Well, in the case of a cancer that has developed high levels of resistance to Keytruda, the addition of leronlimab would likely disable those biochemical mechanisms which the cancer tumor developed in order to outsmart the PD1 blockade.

So, in cases where Keytruda was once effective against a cancer, but over time, has become less and less effective as the tumor became more and more resistant to the PD-1 therapy, then, with the addition of leronlimab, the CCR5 blockade would disable the tumor's capacity to evade the PD-1 blocker's mechanism of action.

Therefore, the addition of leronlimab would restore Keytruda as an effective treatment against that specific cancer.

My Rationale Presented Here