Patent protection on the original formulation of Keytruda would be gone anyway. They are trying to get a new 25 year patent via a combo formulation or a new superior variation of Keytruda. A combo or superior formulation would have to be a completely novel invention not just "you use these two drugs at the same time".

With leronlimab they'd have a superior drug in and of itself with patent protection on the condensed formulation until I believe 2031 and more importantly U.S. exclusivity for 12 years. Not an ideal situation but when approved for cancer leronlimab would crush any Keytruda market share anyway. As an added benefit Merck has the money to launch multiple new trials at the same time so they could have that exclusivity across multiple diseases. Then the problem becomes they have 12 years from first approval to come up with combos or unique new formulas for leronlimab.