On 12 May 2026, the US Patent Trial and Appeal Board (PTAB) issued a final written decision invalidating Halozyme’s US Patent No. 11,952,600 relating to modified PH20 hyaluronidase polypeptides. The patent is one of a number of patents relating to Halozyme’s MDASE™ technology, that Halozyme has alleged in US court proceedings is infringed by MSD’s subcutaneous pembrolizumab (Keytruda Qlex™/ Keytruda SC™).
MSD filed a petition requesting post-grant review of all claims of the US ‘600 patent in November 2024 and the review was instituted in June 2025. Halozyme subsequently disclaimed claims 5-7, leaving claims 1-4 and 8-21 in effect. The PTAB determined that each of those claims was invalid for lack of enablement and failure to comply with the written description requirement.
Between November 2024 and November 2025, MSD filed petitions for post-grant review with the US Patent Trial and Appeal Board challenging the validity of 14 other Halozyme patents. 13 of those petitions have been instituted, while institution of the 14th was denied on 15 May 2026. In addition, in March 2026, MSD filed inter partes review (IPR) petitions in relation to a further three Halozyme patents, which are pending and have not yet been instituted.
Halozyme has sued MSD in the US in relation to SC pembrolizumab. In a complaint filed with the US District Court for the District of New Jersey on 24 April 2025, Halozyme alleged that Keytruda Qlex™ infringes 15 patents owned by Halozyme in relation to the MDASE™ subcutaneous delivery platform. The lawsuit followed reports in March 2025 that Halozyme had offered MSD an opportunity to licence its MDASE patents. At the time, a spokesperson from MSD said the enzyme used in Keytruda Qlex™ was “developed independently” from Halozyme and that MSD “strongly believes” that any Halozyme patents that attempt to cover the enzyme variant are invalid.
The Halozyme patents currently the subject of US litigation and PGR or IPR proceedings are as follows:
| US Patent No. | PGR/IPR No. | Status of PGR/IPR | At Issue in US Proceeding? |
|---|---|---|---|
| 11,952,600 | PGR2025-00003 | Patent Invalidated, 12 May 2026 | Yes |
| 12,018,298 | PGR2025-00004 | Instituted 11 Jun 2025 | Yes |
| 12,152,262 | PGR2025-00006 | Instituted 16 Jun 2025 | Yes |
| 12,123,035 | PGR2025-00009 | Instituted 11 Jul 2025 | No |
| 12,110,520 | PGR2025-00017 | Instituted 8 Sep 2025 | Yes |
| 12,060,590 | PGR2025-00024 | Instituted 16 Oct 2025 | No |
| 12,054,758 | PGR2025-00030 | Instituted 16 Oct 2025 | Yes |
| 12,049,652 | PGR2025-00033 | Instituted 1 Oct 2025 | Yes |
| 12,104,185 | PGR2025-00039 | Instituted 1 Oct 2025 | Yes |
| 12,037,618 | PGR2025-00042 | Instituted 13 Nov 2025 | Yes |
| 12,091,692 | PGR2025-00046 | Instituted 10 Oct 2025 | Yes |
| 12,077,791 | PGR2025-00050 | Instituted 19 Nov 2025 | Yes |
| 12,264,345 | PGR2025-00052 | Instituted 16 Oct 2025 | Yes |
| 12,195,773 | PGR2025-00053 | Instituted 19 Nov 2025 | Yes |
| 12,371,685 | PGR2025-00087 | Institution Denied 15 May 2026 | Yes |
| 11,066,656 | IPR2026-00314 | Pending, petition filed 23 Mar 2026 | Yes |
| 11,041,149 | IPR2026-00313 | Pending, petition filed 23 Mar 2026 | Yes |
| 10,865,400 | IPR2026-00312 | Pending, petition filed 23 Mar 2026 | Yes |
In December 2025, the Munich Regional Court granted Halozyme’s application for a preliminary inunction preventing MSD from distributing and offering Keytruda SC™ for sale in Germany. The decision was based on a finding of the Court that there was imminent infringement of one of Halozyme’s European MDASE™ patents, EP 2797622, in relation to modified PH20 hyaluronidase polypeptides and compositions. MSD has filed invalidation lawsuits against the same Halozyme European patent in four countries: Germany, the United Kingdom, the Netherlands, and France.
MSD’s subcutaneous formulation of pembrolizumab was approved in the US, as Keytruda Qlex™, in September 2025 across 38 indications.