A Commotion in the Blood. By Stephen S. Hall. Page 117 "a further discouragement in terms of the toxins is that without patent protection on a hundred year old treatment, there is little incentive for a drug company to invest upward of $200 million to test the vaccine and find that it works, only to watch competitors stream into the market".
According to the Wikipedia Article, Coley started using his "toxins" in 1893 and published his results. I searched on patents assigned to Parke Davis and the earliest listed in Google Patents was from 1901 and was not related to Coley's toxins. I highly doubt that Parke Davis ever held a patent on Coley's toxins. I also searched for patents invented by William Coley and couldn't find anything related.
As the Wikipedia article documents, there have been studies done and no scientifically supported evidence of efficacy. Research into the performance of treatments is not limited to private drug companies. The NIH funds a great deal of research. I will also point out that companies regularly manufacture off-patent medicines. It is an enormous business.