Hybridoma Technology
In 1983, Wistar Institue applied to the US Patent Office, for a patent of hybridoma technology for producing viral antibodies. Since the technology was published in 1975 by Milstein and Kohler, the application of this technology was obvious and no patent was allowed in USA.
There are also examples where US patent for use of monoclonal antibodies was held invalid by District Court but was later allowed by the High Court of Appeals for different reasons.