That is my thinking... which is why I said, "Perhaps that is what the Keytruda/DCVax-L trial was about".
We do know (1) the phase3 SAP documentation and the MHRA documentation took an inordinate amount of time and pages, (2) a Merck employee with intimate insight into Keytruda worked for NWBO, (3) three keytruda biosimilars are in phase 3 trials now. Look like some greasing of the skids and Merck motivation to me.
On the other hand, if they actually created a third product which combined DCVax-L and Keytruda, that would be a new drug and they'd have patent coverage for the new product.