Institut Pasteur is the holder of European patent No. 0 178 978 filed on 17 September 1985, and entitled "Cloned DNA sequences, hybridizable with genomic RNA of "lymphadenopathy-associated virus (LAV)". The patent covers genetic information allowing for testing the presence or absence of the virus known as HIV.

Siemens Healthcare Diagnostics (Siemens Healthcare) - formerly Bayer Diagnostics - has marketed kits in France for the quantitative diagnosis of the HIV virus under the name Versant HIV-1 RNA 3.0 Assay (bDNA) since 2003.

Institut Pasteur claimed that the kits, as well as their included reagents, implemented the features of the invention described in its patent and sued Siemens Healthcare for infringement of claims 5, 7, 8 and 11 before the First Instance Court of Paris.

Claims 5 and 6 of Institut Pasteur's patent identify the region of a given gene specific to the LAV. Subsequent claims 7 and 8 cover genetic material evidencing the presence of the specific LAV gene, as well as a method for the in-vitro detection of viral infection due to the LAV viruses, using the probe of claim 7. Claim 11 covers more generally genetic information identified as "the purified RNA of LAV virus which has a size from 9.1 to 9.2 kb and which corresponds to the cDNA contained in λJ19 (CNCM I-338)."

Institut Pasteur argued that due to the alleged pioneering nature of its invention relating to the detection of HIV, the patent claim 11 protected the purified RNA of a virus causing HIV in its entirety, and not a specific fragment isolated at random.

Such a broad construction of claim 11 would mean in practice that any testing kit for AIDS could fall within the scope of the Institut Pasteur patent rights.

Siemens Healthcare Diagnostics replied that claim 11 did not relate to all or any of the AIDS virus' purified RNA but only to the complementary RNA contained at a specific location of the genome of the LAV virus.

In order to reach this conclusion, Siemens Healthcare Diagnostics mainly relied on the so called "file wrapper estoppel" theory. Under this theory, any element left aside or given up by the patentee during patent prosecution for the grant of the patent is considered carved out of the scope of the patent, thus limiting the reach of the granted patent. This theory has not yet been fully recognized under French patent law.

In its decision, the First Instance Court of Paris first had to assess the scope of the claims 5, 6, 7, 8 and 11 in order to draw a line between Institut Pasteur's patent rights and the freedom to operate of third parties, before examining the infringement claims.

With regard to the examination of the scope of the claims, the court quoted Articles 1 and 2 of the Protocol on the Interpretation of the European Patent Convention and stressed that proper claim construction combines "a fair protection for the patent owner with a reasonable degree of legal certainty for third parties."

The court then expressly rejected the application of the "file wrapper estoppel" theory in France, holding that "[...] the "file wrapper estoppel" theory which also takes into account the statements made by the applicant during the grant or opposition proceedings in order to interpret a patent cannot be applied."

Nevertheless, the court stated that it was still possible "to refer to the wording of the claims as initially filed and to examine the scope thereof, in particular in light of the amendments made during the grant or opposition proceedings before the European Patent Office" in order to correctly assess the scope of the patent at stake.

Therefore, the court held that "the amendments made to the claims by Institut Pasteur during the examination and opposition proceedings [...] must be taken into account failing which legal certainty for third parties would be violated" The court concluded that because of the statements of Institut Pasteur and the EPO during the prosecution of the patent, claim 11 related to a particular LAV virus RNA strand which was specifically defined by its size and its ability to hybridize with the complementary DNA contained at a specific location of the LAV virus genome. Therefore, claim 11 did not cover the whole genetic information responsible for the virus causing AIDS.

With regard to the infringement claims, the court decided that Siemens Healthcare's detection kit did not infringe the claims 5, 6, 7 and 8. With regard to claim 11, the court said that there was no contributory infringement. Institut Pasteur had not proven that an essential means of this claim would have been provided by Siemens Healthcare Diagnostics when using its kit. There was no evidence that Siemens Healthcare's kit would allow for the accurate isolation of the RNA virus with the same features required by claim 11 as construed by the court.