Appeals for the Federal Circuit reversed the Patent Trial & Appeal Board’s (PTAB) decision, finding no obviousness where the asserted prior art did not disclose a successful method that did not use a photosensitizer. University of Strathclyde v. Clear-Vu Lighting, LLC, Case No. 20-2243 (Fed. Cir. Nov. 4, 2021) (Stoll, J.) The Court held that the PTAB erroneously found a reasonable expectation of success where “[t]he only support for such a finding [was] pure conjecture coupled with hindsight reliance on the teachings in the [asserted] patent.”

Gram-positive bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA), are known to negatively affect health but effective methods of killing (or inactivating) such bacteria have been elusive. Photoinactivation is a way to kill antibiotic-resistant bacteria, and previous methods involved applying a photosensitizing agent to the infection and then activating the agent using light. Through experimentation, scientists at the University of Strathclyde discovered that application of visible (blue) light of wavelengths in the range of 400 – 420 nm was effective at inactivating bacteria such as MRSA without using a photosensitizing agent. The challenged patent claimed this method of using a photosensitizer for inactivating MRSA and other Gram-positive bacteria.

After Clear-Vu Lighting petitioned for inter partes review, the PTAB found the patent invalid as obvious in view of prior art disclosing methods of photoactivation using visible light. The university appealed.

The Federal Circuit reversed, finding that the prior art did not disclose all claim elements and there was no reasonable expectation of success in reaching the claimed invention by combining the prior art.

The Federal Circuit first addressed the PTAB finding that the prior art disclosed all claim limitations, finding that neither of the asserted prior art references taught or suggested “inactivation” of the bacteria without using a photosensitizer—as required by the claims. The Court noted that it “fail[ed] to see why a skilled artisan would opt to entirely omit a photosensitizer when combining [the] references,” finding it “particularly relevant” that one of the references actually “disclosed such a photosensitizer-free embodiment and was wholly unsuccessful in achieving inactivation.”

The PTAB also found that, based on a prior art teaching that “blue light may” inactivate “other bacterial cells that produce porphyrins,” a skilled artisan would have expected that MRSA could be inactivated by blue light without a photosensitizer due to the presence of porphyrins. In defense of the PTAB’s findings, Clear-Vu argued that support for the reasonable expectation of success could be found in the challenged patent itself. Citing its 2012 decision in Otsuka Pharm. v. Sandoz, the Federal Circuit harshly criticized this position, reiterating that the inventor’s own path to the invention is not the proper lens through which to find obviousness; “that is hindsight.”

The Federal Circuit explained that “not only is there a complete lack of evidence in the record that any bacteria were inactivated after exposure [...]

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